Spatially resolved spectroscopy and electrical characterization of microplasmas and switchable microplasma arrays

Abstract

Microwave resonators are used to generate microplasmas in atmospheric-pressure argon. We present spectroscopic and electrical measurements of these microplasmas for both a single resonator and a five-element resonator array with dc voltage-switchable power distribution. These measurements include gas temperatures from fits to rotational emission spectra and electron densities from Stark broadening, both resolved in two spatial dimensions. Peak gas temperatures are found to be near 900 K in the centre of the microplasmas, while electron densities peak near 3 × 10 14 cm −3 . Spectroscopically derived plasma densities are validated by comparison with electrical measurements of the complex plasma impedances. The plasma impedances shift the resonant frequencies and quality factors of the individual resonators, which in turn influence power distribution to the resonators. Data suggest that this feedback loop reinforces the electrical switching mechanism.

Electron confinement and heating in microwave-sustained argon microplasmas

“…Peak values are on the order of a few times 10 20 m À3 , in line with several previous measurements. 14,15,22 The widths of the microplasma filaments also increase with frequency and are on the order of 400 lm, comparable to the electrode sizes.…”

“…The uncovered section of the microstrip is tapered to restrict the plasma's ability to form multiple filaments. 14 The discharge region, including dimensions, is shown in Fig. 2.…”

“…Spectroscopic measurement techniques are identical to those employed previously 14 and are only briefly summarized here. The center of the discharge gap (see Fig.…”

Electron and ion kinetics in three-dimensional confined microwave-induced microplasmas at low gas pressures

“…22 The voltage reflection coefficient S 11 was calculated as the square root of the ratio between the forward and reflected powers. 18 Given a stable glow-discharge microplasma for 5 min at p g of 800 Pa with P in of 1.8 W for TDC microplasma with a t of 600 µm and a d h of 1000 µm (Sample II, Table II), a clear decrease in Au concentration and a remarkable increase in Ni concentration were observed at point b (see Figure 5(b)). This occurred because plasma interacted with the electrodes and removed the surface Au film, which exposed the underlying Ni film.…”

“…One method depends on the Stark broadening of the emission lines. 4,[17][18][19] However, for this method, when n e > 10 16 cm −3 , n e can be obtained with a reasonable accuracy in an argon microplasma at atmospheric pressure using Ar 2p-1s lines (in Paschen's notation) or, when n e > 10 14 cm −3 , using the hydrogen Balmer α and β lines (H α , H β ). 4 This phenomenon was due to the presence of van der Waals, resonance and Doppler broadenings, the sum of which may dominate line broadening when n e is low.…”