Microwave Hydrogen Plasma Atomic Emission Spectrometry Diagnostics

Atomic hydrogen plays important roles in chemical vapor deposition of functional materials, plasma etching and new chemical synthesis approaches of hydrogen-containing compounds. The present work reports experimental determinations of atomic hydrogen in microwave discharge hydrogen plasmas formed from TM01 MW mode in an ASTeX-type reactor via optical emission spectroscopy by using Ar as an actinometer. The absolute emission intensities of atomic hydrogen Balmer lines and Ar-750.4 nm as a function of gas flow rates of H2 have been discussed respectively. The relative intensities of H atom Balmer lines and Ar-750.4 nm emissions as functions of input power, gas pressure and the position inside the visible MW plasma ball have been investigated. At an input MW power density of 13.5 W/cm3, the approximate hydrogen dissociation fractions, decreased from 0.11 to 0.04 with gas pressure varying from 5 to 25 Torr, were calculated based on some of the available electron-impact excitation and quenching cross sections in the literatures. The influences of the above cross sections, the electron and gas temperature of the plasmas on the extraction of hydrogen dissociation fraction data have been discussed.