Characterization of 13.56 MHz RF atmospheric pressure plasma sources for ion mobility spectrometry

Abstract

A 13.56 MHz atmospheric pressure capacitively coupled plasma (CCP) source, and an inductively coupled plasma (ICP) source has been developed for potential applications to ion mobility spectrometry. Utilizing double probe measurements, the electron temperatures (T_e) and ion densities (n_i) of the sources were obtained. These parameters were obtained over a range of input powers, flow rates, and probe distances. Typical plasma parameters of the devices at 40 W input power, and 5 L/min flow rates are T_e = 0.61 eV, n_i = 2.0 x 10²¹ m⁻³ for the CCP source, and T_e = 0.64 eV, n_i = 1.3 x 10²¹ m⁻³ for the ICP source. When coupled to the IMS device at these parameters, the CCP source reports a DC signal even at low electric fields when a shutter bias is applied. This could be attributed to the significant density of ions observed at a distance larger than the distance of the plasma source to the shutter which were clarified with spatially resolved probe measurements.