Measurement of the fluorine atom concentration in a carbon tetrafluoride and helium atmospheric-pressure plasma

The fluorine atom concentration has been measured in the downstream region of a low-temperature, atmospheric-pressure plasma fed with 739.0 Torr helium and 12.6 Torr carbon tetrafluoride (3.1 × 1017 cm−3). The fluorine atoms were titrated with H2 molecules, and the HF reaction product was detected by infrared spectroscopy. The radio-frequency gas discharge produced 1.2 × 1015 cm−3 of F atoms, which was about two orders of magnitude higher than that found in low-pressure plasmas. The average electron density and temperature in the plasma was estimated to be 6.1 × 1011 cm−3 and 2.5 eV, respectively. A numerical model of the plasma indicated that most of the fluorine atoms were generated by the reaction of CF4 with metastable helium atoms.