Sang Chul Jung

Macro- and micro-scale simulation of growth rate and composition in MOCVD of yttria-stabilized zirconia

Abstract Yttria-stabilized zirconia (YSZ) thin film was grown by low-pressure metalorganic chemical vapor deposition (LPMOCVD) using β -diketonate complexes of zirconium and yttrium, tetrakis(2,2,6,6-tetramethyl-3,5-heptadionato) zirconium and tris(2,2,6,6-tetramethyl-3,5-heptadionato) yttrium, respectively. Growth rate distribution and film composition in a hot wall tubular reactor were quantitatively reproduced by a transport model including gas-phase and surface reactions, assuming linear additivity of the individual growth rates of zirconia (ZrO 2 ) and yttria (Y 2 O 3 ). At low temperatures (773, 823xa0K), the growth rates are controlled by the gas-phase and surface reactions. Since the rate constants of Y 2 O 3 are larger than those of ZrO 2 at low temperatures, the film is richer in Y than the feed ratio. However, at high temperatures (>848xa0K), the growth rates of each oxide system are limited by the mass transfer rates of each intermediate, and the film composition in the reactor tube is nearly equal to the feed ratio. The shapes of YSZ film grown on micro-size trenches can be qualitatively interpreted by a Monte Carlo simulation assuming a linear combination of the growth rates of ZrO 2 and Y 2 O 3 . The surface reaction of Y 2 O 3 is faster than that of ZrO 2 at low temperatures, thus the film near the mouth of the trench is richer in Y than that at the bottom. However, at high temperature, the film composition becomes constant regardless of its position in the trench, because its growth rate is limited by the mass transfer rates of the intermediates.

Preparation, Crystal Structure, and Photocatalytic Activity of TiO2 Films by Chemical Vapor Deposition

Photocatalytic activities of TiO2 films were experimentally studied. TiO2 films with different crystal structures (amorphous, anatase, rutile) were prepared by a Low Pressure Metal Organic Chemical Vapor Deposition (LPMOCVD) at different reaction temperatures and also by a Sol-Gel method using TTIP (Titanium Tetra Iso-Pro-poxyde). The Effect of CVD preparation method, CVD reaction conditions, crystal structure and wave-length of UV light on the photocatalytic decomposition rate of methylene blue in aqueous solution were studied. First, the characteristics of CVD preparation of TiO2 films, such as the CVD film growth rate, crystal structure and morphology of the grown TiO2 films, were experimentally studied as a function of CVD reaction temperature. Secondly, photocatalytic activities of TiO2 films were evaluated by using two types of photo-reactors. The results indicated that TiO2 films prepared by CVD exhibit higher photocatalytic activity than a catalyst prepared by the Sol-Gel method. Among the CVD grown TiO2 films, anatase and rutile showed high photocatalytic activities. However, amorphous TiO2 films showed lower activities. The activity of the photocatalysts of anatase films was excellent under all types of UV-lamps. The activity of CVD-prepared anatase films was four to seven times higher than that of photocatalyst films prepared by the Sol-Gel method.

The growth of LiNbO3 thin film by LPMOCVD using β-diketonate complexes

We studied the material characteristics of polycrystalline films of lithiumniobate (LiNbO3) and its components (Li2O and Nb2O5) prepared by Low Pressure Metal Organic Chemical Vapor Deposition (LPMOCVD). Precursors are Li(DPM) and Nb(DPM)2Cl3, and the carrier gas is nitrogen or argon with 50 % of oxygen at 5 Torr. We proposed a quantitative model for Nb2O5 film growth. Li2O film grows on alumina substrate under argon+oxygen atmosphere, but Li2CO3 grows under nitrogen+oxygen atmosphere. On silicon or silica substrate, both react to form lithium silicates. By feeding both precursors, we found the optimum condition for preparing LiNbO3 film from a film composition map as a function of the reaction temperature vs Li mol % in feed gas.

Photocatalytic Activity of Titanate Nanotube Powders in a Hybrid Pollution Control System

The photocatalytic activity on decomposition of Rhodamine B (RB) of titanate nanotubes (TNTs) synthesized by alkali hydrothermal treatment method was evaluated using a microwave/UV/photocatalyst hybrid system. The effects of each element technique as well as the synergy effects on decomposition of organic material were investigated. When TNTs were ion-exchanged with HCl, Na

Effect of Doping of Fe into TiO2 Layer in Fe2O3/TiO2/FTO System for High Performance of Water Splitting

Hydrogen has unique physical and chemical properties which present benefits and challenges to its successful widespread adoption as a fuel. The photoelectrochemical (PEC) water splitting process with semiconductor metal oxides can be a promising solution to the global energy problem. Although amongst metal oxides Fe2O3 by 2.2 eV bang gap energy is more applicable, for reducing the recombination of electron and hole, Fe was doped into TiO2. In this study Fe2O3/Fe doped TiO2 photocatalysts were compared with Fe-doped TiO2 and TiO2 structures by using layer by layer-self-assemble (LBL-SA) method and dipping process on FTO glass. According to our results the Fe2O3 coated on Fe doped TiO2 /FTO has had best results.

Characterization of Pt-Based Catalyst by Consecutive Experiments of Toluene Oxidation

Catalytic oxidation of toluene was carried out to investigate the effect of consecutive run on the catalytic property and performance of 1 wt.% Pt/γ-Al2O3 and the reduced 1 wt.% Pt/γ-Al2O3. The properties were characterized by X-ray diffraction (XRD), the Brunauer Emmett Teller (BET) surface area, temperature programmed reduction (TPR), and transmission electron microscopy (TEM) analyses. In consecutive experiments the second catalytic run resulted in a significant increase of the toluene conversion compared to the first catalytic run, but the toluene conversion in the third catalytic run was similar to that of the second catalytic run. In addition, the reducing treatment of the catalyst led to an increase in the catalytic activity. The increasing catalytic activity in consecutive runs was dependent on the platinum particle size and the oxidation state of the platinum. The increase in platinum particle size during reaction and the reduction in the oxidation state of platinum by hydrogen pretreatment were responsible for the increase in the catalytic activity.

Preparations of Platinum Nanoparticles and Their Catalytic Performances.

This work investigates the effect of reducing agents and stabilizing agent on the preparation of platinum nanoparticles. We used H2PtCl6 as a precursor and hydrogen and sodium borohydride as reducing agents to prepare colloidal platinum nanoparticles. Polyvinylpyrrolidones (PVPs) is used as a stabilizing agent. Hydrogen and sodium borohydride are used as reducing agents. The prepared platinum nanoparticles are characterized by transmission electron microscopy (TEM) and X-ray diffractometer (XRD). The concentrations of the precursor and the stabilizing agent influence the size of platinum nanoparticles, while the reducing agents influence the morphologies and structures of platinum nanoparticles. Supported platinum catalysts (CPt-NaBH4, CPt-H2) are prepared from colloidal platinum nanoparticles and γ-Al2O3. For comparison, another supported platinum catalyst (IPt) is prepared by the conventional impregnation method with an aqueous H2PtCL6 solution and γ-AL2O3. The catalytic activities of CPts are superior to that of IPt on the basis of benzene conversion.

Additive effect of nano-size platinum to pretreated iron based catalyst on complete oxidation of toluene.

Catalytic oxidation of toluene (VOC) was carried out to assess the properties and catalytic activities of iron oxide catalyst promoted with nano size platinum. The properties of the prepared catalysts were characterized by the Brunauer Emmett Teller (BET) surface area method and by conducting Temperature programmed reduction (TPR), X-ray diffraction (XRD), and Tansmission electron microscopy (TEM) analyses. The experimental results showed that the addition of platinum to spent iron based catalyst shifted its conversion curve for the total oxidation of toluene to lower temperature. It was also observed that the increase in toluene conversion due to the addition of nano-size platinum was highly dependent on the surface oxygen mobility of the catalyst.