Yong-Chan Jeong

Y-doped BaZrO₃에서의 산소 공공과 프로톤의 이동

We studied the transfer of oxygen vacancy and proton in Y-doped BaZrO₃(BYZ) using density functional theory (DFT). An oxygen vacancy was generated in the 2×2×2 BYZ superstructure by replacing two Zr atoms with two Y atoms to satisfy the charge neutrality condition. The O vacancy transfer between the first and second nearest O atom sites from a Y atom showed the lowest activation energy barrier of 0.42 eV, compared to the other transfers between first and first, and second and second in the superstructure. Two protons were inserted in the structure by adding a proton and hydroxyl that were supplied by the dissociation of a water molecule. The two protons bonded to the first and second nearest O atoms were energetically the most favorable. The activation energy barrier for a proton transfer in the structure was 0.51 eV, when either proton transferred to its neighbor O atom. This value was well matched with the experimentally determined one.

BaZrO₃의 부피 변화가 프로톤 전도 에너지 장벽에 미치는 영향

We studied the energy barrier for proton conduction with volume variation in BaZrO₃ using a first principles study to investigate an optimum volume for the proton conduction. The volume increase of BaZrO₃ was expected to decrease the energy barrier for proton rotation and to increase that for proton transfer, and these trends could be extrapolated when the volume was decreased. However, the energy barriers for the proton transfer with the volume decrease were increased, while all the other energy barriers varied as expected. We could explain this unexpected behavior by the bent Zr?O?Zr structure, when the volume was decreased.

Effect of amino ligand size of Si precursors on initial reaction with an –OH-terminated Si(001) surface for atomic layer deposition

The effect of the amino ligand size of Si precursors on the initial reaction with an –OH-terminated Si(001) surface was investigated on the basis of the density functional theory for atomic layer deposition (ALD). The following six Si precursors were chosen in order of increasing ligand size to compare their initial reactions on the surface: dimethylaminosilane (SiH3[N(CH3)2], DMAS), ethylmethylaminosilane (SiH3[N(CH3C2H5)], EMAS), diethylaminosilane (SiH3[N(C2H5)2], DEAS), ethylisopropylaminosilane (SiH3[N(C2H5C3H7)], EIPAS), diisopropylaminosilane (SiH3[N(C3H7)2], DIPAS), and dipropylaminosilane (SiH3[N(C3H7)2], DPAS). The adsorption energies of the precursors and reaction energy barriers, and the desorption energies of the by-products were compared as a function of ligand size to evaluate the processing temperature range for ALD. DIPAS showed the widest temperature range for ALD among the six Si precursors.

Effect of Copper Oxide on Migration and Interaction of Protons in Barium Zirconate

The effect of copper oxide on migration and interaction of protons in barium zirconate was investigated using density functional theory. One copper atom was substituted for a zirconium atom site, and a proton was added to a 3×3×3 barium zirconate superstructure. An energy barrier of 0.89 eV for proton migration was the highest among several energy barriers. To investigate the interaction between multiple protons and a copper atom, two protons were added to the superstructure. Various proton positions were determined by the interaction between the two protons and the copper atom.

Effects of Potassium Ion Substitution on Lattice Parameters and Proton Migration in Barium Phosphate

The effects of substituting a potassium ion for a barium ion in barium phosphate on lattice parameters and proton migration were investigated using density functional theory. A proton inserted into the material preferred to be attached to an oxygen ion near the potassium ion to compensate for the positive charge of the potassium ion that is less than that of the barium ion. Lattice parameters were investigated as a function of the potassium ion concentration. The lattice parameter a increased linearly with the potassium ion concentration, while the lattice parameter c remained almost constant. These trends were in good agreement with the experimental results. When the proton migrated from the ab-plane containing the potassium ion to the plane free of the potassium ion, a high energy barrier of 0.58 eV was required for proton migration. This value was also in good agreement with the experimentally measured energy barriers (0.53–0.58 eV).

Regular Distribution of -OH Fragments on a Si (001)-c(4×2) Surface by Dissociation of Water Molecules

Adsorption of a water molecule on a Si (001) surface and its dissociation were studied using density functional theory to study the distribution of -OH fragments on the Si surface. The Si (001) surface was composed of Si dimers, which buckle in a zigzag pattern below the order-disorder transition temperature to reduce the surface energy. When a water molecule approached the Si surface, the O atom of the water molecule favored the down-buckled Si atom, and the H atom of the water molecule favored the up-buckled Si atom. This is explained by the attractions between the negatively charged O of the water and the positively charged down-buckled Si atom and between the positively charged H of the water and the negatively charged up-buckled Si atom. Following the adsorption of the first water molecule on the surface, a second water molecule adsorbed on either the inter-dimer or intra-dimer site of the Si dimer. The dipole-dipole interaction of the two adsorbed water molecules led to the formation of the water dimer, and the dissociation of the water molecules occurred easily below the order-disorder transition temperature. Therefore, the 1/2 monolayer of -OH on the water-terminated Si (001) surface shows a regular distribution. The results shed light on the atomic layer deposition process of alternate gate dielectric materials, such as .