ZnO thin films were synthesized on Si substrates by MOCVD using diethyl zinc as a precursor. Effects of O_2/DEZ gas mixing ratio on the growth rate, surface morphology, preferred orientation, and electrical properties of the ZnO thin films were investigated with SEM, XRD, and Hall measurement. The surface reflectance variations of ZnO thin films were analyzed using laser-photometer apparatus. As the O_2/DEZ mixing ratio increased, growth rate and I_(002)/I_(101) in XRD of ZnO thin films decreased, and the crystal structure was changed from columnar to planar structure. All ZnO films deposited at various CVD conditions exhibited c-axis (002) plane preferred orientation. The electrical properties of ZnO thin films mainly depended on the carrier mobility.

We investigated the dielectric and mechanical properties of ceramic polymer composite xBNT - (1-x)LCP (x= 0, 10, 20, 30, 40 vol.%). The disk shaped BNT (BaNd2Ti4O12) - LCP (liquid crystal polymer) composite samples were prepared by compression molding method. With increasing the BNT content in composites from 10 to 40 vol.%, the dielectric constant increased but the dielectric loss as well as bending strength of composites reduced. These composites were well described with modified Lichtenecker`s model having k = 0.392 and 0.303 for the first and second ball milled BNT filled composites, which means that the BNT filler in composites are well dispersed. The dielectric constant of the composite comprised of the second milled BNT (D50 = 1.39 um) was higher that of the composite of the first milled BNT (D50= 2.45 um), which seems to be related with the different particle size and dispersion of BNT fillers in LCP matrix. The bending strength of the composite containing the second milled BNT was superior to that of the composite of the first milled BNT.

Abstract: Cu doped SnO(2) thick films for gas sensors were fabricated by screen printing method on alumina substrates and annealed at 500℃ in air, respectively. Structural properties of SnO(2) by X-ray diffraction showed (110), (101) and (211) dominant tetragonal phase. The effects of catalyst Cu in SnO(2)-based gas sensors were investigated. Sensitivity of SnO(2):Cu sensors to 2,000 ppm CO(2) gas and 50 ppm H(2)S gas was investigated for various Cu concentration. The highest sensitivity to CO(2) gas and H(2)S gas of Cu doped SnO(2) gas sensors was observed at the 8 wt% and 12 wt% Cu concentration, respectively. The improved sensitivity in the Cu doped SnO(2) gas sensors was explained by decrease of electron depletion region in Cu and SnO(2) junction, and increase of reactive oxygen and surface area in the SnO(2).

Abstract: Nanoporous titanium dioxide (TiO(2)) is very attractive material for various applications due to the high surface to volume ratio. In this study, we have fabricated nanoporous TiO(2) thin films on Si by anodic oxidation. 500-nm-thick titanium (Ti) films were deposited on Si by using electron beam evaporation. Nanoporous structures in the Ti films were obtained by anodic oxidization using ethylene glycol electrolytes containing 0.3 wt% NH(4)F and 2 vol% H(2)O under an applied bias of 5 V. The diameter of nanopores in the Ti films linearly increased with anodization time and the whole Ti layer could become nanoporous after anodizing for 3 hours, resulting in vertically aligned nanotubes with the length of 200～ 300 nm and the diameter of 50～80 nm. Upon annealing at 600℃ in air, the anodized Ti films were fully crystallized to TiO(2) of rutile and anatase phases. We believe that our method to fabricate nanoporous TiO(2) films on Si is promising for applications to thin-film gas sensors and thin-film photovoltaics.