Li Han

Structural and optical properties of hydrogenated amorphous silicon carbide films by helicon wave plasma-enhanced chemical vapour deposition

Hydrogenated amorphous silicon carbide (a-Si1−xCx : H) films with different carbon concentrations have been deposited using the helicon wave plasma-enhanced chemical vapour deposition technique under the condition of strong hydrogen dilution. The a-Si1−xCx:H films with carbon content x up to 0.64 have been deposited. Their structural and optical properties are investigated using Fourier transform infrared spectroscopy, Raman scattering, ultraviolet–visible transmittance spectroscopy and x-ray photoelectron spectroscopy. The deposition rate, optical band gap and B factor related to structural disorder are found to monotonically change in the investigated range with methane–silane gas flow ratios. It is found that the deposited films exist with the structure of Si-like clusters and Si–C networks when silicon content is high, while they consist mainly of C-like clusters and Si–C networks for carbon-rich samples. A large optical band gap is obtained in high carbon concentration samples, which is attributed to the high density characteristic of helicon wave plasmas and the strong hydrogen dilution condition.

Effect of gas pressure on the synthesis of carbon nitride films during plasma-enhanced chemical vapor deposition

Carbon nitride thin films have been synthesized on Si(100) substrate by d.c.-glow discharge plasma enhanced hot filament chemical vapor deposition. The effect of gas pressure on the properties of the deposited films was investigated by scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. The influence of gas pressure on the growth mechanism of carbon nitride films has been discussed and it was concluded that higher pressure is favorable to the synthesis of crystalline carbon nitride.

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.

Monte Carlo simulation of fast electrons and heavy particles in the CDS of nitrogen dc glow discharge

The characteristics of fast electrons (e-) and heavy particles (N2+, N+, N2f, Nf) in the cathode dark space (CDS) of nitrogen dc glow discharge are simultaneously studied by Monte Carlo simulation. The calculated energy and angular distributions of these particles at different positions from the cathode provide a clear picture of their transport behaviours within the CDS. The density and mean energy of these particles indicate that the electrons and the atomic ions (N+) are the main high-energy species and the molecular ions (N2+) are the major ions in the CDS. It can be seen from the energy distributions of the bombarding particles at the cathode surface that the molecular ions and the fast atoms (Nf) are the main active species participating in the cathode nitride material synthesis process. The influence of the backscattering of the electrons from the negative glow to the CDS is also investigated. All the calculated results provide good information on the spatial characteristics of the particles considered in this paper and also their internal connections in the CDS of nitrogen dc glow discharge.

Formation process of Si nanoparticles deposited by pulse laser ablation

The deposited dynamic process of Si nanoparticles prepared by pulsed laser ablation is numerically simulated by using the direct simulation Monte Carlo method. It is found that there is a mixed region where the high-density Si vapor peak and the gas peak are overlapped. The Si nanoparticles are formed by Si vapor condensation in the region and their sizes depend on the properties of the region such as density and range. The properties of the mixed region are changed constantly when its position are oscillated with time is increased, and get to stable state at certain a time, i.e., oscillating time. The oscillating time determines the distribution of nanoparticles in size. The influence of the experimental parameters on oscillating time of the mixed region is analyzed theoretically. The results show that the Si-based nanostructure materials with more uniform nanoparticles in size can be obtained by using appropriate proportion of He and Ar as ambient gas.

Preparation of nanocrystalline silicon films by excimer-laser-induced crystallization

Excimer laser-induced crystallization (ELC) technique has been used to prepare nanocrystal silicon (nc-Si) from amorphous silicon (a-Si) thin films on silicon or glass substrate. The a-Si films without hydrogen grown by pulsed laser deposition (PLD) are chosen as precursor to avoid the problem of hydrogen effluence during annealing. The analysis has been performed by scanning electron microscopy (SEM), Raman scattering spectroscopy and high-resolution transmission electron microscopy (HRTEM). Experimental results show that the silicon nanocrystals can be formed by laser annealing. The growth characters of nc-Si are strongly dependent on the laser energy density. It is shown that the volume of melted Si essentially predominates the grain size of nc-Si, and the surface tension of crystallized silicon is responsible for the mechanism of nc-Si growth

Structure and size distribution of silicon nanocrystals prepared by pulsed laser ablation in inert background gas

Silicon nanocrystals have been synthesized using pulsed laser ablation in argon background gas. The morphology structure and the size distribution of the silicon nanocrystals depending on the background gas pressure (0.1 Pa-100 Pa) have been studied. Experiment results show that the morphology of the silicon nanograins transits from amorphous-like continuous thin film to dispersed nanocrystals with the decreasing of argon pressure. The size of the silicon nanograins increases with the increase of argon pressure (less than 100 Pa). Under higher pressure the size of the silicon nanograins does not increase with the increase of the background pressure monotonously, it comes to a maximum at a critical gas pressure, then begins to decrease when increasing the gas pressure.