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Kim B, Kim S, Lee TH, Yang D, Lee D, Sohn W, Yoon E, Park Y, Jang HW. Enhancing Performance of Ultraviolet C Photodetectors Through Single-Domain Epitaxy of Monoclinic β-Ga 2 O 3 Films and Tailored Anti-Reflection Coating. Small Methods 2023:e2300933. [PMID: 37882332 DOI: 10.1002/smtd.202300933] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2023] [Revised: 09/16/2023] [Indexed: 10/27/2023]
Abstract
Implementing high-performance ultraviolet C photodetectors (UVC PDs) based on β-Ga2 O3 films is challenging owing to the anisotropic crystal symmetry between the epitaxial films and substrates. In this study, highly enhanced state-of-the-art photoelectrical performance is achieved using single-domain epitaxy of monoclinic β-Ga2 O3 films on a hexagonal sapphire substrate. Unlike 3D β-Ga2 O3 films with twin domains, 2D β-Ga2 O3 films exhibit a single domain with a smooth surface and low concentration of point defects, which enable efficient charge separation by suppressing boundary-induced recombination. Furthermore, a tailored anti-reflection coating (ARC) is adopted as a light-absorbing medium to improve charge generation. The tailored nanostructure, which features a gradient refractive index, not only substantially reduces the reflection, but also suppresses the surface leakage current as a passivation layer. This study provides fundamental insights into the single-domain epitaxy of β-Ga2 O3 films and the application of ARC for the development of high-performance UVC PDs.
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Affiliation(s)
- Byungsoo Kim
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul, 08826, Republic of Korea
| | - Seungju Kim
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul, 08826, Republic of Korea
| | - Tae Hyung Lee
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul, 08826, Republic of Korea
| | - Duyoung Yang
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul, 08826, Republic of Korea
| | - Dongyup Lee
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul, 08826, Republic of Korea
| | - Woonbae Sohn
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul, 08826, Republic of Korea
| | - Euijoon Yoon
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul, 08826, Republic of Korea
| | - Yongjo Park
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul, 08826, Republic of Korea
- Advanced Institute of Convergence Technology, Seoul National University, Suwon, 16229, Republic of Korea
| | - Ho Won Jang
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul, 08826, Republic of Korea
- Advanced Institute of Convergence Technology, Seoul National University, Suwon, 16229, Republic of Korea
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Son J, Park H, Yoon E, Kim JI, Choi CH. Development of Novel Focal Irradiation Tool for High-Precision Irradiation Using Clinical Brachytherapy System. Int J Radiat Oncol Biol Phys 2023; 117:e655-e656. [PMID: 37785945 DOI: 10.1016/j.ijrobp.2023.06.2085] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/04/2023]
Abstract
PURPOSE/OBJECTIVE(S) Several small animals, including mice, are used to conduct research on state-of-the-art radiation therapy techniques or treatment-related toxicity. However, it is difficult to conduct the focal irradiation to a shallow depth on small animals, because irradiation using LINAC has limitations in energy and field size. The purpose of this paper was to develop a focal irradiation tool for high-precision irradiation and to evaluate beam characteristics. MATERIALS/METHODS We designed the collimator of 1 mm diameter consisting of tungsten material for high-precision irradiation applied to the clinical brachytherapy system and the percent depth dose and horizontal profile were measured. We compared the depth dose and horizontal profile with 4 mm diameter SRS cone for 6 MV in LINAC. We measured the PDD and horizontal profile using EBT3 film for high-precision irradiation of 1 mm diameter using Ir-192 source. In case of 4 mm diameter, the beam was measured using edge detector. In addition, all measurements were compared with the results of planning tool simulation. RESULTS In case of focal irradiation tool, the maximum dose showed at the surface for both measurement and simulation, and 26% and 32% doses at 1 mm depth, respectively. In addition, FWHM at a 1 mm depth showed that high-precision irradiation was possible with measurement and simulation results of 1.86 and 1.28 mm. In case of LINAC, the maximum dose was showed at a depth of 1 cm and 0.8 cm in the measurement and simulation, respectively. Even if the smallest cone is used, the FWHM at a dmax depth was 4.0 mm in both simulation and measurement. CONCLUSION We overcame the limitation for energy and field size through the focal irradiation tool for high-precision irradiation. The focal irradiation tool enables high dose delivery to the shallow depth. In addition, small FWHM reduced dose delivery to the periphery at a specific depth and enabled accurate dose delivery. These results mean that the focal irradiation tool can be useful in small animal experiments that require accurate doses near the shallow depth.
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Affiliation(s)
- J Son
- Department of Radiation Oncology, Seoul National University Hospital, Seoul, Korea, Republic of (South) Korea
| | - H Park
- Department of Radiological Convergence Engineering, Yonsei University, Seoul, Korea, Republic of (South) Korea
| | - E Yoon
- Interdisciplinary Program in Bioengineering, Seoul National University, Seoul, Korea, Republic of (South) Korea
| | - J I Kim
- Department of Radiation Oncology, Seoul National University Hospital, Seoul, Korea, Republic of (South) Korea
| | - C H Choi
- Department of Radiation Oncology, Seoul National University Hospital, Seoul, Korea, Republic of (South) Korea
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Oh J, Kim D, Yang D, Hwang K, Hwang J, Kim J, Lee S, Ryu J, Park S, Shin JK, Kim Y, Park Y, Yoon E, Jang HW. Self-Assembled Size-Tunable Microlight-Emitting Diodes Using Multiple Sapphire Nanomembranes. ACS Appl Mater Interfaces 2022; 14:25781-25791. [PMID: 35623063 DOI: 10.1021/acsami.2c05483] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Microlight-emitting diode (Micro-LED) is the only display production technology capable of meeting the high-performance requirements of future screens. However, it has significant obstacles in commercialization due to etching loss and efficiency reduction caused by the singulation process, in addition to expensive costs and a significant amount of time spent on transfer. Herein, multiple-sapphire nanomembrane (MSNM) technology has been developed that enables the rapid transfer of arrays while producing micro-LEDs without the need for any singulation procedure. Individual micro-LEDs of tens of μm size were formed by the pendeo-epitaxy and coalescence of GaN grown on 2 μm width SNMs spaced with regular intervals. We have successfully fabricated micro-LEDs of different sizes including 20 × 20 μm2, 40 × 40 μm2, and 100 × 100 μm2, utilizing the membrane design. It was confirmed that the 100 × 100 μm2 micro-LED manufactured with MSNM technology not only relieved stress by 80.6% but also reduced threading dislocation density by 58.7% compared to the reference sample. It was proven that micro-LED arrays of varied chip sizes using MSNM were all transferred to the backplane. A vertical structure LED device could be fabricated using a 100 × 100 μm2 micro-LED chip, and it was confirmed to have a low operation voltage. Our work suggests that the development of the MSNM technology is promising for the commercialization of micro-LED technology.
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Affiliation(s)
- Jehong Oh
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826 Republic of Korea
| | - Dongho Kim
- Samsung Advanced Institute of Technology, Suwon 16678, Republic of Korea
| | - Duyoung Yang
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826 Republic of Korea
| | - Kyungwook Hwang
- Samsung Advanced Institute of Technology, Suwon 16678, Republic of Korea
| | - Junsik Hwang
- Samsung Advanced Institute of Technology, Suwon 16678, Republic of Korea
| | - Jongmyeong Kim
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826 Republic of Korea
| | - Seungmin Lee
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826 Republic of Korea
| | - Jungel Ryu
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826 Republic of Korea
| | - Sohyeon Park
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826 Republic of Korea
| | - Jai-Kwang Shin
- Samsung Advanced Institute of Technology, Suwon 16678, Republic of Korea
| | - Yongsung Kim
- Samsung Advanced Institute of Technology, Suwon 16678, Republic of Korea
| | - Yongjo Park
- Advanced Institute of Convergence Technology, Seoul National University, Suwon 16229 Republic of Korea
| | - Euijoon Yoon
- Korea Institute of Energy Technology, Naju 58330, Republic of Korea
| | - Ho Won Jang
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826 Republic of Korea
- Advanced Institute of Convergence Technology, Seoul National University, Suwon 16229 Republic of Korea
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Yang D, Kim B, Oh J, Lee TH, Ryu J, Park S, Kim S, Yoon E, Park Y, Jang HW. α-Gallium Oxide Films on Microcavity-Embedded Sapphire Substrates Grown by Mist Chemical Vapor Deposition for High-Breakdown Voltage Schottky Diodes. ACS Appl Mater Interfaces 2022; 14:5598-5607. [PMID: 35040629 DOI: 10.1021/acsami.1c21845] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
α-Gallium oxide, with its large band gap energy, is a promising material for utilization in power devices. Sapphire, which has the same crystal structure as α-Ga2O3, has been used as a substrate for α-Ga2O3 epitaxial growth. However, lattice and thermal expansion coefficient mismatches generate a high density of threading dislocations (TDs) and cracks in films. Here, we demonstrated the growth of α-Ga2O3 films with reduced TD density and residual stress on microcavity-embedded sapphire substrates (MESS). We fabricated the two types of substrates with microcavities: diameters of 1.5 and 2.2 μm, respectively. We confirmed that round conical-shaped cavities with smaller diameters are beneficial for the lateral overgrowth of α-Ga2O3 crystals with lower TD densities by mist chemical vapor deposition. We could obtain crack-free high-crystallinity α-Ga2O3 films on MESS, while the direct growth on a bare sapphire substrate resulted in an α-Ga2O3 film with a number of cracks. TD densities of α-Ga2O3 films on MESS with 1.5 and 2.2 μm cavities were measured to be 1.77 and 6.47 × 108 cm-2, respectively. Furthermore, cavities in MESS were certified to mitigate the residual stress via the redshifted Raman peaks of α-Ga2O3 films. Finally, we fabricated Schottky diodes based on α-Ga2O3 films grown on MESS with 1.5 and 2.2 μm cavities, which exhibited high breakdown voltages of 679 and 532 V, respectively. This research paves the way to fabricating Schottky diodes with high breakdown voltages based on high-quality α-Ga2O3 films.
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Affiliation(s)
- Duyoung Yang
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826, Republic of Korea
| | - Byungsoo Kim
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826, Republic of Korea
| | - Jehong Oh
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826, Republic of Korea
| | - Tae Hyung Lee
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826, Republic of Korea
| | - Jungel Ryu
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826, Republic of Korea
| | - Sohyeon Park
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826, Republic of Korea
| | - Seungsoo Kim
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826, Republic of Korea
| | - Euijoon Yoon
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826, Republic of Korea
| | - Yongjo Park
- Advanced Institute of Convergence Technology, Seoul National University, Suwon 16229, Republic of Korea
| | - Ho Won Jang
- Department of Materials Science and Engineering, Research Institute of Advanced Materials, Seoul National University, Seoul 08826, Republic of Korea
- Advanced Institute of Convergence Technology, Seoul National University, Suwon 16229, Republic of Korea
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Choi D, Kim JH, Kwon DC, Shin CH, Ryu H, Yoon E, Lee HC. Crystalline silicon nanoparticle formation by tailored plasma irradiation: self-structurization, nucleation and growth acceleration, and size control. Nanoscale 2021; 13:10356-10364. [PMID: 34105564 DOI: 10.1039/d1nr00628b] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
Crystalline silicon nanoparticles at the nanometer scale have been attracting great interest in many different optoelectronic applications such as photovoltaic and light-emitting-diode devices. Formation, crystallization, and size control of silicon nanoparticles in nonharsh and nontoxic environments are highly required to achieve outstanding optoelectronic characteristics. The existing methods require high temperature, use of HF solution, and an additional process for the uniform redistribution of nanoparticles on the substrate and there are difficulties in controlling the size. Herein, we report a new self-assembly method that applies the controlled extremely low plasma ion energy near the sputtering threshold energy in rare gas environments as nonharsh and nontoxic environments. This method produces silicon nanoparticles by crystallization nucleation directly at the surface of the amorphous film via plasma surface interactions. It is evidently observed that the nucleation and growth rates of the crystalline silicon nanoparticles are promoted by the enhanced plasma ion energy. The crystalline silicon nanoparticle size is tailored to the nanometer scale by the plasma ion energy control.
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Affiliation(s)
- Daehan Choi
- Korea Research Institute of Standards and Science, Daejeon 34113, South Korea. and Department of Materials Science and Engineering, Seoul National University, Seoul 08826, South Korea
| | - Jung Hyung Kim
- Korea Research Institute of Standards and Science, Daejeon 34113, South Korea.
| | - Deuk Chul Kwon
- Korea Institute of Fusion Energy, Gunsan 54004, South Korea
| | - Chae Ho Shin
- Korea Research Institute of Standards and Science, Daejeon 34113, South Korea.
| | - Hyun Ryu
- Korea Research Institute of Standards and Science, Daejeon 34113, South Korea.
| | - Euijoon Yoon
- Department of Materials Science and Engineering, Seoul National University, Seoul 08826, South Korea
| | - Hyo-Chang Lee
- Korea Research Institute of Standards and Science, Daejeon 34113, South Korea. and Department of Electrical Engineering, Hanyang University, Seoul 04763, South Korea
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Lee GD, Robertson AW, Lee S, Lin YC, Oh JW, Park H, Joo YC, Yoon E, Suenaga K, Warner JH, Ewels CP. Direct observation and catalytic role of mediator atom in 2D materials. Sci Adv 2020; 6:eaba4942. [PMID: 32577521 PMCID: PMC7286694 DOI: 10.1126/sciadv.aba4942] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/09/2019] [Accepted: 04/15/2020] [Indexed: 06/11/2023]
Abstract
The structural transformations of graphene defects have been extensively researched through aberration-corrected transmission electron microscopy (AC-TEM) and theoretical calculations. For a long time, a core concept in understanding the structural evolution of graphene defects has been the Stone-Thrower-Wales (STW)-type bond rotation. In this study, we show that undercoordinated atoms induce bond formation and breaking, with much lower energy barriers than the STW-type bond rotation. We refer to them as mediator atoms due to their mediating role in the breaking and forming of bonds. Here, we report the direct observation of mediator atoms in graphene defect structures using AC-TEM and annular dark-field scanning TEM (ADF-STEM) and explain their catalytic role by tight-binding molecular dynamics (TBMD) simulations and image simulations based on density functional theory (DFT) calculations. The study of mediator atoms will pave a new way for understanding not only defect transformation but also the growth mechanisms in two-dimensional materials.
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Affiliation(s)
- Gun-Do Lee
- Department of Materials Science and Engineering, Seoul National University, Seoul, Republic of Korea
- Research Institute of Advanced Materials, Seoul National University, Seoul, Republic of Korea
| | - Alex W. Robertson
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK
| | - Sungwoo Lee
- Department of Materials Science and Engineering, Seoul National University, Seoul, Republic of Korea
| | - Yung-Chang Lin
- National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8565, Japan
| | - Jeong-Wook Oh
- Department of Chemistry, Seoul National University, Seoul, Republic of Korea
| | - Hwanyeol Park
- Memory Thin Film Technology Team, Giheung Hwaseong Complex, Samsung Electronics, 445-701, Republic of Korea
| | - Young-Chang Joo
- Department of Materials Science and Engineering, Seoul National University, Seoul, Republic of Korea
- Research Institute of Advanced Materials, Seoul National University, Seoul, Republic of Korea
| | - Euijoon Yoon
- Department of Materials Science and Engineering, Seoul National University, Seoul, Republic of Korea
- Research Institute of Advanced Materials, Seoul National University, Seoul, Republic of Korea
| | - Kazu Suenaga
- National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8565, Japan
| | - Jamie H. Warner
- Department of Mechanical Engineering, University of Texas at Austin, 204 Dean Keeton Street, Austin, TX 78712, USA
| | - Christopher P. Ewels
- Institut des Matériaux Jean Rouxel (IMN), Université de Nantes, CNRS UMR 6502, 2 Rue de la Houssinière, F-44322 Nantes, France
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Lee S, Kim J, Oh J, Ryu J, Hwang K, Hwang J, Kang S, Choi JH, Sim YC, Cho YH, Chung TH, Jeong T, Park Y, Yoon E. A discrete core-shell-like micro-light-emitting diode array grown on sapphire nano-membranes. Sci Rep 2020; 10:7506. [PMID: 32371935 PMCID: PMC7200800 DOI: 10.1038/s41598-020-64478-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2019] [Accepted: 04/10/2020] [Indexed: 11/25/2022] Open
Abstract
A discrete core-shell-like micro-light-emitting diode (micro-LED) array was grown on a 100 nm-thick sapphire nano-membrane array without harmful plasma etching for chip singulation. Due to proper design for the sapphire nano-membrane array, an array of multi-faceted micro-LEDs with size of 4 μm × 16 μm was grown. Threading dislocation density in the micro-LED formed on sapphire nano-membrane was reduced by 59.6% due to the sapphire nano-membranes, which serve as compliant substrates, compared to GaN formed on a planar substrate. Enhancements in internal quantum efficiency by 44% and 3.3 times higher photoluminescence intensity were also observed from it. Cathodoluminescence emission at 435 nm was measured from c-plane multiple quantum wells (MQWs), whereas negligible emissions were detected from semi-polar sidewall facets. A core-shell-like MQWs were formed on all facets, hopefully lowering concentration of non-radiative surface recombination centers and reducing leakage current paths. This study provides an attractive platform for micro-LEDs by using sapphire nano-membrane.
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Affiliation(s)
- Seungmin Lee
- Department of Materials Science and Engineering, Seoul National University, Seoul, 08826, Korea
| | - Jongmyeong Kim
- Department of Materials Science and Engineering, Seoul National University, Seoul, 08826, Korea
| | - Jehong Oh
- Department of Materials Science and Engineering, Seoul National University, Seoul, 08826, Korea
| | - Jungel Ryu
- Department of Materials Science and Engineering, Seoul National University, Seoul, 08826, Korea
| | - Kyungwook Hwang
- Samsung Advanced Institute of Technology, Suwon, 16678, Korea
| | - Junsik Hwang
- Samsung Advanced Institute of Technology, Suwon, 16678, Korea
| | - Sungjin Kang
- Samsung Advanced Institute of Technology, Suwon, 16678, Korea
| | - Jun Hee Choi
- Samsung Advanced Institute of Technology, Suwon, 16678, Korea
| | - Young Chul Sim
- Department of Physics and KI for the NanoCentury, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Korea
| | - Yong-Hoon Cho
- Department of Physics and KI for the NanoCentury, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Korea
| | - Tae Hoon Chung
- Micro-LED Research Center, Korea Photonics Technology Institute, Gwangju, 61007, Korea
| | - Tak Jeong
- Micro-LED Research Center, Korea Photonics Technology Institute, Gwangju, 61007, Korea
| | - Yongjo Park
- Department of Materials Science and Engineering, Seoul National University, Seoul, 08826, Korea
| | - Euijoon Yoon
- Department of Materials Science and Engineering, Seoul National University, Seoul, 08826, Korea. .,Research Institute of Advanced Materials, Seoul National University, Seoul, 08826, Korea. .,Inter-university Semiconductor Research Center, Seoul National University, Seoul, 08826, Korea.
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Yoon E, Beall D, Wilson G, Bishop R, Tally W, DePalma M. 4:12 PM Abstract No. 354 Viable allograft for intervertebral disc supplementation: provisional results of the Viable Allograft Supplemented Disc Regeneration Trial (VAST). J Vasc Interv Radiol 2020. [DOI: 10.1016/j.jvir.2019.12.412] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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Park H, Woo D, Lee JM, Park SJ, Lee S, Kim HJ, Yoon E, Lee GD. The influence of hydrogen concentration in amorphous carbon films on mechanical properties and fluorine penetration: a density functional theory and ab initio molecular dynamics study. RSC Adv 2020; 10:6822-6830. [PMID: 35493897 PMCID: PMC9049780 DOI: 10.1039/c9ra09328a] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2019] [Accepted: 01/30/2020] [Indexed: 11/21/2022] Open
Abstract
Amorphous carbon (a-C) films have attracted significant attention due to their reliable structures and superior mechanical, chemical and electronic properties, making them a strong candidate as an etch hard mask material for the fabrication of future integrated semiconductor devices. Density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations were performed to investigate the energetics, structure, and mechanical properties of the a-C films with an increasing sp3 content by adjusting the atomic density or hydrogen content. A drastic increase in the bulk modulus is observed by increasing the atomic density of the a-C films, which suggests that it would be difficult for the films hardened by high atomic density to relieve the stress of the individual layers within the overall stack in integrated semiconductor devices. However, the addition of hydrogen into the a-C films has little effect on increasing the bulk modulus even though the sp3 content increases. For the F blocking nature, the change in the sp3 content by both atomic density and H concentration makes the diffusion barrier against the F atom even higher and suppresses the F diffusion, indicating that the F atom would follow the diffusion path passing through the sp2 carbon and not the sp3 carbon due to the significantly high barrier. For the material design of a-C films with adequate doped characteristics, our results can provide a new straightforward strategy to tailor the a-C films with excellent mechanical and other novel physical and chemical properties.
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Affiliation(s)
- Hwanyeol Park
- Department of Materials Science and Engineering, Seoul National University Seoul 08826 Korea .,Memory Thin Film Technology Team, Giheung Hwaseong Complex, Samsung Electronics 445-701 South Korea
| | - Daekwang Woo
- Memory Thin Film Technology Team, Giheung Hwaseong Complex, Samsung Electronics 445-701 South Korea
| | - Jong Myeong Lee
- Memory Thin Film Technology Team, Giheung Hwaseong Complex, Samsung Electronics 445-701 South Korea
| | - Se Jun Park
- Memory Thin Film Technology Team, Giheung Hwaseong Complex, Samsung Electronics 445-701 South Korea
| | - Sungwoo Lee
- Department of Materials Science and Engineering, Seoul National University Seoul 08826 Korea
| | - Ho Jun Kim
- Department of Mechanical Engineering, Dong-A University Busan 49315 South Korea
| | - Euijoon Yoon
- Department of Materials Science and Engineering, Seoul National University Seoul 08826 Korea .,Research Institute of Advanced Materials, Inter-university Semiconductor Research Center, Seoul National University Seoul 08826 South Korea
| | - Gun-Do Lee
- Department of Materials Science and Engineering, Seoul National University Seoul 08826 Korea .,Research Institute of Advanced Materials, Inter-university Semiconductor Research Center, Seoul National University Seoul 08826 South Korea
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Park H, Han DH, Lim HT, Yoon E, Lee GD. Thermodynamic insights into interfacial interactions in TiN/amorphous Al2O3 heterostructures: ab initio molecular dynamics and first principles investigation. Inorg Chem Front 2020. [DOI: 10.1039/d0qi00839g] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The nature and the mechanism of the film interaction with the substrate at the film/substrate interface are still far from being fully understood.
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Affiliation(s)
- Hwanyeol Park
- Department of Materials Science and Engineering
- Seoul National University
- Seoul 151-744
- Korea
- Memory Thin Film Technology Team
| | - Dong-Hoon Han
- Memory Metal Technology Team
- Giheung Hwaseong Complex
- Samsung Electronics
- South Korea
| | - Hong Taek Lim
- Memory Metal Technology Team
- Giheung Hwaseong Complex
- Samsung Electronics
- South Korea
| | - Euijoon Yoon
- Department of Materials Science and Engineering
- Seoul National University
- Seoul 151-744
- Korea
- Research Institute of Advanced Materials and Inter-university Semiconductor Research Center
| | - Gun-Do Lee
- Department of Materials Science and Engineering
- Seoul National University
- Seoul 151-744
- Korea
- Research Institute of Advanced Materials and Inter-university Semiconductor Research Center
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Robertson AW, Lee GD, Lee S, Buntin P, Drexler M, Abdelhafiz AA, Yoon E, Warner JH, Alamgir FM. Atomic Structure and Dynamics of Epitaxial Platinum Bilayers on Graphene. ACS Nano 2019; 13:12162-12170. [PMID: 31553564 DOI: 10.1021/acsnano.9b06701] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Platinum atomic layers grown on graphene were investigated by atomic resolution transmission electron microscopy (TEM). These TEM images reveal the epitaxial relationship between the atomically thin platinum layers and graphene, with two optimal epitaxies observed. The energetics of these epitaxies influences the grain structure of the platinum film, facilitating grain growth via in-plane rotation and assimilation of neighbor grains, rather than grain coarsening from the movement of grain boundaries. This growth process was enabled due to the availability of several possible low-energy intermediate states for the rotating grains, the Pt-Gr epitaxies, which are minima in surface energy, and coincident site lattice grain boundaries, which are minima in grain boundary energy. Density functional theory calculations reveal a complex interplay of considerations for minimizing the platinum grain energy, with free platinum edges also having an effect on the relative energetics. We thus find that the platinum atomic layer grains undergo significant reorientation to minimize interface energy (via epitaxy), grain boundary energy (via low-energy orientations), and free edge energy. These results will be important for the design of two-dimensional graphene-supported platinum catalysts and obtaining large-area uniform platinum atomic layer films and also provide fundamental experimental insight into the growth of heteroepitaxial thin films.
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Affiliation(s)
- Alex W Robertson
- Department of Materials , University of Oxford , Parks Road , Oxford , OX1 3PH , United Kingdom
| | - Gun-Do Lee
- Department of Materials Science and Engineering , Seoul National University , Gwanak-gu , Seoul 08826 , South Korea
- Research Institute of Advanced Materials , Seoul National University , Gwanak-gu , Seoul 08826 , Republic of Korea
| | - Sungwoo Lee
- Department of Materials Science and Engineering , Seoul National University , Gwanak-gu , Seoul 08826 , South Korea
- Research Institute of Advanced Materials , Seoul National University , Gwanak-gu , Seoul 08826 , Republic of Korea
| | - Parker Buntin
- School of Materials Science and Engineering , Georgia Institute of Technology , Atlanta , Georgia 30332 , United States
| | - Matthew Drexler
- School of Materials Science and Engineering , Georgia Institute of Technology , Atlanta , Georgia 30332 , United States
| | - Ali A Abdelhafiz
- School of Materials Science and Engineering , Georgia Institute of Technology , Atlanta , Georgia 30332 , United States
| | - Euijoon Yoon
- Department of Materials Science and Engineering , Seoul National University , Gwanak-gu , Seoul 08826 , South Korea
- Research Institute of Advanced Materials , Seoul National University , Gwanak-gu , Seoul 08826 , Republic of Korea
| | - Jamie H Warner
- Department of Materials , University of Oxford , Parks Road , Oxford , OX1 3PH , United Kingdom
| | - Faisal M Alamgir
- School of Materials Science and Engineering , Georgia Institute of Technology , Atlanta , Georgia 30332 , United States
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12
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Timor-Tritsch IE, Foley CE, Brandon C, Yoon E, Ciaffarrano J, Monteagudo A, Mittal K, Boyd L. New sonographic marker of borderline ovarian tumor: microcystic pattern of papillae and solid components. Ultrasound Obstet Gynecol 2019; 54:395-402. [PMID: 30950132 DOI: 10.1002/uog.20283] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2018] [Revised: 01/02/2019] [Accepted: 01/24/2019] [Indexed: 06/09/2023]
Abstract
OBJECTIVE To describe and evaluate the utility of a new sonographic microcystic pattern, which is typical of borderline ovarian tumor (BOT) papillary projections, solid component(s) and/or septa, as a new ultrasound marker that is capable of distinguishing BOT from other adnexal masses, and to present/obtain histologic confirmation. METHODS In this retrospective study, we identified women with a histologic diagnosis of BOT following surgical resection who had undergone preoperative transvaginal ultrasound (TVS) examination. All images were reviewed for presence or absence of thin-walled, fluid-filled cluster(s) of 1-3-mm cystic formations, associated with solid component(s), papillary projections and/or septa. From the same cases, histopathologic slides of each BOT were examined for presence of any of these microcystic features which had been identified on TVS. To confirm that the microcystic TVS pattern is unique to BOTs, we also selected randomly from our ultrasound and surgical database 20 cases of epithelial ovarian cancer and 20 cases of benign cystadenoma, for review by the same pathologists. To confirm the novelty of our findings, we searched PubMed for literature published in the English language between 2010 and 2018 to determine whether the association between microcystic tissue pattern and BOT has been described previously. RESULTS Included in the final analysis were 62 patients (67 ovaries) with preoperative TVS and surgically confirmed BOT on pathologic examination. The mean patient age at surgery was 39.8 years. The mean BOT size at TVS was 60.7 mm. Of the 67 BOTs, 47 (70.1%) were serous, 15 (22.4%) were mucinous and five (7.5%) were seromucinous. We observed on TVS a microcystic pattern in the papillary projections, solid component(s) and/or septa in 60 (89.6%) of the 67 BOTs, including 46 (97.9%) of the 47 serous BOTs, 11 (73.3%) of the 15 mucinous BOTs and three (60.0%) of the five seromucinous BOTs. On microscopic evaluation, 60 (89.6%) of the 67 samples had characteristic 1-3-mm fluid-filled cysts similar to those seen on TVS. In seven cases there was a discrepancy between sonographic and histologic observation of a microcystic pattern. The 20 cystadenomas were mostly unilocular and/or multilocular and largely avascular. None of them or the 20 epithelial ovarian malignancies displayed microcystic characteristics, either on TVS or at histology. On review of 23 published articles in the English medical literature, containing 163 sonographic images of BOT, we found that, while all images contained it, there was no description of the microcystic tissue pattern. CONCLUSION We report herein a novel sonographic marker of BOT, a 'microcystic pattern' of BOT papillary projections, solid component(s) and/or septa. This was seen in the majority of both serous and mucinous BOT cases. Importantly, based on comparison of sonographic images and histopathology of benign entities and malignancies, the microcystic appearance seems to be unique to BOTs. No similar description has been published previously. Utilization of this new marker should help to identify BOT correctly, discriminating it from ovarian cancer and benign ovarian pathology, and should ensure appropriate clinical and surgical management. Copyright © 2019 ISUOG. Published by John Wiley & Sons Ltd.
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Affiliation(s)
- I E Timor-Tritsch
- New York University School of Medicine, Langone Health, Department of Obstetrics & Gynecology, Division of Obstetrical and Gynecologic Ultrasound, New York, NY, USA
| | - C E Foley
- New York University School of Medicine, Langone Health, Department of Obstetrics & Gynecology, Division of Obstetrical and Gynecologic Ultrasound, New York, NY, USA
| | - C Brandon
- New York University School of Medicine, Langone Health, Department of Obstetrics & Gynecology, Division of Obstetrical and Gynecologic Ultrasound, New York, NY, USA
| | - E Yoon
- New York University School of Medicine, Department of Pathology, Division of Surgical Pathology, New York, NY, USA
| | - J Ciaffarrano
- New York University School of Medicine, Department of Pathology, Division of Surgical Pathology, New York, NY, USA
| | - A Monteagudo
- Carnegie Imaging for Women, Icahn School of Medicine at Mount Sinai, New York, NY, USA
| | - K Mittal
- New York University School of Medicine, Department of Pathology, Division of Surgical Pathology, New York, NY, USA
| | - L Boyd
- New York University School of Medicine, Langone Health, Department of Obstetrics & Gynecology, Division of Gynecologic Oncology, New York, NY, USA
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13
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Lee JK, Lee GD, Lee S, Yoon E, Anderson HL, Briggs GAD, Warner JH. Atomic Scale Imaging of Reversible Ring Cyclization in Graphene Nanoconstrictions. ACS Nano 2019; 13:2379-2388. [PMID: 30673212 DOI: 10.1021/acsnano.8b09211] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We present an atomic level study of reversible cyclization processes in suspended nanoconstricted regions of graphene that form linear carbon chains (LCCs). Before the nanoconstricted region reaches a single linear carbon chain (SLCC), we observe that a double linear carbon chain (DLCC) structure often reverts back to a ribbon of sp2 hybridized oligoacene rings, in a process akin to the Bergman rearrangement. When the length of the DLCC system only consists of ∼5 atoms in each LCC, full recyclization occurs for all atoms present, but for longer DLCCs we find that only single sections of the chain are modified in their bonding hybridization and no full ring closure occurs along the entire DLCCs. This process is observed in real time using aberration-corrected transmission electron microscopy and simulated using density functional theory and tight binding molecular dynamics calculations. These results show that DLCCs are highly sensitive to the adsorption of local gas molecules or surface diffusion impurities and undergo structural modifications.
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Affiliation(s)
- Ja Kyung Lee
- Department of Materials , University of Oxford , Parks Road , Oxford OX1 3PH , United Kingdom
| | - Gun-Do Lee
- Department of Materials Science and Engineering , Seoul National University , Seoul 151-743 , Korea
| | - Sungwoo Lee
- Department of Materials Science and Engineering , Seoul National University , Seoul 151-743 , Korea
| | - Euijoon Yoon
- Department of Materials Science and Engineering , Seoul National University , Seoul 151-743 , Korea
| | - Harry L Anderson
- Department of Chemistry , University of Oxford , Mansfield Road , Oxford OX1 3TA , United Kingdom
| | - G Andrew D Briggs
- Department of Materials , University of Oxford , Parks Road , Oxford OX1 3PH , United Kingdom
| | - Jamie H Warner
- Department of Materials , University of Oxford , Parks Road , Oxford OX1 3PH , United Kingdom
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Jang J, Lee SY, Park H, Yoon S, Park GS, Lee GD, Park Y, Kim M, Yoon E. Solid-Phase Epitaxial Growth of an Alumina Layer Having a Stacking-Mismatched Domain Structure of the Intermediate γ-Phase. ACS Appl Mater Interfaces 2018; 10:41487-41496. [PMID: 30398854 DOI: 10.1021/acsami.8b13818] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Solid-phase epitaxy (SPE), a solid-state phase transition of materials from an amorphous to a crystalline phase, is a convenient crystal growing technique. In particular, SPE can be used to grow α-Al2O3 epitaxially with a novel structure that provides an effective substrate for improved performance of light-emitting diodes (LEDs). However, the inevitable two-step phase transformation through the γ-Al2O3 phase hinders the expected improved crystallinity of α-Al2O3, and thereby further enhancement of LED performance. Herein, we provide a fundamental understanding of the SPE growth mechanism from amorphous to metastable γ-Al2O3 using transmission electron microscopy (TEM) and density functional theory (DFT) calculations. The nanobeam precession electron diffraction technique enabled clear visualization of the double-positioning domain distribution in the SPE γ-Al2O3 film and emphasized the need for careful selection of the viewing directions for any investigation of double-positioning domains. Void and stacking fault defects further investigated by high-resolution scanning TEM (STEM) analyses revealed how double-positioning domains and other SPE growth behaviors directly influence the crystallinity of SPE films. Additionally, DFT calculations revealed the origins of SPE growth behavior. The double-positioning γ-Al2O3 domains randomly nucleate from the α-Al2O3 substrate regardless of the α-Al2O3 termination layer, but the large energy requirement for reversal of the γ-Al2O3 stacking sequence prevents it from switching the domain type during the crystal growth. We expect that this study will be useful to improve the crystallinity of SPE γ- and α-Al2O3 films.
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Affiliation(s)
- Jeonghwan Jang
- Department of Materials Science and Engineering , Seoul National University , Seoul 151-744 , Korea
| | - Seung-Yong Lee
- Research Institute of Advanced Materials , Seoul National University , Seoul 151-744 , Korea
| | - Hwanyeol Park
- Department of Materials Science and Engineering , Seoul National University , Seoul 151-744 , Korea
| | - Sangmoon Yoon
- Research Institute of Advanced Materials , Seoul National University , Seoul 151-744 , Korea
| | - Gyeong-Su Park
- Department of Materials Science and Engineering , Seoul National University , Seoul 151-744 , Korea
| | - Gun-Do Lee
- Department of Materials Science and Engineering , Seoul National University , Seoul 151-744 , Korea
- Research Institute of Advanced Materials , Seoul National University , Seoul 151-744 , Korea
| | - Yongjo Park
- Department of Materials Science and Engineering , Seoul National University , Seoul 151-744 , Korea
- Energy Semiconductor Research Center, Advanced Institutes of Convergence Technology , Seoul National University , Suwon 443-270 , Korea
| | - Miyoung Kim
- Department of Materials Science and Engineering , Seoul National University , Seoul 151-744 , Korea
- Research Institute of Advanced Materials , Seoul National University , Seoul 151-744 , Korea
| | - Euijoon Yoon
- Department of Materials Science and Engineering , Seoul National University , Seoul 151-744 , Korea
- Research Institute of Advanced Materials , Seoul National University , Seoul 151-744 , Korea
- Energy Semiconductor Research Center, Advanced Institutes of Convergence Technology , Seoul National University , Suwon 443-270 , Korea
- Inter-university Semiconductor Research Center , Seoul National University , Seoul 151-744 , Korea
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15
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Park H, Lee S, Kim HJ, Woo D, Lee JM, Yoon E, Lee GD. Overall reaction mechanism for a full atomic layer deposition cycle of W films on TiN surfaces: first-principles study. RSC Adv 2018; 8:39039-39046. [PMID: 35558318 PMCID: PMC9090620 DOI: 10.1039/c8ra07354f] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2018] [Accepted: 10/31/2018] [Indexed: 12/02/2022] Open
Abstract
We investigated the overall ALD reaction mechanism for W deposition on TiN surfaces based on DFT calculation as well as the detailed dissociative reactions of WF6. Our calculated results suggest that the overall reactions of the WF6 on the B-covered TiN surfaces are energetically much more favorable than the one on the TiN surfaces, which means that the high reactivity of WF6 with the B-covered TiN surface is attributed to the presence of B-covered surface made by B2H6 molecules. As a result, an effect of the B2H6 flow serves as a catalyst to decompose WF6 molecules. Two additional reaction processes right after WF6 bond dissociation, such as W substitution and BF3 desorption, were also explored to clearly understand the detailed reactions that can occur by WF6 flow. At the first additional reaction process, W atoms can be substituted into B site and covered on the TiN surfaces due to the stronger bonding nature of W with the TiN surface than B atoms. At the second additional reaction process, remaining atoms, such as B and F, can be easily desorbed as by-product, that is, BF3 because BF3 desorption is an energetically favorable reaction with a low activation energy. Furthermore, we also investigated the effect of H2 post-treatment on W-covered TiN surface in order to remove residual F adatoms, which are known to cause severe problems that extremely degrade the characteristics of memory devices. It was found that both H2 dissociative reaction and HF desorption can occur sufficiently well under somewhat high temperature and H2 ambience, which is confirmed by our DFT results and previously reported experimental results. These results imply that the understanding of the role of gas molecules used for W deposition gives us insight into improving the W ALD process for future memory devices. We investigated the overall ALD reaction mechanism for W deposition on TiN surfaces based on DFT calculation as well as the detailed dissociative reactions of WF6.![]()
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Affiliation(s)
- Hwanyeol Park
- Department of Materials Science and Engineering, Seoul National University Seoul 08826 Korea
| | - Sungwoo Lee
- Department of Materials Science and Engineering, Seoul National University Seoul 08826 Korea
| | - Ho Jun Kim
- Department of Mechanical Engineering, Dong-A University Busan 49315 South Korea
| | - Daekwang Woo
- Memory Thin Film Technology Team, Giheung Hwaseong Complex, Samsung Electronics 445-701 South Korea
| | - Jong Myeong Lee
- Memory Thin Film Technology Team, Giheung Hwaseong Complex, Samsung Electronics 445-701 South Korea
| | - Euijoon Yoon
- Department of Materials Science and Engineering, Seoul National University Seoul 08826 Korea .,Research Institute of Advanced Materials and Inter-University Semiconductor Research Center, Seoul National University Seoul 08826 South Korea
| | - Gun-Do Lee
- Department of Materials Science and Engineering, Seoul National University Seoul 08826 Korea .,Research Institute of Advanced Materials and Inter-University Semiconductor Research Center, Seoul National University Seoul 08826 South Korea
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Yoon E, Coburn C, Laken M. A VALIDATION STUDY OF THE CENTER FOR EPIDEMIOLOGIC STUDIES DEPRESSION WITH OLDER AFRICAN AMERICANS IN THE SOUTH. Innov Aging 2018. [DOI: 10.1093/geroni/igy023.1997] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
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Kim SY, Kim JH, Lee S, Kwak J, Jo Y, Yoon E, Lee GD, Lee Z, Kwon SY. The impact of substrate surface defects on the properties of two-dimensional van der Waals heterostructures. Nanoscale 2018; 10:19212-19219. [PMID: 30303224 DOI: 10.1039/c8nr03777a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The recent emergence of vertically stacked van der Waals (vdW) heterostructures provides new opportunities for these materials to be employed in a wide range of novel applications. Understanding the interlayer coupling in the stacking geometries of the heterostructures and its effect on the resultant material properties is particularly important for obtaining materials with desirable properties. Here, we report that the atomic bonding between stacked layers and thereby the interlayer properties of the vdW heterostructures can be well tuned by the substrate surface defects using WS2 flakes directly grown on graphene. We show that the defects of graphene have no significant effect on the crystal structure or the quality of the grown WS2 flakes; however, they have a strong influence on the interlayer interactions between stacked layers, thus affecting the layer deformability, thermal stability, and physical and electrical properties. Our experimental and computational investigations also reveal that WS2 flakes grown on graphene defects form covalent bonds with the underlying graphene via W atomic bridges (i.e., formation of larger overlapping hybrid orbitals), enabling these flakes to exhibit different intrinsic properties, such as higher conductivity and improved contact characteristics than heterostructures that have vdW interactions with graphene. This result emphasizes the importance of understanding the interlayer coupling in the stacking geometries and its correlation effect for designing desirable properties.
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Affiliation(s)
- Se-Yang Kim
- School of Materials Science and Engineering, Low-Dimensional Carbon Materials Center, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Republic of Korea.
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18
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Kwak J, Jo Y, Song S, Kim JH, Kim SY, Lee JU, Lee S, Park J, Kim K, Lee GD, Yoo JW, Kim SY, Kong YM, Lee GH, Lee WG, Park J, Xu X, Cheong H, Yoon E, Lee Z, Kwon SY. Single-Crystalline Nanobelts Composed of Transition Metal Ditellurides. Adv Mater 2018; 30:e1707260. [PMID: 29882243 DOI: 10.1002/adma.201707260] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/13/2017] [Revised: 04/23/2018] [Indexed: 06/08/2023]
Abstract
Following the celebrated discovery of graphene, considerable attention has been directed toward the rich spectrum of properties offered by van der Waals crystals. However, studies have been largely limited to their 2D properties due to lack of 1D structures. Here, the growth of high-yield, single-crystalline 1D nanobelts composed of transition metal ditellurides at low temperatures (T ≤ 500 °C) and in short reaction times (t ≤ 10 min) via the use of tellurium-rich eutectic metal alloys is reported. The synthesized semimetallic 1D products are highly pure, stoichiometric, structurally uniform, and free of defects, resulting in high electrical performances. Furthermore, complete compositional tuning of the ternary ditelluride nanobelts is achieved with suppressed phase separation, applicable to the creation of unprecedented low-dimensional materials/devices. This approach may inspire new growth/fabrication strategies of 1D layered nanostructures, which may offer unique properties that are not available in other materials.
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Affiliation(s)
- Jinsung Kwak
- School of Materials Science and Engineering & Low-Dimensional Carbon Material Center, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Republic of Korea
| | - Yongsu Jo
- School of Materials Science and Engineering & Low-Dimensional Carbon Material Center, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Republic of Korea
| | - Seunguk Song
- School of Materials Science and Engineering & Low-Dimensional Carbon Material Center, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Republic of Korea
| | - Jung Hwa Kim
- School of Materials Science and Engineering & Low-Dimensional Carbon Material Center, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Republic of Korea
| | - Se-Yang Kim
- School of Materials Science and Engineering & Low-Dimensional Carbon Material Center, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Republic of Korea
| | - Jae-Ung Lee
- Department of Physics, Sogang University, Seoul, 04107, Republic of Korea
| | - Sungwoo Lee
- Department of Materials Science and Engineering & Research Institute of Advanced Materials, Seoul National University, Seoul, 08826, Republic of Korea
| | - Jungmin Park
- School of Materials Science and Engineering & Low-Dimensional Carbon Material Center, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Republic of Korea
| | - Kangwon Kim
- Department of Physics, Sogang University, Seoul, 04107, Republic of Korea
| | - Gun-Do Lee
- Department of Materials Science and Engineering & Research Institute of Advanced Materials, Seoul National University, Seoul, 08826, Republic of Korea
| | - Jung-Woo Yoo
- School of Materials Science and Engineering & Low-Dimensional Carbon Material Center, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Republic of Korea
| | - Sung Youb Kim
- School of Mechanical, Aerospace, and Nuclear Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Republic of Korea
| | - Young-Min Kong
- School of Materials Science and Engineering, University of Ulsan, Ulsan, 44610, Republic of Korea
| | - Gwan-Hyoung Lee
- Department of Materials Science and Engineering, Yonsei University, Seoul, 03772, Republic of Korea
| | - Wan-Gyu Lee
- Global Nanotechnology Development Team, National NanoFab Center, Daejeon, 34141, Republic of Korea
| | - Jucheol Park
- Gumi Electronics & Information Technology Research Institute, Gumi, 39171, Republic of Korea
| | - Xiaodong Xu
- Department of Physics & Department of Materials Science and Engineering, University of Washington, Seattle, WA, 98105, USA
| | - Hyeonsik Cheong
- Department of Physics, Sogang University, Seoul, 04107, Republic of Korea
| | - Euijoon Yoon
- Department of Materials Science and Engineering & Research Institute of Advanced Materials, Seoul National University, Seoul, 08826, Republic of Korea
| | - Zonghoon Lee
- School of Materials Science and Engineering & Low-Dimensional Carbon Material Center, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Republic of Korea
| | - Soon-Yong Kwon
- School of Materials Science and Engineering & Low-Dimensional Carbon Material Center, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 44919, Republic of Korea
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Park H, Lee S, Kim HJ, Woo D, Park SJ, Kim K, Yoon E, Lee GD. Effects of H 2 and N 2 treatment for B 2H 6 dosing process on TiN surfaces during atomic layer deposition: an ab initio study. RSC Adv 2018; 8:21164-21173. [PMID: 35539938 PMCID: PMC9080878 DOI: 10.1039/c8ra02622j] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2018] [Accepted: 05/27/2018] [Indexed: 11/21/2022] Open
Abstract
For the development of the future ultrahigh-scale integrated memory devices, a uniform tungsten (W) gate deposition process with good conformal film is essential for improving the conductivity of the W gate, resulting in the enhancement of device performance. As the memory devices are further scaled down, uniform W deposition becomes more difficult because of the experimental limitations of the sub-nanometer scale deposition even with atomic layer deposition (ALD) W processes. Even though it is known that the B2H6 dosing process plays a key role in the deposition of the ALD W layer with low resistivity and in the removal of residual fluorine (F) atoms, the roles of H2 and N2 treatments used in the ALD W process have not yet been reported. To understand the detailed ALD W process, we have investigated the effects of H2 and N2 treatment on TiN surfaces for the B2H6 dosing process using first-principles density functional theory (DFT) calculations. In our DFT calculated results, H2 treatment on the TiN surfaces causes the surfaces to become H-covered TiN surfaces, which results in lowering the reactivity of the B2H6 precursor since the overall reactions of the B2H6 on the H-covered TiN surfaces are energetically less favorable than the TiN surfaces. As a result, an effect of the H2 treatment is to decrease the reactivity of the B2H6 molecule on the TiN surface. However, N2 treatment on the Ti-terminated TiN (111) surface is more likely to make the TiN surface become an N-terminated TiN (111) surface, which results in making a lot of N-terminated TiN (111) surfaces, having a very reactive nature for B2H6 bond dissociation. As a result, the effect of N2 treatment serves as a catalyst to decompose B2H6. From the deep understanding of the effect of H2 and N2 during the B2H6 dosing process, the use of proper gas treatment is required for the improvement of the W nucleation layers. Our results showed the effects of H2 and N2 treatment on TiN surfaces, using density functional theory calculations. These imply that the understanding of gas treatment gives us insight into improving the W ALD process for future memory devices.![]()
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Affiliation(s)
- Hwanyeol Park
- Department of Materials Science and Engineering, Seoul National University Seoul 08826 Korea
| | - Sungwoo Lee
- Department of Materials Science and Engineering, Seoul National University Seoul 08826 Korea
| | - Ho Jun Kim
- Department of Mechanical Engineering, Dong-A University Busan 49315 South Korea
| | - Daekwang Woo
- Memory Thin Film Technology Team, Giheung Hwaseong Complex, Samsung Electronics 445-701 South Korea
| | - Se Jun Park
- Memory Thin Film Technology Team, Giheung Hwaseong Complex, Samsung Electronics 445-701 South Korea
| | - Kangsoo Kim
- Memory Thin Film Technology Team, Giheung Hwaseong Complex, Samsung Electronics 445-701 South Korea
| | - Euijoon Yoon
- Department of Materials Science and Engineering, Seoul National University Seoul 08826 Korea .,Research Institute of Advanced Materials and Inter-University Semiconductor Research Center, Seoul National University Seoul 08826 South Korea
| | - Gun-Do Lee
- Department of Materials Science and Engineering, Seoul National University Seoul 08826 Korea .,Research Institute of Advanced Materials and Inter-University Semiconductor Research Center, Seoul National University Seoul 08826 South Korea
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Moon YJ, Kim JH, Cho JW, Na JY, Lee TI, Lee D, Bae D, Yoon E, Kim SK. Microstructured void gratings for outcoupling deep-trap guided modes. Opt Express 2018; 26:A450-A461. [PMID: 29801265 DOI: 10.1364/oe.26.00a450] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2018] [Accepted: 03/29/2018] [Indexed: 06/08/2023]
Abstract
Breaking the total internal reflection far above a critical angle (i.e., outcoupling deep-trap guided modes) can dramatically improve existing light-emitting devices. Here, we report a deep-trap guided modes outcoupler using densely arranged microstructured hollow cavities. Measurements of the leaky mode dispersions of hollow-cavity gratings accurately quantify the wavelength-dependent outcoupling strength above a critical angle, which is progressively improved over the full visible spectrum by increasing the packing density. Comparing hollow- and filled-cavity gratings, which have identical morphologies except for their inner materials (void vs. solid sapphire), reveals the effectiveness of using the hollow-cavity grating to outcouple deep-trap guided modes, which results from its enhanced transmittance at near-horizontal incidence. Scattering analysis shows that the outcoupling characteristics of a cavity array are dictated by the forward scattering characteristics of their individual cavities, suggesting the importance of a rationally designed single cavity. We believe that a hollow-cavity array tailored for different structures and spectra will lead to a technological breakthrough in any type of light-emitting device.
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Kang SG, Moon D, Jang J, Kim JY, Suh JY, Yoon E, Han HN, Choi IS. Flaw-Containing Alumina Hollow Nanostructures Have Ultrahigh Fracture Strength To Be Incorporated into High-Efficiency GaN Light-Emitting Diodes. Nano Lett 2018; 18:1323-1330. [PMID: 29361232 DOI: 10.1021/acs.nanolett.7b05009] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
In the present study, we found that α-alumina hollow nanoshell structure can exhibit an ultrahigh fracture strength even though it contains a significant number of nanopores. By systematically performing in situ mechanical testing and finite element simulations, we could measure that the fracture strength of an α-alumina hollow nanoshell structure is about four times higher than that of the conventional bulk size α-alumina. The high fracture strength of the α-alumina hollow nanoshell structure can be explained in terms of conventional fracture mechanics, in that the position and size of the nanopores are the most critical factors determining the fracture strength, even at the nanoscales. More importantly, by deriving a fundamental understanding, we would be able to provide guidelines for the design of reliable ceramic nanostructures for advanced GaN light-emitting diodes (LEDs). To that end, we demonstrated how our ultrastrong α-alumina hollow nanoshell structures could be successfully incorporated into GaN LEDs, thereby greatly improving the luminous efficiency and output power of the LEDs by 2.2 times higher than that of conventional GaN LEDs.
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Affiliation(s)
- Sung-Gyu Kang
- Department of Materials Science and Engineering, RIAM, Seoul National University , Seoul 08826, Republic of Korea
- High Temperature Energy Materials Research Center, Korea Institute of Science and Technology , Seoul 02792, Republic of Korea
| | - Daeyoung Moon
- Department of Materials Science and Engineering, RIAM, Seoul National University , Seoul 08826, Republic of Korea
| | - Jeonghwan Jang
- Department of Materials Science and Engineering, RIAM, Seoul National University , Seoul 08826, Republic of Korea
| | - Ju-Young Kim
- School of Materials Science and Engineering, Ulsan National Institute of Science and Technology , Ulsan 44919, Republic of Korea
| | - Jin-Yoo Suh
- High Temperature Energy Materials Research Center, Korea Institute of Science and Technology , Seoul 02792, Republic of Korea
| | - Euijoon Yoon
- Department of Materials Science and Engineering, RIAM, Seoul National University , Seoul 08826, Republic of Korea
| | - Heung Nam Han
- Department of Materials Science and Engineering, RIAM, Seoul National University , Seoul 08826, Republic of Korea
| | - In-Suk Choi
- High Temperature Energy Materials Research Center, Korea Institute of Science and Technology , Seoul 02792, Republic of Korea
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22
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Nam DH, Lee S, Lee YJ, Jo JH, Yoon E, Yi KW, Lee GD, Joo YC. Gaseous Nanocarving-Mediated Carbon Framework with Spontaneous Metal Assembly for Structure-Tunable Metal/Carbon Nanofibers. Adv Mater 2017; 29:1702958. [PMID: 28804961 DOI: 10.1002/adma.201702958] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/26/2017] [Revised: 07/16/2017] [Indexed: 06/07/2023]
Abstract
Vapor phase carbon (C)-reduction-based syntheses of C nanotubes and graphene, which are highly functional solid C nanomaterials, have received extensive attention in the field of materials science. This study suggests a revolutionary method for precisely controlling the C structures by oxidizing solid C nanomaterials into gaseous products in the opposite manner of the conventional approach. This gaseous nanocarving enables the modulation of inherent metal assembly in metal/C hybrid nanomaterials because of the promoted C oxidation at the metal/C interface, which produces inner pores inside C nanomaterials. This phenomenon is revealed by investigating the aspects of structure formation with selective C oxidation in the metal/C nanofibers, and density functional theory calculation. Interestingly, the tendency of C oxidation and calculated oxygen binding energy at the metal surface plane is coincident with the order Co > Ni > Cu > Pt. The customizable control of the structural factors of metal/C nanomaterials through thermodynamic-calculation-derived processing parameters is reported for the first time in this work. This approach can open a new class of gas-solid reaction-based synthetic routes that dramatically broaden the structure-design range of metal/C hybrid nanomaterials. It represents an advancement toward overcoming the limitations of intrinsic activities in various applications.
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Affiliation(s)
- Dae-Hyun Nam
- Department of Materials Science and Engineering, Seoul National University, Seoul, 151-742, Republic of Korea
| | - Sungwoo Lee
- Department of Materials Science and Engineering, Seoul National University, Seoul, 151-742, Republic of Korea
| | - Young-Joo Lee
- Department of Materials Science and Engineering, Seoul National University, Seoul, 151-742, Republic of Korea
| | - Jun-Hyun Jo
- Department of Materials Science and Engineering, Seoul National University, Seoul, 151-742, Republic of Korea
| | - Euijoon Yoon
- Department of Materials Science and Engineering, Seoul National University, Seoul, 151-742, Republic of Korea
- Research Institute of Advanced Materials (RIAM), Seoul National University, Seoul, 151-742, Republic of Korea
| | - Kyung-Woo Yi
- Department of Materials Science and Engineering, Seoul National University, Seoul, 151-742, Republic of Korea
- Research Institute of Advanced Materials (RIAM), Seoul National University, Seoul, 151-742, Republic of Korea
| | - Gun-Do Lee
- Department of Materials Science and Engineering, Seoul National University, Seoul, 151-742, Republic of Korea
- Research Institute of Advanced Materials (RIAM), Seoul National University, Seoul, 151-742, Republic of Korea
| | - Young-Chang Joo
- Department of Materials Science and Engineering, Seoul National University, Seoul, 151-742, Republic of Korea
- Research Institute of Advanced Materials (RIAM), Seoul National University, Seoul, 151-742, Republic of Korea
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23
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Abstract
The special properties of graphene can be largely influenced by point defects in the lattice. However, TEM studies of topological defects in few-layered graphene have rarely been reported. In this work, the two simplest forms of point defects monovacancy and divacancy in twisted bilayer graphene are characterized using aberration-corrected transmission electron microscopy (AC-TEM) at 80 kV. A convenient approach by using a negative mask in the fast Fourier transform (FFT) has been applied to separate the image signal of the two graphene layers. In the study combined with density functional theory (DFT) calculations and tight-binding molecular dynamics simulations, the analysis of the defect structure and movement shows the stability and migration behavior of both defects. DFT calculations indicate that the migration of monovacancy in bilayer graphene needs to overcome a higher energy barrier.
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Affiliation(s)
- Chuncheng Gong
- Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, UK.
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24
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Kampasi K, Seymour J, Stark E, Buzsaki G, Wise KD, Yoon E. Efficient assembly of multi-color fiberless optoelectrodes with on-board light sources for neural stimulation and recording. Annu Int Conf IEEE Eng Med Biol Soc 2017; 2016:4479-4482. [PMID: 28269273 DOI: 10.1109/embc.2016.7591722] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Fiberless optoelectrodes are an emerging tool to enable brain circuit mapping by providing precise optical modulation and electrical monitoring of many neurons. While optoelectrodes having an on-board light source offer compact and optically efficient device solutions, many of them fail to provide robust thermal and electrical design to fully exploit the recording capabilities of the device. In this work, we present a novel fiberless multicolor optoelectrode solution, which meets the optical and thermal design requirements of an in vivo neural optoelectrode and offers potential for low-noise neural recording. The total optical loss measured for 405 nm and 635 nm wavelengths through the waveguide is 11.7±1.1 dB and 9.9±0.7 dB, corresponding to respective irradiances of 1928 mW/mm2 and 2905 mW/mm2 at the waveguide tip from 6 mW laser diode chips. The efficient thermal packaging enables continuous device operation for up to 190 seconds at 10% duty cycle. We validated the fully packaged device in the intact brain of anesthetized mice co-expressing Channelrhodopsin-2 and Archaerhodopsin in the hippocampal CA1 region and achieved activation and silencing of the same neurons. We discuss improvements made to reduce the stimulation artifact induced by applying currents to the laser diode chips.
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25
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Lee S, Kim D, Robertson AW, Yoon E, Hong S, Ihm J, Yu J, Warner JH, Lee GD. Graphene as a flexible template for controlling magnetic interactions between metal atoms. J Phys Condens Matter 2017; 29:085001. [PMID: 28081016 DOI: 10.1088/1361-648x/aa5167] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Metal-doped graphene produces magnetic moments that have potential application in spintronics. Here we use density function theory computational methods to show how the magnetic interaction between metal atoms doped in graphene can be controlled by the degree of flexure in a graphene membrane. Bending graphene by flexing causes the distance between two substitutional Fe atoms covalently bonded in graphene to gradually increase and these results in the magnetic moment disappearing at a critical strain value. At the critical strain, a carbon atom can enter between the two Fe atoms and blocks the interaction between relevant orbitals of Fe atoms to quench the magnetic moment. The control of interactions between doped atoms by exploiting the mechanical flexibility of graphene is a unique approach to manipulating the magnetic properties and opens up new opportunities for mechanical-magnetic 2D device systems.
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Affiliation(s)
- Sungwoo Lee
- Department of Materials Science and Engineering, Seoul National University, Seoul 08826, Korea
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26
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Kleer CG, Martin EE, Anwar T, Arellano-Garcia C, Lama A, Medhora N, Chen YC, Yoon E, Ge C, Franceschi R, Gonzalez ME. Abstract P4-03-03: Microenvironment induced DDR2 mediates stromal-cancer interactions and metastasis growth in breast cancer. Cancer Res 2017. [DOI: 10.1158/1538-7445.sabcs16-p4-03-03] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Abstract
This abstract was not presented at the symposium.
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Affiliation(s)
- CG Kleer
- University of Michigan, Ann Arbor, MI
| | - EE Martin
- University of Michigan, Ann Arbor, MI
| | - T Anwar
- University of Michigan, Ann Arbor, MI
| | | | - A Lama
- University of Michigan, Ann Arbor, MI
| | - N Medhora
- University of Michigan, Ann Arbor, MI
| | - Y-C Chen
- University of Michigan, Ann Arbor, MI
| | - E Yoon
- University of Michigan, Ann Arbor, MI
| | - C Ge
- University of Michigan, Ann Arbor, MI
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27
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Abstract
In the fabrication process of memory devices, a void-free tungsten (W) gate process with good conformability is very important for improving the conductivity of the W gate, leading to enhancement of device performance.
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Affiliation(s)
- Hwanyeol Park
- Department of Materials Science and Engineering
- Seoul National University
- Seoul 08826
- Korea
| | - Sungwoo Lee
- Department of Materials Science and Engineering
- Seoul National University
- Seoul 08826
- Korea
| | - Ho Jun Kim
- Memory Thin Film Technology Team
- Samsung Electronics
- Hwaseong-si 445-701
- South Korea
| | - Euijoon Yoon
- Department of Materials Science and Engineering
- Seoul National University
- Seoul 08826
- Korea
- Research Institute of Advanced Materials
| | - Gun-Do Lee
- Department of Materials Science and Engineering
- Seoul National University
- Seoul 08826
- Korea
- Research Institute of Advanced Materials
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28
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Robertson AW, Lin YC, Wang S, Sawada H, Allen CS, Chen Q, Lee S, Lee GD, Lee J, Han S, Yoon E, Kirkland AI, Kim H, Suenaga K, Warner JH. Atomic Structure and Spectroscopy of Single Metal (Cr, V) Substitutional Dopants in Monolayer MoS 2. ACS Nano 2016; 10:10227-10236. [PMID: 27934090 DOI: 10.1021/acsnano.6b05674] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Dopants in two-dimensional dichalcogenides have a significant role in affecting electronic, mechanical, and interfacial properties. Controllable doping is desired for the intentional modification of such properties to enhance performance; however, unwanted defects and impurity dopants also have a detrimental impact, as often found for chemical vapor deposition (CVD) grown films. The reliable identification, and subsequent characterization, of dopants is therefore of significant importance. Here, we show that Cr and V impurity atoms are found in CVD grown MoS2 monolayer 2D crystals as single atom substitutional dopants in place of Mo. We attribute these impurities to trace elements present in the MoO3 CVD precursor. Simultaneous annular dark field scanning transmission electron microscopy (ADF-STEM) and electron energy loss spectroscopy (EELS) is used to map the location of metal atom substitutions of Cr and V in MoS2 monolayers with single atom precision. The Cr and V are stable under electron irradiation at 60 to 80 kV, when incorporated into line defects, and when heated to elevated temperatures. The combined ADF-STEM and EELS differentiates these Cr and V dopants from other similar contrast defect structures, such as 2S self-interstitials at the Mo site, preventing misidentification. Density functional theory calculations reveal that the presence of Cr or V causes changes to the density of states, indicating doping of the MoS2 material. These transferred impurities could help explain the presence of trapped charges in CVD prepared MoS2.
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Affiliation(s)
- Alex W Robertson
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
| | - Yung-Chang Lin
- Nanotube Research Center, National Institute of Advanced Industrial Science and Technology (AIST) , AIST Central 5, Tsukuba 305-8564, Japan
| | - Shanshan Wang
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
| | - Hidetaka Sawada
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
- JEOL Limited, 3-1-2 Musashino, Akishima, Tokyo 196-8558, Japan
- Electron Physical Sciences Imaging Center, Diamond Light Source Limited, Didcot, Oxfordshire OX11 0DE, United Kingdom
| | - Christopher S Allen
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
- Electron Physical Sciences Imaging Center, Diamond Light Source Limited, Didcot, Oxfordshire OX11 0DE, United Kingdom
| | - Qu Chen
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
| | - Sungwoo Lee
- Department of Materials Science and Engineering, Seoul National University , Seoul 151-742, Korea
| | - Gun-Do Lee
- Department of Materials Science and Engineering, Seoul National University , Seoul 151-742, Korea
| | - Joohee Lee
- Department of Materials Science and Engineering, Seoul National University , Seoul 151-742, Korea
| | - Seungwu Han
- Department of Materials Science and Engineering, Seoul National University , Seoul 151-742, Korea
| | - Euijoon Yoon
- Department of Materials Science and Engineering, Seoul National University , Seoul 151-742, Korea
| | - Angus I Kirkland
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
- Electron Physical Sciences Imaging Center, Diamond Light Source Limited, Didcot, Oxfordshire OX11 0DE, United Kingdom
| | - Heeyeon Kim
- Convergence Materials Laboratory, Korea Institute of Energy Research , 152 Gajeong-ro, Yuseong-gu, Daejeon 305-343, Korea
| | - Kazu Suenaga
- Nanotube Research Center, National Institute of Advanced Industrial Science and Technology (AIST) , AIST Central 5, Tsukuba 305-8564, Japan
| | - Jamie H Warner
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
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29
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Gong C, He K, Lee GD, Chen Q, Robertson AW, Yoon E, Hong S, Warner JH. In Situ Atomic Level Dynamics of Heterogeneous Nucleation and Growth of Graphene from Inorganic Nanoparticle Seeds. ACS Nano 2016; 10:9397-9410. [PMID: 27643716 DOI: 10.1021/acsnano.6b04356] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
An in situ heating holder inside an aberration-corrected transmission electron microscope (AC-TEM) is used to investigate the real-time atomic level dynamics associated with heterogeneous nucleation and growth of graphene from Au nanoparticle seeds. Heating monolayer graphene to an elevated temperature of 800 °C removes the majority of amorphous carbon adsorbates and leaves a clean surface. The aggregation of Au impurity atoms into nanoparticle clusters that are bound to the surface of monolayer graphene causes nucleation of secondary graphene layers from carbon feedstock present within the microscope chamber. This enables the in situ study of heterogeneous nucleation and growth of graphene at the atomic level. We show that the growth mechanism consists of alternating C cluster attachment and indentation filling to maintain a uniform growth front of lowest energy. Back-folding of the graphene growth front is observed, followed by a process that involves flipping back and attaching to the surrounding region. We show how the highly polycrystalline graphene seed evolves with time into a higher order crystalline structure using a combination of AC-TEM and tight-binding molecular dynamics (TBMD) simulations. This helps understand the detailed lowest-energy step-by-step pathways associated with grain boundaries (GB) migration and crystallization processes. We find the motion of the GB is discontinuous and mediated by both bond rotation and atom evaporation, supported by density functional theory calculations and TBMD. These results provide insights into the formation of crystalline seed domains that are generated during bottom-up graphene synthesis.
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Affiliation(s)
- Chuncheng Gong
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
| | - Kuang He
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
| | - Gun-Do Lee
- Department of Materials Science and Engineering, Seoul National University , Seoul 151-742, Korea
| | - Qu Chen
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
| | - Alex W Robertson
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
| | - Euijoon Yoon
- Department of Materials Science and Engineering, Seoul National University , Seoul 151-742, Korea
| | - Suklyun Hong
- Department of Physics and Graphene Research Institute, Sejong University , Seoul 143-747, Korea
| | - Jamie H Warner
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
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30
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Abstract
We study the detailed bond reconstructions that occur in S vacancies within monolayer MoS2 using a combination of aberration-corrected transmission electron microscopy, density functional theory (DFT), and multislice image simulations. Removal of a single S atom causes little perturbation to the surrounding MoS2 lattice, whereas the loss of two S atoms from the same atomic column causes a measurable local contraction. Aggregation of S vacancies into linear line defects along the zigzag direction results in larger lattice compression that is more pronounced as the length of the line defect increases. For the case of two rows of S line vacancies, we find two different types of S atom reconstructions with different amounts of lattice compression. Increasing the width of line defects leads to nanoscale regions of reconstructed MoS2 that are shown by DFT to behave as metallic channels. These results provide important insights into how defect structures could be used for creating metallic tracks within semiconducting monolayer MoS2 films for future applications in electronics and optoelectronics.
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Affiliation(s)
- Shanshan Wang
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
| | - Gun-Do Lee
- Department of Materials Science and Engineering, Seoul National University , 151-742 Seoul, South Korea
| | - Sungwoo Lee
- Department of Materials Science and Engineering, Seoul National University , 151-742 Seoul, South Korea
| | - Euijoon Yoon
- Department of Materials Science and Engineering, Seoul National University , 151-742 Seoul, South Korea
| | - Jamie H Warner
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
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31
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Moon YJ, Moon D, Jang J, Na JY, Song JH, Seo MK, Kim S, Bae D, Park EH, Park Y, Kim SK, Yoon E. Microstructured Air Cavities as High-Index Contrast Substrates with Strong Diffraction for Light-Emitting Diodes. Nano Lett 2016; 16:3301-3308. [PMID: 27045458 DOI: 10.1021/acs.nanolett.6b00892] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Two-dimensional high-index-contrast dielectric gratings exhibit unconventional transmission and reflection due to their morphologies. For light-emitting devices, these characteristics help guided modes defeat total internal reflections, thereby enhancing the outcoupling efficiency into an ambient medium. However, the outcoupling ability is typically impeded by the limited index contrast given by pattern media. Here, we report strong-diffraction, high-index-contrast cavity engineered substrates (CESs) in which hexagonally arranged hemispherical air cavities are covered with a 80 nm thick crystallized alumina shell. Wavelength-resolved diffraction measurements and Fourier analysis on GaN-grown CESs reveal that the high-index-contrast air/alumina core/shell patterns lead to dramatic excitation of the low-order diffraction modes. Large-area (1075 × 750 μm(2)) blue-emitting InGaN/GaN light-emitting diodes (LEDs) fabricated on a 3 μm pitch CES exhibit ∼39% enhancement in the optical power compared to state-of-the-art, patterned-sapphire-substrate LEDs, while preserving all of the electrical metrics that are relevant to LED devices. Full-vectorial simulations quantitatively demonstrate the enhanced optical power of CES LEDs and show a progressive increase in the extraction efficiency as the air cavity volume is expanded. This trend in light extraction is observed for both lateral- and flip-chip-geometry LEDs. Measurements of far-field profiles indicate a substantial beaming effect for CES LEDs, despite their few-micron-pitch pattern. Near-to-far-field transformation simulations and polarization analysis demonstrate that the improved extraction efficiency of CES LEDs is ascribed to the increase in emissions via the top escape route and to the extraction of transverse-magnetic polarized light.
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Affiliation(s)
- Yoon-Jong Moon
- Department of Applied Physics, Kyung Hee University , Gyeonggi-do 17104, Republic of Korea
| | - Daeyoung Moon
- Department of Materials Science and Engineering, Seoul National University , Seoul 08826, Republic of Korea
| | - Jeonghwan Jang
- Department of Materials Science and Engineering, Seoul National University , Seoul 08826, Republic of Korea
| | - Jin-Young Na
- Department of Applied Physics, Kyung Hee University , Gyeonggi-do 17104, Republic of Korea
| | - Jung-Hwan Song
- Department of Physics, KAIST , Daejeon 34141, Republic of Korea
| | - Min-Kyo Seo
- Department of Physics, KAIST , Daejeon 34141, Republic of Korea
| | - Sunghee Kim
- Hexa Solution Co., Ltd. , Gyeonggi-do 16229, Republic of Korea
| | - Dukkyu Bae
- Hexa Solution Co., Ltd. , Gyeonggi-do 16229, Republic of Korea
- Energy Semiconductor Research Center, Advanced Institutes of Convergence Technology, Seoul National University , Gyeonggi-do 16229, Republic of Korea
| | - Eun Hyun Park
- Semicon Light Co., Ltd. , Gyeonggi-do 17086, Republic of Korea
| | - Yongjo Park
- Department of Materials Science and Engineering, Seoul National University , Seoul 08826, Republic of Korea
- Energy Semiconductor Research Center, Advanced Institutes of Convergence Technology, Seoul National University , Gyeonggi-do 16229, Republic of Korea
| | - Sun-Kyung Kim
- Department of Applied Physics, Kyung Hee University , Gyeonggi-do 17104, Republic of Korea
| | - Euijoon Yoon
- Department of Materials Science and Engineering, Seoul National University , Seoul 08826, Republic of Korea
- Energy Semiconductor Research Center, Advanced Institutes of Convergence Technology, Seoul National University , Gyeonggi-do 16229, Republic of Korea
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32
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Geum DM, Park MS, Lim JY, Yang HD, Song JD, Kim CZ, Yoon E, Kim S, Choi WJ. Ultra-high-throughput Production of III-V/Si Wafer for Electronic and Photonic Applications. Sci Rep 2016; 6:20610. [PMID: 26864968 PMCID: PMC4750074 DOI: 10.1038/srep20610] [Citation(s) in RCA: 65] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2015] [Accepted: 01/08/2016] [Indexed: 11/09/2022] Open
Abstract
Si-based integrated circuits have been intensively developed over the past several decades through ultimate device scaling. However, the Si technology has reached the physical limitations of the scaling. These limitations have fuelled the search for alternative active materials (for transistors) and the introduction of optical interconnects (called "Si photonics"). A series of attempts to circumvent the Si technology limits are based on the use of III-V compound semiconductor due to their superior benefits, such as high electron mobility and direct bandgap. To use their physical properties on a Si platform, the formation of high-quality III-V films on the Si (III-V/Si) is the basic technology ; however, implementing this technology using a high-throughput process is not easy. Here, we report new concepts for an ultra-high-throughput heterogeneous integration of high-quality III-V films on the Si using the wafer bonding and epitaxial lift off (ELO) technique. We describe the ultra-fast ELO and also the re-use of the III-V donor wafer after III-V/Si formation. These approaches provide an ultra-high-throughput fabrication of III-V/Si substrates with a high-quality film, which leads to a dramatic cost reduction. As proof-of-concept devices, this paper demonstrates GaAs-based high electron mobility transistors (HEMTs), solar cells, and hetero-junction phototransistors on Si substrates.
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Affiliation(s)
- Dae-Myeong Geum
- Korea Institute of Science and Technology (KIST), Hwarangno 14-gil 5, Seongbuk-gu, Seoul, 136-791, Korea.,Department of Materials Science and Engineering, Seoul National University, Gwanak-gu, Seoul, 151-742, Korea
| | - Min-Su Park
- Korea Institute of Science and Technology (KIST), Hwarangno 14-gil 5, Seongbuk-gu, Seoul, 136-791, Korea
| | - Ju Young Lim
- Korea Photonics Technology Institute (KOPTI), Cheomdan venture-ro 108-gil 9, Buk-gu, Gwanju-si, 500-799, Korea
| | - Hyun-Duk Yang
- Korea Institute of Science and Technology (KIST), Hwarangno 14-gil 5, Seongbuk-gu, Seoul, 136-791, Korea
| | - Jin Dong Song
- Korea Institute of Science and Technology (KIST), Hwarangno 14-gil 5, Seongbuk-gu, Seoul, 136-791, Korea
| | - Chang Zoo Kim
- Korea Advanced Nanofab Center (KANC), Gwanggyo-ro 109, Yeongtong-gu, Suwon-si, Gyeonggi-do, 443-270, Korea
| | - Euijoon Yoon
- Department of Materials Science and Engineering, Seoul National University, Gwanak-gu, Seoul, 151-742, Korea
| | - SangHyeon Kim
- Korea Institute of Science and Technology (KIST), Hwarangno 14-gil 5, Seongbuk-gu, Seoul, 136-791, Korea
| | - Won Jun Choi
- Korea Institute of Science and Technology (KIST), Hwarangno 14-gil 5, Seongbuk-gu, Seoul, 136-791, Korea
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33
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Abstract
We study the bond lengths of silicon (Si) atoms attached to both armchair and zigzag edges using aberration corrected transmission electron microscopy with monochromation of the electron beam. An in situ heating holder is used to perform imaging of samples at 800 °C in order to reduce chemical etching effects that cause rapid structure changes of graphene edges at room temperature under the electron beam. We provide detailed bond length measurements for Si atoms both attached to edges and also as near edge substitutional dopants. Edge reconstruction is also involved with the addition of Si dopants. Si atoms bonded to the edge of graphene are compared to substitutional dopants in the bulk lattice and reveal reduced out-of-plane distortion and bond elongation. An extended linear array of Si atoms at the edge is found to be energy-favorable due to inter-Si interactions. These results provide detailed structural information about the Si-C bonds in graphene, which may have importance in future catalytic and electronic applications.
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Affiliation(s)
- Qu Chen
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
| | - Alex W Robertson
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
| | - Kuang He
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
| | - Chuncheng Gong
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
| | - Euijoon Yoon
- Department of Materials Science and Engineering, Seoul National University , Seoul 151-742, Korea
| | - Angus I Kirkland
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
| | - Gun-Do Lee
- Department of Materials Science and Engineering, Seoul National University , Seoul 151-742, Korea
| | - Jamie H Warner
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
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34
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Abstract
The atomic structure of subnanometer pores in graphene, of interest due to graphene's potential as a desalination and gas filtration membrane, is demonstrated by atomic resolution aberration corrected transmission electron microscopy. High temperatures of 500 °C and over are used to prevent self-healing of the pores, permitting the successful imaging of open pore geometries consisting of between -4 to -13 atoms, all exhibiting subnanometer diameters. Picometer resolution bond length measurements are used to confirm reconstruction of five-membered ring projections that often decorate the pore perimeter, knowledge which is used to explore the viability of completely self-passivated subnanometer pore structures; bonding configurations where the pore would not require external passivation by, for example, hydrogen to be chemically inert.
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Affiliation(s)
- Alex W Robertson
- Department of Materials, University of Oxford , Parks Road, Oxford, OX1 3PH, United Kingdom
| | - Gun-Do Lee
- Department of Materials Science and Engineering, Seoul National University , Seoul, Korea
| | - Kuang He
- Department of Materials, University of Oxford , Parks Road, Oxford, OX1 3PH, United Kingdom
| | - Chuncheng Gong
- Department of Materials, University of Oxford , Parks Road, Oxford, OX1 3PH, United Kingdom
| | - Qu Chen
- Department of Materials, University of Oxford , Parks Road, Oxford, OX1 3PH, United Kingdom
| | - Euijoon Yoon
- Department of Materials Science and Engineering, Seoul National University , Seoul, Korea
| | - Angus I Kirkland
- Department of Materials, University of Oxford , Parks Road, Oxford, OX1 3PH, United Kingdom
| | - Jamie H Warner
- Department of Materials, University of Oxford , Parks Road, Oxford, OX1 3PH, United Kingdom
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35
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Chen X, Jung J, Qi Z, Zhu L, Park S, Zhu L, Yoon E, Shao J. Infrared photoreflectance investigation of resonant levels and band edge structure in InSb. Opt Lett 2015; 40:5295-5298. [PMID: 26565858 DOI: 10.1364/ol.40.005295] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Temperature-dependent infrared photoreflectance (PR) is employed on InSb for clarifying resonant levels (RLs) and band edge structure. Abundant PR features are well resolved around the bandgap and are verified to be of electronic inter-level transitions rather than the Franz-Keldysh oscillations. The evolution of the critical energies with temperature reveals the nature of the PR processes, from which one acceptor RL, two donor RLs, and a shallow acceptor level are quantitatively identified, and a detailed band edge structure is derived. The results show that temperature-dependent infrared PR analysis can serve as an efficient vehicle for clarifying both bound and resonant levels in semiconductors.
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36
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Gong C, Robertson AW, He K, Lee GD, Yoon E, Allen CS, Kirkland AI, Warner JH. Thermally Induced Dynamics of Dislocations in Graphene at Atomic Resolution. ACS Nano 2015; 9:10066-10075. [PMID: 26461042 DOI: 10.1021/acsnano.5b05355] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Thermally induced dislocation movements are important in understanding the effects of high temperature annealing on modifying the crystal structure. We use an in situ heating holder in an aberration corrected transmission electron microscopy to study the movement of dislocations in suspended monolayer graphene up to 800 °C. Control of temperature enables the differentiation of electron beam induced effects and thermally driven processes. At room temperature, the dynamics of dislocation behavior is driven by the electron beam irradiation at 80 kV; however at higher temperatures, increased movement of the dislocation is observed and provides evidence for the influence of thermal energy to the system. An analysis of the dislocation movement shows both climb and glide processes, including new complex pathways for migration and large nanoscale rapid jumps between fixed positions in the lattice. The improved understanding of the high temperature dislocation movement provides insights into annealing processes in graphene and the behavior of defects with increased heat.
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Affiliation(s)
- Chuncheng Gong
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
| | - Alex W Robertson
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
| | - Kuang He
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
| | - Gun-Do Lee
- Department of Materials Science and Engineering, Seoul National University , Seoul 151-742, Korea
| | - Euijoon Yoon
- Department of Materials Science and Engineering, Seoul National University , Seoul 151-742, Korea
| | - Christopher S Allen
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
| | - Angus I Kirkland
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
| | - Jamie H Warner
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
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37
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Robertson AW, Lee GD, He K, Fan Y, Allen CS, Lee S, Kim H, Yoon E, Zheng H, Kirkland AI, Warner JH. Partial Dislocations in Graphene and Their Atomic Level Migration Dynamics. Nano Lett 2015; 15:5950-5955. [PMID: 26313338 DOI: 10.1021/acs.nanolett.5b02080] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We demonstrate the formation of partial dislocations in graphene at elevated temperatures of ≥500 °C with single atom resolution aberration corrected transmission electron microscopy. The partial dislocations spatially redistribute strain in the lattice, providing an energetically more favorable configuration to the perfect dislocation. Low-energy migration paths mediated by partial dislocation formation have been observed, providing insights into the atomistic dynamics of graphene during annealing. These results are important for understanding the high temperature plasticity of graphene and partial dislocation behavior in related crystal systems, such as diamond cubic materials.
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Affiliation(s)
- Alex W Robertson
- Department of Materials, University of Oxford , Parks Road, Oxford, OX1 3PH, United Kingdom
| | - Gun-Do Lee
- Department of Materials Science and Engineering, Seoul National University , Seoul, Korea
| | - Kuang He
- Department of Materials, University of Oxford , Parks Road, Oxford, OX1 3PH, United Kingdom
| | - Ye Fan
- Department of Materials, University of Oxford , Parks Road, Oxford, OX1 3PH, United Kingdom
| | - Christopher S Allen
- Department of Materials, University of Oxford , Parks Road, Oxford, OX1 3PH, United Kingdom
| | - Sungwoo Lee
- Department of Materials Science and Engineering, Seoul National University , Seoul, Korea
| | - Heeyeon Kim
- Energy Materials Laboratory, Korean Institute of Energy Research , 152 Gajeong-ro, Yuseong-gu, Daejeon 305-343, Korea
| | - Euijoon Yoon
- Department of Materials Science and Engineering, Seoul National University , Seoul, Korea
| | - Haimei Zheng
- Materials Science Division, Lawrence Berkeley National Lab , Berkeley, California 94720, United States
| | - Angus I Kirkland
- Department of Materials, University of Oxford , Parks Road, Oxford, OX1 3PH, United Kingdom
| | - Jamie H Warner
- Department of Materials, University of Oxford , Parks Road, Oxford, OX1 3PH, United Kingdom
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38
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Abstract
Graphene edges and their functionalization influence the electronic and magnetic properties of graphene nanoribbons. Theoretical calculations predict saturating graphene edges with hydrogen lower its energy and form a more stable structure. Despite the importance, experimental investigations of whether graphene edges are always hydrogen-terminated are limited. Here we study graphene edges produced by sputtering in vacuum and direct measurements of the C-C bond lengths at the edge show ~86% contraction relative to the bulk. Density functional theory reveals the contraction is attributed to the formation of a triple bond and the absence of hydrogen functionalization. Time-dependent images reveal temporary attachment of a single atom to the arm-chair C-C bond in a triangular configuration, causing expansion of the bond length, which then returns back to the contracted value once the extra atom moves on and the arm-chair edge is returned. Our results provide confirmation that non-functionalized graphene edges can exist in vacuum.
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Affiliation(s)
- Kuang He
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK
| | - Gun-Do Lee
- Department of Materials Science and Engineering, Seoul National University, Seoul 151-742, Korea
| | - Alex W Robertson
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK
| | - Euijoon Yoon
- Department of Materials Science and Engineering, Seoul National University, Seoul 151-742, Korea
| | - Jamie H Warner
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK
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Gong C, He K, Robertson AW, Yoon E, Lee GD, Warner JH. Spatially dependent lattice deformations for dislocations at the edges of graphene. ACS Nano 2015; 9:656-662. [PMID: 25496495 DOI: 10.1021/nn505996c] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We show that dislocations located at the edge of graphene cause different lattice deformations to those located in the bulk lattice. When a dislocation is located near an edge, a decrease in the rippling and increase of the in-plane rotation occurs relative to the dislocations in the bulk. The increased in-plane rotation near the edge causes bond rotations at the edge of graphene to reduce the overall strain in the system. Dislocations were highly stable and remained fixed in their position even when located within a few lattice spacings from the edge of graphene. We study this behavior at the atomic level using aberration-corrected transmission electron microscopy. These results show detailed information about the behavior of dislocations in 2D materials and the strain properties that result.
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Affiliation(s)
- Chuncheng Gong
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
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40
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Abstract
Graphene has three experimentally confirmed periodic edge terminations, zigzag, reconstructed 5-7, and arm-chair. Theory predicts a fourth periodic edge of graphene called the extended Klein (EK) edge, which consists of a series of single C atoms protruding from a zigzag edge. Here, we confirm the existence of EK edges in both graphene nanoribbons and on the edge of bulk graphene using atomic resolution imaging by aberration-corrected transmission electron microscopy. The formation of the EK edge stems from sputtering and reconstruction of the zigzag edge. Density functional theory reveals minimal energy for EK edge reconstruction and bond distortion both in and out of plane, supporting our TEM observations. The EK edge can now be included as the fourth member of observed periodic edge structures in graphene.
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Affiliation(s)
- Kuang He
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
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41
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Abstract
We use time-dependent HRTEM to reveal that stable dislocation pairs in graphene are formed from an initial complex multi-vacancy cluster that undergoes multiple bond rotations and adatom incorporation. In the process, it is found that the transformation from the formed complex multi-vacancy cluster can proceed without the increase of vacancy because many atoms and dimers are not only evaporated but also actively adsorbed. In tight-binding molecular dynamics simulations, it is confirmed that adatoms play an important role in the reconstruction of non-hexagonal rings into hexagonal rings. From density functional theory calculations, it is also found from simulations that there is a favorable distance between two dislocations pointing away from each other (i.e. formed from atom loss). For dislocation pairs pointing away from each other, the hillock-basin structure is more stable than the hillock-hillock structure for dislocation pairs pointing away from each other (i.e. formed from atom loss).
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Affiliation(s)
- Gun-Do Lee
- Department of Materials Science and Engineering, Seoul National University, Seoul 151-742, Republic of Korea
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Kim YS, Joo K, Jerng SK, Lee JH, Yoon E, Chun SH. Direct growth of patterned graphene on SiO2 substrates without the use of catalysts or lithography. Nanoscale 2014; 6:10100-5. [PMID: 25034505 DOI: 10.1039/c4nr02001d] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
We demonstrate a one-step fabrication of patterned graphene on SiO2 substrates through a process free from catalysts, transfer, and lithography. By simply placing a shadow mask during the plasma enhanced chemical vapor deposition (PECVD) of graphene, an arbitrary shape of graphene can be obtained on SiO2 substrate. The formation of graphene underneath the shadow mask was effectively prevented by the low-temperature, catalyst-free process. Growth conditions were optimized to form polycrystalline graphene on SiO2 substrates and the crystalline structure was characterized by Raman spectroscopy and transmission electron microscopy (TEM). Patterned graphene on SiO2 functions as a field-effect device by itself. Our method is compatible with present device processing techniques, and should be highly desirable for the proliferation of graphene applications.
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Affiliation(s)
- Yong Seung Kim
- Graphene Research Institute, Sejong University, Seoul 143-747, Korea.
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Robertson AW, Lee GD, He K, Yoon E, Kirkland AI, Warner JH. The role of the bridging atom in stabilizing odd numbered graphene vacancies. Nano Lett 2014; 14:3972-80. [PMID: 24959991 DOI: 10.1021/nl501320a] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Vacancy defects in graphene with an odd number of missing atoms, such as the trivacancy, have been imaged at atomic resolution using aberration corrected transmission electron microscopy. These defects are not just stabilized by simple bond reconstructions between under-coordinated carbon atoms, as exhibited by even vacancies such as the divacancy. Instead we have observed reconstructions consisting of under-coordinated bridging carbon atoms spanning the vacancy to saturate edge atoms. We report detailed studies of the effect of this bridging atom on the configuration of the trivacancy and higher order odd number vacancies, as well as its role in defect stabilization in amorphous systems. Theoretical analysis using density functional theory and tight-binding molecular dynamics calculations demonstrate that the bridging atom enables the low energy reconfiguration of these defect structures.
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Affiliation(s)
- Alex W Robertson
- Department of Materials, University of Oxford , Parks Road, Oxford, OX1 3PH, United Kingdom
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44
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He Z, He K, Robertson AW, Kirkland AI, Kim D, Ihm J, Yoon E, Lee GD, Warner JH. Atomic structure and dynamics of metal dopant pairs in graphene. Nano Lett 2014; 14:3766-3772. [PMID: 24945707 DOI: 10.1021/nl500682j] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We present an atomic resolution structural study of covalently bonded dopant pairs in the lattice of monolayer graphene. Two iron (Fe) metal atoms that are covalently bonded within the graphene lattice are observed and their interaction with each other is investigated. The two metal atom dopants can form small paired clusters of varied geometry within graphene vacancy defects. The two Fe atoms are created within a 10 nm diameter predefined location in graphene by manipulating a focused electron beam (80 kV) on the surface of graphene containing an intentionally deposited Fe precursor reservoir. Aberration-corrected transmission electron microscopy at 80 kV has been used to investigate the atomic structure and real time dynamics of Fe dimers embedded in graphene vacancies. Four different stable structures have been observed; two variants of an Fe dimer in a graphene trivacancy, an Fe dimer embedded in two adjacent monovacancies and an Fe dimer trapped by a quadvacancy. According to spin-sensitive DFT calculations, these dimer structures all possess magnetic moments of either 2.00 or 4.00 μB. The dimer structures were found to evolve from an initial single Fe atom dopant trapped in a graphene vacancy.
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Affiliation(s)
- Zhengyu He
- Department of Materials, University of Oxford , Parks Road, Oxford, OX1 3PH, United Kingdom
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45
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Kim YS, Joo K, Jerng SK, Lee JH, Moon D, Kim J, Yoon E, Chun SH. Direct integration of polycrystalline graphene into light emitting diodes by plasma-assisted metal-catalyst-free synthesis. ACS Nano 2014; 8:2230-2236. [PMID: 24506543 DOI: 10.1021/nn405477f] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The integration of graphene into devices is a challenging task because the preparation of a graphene-based device usually includes graphene growth on a metal surface at elevated temperatures (∼1000 °C) and a complicated postgrowth transfer process of graphene from the metal catalyst. Here we report a direct integration approach for incorporating polycrystalline graphene into light emitting diodes (LEDs) at low temperature by plasma-assisted metal-catalyst-free synthesis. Thermal degradation of the active layer in LEDs is negligible at our growth temperature, and LEDs could be fabricated without a transfer process. Moreover, in situ ohmic contact formation is observed between DG and p-GaN resulting from carbon diffusion into the p-GaN surface during the growth process. As a result, the contact resistance is reduced and the electrical properties of directly integrated LEDs outperform those of LEDs with transferred graphene electrodes. This relatively simple method of graphene integration will be easily adoptable in the industrialization of graphene-based devices.
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Affiliation(s)
- Yong Seung Kim
- Graphene Research Institute, Sejong University , Seoul 143-747, Korea
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46
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Robertson AW, Lee GD, He K, Yoon E, Kirkland AI, Warner JH. Stability and dynamics of the tetravacancy in graphene. Nano Lett 2014; 14:1634-1642. [PMID: 24588782 DOI: 10.1021/nl500119p] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
The relative prevalence of various configurations of the tetravacancy defect in monolayer graphene has been examined using aberration corrected transmission electron microscopy (TEM). It was found that the two most common structures are extended linear defect structures, with the 3-fold symmetric Y-tetravacancy seldom imaged, in spite of this being a low energy state. Using density functional theory and tight-binding molecular dynamics calculations, we have determined that our TEM observations support a dynamic model of the tetravacancy under electron irradiation, with Stone-Wales bond rotations providing a mechanism for defect relaxation into lowest energy configurations. The most prevalent tetravacancy structures, while not necessarily having the lowest formation energy, are found to have a local energy minimum in the overall energy landscape for tetravacancies, explaining their relatively high occurrence.
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Affiliation(s)
- Alex W Robertson
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
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47
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Warner JH, Lee GD, He K, Robertson AW, Yoon E, Kirkland AI. Bond length and charge density variations within extended arm chair defects in graphene. ACS Nano 2013; 7:9860-9866. [PMID: 24148018 DOI: 10.1021/nn403517m] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Extended linear arm chair defects are intentionally fabricated in suspended monolayer graphene using controlled focused electron beam irradiation. The atomic structure is accurately determined using aberration-corrected transmission electron microscopy with monochromation of the electron source to achieve ∼80 pm spatial resolution at an accelerating voltage of 80 kV. We show that the introduction of atomic vacancies in graphene disrupts the uniformity of C-C bond lengths immediately surrounding linear arm chair defects in graphene. The measured changes in C-C bond lengths are related to density functional theory (DFT) calculations of charge density variation and corresponding DFT calculated structural models. We show good correlation between the DFT predicted localized charge depletion and structural models with HRTEM measured bond elongation within the carbon tetragon structure of graphene. Further evidence of bond elongation within graphene defects is obtained from imaging a pair of 5-8-5 divacancies.
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Affiliation(s)
- Jamie H Warner
- Department of Materials, University of Oxford , Parks Road, Oxford OX1 3PH, United Kingdom
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48
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Jerng SK, Joo K, Kim Y, Yoon SM, Lee JH, Kim M, Kim JS, Yoon E, Chun SH, Kim YS. Ordered growth of topological insulator Bi2Se3 thin films on dielectric amorphous SiO2 by MBE. Nanoscale 2013; 5:10618-10622. [PMID: 24056725 DOI: 10.1039/c3nr03032f] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Topological insulators (TIs) are exotic materials which have topologically protected states on the surface due to strong spin-orbit coupling. However, a lack of ordered growth of TI thin films on amorphous dielectrics and/or insulators presents a challenge for applications of TI-junctions. We report the growth of topological insulator Bi2Se3 thin films on amorphous SiO2 by molecular beam epitaxy (MBE). To achieve the ordered growth of Bi2Se3 on an amorphous surface, the formation of other phases at the interface is suppressed by Se passivation. Structural characterizations reveal that Bi2Se3 films are grown along the [001] direction with a good periodicity by the van der Waals epitaxy mechanism. A weak anti-localization effect of Bi2Se3 films grown on amorphous SiO2 shows a modulated electrical property by the gating response. Our approach for ordered growth of Bi2Se3 on an amorphous dielectric surface presents considerable advantages for TI-junctions with amorphous insulator or dielectric thin films.
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Affiliation(s)
- Sahng-Kyoon Jerng
- Department of Physics and Graphene Research Institute, Sejong University, Seoul 143-747, Korea.
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49
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Abstract
Ripples in graphene are an out-of-plane distortion that help stabilize suspended monolayer graphene. The introduction of disclinations and dislocations into the lattice of graphene is predicted to extensively ripple graphene to form "hillocks" to accommodate the strain in the system. Here, we confirm this theoretical prediction by intentionally introducing large numbers of dislocations into a predefined area of pristine monolayer graphene by scanning focused electron beam irradiation and imaging the rippled atomic lattice structure with aberration-corrected transmission electron microscopy. Hillocks are observed and analyzed using geometric phase analysis to determine heights of ~0.5 nm. Time-dependent imaging shows the rippling is dynamic under the electron beam and can fluctuate between different structural configurations. This demonstrates a means of perturbing the structure of graphene in all three spatial dimensions with nanoscale precision.
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Affiliation(s)
- Jamie H Warner
- Department of Materials, University of Oxford , Parks Rd, Oxford, OX1 3PH, United Kingdom
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50
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Abstract
The motion and annihilation of a grain boundary (GB) in graphene are investigated by tight-binding molecular dynamics (TBMD) simulation and ab initio local density approximation total energy calculation. A meandering structure of the GB is found to be energetically more favorable than other structures, in good agreement with experiment. It is observed in the TBMD simulation that evaporation of carbon dimers and sequential Stone-Wales transformations of carbon bonds lead to rapid motion and annihilation of the GB. The dimer erection and evaporation are found to proceed by formation of an adatom due to bond breaking. These results shed interesting light on the fabrication of high-quality graphene.
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Affiliation(s)
- Gun-Do Lee
- Department of Materials Science and Engineering, Seoul National University, Seoul 151-742, Republic of Korea.
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