"Hanchul Kim" / Journal: journal of applied physics - Searchworks@Jio Institute Digital Library Search Results

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Author: Jung Hyun Oh, Moon-Gyu Jang, Hanchul Kim, Moon, S. E., and Mincheol Shin
Subjects: PHONONS, HETEROSTRUCTURES, SILICON compounds, PLATINUM silicide, GREEN'S functions, SCATTERING (Physics), INTERFACES (Physical sciences)
Abstract: Using a Green function method based on an atomic vibration model, herein we report the results from our investigation of phonon transport through multiple Si/PtSi layered structures. In contrast with values predicted using elastic wave theory and an impedance mismatch method, we find that a detailed atomic-vibration approach exhibits significantly suppressed phonon transport and leads to a 30-times reduction of the thermal conductance, compared to that of Si bulk. We attribute the origin of the suppression to the lack of PtSi phonon modes in the energy range of 20-30 meV, and to the effects of interface scattering between Si and PtSi layers. [ABSTRACT FROM AUTHOR]
Published: 2015
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Author: Miyoung Kim and Hanchul Kim
Subjects: Ferromagnetism -- Analysis, Iron alloys -- Magnetic properties, Iron alloys -- Electric properties, Platinum -- Electric properties, Platinum -- Magnetic properties, Dielectric films -- Electric properties, Dielectric films -- Magnetic properties, Thin films -- Electric properties, Thin films -- Magnetic properties, Physics
Abstract: The structural properties and magnetic phase stability of [Fe.sub.(x)][Pt.sub.(1-x)] alloys in [L1.sub.2] crystal structure in bulk as well as thin film on Pt (110) substrate are analyzed by using highly precise full-potential linearized augmented plane-wave method within generalized gradient approximation. The ferromagnetic (FM) preference of thin film is predicted to fast suppress as the film thickness has increased and the antiferromagnetic (AFM) preference is recovered for the film thickness of five atomic layers.
Published: 2009

Author: Dae Hwan Kim, Ji-Young Noh, Gun Hee Kim, Byung-Du Ahn, Hanchul Kim, Yong-Sung Kim, Jun Ho Song, Jun Hyung Lim, Ho-Hyun Nahm, and Je-Hun Lee
Subjects: Amorphous semiconductors, Effective mass (solid-state physics), Molecular geometry, Atomic orbital, Chemistry, Inorganic chemistry, Analytical chemistry, General Physics and Astronomy, Energy level, Density functional theory, Electron, Stoichiometry
Abstract: Based on density-functional theory calculations, the effects of cation compositions on electronic structures of In-Sn-Zn-O amorphous semiconductors were investigated. We considered various composition ratios of In, Sn, and Zn in O stoichiometric condition, and found that the conduction band minimum (CBM) energy level decreases and the valence band tail (VBT) energy level extent increases as the sum of In and Sn ratios (RIn+RSn) increases. The CBM lowering is attributed to the increased overlap of the In-5s and Sn-5s orbitals as the RIn+RSn increases, and correspondingly the electron effective masses (me*) are found to be reduced. The VBT increase is found to be due to the increased density of the In and Sn atoms, near which the O-2p inter-site ppσ* coupling is larger than that near the Zn atoms. The acute O-(In,Sn)-O angles are suggested to be structurally important, giving the stronger O-O ppσ* coupling.
Published: 2013

Author: Ji-Young Noh, Hanchul Kim, Changhan Park, and Yong-Sung Kim
Subjects: Free electron model, Range (particle radiation), Electron density, Materials science, Condensed matter physics, Dopant, Doping, Wide-bandgap semiconductor, General Physics and Astronomy, chemistry.chemical_element, Condensed Matter::Materials Science, chemistry, Aluminium, Condensed Matter::Superconductivity, Physics::Atomic and Molecular Clusters, Density functional theory
Abstract: We investigate the maximum available free electron carrier density in Al-doped n-type ZnO, based on density-functional theory calculations. The Coulomb interactions between the Al dopants and the Zn-vacancy native acceptors are found to limit the carrier density. In typical growth conditions, the n-type doping limit is found to be in the range of 1019 ∼ 1021 cm−3.
Published: 2013

Author: Hanchul Kim and Miyoung Kim
Subjects: Tetragonal crystal system, Materials science, Ferromagnetism, Condensed matter physics, Phase (matter), Alloy, Relaxation (NMR), engineering, General Physics and Astronomy, Antiferromagnetism, Substrate (electronics), engineering.material, Thin film
Abstract: The structural properties and magnetic phase stability of Fe(x)Pt(1−x) alloys in L12 crystal structure in bulk as well as thin film on Pt (110) substrate are studied by means of the highly precise full-potential linearized augmented plane-wave method within generalized gradient approximation. The antiferromagnetic (AFM) phase is found to be preferred over the ferromagnetic (FM) phase for FePt3 bulk alloy in agreement with experiment while FexPt(1−x), where x=0.25 and 0.5 with a film thickness smaller than 0.5nm, favor the FM phase. The total energy calculation assuming pseudomorphic strain reveals that the AFM preference for bulk is maintained in wide range of tetragonal distortion up to the value of 22% reached by the surface relaxation of thin film, implying that the magnetic configuration change from AFM to FM at the thin film surface is originated in rather complex surface effects beyond the structural relaxation. The FM preference of thin film is predicted to fast suppress as the film thickness incre...
Published: 2009

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