Jiann Shieh

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.

Hydrogen plasma dry etching method for field emission application

The ability to fabricate large-area, uniform emitters is an important factor in many vacuum microelectronics applications, especially for field emission displays. In this letter, we measured the field emission properties of uniform silicon nanowire emitters prepared by hydrogen plasma etching using in situ high-resolution scanning electron microscopy and a tungsten anode of 1μm diameter. Our results indicate that the field emission properties are improved upon increasing the etching time; this process sharpens the nanowires’ geometry and lowers their work function. These highly uniform (with respect to length, diameter, and distribution) nanowires display great potential for application within many field emission nanoelectronics devices.

Functionally gradient PECVD Ti(C,N) coatings

Ti(C,N) hard coating is well known as a suitable material for protecting substrate, and functionally gradient design is a method to improve the performance of it. In this study, functionally gradient Ti(C,N) coatings were performed by the technique of capacitive RF PECVD based on the investigation of Ti(C,N) monolayers with different C and N ratios. The results show that the composition and growth rate of Ti(C,N) monolayers are influenced by the nitrogen/methane ratio as other deposition parameters are fixed. A model is also proposed from the results obtained and is employed to calculate the reaction gas ratio and duration time needed for deposition in the gradient coating. The elements of Ti and N in the gradient coatings were analyzed by Auger electron spectroscopy (AES) and revealed that the composition changed linearly as designed. The residual stress of the gradient coatings was also measured to show that the gradient design provides the possibility for adjusting the stress distribution of PECVD hard coatings.