39 results on '"Kyeongjae Cho"'
Search Results
2. DFT modeling of atomic layer deposition of Ru interconnect metal for EUV scaling
- Author
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Matthew Bergschneider, Nickolas Ashburn, Xiuyao Lang, Andrew C. Kummel, and Kyeongjae Cho
- Subjects
Mechanics of Materials ,Mechanical Engineering ,General Materials Science ,Condensed Matter Physics - Published
- 2023
3. Spin-defect qubits in two-dimensional transition metal dichalcogenides operating at telecom wavelengths
- Author
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Yeonghun Lee, Yaoqiao Hu, Xiuyao Lang, Dongwook Kim, Kejun Li, Yuan Ping, Kai-Mei C. Fu, and Kyeongjae Cho
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Multidisciplinary ,General Physics and Astronomy ,General Chemistry ,General Biochemistry, Genetics and Molecular Biology - Abstract
Solid state quantum defects are promising candidates for scalable quantum information systems which can be seamlessly integrated with the conventional semiconductor electronic devices within the 3D monolithically integrated hybrid classical-quantum devices. Diamond nitrogen-vacancy (NV) center defects are the representative examples, but the controlled positioning of an NV center within bulk diamond is an outstanding challenge. Furthermore, quantum defect properties may not be easily tuned for bulk crystalline quantum defects. In comparison, 2D semiconductors, such as transition metal dichalcogenides (TMDs), are promising solid platform to host a quantum defect with tunable properties and a possibility of position control. Here, we computationally discover a promising defect family for spin qubit realization in 2D TMDs. The defects consist of transition metal atoms substituted at chalcogen sites with desirable spin-triplet ground state, zero-field splitting in the tens of GHz, and strong zero-phonon coupling to optical transitions in the highly desirable telecom band.
- Published
- 2022
4. Ambient effect on the Curie temperatures and magnetic domains in metallic two-dimensional magnets
- Author
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Yu Gong, Kyeongjae Cho, John Cumings, Nagarajan Valanoor, Alemayehu S. Admasu, Zhiyin Tu, Ti Xie, Yeonghun Lee, Ichiro Takeuchi, Jinling Zhou, Cheng Gong, and Sang-Wook Cheong
- Subjects
Materials science ,Magnetic domain ,Magnetism ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Curie ,General Materials Science ,Materials of engineering and construction. Mechanics of materials ,QD1-999 ,Condensed matter physics ,Spintronics ,Mechanical Engineering ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,0104 chemical sciences ,Chemistry ,Ferromagnetism ,chemistry ,Mechanics of Materials ,Magnet ,TA401-492 ,Curie temperature ,0210 nano-technology ,Tellurium - Abstract
The emergent magnetic two-dimensional (2D) materials provide ideal solid-state platforms for a broad range of applications including miniaturized spintronics, nonreciprocal optics, and magnetoelectric sensors. Owing to the general environmental sensitivity of 2D magnets, the understanding of ambient effects on 2D magnetism is critical. Apparently, the nature of itinerant ferromagnetism potentially makes metallic 2D magnets insensitive to environmental disturbance. Nevertheless, our systematic study showed that the Curie temperature of metallic 2D Fe3GeTe2 decreases dramatically in the air but thick Fe3GeTe2 exhibits self-protection. Remarkably, we found the air exposure effectively promotes the formation of multiple magnetic domains in 2D Fe3GeTe2, but not in bulk Fe3GeTe2. Our first-principles calculations support the scenario that substrate-induced roughness and tellurium vacancies boost the interaction of 2D Fe3GeTe2 with the air. Our elucidation of the thickness-dependent air-catalyzed evolution of Curie temperatures and magnetic domains in 2D magnets provides critical insights for chemically decorating and manipulating 2D magnets.
- Published
- 2021
5. Nonadiabatic dynamics of cobalt tricarbonyl nitrosyl for ligand dissociation induced by electronic excitation
- Author
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Kyeongjae Cho, Grigory Kolesov, Xiaolong Yao, Efthimios Kaxiras, and Yeonghun Lee
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Electronic structure ,Science ,Chemical physics ,chemistry.chemical_element ,02 engineering and technology ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Article ,Dissociation (chemistry) ,Molecule ,Multidisciplinary ,Chemistry ,Ligand ,Synthesis and processing ,Dynamics (mechanics) ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Chemical bond ,Medicine ,Atomistic models ,Density functional theory ,0210 nano-technology ,Cobalt ,Excitation - Abstract
We utilize real-time time-dependent density functional theory and Ehrenfest dynamics scheme to investigate excited-state nonadiabatic dynamics of ligand dissociation of cobalt tricarbonyl nitrosyl, Co(CO)3NO, which is a precursor used for cobalt growth in advanced technologies, where the precursor’s reaction is enhanced by electronic excitation. Based on the first-principles calculations, we demonstrate two dissociation pathways of the NO ligand on the precursor. Detailed electronic structures are further analyzed to provide an insight into dynamics following the electronic excitations. This study sheds light on computational demonstration and underlying mechanism of the electronic-excitation-induced dissociation, especially in molecules with complex chemical bonds such as the Co(CO)3NO.
- Published
- 2021
6. Giant renormalization of dopant impurity levels in 2D semiconductor MoS2
- Author
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Kyeongjae Cho, Yong-Sung Kim, Robert M. Wallace, Jeongwoon Hwang, and Chenxi Zhang
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Materials science ,lcsh:Medicine ,02 engineering and technology ,Dielectric ,01 natural sciences ,Article ,Renormalization ,Nanoscience and technology ,Impurity ,0103 physical sciences ,Monolayer ,lcsh:Science ,010306 general physics ,Multidisciplinary ,Condensed matter physics ,Dopant ,business.industry ,lcsh:R ,Doping ,021001 nanoscience & nanotechnology ,Semiconductor ,Halogen ,lcsh:Q ,0210 nano-technology ,business - Abstract
Substitutional doping in 2D semiconductor MoS2 was investigated by charge transition level (CTL) calculations for Nitrogen group (N, P, As, Sb) and Halogen group (F, Cl, Br, I) dopants at the S site of monolayer MoS2. Both n-type and p-type dopant levels are calculated to be deep mid-gap states (~1 eV from band edges) from DFT total energy-based CTL and separate DFT + GW calculations. The deep dopant levels result from the giant renormalization of hydrogen-like defect states by reduced dielectric screening in ultrathin 2D films. Theoretical analysis based on Keldysh formulation provides a consistent impurity binding energy of ~1 eV for dielectric thin films. These findings of intrinsic deep impurity levels in 2D semiconductors MoS2 may be applicable to diverse novel emerging device applications.
- Published
- 2020
7. Polarity governs atomic interaction through two-dimensional materials
- Author
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Yuewei Zhang, Doyoon Lee, Kevin M. Daniels, Yang Shao-Horn, Tom Osadchy, D. Kurt Gaskill, Richard J. Molnar, Sang-Hoon Bae, Suresh Sundram, Kyusang Lee, Rachael L. Myers-Ward, Jeffrey C. Grossman, Yang Yu, Jeehwan Kim, Huashan Li, Kuan Qiao, Abdallah Ougazzaden, Yifan Nie, Yunjo Kim, Siddharth Rajan, Kyeongjae Cho, Wei Kong, Science et Technologie du Lait et de l'Oeuf (STLO), Institut National de la Recherche Agronomique (INRA)-AGROCAMPUS OUEST, Georgia Tech - CNRS [Metz] (UMI2958), Ecole Nationale Supérieure des Arts et Metiers Metz-SUPELEC-Georgia Institute of Technology [Atlanta]-Georgia Institute of Technology [Lorraine, France]-CentraleSupélec-Centre National de la Recherche Scientifique (CNRS)-Université de Franche-Comté (UFC), Centre for Crop System Analysis, Wageningen University and Research Center (WUR), NASA Headquarters, Massachusetts Institute of Technology (MIT), Georgia Tech Lorraine [Metz], Université de Franche-Comté (UFC), Université Bourgogne Franche-Comté [COMUE] (UBFC)-Université Bourgogne Franche-Comté [COMUE] (UBFC)-Ecole Supérieure d'Electricité - SUPELEC (FRANCE)-Georgia Institute of Technology [Atlanta]-CentraleSupélec-Ecole Nationale Supérieure des Arts et Metiers Metz-Centre National de la Recherche Scientifique (CNRS), Institute of Water Resources and Hydropower Research, MASSACHUSETTS INSTITUTE OF TECHNOLOGY CAMBRIDGE USA, Partenaires IRSTEA, Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA), Sun Yat-Sen University [Guangzhou] (SYSU), and Wageningen University and Research [Wageningen] (WUR)
- Subjects
Materials science ,Polarity (physics) ,02 engineering and technology ,010402 general chemistry ,Epitaxy ,01 natural sciences ,law.invention ,law ,Monolayer ,General Materials Science ,Nanoscience & Nanotechnology ,Thin film ,Polarization (electrochemistry) ,[PHYS]Physics [physics] ,Graphene ,Mechanical Engineering ,Intermolecular force ,[CHIM.MATE]Chemical Sciences/Material chemistry ,General Chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,0104 chemical sciences ,Membrane ,Mechanics of Materials ,Chemical physics ,0210 nano-technology - Abstract
International audience; The transparency of two-dimensional (2D) materials to intermolecular interactions of crystalline materials has been an unresolved topic. Here we report that remote atomic interaction through 2D materials is governed by the binding nature, that is, the polarity of atomic bonds, both in the underlying substrates and in 2D material interlayers. Although the potential field from covalent-bonded materials is screened by a monolayer of graphene, that from ionic-bonded materials is strong enough to penetrate through a few layers of graphene. Such field penetration is substantially attenuated by 2D hexagonal boron nitride, which itself has polarization in its atomic bonds. Based on the control of transparency, modulated by the nature of materials as well as interlayer thickness, various types of single-crystalline materials across the periodic table can be epitaxially grown on 2D material-coated substrates. The epitaxial films can subsequently be released as free-standing membranes, which provides unique opportunities for the heterointegration of arbitrary single-crystalline thin films in functional applications.
- Published
- 2018
8. 2D MoS2 as an efficient protective layer for lithium metal anodes in high-performance Li–S batteries
- Author
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Vish Prasad, Jeongwoon Hwang, Kyeongjae Cho, Juhong Park, Eunho Cha, Wonbong Choi, and Mumukshu D. Patel
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Materials science ,Biomedical Engineering ,Nucleation ,Bioengineering ,02 engineering and technology ,Electrolyte ,010402 general chemistry ,01 natural sciences ,law.invention ,Metal ,law ,General Materials Science ,Electrical and Electronic Engineering ,Dissolution ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,Cathode ,0104 chemical sciences ,Anode ,Chemical engineering ,visual_art ,visual_art.visual_art_medium ,0210 nano-technology ,Current density ,Faraday efficiency - Abstract
Among the candidates to replace Li-ion batteries, Li–S cells are an attractive option as their energy density is about five times higher (~2,600 Wh kg−1). The success of Li–S cells depends in large part on the utilization of metallic Li as anode material. Metallic lithium, however, is prone to grow parasitic dendrites and is highly reactive to several electrolytes; moreover, Li–S cells with metallic Li are also susceptible to polysulfides dissolution. Here, we show that ~10-nm-thick two-dimensional (2D) MoS2 can act as a protective layer for Li-metal anodes, greatly improving the performances of Li–S batteries. In particular, we observe stable Li electrodeposition and the suppression of dendrite nucleation sites. The deposition and dissolution process of a symmetric MoS2-coated Li-metal cell operates at a current density of 10 mA cm−2 with low voltage hysteresis and a threefold improvement in cycle life compared with using bare Li-metal. In a Li–S full-cell configuration, using the MoS2-coated Li as anode and a 3D carbon nanotube–sulfur cathode, we obtain a specific energy density of ~589 Wh kg−1 and a Coulombic efficiency of ~98% for over 1,200 cycles at 0.5 C. Our approach could lead to the realization of high energy density and safe Li-metal-based batteries. An ~10-nm-thick MoS2 layer stabilizes lithium metal anodes and the composite can be used in full-cell Li–S batteries with enhanced performances.
- Published
- 2018
9. Atomic disorders in layer structured topological insulator SnBi2Te4 nanoplates
- Author
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Kyeongjae Cho, Enze Zhang, Faxian Xiu, John Drennan, Zhongchang Wang, Yan Lu, Fantai Kong, Zhigang Chen, Yichao Zou, Lihua Wang, and Jin Zou
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Materials science ,Nanostructure ,Spintronics ,Nanotechnology ,02 engineering and technology ,Electronic structure ,Chemical vapor deposition ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,Chemical physics ,Topological insulator ,0103 physical sciences ,Scanning transmission electron microscopy ,General Materials Science ,Density functional theory ,Electrical and Electronic Engineering ,010306 general physics ,0210 nano-technology ,Ternary operation - Abstract
Identification of atomic disorders and their subsequent control has proven to be a key issue in predicting, understanding, and enhancing the properties of newly emerging topological insulator materials. Here, we demonstrate direct evidence of the cation antisites in single-crystal SnBi2Te4 nanoplates grown by chemical vapor deposition, through a combination of sub-angstrom-resolution imaging, quantitative image simulations, and density functional theory calculations. The results of these combined techniques revealed a recognizable amount of cation antisites between Bi and Sn, and energetic calculations revealed that such cation antisites have a low formation energy. The impact of the cation antisites was also investigated by electronic structure calculations together with transport measurement. The topological surface properties of the nanoplates were further probed by angle-dependent magnetotransport, and from the results, we observed a two-dimensional weak antilocalization effect associated with surface carriers. Our approach provides a pathway to identify the antisite defects in ternary chalcogenides and the application potential of SnBi2Te4 nanostructures in next-generation electronic and spintronic devices.
- Published
- 2017
10. Atomic Mechanism of Arsenic Monolayer Doping on oxide-free Silicon(111)
- Author
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Roberto C. Longo, Abraham Vega, Yves J. Chabal, Wilfredo Cabrera, Peter Thissen, Eric C. Mattson, and Kyeongjae Cho
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inorganic chemicals ,Materials science ,Silicon ,Mechanical Engineering ,Doping ,technology, industry, and agriculture ,chemistry.chemical_element ,Infrared spectroscopy ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Photochemistry ,01 natural sciences ,0104 chemical sciences ,chemistry ,Low-energy ion scattering ,Mechanics of Materials ,Desorption ,Monolayer ,Molecule ,General Materials Science ,0210 nano-technology ,Spectroscopy - Abstract
The reaction pathway for shallow arsenic doping of silicon by methylarsenic acid molecules directly grafted on oxide-free, H-terminated Si(111) surfaces is unraveled combining Infrared absorption spectroscopy, X-ray Photoelectron Spectroscopy, Low Energy Ion Scattering and ab initio Molecular Dynamics simulations. The overall driving force is identified as a thermodynamic instability of As+5 in contact with silicon, which initiates a self-decomposition of chemisorbed methylarsenic molecules at ∼600 K. As the temperature is increased, the As-C bond breaks -- the weakest link of the adsorbed molecule -- with release of the organic ligand and a rearrangement from a monodentate to a bidentate bonding configuration. In this process, oxygen atoms evolve by partial desorption as H2O and partial incorporation into the surface Si atom backbonds. At ∼1050 K, diffusion of As into the sub-surface region of silicon is observed. There is no evidence for As desorption and no remaining C contamination.
- Published
- 2016
11. Intrinsic Origins of Crack Generation in Ni-rich LiNi0.8Co0.1Mn0.1O2 Layered Oxide Cathode Material
- Author
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Taesoon Hwang, Duho Kim, Maenghyo Cho, Min-Sik Park, Jin Myoung Lim, and Kyeongjae Cho
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Multidisciplinary ,Materials science ,Mineralogy ,02 engineering and technology ,Electronic structure ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Transition metal ,Chemical physics ,Critical energy ,Lattice (order) ,Energy density ,0210 nano-technology ,Anisotropy ,Oxide cathode ,Mechanical instability - Abstract
Ni-rich LiNi0.8Co0.1Mn0.1O2 layered oxide cathodes have been highlighted for large-scale energy applications due to their high energy density. Although its specific capacity is enhanced at higher voltages as Ni ratio increases, its structural degradation due to phase transformations and lattice distortions during cycling becomes severe. For these reasons, we focused on the origins of crack generation from phase transformations and structural distortions in Ni-rich LiNi0.8Co0.1Mn0.1O2 using multiscale approaches, from first-principles to meso-scale phase-field model. Atomic-scale structure analysis demonstrated that opposite changes in the lattice parameters are observed until the inverse Li content x = 0.75; then, structure collapses due to complete extraction of Li from between transition metal layers. Combined-phase investigations represent the highest phase barrier and steepest chemical potential after x = 0.75, leading to phase transformations to highly Li-deficient phases with an inactive character. Abrupt phase transformations with heterogeneous structural collapse after x = 0.81 (~220 mAh g−1) were identified in the nanodomain. Further, meso-scale strain distributions show around 5% of anisotropic contraction with lower critical energy release rates, which cause not only micro-crack generations of secondary particles on the interfaces between the contracted primary particles, but also mechanical instability of primary particles from heterogeneous strain changes.
- Published
- 2017
12. Combined effects of defects and hydroxyl groups on the electronic transport properties of reduced graphene oxide
- Author
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Bin Shan, Xiao Liu, Yanwei Wen, Zhangru Chen, Kyeongjae Cho, and Rong Chen
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Local density of states ,Graphene ,Chemistry ,Fermi level ,Oxide ,Charge density ,Conductance ,General Chemistry ,Conductivity ,law.invention ,chemistry.chemical_compound ,symbols.namesake ,law ,Computational chemistry ,Chemical physics ,symbols ,General Materials Science ,Density functional theory ,Physics::Chemical Physics - Abstract
The effects of four typical defects on the hydroxyl groups’ migration and the conductivity of graphene have been studied using density functional theory and nonequilibrium Green’s function formalism. An obvious anisotropy of the diffusion barriers along different paths is correlated to the symmetric behavior of spin-polarized charge density around the defects. The migration energy scenario indicates that the defects effectively hinder the hydroxyl groups’ migration toward them, indicating that most hydroxyl groups could be stabilized outside the defect region in reduced graphene oxide. Through the electronic transport calculations and local density of states analysis, hydroxyl groups locating outside of the defect region will cause the transport channels near the Fermi level to disappear and reduce the conductance considerably.
- Published
- 2014
13. Rational design of redox mediators for advanced Li–O2 batteries
- Author
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Hyeokjo Gwon, Kyeongjae Cho, Jihyun Hong, Byungju Lee, Youngmin Ko, Hee-Dae Lim, Minah Lee, Jinsoo Kim, Yongping Zheng, and Kisuk Kang
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Renewable Energy, Sustainability and the Environment ,Chemistry ,Rational design ,Energy Engineering and Power Technology ,Nanotechnology ,02 engineering and technology ,Electrolyte ,Overpotential ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Redox ,0104 chemical sciences ,Electronic, Optical and Magnetic Materials ,Catalysis ,Fuel Technology ,Ionization energy ,0210 nano-technology ,HOMO/LUMO ,Efficient energy use - Abstract
The discovery of effective catalysts is an important step towards achieving Li–O2 batteries with long cycle life and high round-trip efficiency. Soluble-type catalysts or redox mediators (RMs) possess great advantages over conventional solid catalysts, generally exhibiting much higher efficiency. Here, we select a series of organic RM candidates as a model system to identify the key descriptor in determining the catalytic activities and stabilities in Li–O2 cells. It is revealed that the level of ionization energies, readily available parameters from a database of the molecules, can serve such a role when comparing with the formation energy of Li2O2 and the highest occupied molecular orbital energy of the electrolyte. It is demonstrated that they are critical in reducing the overpotential and improving the stability of Li–O2 cells, respectively. Accordingly, we propose a general principle for designing feasible catalysts and report a RM, dimethylphenazine, with a remarkably low overpotential and high stability. Soluble catalysts such as redox mediators are promising in enhancing energy efficiency of Li–O2 batteries. Here, the authors propose a design principle for finding efficient redox mediators and demonstrate the application of such a new catalyst.
- Published
- 2016
14. Ab-initio study of silicon and tin as a negative electrode materials for lithium-ion batteries
- Author
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Janghyuk Moon, Kyeongjae Cho, and Maenghyo Cho
- Subjects
Amorphous silicon ,Bulk modulus ,Materials science ,Silicon ,Mechanical Engineering ,Inorganic chemistry ,Nanocrystalline silicon ,Ionic bonding ,chemistry.chemical_element ,Industrial and Manufacturing Engineering ,Amorphous solid ,chemistry.chemical_compound ,chemistry ,Physical chemistry ,Density functional theory ,Electrical and Electronic Engineering ,Tin - Abstract
An investigation of Li-M (M: Si, Sn) components using density functional theory (DFT) is presented. Calculation of total energy, structural optimizations, bulk modulus and elastic constants with Li-Sn, Li-Si are performed through DFT calculations. From the comparable study of Li-Sn and Li-Si, it is found that silicon experience drastic mechanical degradation during lithiation than tin-based Li-Sn components. With increasing lithium net charge transfer to metals, the filling of anti-bonding orbital makes M-M covalent bonding weak ionic bonding in both Li-Si and Li-Sn. However, the difference of change of mechanical degradation during lithiation in Li-Si and Li-Sn results from the sensitivity of transition of covalent bonding. We check this from sharp decreasing of yield stress in Li-Si case. Furthermore, we simply make up amorphous Si cell with an additional Li atom at the center of the largest void to simulate the lithiation of amorphous silicon. Volume expansion of amorphous silicon cell agrees with the experiment observation and theoretical data of Li-Si compounds.
- Published
- 2012
15. Thermal conductivity of isotopically modified graphene
- Author
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Shanshan Chen, Qingzhi Wu, Columbia Mishra, Junyong Kang, Hengji Zhang, Kyeongjae Cho, Weiwei Cai, Alexander A. Balandin, and Rodney S. Ruoff
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Physics ,Surface Properties ,Graphene ,Mechanical Engineering ,Temperature ,Thermal Conductivity ,General Chemistry ,Molecular Dynamics Simulation ,Condensed Matter Physics ,Nanostructures ,law.invention ,Chemical engineering ,Mechanics of Materials ,law ,Thermal ,Kinetic isotope effect ,Graphite ,General Materials Science - Abstract
In addition to its exotic electronic properties graphene exhibits unusually high intrinsic thermal conductivity. The physics of phonons--the main heat carriers in graphene--has been shown to be substantially different in two-dimensional (2D) crystals, such as graphene, from in three-dimensional (3D) graphite. Here, we report our experimental study of the isotope effects on the thermal properties of graphene. Isotopically modified graphene containing various percentages of 13C were synthesized by chemical vapour deposition (CVD). The regions of different isotopic compositions were parts of the same graphene sheet to ensure uniformity in material parameters. The thermal conductivity, K, of isotopically pure 12C (0.01% 13C) graphene determined by the optothermal Raman technique, was higher than 4,000 W mK(-1) at the measured temperature T(m)~320 K, and more than a factor of two higher than the value of K in graphene sheets composed of a 50:50 mixture of 12C and 13C. The experimental data agree well with our molecular dynamics (MD) simulations, corrected for the long-wavelength phonon contributions by means of the Klemens model. The experimental results are expected to stimulate further studies aimed at a better understanding of thermal phenomena in 2D crystals.
- Published
- 2012
16. Conduction of Li+ cations in ethylene carbonate (EC) and propylene carbonate (PC): comparative studies using density functional theory
- Author
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Kyeongjae Cho, Mahesh Datt Bhatt, and Maenghyo Cho
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Inorganic chemistry ,Solvation ,Condensed Matter Physics ,Electrochemistry ,Lithium-ion battery ,Gibbs free energy ,chemistry.chemical_compound ,symbols.namesake ,chemistry ,Electron affinity ,Propylene carbonate ,symbols ,Physical chemistry ,General Materials Science ,Density functional theory ,Electrical and Electronic Engineering ,Ethylene carbonate - Abstract
Density functional theory is used to study the interaction of Li+ cation with ethylene carbonate (EC) and propylene carbonate (PC) comparatively, which are the most popular solvents used in lithium-ion battery composite. In our theoretical calculations, we use DFT hybrid parameter B3LYP5 with a basis set 6–31G** by means of PCGAMESS/Firefly software package. We analyze the optimized structures of EC, PC, and their clusters including lithium-ion. We then calculate solvation energy, desolvation energy, electron affinity, Gibbs free energy, heats of formation of Li+ solvated by EC and PC, and the charge on Li+. From the above analysis, we observe EC as a better solvent than PC in applications of lithium-ion batteries.
- Published
- 2011
17. Publisher Correction: 2D MoS2 as an efficient protective layer for lithium metal anodes in high-performance Li–S batteries
- Author
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Juhong Park, Kyeongjae Cho, Wonbong Choi, Mumukshu D. Patel, Vish Prasad, Jeongwoon Hwang, and Eunho Cha
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Physics ,Biomedical Engineering ,Bioengineering ,Geometry ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,Anode ,General Materials Science ,Electrical and Electronic Engineering ,Lithium metal ,Layer (object-oriented design) ,Diffusion (business) ,0210 nano-technology - Abstract
In the version of this Article originally published, a technical error in typesetting led to the traces in Fig. 3a being trimmed and made to overlap. The figure has now been corrected with the traces as supplied by the authors; the original and corrected Fig. 3a are shown below. Also, in the last paragraph of the section "Mechanistic study on Li diffusion in MoS2" the authors incorrectly included the term 'high-concentration' in the text "the Li diffusion will be dominated by high-concentration Li migration on the surface of T-MoS2 with a much smaller energy barrier (0.155 eV) to overcome". This term has now been removed from all versions of the Article. Finally, the authors have added an extra figure in the Supplementary Information (Supplementary Fig. 19) to show galvanostatic tests at 1 and 3 mA cm-2 for the MoS2-coated Li symmetric cells. The caption to Fig. 3 of the Article has been amended to reflect this, with the added wording "Galvanostatic tests at 1 and 3 mA cm-2 can be found in Supplementary Fig. 19."
- Published
- 2018
18. Experimental and Theoretical Study of CO Oxidation on PdAu Catalysts with NO Pulse Effects
- Author
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Neeti Kapur, Bin Shan, Timothy J. Truex, Jangsuk Hyun, Kyle J. Fujdala, Xianghong Hao, and Kyeongjae Cho
- Subjects
Metal ,Adsorption ,Chemistry ,visual_art ,Inorganic chemistry ,visual_art.visual_art_medium ,Reactivity (chemistry) ,General Chemistry ,Oxidation Activity ,NO binding ,Photochemistry ,Catalysis - Abstract
The effect of NO on CO oxidation was studied for Pt, Pd and PdAu catalysts. It was found that NO inhibits significantly the CO oxidation reactivity on both Pt and Pd catalysts. On PdAu catalyst, however, the presence of NO resulted in an enhancement of CO oxidation activity. In order to gain an atomistic understanding of this effect, density-function theory (DFT) calculations were performed on the adsorption and reaction properties of NO and CO on these metal surfaces. We have identified that the inhibition effects on Pt and Pd catalysts are due to stronger NO binding, and that the enhanced reactivity on PdAu is due to the reduced NO oxidation barrier on PdAu leading to NO2 formation.
- Published
- 2009
19. Energy-filtered cold electron transport at room temperature
- Author
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Ramkumar Subramanian, Seong Jin Koh, Vishva Ray, Jiyoung Kim, Kyeongjae Cho, Weichao Wang, Liang Chieh Ma, and Pradeep Bhadrachalam
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Multidisciplinary ,Materials science ,General Physics and Astronomy ,02 engineering and technology ,General Chemistry ,Electron ,Effective temperature ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,021001 nanoscience & nanotechnology ,Bioinformatics ,01 natural sciences ,7. Clean energy ,Molecular physics ,Electron transport chain ,Article ,General Biochemistry, Genetics and Molecular Biology ,Filter (large eddy simulation) ,0103 physical sciences ,010306 general physics ,0210 nano-technology ,Computer Science::Databases ,Quantum well ,Energy (signal processing) - Abstract
Fermi-Dirac electron thermal excitation is an intrinsic phenomenon that limits functionality of various electron systems. Efforts to manipulate electron thermal excitation have been successful when the entire system is cooled to cryogenic temperatures, typically, Electrons can behave as if they are at a temperature different from that of the solid in which they are embedded. Here, the authors demonstrate a room temperature device that can generate electrons with an effective temperature of 45 K by using quantum wells to filter out energetic particles.
- Published
- 2014
20. [Untitled]
- Author
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Kyeongjae Cho, Atsushi Kawamoto, and Robert W. Dutton
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Materials science ,Gate dielectric ,Nanotechnology ,Hardware_PERFORMANCEANDRELIABILITY ,Dielectric ,Engineering physics ,Work related ,Computer Science Applications ,Computational Theory and Mathematics ,CMOS ,Gate oxide ,Hardware_INTEGRATEDCIRCUITS ,General Materials Science ,Scaling ,Quantum tunnelling ,High-κ dielectric - Abstract
Aggressive scaling has led to silicon dioxide (SiO2) gate dielectrics as thin as 15 A in state-of-the-art CMOS technologies. As a consequence, static leakage power due to direct tunneling through the gate oxide has been increasing at an exponential rate. As technology roadmaps call for sub-10 A gate oxides within the next five years, a variety of alternative high-k materials are being investigated as possible replacements for SiO2. The higher dielectric constants in these materials allow the use of physically thicker films, potentially reducing the tunneling current while maintaining the gate capacitance needed for scaled device operation. Recognizing that the current Si/SiO2 system benefits from nearly 30 years of research, developing a replacement material for SiO2 presents an immense challenge. This has prompted recent interest in novel computational approaches, such as first principles density functional theory (DFT) simulations, to computationally screen candidate dielectrics by predicting their properties based on the microscopic interactions within the system. This paper provides perspectives on the application of DFT simulations to address challenging problems of high-k gate dielectric research. We provide background and motivation for the development of high-k materials and highlight opportunities for theoretical study of such materials. We also describe specific examples of recent first principles work related to two particularly promising materials systems: silicates and aluminates.
- Published
- 2001
21. Study of lithium defects in lithium phosphate and in the interface with metallic Li
- Author
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Roberto C. Longo, Kyeongjae Cho, Ka Xiong, and Santosh Kc
- Subjects
Materials science ,Wide-bandgap semiconductor ,chemistry.chemical_element ,Electrolyte ,Ion ,Metal ,chemistry ,Vacancy defect ,Interstitial defect ,visual_art ,visual_art.visual_art_medium ,Ionic conductivity ,Physical chemistry ,Lithium - Abstract
Using first-principles calculations, we investigate lithium vacancy and interstitial defects in lithium phosphate (γ-Li3PO4) and in its interface with metallic Li. We find that γ-Li3PO4 is good electronic insulator with a wide band gap of 6 eV. The calculated formation energies of Li vacancies are higher than those of Li interstitials, which indicate that the ionic conductivity is determined by the migration of Li interstitial defects in bulk electrolyte. The Li vacancy-interstitial pair defect formation energy in the Li/γ-Li3PO4 interface is comparable to the sum of Li vacancy defect at the electrode and Li ion interstitial defect in the electrolyte. Our calculation indicates that the low ionic conductivity of Li/electrolyte interface is associated with the high Li ion defect formation energy. Our study provides some useful insights on Li defect formation and migration mechanisms at the electrode-electrolyte interface and, hence, a research direction for designing future Li-ion batteries.
- Published
- 2013
22. Atomic and electronic structure of superionic solid electrolyte Li10GeP2S12
- Author
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Ka Xiong, Roberto Longo Pazos, and Kyeongjae Cho
- Subjects
Materials science ,Condensed matter physics ,Band gap ,Computational chemistry ,Interstitial diffusion ,Vacancy defect ,Electrolyte ,Electronic structure ,Conductivity ,Electronic properties ,Ion - Abstract
We investigate the electronic structure of interstitial Li and Li vacancy in Li10GeP2S12 by first principles calculations. We find that the Li vacancy and interstitial Li+ ion do not introduce states in the band gap hence they do not deteriorate the electronic properties of Li10GeP2S12. The energy barrier for Li interstitial diffusion in Li10GeP2S12 is estimated to be 1.4 eV, which is much larger than that of the Li vacancy in Li10GeP2S12. This fact suggests that the ion conductivity arises from the migration of Li vacancy.
- Published
- 2012
23. First principles study of defects in solid electrolyte lithium thiophosphate Li7P3S11
- Author
-
Weichao Wang, Kyeongjae Cho, Roberto Longo Pazos, and Ka Xiong
- Subjects
Materials science ,chemistry ,Condensed matter physics ,Band gap ,Vacancy defect ,Inorganic chemistry ,Wide-bandgap semiconductor ,chemistry.chemical_element ,Lithium ,Electronic structure ,Electrolyte ,Conductivity ,Ion - Abstract
We investigate the electronic structure of interstitial Li and Li vacancy in Li7P3S11 by first principles calculations. We find that Li7P3S11 is a good insulator with a wide band gap of 3.5 eV. We find that the Li vacancy and interstitial Li+ ion do not introduce states in the band gap hence they do not deteriorate the electronic properties of Li7P3S11. The calculated formation energies of Li vacancies are much larger than those of Li interstitials, indicating that the ion conductivity may arise from the migration of interstitial Li.
- Published
- 2011
24. First principles study of electronic structures of dopants in Mg2Si
- Author
-
S. Sobhani, Bruce E. Gnade, Weichao Wang, Ka Xiong, Rahul P. Gupta, and Kyeongjae Cho
- Subjects
Materials science ,Condensed matter physics ,Dopant ,Band gap ,Thermoelectric effect ,Density of states ,Valence band ,Electronic structure ,Edge (geometry) ,Hybrid functional - Abstract
We investigate the impact of various dopants (Na, Ag, Cd, Zn, Al, Ga, In, Tl, Ge, and Sn) on the electronic structure of Mg2Si by first principles calculations using a hybrid functional that does not need a band gap correction. We find that for Na and Ge in Mg2Si, the impurity-induced states do not affect the density of states at both edges of the valence band and the conduction band. Ag- and Sn affect slightly the density of states at the valence band edge, while Cd and Zn affect slightly the density of state at the conduction band edge. Al and In could modify significantly the density of states at the conduction band edge. Ga introduces states just at the bottom of the conduction band. Tl introduces states in the band gap. This study provides useful information on optimizing the thermoelectric efficiency of Mg2Si.
- Published
- 2011
25. Development and Application of Chen-Mobius Lattice Inversion Potential for Pd-Au Alloy
- Author
-
Kyeongjae Cho, Neeti Kapur, Xianghong Hao, Xianbao Duan, Bin Shan, and Zhengzheng Chen
- Subjects
Molecular dynamics ,Materials science ,Chemical physics ,Quantum mechanics ,Lattice (order) ,Alloy ,engineering ,Melting point ,Nanoparticle ,Particle size ,engineering.material ,Bimetallic strip ,Catalysis - Abstract
Bimetallic Pd-Au nanoparticles have received much attention due to their potential applications in catalysis. We have developed a Pd-Au alloy potential based on Chen-Mobius lattice inversion method and applied it to the investigation of the melting of Pd-Au binary nanoparticles via molecular dynamics simulations. Our simulation results show the particle size dependence of the melting point and an enrichment of Au atoms to the surface near melting temperature.
- Published
- 2011
26. Improvement in Contact Resistivity to thin film Bi2Te3
- Author
-
Bruce E. Gnade, Kyeongjae Cho, Rahul P. Gupta, John B. White, and Ka Xiong
- Subjects
Metal ,Materials science ,Surface preparation ,Sputtering ,Electrical resistivity and conductivity ,Annealing (metallurgy) ,visual_art ,Contact resistance ,Thermoelectric effect ,visual_art.visual_art_medium ,Composite material ,Thin film - Abstract
A study of the impact of surface preparation and post-deposition annealing on contact resistivity for sputtered Ni and Co contacts to thin film Bi2Te3 is presented. The contact resistance values obtained using the transfer length method (TLM) for Ni is compared to Co as a potential contact metal to Bi2Te3. Post-deposition annealing at 100°C on samples that were sputter cleaned reduces the contact resistivity to < 10-7 Ω-cm2 for both Ni and Co contacts to Bi2Te3. Co provided similar contact resistance values as Ni, but had better adhesion and less diffusion into the thermoelectric (TE) material, making it a suitable candidate for contact metallization to Bi2Te3 based devices.
- Published
- 2010
27. Impact of Dopants on the PbTe Thermoelectric Efficiency
- Author
-
Rahul P. Gupta, Bruce E. Gnade, Ka Xiong, John B. White, and Kyeongjae Cho
- Subjects
Materials science ,Thermoelectric generator ,Condensed matter physics ,Dopant ,Impurity ,Thermoelectric effect ,Doping ,Charge (physics) ,Electronic structure ,Thermoelectric materials - Abstract
We investigated the impact of doping group III elements (Al, Ga, In and Tl) on the electronic structure of PbTe by first principles calculations. The impurity-induced defect level changes with respect to the charge state of the impurity. We find that among the four elements, Tl is the best candidate for the enhancement of thermoelectric efficiency, consistent with the experimental data.
- Published
- 2010
28. First-Principles study of HfO2/:GaAs interface passivation by Si and Ge
- Author
-
Kyeongjae Cho, Min Huang, Ka Xiong, Geunsik Lee, Robert M. Wallace, and Weichao Wang
- Subjects
Materials science ,Passivation ,Interface (Java) ,business.industry ,Optoelectronics ,Charge (physics) ,Electronic structure ,business ,Electron loss ,Layer (electronics) - Abstract
We investigated the HfO2:GaAs interface electronic structure and interface passivation by first principles calculations. The HfO2:GaAs interface of HfO2 terminated with four O atoms and GaAs terminated two Ga atoms is found to be the most energetically favorable. It is found that the interface states mainly arise from the interfacial charge mismatch, more specifically from the electron loss of interfacial As. Si or Ge as an interfacial passivating layer helps to maintain the charge of interfacial As and hence reduce the interface states.
- Published
- 2009
29. Theoretical and Experimental Study of Tip Electronic Structure in Scanning Tunneling Microscope
- Author
-
Scott W. Schmucker, Kyeongjae Cho, John N. Randall, Joseph N Lyding, Min Huang, Heesung Choi, Kevin He, and Joshua B. Ballard
- Subjects
Materials science ,Fermi level ,Scanning tunneling spectroscopy ,Spin polarized scanning tunneling microscopy ,Electronic structure ,Conductive atomic force microscopy ,Molecular physics ,law.invention ,symbols.namesake ,law ,symbols ,Density of states ,Density functional theory ,Scanning tunneling microscope - Abstract
The atomic and electronic structures of pyramidal model STM tips of transition metals (W, Rh, Pd, Ir and Pt) were investigated using density functional theory (DFT) method. The calculated density of states show that d electrons of the apex atoms in the M4 (M = W, Rh, Pd, Ir, Pt) model tips behave differently near the Fermi level, with the dz2 state being dominant only for W tip. The electronic structures of pyramid structures of W and Pd single-atom tips with larger sizes are studied and compared. The density of states of Pd apex atom and W apex atom show different occupation of d-bands leading to asymmetric density of states for Pd tip. The asymmetric tunneling currents measured by W and Pt-Ir STM tips are explained by the calculated electronic structures of W and Pd model tips.
- Published
- 2009
30. First Principles Study of Metal/Bi2Te3Interfaces: Implications to Improve Contact Resistance
- Author
-
Husam N. Alshareef, Bruce E. Gnade, Rahul P. Gupta, Ka Xiong, Kyeongjae Cho, John B. White, and Weichao Wang
- Subjects
Metal ,Materials science ,Condensed matter physics ,visual_art ,Contact resistance ,Thermoelectric effect ,visual_art.visual_art_medium ,Electronic structure ,Ohmic contact - Abstract
We investigate the band offsets and stability for Ni/Bi2Te3and Co/Bi2Te3interfaces by first principles calculations. It is found that the surface termination strongly affects the band offsets. Ni and Co are found to form Ohmic contacts to Bi2Te3. The interface formation energies for Co/Bi2Te3interfaces are much lower than those of Ni/Bi2Te3interfaces. Our calculations are consistent with the experimental data.
- Published
- 2009
31. Diffusion Mechanism for Self Assembly on Inhomogeneously Strained Surfaces
- Author
-
Kyeongjae Cho, Mats I. Larsson, Bruce M. Clemens, and R. F. Sabiryanov
- Subjects
Surface diffusion ,Nanostructure ,Materials science ,Condensed matter physics ,Annealing (metallurgy) ,Nanowire ,Nucleation ,Kinetic Monte Carlo ,Self-assembly ,Diffusion (business) - Abstract
Growth of nanostructures with controlled shape, on inhomogeneously strained surfaces, is investigated by means of kinetic Monte Carlo (KMC) simulations. We propose a method to assemble self organized sub-lithographic nanostructures. The method is based on a strain-assisted mechanism for adatom surface diffusion and nucleation. For an inhomogeneous surface strain field there is normally a driving force toward the most tensile strained areas. It is shown by means of KMC simulations, that almost straight and continuous Ag nanowires can be produced on the Pt(111) surface if the growth is followed by high-temperature annealing. We suggest also how the method can be utilized as the first step of a process to reduce the circuit line width.
- Published
- 2003
32. First Principles Modeling Of High-K Dielectric Materials
- Author
-
Gyuchang Jun and Kyeongjae Cho
- Subjects
chemistry.chemical_compound ,Materials science ,Transition metal ,chemistry ,Gate oxide ,Chemical physics ,Gate dielectric ,Oxide ,Dielectric ,Amorphous solid ,ABINIT ,High-κ dielectric - Abstract
First-principles calculations are performed for high-K gate dielectric materials using model bulk and interface systems. Detailed electronic structures and atomic configurations are investigated for transition metal (Hf and Zr) oxide, metal doped silicate bulk system and a model Si-silicate interface system. Pseudo polymorphs of metal oxides are investigated to elucidate the underlying driving mechanisms in microscopic configurations of metal oxides and silicates in amorphous structures. We studied energetics and electronic structure of metal oxide pseudo morph with varying oxygen coordination. Dielectric constants of metal oxide and silicate materials are also investigated using the density functional perturbation theory method implemented in the ABINIT code. Electronic and dielectric properties of silica interface layers between high-κ dielectric and Si substrate are investigated leading to a confirmation that 1 nm is the physical limit of gate oxide thickness. Furthermore silica interface layer is found to have small dielectric constant of 3.4∼3.9.
- Published
- 2002
33. Kinetic Monte Carlo Simulations of Strain-Induced Nanopatterning on Hexagonal Surfaces
- Author
-
Kyeongjae Cho, William D. Nix, R. F. Sabiryanov, Byeongchan Lee, Mats I. Larsson, and Bruce M. Clemens
- Subjects
Condensed Matter::Materials Science ,Materials science ,Field (physics) ,Condensed matter physics ,Quantum dot ,Atom ,Dynamic Monte Carlo method ,Kinetic Monte Carlo ,Diffusion (business) ,Epitaxy ,k-nearest neighbors algorithm - Abstract
Guided self assembly of periodic arrays of quantum dots has recently emerged as an important research field not only to reduce component size and manufacturing cost but also to explore and apply quantum mechanical effects in novel nanodevices. The intention of this kinetic Monte Carlo (KMC) simulation study is to investigate self-organized nanopatterning on hexagonal surfaces for relaxed periodic surface strain fields applied to Pt(111) epitaxy. The KMC model is a full diffusion bond-counting model including nearest neighbor as well as second-nearest neighbor interactions with an event catalogue consisting of 8989 events modeling the effect of the biaxial surface strain field. The strain dependence of the fcc site and the saddle point for a Pt adatom migrating on top of the Pt(111) surface is calculated using the embedded atom method. Both the valley and the saddle point energies show an excellent linear dependence on the strain. These results are applied in the KMC model. The surface strain in this study is caused by a hexagonal network of dislocations at the interface between the substrate and a mismatched epitaxial layer. How the selforganization of deposited atoms is influenced by the surface strain will be addressed.
- Published
- 2002
34. Chemical Bonding of Polymer on Carbon Nanotube
- Author
-
Chengyu Wei, Kyeongjae Cho, and Deepak Srivastava
- Subjects
chemistry.chemical_classification ,Quantitative Biology::Biomolecules ,Materials science ,Nanotechnology ,Polymer ,Carbon nanotube ,engineering.material ,Smart polymer ,law.invention ,Condensed Matter::Soft Condensed Matter ,Condensed Matter::Materials Science ,Molecular dynamics ,Chemical bond ,chemistry ,Coating ,law ,engineering ,Molecule ,Composite material ,Nanoscopic scale - Abstract
Recently, carbon nanotubes are considered as nanoscale fibers, which can strengthen polymer composite materials. Nanotube-polymer composite materials can be used for micron scale devices with designed mechanical properties and smart polymer coating to protect materials under extreme physical conditions such as microsatellites. To explore these possibilities it is important to develop a detailed atomic scale understanding of the mechanical coupling between polymer matrix and embedded nanotubes. In this work we study the chemical bonding between polymer molecules and carbon nanotubes (CNTs) using molecular dynamics. Study shows that the bonding between polyethylene and a CNT is energetically favorable. Chemical bonds can be formed at multiple sites, which make the mechanical load transfer from the polymer chain to the tube more favorable. We will discuss about the resulting mechanical coupling between the CNTs and polymer matrix to develop efficient nano-composite materials.
- Published
- 2001
35. Ab initio Study of Metal Atoms on SWNT Surface
- Author
-
Shu Peng and Kyeongjae Cho
- Subjects
Nanotube ,Materials science ,Diffusion barrier ,Binding energy ,Inorganic chemistry ,Ab initio ,chemistry.chemical_element ,Carbon nanotube ,law.invention ,Pseudopotential ,Adsorption ,chemistry ,Chemical physics ,law ,Titanium - Abstract
Interactions of metal atoms (Al, Ti) with semiconducting single walled carbon nanotube (SWNT) are investigated using first-principles pseudopotential calculations. Six different adsorption configurations for aluminum and titanium atoms are studied. Comparison of the energetics of these metal atoms on (8,0) SWNT surface shows significant differences in binding energy and diffusion barrier. These differences give an insight to explain why most of metal atoms (such as Al) form discrete particles on nanotube while continuous nanowires are obtained by using titanium in the experiment.
- Published
- 2001
36. Temperature and Strain-Rate Dependent Plastic Deformation of Carbon Nanotube
- Author
-
Kyeongjae Cho and Chengyu Wei
- Subjects
Work (thermodynamics) ,Molecular dynamics ,Materials science ,Strain (chemistry) ,law ,Thermal fluctuations ,Carbon nanotube ,Plasticity ,Strain rate ,Composite material ,Rotation ,law.invention - Abstract
In this work we use classical molecular dynamics to study strain rate and temperature dependent plasticity of carbon nanotube (CNT) under compressive strain. We focus on two types of defects: sp3 bond formation and bond rotation. Our simulation shows that thermal fluctuations help the strained CNT to overcome the local energy barrier to obtain plastic deformation. The yielding strain of a compressed CNT found to be strain-rate and temperature dependent, and low strain rate limit of the yielding strain is estimated to be less that 6%.
- Published
- 2001
37. External Chemical Reactivity of Fullerenes and Nanotubes
- Author
-
Seongjun Park, Kyeongjae Cho, and Deepak Srivastava
- Subjects
Fullerene chemistry ,Fullerene ,Materials science ,Graphene ,Ab initio ,Selective chemistry of single-walled nanotubes ,Carbon nanotube ,law.invention ,Carbon nanobud ,law ,Chemical physics ,Physics::Atomic and Molecular Clusters ,Organic chemistry ,Density functional theory - Abstract
The external chemical reactivity of graphene sheet, fullerenes and carbon nanotubes has been investigated. The total reaction energy is analyzed with several contributing terms and formulated as a function of the pyramidal angles of C atoms. We have determined the parameters for the formulae from ab initio simulation of graphene. We have applied them to predict hydrogenation energy of several nanotubes and C60, and demonstrated that the predicted total reaction energies are very close to the results of total energy pseudo-potential density functional theory calculations. This analysis can be used to predict the reaction energy and local bonding configuration of a reactant with diverse fullerenes and nanotubes within 0.1 eV accuracy.
- Published
- 2001
38. Endo-fullerenes and Doped Bucky Onions as Seed Materials for Solid State Quantum Bits
- Author
-
Deepak Srivastava, Kyeongjae Cho, and Seongjun Park
- Subjects
Materials science ,Fullerene ,Solid-state physics ,Condensed matter physics ,Dopant ,Spins ,Qubit ,Doping ,Thermal stability ,Quantum ,Molecular physics - Abstract
Two different models for solid-state quantum bits have been investigated. Both are based on the nuclear spin of doped atoms in endo-fullerenes or bucky-onions. 1H or 31P have been tested as suitable dopant atoms because they have half nuclear spins. The thermal stability and electronic properties of the dopant atoms and the encapsulating cages have been examined with ab-initio pseudo potential density functional methods, and the results show that both models are suitable for single qubit applications.
- Published
- 2001
39. First-Principles Study of SI(lll) Homoepitaxy
- Author
-
Efthimios Kaxiras and Kyeongjae Cho
- Subjects
Pseudopotential ,Surface (mathematics) ,Condensed Matter::Materials Science ,Materials science ,Chemical physics ,Cluster (physics) ,Diffusion (business) ,Epitaxy ,Flux rate ,Energy (signal processing) - Abstract
Epitaxial growth on the Si(111) surface is studied using first-principles total-energy pseudopotential calculations. The energetics of added Si atoms essentially determines epitaxial growth modes under different growth conditions (surface temperature, Si flux rate, and surface step density). We have determined the surface adatom diffusion barriers and cluster formation energies; we use these microscopic energy parameters to address the possibilities for macroscopic morphological evolution of the surface under different conditions.
- Published
- 1998
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