Bumjoon Kim

Photocatalytic TiO2 deposition by chemical vapor deposition

Dip-coating, spray-coating or spin-coating methods for crystalline thin film deposition require post-annealing process at high temperature. Since chemical vapor deposition (CVD) process is capable of depositing high-quality thin films without post-annealing process for crystallization, CVD method was employed for the deposition of TiO2 films on window glass substrates. Post-annealing at high temperature required for other deposition methods causes sodium ion diffusion into TiO2 film from window glass, resulting in the degradation of photocatalytic efficiency. Anatase-structured TiO2 thin films were deposited on window glass by CVD, and the photocatalytic dissociation rates of benzene with CVD-grown TiO2 under UV exposure were characterized. As the TiO2 film deposition temperature was increased, the (112)-preferred orientations were observed in the film. The (112)-preferred orientation of TiO2 thin film resulted in a columnar structure with a larger surface area for benzene dissociation. Obviously, benzene dissociation rate was maximum when the degree of the (112) preferential orientation was maximum. It is clear that the thin film TiO2 should be controlled to exhibit the preferred orientation for the optimum photocatalytic reaction rate. CVD method is an alternative for the deposition of photocatalytic TiO2.

Structural Analysis on Photocatalytic Efficiency of TiO2 by Chemical Vapor Deposition

Structural analysis of anatase TiO2 films on window glass by chemical vapor deposition (CVD) was performed. Relationships between preferred orientation and photocatalytic activity of polycrystalline TiO2 films were investigated. Photocatalytic activity was affected by crystalline orientation that depended on the deposition temperature. -oriented TiO2 films were obtained at 360°C, while -oriented films were obtained at other temperatures. Photocatalytic activity of the -oriented film was greater than that of the -oriented film. The film with -preferred orientation exhibited a columnar structure resulting in a larger surface area for photocatalytic reaction than the films with -preferred orientation. Also, the film with -preferred orientation exhibited a facet consisting of s-faces {100} which showed the larger surface energy theoretically. It is clear that fabrication of the thin film TiO2 by CVD should be controlled to exhibit the -preferred orientation for the optimum photocatalytic efficiency.

Influence of the Density of Crack-Initiating Defects on Crack Spacing for GaN Films on Si(111) Substrate

This study examines the cracking of GaN films grown on Si(111) substrates, with particular focus on the effect of the density of crack-initiating defects (CIDs) on the crack spacing. The relationship between the CID density and crack spacing was examined by comparing specimens of the same thickness and under the same stress but with different CID density. The CID density in the GaN layer was changed by varying the ion-implanted area using patterning prior to metal–organic chemical vapor deposition (MOCVD) growth. The crack spacing decreased with increasing CID density, but this effect could not be explained by the previous model. Therefore, a CID-density related factor, nd, was newly introduced to explain the crack spacing and film stress relationship.

PROPERTIES OF COPPER LAYER ON Si(100) FROM Cu(dmamb)2

Cu seed layer was deposited by chemical vapor deposition using new Cu precursor, Cu(dmamb)2. The Cu layers still need the barrier layer to prevent the diffusion, so Ta and Ti were used for the barrier layer on Si(100). Low temperature (LT) copper buffer layer was introduced and the effect of the buffer on the Cu films was investigated. The grown Cu layers were analyzed using FESEM, XRD, and four point probe measurement. The Cu seed layers were successfully deposited using Cu(dmamb)2 precursor. Better thickness uniformity was obtained in the Cu films with the LT Cu buffer, which lowered the electrical resistivity.