• Proceedings of the Korean Vacuum Society Conference
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• 2000.02a
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• pp.142-142
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• 2000

We performed a total energy calculation of clean alumunum surfaces of three low indices based on a density functional theory with a local density approximation, using the Ceperly-Alder exhange correlation parametrized by Perdew and Zunger. Pseudopotentials were generated for Al of which the plane wave cut-off was 15Ry. We used Gaussian broadening of a Fermi level to accelerate the convergence of our calculation with the Gaussian energy smearing parameter of 0.005Ry. First, we determine the lattice constant of the aluminum of an face-centered-cubic structure to be 3.96 which is comparable to the experimental data of 4.05 . The cohesive energy of 4.20eV/atom and the bulk modulus of 0.775$\times$1012dyne/cm2 are also comparable to the experimental values of 3.39eV/atom and 0.772$\times$1012dyne/cm2, respectively. Then we investigated the surface relaxation of (100), (110) and (111) surfaces using a 9-layer slab separated by 6-layer thick vacuum. The results are consistent with the existing experimental results.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.05a
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• pp.215-215
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• 2012

본 연구에서는 화학적 도핑 방법 및 플라즈마 표면 처리방법을 이용하여 그래핀 내 Electron & Hole carrier 들의 농도를 변화시켜, 전계효과에 따른 Graphene Field Effect Transistors (GFETs) 소자의 전기적 특성 변화를 확인 하였으며, 전기적 특성 결과 중에 Dirac-point (DP) 이동에 따른 그래핀 $E_F$ (Fermi-energy) level 변화를 계산 및 유추 하였으며, Ultraviolet Photoelectron Spectroscpy (UPS)를 이용하여 실제적으로 He 소스 광전자를 그래핀 샘플 표면에 입사하여 나오는 전자들의 Kinetic Energy($E_K$) 결과를 이용하여 Work function (WF) 변화를 확인 및 검증하였다.

• Bulletin of the Korean Chemical Society
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• v.16 no.4
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• pp.299-304
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• 1995

In order to find out the relationship between electronic structures of metal oxychlorides (MOCl) and their physicochemical properties, we have carried out the tight-binding band electronic structure calculations with Extended Huckel (EH) method for TiOCl, VOCl and FeOCl. The relative contribution of metal atom to DOS at Fermi level increases in the order of Ti, V and Fe, which is parallel to the reactivities of MOCl toward guest species. The M2+ ion plays a crucial role in the electric conductivity of MOCl and its intercalation compounds. Hopping conduction theory is applied to explain the increase of conductivity after intercalation.

• Korean Journal of Materials Research
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• v.17 no.12
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• pp.637-641
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• 2007

The total energy and strength of Mg alloy doped with Al, Ca and Zn, were calculated using the density functional theory. The calculations was performed by two programs; the discrete variational $X{\alpha}\;(DV-X{\alpha})$ method, which is a sort of molecular orbital full potential method; Vienna Ab-initio Simulation Package (VASP), which is a sort of pseudo potential method. The fundamental mixed orbital structure in each energy level near the Fermi level was investigated with simple model using $DV-X{\alpha}$. The optimized crystal structures calculated by VASP were compared to the measured structure. The density of state and the energy levels of dopant elements was discussed in association with properties. When the lattice parameter obtained from this study was compared, it was slightly different from the theoretical value but it was similar to Mk, and we obtained the reliability of data. A parameter Mk obtained by the $DV-X{\alpha}$ method was proportional to electronegativity and inversely proportional to ionic radii. We can predict the mechanical properties because $\Delta{\overline{Mk}}$is proportional to hardness.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.7
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• pp.589-593
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• 2005

The electronic states of ZnO doped with Al, Ga and In, which belong to III family elements in periodic table, were calculated using the density functional theory. In this study, the calculation was performed by two Programs; the discrete variational Xa (DV-Xa) method, which is a sort of molecular orbital full potential method; Vienna Ab-initio Simulation Package (VASP), which is a sort of pseudo potential method. The fundamental mixed orbital structure in each energy level near the Fermi level was investigated with simple model using DV-Xa. The optimized crystal structures calculated by VASP were compared to the measured structures. The density of state and the energy levels of dopant elements were shown and discussed in association with properties.

• Proceedings of the KIEE Conference
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• 2002.07c
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• pp.1609-1611
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• 2002

Multi-layer organic electroluminescent(EL) devices with Al-CsF composite as a cathode were fabricated. This device privides low driving voltage and high quantum efficiency. CsF is evaporated onto and diffuse into electron transport layer. $Alq_3$. The Fermi level of $Alq_3$ moves towards the LUMO level.

• Korean Journal of Materials Research
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• v.30 no.3
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• pp.117-122
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• 2020

The effects of fast neutron irradiation on the electrical and optical properties of Li (3 at%) doped ZnSnO (ZTO) thin films fabricated using a sol-gel process are investigated. From the results of Li-ZTO TFT characteristics according to change of neutron irradiation time, the saturation mobility is found to increase and threshold voltage values shift to a negative direction from 1,000 s neutron irradiation time. X-ray photoelectron spectroscopy analysis of the O 1s core level shows that the relative area of oxygen vacancies is almost unchanged with different irradiation times. From the results of band alignment, it is confirmed that, due to the increase of electron carrier concentration, the Fermi level (E_F) of the sample irradiated for 1,000 s is located at the position closest to the conduction band minimum. The increase in electron concentration is considered by looking at the shallow band edge state under the conduction band edge formed by fast neutron irradiation of more than 1,000 s.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.265-265
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• 2013

We have investigated the influences of dangling bonds generated by alpha particle irradiation on friction and adhesion properties of graphene. Single layer of graphene grown with chemical vapor deposition on copper foil was irradiated by the alpha beam with the average energy of 3.04 MeV and the irradiation dosing between $1{\times}10^{14}$ and $1{\times}10^{15}$/$cm^3$. Raman spectroscopic showed that the ${\pi}$ electron states below Fermi level arises and the $I_D$/$I_G$ increases as increasing the dosing of alpha particle irradiation. The core level X-ray photoelectron (XPS) revealed that these defects represent the creation of various carbon-related defects and dangling bond. The nanoscale tribological properties were investigated with atomic force microscopy in ultrahigh vacuum. The friction appeared to increase remarkably as increasing the amount of dosing, indicating that the dangling bonds on graphene layers enhances the energy dissipations in friction. This trend can be explained by the additional channel of energy dissipation by dangling bond or O- and H- terminated clusters created by alpha particle irradiation.

• Bulletin of the Korean Chemical Society
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• v.30 no.6
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• pp.1353-1356
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• 2009

This study examined the adsorption of CO on a Mo(110) surface by Thermal Desorption Spectroscopy (TDS) and synchrotron-radiation based photoemission spectroscopy (SRPES). CO desorption was observed at approximately 400 K ($\alpha$-CO) and > 900 K ($\beta$-CO). When CO was exposed to Mo(110) at 100 K, it showed a tilted structure at low CO coverage and a vertical structure after saturation of the tilted CO. After heating the CO-precovered sample to 900 K, a broad peak at 12 eV below the Fermi level was identified in the valence level spectra, which was assigned to either the 4$\sigma$-molecular orbital of CO, or 2s of dissociated carbon. TDS results of the $\beta$-CO showed a first order desorption. These results are in a good agreement with the observations of CO adsorption on W(110) surfaces.

• Journal of Korean Society of Environmental Engineers
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• v.38 no.5
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• pp.242-248
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• 2016

The overall reaction rate of fuel cell is governed by oxygen reduction reaction (ORR) in the cathode due to its slowest reaction compared to the oxidation of hydrogen in the anode. The ORR efficiency can be readily evaluated by examining the adsorption strength of atomic oxygen on the surface of catalysts (i.e., known as a descriptor) and the adsorption energy can be controlled by transforming the surface geometry of catalysts. In the current study, the effect of the surface geometry of catalysts (i.e., strain effect) on the adsorption strength of atomic oxygen on platinum catalysts was analyzed by using density functional theory (DFT). The optimized lattice constant of Pt ($3.977{\AA}$) was increased and decreased by 1% to apply tensile and compressive strain to the Pt surface. Then the oxygen adsorption strengths on the modified Pt surfaces were compared and the electron charge density of the O-adsorbed Pt surfaces was analyzed. As the interatomic distance increased, the oxygen adsorption strength became stronger and the d-band center of the Pt surface atoms was shifted toward the Fermi level, implying that anti-bonding orbitals were shifted to the conduction band from the valence band (i.e., the anti-bonding between O and Pt was less likely formed). Consequently, enhanced ORR efficiency may be expected if the surface Pt-Pt distance can be reduced by approximately 2~4% compared to the pure Pt owing to the moderately controlled oxygen binding strength for improved ORR.