Misook Kang

Effects of the oxygen fraction and substrate bias power on the electrical and optical properties of silicon oxide films by plasma enhanced chemical vapour deposition using TMOS/O2 gas

Thin oxide films are deposited from tetramethoxysilane in an inductively coupled oxygen glow discharge supplied with radio frequency power. The chemical bonding states of deposited films are analysed by Fourier transform infrared spectroscopy. The deposition rate and optical properties are determined from spectroscopic ellipsometry. Capacitance–voltage measurements are performed in MOS capacitors to obtain the electrical properties of the deposited films. With these tools, the effects of the substrate bias power and the oxygen mole fraction in the gas on the properties of the film are investigated. The refractive index first decreases with an increase in the oxygen mole fraction, and then increases again, showing a behaviour opposite to that of the deposition rate. The deposition rate increases with increasing substrate bias power and then saturates, while the refractive index increases slightly with an increase in the substrate bias power. The fixed oxide charge density decreases with increasing oxygen fraction and with increasing substrate bias power, while the interface trap density increases with increasing oxygen fraction and with increasing substrate bias power.

Surface modification of layered perovskite Sr 2 TiO 4 for improved CO 2 photoreduction with H 2 O to CH 4

Layered perovskite Sr2TiO4 photocatalyst was synthesized by using sol-gel method with citric acid. In order to increase the surface area of layered perovskite Sr2TiO4, and thus to improve its photocatalytic activity for CO2 reduction, its surface was modified via hydrogen treatment or exfoliation. The physical and chemical properties of the prepared catalysts were characterized by X-ray diffraction, high-resolution transmission electron microscopy, elemental mapping analysis, energy-dispersive X-ray spectroscopy, N2 adsorption-desorption, UV-Vis spectroscopy, X-ray photoelectron spectroscopy, photoluminescence, and electrophoretic light scattering. CO2 photoreduction was performed in a closed reactor under 6 W/cm2 UV irradiation. The gaseous products were analyzed using a gas chromatograph equipped with flame ionization and thermal conductivity detectors. The exfoliated Sr2TiO4 catalyst (E-Sr2TiO4) exhibited a narrow band gap, a large surface area, and high dispersion. Owing to these advantageous properties, E-Sr2TiO4 photocatalyst showed an excellent catalytic performance for CO2 photoreduction reaction. The rate of CH4 production from the photoreduction of CO2 with H2O using E-Sr2TiO4 was about 3431.77 μmol/gcat after 8 h.

Ni Substitution Effect on the Fe Position of Spinel Fe2MnO4 Particles for Chemical Looping Combustion

The purpose of this study was to use a spinel structure to improve the performance and stability of chemical looping combustion processes. The oxygen carrier employed was Fe2MnO4, in which Ni was substituted at the Fe sites. Fe2-xNixMnO4 spinel particles were successfully synthesized by a sol-gel method. The obtained particles were characterized by X-ray diffraction (XRD), scanning electron microscopy, and CH4-/CO-temperature programmed desorption experiments. The XRD analysis confirmed that all the synthesized particles presented spinel structure. The performance of the particles was evaluated in redox cycle experiments under H2/air and CH4/air at 850 °C using a thermogravimetric analyzer. The Ni-substituted particles exhibited a higher performance than Fe2Mn1, being Fe1Ni1Mn1 the sample with the highest oxygen transfer capacity (19.68 wt% in H2/air and 15.90 wt% in CH4/air).

Photoreduction of Carbon Dioxide to Methane Over Sb1.5Sn8.5−x TixO19.0 with High Conductivity

In order to enhance the photoreduction of CO2 to CH4, a new type of photocatalyst, Sb1.5Sn8.5-xTixO19.0, with high conductivity and low bandgap was developed by partially incorporating Ti into the framework of Sb1.5Sn8.5O19.0 (antimony-doped tin oxide, ATO) using a controlled hydrothermal method. XRD and TEM analyses indicated that the Sb1.5Sn8.5-xTixO19.0 particles exhibited a tetragonal crystal structure and were approximately 20 nm in size. Furthermore, the bandgap and conductivity of these materials increased with increasing Ti content. A study of the photoreduction of CO2 with H2O revealed a remarkable increase in the generation of CH4 over the Sb1.5Sn8.5-xTixO19.0 catalysts. In particular, CH4 generation was the highest when Sb1.5Sn8.5Ti1.0O19.0 was used as the photocatalyst, and was three-fold higher than that achieved by using anatase TiO2. Photoluminescence studies showed that the enhanced photocatalytic activity of the Sb1.5Sn8.5-xTixO19.0 materials could be attributed to the interfacial transfer of photogenerated charges, which led to an effective charge separation and inhibition of the recombination of photogenerated electron-hole (e-/h+) pairs.