Kyun Ahn

ZnO nanobarbed fibers: Fabrication, sensing NO2 gas, and their sensing mechanism

ZnO nanobarbed fibers (NBFs) are synthesized by the epitaxial growth of 1–D ZnO nanorods (NRs) on ZnO nanofibers (NFs) via electrospinning and chemical bath deposition. The change in resistance of the NBFs in the presence or absence of a gas was explained using the surface depletion model and modified grain boundary model, in which the junction points of the NFs and NRs are considered. The NBF structure showed extraordinary NO2 sensing performance for gas concentrations up to 30 ppb. This indicates that NBF structures have great potential for use as gas sensing materials.

Enhanced photocatalytic activity of TiO2 nanobarbed fibers treated with atmospheric pressure plasma using O2 gas

TiO2 nanobarbed fibers (NBFs) were prepared by growing rutile TiO2 nanorods on anatase TiO2 nanofibers via electrospinning and hydrothermal reaction processes. There was a large increase in the photocatalytic activity of O2-plasma-treated (OP)-TiO2 NBFs relative to that of the TiO2 NBFs; this is due to the hydroxylation of the surface of the TiO2 NBFs by OP treatment. The repeatability of the photocatalytic activity of the OP-TiO2 NBFs was found to be high and the decolorization rate after ten cycles was 88.3% of the initial value. These results indicate that OP-TiO2 NBFs have great potential for use as a photocatalyst.

Biofield-effect protein-sensor: Plasma functionalization of polyaniline, protein immobilization, and sensing mechanism

We report the fabrication of a biofield-effect protein-sensor (BioFEP) based on atmospheric-pressure plasma (AP) treatment of a conducting polyaniline (PANI) film. Successive H2 and O2 AP (OHAP) treatment generated dominant hydrophilic –OH and O=CO– functional groups on the PANI film surface, which served as strong binding sites to immobilize bovine serum albumin (BSA) protein molecules. The output current changes of the BioFEP as a function of BSA concentration were obtained. The resistance of the OHAP surface could be sensitively increased from 2.5 × 108 Ω to 2.0 × 1012 Ω with increasing BSA concentrations in the range of 0.025–4 μg/ml. The results suggest that the method is a simple and cost-effective tool to determine the concentration of BSA by measuring electrical resistance.

Optical properties of hierarchical-nanostructured TiO2 and its time-dependent photo-degradation of gaseous acetaldehyde

The TiO2 hierarchical nanostructures (HNs) composed of rutile TiO2 nanowires on anatase TiO2 nanofibers had higher photocatalytic activities of 62% and 48% than the commercial TiO2 nanoparticles (∼21 nm diameter) in the continuous flow mode and closed-circulation mode, respectively, leading to an efficient degradation of gaseous acetaldehyde under UV-light irradiation. This behavior may be attributed to the effective TiO2 HNs with specific surface area of 85.1 m2/g and lower radiative recombination of self-trapped excitons, enabling an effective electron-hole separation.

Optical and Dielectric Properties of Transparent Epitaxial GdVO4/n-GaN/Sapphire Heterostructure

GdVO4 (GVO) thin films were successfully deposited on n-GaN/Al2O3 substrates used as a bottom electrode at 600 °C by radio frequency magnetron sputtering. The GVO films annealed at temperatures up to 800 °C exhibited epitaxial growth but the films annealed above 900 °C showed polycrystalline properties. In the photoluminescence (PL) spectrum, broadband emission was observed at 450 nm for all the films. The auger electron spectroscopy (AES) line-shape of the annealed films was similar to that of the as-deposited film but the Gd/V and Gd/O ratios increased linearly with increasing annealing temperature. The dielectric constant and dielectric loss of the GdVO4 films decreased with increasing annealing temperature with values of 12–26 and 0.04–0.05 at 1 MHz, respectively.