Chien-Cheng Li

Growth of β-Ga2O3 and GaN nanowires on GaN for photoelectrochemical hydrogen generation

Enhanced photoelectrochemical (PEC) performances of Ga(2)O(3) and GaN nanowires (NWs) grown in situ from GaN were demonstrated. The PEC conversion efficiencies of Ga(2)O(3) and GaN NWs have been shown to be 0.906% and 1.09% respectively, in contrast to their 0.581% GaN thin film counterpart under similar experimental conditions. A low crystallinity buffer layer between the grown NWs and the substrate was found to be detrimental to the PEC performance, but the layer can be avoided at suitable growth conditions. A band bending at the surface of the GaN NWs generates an electric field that drives the photogenerated electrons and holes away from each other, preventing recombination, and was found to be responsible for the enhanced PEC performance. The enhanced PEC efficiency of the Ga(2)O(3) NWs is aided by the optical absorption through a defect band centered 3.3 eV above the valence band of Ga(2)O(3). These findings are believed to have opened up possibilities for enabling visible absorption, either by tailoring ion doping into wide bandgap Ga(2)O(3) NWs, or by incorporation of indium to form InGaN NWs.

Performance characterization of nonevaporable porous Ti getter films

The highly porous Ti film getters on (100) silicon substrates have been successfully grown by dc magnetron sputtering with varying glancing angle. The porous films were formed when the glancing angle was higher than 30°. The larger the glancing angle, the higher the porosity and specific surface area of the Ti films. The porous films were composed of isolated columnar crystals, and they have a larger capability to absorb oxygen than dense Ti films do. Differential scanning calorimetry analysis shows that the exothermal reaction temperature for a dense Ti film is 348°C. However, that for the porous Ti film ranges from 291to394°C. The suitable operation condition of porous Ti film getters can be evaluated using thermal desorption spectroscopy. The reversible and irreversible reactions may occur during gas desorption/adsorption of porous Ti films.

Microstructures, surface areas, and oxygen absorption of Ti and Ti–Zr–V films grown using glancing-angle sputtering

Highly porous Ti and TiZrV getter film coatings have been successfully grown on (100) silicon substrates using the glancing-angle direct-current magnetron sputtering method. The evolution of the microstructures of the Ti and the TiZrV films strongly depends on the sputtering flux rate, surface diffusion rate, nucleation rate, compositions, and self-shadowing geometry of the nuclei on the sputtering flux. The larger the glancing angle, the higher the porosity and specific surface area of the Ti and TiZrV films. The weight-gain results strongly depend on several factors, such as specific surface area, the surface structure of the getter film, the diffusion rate of O in the getter film, the reactivity of Ti, Zr, and V on O, and the order of the stabilities of Ti, Zr, and V oxides on the film’s surface. Porous Ti film absorbs oxygen better than porous TiZrV film does due to its higher surface area and the high diffusion rate of O in Ti films.

Giant room temperature electric-field-assisted magnetoresistance in La0.7Sr0.3MnO3/n-Si nanotip heterojunctions

An on-chip approach for fabricating ferromagnetic/semiconductor-nanotip heterojunctions is demonstrated. The high-density array of Si nanotips (SiNTs) is employed as a template for depositing La(0.7)Sr(0.3)MnO(3) (LSMO) rods with a pulsed-laser deposition method. Compared with the planar LSMO/Si thin film, the heterojunction shows a large enhancement of room temperature magnetoresistance (MR) ratio up to 20% under 0.5 T and a bias current of 20 µA. The MR ratio is found to be tunable, which increases with increasing external bias and the aspect ratios of the nanotips. Electric-field-induced metallization, in conjunction with nanotip geometry, is proposed to be the origin for the giant MR ratio.

Catalytic Performance of Nanostructured Plate-type Cu and Cu-Fe on ZnO Nanorods for Steam Reforming of Methanol

The Cu-type and (Cu-Fe)-type film catalysts have been successfully prepared by the electroless plating on ZnO nanorods/stainless steel substrates. The microstructure features of the (Cu-Fe)-type films are high porosity and plate-type grains. The addition of iron into Cu-type film can improve the reducibility and the stability of the film catalysts. The reduction temperature of the (Cu-Fe)-type film catalysts decreases with increasing the addition of Fe. For Cu-5 at% Fe film, the reduction temperature is in the range of 195°C to 216°C as comparison in the range of 208°C to 233°C of the Cu-type film catalysts.