Soong Keun Hyun

Hydrogen gas sensing of Co3O4-Decorated WO3 nanowires

Co3O4 nanoparticle-decorated WO3 nanowires were synthesized by the thermal oxidation of powders followed by a solvothermal process for Co3O4 decoration. The Co3O4 nanoparticle-decorated WO3 nanowire sensor exhibited a stronger and faster electrical response to H2 gas at 300 °C than the pristine WO3 nanowire counterpart. The former showed faster response and recovery than the latter. The pristine and Co3O4-decorated WO3 nanowire sensors showed the strongest response to H2 gas at 225 and 200 °C, respectively. The Co3O4-decorated WO3 nanowire sensor showed selectivity for H2 gas over other reducing gases. The enhanced sensing performance of the Co3O4-decorated WO3 nanowire sensor was explained by a combination of mechanisms: modulation of the depletion layer width forming at the Co3O4-WO3 interface, modulation of the potential barrier height forming at the interface, high catalytic activity of Co3O4 for the oxidation of H2, active adsorption of oxygen by the Co3O4 nanoparticle surface, and creation of more active adsorption sites by Co3O4 nanoparticles.

Ultraintense UV emission from ZnO-sheathed ZnS nanorods

Short-wavelength luminescence is essential for high-performance optoelectronic device applications. There have been efforts to obtain intense ultraviolet (UV) emission by encapsulating ZnO one-dimensional (1D) nanostructures with materials such as ZnS. However, the encapsulation of ZnS 1D nanostructures with ZnO has not been reported. In this paper, we report ultraintense UV emission from ZnS nanorods coated with ZnO, i.e., ZnS-core/ZnO-shell nanorods. UV emission from the ZnS-core/ZnO-shell nanorods was much more intense than that obtained from the extensively studied ZnO-core/ZnS-shell nanorods. The highest intensity of the near-band-edge emission from the ZnS-core/ZnO-shell nanorods was obtained with a ZnO shell layer thickness of 35 nm, which is ∼16 times higher than that of pristine ZnS nanorods. Moreover, the deep level (DL) emission was suppressed completely. The substantial enhancement of the UV emission from the ZnS nanorods and the complete suppression of the DL emission by ZnO sheathing can be rationalized by combining the following four effects: the reinforcement of the UV emission by the overlap of the UV emissions from the ZnS core and ZnO shell, enhancement of the emission from the ZnO shell by the carrier transfer from the ZnS core to the ZnO shell, suppression of the capture of carriers by the surface states on the ZnS surface, and suppression of the visible emission and nonradiative recombination in ZnS.