Electrical and spectral characterization of an atmospheric pressure He/CF4 plasma jet

Surface modification of polymeric materials based on non-equilibrium plasma fed with helium (He) and tetrafluoromethane (CF4) has gained much attention. In this paper, an atmospheric pressure plasma jet (APPJ) generated in He/CF4 mixtures is developed, and it is characterized systematically by electrical and optical methods. It is found that the He/CF4 APPJ presents three kinds of discharge modes, i.e., glow discharge, unstable glow discharge, and filamentary discharge under different operation parameters including applied voltage and gas composition. With the increase in applied voltage, the discharge mode transits from glow to filamentary discharge gradually, while the gas composition has significant influences on ignition/extinction voltages and excited species. The discharge modes under different parameters are obtained, and the applied voltage is regarded as the main reason for discharge mode transition. The excited species in the He/CF4 APPJ mainly include the excited helium atoms, the fluorine groups, and the impurities originated from air, whose generation reactions are discussed. The evolution of excited species under different parameters and discharge modes is acquired. The discharge modes and excited species of the He/CF4 APPJ can be well modulated by changing applied voltage and CF4 volume fraction.