Xinzhan Wang

Textured diamond films growth on (100) silicon via electron-assisted hot filament chemical vapor deposition

Textured (100) diamond films are successfully grown on single-crystalline (100) silicon substrate by electron assisted hot filament chemical vapor deposition from a gas mixture of methane and hydrogen. The effects of various parameters have been studied. The optimal growth conditions are obtained and the oriental growth character is discussed.

Spectral characteristics of surface-plasmon?enhanced photoluminescence in nanocrystalline SiC films

Multilayer structures of nanocrystalline (nc-) SiC/silicon nitride spacer/Ag island films were designed by varying the spacer thickness, and the spectral characteristics of surface-plasmons (SPs)–enhanced photoluminescence (PL) in nc-SiC films have been investigated. The optical transmission spectra show that there are two SPs resonant optical absorption bands in the out-of-plane and in-plane modes for the Ag island film on the sample surface. While PL quenching occurred for the sample with the thinnest spacer, the maximum PL enhancement for nc-SiC is achieved when the thickness of the spacer is suitable, suggesting that the SP enhancement can dominate over nonradiative energy dissipation by varying the spacer thickness. In the case of PL enhancement, the PL excitation spectrum shows an enhancement peak at the resonant wavelength of the out-of-plane mode of SPs, indicating that the excitation enhancement in nc-SiC films occurs due to the incident-light resonant coupling with out-of-plane SPs. Whereas, the increased PL decay rate is observed in the temporal PL spectrum, implying that the SPs scattering enhancement in the nc-SiC film is induced by in-plane SP resonant coupling. In the case of PL quenching, although an enhancement factor less than 1 is observed in the PL excitation spectrum, an increased light emission decay rate is also revealed in the temporal PL spectrum, which indicates that the nonradiative energy dissipation of light emission in the Ag island film is the main coupling mechanism when the spacer is too thin.

Preparation of silver island films with tunable surface plasmon resonance

Silver (Ag) island films have been prepared by pulsed laser ablation in vacuum using a XeCl excimer laser. The effects of the number of ablation pulses, the temperature and time of post-annealing on morphology and surface plasmons properties of the prepared Ag island films were investigated by extinction spectra and scanning electron microscopy. It is found that the films deposited with the ablation pulses of 60 or less are isolated Ag nanoparticles and the mean size of the nanoparticles increases monotonically with increasing the number of ablation pulses. Further increase of the number of ablation pulses up to 240, quasi-percolated Ag films are obtained, and for 600 pulses or more, continuous films will be formed. Extinction spectra results show that localized surface plasmons (LSPs) are supported by the Ag island films, while propagating surface plasmons are supported by the continuous Ag films. The LSPs of Ag island films consist of inplane and out-of-plane modes. By changing the ablation pulse numbers and annealing conditions, the longitudinal and transverse dimensions of Ag islands could be adjusted, and then the peak positions and peak widths of in-plane and outof- plane LSPs resonance modes could be effectively controlled.

MICROSTRUCTURAL PROPERTIES OF NC-Si/SiO2 FILMS IN SITU GROWN BY REACTIVE MAGNETRON CO-SPUTTERING

Nanocrystalline silicon embedded in silicon oxide (nc-Si/SiO2) films have been in situ grown at a low substrate temperature of 300°C by reactive magnetron co-sputtering of Si and SiO2 targets in a mixed Ar/H2 discharge. The influences of H2 flow rate (FH) on the microstructural properties of the deposited nc-Si/SiO2 films were investigated. The results of XRD and the deposition rate of nc-Si/SiO2 films show that the introduction of H2 contributes to the growth of nc-Si grains in silicon oxide matrix. With further increasing FH, the average size of nc-Si grains increases and the deposition rate of nc-Si/SiO2 films decreases gradually. Fourier transform infrared spectra analyses reveal that introduction of hydrogen contributes to the phase separation of nc-Si and SiOx in the deposited films. Moreover, the Si–O4-nSin(n = 0, 1) concentration of the deposited nc-Si/SiO2 films reduces with the increase of FH, while that of Si–O4-nSin(n = 2, 3) concentration increases. These results can be explained by that active hydrogen atoms increase the probability of reducing oxygen from precursor in the plasma and prompting oxygen desorption from the growing surface. This low-temperature procedure for preparing nc-Si/SiO2 films opens up the possibility of fabricating the silicon-based thin-film solar cells onto low-cost glass substrates using nc-Si/SiO2 films.