Si-Ok Ryu

Growth Kinetics of Thin-Film Cadmium Sulfide by Ammonia-Thiourea Based CBD

In this work, chemical bath deposition (CBD) of CdS was monitored using a quartz crystal microbalance as a function of time, temperature, reactant concentration (ex situ atomic absorption measurement), and pH level. It is found that the reaction could be limited by mass transport at certain concentrations and temperatures. The measurements also indicate the total Cd concentration in the solution changes dramatically in the linear growth regime with a constant deposition rate. One possible explanation is that the linear growth regime is actually a combination of molecule-by-molecule growth and cluster-by-cluster growth mode. This hypothesis is further supported by real time dynamic light scattering and transmission electron microscopy measurements.

Investigate the Reacting Flux of Chemical Bath Deposition by a Continuous Flow Microreactor

Chemical bath deposition CBD is a commonly used and inexpensive technique to deposit a variety of semiconductor and oxide thin films for a variety of different applications. In this work, a continuous flow microreactor was used to better control the reacting flux present during the CBD reaction by offering a better temporal resolution. High quality CdS films at various thicknesses could be obtained by using a flux that avoided the formation of nanoparticles. The chemistry and growth kinetics of CdS CBD were elucidated using this microreactor. The results suggest that HS x7f ions formed during the thiourea hydrolysis

Chemical nanoparticle deposition of transparent ZnO thin films

A novel approach to deposit transparent ZnO thin films is reported. This approach uses a continuous-flow microreactor to generate a flux of nanoparticles which then impinge on a heated substrate. The as-deposited film consists of highly transparent nanocrystalline ZnO with a dilated optical bandgap of 4.35 eV. Functional ZnO metal-insulator-semiconductor field-effect-transistors (MISFETs) were successfully fabricated using this technique after a post-air-annealing process. A MISFET with an effective mobility of 0.16 cm 2 /V s and a current on-to-off ratio of ∼10 4 was produced. This approach is promising as a low-cost technique for fabricating nanostructured thin films.

A Study on Selective Oxidation of Hydrogen Sulfide over Zeolite-NaX and -KX Catalysts

Selective oxidation of hydrogen sulfide (H2S) was studied on zeolite-NaX and zeolite-KX. Elemental sulfur yield over zeolite-NaX was achieved about 90% at 225 °C for the first 4 hours, but it gradually decreased to 55% at 40 hours after the reaction started. However, yield of elemental sulfur on zeolite-KX was obtained within the range of 86% at 250 °C after 40 hours. The deactivation of the zeolite-NaX and -KX catalysts was caused by the coverage of a sulfur compound, produced by the selective oxidation of H2S over the catalysts. The coverage of a sulfur compound over the zeolite-NaX and -KX was confirmed by the TPD (temperature-programmed desorption) tests utilizing thermogravimetric analysis and FT-IR analysis. Even though high temperature was required to prevent the deactivation of zeolite-NaX, the temperature cannot be raised to 250 °C or above due to the SO2 production and the decrease of thermodynamic equilibrium constant. Zeolite-KX was superior to the zeolite-NaX for both its selectivity to elemental sulfur and its resistance to deactivation in the selective oxidation of H2S.

The study on the selective oxidation of H2S over the mixture zeolite NaX-WO3 catalysts

At temperatures lower than 250 °C the deactivation of zeolite NaX catalyst occurred in the presence of water vapor. The gradual accumulation of water vapor on the surface of catalyst could cause deactivation of catalyst. The zeolite NaX-WO3 catalysts were prepared to study a method preventing deactivation of catalysts from the adsorption of water vapor. The zeolite NaX-WO3 (9 : 1) with a low content of WO3 showed the highest conversion of H2S. It is believed that the addition of WO3 caused either a decrease of the strong adsorption of water vapor on the zeolite NaX or an increase of the reducibility of WO3 by some interactions between zeolite NaX and WO3.

ZnS Thin Films Deposited by a Spin Successive Ionic Layer Adsorption and Reaction Process

In this article, we reported a spin successive ionic layer adsorption and reaction (SILAR) method for the first time. ZnS thin films were deposited by spin SILAR using ZnCl2 and Na2S aqueous precursor solutions at room temperature and atmosphere pressure. The optical, structural, and morphological characterizations of the films were studied by scanning electron microscopy, atomic force microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and UV/visible spectroscopy. Smooth (average roughness <3 nm), uniform, and highly transparent ZnS (transmittance of over 90% in the visible band) thin films could be successfully deposited using this technique with shorter cycle time and much less solvent usage.

A study on the SO2 reduction by CO over SnO2-ZrO2 catalysts

SO 2 which is an air pollutant causing acid rain and smog can be converted into elemental sulfur in direct sulfur recovery process (DSRP). SO 2 reduction was performed over catalyst. In this study, SnO 2 -ZrO 2 catalysts with Sn/Zr mole ratio were prepared by a co-precipitation method and CO was used as reduction agent. The reactivity profile of SO 2 reduction was investigated at the various reaction conditions. SnO 2 -ZrO 2 (Sn/Zr=2/1) catalyst showed the best performance for SO 2 reduction. As a result, SO 2 conversion and sulfur yield were about 100% and 97%, respectively, under the optimized conditions such as 325 °C and 10000 cm 3 /g -cat . h.