Frequency-locked measurement of floating potential fluctuations in cold micro-plasma jets: Interactive surface feedback effects on reactive species generation

Abstract

Frequency-locked measurements of floating potential fluctuations are carried out in a cold atmospheric pressure micro-plasma jet interacting with substrates of varying electrical permittivity (εr). The range of fluctuation frequencies (∼ 0.5–9 kHz) is compared with that determined from the time series of floating potential fluctuations and its fast Fourier transform. Results of these independent methods to determine the fluctuation frequencies are found to agree reasonably well, thereby affirming their existence in the micro-plasma jet. Substrate feedback effects dictated by εr are found to influence the amplitude of fluctuations and threshold breakdown voltage. The spectral emission line intensity corresponding to the reactive oxygen and nitrogen species, which is critical for biomedical applications, decrease drastically in the presence of stronger levels of fluctuations, indicating a bearing on their generation.