Emission Spectroscopy Diagnosis Of Hydrogen Microwave Plasma

Hydrogen plasma generally generated by DC, RF and microwave has numerous potential applications in plasma chemical vapor deposition, plasma reaction kinetics, chemical synthesis and other research work. In situ, nonintrusive diagnosis of hydrogen plasma are often the key to understanding the physical-chemical processes in the plasma and controlling the plasma behavior. In this paper, plasma parameters and interrelated plasma reaction process in two kinds of hydrogen microwave discharges system have been measured by atomic emission spectroscopy.(1) The H Balmer emission lines have been measured on a high-pressure (10-40kPa) microwave discharges using pure hydrogen. The line strength, the line profiles and the linewidth of H atom Balmer lines (Hα, Hβ, Hγ) have been studied. The influence of the microwave power and working pressure on the electronic excitation temperature, electron density, electric field strength and ion temperature were investigated detailedly. The results indicate that: The profile of H atomic lines is in accord with Voigt profiles in theory. The linewidth of H_α, H_β, and H_γlines increases in turn. The relative intensity of spectral lines, the electron density and the electric field increase with the increase of microwave power, and increase gradually to a peak value and then decreases with the increase of pressure, and all reach the maximum at a pressure of 25kPa when the microwave power was set at 800W. The electronic excitation temperature continuously reduced with the increase of pressure and the changes of pressure have little effect on ion temperature. With the microwave power increase, the electronic excitation temperature and ion temperature increase with a different extent.(2) A microwave plasma jet device has been designed to excite and maintain stable plasma on atmospheric press. The emission spectra of SiCl₄/H₂ mixed gas discharge were investigated. The process and products of SiCl₄ decomposition are analysed. The emission intensity of H_αline and the decomposition efficiency of SiCl₄ at different initial concentration were examined. The results indicate that: The lines of H_α, H_β, Si[251-253nm, (4s³P⁰â†'3p²¹D)]and the bands of SiCl molecule[281-282nm, (B′²Î”â†'X²Î ) and 287-288nm, (B²Î£+â†'X²Î )] have been observed. The mechanism of SiCl₄ decomposition is that the SiCl₄ molecular lost one Cl atom each time to form SiCl_x by the electron collision firstly, and the hydrogen atoms was the assistance in the later reaction,to further transform SiClx to Si and HCl. The addition of hydrogen was able to increase the decomposition efficiency of SiCl₄. When microwave power was 800W, the emission intensity of H_αline decreases with the increase of concentration SiCl₄. The decomposition efficiency of SiCl₄ can be maintained above 95% when concentration of SiCl₄ was less than 1%. The spatial distribution of excited hydrogen atoms at the plasma jet was measured. The results show that the density of hydrogen atoms at the middle centrally is greater than that at both ends of the plasma jet.