Dae-Chul Park

Surface modification of zinc oxide nanoparticles by aminopropyltriethoxysilane

Commercial zinc oxide nanoparticles (20–30 nm) were coated by aminopropyltriethoxysilane (APTES) under varying environments. Three different processes, acidic, basic and toluene were used. The effects of coating conditions (acidic, basic and toluene) on the grafting, structural and optical properties of these nanoparticles were studied. In the three cases, it was possible to control the coating and according to X-ray diffraction, BET, TEM and SEM results, it is clear that the APTES coating plays a role of growth inhibitor even at 800 °C...

Oxygen defects related to electrical properties of La-doped BaTiO3

The oxygen diffusion coefficients of undoped and La-doped BaTiO3 were evaluated by secondary ion mass spectrometry (SIMS). The La-doped BaTiO3 has markedly lower oxygen diffusion coefficient than the undoped BaTiO3. Regarding the effect of the amount of La doped, the volume diffusion coefficient of oxygen was found to be dependent on the amount of La doped. The oxygen diffusion behavior of samples synthesized by various cooling processes was also compared. The samples that were very slowly cooled (2°C/h from 1250 to 700°C) showed markedly low oxygen diffusion coefficient in the low-temperature region. It was found that the difference in cooling rate during the calcination process has significant effect on the oxygen diffusion behavior of La-doped BaTiO3. Regarding the electrical properties of samples, the dielectric properties were strongly influenced by the cooling rate, whereas the dc resistivities were not influenced by the cooling rate.

SIMS depth profiling of N and In in a ZnO single crystal

Nitrogen (4 x 10 15 ions/cm 2 ) and indium (1 x 10 16 ions/cm 2 ) ions with 200 and 170 keV, respectively, were co-implanted into a ZnO single crystal at room temperature. The ion-implanted sample was annealed at 800 °C under an oxygen atmosphere. The diffusion behaviors of N and In in relation to annealing times were studied by SIMS. Diffusion of N in the crystal was not detected, while In was observed to diffuse deeper into the single crystal during annealing. Due to diffusion of In away from the surface, a second peak of In was created which overlapped with that of N at the limited region of the ZnO crystal. It was confirmed by TEM observation that a band-like layer was formed in the post-annealed sample.

Diffusion and solubility of holmium ions in barium titanate ceramics

Ho ion solubility and diffusivity were evaluated in barium titanate ceramics in which Ho ions were implanted with an accelerating voltage of 500 keV. The depth profile of the ions was composed of three regions in the post-annealed sample: the first was the precipitation region, the second was a region created by lattice diffusion of Ho ions, and the third was a region created by grain-boundary diffusion. The Ho lattice diffusion characteristics were similar to those of Ni ion diffusion in barium titanate ceramics, and we concluded that the diffusion mechanism was the same as that responsible for Ni ions. The Ho ions diffused through the B-site (Ti-site) and were then exchanged with A-site ions. This mechanism suggests that a small number of Ho ions dissolved in the B-site. Preferential grain-boundary diffusion was also observed. The grain-boundary diffusion coefficients were four to five orders of magnitude larger than the volume diffusion coefficients. The solubility of Ho ions was estimated to be a few thousand parts per million in barium titanate ceramics.