Wei Hao Lai

High Sensitivity Semiconductor NO 2 Gas Sensor Based on Mesoporous WO 3 Thin Film

A NO 2 gas sensor based on mesoporous WO 3 thin film with low operating temperatures and its sensing characteristics are reported. The mesoporous WO 3 thin film exhibits regular pores with an average pore size of 5 nm andspecific surface area of 151 m 2 /g. Excellent sensing properties are found upon exposure to 3 ppm of NO 2 at 35-100°C for mesoporous WO 3 thin film. The sensor response is 180 for 3 ppm NO 2 at 100°C. The ability to sense NO 2 at such low temperatures is attributed to the large surface area (151 m 2 /g) that offers many active sites for reaction with NO 2 molecules.

Fabrication of one-dimensional mesoporous tungsten oxide

Mesoporous tungsten oxide nanofibres and tube-like nanofibres are fabricated by the gas-filled assistant sol–gel immersion method with porous anodic alumina membrane confinement. Tube-like nanofibres are obtained at an immersion time of less than 3 min, but nanofibres are obtained at an immersion time of more than 5 min under 50 psi nitrogen gas pressure. The results show that the gas-filled method has a higher efficiency to induce mesoporous materials into membrane channels. One-dimensional (1D) mesoporous tungsten oxide nanowire is characterized as a triclinic crystal with discontinuous lattice morphology at the mesopores. The one-dimensional tungsten oxide with disordered mesopores obtained indicates that the liquid-crystal mechanism should be applied for the formation of the mesoporous structure. The gas-filled immersion method provides a convenient and low-cost route for the fast production of mesoporous tungsten oxide nanofibres and tube-like nanofibres.

Effects of mesoporous structure on grain growth of nanostructured tungsten oxide

The effects of mesoporous structure on grain growth were investigated in this study. The synthesis was accomplished using block copolymer as the organic template and tungsten chloride as the inorganic precursor. Thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy, x-ray diffractometry (XRD), transmission electron microscopy, and N 2 adsorption/desorption isotherms were used to characterize the microstructures obtained for different temperatures. TGA and XRD analyses demonstrate that copolymers were expelled at 150–250 °C, and mesoporous structure was stable up to 350 °C. The pore diameter and the surface area evaluated from the Barrett-Joyner-Halenda model and Brunauer–Emmett–Teller method indicated that the average pore diameter is 4.11 nm and specific surface area is 191.5 m 2 /g for 250 °C calcination. Arrhenius equation used to calculate the activation energy for grain growth demonstrates that the activation energy for grain growth was about 38.1 kJ/mol before mesostructure collapse and 11.3 kJ/mol after collapse. These results show evidence of two different mechanisms governing the process of grain growth. The presence of the pore can be related to the obstacle for grain growth.

Surface plasmon resonance of gold nano-sea-urchin

The authors synthesized high-quality gold nano-sea-urchin in aqueous solution with an environment-friendly method. They found that the gold nano-sea-urchin can induce the interaction of surface plasmon resonance (SPR) mode with substrate. The SPR peak splits and blueshifts from 630to440nm and the result has potential application for enhanced-Raman scattering, optical communications, and solar cells.

Ellipsometric Advances for Local Surface Plasmon Resonance to Determine Chitosan Adsorption on Layer-by-Layer Gold Nanoparticles

The ellipsometric measurement of local surface plasmon resonance (LSPR) caused by the adsorption of chitosan on layer-by-layer gold nanoparticles (Au NPs) was investigated. Six nanometer (6 nm) Au NPs were prepared and layer-by-layer Au NPs were fabricated to shift the LSPR to 520, 540, and 560 nm, respectively, due to the Mie theory. The thicknesses and the fractions of the layer-by-layer Au NPs were measured accurately using a combination of the Fresnel equation and the Maxwell–Garnett equations for ellipsometry. Furthermore, the position of the LSPR was shifted by chitosan. Using trajectory to record the trace of polarized light for ellipsometry resulting from LSPR, it was found that LSPR is predominantly induced when the LSPR position is close to the wavelength of the ellipsometric measurement. The trajectory circle of LSPR is very large for an increase of chitosan adsorption on Au NPs when the LSPR position is close to the detected wavelength. The linear approximation aspect quantifying the trajectory corresponds with the change of LSPR for the adsorption of chitosan, except for cases with low incidence and Brewster angles. The aspects and technologies of ellipsometry will benefit from the findings in this study, with potential applications in the fields of determination of molecular adsorption.

How the Optical Properties of Au Nanoparticles are Affected by Surface Plasmon Resonance

Gold nanoparticles (Au NPs) have been attracting more attention because they have many color varieties in the visible region based on plasmon resonance, which is due to the collective oscillation of the electrons at the surface of the nanoparticles. We prepared 6 nm Au NPs to modify the surface of the glass substrate. Surface plasmons resonance of Au NPs in toluene is between 500 nm and 600 nm. When Au NPs are modified on the glass substrate, the peak of surface plasmons resonance of Au NPs is shifted. We employed spectral ellipsometry to detect optical properties. Then the characteristics of surface plasmons resonance of Au NPs is determined by reflective index. The performance of surface plasmons resonance of Au NPs on the glass substrate is simulated and shown.

Gas Sensing Properties of ZnO:Al Thin Films Prepared by RF Magnetron Sputtering

The ZnO:Al thin films were prepared by RF magnetron sputtering on Si substrate using Pt as interdigitated electrodes. The structure was characterized by XRD and SEM analyses, and the ethanol vapor gas sensing as well as electrical properties have been investigated and discussed. The gas sensing results show that the sensitivity for detecting 400 ppm ethanol vapor was ~20 at an operating temperature of 250square. The high sensitivity, fast recovery, and reliability suggest that ZnO:Al thin film prepared by RF magnetron sputtering can be used for ethanol vapor gas sensing.