A “comb” structure of beam intensity distribution is designed and achieved to measure a target displacement of micrometer level in laser plasma propulsion. Base on the “comb” structure, the target displacement generated by nanosecond laser ablation solid target is measured and discussed. It is found that the “comb” structure is more suitable for a thin film target with a velocity lower than tens of millimeters per second. Combing with a light-electric monitor, the ‘comb’ structure can be used to measure a large range velocity.
Nanocrystalline SiC films have been synthesized on Si substrate using hot filament chemical vapor deposition with methane and silane as reaction gases. The microstructure, morphology and photoluminescence of the films are characterized by x-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy and photoluminescence respectively. Results show that the films deposited at relatively low substate temperature are composed of SiC nanocrystallines embedded in SiC amorphous matrix. The size of the nanocrystallites is about 5 nm. The visible-light emitting at the range of 400nm and 550nm has been observed from the nanocrystalline films at room temperature.
Pulse laser ablating graphite is adopted to deposit SiC films on Si(111) under different laser fluence and substrate temperature. Experiment results show that the deposited films present different morphology and X-ray diffraction characteristics. Single crystalline SiC is obtained when the laser fluence is 10J/cm<SUP>2</SUP> and the deposition temperature is 900 degree(s)C. At lower laser fluence or lower substrate temperature, a carbon overlayer is formed. Meanwhile the surface roughness of the films becomes relative smooth and the deposition rate increase with laser fluence. The stress accumulation during film growth releases gradually as the substrate temperature increase. The mechanism of the crystalline SiC formation in the initial stage that the energetic carbon species penetrate several layers below the silicon surface by subplantation and transversely migration in silicon substrate is discussed. All the results suggest that the energy of incident atom play an important role in growth silicon carbon at low substrate temperature.