Papers by Author: Yong Chae Chung

Abstract: The electronic structure and defect states of 6.25% transition metal (TM = Fe and Co) doped rutile titanium dioxide were investigated by ab initio ultrasoft pseudopotential plane wave method based on density functional theory. When a Fe or Co atom was substituted for a Ti site of TiO2 lattice, additional unoccupied 3d-states of TM appeared as defect states in band-gap and occupied 3d-states represented metallic behavior (half-filled states).It was found that two occupied defect states and one half-filled defect state were the 3d-states of TM from the calculation of band decomposed charge density. The higher unoccupied states were hybridized with unoccupied oxygen 2p-states and located at the middle of band-gap.

Abstract: We used ab initio pseudopotential plane wave methods to study the magnetic and electronic properties of transition-metal doped ¯-SiC. It is found that the SiC:Cr reveals stable ferromagnetism with permanent magnetic moments as large as 2 μB regardless of substitution site. In addition, the SiC:CrSi is predicted to have good electron mobility and wide spin band-gap of 1.58 eV with the Fermi level at the center of the gap, which is desirable for realizing spintronic devices.

Abstract: The structural configurations of atom constituting materials are one of the fundamental factors in the study of physical properties of materials. Presented in this paper is a mathematical and computational methodology to efficiently classify a given atomic structure of an arbitrary material into groups of atoms in BCC, FCC, and HCP crystal structures. The approach is based on the angle distributions among neighboring atoms efficiently identified by a computational geometry technique called Voronoi diagram. In this paper, the presented mathematical theory was applied to analyze a multi-layer atomic structure in a geometric perspective so that a best condition for thin film growth can be found.

Abstract: The local acceleration effects, which are peculiar phenomena during atomic scale deposition process, were investigated byMolecular Dynamics (MD) simulation. The values of local acceleration were distributed widely for various surface orientations. Deposited atoms were accelerated along the potential energy surface, and accelerated values were evidently dependent on the local configuration of the surface. In contrast, the local acceleration became negligibly small for clusters consisting of many atoms.

Abstract: Using the ab initio pseudopotential calculations, the surface diffusion and incorporation process at the interface of Fe-Al multilayer system were quantitatively investigated. The hollow site was most stable adsorption site on both Al (001) and Fe (001) surface. The adsorption energies were 8.62 eV for Fe/Al (001) and 5.30 eV for Al/Fe (001) system. The calculated energy barriers for the surface diffusion of adatom were 0.89 eV and 0.61 eV for each system. The energy barrier for the incorporation of Fe adatom into the Al substrate was calculated to be 0.38 eV and the energy gain of the system was 0.49 eV. However, the Al adatom required relatively large energy barrier, 0.99 eV for the incorporation into the Fe substrate resulting in 0.13 eV increase in total energy of the system.