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Advanced Quantum-Nano Materials & Optoelectronics Laboratory
 
 

QR code_Prof. Jihoon Lee

Kwangwoon Univ. KOR ver website

Kwangwoon Univ. Eng ver website

Kwangwoon College of Electronics and Informattion Engineering

Dept. of Electronics and Communications Engineering

 

University of Arkansas


Sam M. Walton College of Business

 

ERC 선도연구센터

BK 21 PLUS

Engineering Research Center, Holo-Digilog Human Media

Ministry of Science, ICT and Future Planning

Ministry Of Education

NIPA

KCC

Ministry of Education, Science and Technology

ITRC logo

ITRC Forum 2011

 

 

- Journal Editor -

3D Research

NRL cover

 

 

- Research Highlight -

 

Journal Cover: Precise Control of Configuration, Size and Density of Self-assembled Au Nanostructures on 4H-SiC (0001) by Systematic Variation of Deposition Amount, Annealing Temperature and Duration

(Journal cover,
CrystEngComm)
Volume 18
Issue 19

(2016)

Journal cover,CrystEngComm Volume 16 Issue 21 (2014)

(Journal cover,
CrystEngComm)
Volume 16
Issue 21

(2014)

 

Physica Status Solidi (a)) Volume 209 issue 6

(Journal cover,
Physica Status Solidi (a))
Volume 209
Issue 6

(2012)

 

Journal cover, Physica Status Solidi (a) Volume 208 Issue 1 (2011)

(Journal cover,
Physica Status Solidi (a))
Volume 208
Issue 1

(2011)

 

( Journal cover, IEEE Transactions on Nanotechnology) Volume 9 Issue 2  (2010)
( Journal cover,
IEEE Transactions on Nanotechnology)
Volume 9
Issue 2

(2010)

 

Wiley's Material Science online portal, Materials Views

(Materials Views, Wiley's Material Science)
"Nano Rings and Nano Pyramids"
(2010)

 


(Journal cover, Physica Status Solidi (a)) Volume 207 Issue 2  (2010)
(Journal cover,
Physica Status Solidi (a))
Volume 207
Issue 2

(2010)

 

(Journal cover, Applied Physics Letters) Volume 89 Issue 20  (2006)
(Journal cover,
Applied Physics Letters)
Volume 89
Issue 20

(2006)

 



(2006 MRS Fall Meeting Scene)
"Self-Assembly of InGaAs Quantum Dot Molecules (QDMs)"
(2006)

 

(Journal cover, Applied Physics Letters) Volume 88 Issue 23  (2006)

(Journal cover,
Applied Physics Letters)
Volume 88
Issue 23

(2006)

 

www.nanowerk.com

(NanoWerk, Spotlight)
"Quantum dot necklaces and other QD chains"
(April 12, 2006)

 

 


- PUBLICATIONS -

Journal Papers


* AUTHORS (in the order of authorship)
** TYPE: A: article, B: full book, CB: chapter of book, E: editor, & R: review, V: Video journal
***
IF: ISI® impact factor
*** Trend of Impact Factor of journals with interest (JCR IF 2015
)

 

TITLE: Ag Nanostructures on GaN (0001): Morphology Evolution controlled by the solid state dewetting of thin films and corresponding optical properties
AUTHORS: . Kunwar, M. Sui, Q. Zhang, P. Pandey, M. Y. Li and J. H. Lee
JOURNAL/BOOK TITLE:
Crystal growth & design
VOLUME: 16                                 FIRST PAGE: 6974
YEAR OF PUBLICATION:
2017                              KEY: A                      IF: 4.055


Abstract


 

Silver (Ag) nanostructures have demonstrated the feasibilities being utilized in various optoelectronic, catalytic, biomedical and sensor devices due to the excellent surface plasmon resonance characteristics. The geometrical structure, spacing and spatial arrangement of nanostructures are crucial for controlling the properties and device performance. Herein, we demonstrate the fabrication of various configurations of self-assembled Ag nanostructures on GaN (0001) by the systematic control of deposition thickness and annealing duration. The surface morphology evolution is thoroughly investigated and the corresponding influence on optical properties are probed. The evolution of Ag nanostructures in response to the thermal annealing is described based on the dewetting of thin films, Volmer-Weber growth model, coalescence growth and surface energy minimization mechanism. For the deposition amount variation between 1 and 100 nm, the Ag nanostructures show gradual morphological transitions such as: small NPs to enlarged NPs between 1 and 7 nm, elongated nanostructures to cluster networks between 10 and 30 nm and void evolution with layered nanostructures between 40 and 100 nm. In addition, the annealing duration effect has been studied between 0 and 3600 s, where the Ag nanostructures exhibit the evolution of network-like, elongated and isolated irregular shapes, ascribed to the Ostwald’s ripening along with the Ag sublimation. Furthermore, the corresponding Raman, photoluminescence (PL) and reflectance spectra reveal the morphology dependent behaviors and are discussed based on the phonon, emission band, scattering, absorption and surface plasmon effect.

 

Graphical Abstract



Ag Nanostructures on GaN (0001): Morphology Evolution controlled by the solid state dewetting of thin films and corresponding optical properties

Ag Nanostructures on GaN (0001): Morphology Evolution controlled by the solid state dewetting of thin films and corresponding optical properties

 

 

TITLE: Determination of growth regimes of Pd nanostructures on c-plane sapphire by the control of deposition amount at different annealing temperatures”
AUTHORS: S. Kunwar, M. Sui, P. Pandey, Q. Zhang, M. Y. Li, H. Bhandari and J. H. Lee
JOURNAL/BOOK TITLE:
Physical Chemistry Chemical Physics
VOLUME: 19                                 FIRST PAGE: 15084
YEAR OF PUBLICATION:
2017                              KEY: A                      IF: 4.123


Abstract


 

Metallic nanoparticles (NPs) with the tunable physical, optical and catalytic properties lead to a wide range of applications including various optoelectronics, sensors and fuel cells. In this paper, we demonstrate the evolution of various physical properties, configurations, size and density of palladium (Pd) nanostructures on sapphire (Al2O3) (0001) by the systematic control of deposition amount (DA) at distinct annealing temperatures. The transformation of deposited thin films into the various Pd NPs is achieved by the dewetting of thin film by means of surface diffusion, nucleation, Volmer-Weber growth and surface energy minimization mechanism. Depending on the evolution of size, density and configuration, five distinctive regimes of Pd nanostructures are demonstrated: (i) nucleation and evolution of small NPs between 1 and 3 nm (ii) medium NPs with the dominating vertical growth between 5 and 20 nm, (iii) laterally expanded large NPs between 30 and 40 nm, (iv) irregular coalesced Pd NPs between 50 and 80 nm, and finally (v) voids evolution between 100 and 200 nm. Initial film thickness and annealing temperature play major roles on the dewetting process and the resulting Pd nanostructures are notably distinguished. The fabricated Pd nanostructures has the influence on the lattice vibration modes of sapphire (0001) such as gradual decrement in the intensity and left shift of peak position with the increased surface coverage. In addition, the optical properties are studied by UV-VIS-NIR (300 – 1100 nm) reflectance spectra, which shows the reflectance, absorption and scattering over the wavelength and are closely related to the morphology evolution of Pd nanostructures.

 

Graphical Abstract



Determination of growth regimes of Pd nanostructures on c-plane sapphire by the control of deposition amount at different annealing temperatures

Determination of growth regimes of Pd nanostructures on c-plane sapphire by the control of deposition amount at different annealing temperatures

 

TITLE: Au-assisted Fabrication of Nano-holes on c-plane Sapphire via Thermal Treatment guided by Au Nanoparticles as Catalysts
AUTHORS: M. Sui, P. Pandey, M. Y. Li, Q. Zhang, S. Kunwar and J. H. Lee
JOURNAL/BOOK TITLE:
Applied Surface Science
VOLUME: 39
3                                 FIRST PAGE: 23
YEAR OF PUBLICATION:
2017                              KEY: A                      IF: 3.387


Abstract


 

Nanoscale patterning of sapphires is a challenging task due to the high mechanical strength, chemical stability as well as thermal durability. In this paper, we demonstrate a gold droplet assisted approach of nano-hole fabrication on c-plane sapphire via a thermal treatment. Uniformly distributed nano-holes are fabricated on the sapphire surface guided by dome shaped Au nanoparticles (NPs) as catalysts and the patterning process is discussed based on the disequilibrium of vapor, liquid, solid interface energies at the Au NP/sapphire interface induced by the Au evaporation at high temperature. Followed by the re-equilibration of interface energy, transport of alumina from the beneath of NPs to the sapphire surface can occur along the NP/sapphire interface resulting in the formation of nano-holes. The fabrication of nano-holes using Au NPs as catalysts is a flexible, economical and convenient approach and can find applications in various optoelectronics.

 

Graphical Abstract



 

Au-assisted Fabrication of Nano-holes on c-plane Sapphire via Thermal Treatment guided by Au Nanoparticles as Catalysts

Au-assisted Fabrication of Nano-holes on c-plane Sapphire via Thermal Treatment guided by Au Nanoparticles as Catalysts

 

 

TITLE: Morphological and Optical Evolution of Silver Nanoparticles on Sapphire (0001) along with the Concurrent Influence of Diffusion, Ostwald’s Ripening and Sublimation
AUTHORS: P. Pandey,
S. Kunwar, M. Sui, Q. Zhang, M. Y. Li and J. H. Lee
JOURNAL/BOOK TITLE:
IEEE Transactions on Nanotechnology
VOLUME: 16                                 FIRST PAGE: 321
YEAR OF PUBLICATION:
2017                              KEY: A                      IF: 2.485


Abstract


 

Ag nanoparticles (NPs) have found a number of applications in various fields such as optoelectronics, sensors and catalysts and the optical, physical and chemical properties of Ag NPs can be modified by the control of size, density and configuration as well as their spacing. Therefore, in this paper, we demonstrate the size, shape and spacing control of Ag NPs by the systematic control of annealing duration between 0 and 3600 s on sapphire (0001) (Al2O3). The Ag NPs show a sharp distinction in morphology along with the controlled duration at 20 and 14 nm thickness and the evolution trend is systematically discussed based on the concurrent influence of surface diffusion, Ostwald’s ripening and sublimation. With the relatively thicker film of 20 nm, the fabrication of irregular and round NPs is demonstrated along with the gradually reduced size up on the annealing at 750 oC for the duration between 0 and 900 s. Between 1800 and 3600 s, tiny grain-like particles result as a consequence of an extensive sublimation. Meanwhile, with the film thickness of 14 nm at 400 oC, densely packed small NPs are resulted between 0 and 3600 s due to the limited surface diffusion. At the same time, the optical characterizations such as Raman and reflectance spectroscopy show a distinctive trend of spectra, i.e. intensity, peak position and FWHM, based on the evolution of Ag NPs and are discussed in conjunction with the specific morphology and surface coverage of the Ag NPs.

 

Graphical Abstract



Morphological and Optical Evolution of Silver Nanoparticles on Sapphire (0001) along with the Concurrent Influence of Diffusion, Ostwald’s Ripening and Sublimation

Morphological and Optical Evolution of Silver Nanoparticles on Sapphire (0001) along with the Concurrent Influence of Diffusion, Ostwald’s Ripening and Sublimation

 

 

 

TITLE: Study on the Dimensional, Configurational and Optical Evolution of Palladium Nanostructures on c-plane Sapphire by the Control of Annealing Temperature and Duration
AUTHORS:
M. Sui, Q. Zhang, S. Kunwar, P. Pandey, M. Y. Li and J. H. Lee
JOURNAL/BOOK TITLE:
Applied Surface Science
VOLUME: 416                                 FIRST PAGE: 1
YEAR OF PUBLICATION:
2017                              KEY: A                      IF: 3.387


Abstract


 

Metallic nanostructures can find various applications such as in optoelectronic devices, nanostructure synthesis and catalytic applications and their applicability vary depending on their size, density and configuration dependent properties. In this paper, the dimensional and configurational evolution of self-assembled palladium (Pd) nanostructures is systematically studied on c-plane sapphire with the control of annealing temperature (AT) and annealing duration with the initial Pd layers of various thicknesses. Depending on the AT, two distinct growth regimes are observed based on the concurrent effect of surface diffusion, surface energy minimization and Pd sublimation: i.e. (i) agglomeration of Pd nano-clusters from voids (500 < AT ≤ 650 °C) and (ii) round nanoparticle (NP) fabrication (650 °C < AT ≤ 900 °C). At 950 °C, due to the sublimation of Pd atoms, substantial decrease in the NP dimension is witnessed and results in the ring patterns around the NPs. Additional investigation is performed at 950 °C to reveal the annealing duration effect on the NP evolution. Due to the dual effect of the Oswald ripening and atom sublimation, initially the dimension of NPs is grown and then gradually decays along with the duration, resulting in an inverted ‘V’ pattern evolution in diameter and height. Moreover, the evolution of optical properties such as absorption band and average reflectance are studied with the corresponding reflectance spectra as a function of wavelength over UV, visible and NIR region. The Raman spectra analysis depicts the variation of lattice vibration peak intensity and position based on the surface morphology of the Pd nanostructures.

 

Graphical Abstract



Study on the Dimensional, Configurational and Optical Evolution of Palladium Nanostructures on c-plane Sapphire by the Control of Annealing Temperature and Duration

Study on the Dimensional, Configurational and Optical Evolution of Palladium Nanostructures on c-plane Sapphire by the Control of Annealing Temperature and Duration

 

 

 

TITLE: Determination of growth regimes of Pt nanostructures on GaN (0001) based on the control of Pt thickness and annealing time: morphological evolution of Pt nanostructures from the nanoparticles, nanoclusters to porous network
AUTHORS:
P. Pandey, M. Sui, S. Kunwar, M. Y. Li, Q. Zhang and J. H. Lee
JOURNAL/BOOK TITLE:
Journal of Materials: Design and Applications
VOLUME:                                  FIRST PAGE:
YEAR OF PUBLICATION:
2017                              KEY: A                      IF: 1.625


Abstract


 

Pt nanostructures are applicable in various applications such as sensors, solar cells, light emitting devices (LEDs) and catalysis and only slight changes in their configuration, density and size can induce significant changes in their properties and thus the functionality in the related applications. In this paper, the systematical evolution of Pt nanostructures such as nanoparticles (NPs), nanoclusters and porous network on GaN (0001) is demonstrated by the systematic thermal annealing of Pt thin films based on the combinational effects such as thermal dewetting, Volmer-Weber growth model and coalescence growth. In particular, small dome shaped self-assembled Pt NPs with relatively smaller deposition amount (< 2 nm) and wiggly Pt nanoclusters between 3 and 5 nm are formed based on the Volmer-Weber growth model and the partial coalescence of Pt NPs respectively. Between 10 and 30 nm, the growth of Pt nanoclusters is observed and eventually with the increased Pt thickness range between 40 and 100 nm, nanoclusters gradually develop into the porous Pt network by connecting neighboring structures owing to the enhanced coalescence growth. Meanwhile, along with the annealing time variation between 0 and 3600 s, the rate of dewetting is increased and as a result the evolution of densely packed to separated nanoclusters are formed. In addition, the optical properties of corresponding Pt nanostructures demonstrate that the photoluminescence (PL) and Raman intensity are reduced along with the evolution of the surface coverage of Pt nanostructures whereas the average reflectance is significantly enhanced accordingly at the same time.

 

Graphical Abstract



Determination of growth regimes of Pt nanostructures on GaN (0001) based on the control of Pt thickness and annealing time: morphological evolution of Pt nanostructures from the nanoparticles, nanoclusters to porous network

Determination of growth regimes of Pt nanostructures on GaN (0001) based on the control of Pt thickness and annealing time: morphological evolution of Pt nanostructures from the nanoparticles, nanoclusters to porous network

 

 

 

TITLE: Effects of Annealing Temperature and Duration on the Morphological and Optical Evolution of Self-Assembled Pt Nanostructures on c-plane Sapphire
AUTHORS:
M. Sui, M. Y. Li, S. Kunwar, P. Pandey,Q. Zhang, and J. H. Lee
JOURNAL/BOOK TITLE:
PLOS ONE
VOLUME: 12                                 FIRST PAGE: e0177048
YEAR OF PUBLICATION:
2017                              KEY: A                      IF: 2.806


Abstract


 

Metallic nanostructures (NSs) have been widely adapted in various applications and their physical, chemical, optical and catalytic properties are strongly dependent on their surface morphologies. In this work, the morphological and optical evolution of self-assembled Pt nanostructures on c-plane sapphire (0001) is demonstrated by the control of annealing temperature and dwelling duration with the distinct thickness of Pt films. The formation of Pt NSs is led by the surface diffusion, agglomeration and surface and interface energy minimization of Pt thin films, which relies on the growth parameters such as system temperature, film thickness and annealing duration. The Pt layer of 10 nm shows the formation of overlaying NPs below 650 °C and isolated Pt nanoparticles above 700 °C based on the enhanced surface diffusion and Volmer-Weber growth model whereas larger wiggly nanostructures are formed with 20 nm thick Pt layers based on the coalescence growth model. The morphologies of Pt nanostructures demonstrate a sharp distinction depending on the growth parameters applied. By the control of dwelling duration, the gradual transition from dense Pt nanoparticles to networks-like and large clusters is observed as correlated to the Rayleigh instability and Ostwald ripening. The various Pt NSs show a significant distinction in the reflectance spectra depending on the morphology evolution: i.e. the enhancement in UV-visible and NIR regions and the related optical properties are discussed in conjunction with the Pt NSs morphology and the surface coverage.

 

Graphical Abstract



Effects of Annealing Temperature and Duration on the Morphological and Optical Evolution of Self-Assembled Pt Nanostructures on c-plane Sapphire

Effects of Annealing Temperature and Duration on the Morphological and Optical Evolution of Self-Assembled Pt Nanostructures on c-plane Sapphire

 

 

 

TITLE: Effect of Systematic Control of Pd Thickness and Annealing Temperature on the Fabrication and Evolution of Palladium Nanostructures on Si (111) via the Solid State Dewetting
AUTHORS:
S. Kunwar, P. Pandey, M. Sui, Q. Zhang, M. Y. Li and J. H. Lee
JOURNAL/BOOK TITLE:
Nanoscale Research Letters
VOLUME: 12                                  FIRST PAGE: 364
YEAR OF PUBLICATION:
2017                              KEY: A                      IF: 2. 833


Abstract


 

Si-based optoelectronic devices embedded with metallic nanoparticles (NPs) have demonstrated the NP shape, size, spacing and crystallinity dependent light absorption and emission induced by the localized surface plasmon resonance. In this work, we demonstrate various size and configuration of palladium (Pd) nanostructures on Si (111) by the systematic thermal annealing with the variation of Pd thickness and annealing temperature. The evolution of Pd nanostructures are systematically controlled by the dewetting of thin film by means of the surface diffusion in conjunction with the surface and interface energy minimization and Volmer-weber growth model. Depending on the control of deposition amount ranging between 0.5 and 100 nm at various annealing temperature, four distinctive regimes of Pd nanostructures are demonstrated: i) small pits and grain formation, ii) nucleation and growth of NPs, iii) lateral evolution of NPs and iv) merged nanostructures. In addition, by the control of annealing between 300 and 800 ºC, the Pd nanostructures show the evolution of small pits and grains, isolated NPs and finally Pd NP assisted nano-hole formation along with the Si decomposition and Pd-Si inter-diffusion. The Raman analysis showed the discrepancies on phonon modes of Si (111) such that the decreased peaks intensity with left shift after the fabrication of Pd nanostructures. Furthermore, the UV-VIS-NIR reflectance spectra revealed the existence of surface morphology dependent absorption, scattering and reflectance properties.

 

Graphical Abstract



Effect of Systematic Control of Pd Thickness and Annealing Temperature on the Fabrication and Evolution of Palladium Nanostructures on Si (111) via the Solid State Dewetting

Effect of Systematic Control of Pd Thickness and Annealing Temperature on the Fabrication and Evolution of Palladium Nanostructures on Si (111) via the Solid State Dewetting

 

 

 

TITLE: Nanoscale morphology and optical property evolution of Pt Nanostructures on GaN (0001) by the systematic control of Annealing Temperature and Duration with various Pt thickness
AUTHORS:
S. Kunwar, P. Pandey, M. Sui, Q. Zhang, M. Y. Li and J. H. Lee
JOURNAL/BOOK TITLE:
Materials Research Express
VOLUME:  4                                FIRST PAGE: 065019
YEAR OF PUBLICATION:
2017                              KEY: A                      IF: 1.068


Abstract


 

By the controlled fabrication of Pt nanostructures, various surface morphology dependent electronic, catalytic and optical properties can be exploited for the wide range of applications. In this paper, the evolution of Pt nanostructures on GaN (0001) by the solid-state dewetting of Pt thin films is investigated. Controlling the annealing temperature, time and film thickness allow to fabricate distinct size, density and configurations of Pt nanostructures. For 10 nm Pt thickness, tiny voids and Pt hillocks up to 550 °C, extensive void expansion and Pt nanostructure evolution between 600 and 750 °C and finally Pt nanostructures assisted nanoholes penetration on GaN surface above 800 °C are demonstrated. Furthermore, comparatively elongated Pt nanostructures and NHs are resulted with 20 nm Pt thickness and voids growth and connected Pt nanostructure are formed by annealing duration control. The transformation of Pt films to nanostructures is governed by the surface diffusion, Rayleigh instability, Volmer-Weber growth and energy minimization mechanism whereas NHs penetration is commenced by the decomposition of GaN, Pt-Ga alloying and nitrogen desorption at high temperature. In addition, the optical characteristic of Pt nanostructures on GaN (0001) by reflectance, photoluminescence (PL) and Raman spectroscopy demonstrate the surface morphology dependent spectral response.

 

Graphical Abstract



Nanoscale morphology and optical property evolution of Pt Nanostructures on GaN (0001) by the systematic control of Annealing Temperature and Duration with various Pt thickness

Nanoscale morphology and optical property evolution of Pt Nanostructures on GaN (0001) by the systematic control of Annealing Temperature and Duration with various Pt thickness

 

 

 

TITLE: Fabrication and determination of growth regimes of various Pd NPs based on the control of deposition amount and temperature on c-plane GaN
AUTHORS:
M. Sui, S. Kunwar, P. Pandey, Q. Zhang, M. Y. Li and J. H. Lee
JOURNAL/BOOK TITLE:
b
VOLUME:                                  FIRST PAGE:
YEAR OF PUBLICATION:
2017                              KEY: A                      IF: 1.673


Abstract


 

Palladium (Pd) nanostructures have been actively adapted for various applications and the properties and applicability are closely depending on their shape, size and density. In this paper, the evolution of self-assembled Pd nanostructures on hexagonal c-plane GaN is presented by the systematical control of Pd deposition amount (DA) at distinctive temperatures. Pd nanostructures of various configuration, size and density are demonstrated based on the solid-state dewetting of Pd thin films and a clear distinction in the growth regimes is observed. Three growth regimes are clearly observed depending on the variation of DA: i.e. (i) the agglomeration of Pd nanoparticles (NPs), (ii) the coalescence of wiggly Pd nanostructures and finally (iii) the growth of nano-voids and layer. Owing to the temperature dependent dewetting process, the growth regimes are markedly shifted, resulting in the distinctive Pd nanostructures within the identical DA range. The results are discussed in conjunction with the surface diffusion, Volmer-Weber and coalescence growth model, and surface/interface energy minimization mechanism. In addition, the evolution of optical properties, emission band and lattice properties are probed by reflectance, PL and Raman spectroscopy, which exhibits varying spectral intensity and peak positions according to the surface morphology of Pd nanostructures.

 

Graphical Abstract



Fabrication and determination of growth regimes of various Pd NPs based on the control of deposition amount and temperature on c-plane GaN

Fabrication and determination of growth regimes of various Pd NPs based on the control of deposition amount and temperature on c-plane GaN

 

 

 

TITLE: “Effect of Annealing Temperature on Morphological and Optical Transition of Silver Nanoparticles on c-Plane Sapphire”
AUTHORS: P. Pandey,
S. Kunwar, M. Sui, M. Y. Li, Q. Zhang,and J. H. Lee
JOURNAL/BOOK TITLE:
Journal of Nanoscience and Nanotechnology
VOLUME: 17                                FIRST PAGE:
YEAR OF PUBLICATION:
2017                              KEY: A                      IF: 1.483


Abstract


 

As a promising candidate for the improved performance, silver nanoparticles (Ag NPs) have been successfully adapted in various applications such as photovoltaics, light emitting diodes (LEDs), sensors and catalysis by taking the advantage of their controllable plasmonic properties. In this paper, the control on the morphologies and optical properties of Ag NPs on c-plane sapphire (0001) is demonstrated by the systematic control of annealing temperature (between 200 and 950 oC) with 20 and 6 nm thick Ag films through the solid state dewetting. With the relatively thicker film of 20 nm, various configuration and size of Ag NPs are fabricated such as irregular, round dome-shaped and tiny Ag NPs depending on the annealing temperature. In a shrill contrast, the 6 nm Ag set exhibits a sharp distinction with the formation of densely packed small NPs and ultra-highly dense tiny Ag NPs due to the higher dewetting rate. While, the surface diffusion assumes the main driving force in the evolution process of Ag NP morphologies up to 550 °C, the sublimation of Ag atoms has played a significant role on top on the surface diffusion between 600 and 950 °C. The reflectance spectra of Ag NPs exhibit the quadrupolar resonance and dipolar resonance peaks, and the evolution of peaks, shift and average reflectance were discussed based on the Ag NPs size and surface coverage. In particular, the dipolar resonance peak in the reflectance spectra red shifts from ~ 475 to ~ 570 nm due to the size increment of Ag NPs (38.31 to 74.68 nm). The wide surface coverage of Ag NPs exhibits the highest average reflectance (~ 27 %) and the lowest Raman intensity.

 

Graphical Abstract



Effect of Annealing Temperature on Morphological and Optical Transition of Silver Nanoparticles on c-Plane Sapphire

Effect of Annealing Temperature on Morphological and Optical Transition of Silver Nanoparticles on c-Plane Sapphire

 

 

 

TITLE: Various Silver Nanostructures on Sapphire Using Plasmon Self-Assembly and Dewetting of Thin Films
AUTHORS:
S. Kunwar, M. Sui, Q. Zhang, P. Pandey, M. Y. Li and J. H. Lee
JOURNAL/BOOK TITLE:
Nano-Micro Letters
VOLUME: 9                                 FIRST PAGE: 17
YEAR OF PUBLICATION:
2016                              KEY: A                      IF: 4.849


Abstract


 

Silver (Ag) nanostructures demonstrate outstanding optical, electrical, magnetic and catalytic properties and are being utilized in the range of application such as photonic, energy, sensors and biomedical devices. The target application and the performance can be inherently tuned by the control of configuration, shape and size of Ag nanostructures. In this work, we demonstrate the systematical fabrication of various configurations of Ag nanostructures on sapphire (0001) controlled by the Ag deposition thickness at various annealing environment. In particular, depending on the thickness of Ag thin film at 550 °C, the evolution of Ag particles (between 2 and 20 nm), irregular nanoclusters (between 30 and 60 nm) and nanocluster networks (between 80 and 200 nm) are demonstrated. The results are systematically analyzed and explained based on the solid-state dewetting, surface diffusion, Volmer-Weber growth model, coalescence and surface energy minimization mechanism. The growth behavior of Ag nanostructures is remarkably differentiated at higher annealing temperature (750 °C) due to the sublimation and temperature dependent characteristic of dewetting process. In addition, Raman and reflectance spectra analysis revealed the morphology dependence optical properties of Ag nanostructures.

 

Graphical Abstract



Various Silver Nanostructures on Sapphire Using Plasmon Self-Assembly and Dewetting of Thin Films

Various Silver Nanostructures on Sapphire Using Plasmon Self-Assembly and Dewetting of Thin Films

 

 

 

TITLE: Nanoparticles to Nanoholes: Fabrication of Porous GaN with Precisely Controlled Dimension via the Enhanced GaN Decomposition by Au nanoparticles
AUTHORS: P. Pandey, M. Sui, M. Y. Li, Q. Zhang, S. Kunwar,
J. Wu, Z. M. Wang, G. J. Salamo and J. H. Lee
JOURNAL/BOOK TITLE:
Crystal Growth & Design
VOLUME: 16                                 FIRST PAGE: 3334
YEAR OF PUBLICATION:
2016                              KEY: A                      IF: 4.891


Abstract


 

Porous GaN exhibits unique optoelectronic, chemical, and physical properties such as shift of band gap, increased surface area ratio, excellent chemical, mechanical, and thermal stability as well as efficient luminescence as compared to its bulk counterpart. Herein, we demonstrate a precise, efficient, and still cost-effective method of the fabrication of porous GaN through the enhanced GaN decomposition by using Au nanoparticles (NPs) as a catalyst, in which the size, density, and shape of the pores (nanoholes, NHs) can be precisely controlled. By the thermal annealing assisted with the Au NPs, the NHs are successfully fabricated, and the existence of Au NPs significantly accelerate the GaN decomposition at the interface between the NPs and GaN due to the Ga absorption by the Au NPs. We systematically study the formation mechanism of NHs assisted by the Au NPs by means of annealing temperature, duration, and Au deposition amount, and the results are systematically analyzed and discussed.

 

Graphical Abstract



Nanoparticles to Nanoholes: Fabrication of Porous GaN with Precisely Controlled Dimension via the Enhanced GaN Decomposition by Au nanoparticles

Nanoparticles to Nanoholes: Fabrication of Porous GaN with Precisely Controlled Dimension via the Enhanced GaN Decomposition by Au nanoparticles

 

 


TITLE: Journal Cover: Precise Control of Configuration, Size and Density of Self-assembled Au Nanostructures on 4H-SiC (0001) by Systematic Variation of Deposition Amount, Annealing Temperature and Duration
AUTHORS: M. Y. Li, M. Sui,P. Pandey, Q. Zhang, S. Kunwar, G. J. Salamo and J. H. Lee
JOURNAL/BOOK TITLE:
CrystEngComm
VOLUME: 18                                  FIRST PAGE: 3347
YEAR OF PUBLICATION:
2016                              KEY: A                      IF: 4.043
Journal Cover: Precise Control of Configuration, Size and Density of Self-assembled Au Nanostructures on 4H-SiC (0001) by Systematic Variation of Deposition Amount, Annealing Temperature and Duration
 

 

TITLE: Precise Control of Configuration, Size and Density of Self-assembled Au Nanostructures on 4H-SiC (0001) by Systematic Variation of Deposition Amount, Annealing Temperature and Duration
AUTHORS: M. Y. Li, M. Sui,P. Pandey, Q. Zhang, S. Kunwar, G. J. Salamo and J. H. Lee
JOURNAL/BOOK TITLE:
CrystEngComm
VOLUME: 18                                 FIRST PAGE: 3347
YEAR OF PUBLICATION:
2016                              KEY: A                      IF: 4.043


Abstract


 

The precise control over the configuration, size and density of Au nanoparticles (NPs) has offered an efficient route to enhance and optimize the performance and usability of various NP-based applications. In this study we successfully demonstrate the precise control of configuration, size and density of the self-assembled Au nanostructures on 4H-SiC (0001) via the systematic variation of deposition amount, annealing temperature and duration. Depending on the deposition amount at fixed annealing temperature and duration, the self-assembled Au NPs are successfully fabricated based on the Volmer-Weber growth model, and the NPs nucleate as round-dome shape and evolve into the hexagonal nano-crystals with the facet formation along with the increased deposition amounts. For the variation of annealing temperatures, the Au nanostructures radically develope into two distinct regimes: i.e. irregular Au nano-mounds (Regime I) between 400 and 700 °C based on the diffusion limited agglomeration (DLA) model and round-dome shaped droplets (DPs) (Regime II) between 750 and 900 °C. Depending on the dwelling time, the size and density evolution of round-dome shape Au DPs are dicusscussed based on the Ostwald-ripening theory.

 

Graphical Abstract



Precise Control of Configuration, Size and Density of Self-assembled Au Nanostructures on 4H-SiC (0001) by Systematic Variation of Deposition Amount, Annealing Temperature and Duration

Precise Control of Configuration, Size and Density of Self-assembled Au Nanostructures on 4H-SiC (0001) by Systematic Variation of Deposition Amount, Annealing Temperature and Duration

 

 

 

TITLE: Fabrication of Ag Nanostructures by the Systematic Control of Annealing temperature and duration on GaN (0001) via the Solid State Dewetting
AUTHORS: P. Pandey,
S. Kunwar, M. Sui, M. Y. Li, Q. Zhang and J. H. Lee
JOURNAL/BOOK TITLE:
Physica status solidi (a)
VOLUME: 214                                 FIRST PAGE: 1600702
YEAR OF PUBLICATION:
2016                              KEY: A                      IF: 1.775


Abstract


 

The gradual evolution of Ag nanostructures in terms of the configuration, size and density of via the solid state dewetting is demonstrated on GaN (0001) by the systematic control of annealing temperature and duration with various Ag film thickness. Upon the annealing between 150 and 700 oC with the 20 nm Ag film, the hillocks, voids, irregular and round dome shaped Ag nanoparticles (NPs) are fabricated based on various growth mechanisms: i.e. thermal diffusion, and sublimation as well as the surface energy minimization. On the other hand, along with the systematic control of annealing duration between 0 and 3600 s with 10 nm Ag film 700 oC, the Ag NPs show gradually decreased size and density based on the concurrent influence of the Ostwald’s ripening and sublimation of Ag atoms. The Raman, photoluminescence and reflectance spectroscopy of the resulting Ag NPs are characterized in accordance with the various morphology evolution of Ag nanostructures.

 

Graphical Abstract



 

Fabrication of Ag Nanostructures by the Systematic Control of Annealing temperature and duration on GaN (0001) via the Solid State Dewetting

Fabrication of Ag Nanostructures by the Systematic Control of Annealing temperature and duration on GaN (0001) via the Solid State Dewetting

 

 

 

TITLE: Metallic Nanodroplet Induced Coulomb Catalysis for Off-Resonant Plasmonic Enhancement of Photoemission in Semiconductors
AUTHORS: Arup Neogi, Karol Gryczynski, Antonio Llopis, Jie Lin, Kyle Main, Ryoko Shimada, Zhiming Wang, Jihoon Lee, Gregory Salamo, and Arkadii Krokhin
JOURNAL/BOOK TITLE:
ACS Omega
VOLUME: 1                                 FIRST PAGE: 19
YEAR OF PUBLICATION:
2016                              KEY: A  


Abstract


 

The enhancement of light from semiconductors due to surface plasmons coupled resonantly to its emission is limited because of dissipation in the metal and is also restricted by the dielectric characteristics and homogeneity of the metal−semiconductor interface. We report a new mechanism based on electrostatic interactions of carriers and their image charges in metals to generate more photons from optical sources at frequencies that are off-resonant to the localized plasmon frequency. Coulomb catalysis of carrier accumulation resulting from the inhomogeneity of metal nanodroplets on a semiconductor’s surface can result in an enhancement of light that is nondissipative and does not require resonant coupling of plasmons to the emission wavelength. The enhancement occurs because of an increase in the ratio of radiative to nonradiative recombination in the vicinity of metal nanoparticles. It is equally effective with any type of metal and enhances radiation at any frequency, a property that is of principal importance for the realization of widely tunable semiconductor emitters. This fundamental mechanism provides a new perspective for improving the efficiency of light emitters and controlling carrier concentration on the nanoscale. The structural characteristics of the hybrid metal−semiconductor emitters are studied using electron microscopy and atomic force microscopy. We demonstrate the electrostatic mechanism by studying steady-state and transient photoluminescence from two-dimensional semiconductors, such as GaAs/AlGAs quantum wells, and bulk semiconductors, such as ZnO thin films, emitting in the near-IR and UV wavelength regimes, respectively.

 

Graphical Abstract



Metallic Nanodroplet Induced Coulomb Catalysis for Off-Resonant Plasmonic Enhancement of Photoemission in Semiconductors

Metallic Nanodroplet Induced Coulomb Catalysis for Off-Resonant Plasmonic Enhancement of Photoemission in Semiconductors

Metallic Nanodroplet Induced Coulomb Catalysis for Off-Resonant Plasmonic Enhancement of Photoemission in Semiconductors

 

 

 

TITLE: Systematic Control of the Size, Density and Configuration of Pt Nanostructures on Sapphire (0001) by the Variation of Deposition Amount and Dwelling Time
AUTHORS: P. Pandey, M. Sui, Q. Zhang, M. Y. Li, S. Kunwar and J. H. Lee
JOURNAL/BOOK TITLE:
Applied Surface Science
VOLUME: 368                                 FIRST PAGE: 198
YEAR OF PUBLICATION:
2016                              KEY: A                      IF: 3.15


Abstract


 

Metal nanoparticles (NPs) with controllable size, density and configuration can significantly enhance the energy conversion efficiency, detection sensitivity and catalytic activity as witnessed in various optoelectronic, optical sensing and electro-catalytic devices due to their shape and size dependent properties. In this work, we systematically investigate the evolution of the size, density and configuration of Pt nanostructures on sapphire (0001). In particular, we have demonstrated four different configuration and evolution of Pt nanostructures with the systematic control of deposition amount (DA) based on the Volmer-Weber growth model in conjunction with the surface energy minimization mechanism, diffusion and coalescence. The various size and configuration of Pt nanostructures with respect to DA are (i) nucleation of mini-sized round shaped Pt NPs (1 ≤ DA ≤ 5 nm), (ii) growth of large sized Pt NPs (10 ≤ DA ≤ 15 nm), (iii) isolated irregular nanostructures (20 ≤ DA ≤ 30 nm) and (iv) coalesced Pt nanostructures (DA ≥ 40). On the other hand, with the increased dwelling time (DT), irregular Pt NPs are fabricated with the increased size and improved uniformity between 0 and 450 s of annealing. The growth of Pt NPs is saturated when the dwelling time reaches the critical value between 900 and 1800 s, which can be attributed to the Ostwald ripening.

 

Graphical Abstract



Systematic Control of the Size, Density and Configuration of Pt Nanostructures on Sapphire (0001) by the Variation of Deposition Amount and Dwelling Time

Systematic Control of the Size, Density and Configuration of Pt Nanostructures on Sapphire (0001) by the Variation of Deposition Amount and Dwelling Time

 

 

 

TITLE: Optical Properties of a Quantum Dot-Ring System Grown Using Droplet Epitaxy
AUTHORS: Gabriel Linares-García, Lilia Meza-Montes, Eric Stinaff, S. M. Alsolamy, M. E. Ware, Y. I. Mazur, Z. M. Wang, Jihoon Lee and G. J. Salamo
JOURNAL/BOOK TITLE:
Nanoscale Research Letters
VOLUME: 
11                                 FIRST PAGE: 309
YEAR OF PUBLICATION:
2016                              KEY: A                      IF: 2.779


Abstract


 

Electronic and optical properties of InAs/GaAs nanostructures grown by the droplet epitaxy method are studied. Carrier states were determined by k·p theory including effects of strain and In gradient concentration for a model geometry. Wavefunctions are highly localized in the dots. Coulomb and exchange interactions are studied and we found the system is in the strong confinement regime. Microphotoluminescence spectra and lifetimes were calculated and compared with measurements performed on a set of quantum rings in a single sample. Some features of spectra are in good agreement.

 

Graphical Abstract



 

Optical Properties of a Quantum Dot-Ring System Grown Using Droplet Epitaxy


Optical Properties of a Quantum Dot-Ring System Grown Using Droplet Epitaxy

 

 

 

TITLE: Evolution of Self-Assembled Ag Nanostructures on c-plane Sapphire by the Systematic Control of Annealing Temperature
AUTHORS: M. Sui, S. Kunwar, P. Pandey, M. Y. Li, Q. Zhang
and J. H. Lee
JOURNAL/BOOK TITLE:
Superlattices and Microstructures
VOLUME: 100                                 FIRST PAGE: 1128
YEAR OF PUBLICATION:
2016                              KEY: A                      IF: 2.123


Abstract


 

The morphological evolution of various Ag nanostructures on c-plane sapphire is systematically investigated through the solid-state-dewetting by the control of annealing temperature between 200 and 950 °C with the Ag films of 60 and 10 nm. Various configurations of Ag nanostructures including Ag voids, wiggly and round nanoparticles are fabricated with the 60 nm due to the annealing temperature dependent surface diffusion, surface energy minimization and Ag sublimation. As a sharp distinction, highly dense semi-spherical nanoparticles are fabricated with the 10 nm set throughout the temperature range due to a much higher dewetting degree induced by the enhanced surface diffusion with a much thinner film. The reflectance spectra shows a spectral shift along with the size variation, i.e. blue shift with the decreased size and vice versa. The reflectance and Raman spectra reveal a sharp distinction between the two sets along with the strong correlation to the nanostructure morphology.

 

Graphical Abstract



 

Evolution of Self-Assembled Ag Nanostructures on c-plane Sapphire by the Systematic Control of Annealing Temperature

Evolution of Self-Assembled Ag Nanostructures on c-plane Sapphire by the Systematic Control of Annealing Temperature

 

 

 

TITLE: Tuning the Configuration of Au Nanostructures: From Vermiform-like, Rod-like, Triangular, Hexagonal, to Polyhedral Nanostructures on c-plane GaN
Full Text Access: http://rdcu.be/j3CD
AUTHORS: M. Sui, P. Pandey, M. Y. Li, Q. Zhang, S. Kunwar
and J. H. Lee
JOURNAL/BOOK TITLE:
Journal of Material Science
VOLUME: 51                                  FIRST PAGE: 1 - 17
YEAR OF PUBLICATION:
2016                              KEY: A                      IF: 2.302


Abstract


 

The systematic control over the configuration, size and density of Au nanostructures can directly improve or optimize the physical, chemical and optoelectronic properties and thus the functionality in the related applications. In this work, we successfully demonstrate the systematic configurational transition of self-assembled Au nanostructures on c-plane GaN via the precise control of annealing temperature, deposition amount and annealing duration. Depending on the control of annealing temperature, self-assembled Au vermiform-like nanostructures are fabricated and evolve into the faceted Au nanorods and Au hexagons with the minimization of overall surface energy based on the Volmer-Weber growth model. With the deposition amount control, the volume-dependent transition of Au nanostructure configurations from triangles to hexagons and then to polyhedral is clearly observed and discussed based on the combinational effects of growth kinetics and surface free energy distribution. The configurational transition from irregular Au clusters to faceted nanostructures is witnessed along with the incremental variation of annealing duration based on the Ostwald-ripening.

 

Graphical Abstract



Tuning the Configuration of Au Nanostructures: From Vermiform-like, Rod-like, Triangular, Hexagonal, to Polyhedral Nanostructures on c-plane GaN

Tuning the Configuration of Au Nanostructures: From Vermiform-like, Rod-like, Triangular, Hexagonal, to Polyhedral Nanostructures on c-plane GaN

 

 

 

TITLE: Evolution of Morphological and Optical Properties of Self-assembled Ag Nanostructures on c-plane Sapphire (0001) by the precise control of Deposition Amount
AUTHORS:
S. Kunwar, , M. Y. Li, P. Pandey, M. Sui, Q. Zhang and J. H. Lee
JOURNAL/BOOK TITLE:
Materials Research Express
VOLUME: 3                                 FIRST PAGE: 125006
YEAR OF PUBLICATION:
2016                              KEY: A                      IF: 1.068


Abstract


 

Silver (Ag) nanoparticles (NPs) have been widely adapted in various optoelectronic and sensing applications due to the size, shape and density dependent tunable properties. In this work, the systematic control of the size, configuration and density of self-assembled Ag nanostructures on c-plane sapphire (0001) is demonstrated through the solid state dewetting process by the variation of deposition amount (DA) at two distinctive temperature of 400 and 650 °C. The corresponding morphological evolution of Ag nanostructures is systematically discussed based on the diffusion, Volmer-Weber and coalescence growth model. In specific, at the relatively lower temperature of 400 °C, the Ag nanostructures evolve in three distinctive regimes based on the DA control: i.e. the dome-shaped Ag NPs between 2 and 14 nm (regime I), the irregular nano-mounds (NMs) between 20 and 40 nm (regime II), and the coalescence of Ag NMs into a layer between 60 and 200 nm (regime III). Meanwhile, at the relatively higher temperature of 650 °C, due to growth regime shift induced by the enhanced surface diffusion based on the increased thermal energy, the connected Ag NMs are resulted even at higher DAs and evolve along with the gradually increased DAs. The evolution of optical properties such as average reflectivity, plasmonic absorption band and the reflectance maxima (peaks) very sensitively respond to the evolution of size, shape and spacing of Ag nanostructures and discussed based on the surface plasmon, reflection and scattering. Specifically, the dome-shaped configuration exhibits strong absorption in the NIR region and weak absorption in visible region while the elongated NMs show the enhanced absorption in visible region. Furthermore, the Raman spectra (A1g vibrational mode) of the Ag nanostructures demonstrate the strong correlation with the evolution of size, density and surface coverage of the nanostructures.

 

Graphical Abstract



Evolution of Morphological and Optical Properties of Self-assembled Ag Nanostructures on c-plane Sapphire (0001) by the precise control of Deposition Amount

Evolution of Morphological and Optical Properties of Self-assembled Ag Nanostructures on c-plane Sapphire (0001) by the precise control of Deposition Amount

 

 

 

TITLE: From the Au nano-clusters to the nanoparticles on 4H-SiC (0001)
AUTHORS: M. Y. Li, Q. Zhang,P. Pandey, M. Sui, E. S. Kim and J. H. Lee
JOURNAL/BOOK TITLE:
Scientific Reports
VOLUME: 5                                  FIRST PAGE: 13954
YEAR OF PUBLICATION:
2015                              KEY: A                      IF: 5.578


Abstract


 

The control over the configuration, size, and density of Au nanoparticles (NPs) has offered a promising route to control the spatial confinement of electrons and photons, as a result, Au NPs with a various configuration, size and density are witnessed in numerous applications. In this work, we investigate the evolution of self-assembled Au nanostructures on 4H-SiC (0001) by the systematic variation of annealing temperature (AT) with several deposition amount (DA). With the relatively high DAs (8 and 15 nm), depending on the AT variation, the surface morphology drastically evolve in two distinctive phases, i.e. (I) irregular nano-mounds and (II) hexagonal nano-crystals. The thermal energy activates adatoms to aggregate resulting in the formation of self-assembled irregular Au nano-mounds based on diffusion limited agglomeration at comparatively low annealing temperature, which is also accompanied with the formations of hillocks and granules due to the dewetting of Au films and surface reordering. At high temperature, hexagonal Au nano-crystals form with facets along {111} and {100} likely due to anisotropic distribution of surface energy induced by the increased volume of NPs. With the small DA (3 nm), only dome shaped Au NPs are fabricated along with the variation of AT from low to elevated temperature.

 

Graphical Abstract



From the Au nano-clusters to the nanoparticles on 4H-SiC (0001)

From the Au nano-clusters to the nanoparticles on 4H-SiC (0001)

 

 

 

TITLE: Systematic Study on the Self-assembled Hexagonal Au Voids, Nano-clusters and Nanoparticles on GaN (0001)
AUTHORS: P. Pandey, M. Sui, M. Y. Li, Q. Zhang, E. S. Kim and J. H. Lee
JOURNAL/BOOK TITLE:
PLOS ONE
VOLUME: 10(8)
                                  FIRST PAGE: e0134637
YEAR OF PUBLICATION:
2015                              KEY: A                      IF: 3.324


Abstract


 

Au nano-clusters and nanoparticles (NPs) have been widely utilized in various electronic, optoelectronic, and bio-medical applications due to their great potentials. The size, density and configuration of Au NPs play a vital role in the performance of these devices. In this paper, we present a systematic study on the self-assembled hexagonal Au voids, nano-clusters and NPs fabricated on GaN (0001) by the variation of annealing temperature and deposition amount. At relatively low annealing temperatures between 400 and 600 oC, the fabrication of hexagonal shaped Au voids and Au nano-clusters are observed and discussed based on the diffusion limited aggregation model. The size and density of voids and nano-clusters can systematically be controlled. The self-assembled Au NPs are fabricated at comparatively high temperatures from 650 to 800 oC based on the Volmer-Weber growth model and also the size and density can be tuned accordingly. The results are symmetrically analyzed and discussed in conjunction with the diffusion theory and thermodynamics by utilizing AFM and SEM images, EDS maps and spectra, FFT power spectra, cross-sectional line-profiles and size and density plots.

 

Graphical Abstract



Systematic Study on the Self-assembled Hexagonal Au Voids, Nano-clusters and Nanoparticles on GaN (0001)

Systematic Study on the Self-assembled Hexagonal Au Voids, Nano-clusters and Nanoparticles on GaN (0001)

 

 

 

TITLE: Systematic Control of Self-Assembled Au Nanoparticles and Nanostructures Through the Variation of Deposition Amount, Annealing Duration, and Temperature on Si (111)
AUTHORS: M. Y. Li, M. Sui,P. Pandey, Q. Zhang, E. S. Kim and J. H. Lee
JOURNAL/BOOK TITLE:
Nanoscale Research Letters
VOLUME:  
10                                FIRST PAGE: 494
YEAR OF PUBLICATION:
2015                              KEY: A                      IF: 2.779


Abstract


 

The size, density, and configurations of Au nanoparticles (NPs) can play important roles in controlling the electron mobility, light absorption, and localized surface plasmon resonance, and further in the Au NP-assisted nanostructure fabrications. In this study, we present a systematical investigation on the evolution of Au NPs and nanostructures on Si (111) by controlling the deposition amount (DA), annealing temperature (AT), and dwelling time (DT). Under an identical growth condition, the morphologies of Au NPs and nanostructures drastically evolve when the DA is only slightly varied, based on the Volmer-Weber and coalescence models: i.e. I: mini NPs, II: mid-sized round dome-shaped Au NPs, III: large Au NPs, and IV: coalesced nanostructures. With the AT control, three distinctive ranges are observed: i.e., NP nucleation, Au NPs maturation and melting. The gradual dimensional expansion of Au NPs is always compensated with the density reduction, which is explained with the thermodynamic theory. The DT effect is relatively minor on Au NPs, a sharp contrast to other metallic NPs, which is discussed based on the Ostwald-ripening.

 

Graphical Abstract



Systematic Control of Self-Assembled Au Nanoparticles and Nanostructures Through the Variation of Deposition Amount, Annealing Duration, and Temperature on Si (111)

Systematic Control of Self-Assembled Au Nanoparticles and Nanostructures Through the Variation of Deposition Amount, Annealing Duration, and Temperature on Si (111)

 

 

 

TITLE: Diamagnetic and paramagnetic shifts in self-assembled InAs lateral quantum dot molecules
AUTHORS: Xinran Zhou, Miquel Royo, Weiwen Liu, Jihoon H. Lee, Gregory. J. Salamo, Juan I. Climente, and Matthew F. Doty
JOURNAL/BOOK TITLE:
Physical Review B
VOLUME: 91                                 FIRST PAGE: 205427
YEAR OF PUBLICATION:
2015                              KEY: A                      IF: 3.664


Abstract


 

We uncover the underlying physics that explains the energy shifts of discrete states of individual InAs lateral quantum dot molecules (LQDMs) as a function of magnetic fields applied in the Faraday geometry. We observe that ground states of the LQDM exhibit a diamagnetic shift while excited states exhibit a paramagnetic shift. We explain the physical origin of the transition between these two behaviors by analyzing the molecular exciton states with effective mass calculations. We find that charge carriers in delocalized molecular states can become localized in single QDs with increasing magnetic field. We further show that the net effects of broken symmetry of the molecule and Coulomb correlation lead to the paramagnetic response.

 

Graphical Abstract



Diamagnetic and paramagnetic shifts in self-assembled InAs lateral quantum dot molecules

Diamagnetic and paramagnetic shifts in self-assembled InAs lateral quantum dot molecules

 

 

 

TITLE: Evolution of Self-Assembled Au NPs by controlling Annealing Temperature and Dwelling Time on Sapphire (0001)
AUTHORS: J. H. Lee, P. Pandey, M. Sui, M. Y. Li, Q. Zhang and S. Kunwar
JOURNAL/BOOK TITLE:
Nanoscale Research Letters
VOLUME:  10                                FIRST PAGE: 380
YEAR OF PUBLICATION: 2015                              KEY: A                      IF:
2.779


Abstract


 

Au nanoparticles (NPs) have been utilized in a wide range of device applications as well as catalysts for the fabrication of nanopores and nanowires, in which the performance of the associated devices and morphology of nanopores and nanowires are strongly dependent on the size, density and configuration of the Au NPs. In this paper, the evolution of self-assembled Au nanostructures and NPs on sapphire (0001) is systematically investigated with the variation of annealing temperature (AT) and dwelling time (DT). At the low temperature range between 300 and 600 oC, three distinct regimes of the Au nanostructure configuration are observed i.e. the vermiform-like Au piles, irregular Au nano-mounds and Au islands. Subsequently, being provided with relatively high thermal energy between 700 to 900 oC, the round dome shaped Au NPs are fabricated based on the Volmer-Weber growth model. With the increased AT, the size of the Au NPs is gradually increased due to more favorable surface diffusion while the density is gradually decreased as a compensation. On the other hand, with the increased DT, the size and density of Au NPs decreases due to the evaporation of Au at relatively high annealing temperature at 950 oC.

 

Graphical Abstract



Evolution of Self-Assembled Au NPs by controlling Annealing Temperature and Dwelling Time on Sapphire (0001)

Evolution of Self-Assembled Au NPs by controlling Annealing Temperature and Dwelling Time on Sapphire (0001)

 

 

 

TITLE: Shape transformation of self-assembled Au nanoparticles by the systematic control of deposition amount on Sapphire (0001)
AUTHORS: P. Pandey, M. Sui, M. Y. Li, Q. Zhang, E. S. Kim and J. H. Lee
JOURNAL/BOOK TITLE:
RSC Advances
VOLUME: 5                                 FIRST PAGE: 66212
YEAR OF PUBLICATION:
2015                              KEY: A                      IF: 3.840


Abstract


 

The shape and size dependent optical, physical and chemical properties of isotropic and anisotropic gold nanoparticles (Au NPs) have attracted significant research interests for the applications in various optoelectronic devices. In this paper, we systematically study the evolution of shape and size of self-assembled Au NPs by the variation of Au deposition amount on Sapphire (Al2O3) (0001). With the sufficient thermal energy (1000 oC) provided, dome shape Au NPs are fabricated on sapphire based on the Volmer-Weber growth model, due to the isotropic surface energy distribution. Furthermore, we observe the incremental variation of Au deposition amount is responsible for the transformation of isotropic to anisotropic Au nanoparticles (nanocrystals). An anisotropic nanoparticles reflect variant properties in their different crystalline surfaces and thus the utilization of anisotropic nanoparticles can lead to the comparatively high efficiency of related device applications. The addition of Au deposition amount leads to the facet formation on the lowest possible energy crystalline planes of NPs such that the orientation of top facet of Au NPs are (111) plane parallel to the (0001) plane of sapphire. However, due to many other higher index facet formation, the NPs look almost dome shaped at high amount of Au deposition. Overall, the shape transformation of NPs from dome, truncated hexagonal pyramid, elongated truncated hexagonal pyramid, truncated cone to multifaceted dome is observed along with the variation of Au deposition amount on Sapphire (Al2O3) (0001).

 

Graphical Abstract



Shape transformation of self-assembled Au nanoparticles by the systematic control of deposition amount on Sapphire (0001)

Shape transformation of self-assembled Au nanoparticles by the systematic control of deposition amount on Sapphire (0001)

 

 

 

TITLE: Configuration, Dimension and Density Control of 3-D Gold Nanostructures on various Type-B GaAs surfaces by the Systematic Variation of Annealing Temperature, Annealing Duration and Deposition Amount
AUTHORS: D Lee, M. Sui, M. Y. Li, P. Pandey, Q. Zhang,
E. S. Kim and J. H. Lee
JOURNAL/BOOK TITLE:
3D Research
VOLUME:  
6                                FIRST PAGE: 28(1) - 28(14)
YEAR OF PUBLICATION:
2015                              KEY: A


Abstract


 

Metallic nanoparticles have received extensive research attention due to their potential to be utilized in catalytic, electronic and optical applications. Tunable feature of quantum effect related to the configuration, dimension as well as the density of nanoparticles makes them appropriate building blocks for their applications at the nano-scale. In this paper, we systematically investigate the fabrication of self-assembled Au nanoparticles on high–index type-B GaAs (n11), where n is 9, 8, 4, and 2. By means of varying annealing temperature, Au deposition amount and annealing duration, the evolution of Au nanoparticles in terms of the average height, lateral diameter and average density is systematically studied. We observe that the variation of annealing temperature leads to an abrupt configuration evolution from the wiggly Au nanostructures to the round-dome shaped nanoparticles due to the limited and/or enhanced surface diffusion at various temperatures. Meanwhile, the variation of deposition amount leads to a wide range of dimensions of Au nanoparticles as a result of the size increase and the corresponding density decrease. Furthermore, based on the annealing duration control, the size of Au nanoparticles tends to be gradually increased owing to the Ostwald-ripening. Meanwhile, the effect of surface index on the size and density is also witnessed. The results are systematically analyzed by using the atomic force microscope images, energy-dispersive X-ray spectroscopy spectra and maps, Fourier filter transforms power spectra, cross-sectional line-profiles and size and density plots.

 

Graphical Abstract



Configuration, Dimension and Density Control of 3-D Gold Nanostructures on various Type-B GaAs surfaces by the Systematic Variation of Annealing Temperature, Annealing Duration and Deposition Amount

Configuration, Dimension and Density Control of 3-D Gold Nanostructures on various Type-B GaAs surfaces by the Systematic Variation of Annealing Temperature, Annealing Duration and Deposition Amount

 

 

 

TITLE: Observation of Shape, Configuration, and Density of Au Nanoparticles on Various GaAs Surfaces via Deposition Amount, Annealing Temperature, and Dwelling Time
AUTHORS: D. Lee, M. Y. Li,
M. Sui, Q. Zhang, P. Pandey, E. S. Kim and J. H. Lee
JOURNAL/BOOK TITLE:
Nanoscale Research Letters
VOLUME:  
10                                FIRST PAGE: 240
YEAR OF PUBLICATION:
2015                              KEY: A                      IF:2.779


Abstract


 

Metallic nanoparticles have been widely witnessed in many applications: serving as the catalysts for various nanowire systems, as the active mediums of various device applications, and also for the nanoscale templates for hybrid quantum structures. In the performance of devices and configurations of the resulting nanostructures, the size and density of nanoparticles play critical roles. In this paper, the control of self-assembled Au droplets on GaAs (100), (110), and (111) is systematically investigated through the variation of deposition amount (DA), annealing temperature (AT), and dwelling time (DT). Based on the
Volmer–Weber growth model, the formation of Au droplets and dramatic evolution of Au nanostructures on various GaAs surfaces is observed from the Au clusters to the round-dome shapes with the AT variation between 250 and 550 °C. With the systematic DA control, a radical size and density evolution of Au droplets shows the size expansion of over 400 % in average height and 800 % in average lateral diameter, while the density shows over two orders of decrease. With the DT variation, the self-assembled Au droplets tend to grow larger due to the Ostwald ripening while a clear distinction among the surface indexes is observed.

 

Graphical Abstract



Observation of Shape, Configuration, and Density of Au Nanoparticles on Various GaAs Surfaces via Deposition Amount, Annealing Temperature, and Dwelling Time

Observation of Shape, Configuration, and Density of Au Nanoparticles on Various GaAs Surfaces via Deposition Amount, Annealing Temperature, and Dwelling Time

 

 

 

TITLE: Self-Assembly of Multiple Stacked Nanorings by Vertically Correlated Droplet Epitaxy
AUTHORS:
J. Wu, Y. Hirono, X. Li, Z. M. Wang, J. H. Lee, M. Benamara, S. Luo, Y. I. Mazur, E. S. Kim, and G. J. Salamo
JOURNAL/BOOK TITLE: Advanced Functional Materials
VOLUME:  24                                FIRST PAGE: 530
YEAR OF PUBLICATION:
2014                              KEY: A                      IF: 10.439


Abstract


 

Fabrication of advanced artificial nanomaterials is a long-term pursuit to fulfill the promises of nanomaterials. In the last ten years, Droplet Epitaxy has been emerging as a versatile fabrication method for various complex nanomaterials, but there is a lack of growth protocol to control the growth vertically. Here we report a vertically correlated Droplet Epitaxy growth method. We find that the nanodroplets form preferable on the preexisting nanorings, which enables fabrication of vertically aligned nanostructures by Droplet Epitaxy. Nucleation thermodynamics and growth kinetics have been proposed to explain the vertically correlated Droplet Epitaxy. Heterojunctions can be realized at nanoscale by the presented method. In addition, the nucleation thermodynamics of nanodroplets observed in this article will allow site-controlled fabrication of nanostructures.

 


Graphical Abstract



Self-Assembly of Multiple Stacked Nanorings by Vertically Correlated Droplet Epitaxy

Self-Assembly of Multiple Stacked Nanorings by Vertically Correlated Droplet Epitaxy

Self-Assembly of Multiple Stacked Nanorings by Vertically Correlated Droplet Epitaxy

 

 

 

TITLE: Origin of nanohole formation by etching based on droplet epitaxy
AUTHORS:X. Li, J. Wu, Z. M. Wang, B. Liang, J. H. Lee, E. S. Kim, and G. J. Salamo
JOURNAL/BOOK TITLE: Nanoscale
VOLUME: 6                                 FIRST PAGE: 2675
YEAR OF PUBLICATION:
2014                              KEY: A                      IF: 6.739   

Abstract



 

The self-organized GaAs nanoholes are fabricated by Ga droplet etching based on droplet epitaxy. A theoretical model is proposed to explain the basic mechanism behind droplet etching. With this model, it is possible to directly simulate the time evolution of nanohole structures. Our analysis shows that the morphology of the holed nanostructures can be controlled through regulating experimental conditions. For instance, high etching rate, high number density of droplets, large size of droplet, or low intensity of As flux can increase the depth of hole. The results based on the proposed model are in good agreement with experimental observations.

 


Graphical Abstract



Origin of nanohole formation by etching based on droplet epitaxy

Origin of nanohole formation by etching based on droplet epitaxy



 

 

TITLE: Droplets to Merged Nanostructures: Evolution of Gold Nanostructures by the Variation of Deposition Amount on Si(111)
AUTHORS: M. Y. Li, M. Sui, E. S. Kim
and J. H. Lee
JOURNAL/BOOK TITLE: Crystal Growth & Design
VOLUME: 14                                 FIRST PAGE: 1128
YEAR OF PUBLICATION:
2014                              KEY: A                      IF: 4.558 


Abstract


 

We studied the evolution of Au nanostructures in dome-shaped Au droplets that merge into Au nanostructures on Si (111) by systematically controlling the Au deposition amount (DA) under a fixed annealing temperature and annealing duration. Even under identical growth conditions, the configuration, density, and size of Au nanostructures drastically vary depending on the amount of Au deposition in the range of 0.5 - 20 nm. Through systematic analysis of the resulting Au nanostructures in determining the average height, density, and surface area ratio, as well as the Fourier filter transform power spectrum and cross-sectional line-profiles, we clearly demonstrate the evolution process of Au nanostructures and thus the control of the size, density, and configurations. The evolution of Au droplets on Si (111) with the increased DAs initially appears to be progressing based on the Volmer–Weber growth mode for the Au DAs up to 4 nm, but with further increased DAs up to 20 nm, it turns out that the growth occurs in the Frank – van der Merwe growth mode, resulting in a layer-by-layer growth. In addition, by the sharp comparison between pre-annealed samples and resulting Au nanostructures, we quantitatively present the evolution of Au nanostructures. This study can find applications in the nanowire fabrication on Si (111).

 

Graphical Abstract



Evolution of Gold Nanostructures by the Variation of Deposition Amount on Si (111): Droplets to Merged Nanostructures
Evolution of Gold Nanostructures by the Variation of Deposition Amount on Si (111): Droplets to Merged Nanostructures


 

 

 

TITLE: Fabrication of self-assembled Au droplets by systematic variation of deposition amount on various type-B GaAs surfaces
AUTHORS: M. Sui, M. Y. Li, E. S. Kim and J. H. Lee
JOURNAL/BOOK TITLE:
Nanoscale Research Letters
VOLUME: 9                                 FIRST PAGE:
436
YEAR OF PUBLICATION:
2014                              KEY: A                      IF: 2.481


Abstract


 

The fabrication of self-assembled Au droplets is successfully demonstrated on various GaAs (n11)B, where n is 2, 4, 5, 7, 8 and 9, by the systematic variation of Au deposition amount (DA) from 2 to 12 nm. Under an identical growth condition, the self-assembled Au droplets of mini to super-sizes are successfully synthesized via the Volmer-Weber growth mode. Depending on the DA, an apparent evolution trend is clearly observed in terms of the average height (AH), lateral diameter (LD) and average density (AD). For example, as compared with the mini Au droplets with the DA of 2 nm: AH 22.5 nm and LD 86.5 nm, the super-sized Au droplets show significantly increased AH by 316% and LD by 320% with 12 nm DA reaching AH: 71.1 and LD: 276.8 nm on GaAs (211)B. In addition, accompanied with the dimensional expansion, the AD of Au droplets drastically swings on the two orders of magnitudes between 3.2 × 10^10 and 4.2 × 10^8 cm^-2. The results are systematically analyzed in aspects of the AFM and SEM images, EDS spectra, cross-sectional line-profiles, FFT power spectra and root mean squared (RMS) roughness as well as the droplet dimension and density summary respectively.

 

Graphical Abstract



Fabrication of self-assembled Au droplets by systematic variation of deposition amount on various type-B GaAs surfaces

Fabrication of self-assembled Au droplets by systematic variation of deposition amount on various type-B GaAs surfaces

 

 

 

TITLE: Mini Droplets to Super Droplets: Evolution of Self-Assembled Au droplets on GaAs (111)B and (110)
AUTHORS: M. Sui, M. Y. Li, E. S. Kim and J. H. Lee
JOURNAL/BOOK TITLE: Journal of Applied Crystallography
VOLUME: 
47                                 FIRST PAGE: 505-510
YEAR OF PUBLICATION:
2014                              KEY: A                      IF: 3.95   


Abstract


 

In this article, the effect of deposition amount on self-assembled Au droplets fabricated on GaAs(111)B and (110) is presented. The investigation is systematically performed by the variation of the Au deposition amount from 2 to 20 nm while fixing the other growth parameters such as annealing temperature and duration to clearly observe the effect. Under identical growth conditions, the self-assembled Au droplets show significantly different size and density depending on the amount of Au deposition: i.e. the average height varies by 436% from 21.8 to 95.5 nm and the average diameter swings by 827% from 52 to 430 nm, showing that the size increase is dominated by the lateral expansion. Meanwhile the average density varies by over two orders of magnitude from 1.24 × 108 to 4.48 × 1010 cm-2 on GaAs(111)B. With relatively low Au deposi­tion amounts, below 3 nm, round dome-shaped mini Au droplets with high packing density can be fabricated, while super large Au droplets result with higher deposition amounts, above 10 nm, with a density two orders of magnitude lower. It is also found that the surface index has a minor effect on the fabrication of self-assembled Au droplets with the variation of deposition amount. The results are systematically analyzed and discussed in terms of atomic force microscopy and scanning electron microscopy images, line profiles, power spectrums, r.m.s. surface roughness, and size and density plots.

 

Graphical Abstract



Mini Droplets to Super Droplets: Evolution of Self-Assembled Au droplets on GaAs (111)B and (110)
Mini Droplets to Super Droplets: Evolution of Self-Assembled Au droplets on GaAs (111)B and (110)
Mini Droplets to Super Droplets: Evolution of Self-Assembled Au droplets on GaAs (111)B and (110)
Mini Droplets to Super Droplets: Evolution of Self-Assembled Au droplets on GaAs (111)B and (110)

 

 

 

TITLE: Annealing Temperature Effect on the Fabrication of Self-assembled Gold Droplets on various Type-B GaAs Surfaces
AUTHORS: M. Sui, M. Y. Li, E. S. Kim and J. H. Lee
JOURNAL/BOOK TITLE:
CrystEngComm
VOLUME:  16                                 FIRST PAGE: 4390
YEAR OF PUBLICATION:
2014                              KEY: A                      IF: 3.858


Abstract


 

In this paper, the fabrication and detailed evolution process of the self-assembled Au droplets are successful demonstrated on diverse GaAs type-B (n11) substrates, where n is 9, 7, 5, 4, and 2. The evolution process is systematically investigated by the variation of the annealing temperature (Ta) from 250 to 550 °C. Self-assembled Au clusters begin to nucleate at 300 °C as a nucleation stage and wiggly nanostructures with the connected geometry are resulted at 350 °C as a transitional stage. Between 400 and 550 °C, the self-assembled Au droplets are successful fabricated and they show the increased average dimensions along with the decreased density as a function of the Ta while showing the improved size uniformity above 500 °C. Depending on the substrates utilized, the resulting Au droplets show the dependency on the index throughout the Ta range, which is systematically analyzed in relation to the RMS roughness.

 


Graphical Abstract



Annealing Temperature Effect on the Fabrication of Self-assembled Gold Droplets on various Type-B GaAs Surfaces

Annealing Temperature Effect on the Fabrication of Self-assembled Gold Droplets on various Type-B GaAs Surfaces

Annealing Temperature Effect on the Fabrication of Self-assembled Gold Droplets on various Type-B GaAs Surfaces

 

 


TITLE: Inside front cover: Annealing Temperature Effect on the Fabrication of Self-assembled Gold Droplets on various Type-B GaAs Surfaces (CrystEngComm, 2014,16, 4342-4342)
AUTHORS: M. Sui, M. Y. Li, E. S. Kim and J. H. Lee
JOURNAL/BOOK TITLE: CrystEngComm
VOLUME:  16                                 FIRST PAGE: 4390
YEAR OF PUBLICATION: 2014                              KEY: A                      IF:
3.858
Journal cover
 

 

TITLE: Effect of deposition amount on the evolution of self-assembled Au droplets on GaAs (111)A and (100)
AUTHORS: M. Y. Li.
, M. Sui, E. S. Kim and J. H. Lee
JOURNAL/BOOK TITLE:
Nanoscale Research Letters
VOLUME:                                  FIRST PAGE:
YEAR OF PUBLICATION:
2014                              KEY: A                      IF: 2.481


Abstract


 

In this paper, we report the effect of Au thickness on the self-assembled Au droplets on GaAs (111)A and (100). The evolution of Au droplets on GaAs (111)A and (100) with the increased Au thickness progress in the Volmer–Weber growth mode; results in distinctive 3-D islands. Under an identical growth condition, depending on the thickness of Au deposition, the self-assembled Au droplets show different size and density distributions, while the average height is increased by ~ 420% and the diameter is increased by ~ 830%, indicating a preferential lateral expansion. Au droplets show an opposite evolution trend; the increased size along with the decreased density as a function of the Au thickness and over the thickness range tested, the density shifts on the orders of over two magnitude between 4.23×1010 and 1.16×108 cm-2. At relatively thinner thicknesses below 4 nm, the self-assembled Au droplets sensitively respond to the thickness variation, evidenced by the sharper slopes of dimensions and density plots. The results are systematically analyzed and discussed in terms of atomic force microscope (AFM), scanning electron microscope (SEM), energy-dispersive x-ray spectroscopy (EDS), cross-sectional surface line-profiles and Fourier filter transform (FFT) power spectra.

 

Graphical Abstract



Effect of deposition amount on the evolution of self-assembled Au droplets on GaAs (111)A and (100)

Effect of deposition amount on the evolution of self-assembled Au droplets on GaAs (111)A and (100)

 

 

 

TITLE: Control of size and density of self-assembled Au droplets via systematic deposition amount control on high-index GaAs type-A surfaces
AUTHORS: M. Y. Li, M. Sui, E. S. Kim and J. H. Lee
JOURNAL/BOOK TITLE:
Japanese Journal of Applied Physics
VOLUME:  53                                FIRST PAGE: 095502
YEAR OF PUBLICATION:
2014                              KEY: A                      IF: 1.057


Abstract


 

Au droplets as a catalyst can be used to determine the size, density, and configuration of nanowires (NWs) during crystallization at the liquid-solid interface, and the growth direction, cross-sectional shape, and even the quality of the NWs can be controlled by adjusting the substrate index utilized. In this study, the control of the size and density of self-assembled Au droplets is systematically demonstrated via the deposition amount (DA) control between 2 and 12 nm on various GaAs type-A substrates: (711)A, (511)A, (411)A, and (311)A. The self-assembled Au droplets are formed owing to the much higher binding energy between Au adatoms than the energy between Au atoms and substrate atoms based on the Volmer–Weber growth mode, and even up to 12 nm DA, the three-dimensional (3D) island phase (droplets) without coalescence is observed. Within the DA range, the self-assembled Au droplets sensitively respond to the DA variation, which results in over 3 times increment in dimensions along with the corresponding change in density on the two orders of magnitude from ~ 108 to ~1010. Depending on the index utilized, the high index effect is not obvious owing to weak binding energy between GaAs substrate and Au adatoms and the wide DA range. The results are systematically analyzed using atomic force microscope (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), cross-sectional line profiles, and Fourier filter transform (FFT) power spectra.

 

Graphical Abstract



Control of size and density of self-assembled Au droplets via systematic deposition amount control on high-index GaAs type-A surfaces

Control of size and density of self-assembled Au droplets via systematic deposition amount control on high-index GaAs type-A surfaces

 

 

 

TITLE: Nucleation, transition and maturing of the self-assembled Au droplets on various Type-A GaAs substrates
AUTHORS: M. Y. Li., M. Sui, E. S. Kim and J. H. Lee
JOURNAL/BOOK TITLE:
Journal of Applied Physics
VOLUME: 116                                 FIRST PAGE: 084301
YEAR OF PUBLICATION:
2014                              KEY: A                      IF: 2.185


Abstract


 

In this study, the fabrication of self-assembled Au droplets is successfully demonstrated on various type-A GaAs substrates: (711)A, (511)A, (411)A, and (311)A. The nucleation of the self-assembled tiny Au clusters is observed at 300 oC. As an intermediate stage, corrugated Au nanostructures are clearly observed at 350 oC on various type-A GaAs surfaces, rarely witnessed on other substrates. Based on the Volmer-Weber growth mode, the dome-shaped Au droplets with excellent uniformities are successfully fabricated between 500 and 550 oC. As a function of annealing temperature, the self-assembled Au droplets show the increased dimensions including average height and diameter, compensated by the decreased average density. Depending on the substrate indices utilized, the size and density of Au droplets show clear differences throughout the whole temperature range. The results are symmetrically analyzed by using AFM images, cross-sectional line-profiles, size and density plots, height distribution histograms and FFT power spectra.

 

Graphical Abstract



Nucleation, transition and maturing of the self-assembled Au droplets on various Type-A GaAs substrates

Nucleation, transition and maturing of the self-assembled Au droplets on various Type-A GaAs substrates

Nucleation, transition and maturing of the self-assembled Au droplets on various Type-A GaAs substrates

 

 

 

TITLE: “From the Nucleation of Wiggling Au Nanostructures To the Dome Shaped Au Droplets on GaAs (111)A, (110), (100) and (111)B
AUTHORS:
M. Y. Li, M. Sui, E. S. Kim and J. H. Lee
JOURNAL/BOOK TITLE:
Nanoscale Research Letters
VOLUME: 9                                 FIRST PAGE: 113
YEAR OF PUBLICATION:
2014                              KEY: A                      IF: 2.481


Abstract


 

In this paper, the systematic evolution process of self-assembled Au droplets is successfully demonstrated on GaAs (111)A, (110), (100), and (111)B. On various GaAs substrates, self-assembled Au clusters begin to nucleate at around 300 [degree sign]C, and then, they develop into wiggly Au nanostructures at 350 [degree sign]C. Between 400 [degree sign]C and 550 [degree sign]C, the self-assembled dome-shaped Au droplets with fine uniformity are fabricated with various sizes and densities based on the Volmer-Weber growth mode. Depending on the annealing temperature, the size including the average height and lateral diameter and the density of Au droplets show the opposite trend of increased size with correspondingly decreased density as a function of the annealing temperature due to the difference in the diffusion length of adatoms at varied activation energy. Under an identical growth condition, depending on the surface index, the size and density of Au droplets show a clear distinction, observed throughout the temperature range. The results are systematically analyzed and discussed in terms of atomic force microscopy (AFM) images, cross-sectional line profiles, and Fourier filter transform (FFT) power spectra as well as the summary plots of the size and density.

 

Graphical Abstract



From the Nucleation of Wiggling Au Nanostructures To the Dome Shaped Au Droplets on GaAs (111)A, (110), (100) and (111)B

From the Nucleation of Wiggling Au Nanostructures To the Dome Shaped Au Droplets on GaAs (111)A, (110), (100) and (111)B

From the Nucleation of Wiggling Au Nanostructures To the Dome Shaped Au Droplets on GaAs (111)A, (110), (100) and (111)B

 

 

 

TITLE: Coulomb interaction signatures in self-assembled lateral quantum dot molecules
AUTHORS: Xinran. R. Zhou, J. H.Lee, Gregory. J. Salamo, Miquel. Royo, Juan. I. Climente, and Matthew. F. Doty
JOURNAL/BOOK TITLE: Physical Review B
VOLUME: 87                                 FIRST PAGE: 125309
YEAR OF PUBLICATION:
2013                              KEY: A                      IF: 3.691

Abstract



 

We use photoluminescence spectroscopy to investigate the ground state of single self-assembled InGaAs lateral quantum dot molecules. We apply a voltage along the growth direction that allows us to control the total charge occupancy of the quantum dot molecule. Using a combination of computational modeling and experimental analysis, we assign the observed discrete spectral lines to specific charge distributions. We explain the dynamic processes that lead to these charge configurations through electrical injection and optical generation. Our systemic analysis provides evidence of inter-dot tunneling of electrons as predicted in previous theoretical work.

 


Graphical Abstract



Coulomb interaction signatures in self-assembled lateral quantum dot moleculesCoulomb interaction signatures in self-assembled lateral quantum dot molecules

Coulomb interaction signatures in self-assembled lateral quantum dot molecules



 

 

TITLE: Epitaxially Self-Assemblied Quantum Dot Pairs
AUTHORS: J. Wu, X. Hu, J. H. Lee, E
. S. Kim, Z. M. Wang
JOURNAL/BOOK TITLE: Advanced Optical Materials
VOLUME: 1(3)                                 FIRST PAGE: 201-
214
YEAR OF PUBLICATION:
2013                              KEY: A                       IF: 4.062

Abstract



 

The present paper reviews the recent efforts and achievements regarding the fabrication techniques of self-assembled quantum dot pairs. Quantum dot pairs, the simplest but most-investigated quantum dot molecules, have attracted significant attention due to their potential applications in quantum information technologies. In the last several decades, the development of epitaxial growth has advanced the design and control of how novel quantum dot pairs form at nanoscale. Both vertically and laterally aligned quantum dot pairs can be grown using the molecular beam epitaxy technique. In this review, we provide assess various growth methods of aligned quantum dot pairs fabricated by molecular beam epitaxy. We highlight the recent development of novel growth techniques and discuss the morphological, electrical, and optical properties of quantum dot pairs. Using advanced epitaxial growth techniques to fabricate well-controlled quantum dot pairs opens the door to developing of advanced quantum information technologies and understanding the unveiled physics and properties of artificial quantum molecules.

 


Graphical Abstract



Self-Assembly of Quantum Dot Pairs

Self-Assembly of Quantum Dot Pairs

Self-Assembly of Quantum Dot Pairs


 

 

TITLE: Effects of Rapid Thermal Annealing on the Optical Properties of Strain-Free Quantum Ring Solar Cells
AUTHORS:
J. Wu, Z. M. Wang, V. G. Dorogan, S. Li, J. H. Lee, Y. I. Mazur, E. S. Kim, and G. J. Salamo
JOURNAL/BOOK TITLE: Nanoscale Research Letters
VOLUME: 8                                 FIRST PAGE: 12
YEAR OF PUBLICATION:
2013                              KEY: A                      IF: 2.52

Abstract



 

Strain-free GaAs/Al0.33Ga0.67As quantum rings are fabricated by droplet epitaxy. Both photoresponse and photoluminescence spectra confirm optical transitions in quantum rings, suggesting that droplet epitaxial nanomaterials are applicable to intermediate band solar cells. The effects of post-growth annealing on the quantum ring solar cells are investigated, and the optical properties of the solar cells with and without thermal treatment are characterized by photoluminescence technique. Rapid thermal annealing treatment has resulted in the significant improvement of material quality, which can be served as a standard process for quantum structure solar cells grown by droplet epitaxy.

 


Graphical Abstract



Optical Properties of Strain-Free Quantum Ring Solar Cells
Optical Properties of Strain-Free Quantum Ring Solar Cells
Optical Properties of Strain-Free Quantum Ring Solar Cells

 

 

 

TITLE: Self-Assembled InGaAs Quantum Dot Clusters with Controlled Spatial and Spectral Properties
AUTHORS: Megan Creasey, Ji-Hoon Lee, Zhi-Ming Wang, Gregory J. Salamo and
Xiaoqin Li
JOURNAL/BOOK TITLE:
Nano Letters
VOLUME: 12                                 FIRST PAGE: 5169–5174
YEAR OF PUBLICATION:
2012                              TYPE: A                      IF: 13.198

Abstract



 

Planar quantum dot clusters (QDCs) consisting of six InGaAs quantum dots (QDs) formed around a GaAs nanomound are the most sophisticated self-assembled QDCs grown by molecular beam epitaxy thus far. We present the first photoluminescence measurements on individual hexa-QDCs with high spatial, spectral, and temporal resolution. In the best QDCs, the excitons confined in individual QDs are remarkably close in energy, exhibiting only a 10 meV spread. In addition, a biexponential decay profile and small variation in decay rates for different QDs was observed. The homogeneous energetics and dynamics suggest that the sizes, shapes, and composition of the QDs within these clusters are highly uniform.

 


Graphical Abstract



Self-Assembled InGaAs Quantum Dot Clusters with Controlled Spatial and Spectral Properties

Self-Assembled InGaAs Quantum Dot Clusters with Controlled Spatial and Spectral Properties

Self-Assembled InGaAs Quantum Dot Clusters with Controlled Spatial and Spectral Properties



 

TITLE: Annealing temperature effect on self-assembled Au droplets on Si (111)
AUTHORS: M. Sui, M. Y. Li, E. S. Kim and J. H. Lee
JOURNAL/BOOK TITLE: Nanoscale Research Letters
VOLUME: 8                                 FIRST PAGE: 525
YEAR OF PUBLICATION:
2013                              KEY: A                      IF: 2.52  


Abstract


 

We investigate the effects of annealing temperature on self-assembled Au droplets on Si (111) substrates. To achieve this, we systematically vary the annealing temperatures while fixing other growth environment. The annealing temperature is varied from 50 to 850 °C with 2 nm Au deposition. With increased annealing temperatures for a fixed thickness of deposition, the height and diameter of Au droplets shows a gradual increase while the density gradually decreases. The results are systematically analyzed in aspects of cross-sectional line-profiles, FFT power spectra, height histogram, surface area ratio, and droplet dimension & density analyses respectively.

 


Graphical Abstract



Effects of annealing temperature on self-assembled Au droplets on Si (111)

Effects of annealing temperature on self-assembled Au droplets on Si (111)

 

 

 

TITLE: Strain-Free Ring-Shaped Nanostructures by Droplet Epitaxy for Photovoltaic Application
AUTHORS: J.
Wu, Z. M. Wang, V. G. Dorogan, S. Li, Z. Zhou, H. Li, J. H. Lee, E. S. Kim, Y. I. Mazur, and G. J. Salamo
JOURNAL/BOOK TITLE: Applied Physics Letters
VOLUME: 101                                 FIRST PAGE: 043904
YEAR OF PUBLICATION:
2012                              TYPE: A                      IF: 3.844

Abstract



 

Droplet epitaxy is a flexible nanomaterial growth technique and is a potential method to fabricate advanced electronic and optoelectronic devices. Here, we report strain-free GaAs/Al0.33Ga0.67As quantum ring solar cells fabricated by droplet epitaxy technique. Photoluminescence is used to study the electronic structure of the lattice-matched GaAs/Al0.33Ga0.67As quantum ring solar cells. Post-growth thermal annealing is used to improve the optical quality of the solar cell as well as device efficiency. A power conversion efficiency of 1.8% is demonstrated from a prototype quantum ring solar cell. This work opens new opportunities for quantum dot solar cells with strainfree nanostructures.

 


Graphical Abstract



Strain-Free Ring-Shaped Nanostructures

Strain-Free Ring-Shaped Nanostructures


 

 

TITLE: Observation of Ga Metal Droplet Formation on Photo-lithographically Patterned GaAs (100) Surface by Droplet Epitaxy
AUTHORS: Lei Gao, Y. K. Hirono, M. Y. Li,
J. Wu, S. M. Song, S. M. Koo, E. S. Kim, Zh. M. Wang, J. H. Lee and G. J. Salamo
JOURNAL/BOOK TITLE: IEEE Transactions on Nanotechnology 
VOLUME:  11                                 FIRST PAGE: 985
YEAR OF PUBLICATION:
2012                             TYPE: A                      IF: 2.292

Abstract
 

A sharp contrast on the density and size of Ga metal droplets is observed on various photo-lithographically patterned GaAs (100). As clearly evidenced by high-resolution scanning electron microscope (HR-SEM), Ga metal droplet density and size surprisingly differ on etched and un-etched surfaces under an identical growth condition. The apparent contrast on the density and size of droplets is clearly observed at the interface between etched and un-etched areas. Ga droplets exhibit much higher density and the size is much smaller on etched surface meanwhile the density is an order of magnitude lower and the size is much larger on un-etched surface. Along different directions, [011] & [01-1], due to anisotropic surface diffusion the density is about twice higher along [011] for the same strip pattern.

 


Graphical Abstract



Observation of Ga Metal Droplet FormationObservation of Ga Metal Droplet Formation

 

 

 

TITLE: Critical Size of Self-Propelled Motion of Droplets on GaAs (100) Surface
AUTHORS: J. Wu, Z. M. Wang, A. Z. Li, M.
Benamara, J. H. Lee, S. D. Koukourinkova, E. S. Kim, G. J. Salamo
JOURNAL/BOOK TITLE: J
ournal of Applied Physics
VOLUME: 112                                 FIRST PAGE: 043523
YEAR OF PUBLICATION:
2012                              TYPE: A                      IF: 2.168

Abstract



 

The running liquid Ga droplets on GaAs surface (001) are presented and analyzed by scanning electron microscope and atomic force microscope. Self-motion of Ga droplet on GaAs surface is confirmed by microscope measurements. The liquid droplets are found to move with an initial critical diameter and constantly increase size during motion. The critical diameter of moving Ga droplets is observed to be 1.9 µm on GaAs (011) surface at preparation temperature 680 °C. A linear relationship is found between droplet diameter and trail length. These experiment results are qualitatively analyzed to understand the phenomenon of self-running Ga droplets on GaAs surface.

 


Graphical Abstract

Critical Size of Self-Propelled Motion

Critical Size of Self-Propelled Motion

 

 

 

TITLE: Increased Light Trapping by Surface Nano-structuring on Si using MWCNT mask etching technique
AUTHORS: M. Y. Hwang, M. Y. Li, H. S. Kim, E. S. Kim, J. H. Lee and S. M. Koo
JOURNAL/BOOK TITLE: Journal of Nanoelectronics and Optoelectronics
VOLUME: 7                                  FIRST PAGE: 311
YEAR OF PUBLICATION: 2012                                   TYPE: A                        IF:
0.90

Abstract



 


We demonstrate an increased light-trapping on Si using surface nano-structuring technique. For comparison, four samples are prepared using conventional photolithography and carbon nanotube etch-mask technique. With a bare-Si set as a reference, the square-patterned Si using conventional photolithography shows an improved average light-trapping by ~12 %. When multi-walled carbon nanotubes (MWCNT) dispersed in isopropyl-alcohol is used as a etch mask, the average light-trapping level is improved by ~22 %. The average light-trapping is increased to ~ 38 % with MWCNT etch-masked Si with HMDS dispersion. The increase in light trapping level is most significant in UV region and becomes less noteworthy as wavelength increases. The increased light-trapping can be due to increased surface roughness and thus area. This result can find applications where the light-trapping is vital such as photovoltaics, photo-diodes and photo-transistors.


 


Graphical Abstract



Increased Light Trapping by Surface Nano-structuring Increased Light Trapping by Surface Nano-structuring

 


 

TITLE: Formation of Ga droplets on patterned GaAs (100) by molecular beam epitaxy
AUTHORS: M. Y. Li, Y. K. Hirono, S. D. Koukourinkova, M. Sui, S. M. Song, E. S. Kim, J. H. Lee, and G. J. Salamo
JOURNAL/BOOK TITLE:
Nanoscale Research Letters
VOLUME: 7                                 FIRST PAGE: 550(1) 
YEAR OF PUBLICATION:
2012                             TYPE: A                      IF:2.73

Abstract



 

In this paper, the formation of Ga droplets on photo-lithographically patterned GaAs (100) and the control of the size and density of Ga droplets by droplet epitaxy using molecular beam epitaxy are demonstrated. In extension of our previous result from the journal Physical Status Solidi A, volume 209 in 2012, the sharp contrast of the size and density of Ga droplets is clearly observed by high-resolution scanning electron microscope, atomic force microscope, and energy dispersive X-ray spectrometry. Also, additional monolayer (ML) coverage is added to strength the result. The density of droplets is an order of magnitude higher on the trench area (etched area), while the size of droplets is much larger on the strip top area (un-etched area). A systematic variation of ML coverage results in an establishment of the control of size and density of Ga droplets. The cross-sectional line profile analysis and root mean square roughness analysis show that the trench area (etched area) is approximately six times rougher. The atomic surface roughness is suggested to be the main cause of the sharp contrast of the size and density of Ga droplets and is discussed in terms of surface diffusion.

 


Graphical Abstract



Control of Size and Density of Liquid Ga Metal Droplets

Control of Size and Density of Liquid Ga Metal Droplets


 

 

TITLE: Influence of Ga coverage on the sizes of GaAs quantum dash pairs grown by high temperature droplet epitaxy
AUTHORS: J. Wu, Zh. M. Wang, S. Li,
J. H. Lee, Y. I. Mazur and G. J. Salamo
JOURNAL/BOOK TITLE: Physica
Status Solidi (RRL) - Rapid Research Letters
VOLUME: 6                                 FIRST PAGE: 309
YEAR OF PUBLICATION:
2012                             TYPE: A                      IF:2.218

Abstract



 

We investigate the formation of GaAs quantum dot pairs with different by droplet epitaxy. The GaAs quantum dot pairs of various sizes are fabricated by high temperature droplet epitaxy. Dual-sized quantum dot pairs are observed along [01-1] orientation. Depending on the Ga coverage, the width of the quantum dot pairs can be tuned from ~100 nm to ~300 nm while keeping the height in the range of 4 nm to 10 nm. Very narrow PL spectrum with FWHM=4.3 nm is observed for QDPs with 13 ML Ga coverage.

 


Graphical Abstract



Influence of Ga coverage on the Sizes and Shapes
Influence of Ga coverage on the Sizes and Shapes

 

 

 

TITLE: Nanocrystalline GaZnO films for transparent electrode to silicon carbide
AUTHORS: J. H. Lee, J. H. Kim, K. M. Do, B. M. Moon, J. H. Lee and S. M. Koo
JOURNAL/BOOK TITLE: Journal of Nanoelectronics and Optoelectronics
VOLUME: 7                                 FIRST PAGE: 260
YEAR OF PUBLICATION:
2012                                   TYPE: A                      IF:0.90

Abstract



 


Nanocrystalline 2% Ga doped zinc oxide (GaZnO) thin films were epitaxially deposited on n-type 4H-SiC (0001) by a pulsed laser deposition (PLD) at different substrate temperatures of 250, 400, and 550 oC, respectively. Structural and electrical properties of nanocrystalline GaZnO thin film on 4H-SiC were investigated by using X-ray diffraction, atomic force microscopy (AFM), Hall effect measurement, transmission line method (TLM), and Auger electron spectroscopy (AES). The nanocrystalline GaZnO film deposited at 400 oC show the lowest resistivity of 3.3 x 10-4 Ω cm, and highly c-axis oriented crystalline quality with being sharper and higher diffraction angle, which result in. The specific contact resistance (ρc), measured from the Au/Ti/GaZnO/SiC of ~ 0.05 Ω cm2. The relative amount of activated Ga3+ ions was 2.02% in GaZnO film by AES measurement.


 


Graphical Abstract



Nanocrystalline GaZnO films

Nanocrystalline GaZnO films

Nanocrystalline GaZnO films



 


TITLE: Inside Back Cover: Sharp contrast of the density and size of Ga metal droplets on photolithographically patterned GaAs (100) by droplet epitaxy under an identical growth environment (Phys. Status Solidi A 6/2012)
AUTHORS: M. Y. Li, J. H. Lee, Zh. M. Wang, Y. K. Hirono, J. Wu, S. M. Song, S. M. Koo, E. S. Kim and G. J. Salamo
JOURNAL/BOOK TITLE: Physica Status Solidi (a)
VOLUME: 209                                  FIRST PAGE: 1075
YEAR OF PUBLICATION:
2012                             TYPE: A                      IF: 1.221
Sharp Contrast of the Density and Size of Ga Metal Droplets
 

 

TITLE: Sharp Contrast of the Density and Size of Ga Metal Droplets on Photolithographically Patterned GaAs (100) by Droplet Epitaxy under an Identical Growth Environment
AUTHORS: M. Y. Li, J. H. Lee, Zh. M. Wang, Y. K. Hirono, J. Wu, S. M. Song, S. M. Koo, E. S. Kim and G. J. Salamo
JOURNAL/BOOK TITLE: Physica Status Solidi (a)
VOLUME: 209                                  FIRST PAGE: 1075
YEAR OF PUBLICATION:
2012                             TYPE: A                      IF: 1.221

Abstract



 

A sharp contrast of the density and size of Ga metal droplets (MDs) on strip patterned GaAs (100) is demonstrated through droplet epitaxy (DE) and photolithography technique. As clearly evidenced by scanning electronic microscope (SEM) and atomic force microscope (AFM), MD density between etched (patterned) and un-etched (un-patterned) surfaces can be sharply different up to one order of magnitude under an identical growth condition. Etched surface exhibits much higher density and smaller diameter and height of MDs.

 


Graphical Abstract



Sharp contrast of the density and size of Ga metal dropletsSharp contrast of the density and size of Ga metal droplets

 

 

 

TITLE: Fabrication and characterization of ZnO film-based heterojunction diodes on 4H-SiC
AUTHORS: J. H. Kim, K. M. Do, J. W. Kim, J. C. Jung, J. H. Lee, B. M. Moon, and S. M. Koo
JOURNAL/BOOK TITLE: Journal of Nanoelectronics and Optoelectronics
VOLUME: 7                                 FIRST PAGE: 271
YEAR OF PUBLICATION: 2012                                   TYPE: A                      IF:
0.90

Abstract



 


Nanocrystalline n-ZnO/p-4H-SiC heterojunction diodes were successfully fabricated and characterized. The epitaxially grown ZnO films were obtained by using a pulsed laser deposition method. X-ray diffraction (XRD) pole figure analysis showed that the c-oriented ZnO films were grown on 4H-SiC (0001) substrates with in-plane orientation of ZnO [11-20 ]||4H-SiC [11-20 ], which is attributed to the small lattice mismatch of ZnO with 4H-SiC (~5.5%). The ZnO films with nano-sized grains were confirmed by surface morphology analysis. In order to investigate the electrical properties, the Ohmic contact electrodes were formed directly onto the ZnO and 4H-SiC surfaces. Current-voltage characteristics of the heterojunction diodes had a good rectifying behavior with an on/off ratio above 108. The current transport mechanisms in different bias regions were also discussed


 


Graphical Abstract



Fabrication and characterization of ZnO film
Fabrication and characterization of ZnO film

 

 

 

TITLE: Spectroscopic signatures of many-body interactions and delocalized states in self-assembled lateral quantum dot molecules
AUTHORS: X. Zhou, S. Sanwlani, W. Liu, J. H. Lee, Zh. M. Wang, G. Salamo, and M. F. Doty
JOURNAL/BOOK TITLE: Physical Review B
VOLUME: 84                                 FIRST PAGE: 205411
YEAR OF PUBLICATION:
2011                              TYPE: A                      IF: 3.772

(Selected by the editors of PRB to be an Editor's Suggestion: Highlighed Articles)


Abstract



 

Lateral quantum dot molecules consist of at least two closely spaced InGaAs quantum dots arranged such that the axis connecting the quantum dots is perpendicular to the growth direction. These quantum dot complexes are called molecules because the small spacing between the quantum dots is expected to lead to the formation of molecular-like delocalized states.We present optical spectroscopy of ensembles and individual lateral quantum dot molecules as a function of electric fields applied along the growth direction. The results allow us to characterize the energy level structure of lateral quantum dot molecules and the spectral signatures of both charging and many-body interactions.We present experimental evidence for the existence of molecular-like delocalized states for electrons in the first excited energy shell.

 


Graphical Abstract



Spectroscopic signatures of many-body interactions

Spectroscopic signatures of many-body interactions

 

 

 

TITLE: In(Ga)As/GaAs(001) quantum dot molecules probed by nano-focus high resolution x-ray diffraction with 100nm resolution
AUTHORS: M.Dubslaff, M.Hanke, M.Burghammer, S.SchÄoder, R.Hoppe, C.G.Schroer, Yu.I.Mazur, Zh.M.Wang, J. H. Lee, G.J.Salamo
JOURNAL/BOOK TITLE:
Applied Physics Letters
VOLUME: 98                                  FIRST PAGE: 213105
YEAR OF PUBLICATION: 2011                                    TYPE: A                        IF: 3.554


Abstract



 

In(Ga)As quantum dots, which laterally self-assemble into quantum dot molecules, have been studied by scanning x-ray nanodiffraction, finite element calculations and subsequent kinematical diffraction simulations. X-ray beam sizes of 100 nm enable small scattering volumes comparable to the object size at extremely high local flux densities ~10^4 photons nm^−2 s^−1. By that bulkcontributions to the scattering are effectively reduced. Area maps of various individual quantum dot molecules have been measured, whereas the diffraction patterns therein reveal spatially resolved information about the inter quantum dot position correlation function. © 2011 American Institute of Physics. [doi:10.1063/1.3593960]


 



Graphical Abstract



Appl. Phys. Lett. 98, 213105  (2011)

 

 

 

TITLE: Enhanced photo-sensitivity through Increased Light Trapping by Nano-structuring using MWCNT etch mask
AUTHORS: M. Y. Hwang, H. S. Kim, E. S. Kim, J. H. Lee and S. M. Koo
JOURNAL/BOOK TITLE: Nanoscale Research Letters
VOLUME: 6                                 FIRST PAGE: 573
YEAR OF PUBLICATION:
2011                                   TYPE: A                      IF: 2.557

Abstract



 

We demonstrate an enhanced photo-sensitivity through an increased light-trapping using surface nano-structuring technique by inductively coupled plasma (ICP) etching on multi-walled carbon nanotube (MWCNT) etch masked Si with hexamethyl-disilazane (HMDS) dispersion. In order for a systematic comparison, four samples are prepared respectively by conventional photolithography and ICP etching using MWCNT as a etch mask. MWCNT etched Si with HMDS dispersion shows the highest RMS roughness and the lowest reflectance of the four. Two test device structures are fabricated with active regions of bare-Si as a reference and MWCNT etch masked Si with HMDS dispersion. The increased light trapping was most significant at mid-UV, somewhat less at visible and less noticeable at infrared. With an ICP etched Si using CNT HMDS dispersion, photo-sensitivity is very sharply increased. This result can lead to applications in optoelectronics where the enhancement in light trapping is important.

 


Graphical Abstract



Nanoscale Research Letters 2011, 6:573

Nanoscale Research Letters 2011, 6:573




 

TITLE: Low Density Quantum Dot Molecules by Selective Etching using In Droplet as a Mask
AUTHORS: J. H. Lee, Zh. M. Wang, Y. K. Hirono, V. G. Dorogan, Y. I Mazur, E. S. Kim, S. M. Koo, S. H. Park, S. M. Song and G. J. Salamo
JOURNAL/BOOK TITLE: IEEE Transactions on Nanotechnology 
VOLUME: 10                                  FIRST PAGE: 600
YEAR OF PUBLICATION: 2011                                   KEY: A                         IF: 2.154

Abstract



 

We demonstrate low-density quantum dot molecules (QDMs) by selective etching using In droplets as a mask. Selective etching is performed with InGaAs QDMs buried underneath GaAs capping layer, on which In droplets are formed by droplet epitaxy using molecular beam epitaxy. During the chemical etching, the droplets act as a mask and QDMs underneath the droplets that only survive. Photoluminescence measurement from the selectively etched QDMs in mesa structures shows a much reduced intensity, which indicates low-density QDMs. This technique provides a simple and flexible method to attain low-densityQDMs. The density can be easily modified by the control of the size and density of In droplets, which is suitable for single QDM spectroscopy and for their device applications.

 


Graphical Abstract



IEEE TRANSACTIONS ON NANOTECHNOLOGY, VOL. 10, NO. 3, MAY 2011IEEE TRANSACTIONS ON NANOTECHNOLOGY, VOL. 10, NO. 3, MAY 2011

 


 

TITLE: Anti-Reflective Nano- and Micro-Structures On 4H-SiC for Photodiodes
AUTHORS: M. S. Kang, S. J. Joo, W. Bahng, J. H. Lee, and S. M. Koo
JOURNAL/BOOK TITLE: Nanoscale Research Letters
VOLUME: 6                                 FIRST PAGE: 236
YEAR OF PUBLICATION: 2011                                   TYPE: A                       IF: 2.894

Abstract



 

In this study, nano-scale honeycomb-shaped structures with anti-reflection properties were successfully formed on SiC. The surface of 4H-SiC wafer after a conventional photolithography process was etched by inductively coupled plasma. We demonstrate that the reflection characteristic of the fabricated photodiodes has significantly reduced by 55% compared with the reference devices. As a result, the optical response Iillumination/Idark of the 4H-SiC photodiodes were enhanced up to 178%, which can be ascribed primarily to the improved light trapping in the proposed nano-scale texturing.

 


Graphical Abstract



Nanoscale Research Letters 2011, 6:236

Nanoscale Research Letters 2011, 6:236

 


 

TITLE: Evolution of self-assembled InGaAs tandem nanostructures consisting a hole and pyramid on type-A high index GaAs substrates by droplet epitaxy
AUTHORS: J. H. Lee, Zh. M. Wang, E. S. Kim, N. Y. Kim, S. H. Park and G. J. Salamo
JOURNAL/BOOK TITLE: IEEE Transactions on Nanotechnology 
VOLUME: 10                                 FIRST PAGE: 395
YEAR OF PUBLICATION: 2011                                    TYPE: A                        IF: 2.154

Abstract



 

The evolution of self-assembled InGaAs tandem nanostructures consisting a hole and pyramid is demonstrated using droplet epitaxy on various type-A high-index GaAs surfaces: (311)A (411)A, (511)A and (711)A. Under an identical fabrication condition depending on the index of surfaces, the resulting density and size of nanostructures are characteristic. The variation of density and size of nanostructures is explained with the relationship of the density of monolayer steps. An empirical model that describes the mechanism of self-assembled tandem nanostructures consisting a hole and pyramid is suggested as the concurrent occurrence of intermixing between droplets and substrate, dissolution of substrate and anisotropic surface diffusion.

 


Graphical Abstract



IEEE TRANSACTIONS ON NANOTECHNOLOGY, VOL. 10, NO. 3, MAY 2011

IEEE TRANSACTIONS ON NANOTECHNOLOGY, VOL. 10, NO. 3, MAY 2011



 


TITLE: Inside Back Cover: InxGa1−xAs quantum wire network-like and ordered checker board-like nanostructures on GaAs (311) by low In composition multi-layer stacking (Phys. Status Solidi A 1/2011)
AUTHORS: J. H. Lee, Zh. M. Wang, V. Yazdanpanah, E. S. Kim, S. M. Koo, S. M. Song and G. J. Salamo
JOURNAL/BOOK TITLE: Physica Status Solidi (a)
YEAR OF PUBLICATION: 2011                                   TYPE: A                      IF: 1.21
PSSA 2011 Jan
 

 

TITLE: InxGa1-xAs Quantum Wire Network-like & Ordered Checker Board-like Nanostructures on GaAs (311) by Low In composition Multi-layer Stacking
AUTHORS: J. H. Lee, Zh. M. Wang, V. Yazdanpanah, E. S. Kim, S. M. Koo, S. M. Song and G. J. Salamo
JOURNAL/BOOK TITLE: Physica Status Solidi (a)
VOLUME: 208                                 FIRST PAGE: 47
YEAR OF PUBLICATION: 2011                                    TYPE: A                      IF: 1.221

(Featured on the Journal cover of the volume 208, issue 1 of Physica Status Solidi (a))


Abstract



 

Unique quantum wire (QWR) network-like nanostructures (QWRNNs) and ordered checker board-like nanostructures (OCBNs) were demonstrated on GaAs (311) A and B by applying a low In composition multiple-layer stacking technique. More specifically, the combination of low In composition and multilayer systems, [In0.18Ga0.82As/GaAs]m wherem¼1, 4, 8, 10, 12, and 16 periods, have been investigated on GaAs (311) A and B by molecular beam epitaxy (MBE). Under a same growth condition, QWRNNs were demonstrated on GaAs (311)A whileOCBNswere fabricated on GaAs (311)B as a result of the strain accumulation and transfer through the multiple layers stacked.An appropriate control of the number of layers stacked and spacer thickness can result in an improved ordering and uniformity of QWRNNs and OCBNs.

 


Graphical Abstract



Phys. Status Solidi A 208, No. 1 (2011)

 


 

TITLE: InGaAs Quantum Dot Molecules during Selective Etching using In Droplet Mask
AUTHORS: J. H. Lee, Zh. M. Wang, Y. K. Hirono, E. S. Kim, S. M. Koo, V. G. Dorogan, Y. I. Mazur, S. M. Song, G. Y. Park and G. J. Salamo
JOURNAL/BOOK TITLE: Journal of physics D: Applied physics
VOLUME: 44                                   FIRST PAGE: 025102
YEAR OF PUBLICATION: 2011                                   TYPE: A                        IF: 2.083

Abstract



 

We investigated the optical transition of InGaAs quantum dot molecules (QDMs) during selective etching of GaAs using In droplets to demonstrate low-density QDMs. During the selective etching, In droplets act as nanoscale masks and only QDMs underneath the droplets survive, by which process low-density QDMs are fabricated. The thickness of selective GaAs etching is systematically varied and a gradual red-shift is observed with the increased etching thickness. The continuing red-shift can be explained by the strain relaxation due to GaAs etching. This technique to achieve low-density QDMs by selective etching using droplets as nanoscale mask is a simple and flexible approach. This study can find applications in single QDM spectroscopy and other spectroscopic techniques.

 


Graphical Abstract



J. Phys. D: Appl. Phys. 44 (2011) 025102 J. Phys. D: Appl. Phys. 44 (2011) 025102

 


 

TITLE: Instability of various configurations of in nano-crystals on GaAs (100) by droplet epitaxy
AUTHORS: J. H. Lee
JOURNAL/BOOK TITLE: CRYSTENGCOMM
VOLUME: 13                                 FIRST PAGE: 771
YEAR OF PUBLICATION: 2011                                    TYPE: A                       IF: 4.183 

Abstract



 

Remarkably we observe the instability of various configurations of In nano-crystals on GaAs (100). Various configurations of In nanocrystals are formed by a droplet epitaxy (DE) approach using molecular beam epitaxy (MBE). The configurations of In nanocrystals are round, squares and elongated rod shapes. When In crystals are exposed to air, a random pit begins to form. The pit formation was observed to be as deep as over 10 nm underneath the GaAs surface. Regardless of the shapes and configurations, In crystals desorb from the GaAs surface, which results in the development of strip patterns over 10 mm wide and hundreds of mm long.

 


Graphical Abstract



CrystEngComm, 2011, 13, 771?775 | 773

 

 

 

TITLE: Crystallographic plane-orientation dependent atomic force microscopy-based local oxidation of silicon carbide
AUTHORS: J. J. Ahn, Y. D. Jo, S. C. Kim, J. H. Lee, and S. M. Koo
JOURNAL/BOOK TITLE: Nanoscale Research Letters
VOLUME: 6                                 FIRST PAGE: 235
YEAR OF PUBLICATION: 2011                                    TYPE: A                       IF: 2.894

Abstract



 

The effect of crystalline plane orientations of Silicon carbide (SiC) (a-, m-, and c-planes) on the local oxidation on 4H-SiC using atomic force microscopy (AFM) was investigated. It has been found that the AFM-based local oxidation (AFM-LO) rate on SiC is closely correlated to the atomic planar density values of different crystalline planes (a-plane, 7.45 cm-2; c-plane, 12.17 cm-2; and m-plane, 6.44 cm-2). Specifically, at room temperature and under about 40% humidity with a scan speed of 0.5 μm/s, the height of oxides on a- and m-planes 4H-SiC is 6.5 and 13 nm, respectively, whereas the height of oxides on the c-plane increased up to 30 nm. In addition, the results of AFM-LO with thermally grown oxides on the different plane orientations in SiC are compared.

 



Graphical Abstract



Nanoscale Research Letters 2011, 6:235

Nanoscale Research Letters 2011, 6:235

 



TITLE: Journal cover of Volume 9, Issue 2 of IEEE Transactions on Nanotechnology
AUTHORS: J. H. Lee, Zh. M. Wang, Yu. Mazur, V. G. Dorogan, M. E. Ware and G. J. Salamo
JOURNAL/BOOK TITLE: IEEE Transactions on Nanotechnology 
VOLUME: 9                                 FIRST PAGE: 149
YEAR OF PUBLICATION: 2010                                 TYPE: A                      IF: 2.154
Journal cover of the volume 9, issue 2 of IEEE Transactions on Nanotechnology
 


TITLE:Evolution of Various Nanostructures and Preservation of Self-Assembled InAs Quantum Dots during GaAs Capping
AUTHORS:J. H. Lee, Zh. M. Wang, Yu. Mazur, V. G. Dorogan, M. E. Ware and G. J. Salamo
JOURNAL/BOOK TITLE: IEEE Transactions on Nanotechnology 
VOLUME: 9                                 FIRST PAGE: 149
YEAR OF PUBLICATION:
2010                                  TYPE: A                      IF: 2.154

(Featured on the Journal cover of the volume 9, issue 2 of IEEE Transactions on Nanotechnology )

Abstract



 

The fabrication of nanostructures such as quantum rods (QRDs), quantum dot pairs (QDPs), bridged QDPs, and dimpled QDs (DQDs) is achieved by an application of a shallow GaAs layer using solid source molecular beam epitaxy (MBE). More specifically, the shape transition and evolution process as well as the preservation of original dome shape of self-assembled InAs quantum dots (QDs) are studied during the thin capping of GaAs layers in terms of morphology and optical property. As QDs are required to be capped for their applications and optical characterizations, it is critical to understand the mechanism during the capping process. QDs go through a significant shape transition and eventually evolve into various nanostructures at temperatures between 500 ?C and 400 ?C, while the original dome shape can be maintained at temperatures below 360 ?C. The shape evolutions aremainly driven by diffusion process induced by redistribution of surface chemical potential and strain matrix. Photoluminescence (PL) results show a blue-shift with increasing capping temperature for a fixed capping thickness, which adequately matches with morphological evolution.

 



Graphical Abstract



IEEE TRANSACTIONS ON NANOTECHNOLOGY, VOL. 9, NO. 2, MARCH 2010       IEEE TRANSACTIONS ON NANOTECHNOLOGY, VOL. 9, NO. 2, MARCH 2010

 

 

 

TITLE: High Temperature-Stable Operation of Nano-Ribbon Field-Effect Transistors
AUTHORS: C. Y. Choi, J. H. Lee, J. H. Koh, J. G. Ha, S. M. Koo, and S. Kim
JOURNAL/BOOK TITLE:Nanoscale Research Letters
VOLUME: 5                                  FIRST PAGE: 1795
YEAR OF PUBLICATION: 2010                                   TYPE: A                      IF:2.894

Abstract



 

We experimentally demonstrated that nanoribbon field-effect transistors can be used for stable hightemperature applications. The on-current level of the nanoribbon FETs decreases at elevated temperatures due to the degradation of the electron mobility. We propose two methods of compensating for the variation of the current level with the temperature in the range of 25–150 C, involving the application of a suitable (1) positive or (2) negative substrate bias. These two methods were compared by two-dimensional numerical simulations. Although both approaches show constant on-state current saturation characteristics over the proposed temperature range, the latter shows an improvement in the off-state control of up to five orders of magnitude (-5.2 x 10^-6).

 


Graphical Abstract



Nanoscale Res Lett (2010) 5:1795?1799      Nanoscale Res Lett (2010) 5:1795?1799

 

 

 

TITLE: Strongly Confined Excitons in Self-assembled InGaAs Quantum Dot Clusters Produced by a Hybrid Growth Method
AUTHORS: Megan Creasey, Xiaoqin Li, J. H. Lee, Zh. M. Wang, and G. J. Salamo
JOURNAL/BOOK TITLE: Journal of Applied Physics
VOLUME: 107                           FIRST PAGE: 104302 
YEAR OF PUBLICATION: 2010                                   KEY: A                       IF: 2.201

Abstract



 

We investigate the optical properties of newly developed InGaAs quantum dot clusters (QDCs). The QDCs are produced using a hybrid growth method that combines droplet homoepitaxy and Stranski–Krastanov growth modes. We focus on a particular geometry, where six individual quantum dots (QDs) spontaneously form a structure morphologically similar to a benzene ring. We observe narrow exciton resonances in microphotoluminescence measurements. Temperature and excitation density dependence of the exciton resonances are investigated. Our experiments suggest that excitons are strongly confined in individual QDs instead of residing in all QDs in the cluster. © 2010 American Institute of Physics. [doi:10.1063/1.3369389]

 


Graphical Abstract



J. Appl. Phys. 107, 104302 (2010)

 


 

TITLE: Various Quantum- and Nano-structures by using III-V Droplet Epitaxy on GaAs Substrates
AUTHORS: J. H. Lee, Zh. M. Wang, E. S. Kim, N. Y. Kim, S. H. Park and G. J. Salamo
JOURNAL/BOOK TITLE:
Nanoscale Research Letters
VOLUME: 5                                 FIRST PAGE: 308
YEAR OF PUBLICATION: 2010                                    TYPE: A                      IF: 2.894

Abstract



 

We report on various self-assembled In(Ga)As nanostructures by droplet epitaxy on GaAs substrates using molecular beam epitaxy. Depending on the growth condition and index of surfaces, various nanostructures can be fabricated: quantum dots (QDs), ring-like and holed-triangular nanostructures. At near room temperatures, by limiting surface diffusion of adatoms, the size of In droplets suitable for quantum confinement can be fabricated and thus InAs QDs are demonstrated on GaAs (100) surface. On the other hand, at relatively higher substrate temperatures,by enhancing the surface migrations of In adatoms, super lower density of InGaAs ring-shaped nanostructures can be fabricated on GaAs (100). Under an identical growth condition, holed-triangular InGaAs nanostructures can be fabricated on GaAs type-A surfaces, while ringshaped nanostructures are formed on GaAs (100). The formation mechanism of various nanostructures can be understood in terms of intermixing, surface diffusion, and surface reconstruction.

 


Graphical Abstract



Nanoscale Res Lett (2010) 5:308?314

 

 


TITLE: Back Cover (Phys. Status Solidi A 2/2010)

AUTHORS: J. H. Lee, Zh. M. Wang, E. S. Kim, N. Y. Kim, S. H. Park and G. J. Salamo

JOURNAL/BOOK TITLE: Physica Status Solidi (a)

YEAR OF PUBLICATION: 2010                                  TYPE: A                           IF: 1.21
Self-assembled InGaAs tandem nanostructures consisting a hole and pyramid on GaAs (311)A by droplet epitaxy
 

 

TITLE: Self-assembled InGaAs tandem nanostructures consisting a hole and pyramid on GaAs (311)A by droplet epitaxy
AUTHORS: J. H. Lee, Zh. M. Wang, E. S. Kim, N. Y. Kim, S. H. Park and G. J. Salamo
JOURNAL/BOOK TITLE: Physica Status Solidi (a)
VOLUME: 207                                 FIRST PAGE: 348
YEAR OF PUBLICATION: 2010                                  TYPE: A                      IF: 1.21
(Featured on the Journal cover of the volume
207, issue 2 of Physica Status Solidi (a))

Abstract



 

We report on the fabrication self-assembled tandem (pyramidalholed) InGaAs nanostructures on GaAs (311)A in comparison with the nanostructures on (100) surface. Under an identicalgrowth condition, the fabricated nanostructures are characteristically dissimilar; ring-shaped nanostructures on GaAs (100) and pyramidal-holed nanostructures on (311)A. The underlying formation mechanism of these interesting nanostructures can be understood in terms of intermixing, dissolution of GaAs substrate and surface diffusion driven by a surface reconstruction. The size and density of nanostructures can be controlled by modifying the droplet size, density, and thermal energy applied during the fabrication of droplets and nanostructures. These unique InGaAs nanostructures can offer promising applications in optoelectronics.

 


Graphical Abstract



 


 

TITLE: Various Configurations of In Nanostructures on GaAs (100) by Droplet Epitaxy
AUTHORS: J. H. Lee, Zh. M. Wang, Y. K. Hirono, E. S. Kim, N. Y. Kim, S. H. Park, C. Wang and G. J. Salamo
JOURNAL/BOOK TITLE: CRYSTENGCOMM
VOLUME: 12                                   FIRST PAGE: 3404
YEAR OF PUBLICATION: 2010                                    TYPE: A                      IF: 4.183 

Abstract



 

In sharp contrast to the general belief in the round shape of In droplets, we report various configurations of In nanostructures. Various configurations of self-assembled In nanostructures are demonstrated by droplet epitaxy on GaAs (100) using molecular beam epitaxy. Square, rectangle, pentagonal geometries and elongated rod-like configurations are realized on GaAs (100). The formation of facets is clearly observed on the top and side of the In nanostructures. Co-existence of both round and square shapes of In nanostructures is captured, which shows the sharp transition between the two.

 


Graphical Abstract



CrystEngComm, 2010, 12, 3404?3408

 


 

TITLE: On the complex behavior of strain relaxation in (In,Ga)As/GaAs (001) quantum dot molecules
AUTHORS: M. Hanke, M. Dubslaff, M. Schmidbauer, Zh. M. Wang, Yu. I. Mazur, P. M. Lytvyn, J. H. Lee, and G. J. Salamo
JOURNAL/BOOK TITLE: Applied Physics Letters
VOLUME: 95                                   FIRST PAGE: 023103
YEAR OF PUBLICATION: 2009                                   KEY: A                      IF: 3.726

Abstract



 

A detailed growth scenario of surface quantum dot molecules QDM in the system (In,Ga)As/ GaAs(001) has been investigated in terms of shape and elastic strain evolution. QDMs are grown by a combined approach using droplet epitaxy for initial homoepitaxial GaAs mounds, which subsequently serve as nucleation spots for surrounding In,GaAs surface quantum dots. Atomic force micrographs trace a detailed pathway toward the final QDM containing up to six quantum dots with perfect inherent symmetry. Synchrotron-based grazing incidence diffraction together with grazing incidence small angle x-ray scattering reveal a relaxation behavior, which for all growth stages comprises a strained lattice along 1¯10 and partial elastic relaxation along [110]. Numerical finite element calculations on the three-dimensional strain profile support the experimental findings. © 2009 American Institute of Physics. [DOI: 10.1063/1.3176409]

 


Graphical Abstract



Appl. Phys. Lett. 95, 023103 (2009)Appl. Phys. Lett. 95, 023103 (2009)

 


 

TITLE: Size and density control of In droplets at near room temperatures
AUTHORS: J. H. Lee, Zh. M. Wang, N. Y. Kim and G. J. Salamo
JOURNAL/BOOK TITLE: Nanotechnology 
VOLUME: 20                              FIRST PAGE: 285602
YEAR OF PUBLICATION: 2009                                   TYPE: A                      IF: 3.446

Abstract



 

We report on the ability to control the size and density of In droplets on GaAs(100) substrates at near room temperatures using solid source molecular beam epitaxy. We specifically demonstrate the height, diameter and density control of In droplets as functions of substrate temperature (Tsub) and monolayer (ML) coverage. For a range of density (∼109–1010 cm−2), the growth window is revealed to be between 20 and 70 ?C. For a fixed ML coverage, the size and density of droplets can be controlled by controlling the Tsub. For a fixed Tsub, by controlling the ML coverage, droplet size and density can be controlled. Even at near room temperatures (20–70 ?C), In atoms are extremely sensitive to surface diffusion and this enables the control of the size and density of droplets. This study provides an aid to understanding the formation of In droplets at near room temperatures and can find applications in the formation of quantum structures and/or nanostructures based on droplet epitaxy.

 

Graphical Abstract



Nanotechnology 20 (2009) 285602

 


 

TITLE: Tuning the emission profiles of various self-assembled InxGa1−xAs nanostructures by rapid thermal annealing
AUTHORS: J. H. Lee, Zh. M. Wang, Yu. Mazur, V. G. Dorogan, M. E. Ware and G. J. Salamo
JOURNAL/BOOK TITLE: Journal of Applied Physics
VOLUME: 106                                 FIRST PAGE: 073106 
YEAR OF PUBLICATION: 2009                                   TYPE: A                      IF: 2.201

Abstract



 

Tuning the emission profiles of various novel InxGa1−xAs nanostructures, such as quantum rods, quantum dot pairs (QDPs), bridged QDPs, dimpled quantum dots (QDs), and low-temperature-capped QDs, is demonstrated by postgrowth rapid thermal annealing. Specifically, improved optical properties, such as a much narrower full width at half maximum of 16 meV and a continuous blueshift, are demonstrated. The enhanced optical properties are attributed to the interchange of In and Ga atoms induced by both defect-assisted intermixing and strain-assisted intermixing. These results can find applications as an optical enhancement in nanostructures is critical for the improvements on device functionality. © 2009 American Institute of Physics.
[doi:10.1063/1.3213095]

 


Graphical Abstract



J. Appl. Phys. 106, 073106 (2009)

 


 

TITLE: The Control on Size and Density of InAs QDs by Droplet Epitaxy
AUTHORS: J. H. Lee, Zh. M. Wang and G. J. Salamo
JOURNAL/BOOK TITLE: IEEE Transactions on Nanotechnology  
VOLUME: 8                                     FIRST PAGE: 431 
YEAR OF PUBLICATION: 2009                                   TYPE: A                      IF: 2.154


Abstract



 

We report on the ability to grow InAs quantum dots (QDs) by droplet epitaxy (DE) using solid-source molecular beam epitaxy (MBE). In particular, the control of the size and density of InAs QDs at near room temperatures are achieved as a function of substrate temperature and crystallization condition. For a typical range of QD density (∼10^9 to 10^10 cm−2 ), the growth window is revealed to be fairly narrow (∼20 ?C). In droplets are extremely sensitive to surface diffusion and arsenic background pressure even at near room temperatures. As a result, a very careful fabrication procedure is required to crystallize In droplets in order to fabricate desired shape of InAs QDs. For this purpose, we developed a double-step crystallization process, in whichAs background recovery and high-temperature crystallization are introduced. In addition, the results by DE are compared with QDs fabricated by Stranski–Krastanow (S-K) growth approach in terms of size and density. The results can find applications in optoelectronics as the fabrication of QDs by DE approach has more flexibility over S-K approach, i.e., more freedom of size and density control.

 


Graphical Abstract



IEEE TRANSACTIONS ON NANOTECHNOLOGY, VOL. 8, NO. 4, JULY 2009      IEEE TRANSACTIONS ON NANOTECHNOLOGY, VOL. 8, NO. 4, JULY 2009

 


 

TITLE: InAs Quantum Dot Clusters Grown on GaAs Droplet Templates: Surface Morphologies and Optical Properties
AUTHORS: B. L. Liang, V. G. Dorogan, Yu. I. Mazur, N. W. Strom, J. H. Lee, K. A. Sablon, Zh. M. Wang, G. J. Salamo
JOURNAL/BOOK TITLE: Journal of Nanoscience and Nanotechnology
VOLUME: 9                                 FIRST PAGE: 3320
YEAR OF PUBLICATION: 2009                                   KEY: A                      IF: 1.929

Abstract



 

GaAs nano-mounds formed by droplet epitaxy are used as templates for growth of self-assembled InAs quantum dot clusters (QDCs).These QDCs are found to contain an average of thirteen dots per cluster, of which there are two families of different sized quantum dots.Excitation intensitydependent photoluminescence (PL) demonstrates that there is no lateral coupling between the two different size quantum dots.Later al transfer of carriers is observed between different size quantum dots due to thermal activation as seen in their different temperature-dependent optical behaviors.

 


Graphical Abstract



Journal of Nanoscience and Nanotechnology Vol.9, 3320?3324, 2009

 

 

TITLE: Design of Nanostructure Complexes by droplet epitaxy
AUTHORS: J. H. Lee, Zh. M. Wang, Yu. Mazur, V. G. Dorogan, M. E. Ware and G. J. Salamo
JOURNAL/BOOK TITLE: Crystal growth & design
VOLUME: 9                                  FIRST PAGE: 715
YEAR OF PUBLICATION: 2009                                   TYPE: A                      IF: 4.215

Abstract



 

We demonstrate a number of unseen self-assembled nanostructure complexes fabricated on various GaAs surface indexes by droplet epitaxy. Even under identical growth conditions, the configuration of nanostructure complexes is distinctive on each surface. The morphology evolution of nanostructure complexes is kinetically and energetically analyzed in determining the correlation between shape of nanostructure complexes and atomic surface matrixes with atomic ball-stick models. By systematically varying growth environment, we report many uncanny nanostructure complexes on given surface indexes.

 


Graphical Abstract



Crystal Growth & Design, Vol. 9, No. 2, 2009

 

 

 

TITLE: Thermal peculiarity of AlAs-capped InAs quantum dots in a GaAs matrix
AUTHORS: V. G. Dorogan, Yu. I. Mazur, J. H. Lee, Zh. M. Wang, M. E. Ware, and G. J. Salamo
JOURNAL/BOOK TITLE: Journal of Applied Physics
VOLUME: 104                                 FIRST PAGE: 104303
YEAR OF PUBLICATION: 2008        
                           TYPE: A                      IF: 2.201

Abstract



 

GaAs and AlAs thin capping layers as well as postgrowth rapid thermal annealing (RTA) were applied to InAs quantum dots (QDs) grown by molecular beam epitaxy to study the tunability of optical properties of QDs by photoluminescence (PL) methods. The PL of AlAs-capped QDs shows double-peak structure, as opposed to GaAs-capped QDs, which is due to the formation of two families of QDs in the AlAs-capped sample confirmed by the power dependent PL measurements. The PL peak of the GaAs-capped samples subjected to RTA showed blueshift and narrowing with an increase in RTA temperature. This is the result of thermally enhanced In–Ga intermixing. More complex changes in the PL spectrum of AlAs-capped QDs during the RTA procedure were found and explained by the different In compositions in two branches of QDs. The features observed in the temperature dependences of PL peak energy of GaAs- and AlAs-capped samples were interpreted in terms of thermal escape of carriers from smaller QDs with further redistribution between larger QDs and different InAs content in two families of QDs. © 2008 American Institute of Physics. [DOI: 10.1063/1.3020521]

 


Graphical Abstract



J. Appl. Phys. 104, 104303 (2008)

 

 

 

TITLE: Energy Transfer within Ultralow Density Twin InAs Quantum Dots Grown by Droplet Epitaxy
AUTHORS: Bao-Lai Liang, Zhi-Ming Wang, Xiao-Yong Wang, Ji-Hoon Lee, Yuriy I. Mazur, Chih-Kang Shih, and Gregory J. Salamo
JOURNAL/BOOK TITLE: ACS NANO
VOLUME:2                                  FIRST PAGE: 2219
YEAR OF PUBLICATION: 2008                                   TYPE: A                      IF: 5.472

Abstract



 

Ultralow density (~10^6/cm2) of twin InAs quantum dot (QD) hybrid structure was grown by a droplet epitaxy technique. The photoluminescence (PL) from ensemble and individual twin InAs QD structures showed a bimodal behavior and an energy transfer between the well-separated (~190 nm) twin QDs, which was supposedly due to the special wetting ring that built the channel for exciton transfer. This research demonstrates a novel approach to fabricate lateral InAs QD pairs as the candidate for a laterally coupled QD molecule.

 


Graphical Abstract



ACS Nano, 2008, 2 (11), 2219-2224

 

 

 

TITLE: Super-low-density InGaAs semiconductor ring-shaped nanostructures
AUTHORS: Jihoon H. Lee, Zhiming M. Wang, M. E. Ware, Kushal C. Wijesundara, Mauricio Garrido, E. A. Stinaff and Gregory J. Salamo
JOURNAL/BOOK TITLE: Crystal growth & design
VOLUME: 8                                   FIRST PAGE: 1945
YEAR OF PUBLICATION: 2008                                   TYPE: A                      IF: 4.215

Abstract



 

We report on the ability to fabricate super low density InGaAs semiconductor ring-shaped nanocrystals on a GaAs (100) surface by molecular beam epitaxy. Specifically, we demonstrate densities down to 2.3 × 106 cm-2 with only self-assembled methods based on droplet epitaxy. This is several orders of magnitude lower than conventional nanostructures. The formation of these ring-shaped nanostructures is driven by a self-assembled indium nanodrilling mechanism and diffusion during crystallization.

 


Graphical Abstract



Crystal Growth & Design, Vol. 8, No. 6, 2008      Crystal Growth & Design, Vol. 8, No. 6, 2008

 


 

TITLE: “Spectroscopic observation of developing InAs quantum dots on GaAs ringlike-nanostructured templates
AUTHORS: Yu. I. Mazur, Z. Y. AbuWaar, T. D. Mishima,
J. H. Lee, G. G. Tarasov, B. L. Liang, V. G. Dorogan, M. E. Ware, Zh. M. Wang, M. B. Johnson, and G. J. Salamo
JOURNAL/BOOK TITLE: Journal of Applied Physics
VOLUME: 104                                    FIRST PAGE: 044310
YEAR OF PUBLICATION:2008                                   
TYPE: A                      IF: 2.201

Abstract



 

Spectroscopic study of the InAs quantum dot (QD) formation in GaAs ringlike nanostructures is carried out. Ga droplet epitaxy is used to form GaAs ringlike nanostructures. Subsequently InAs is deposited to obtain InAs QDs by self-assembly inside the holes of the nanostructures. Regularly spaced bands in the photoluminescence spectra exhibit state filling properties under increased excitation power. However, it is demonstrated that these bands do not represent excited states of a single ensemble of dots, but are separate ensembles with individual ground state energies, which are coupled through the GaAs ring structure on which they form. The most likely cause of these uniformly spaced ensemble energies is monolayer differences in the effective height of the dots. Temperature, excitation power density, and time dependent photoluminescence measurements are used to demonstrate the significance of the interdot coupling. The photoluminescent properties of these novel nanostructures make them candidates for optoelectronic applications. © 2008 American Institute of Physics. [DOI: 10.1063/1.2970149]

 


Graphical Abstract



J. Appl. Phys. 104, 044310 (2008)

J. Appl. Phys. 104, 044310 (2008)

 

 

 

TITLE: “The Growth and Characterization of Organized Nanostructures"
AUTHORS: J. H. Lee
JOURNAL/BOOK TITLE: (PhD Dissertation) The University of Arkansas Press
YEAR OF PUBLICATION: 2008                                    TYPE: B

 

 

TITLE: Evolution of InGaAs quantum dot molecules
AUTHORS: J. H. Lee, Kim. Sablon, Zh. M. Wang, and G. J. Salamo
JOURNAL/BOOK TITLE: Journal of Applied Physics
VOLUME: 103                                    FIRST PAGE: 054301
YEAR OF PUBLICATION:2008                                    TYPE: A                      IF: 2.201

Abstract



 

The formation and evolution process of self-assembled InGaAs quantum dot molecules (QDMs) are studied in terms of configuration, volume, and types of QDMs. QDMs are formed around self-assembled GaAs nanoscale island induced by adapting a hybrid growth approach combining droplet homoepitaxy and Stranski–Krastanov mode. In distinction from our previous results Lee et al., Appl. Phys. Lett. 89, 202101 (2006), hexa-QDMs are fabricated without the formation of background QDs, which can be due to a combinational effects of enhanced intermixing of Ga and In atoms, enhanced surface diffusion (high mobility) of adatoms, and higher In desorption rate due to the higher thermal energy provided during the fabrication of QDMs. In addition, a detailed evolution mechanism from bi-QDMs two QDs per each GaAs island to hexa-QDMs (six QDs per island) is proposed based on atom diffusion, material transfer, and equilibrium dimension (saturation) of QDs. Under a fixed InAs coverage, depending on postannealing process after liquid Ga droplet formation, highly uniform as well as various types of QDMs can be fabricated and the resulting configurations show a very strong correlation with the size of initial GaAs islands. With relatively smaller GaAs islands, quad-QDMs four QDs per island with a squarelike configuration were formed and also, quad-QDMs with a rectangularlike positioning were fabricated with relatively larger size of islands, while hexa-QDMs were formed with middle sized ones. Relatively, broader size distribution of GaAs nanoisland can be a direct result of Ostwald ripening, which can be well controlled by adjusting postgrowth interruption of liquid Ga droplets. © 2008 American Institute of Physics. [DOI: 10.1063/1.2890149]

 


Graphical Abstract



J. Appl. Phys. 103, 054301 (2008)       J. Appl. Phys. 103, 054301 (2008)

 


 

TITLE: Step bunch assisted two dimensional ordering of In0.19Ga0.81As/GaAs quantum dots on vicinal GaAs(001) surfaces
AUTHORS: Michael Hanke, Zhiming Wang , Yu Mazur , Jihoon Lee , Gregory Salamo , Martin Schmidbauer
JOURNAL/BOOK TITLE: Applied Physics Letters
VOLUME: 92                                    FIRST PAGE: 033111
YEAR OF PUBLICATION: 2008                                   TYPE: A                      IF: 3.726

Abstract



 

We have investigated the self-organized, step bunch assisted formation of In0.19Ga0.81As /GaAs quantum dots in vertical superlattices consisting of one, four, eight, and ten periods. Samples were grown by molecular beam epitaxy on vicinal 2°A and 2°B GaAs[001] substrates. Those with miscut along the [11¯0] (2°B) exclusively show step bunches of an aspect ratio larger than 10 but without the formation of quantum dots. This highly linear pattern is improved during subsequent periods as proved by high resolution x-ray diffraction and grazing incidence diffraction. On the other hand, a miscut along the [110] (2°A) initially causes a crosslike pattern of step bunches, which finally becomes a two-dimensional arrangement of individual quantum dots. © 2008 American Institute of Physics. [DOI: 10.1063/1.2838453]

 


Graphical Abstract



Appl. Phys. Lett. 92, 033111 (2008)

 

 

 

TITLE: Configuration Control of Quantum Dot Molecules by Droplet Epitaxy
AUTHORS: K. A. Sablon, J. H. Lee, Zh. Wang and G. J. Salamo
JOURNAL/BOOK TITLE: Applied Physics Letters
VOLUME: 92                                    FIRST PAGE: 203106
YEAR OF PUBLICATION: 2008                                   TYPE: A                      IF: 3.726

Abstract



 

We demonstrate that by changing the substrate temperature at which Ga droplets form and by varying the InAs deposition, we are able to control the configuration of quantum dots per GaAs mound. The size of the Ga droplets increases with increasing substrate temperature and resulting configurations show a very strong correlation with the size of initial GaAs islands. In distinction from previous reports, we attained two structures: quadmolecules and quantum rod pairs. Quadmolecules are elongated along the [011] crystallographic direction due to strain-driven processes and are directly formed at the edges of the GaAs mounds. On the other hand, quantum rod pairs formed along the [01−1] direction due to higher anisotropic diffusion. © 2008 American Institute of Physics. [DOI: 10.1063/1.2924308]

 


Graphical Abstract



Appl. Phys. Lett. 92, 203106 (2008)

Appl. Phys. Lett. 92, 203106 (2008)

 

 

 

TITLE: Near-field optical spectroscopy of Ga nanoparticles for plasmonics
AUTHORS: Antonio Llopis, Lin Jie, Arup Neogi, Jihoon Lee, Zhiming Wang, and Gregory J. Salamo
JOURNAL/BOOK TITLE: QELS - Technical Digest Series
Article number: 10132597                     ISBN: 978-1-55752-859-9
YEAR OF PUBLICATION: 2008                                   TYPE: A

Abstract



 


Near-field optical spectroscopy of nanoscale Ga droplets on GaAs exhibits quenching of photoluminescence emission due to coupling with surface plasmon. Ga droplets exhibit antenna like behavior associated with a red-shift in the near-field photoluminescence emission. ©2008 Optical Society of America.


 


Graphical Abstract



ⓒ 2008 OSA / CLEO/QELS 2008

 

 

 

TITLE: Formation of hybrid molecules composed of Ga metal particle in direct contact with InGaAs semiconductor quantum ring
AUTHORS: Jihoon H. Lee, Zhiming M. Wang, Kim. Sablon and Gregory J. Salamo
JOURNAL/BOOK TITLE: Crystal growth & design
VOLUME: 8                                   FIRST PAGE: 690
YEAR OF PUBLICATION: 2008                                        TYPE: A                      IF: 4.215

Abstract



 

We demonstrate the formation of hybrid molecules composed of a pair of a metal particle and a semiconductor quantum ring (QR) by using molecular beam epitaxy on a GaAs (100) surface. To form three-dimensional semiconductor InGaAs QRs with a hole in the center of the structure, a thin layer (10 monolayer) of GaAs was applied on InAs quantum dots, which transformed the distribution of surface free energy. These InGaAs QRs were then used as a template for the localization of Ga metal particles; there was one metal particle on a QR. By choosing the optimal surface temperature (most favorable thermal energy), the surface diffusion of Ga adatoms was effectively enhanced. This, in turn, allowed the localization of Ga metal particles on InGaAs QRs, consequently forming hybrid molecules. This study helps understand the formation of various types of hybrid molecules that will be used in applications in optoelectronics.

 


Graphical Abstract



Formation of hybrid molecules

Crystal Growth & Design, Vol. 8, No. 2, 2008Crystal Growth & Design, Vol. 8, No. 2, 2008

 

 

 

TITLE: Spatially localized formation of InAs quantum dots on shallow mesa- and trench patterns regardless of crystallographic directions
AUTHORS:
J. H. Lee, Zh. M. Wang, W. T. Black, Vas. P. Kunets, Yu. I. Mazur, and G. J. Salamo
JOURNAL/BOOK TITLE:
Advanced Functional Materials
VOLUME:
17                                FIRST PAGE: 3187
YEAR OF PUBLICATION:
2007                                    TYPE: A                      IF: 6.808

Abstract



 

We report on the ability to grow InAs quantum dots into patterns of any shape.We specifically demonstrate the spatial localization of InAs quantum dots on mesa and trench patterns varying from line, square and triangle patterns on GaAs (100) substrates by molecular beam epitaxy. Based on the underlying science, this growth approach enables the localization of InAs QDs on GaAs (100) by controlling the sidewall facets and InAs monolayer coverage.

 


Graphical Abstract




Adv. Funct. Mater. 2007, 17, 3187?3193

Adv. Funct. Mater. 2007, 17, 3187?3193

 

 

TITLE: Observation of change in critical thickness of In droplet formation on GaAs (100)
AUTHORS: J H Lee, Zh M Wang, and G J Salamo

JOURNAL/BOOK TITLE: Journal of Physics: Condensed Matter                       
VOLUME: 19                            FIRST PAGE: 176223                          
YEAR OF PUBLICATION: 2007                                     TYPE: A                    
  IF: 1.9

Abstract



 

We present a study on the formation of In droplets on GaAs(100) substrates as functions of substrate temperature and monolayer (ML) deposition by using molecular beam epitaxy (MBE) and atomic force microscopy (AFM). We specifically reveal the change in critical thickness of In deposition to form In droplets at different substrate temperatures. At a relatively high substrate temperature, the critical thickness of In droplets becomes relatively thinner as the amount of As atoms on the surface decreases. The control of the size and density of In droplets is also systematically discussed. This study provides an aid in understanding the formation of In droplets and thus can find applications in the formation of quantum structures and/or nanostructures based on droplet epitaxy.

 


Graphical Abstract



J. Phys.: Condens. Matter 19 (2007) 176223

 

 

 

TITLE: Self-assembled InAs quantum dot formation on GaAs ring-like nanostructure templates
AUTHORS: N. W. Strom, Zh. M. Wang, J. H. Lee, Z. Y. AbuWaar, Yu. I. Mazur, and G. J. Salamo
JOURNAL/BOOK TITLE:
Nanoscale Research Letters  
VOLUME:
2  
                            FIRST PAGE: 112
YEAR OF PUBLICATION:
2007                                      TYPE: A                      IF: 1.731

Abstract



 

The evolution of InAs quantum dot (QD) formation is studied on GaAs ring-like nanostructures fabricated by droplet homo-epitaxy. This growth mode, exclusively performed by a hybrid approach of droplet homo-epitaxy and Stransky-Krastanor (S-K) based QD self-assembly, enables one to form new QD morphologies that may find use in optoelectronic applications. Increased deposition of InAs on the GaAs ring first produced a QD in the hole followed by QDs around the GaAs ring and on the GaAs (100) surface. This behavior indicates that the QDs prefer to nucleate at locations of high monolayer (ML) step density.

 


Graphical Abstract



Nanoscale Res Lett (2007) 2:112?117

 

 

TITLE: Novel Morphologies of InAs Quantum Dot Growth on GaAs Surfaces Containing Nanostructures Formed by Droplet Epitaxy
AUTHORS:
J. H. Lee, Zh. M. Wang, B. L. Liang, K. Sablon, N. W. Strom and G. J. Salamo
JOURNAL/BOOK TITLE:
Material Research Society Symposium Proceeding    
VOLUME:
959                           FIRST PAGE: 0959-M08-02
YEAR OF PUBLICATION: 2007                                        TYPE: A

Abstract



 

Self-assembled InAs quantum dot clusters (QDCs) and InGaAs QD molecules (QDMs) have been demonstrated through a growth technique called “droplet epitaxy” by molecular beam epitaxy (MBE). For QDCs, the size and density of QDs can be controlled with variation of InAs monolayer coverages. For QDMs, Ga contribution from GaAs mound with the interaction of InAs deposition resulted in various number of InGaAs QDs per GaAs mound, ranging from 2 to 6 (bi-QDMs to hexa-QDMs) depending on the specific InAs monolayer deposition. High step density on sidewall of GaAs mound and anisotropy of surface diffusion gave a rise to preferential formation of InAs and InGaAs QDs around GaAs mounds. This hybrid growth approach combining droplet epitaxy and typical QD growth is relatively simple and flexible and doesn’t require further ex-situ surface preparation. This approach of QD arrangement can find applications in optoelectronics as well as physical study of QD interaction.

 


Graphical Abstract



Mater. Res. Soc. Symp. Proc. Vol. 959 ⓒ 2007 Materials Research Society

 

 

TITLE: Optical behavior of GaAs/AlGaAs ring-like nanostructures”,
AUTHORS:
Ziad Y. AbuWaar, Yuriy I.
Mazur, Jihoon H. Lee, Zhiming M. Wang, and Gregory J. Salamo
JOURNAL/BOOK TITLE:
Journal of Applied Physics 
VOLUME:
101                           FIRST PAGE: 024311                          
YEAR OF PUBLICATION:
2007                                         TYPE: A                      IF: 2.201

Abstract



 

Atomic force microscopy and photoluminescence (PL) measurements were carried out to investigate the role of the morphology of GaAs/Al0.3Ga0.7As ringlike nanostructures on their optical properties. A small amount of Ga material (less than three monolayers) was used to fabricate single ringlike and double ringlike DRL nanostructures using droplet epitaxy technique. The height of the ringlike nanostructures increased with the increase of the Ga material while the corresponding PL emission energy was found to decrease as the ringlike nanostructure height increased. The PL peak energy showed a blueshift with increasing excitation intensity that can be understood as due to state filling while increasing temperature showed that the peak energy of the larger DRL nanostructures redshifts at a lower rate than the small ones due to larger confinement potential and lower energy emissions. © 2007 American Institute of Physics. [DOI: 10.1063/1.2425194]

 


Graphical Abstract




J. Appl. Phys. 101, 024311 (2007)

 

 

 

TITLE: Formation of Self-Assembled Sidewall Nanowires on Shallow Patterned GaAs (100)”,
AUTHORS:
J. H. Lee, Zh M Wang, B L Liang, W T Black, Vas P Kunets, Yu I Mazur, and G J Salamo
JOURNAL/BOOK TITLE:
IEEE Transactions on Nanotechnology  
VOLUME: 6                              FIRST PAGE: 70
YEAR OF PUBLICATION:
2007                                         TYPE: A                      IF: 2.154

Abstract



 

The formation of “sidewall nanowires” on shallow patterned mesa strips with a modulation depth of only 35 nm on GaAs (100) was demonstrated using molecular beam epitaxy. While self-assembled GaAs sidewall nanowire formation is observed near mesa strips running along [011], relatively thinner AlAs/GaAs layers are formed on identical mesa strips running along [01-1]. Cross-sectional atomic force microscopy (XAFM) on (011) and (01-1) and AFM on (100) are used to understand the formation of the different morphology of the nanostructures, depending on the direction of the mesas. The data indicates that anisotropic surface diffusion of adatoms, resulting from the characteristic (2 4) GaAs (100) surface reconstruction, is responsible for the sidewall nanowire formation and for the different morphology observed along different directions.

 


Graphical Abstract



IEEE TRANSACTIONS ON NANOTECHNOLOGY, VOL. 6, NO. 1, JANUARY 2007


IEEE TRANSACTIONS ON NANOTECHNOLOGY, VOL. 6, NO. 1, JANUARY 2007

 


 

TITLE: Self-Organization of InAs Quantum-Dot Clusters Directed by Droplet Homoepitaxy
AUTHORS: Zh. M. Wang, B. L. Liang, K. A. Sablon, J. H. Lee, Yu. I. Mazur, N. W. Strom, and G. J. Salamo
JOURNAL/BOOK TITLE:
Small   
VOLUME:
3                              FIRST PAGE: 235
YEAR OF PUBLICATION:
2007                                       TYPE: A                      IF: 6.525

Abstract



 

Recently, droplet heteroepitaxy of GaAs/AlGaAs has attracted much attention due to its demonstrated capability of producing nanostructures with interesting geometrical shapes such as quantum single and double ringlike structures. In the droplet-heteroepitaxy approach, Ga is deposited on an AlGaAs surface to create liquid Ga droplets, and these droplets are exposed to an As flux that transforms the droplets into GaAs nanocrystals. In principle, this same approach can e modified into a similar process of GaAs homo epitaxy, which also allows one to structure GaAs surfaces at the nanometer scale. In this droplet-homoepitaxy approach, the nanostructures formed by the droplets can then be used to encourage the growth of subsequent heteronanostructures such as self-assembled InAs quantum dots (QDs).

 


Graphical Abstract



small 2007, 3, No. 2, 235 ? 238small 2007, 3, No. 2, 235 ? 238

 

 

 

TITLE: Survival of Atomic monolayer steps during oxide desorption on GaAs (100)
AUTHORS:
J. H. Lee, Zh. M. Wang, and G. J. Salamo
JOURNAL/BOOK TITLE: Journal of Applied Physics
VOLUME:
100                           FIRST PAGE: 114330                          
YEAR OF PUBLICATION:
2006                                         TYPE: A                      IF: 2.201

Abstract



 

Significant surface pitting and a degraded surface roughness are almost always observed on GaAs (100) surface after conventional thermal oxide desorption. Here we report on the use of a Ga-triggered low temperature oxide desorption method that can be used to preserve the atomic monolayer (ML) steps. By providing an external supply of atomic Ga at a relatively low substrate temperature of 450 °C without an As4 overpressure, this technique resulted in an atomically smooth GaAs ML steps with a root mean square roughness of 0.25 nm, nearly identical to as-grown GaAs surface (0.2 nm). The demonstrated results show the potential for applications in optoelectronics such as regrowth and patterned substrate growth. © 2006 American Institute of Physics. [DOI: 10.1063/1.2401649]

 


Graphical Abstract



J. Appl. Phys. 100, 114330 (2006)

 

 

 

TITLE: Observation of Ga droplet formation on (311)A and (511)A GaAs surfacess
AUTHORS:
Ziad Y AbuWaar, Zhiming MWang, J. H. Lee, Gregory J Salamo
JOURNAL/BOOK TITLE:
Nanotechnology 
VOLUME:
17                            FIRST PAGE:
4037          
YEAR OF PUBLICATION:
2006                                           TYPE: A                      IF: 3.446

Abstract



 

Using (100) GaAs substrates as a reference, we present a study of the formation of Ga droplets on (311)A and (511)A GaAs substrates in which the effect of both the substrate temperature and the amount of Ga supplied on the droplet density and height for the three different surfaces have been investigated. Droplets on (100) substrates show a round shape; however, they appear as elongated balls with tails along the [¯233] direction of the (311)A substrate and the [¯255] direction of the (511)A substrate. It has been found that the Ga droplets on (511)A surfaces have lower densities and higher heights than those on (100) substrates. In contrast, Ga droplets on (311)A surfaces have lower heights and much higher densities compared to those for both (100) and (511)A. We observed that the decrease in the droplet density with increasing growth temperature for both (311)A and (511)A is more than twice that for the (100)GaAs surface due to the larger drop in the nucleation rate. Based on these observations, we offer a physical explanation based on the thermodynamics and the anisotropy of the high-index surfaces.

 


Graphical Abstract



Observation of Ga droplet

 

 

 

TITLE: Multiple vertically stacked quantum dot clusters with improved size homogeneity
AUTHORS:
J. H. Lee, Zh. M. Wang, B. L. Liang, K. A. Sablon, N. W. Strom, and G. J. Salamo
JOURNAL/BOOK TITLE: Journal of physics D: Applied physics
VOLUME:
40                            FIRST PAGE: 198                                
YEAR OF PUBLICATION:
2006                                         TYPE: A                      IF: 2.104

Abstract



 

clusters within a GaAs matrix are investigated on GaAs (1 0 0) by atomic force microscopy. Droplet homoepitaxy (GaAs nanostructures on planar GaAs) is used to create tiny GaAs nano-mound templates elongated along [0 1−1]. Due to a high density of monolayer steps on the edge of nano-mounds, deposited InAs prefer to form in clusters around the nano-mound templates. By varying the subsequent InAs monolayer coverages and growth temperatures, two distinctive sizes of quantum dots (QDs) are formed around the nano-mounds for the layer stacking. With a fixed GaAs barrier thickness (10 nm) in between the layers, the resulting QDs from the stacked layers show significant improvement in their size uniformity.

 


Graphical Abstract



J. Phys. D: Appl. Phys. 40 (2007) 198?202

 

 

 

TITLE: Annealing effect in InAs quantum dots grown on GaAs droplet template
AUTHORS:
B. L. Liang, Zh. M. Wang, J. H. Le, K. Sablon, Yu. I. Mazur, G. J. Salamo
JOURNAL/BOOK TITLE:
Applied Physics Letters
VOLUME:
89                            FIRST PAGE: 213103
YEAR OF PUBLICATION:
2006                                           TYPE: A                      IF: 3.726

Abstract



 

The authors report on the use of GaAs islands, formed by the droplet epitaxy growth technique, as a template for the growth of clusters of InAs quantum dots. Surface morphology measurements show that the shape and dimensions of the GaAs islands and consequently the formation of InAs quantum dots depend strongly on the annealing temperature and annealing time. This can be explained by the diffusion of gallium atom during the annealing process and the selective formation of InAs quantum dots on the misoriented GaAs island sidewalls. © 2006 American Institute of Physics. [DOI: 10.1063/1.2396928]

 


Graphical Abstract



Appl. Phys. Lett. 89, 213103 (2006)

 

 


TITLE: Journal cover of the volume 89, issue 20 of Applied Physics Letters"
AUTHORS: J. H. Lee, Zh. M. Wang, N. W. Strom, Yu. I. Mazur and G. J. Salamo
JOURNAL/BOOK TITLE: Applied Physics Letters
VOLUME: 89                             FIRST PAGE: 202101
YEAR OF PUBLICATION: 2006       TYPE: A        IF: 3.726
APL 89 20
 

 

TITLE:InGaAs quantum dot molecules around self-assembled GaAs nano-mound templates"
AUTHORS:
J. H. Lee, Zh. M. Wang, N. W. Strom, Yu. I. Mazur and G. J. Salamo
JOURNAL/BOOK TITLE:
Applied Physics Letters
VOLUME:
89                            FIRST PAGE: 202101                                                         
YEAR OF PUBLICATION:
2006                                          TYPE: A                      IF: 3.44

(Featured on the Journal cover of the volume 89, issue 20 of Applied Physics Letters)
(Selected as one of the most downloaded articles of November 2006)


Abstract



 

Several distinctive self-assembled InGaAs quantum dot molecules (QDMs) are studied. The QDMs self-assemble around nanoscale-sized GaAs moundlike templates fabricated by droplet homoepitaxy. Depending on the specific InAs monolayer coverage, the number of QDs per GaAs mound ranges from two to six (bi-QDMs to hexa-QDMs). The Ga contribution from the mounds is analyzed in determining the morphologies of the QDMs, with respect to the InAs coverages ranging between 0.8 and 2.4 ML. Optical characterization shows that the resulting nanostructures are high-quality nanocrystals. © 2006 American Institute of Physics. [DOI: 10.1063/1.2388049]

 


Graphical Abstract



Appl. Phys. Lett. 89, 202101 (2006)

Appl. Phys. Lett. 89, 202101 (2006)


 

 

TITLE: Structural evolution in strained In0.18Ga0.82As staking multilayer on vicinal GaAs surfaces
AUTHORS:
V. Yazdanpanah, Zh. M. Wang, J. H. Lee, and G. J. Salamo
JOURNAL/BOOK TITLE:
New Journal of Physics 
VOLUME:
8                            FIRST PAGE: 233                                                         
YEAR OF PUBLICATION:
2006                                          TYPE: A                      IF: 3.44

Abstract



 

Strain relaxation mechanisms for the growth of m-layers of In0.18Ga0.82As/GaAs on a GaAs(100) substrate, tilted 2? towards the [0–11] direction, have been studied by molecular beam epitaxy (MBE) and atomic force microscopy (AFM). While dislocations alone provide a strain relaxation mechanism for nominal GaAs(100), additional strain relaxation mechanisms were observed for a vicinal GaAs(100) substrate. For m  8, step bunching provided a mechanism for strain relaxation. For m 10, in addition to the step bunching, bunched corners along two [051] and [0–1–5] directions provided the mechanism for strain relaxation. These surface patterns provide potential to act as a template for the growth of more uniform and organized nanostructures. For m = 16, the formation of dislocations provided an additional route for strain relaxation.

 


Graphical Abstract



New Journal of Physics 8 (2006) 233

 

TITLE: Low density InAs quantum dots grown on GaAs nanoholes”,
AUTHORS:
B. L. Liang, Zh. M. Wang, J. H. Lee, K. Sablon, Yu. I. Mazur, G. J. Salamo
JOURNAL/BOOK TITLE: Applied Physics Letters
VOLUME:
89                            FIRST PAGE: 043113
YEAR OF PUBLICATION:
2006                                          TYPE: A                      IF: 3.726

Abstract



 

A growth technique combining droplet epitaxy and molecular beam epitaxy (MBE) is developed to obtain a low density of InAs quantum dots (QDs) on GaAs nanoholes. This growth technique is simple, flexible, and does not require additional substrate processing. It makes possible separate control of the QD density via droplet epitaxy and the QD quality via MBE growth. In this letter the authors report the use of this technique to produce InAs QDs with a low density of 2.7 x 10^8 cm^−2 as well as good photoluminescence properties. The resulting samples are suitable for single QD device fabrication and applications. © 2006 American Institute of Physics. [DOI: 10.1063/1.2244043]

 


Graphical Abstract



Appl. Phys. Lett. 89, 043113 (2006)       Appl. Phys. Lett. 89, 043113 (2006)

 

 

 

TITLE: Evolution between self-assembled single and double ring-like structures
AUTHORS:
J. H. Lee, Zh. M. Wang, Z. Y. AbuWaar, N. W. Strom and G. J. Salamo
JOURNAL/BOOK TITLE:
Nanotechnology 
VOLUME:
17                            FIRST PAGE: 3973          
YEAR OF PUBLICATION:
2006                                           TYPE: A                      IF: 3.446

Abstract



 

The evolution between lattice-matched GaAs/Al0.3Ga0.7As single and double ring-like nanostructures is studied, with an emphasis on the construction and destruction of the observed outer ring. Using droplet epitaxy, this was achieved by directly controlling the Ga surface diffusion on GaAs(100). Double ring-like nanostructures were observed at relatively low temperatures under a fixed As4 flux (beam equivalent pressure (BEP) of 6.4 μTorr) and at a fixed temperature under a high As4 flux. The construction of the outer ring can be controlled through surface diffusion by varying the substrate temperature or the As4 flux. Single ring-like nanostructures were realized both at relatively high temperatures under a fixed As4 flux, and at low temperatures under a relatively low As4 flux.

 


Graphical Abstract




Nanotechnology 17 (2006) 3973?3976

 

 


TITLE: Journal cover of volume 88, issue 23 of Applied Physics Letters
AUTHORS:
Zh M Wang, J. H. Lee, B L Liang, W T Black, Vas P Kunets, Yu I Mazur, and G J Salamo
JOURNAL/BOOK TITLE:
Applied Physics Letters
VOLUME:
88    FIRST PAGE: 233102
YEAR OF PUBLICATION:
2006                   TYPE: A                 IF: 3.726
Journal cover of volume 88, issue 23 of APL
 

 

TITLE: Localized Formation of InAs Quantum Dots on Shallow- patterned GaAs (100)
AUTHORS:
Zh M Wang, J. H. Lee, B L Liang, W T Black, Vas P Kunets, Yu I Mazur, and G J Salamo
JOURNAL/BOOK TITLE:
Applied Physics Letters
VOLUME:
88    FIRST PAGE: 233102
YEAR OF PUBLICATION:
2006                   TYPE: A                 IF: 3.726

(Featured on the Journal cover of volume 88, issue 23 of Applied Physics Letters)

|Abstract



 

Selective formation of InAs quantum dots on the sidewalls of mesa strips along both [01−1] and [011] directions of a GaAs100 surface is demonstrated. This result is in sharp contrast to observations on traditionally deep-patterned substrates, where quantum dots are formed on top mesas and at bottom trenches. This distinction is explained kinetically and energetically. These results may encourage application of organized arrays of quantum dots. © 2006 American Institute of Physics. [DOI: 10.1063/1.2209157]

 


Graphical Abstract



Appl. Phys. Lett. 88, 233102 (2006)

 

 

 

TITLE: Size and density control of InAs quantum dot ensembles on self-assembled nano- structured templates
AUTHORS:
J. H. Lee, Zh. M. Wang, B. L. Liang, K. A. Sablon, N. W. Strom, and G. J. Salamo
JOURNAL/BOOK TITLE:
Semiconductor Science and Technology 
VOLUME: 21                            FIRST PAGE: 1547
YEAR OF PUBLICATION:
2006                                         TYPE: A                      IF: 1.434

Abstract



 

New morphologies of InAs quantum dot (QD) ensembles forming on self-assembled GaAs nano-holed island templates are demonstrated. Droplet homoepitaxy (GaAs/GaAs) is used to generate holed nanoscale-sized mounds that appear to elongate along [0 1 ¯1]. Depending on the InAs monolayer (ML) coverages, subsequent InAs deposition forms different sizes and shapes of QD ensembles. While we initially observe the formation of the QDs at the hole sites when less InAs is deposited, QDs form around the edges of the mounds with greater InAs deposition. By varying the InAs depositions and growth temperatures, we demonstrate an ability to control the size and density of QDs. The observed decrease in the necessary critical thickness required for the InAs 2D–3D transition may be due to the higher density of monolayer steps on the sidewalls of the holes and on the edges of the mounds. This hybrid growth approach overcomes some limitations of typical QD growth on planar GaAs surfaces and may find applications in optoelectronics.

 


Graphical Abstract



Semicond. Sci. Technol. 21 (2006) 1547:1551

 


 

TITLE: InGaAs quantum dots grown on B-type high index GaAs substrates: surface morphologies and optical properties
AUTHORS:
B. L. Liang, Zh. M. Wang, Yu. I. Mazur, V. V. Strelchuck, K. Homles, J. H. Lee, G. J. Salamo
JOURNAL/BOOK TITLE:
Nanotechnology
VOLUME:
17                            FIRST PAGE: 2736                              
YEAR OF PUBLICATION:
2006                                       TYPE: A                      IF: 3.446

Abstract



 


We systematically investigated the correlation between morphological and optical properties of InGaAs self-assembled quantum dots (QDs) grown by solid-source molecular beam epitaxy on GaAs (n11)B (n = 9, 8, 7, 5, 3, 2) substrates. Remarkably, all InGaAs QDs on GaAs(n11)B under investigation show optical properties superior to those for ones on GaAs(100) as regards the photoluminescence (PL) linewidth and intensity. The morphology for growth of InGaAs QDs on GaAs (n11)B, where n = 9, 8, 7, 5, is observed to have a rounded shape with a higher degree of lateral ordering than that on GaAs(100). The optical property and the lateral ordering are best for QDs grown on a (511)B substrate surface, giving a strong correlation between lateral ordering and PL optical quality. Our results demonstrate the potential for high quality InGaAs QDs on GaAs(n11)B for optoelectronic applications.


 


Graphical Abstract



Nanotechnology 17 (2006) 2736?2740 doi:10.1088

 

 


TITLE: Highlighted in the NanoWerk Sport light, April 12th, 2006
AUTHORS:
J. H. Lee, Zh M Wang, B L Liang, W T Black, Vas P Kunets, Yu I Mazur, and G J Salamo
JOURNAL/BOOK TITLE:
Nanotechnology  
VOLUME:
17                            FIRST PAGE: 2275
YEAR OF PUBLICATION:
2006                         TYPE: A          IF: 3.446
Link: QD necklaces and other QD chains
QD necklaces and other QD chains
 

 

TITLE: Selective growth of InGaAs/GaAs quantum dot chains on pre-patterned GaAs (100)
AUTHORS:
J. H. Lee, Zh M Wang, B L Liang, W T Black, Vas P Kunets, Yu I Mazur, and G J Salamo
JOURNAL/BOOK TITLE:
Nanotechnology  
VOLUME:
17                            FIRST PAGE: 2275
YEAR OF PUBLICATION:
2006                         TYPE: A          IF: 3.446

(Highlighted in the NanoWerk Sport light, April 12th, 2006)

Abstract



 

Self-organized InGaAs quantum dot chains grown by molecular beam epitaxy were investigated using vertical stacking techniques on pre-patterned GaAs(100) substrates. The results demonstrate the formation of quantum dot (QD) chains only on desired spatial regions. In addition to QD chains, the results show that almost any shape of lines of QDs are possible depending on the faceted pre-patterned substrate. The experimental results suggest that this approach has the potential to be used to fabricate single QD chains or necklaces or almost any pattern.

 


Graphical Abstract



Nanotechnology 17 (2006) 2275?2278

 


 

TITLE: Ga-Triggered oxide desorption from GaAs (100) and non-(100) Substrates
AUTHORS: J. H. Lee, Zh. M. Wang, and G. J. Salamo
JOURNAL/BOOK TITLE: Applied Physics Letters 
VOLUME: 88                           FIRST PAGE: 252108                          
YEAR OF PUBLICATION: 2006                                       TYPE: A                      IF: 3.726


Abstract



 

Surface pit formation is observed to occur for conventional thermal oxide desorption, regardless of the GaAs surface index. The resulting surface roughening can be substantially reduced by depositing an appropriate amount of Ga in the absence of As flux. The amount of Ga required to optimize the quality of the oxide-free GaAs surface is found to be different for different indexed substrates and is dependent on the oxide thicknesses. Due to the flexibility of the GaAs surface reconstruction, the Ga-triggered oxide desorption is observed to be much more robust than was previously believed. © 2006 American Institute of Physics.

 


Graphical Abstract

APPLIED PHYSICS LETTERS 88, 252108 2006

 

 

 

TITLE: “Control of the morphology of quantum dot structures on III-V semiconductors"
AUTHORS: J. H. Lee
JOURNAL/BOOK TITLE: (M. S. Thesis) The University of Arkansas Press
YEAR OF PUBLICATION: 2005                                       TYPE: B

 

 

TITLE: Surface ordering of (In,Ga)As quantum dots controlled by GaAs substrate indexes
AUTHORS: Zh. M. Wang, Sh. Seydmohamadi, J. H. Lee, and G. J. Salamo
JOURNAL/BOOK TITLE: Applied Physics Letters
VOLUME: 85                            FIRST PAGE: 5031                              
YEAR OF PUBLICATION: 2004                                        TYPE: A                      IF: 3.726

Abstract



 

Self-organized surface ordering of (In,Ga)As quantum dots in a GaAs matrix was investigated using stacked multiple quantum dot layers prepared by molecular-beam epitaxy. While one-dimensional chain-like ordering is formed on singular and slightly misorientated GaAs(100) surfaces, we report on two-dimensional square-like ordering that appears on GaAs(n11)B, where n is 7, 5, 4, and 3. Using a technique to control surface diffusion, the different ordering patterns are found to result from the competition between anisotropic surface diffusion and anisotropic elastic matrix, a similar mechanism suggested before by Solomon [Appl. Phys. Lett. 84, 2073 (2004)].
© 2004 American Institute of Physics. [DOI: 10.1063/1.1823590]

 


Graphical Abstract



Appl. Phys. Lett., Vol. 85, No. 21, 22 November 2004

Appl. Phys. Lett., Vol. 85, No. 21, 22 November 2004

 


 
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