Papers by Author: Wan In Lee

Abstract: We present a study of the photoresist (PR) etching and the low-k materials damage using a ferrite-core inductively coupled plasma (ICP) etcher, in order to develop an etching process for the low-k dielectric devices. We reveal that the N2/O2 flow ratio and bias power affected the PR etching rate. By Fourier transform infrared spectroscopy and HF dipping test, we investigated the effect of the gas flow ratio and bias power on the amount of etching damage to the low-k material.

Abstract: This paper reports the fabrication of indium oxide (In2O3) films using a triethylindium and oxygen mixture. The deposition has been carried out on TiAlN substrates (200-350°C). We have established the correlation between the substrate temperature and the structural properties. The films deposited at 300-350°C were polycrystalline, whereas those deposited at 200°C was close to amorphous. XRD analysis and SEM images indicated that the films grown at 350°C had grained structures with the (222) preferred orientation. The room-temperature photoluminescence spectra of the In2O3 films exhibited a visible light emission.

Abstract: A series of surface-modified TiO2 nanoparticles were prepared and their photocatalytic effects were evaluated by degradation of Acid red dye in aqueous solution under UV light irradiation. Phage display peptide libraries were used for peptide sequence to bind the doped TiO2 particles selectively.

Abstract: The TiO2 nanorod arrays were fabricated by the electrophoretic deposition (EPD) of the 4.5 and 7 nm-sized anatase titania nanoparticles using the anodized aluminum oxide (AAO) as the template. Each of the TiO2 nanoparticle was plus-charged by adjusting the pH of the electrolyte. The growth rate of TiO2 nanorod arrays with this new method was dramatically higher than that of the arrays obtained from the conventional EPD method employing sol-gel solutions. In addition, the robust anatase-phase TiO2 nanorod arrays were obtained without post-thermal treatment. The scanning electron microscope (SEM) images showed that the titania nanoparticles were tightly interconnected to form the highly uniform and well-organized TiO2 nanorod arrays. The diameter of the TiO2 nanorod arrays was 55~58 nm with the length of 15 0m, which corresponded to the size of AAO templates.

Abstract: Hexagonal and cubic mesoporous TiO2 films were prepared by using triblock copolymer-templated sol-gel method via evaporation-induced self-assembly (EISA) process. The mesophase of TiO2 film was controlled by spin-speed during the spin-coating process. The hexagonal mesoporous structure was formed at a high spin-speed around 2000 rpm, whereas the cubic mesostructure was formed at a low spin-speed around 600 rpm. XRD and TEM results indicate that those mesostructures are highly organized with a pore diameter of 7 nm. The prepared cubic and hexagonal mesoporous films were tested as photocatalysts for the decomposition of 2-propanol in gas phase. Both films presented considerably higher photocatalytic activity than a nonporous TiO2 films prepared by a typical sol-gel process without addition of triblock copolymer. Notably, we found that the cubic mesoporous films showed a relatively higher photocatalytic activity than the hexagonal mesostructured film. We believe this is due to the orientation of pore channels open on the surface of mesoporous films.

Abstract: Transparent TiO2, WO3-TiO2, and MoO3-TiO2 films were prepared by spin-coating each colloidal suspension. The monolayer coverage of WO3 on the surface of TiO2 greatly increased the photocatalytic activity in the decomposition of gaseous 2-propanol, whereas the addition of MoO3 considerably decreased the photocatalytic reaction of TiO2. For the estimation of superhydrophilicity, the change of contact angles between the water drop and the film surface was measured as a function of UV-irradiation time. The measured contact angle of WO3-TiO2 film was considerably lower than that of TiO2 before the UV-irradiation, and it decreased to the minimum value about 4 times faster than that of pure TiO2 films with the irradiation of UV light. On the other hand, MoO3-TiO2 films showed a low contact angle at initial point, but their contact angle was very slowly decreased under the UV light. The initial low contact angles suggest the high hydrophilic character of WO3-TiO2 and MoO3-TiO2 films with high Lewis surface acidities. The observed trend suggests that the superhydrophilicity is closely related to the photocatalytic activity.

Abstract: [SiO2]x[TiO2]1-x(x = 0.1, 0.2, 0.3, 0.4) powders were prepared by hydrothermal reaction of titanium isopropoxide (TIP) and tetraethyl-orthosilicate (TEOS) stabilized in acidic ethanol/water solution. The size and phase of TiO2 particles were controlled by adjusting the SiO2 content and the composition of the solvent system. The microstructure and photocatalytic activity of the prepared SiO2-TiO2 nanoparticles were characterized by XRD, TEM, BET, Raman and UV visible spectroscopic techniques. The major phase for all the prepared samples was anatase. The particle size of 0.3SiO2-0.7TiO2 powders prepared with excess amount of ethanol (REtOH = EtOH/alkoxide molar ratio = 120) was about 8.7 nm, while that of the sample prepared with small amount of ethanol (REtOH = 4) was 9.9 nm. The photocatalytic activity of these composite powders under excess ethanol was 1.5 times higher than that of pure TiO2 with respect to the decomposition of 1,4-dichlorobenzene (DCB).