Hongchun Yu

Surface-depletion controlled gas sensing of ZnO nanorods grown at room temperature

The authors report on surface-depletion controlled gas sensing ZnO nanorods. These nanorods were synthesized through a simple wet chemical route at room temperature. The diameter of nanorods is about 15nm, which is close to two times of the Debye length of ZnO. In contrast to the previous report, the sensing is surface-depletion controlled rather than contact controlled and the sensitivity is up to 29.7 against 100ppm ethanol. Such high sensitivity is due to an almost complete depletion of the rods in air, which is confirmed from photoluminescence spectrum and x-ray photoelectron spectroscopy. The gas sensing mechanism controlled by surface depletion provides another approach to realize high-performance gas sensors.

Fast humidity sensors based on CeO2 nanowires

Fast humidity sensors are reported that are based on CeO2 nanowires synthesized by a hydrothermal method. Both the response and recovery time are about 3 s, and are independent of the humidity. The sensitivity increases gradually as the humidity increases, and is up to 85 at 97% RH. The resistance decreases exponentially with increasing humidity, implying ion-type conductivity as the humidity sensing mechanism. A model based on the morphology and surface energy of the nanowires is given to explain these results further. Our experimental results indicate a pathway to improving the performance of humidity sensors.

Bandgap narrowing and ethanol sensing properties of In-doped ZnO nanowires

Indium doping effects on the optical and electrical properties of ZnO nanowires are investigated. The abnormal Raman spectrum shows only a peak centred at 439 cm−1 related to high E2 mode, which is due to In doping. The acceptor binding energy is estimated to be 93 meV from the results of temperature-dependent photoluminescence spectra. The redshift of the bandgap edge is attributed to a merging of donor and conduction bands. The sensitivity of the sensors fabricated from In-doped ZnO nanowires is about 3–1 ppm ethanol, and increases nearly linearly up to 27 as the ethanol concentration is raised to 100 ppm. Our results indicate that the In-doped ZnO nanowires have potential applications in fabricating optoelectrical devices and gas sensors.

The large-scale synthesis of one-dimensional TiO2 nanostructures using palladium as catalyst at low temperature

The synthesis of TiO(2) nanostructures including nanowires and nanobelts has been demonstrated experimentally by anodization of Ti foil in an electrolyte, and by treatment in a PdCl(2) ethanol solution together with UV light irradiation and annealing at a temperature below 800 degrees C. The TiO(2) nanotube arrays resulting from the anodization were used as source precursor and transformed into nanowires and nanobelts respectively with high efficiency during the subsequent processes. The resulting TiO(2) nanowires and nanobelts, characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Raman and surface photovoltage (SPV) spectroscopy, are single rutile crystals of high quality. In addition to the synthesis of the nanostructure at low temperature, this method also shows great advantages for the selectable morphology of the final TiO(2) nanostructures via adjustment of the UV light irradiation time and annealing temperature.