Structural stability,electronic and optical properties of Ni-doped silicon nanowires are investigated by first-principles calculations based on the density functional theory. The results show that Ni can preferentially occupy substitutional sites near the surface of silicon nanowire. The doping of Ni atom in silicon nanowire introduces the impurity levels. The impurity level is mainly contributed by Ni 3d orbital. The decrease of the band gap results from the coupling of Ni 3d and Si 3p states. A strong absorption peak occurs in the low energy region of Ni-doped silicon nanowire,accompanied by the widening of the absorption band.

To determinate the nucleation region of Si nanoparticles formed in gas phase, the single crystalline Si target with high resistivity was ablated by a XeCl excimer laser in pure Ar gas under the ambient pressure of 10Pa, and the nanocrystalline Si films were systemically deposited on pieces of glass or single crystalline (111) Si substrates lined up at a distance of 2.0cm under the plasma. The Raman and X-ray diffraction spectra, scanning electron microscope and atomic force microscope images of the films show that Si nanoparticles were formed on the pieces placed at horizontal distances 0.5 to 2.8cm from the target, the average size of Si nanoparticles monotonically decreased with the distance increasing. The region that Si nanoparticles form in gas phase was estimated on the basis of the PLA dynamics.

The nanocrystalline silicon films were prepared by pulsed laser ablation at the ambient pressures from 1 to 500 Pa of pure Ar gas. The x-ray diffraction spectrum indicates that the films are nanocrystalline, i.e. they are composed of Si nanoparticles. Scanning electron microscopy shows that with increasing gas pressur e, the average size of Si nanoparticles first increases and reaches its maximum (20nm) at 100Pa, and then decreases. The dynamics are analysed theoretically to explain the phenomenon. Furthermore, our result is compared with that in He gas.

In order to investigate the range of nucleation area of Si nanoparticles under different pressures, a single crystalline Si target with high resistivity is ablated by a XeCl excimer laser (wavelength 308 nm, laser fluence 3 J/cm2) in an ambient pressure range from 1 to 200 Pa of pure Ar gas. The Si nanocrystalline films are systemically deposited on glass or single crystalline Si substrates that are lined up at a distance of 2.0 cm under the ablation point. Raman and X-ray diffraction spectra indicate that the films are nanocrystalline. Scanning electron microscope images of the films show that the ambient pressure effect on the average size and the distributing range of Si nanoparticles on the substrate. According to the method of determining the location of nucleation area, it is found that the range of nucleation area of Si nanoparticles first broadens and then narrows with the increase of ambient pressure. The dynamics is analysed theoretically to explain the results.

The inertia fluid model proposed by Yoshida et al. can only interpret the influence of ambient pressure on the average size of nanoparticles prepared by pulsed laser ablation. Basing on the model, the Maxwell velocity distribution of the initial ablated particles is considered, a new analytic expression of the size-distribution of nanoparticles is obtained. The simulation results are consistent with the statistic data from Yoshidas experiments under different He pressures. Additionally, the size-distribution of nanoparticles is simulated using the modified model under different ambient gases (He, Ne and Ar),the simulation results coincide with experimental data. The conclusions may serve as the basis for realizing the uniformity and controllability of Si nanoparticles.