Absolute N-atom density measurement in an Ar/N2 micro-hollow cathode discharge jet by means of ns-two-photon absorption laser-induced fluorescence

Abstract

In this work, nanosecond two-photon absorption laser-induced fluorescence (TALIF) is used to probe the absolute density of nitrogen atoms in a plasma generated using a micro-hollow cathode discharge (MHCD). The MHCD is operated in the normal regime, and the plasma is ignited in an Ar/N2 gas mixture. First, we study a MHCD configuration having the same pressure (50 mbar) on both sides of the electrodes. A good agreement is found between the density of N atoms measured using TALIF in this work and previous measurements using vacuum ultraviolet Fourier transform absorption spectroscopy. Then, we introduce a pressure differential between the two electrodes of the MHCD, creating a plasma jet. The influence of the discharge current, the percentage of N2 in the gas mixture, and pressures on both sides of the MHCD is studied. The current has a small impact on the N-atom density. Furthermore, an optimal N-atom density is found at around 95% of N2 in the discharge. Finally, we demonstrate that the pressure has a different impact depending on the side of the MHCD: the density of N atoms is much more sensitive to the change of the pressure in the low-pressure side when compared to the pressure change in the high-pressure side. This could be due to several competing phenomena: gas residence time in the cathodic region, recirculation, or recombination of the N atoms at the wall. This study contributes to the optimization of MHCD as an efficient N-atom source for material deposition applications.

Absolute atomic nitrogen density spatial mapping in three MHCD configurations

“…Previous studies of the MHCD [8,17] showed that atomic nitrogen is produced inside the MHCD hole and can be transported over long distances (several cm) using a pressure differential. In this study, a substrate is placed in front of the MHCD and we measure the spatial N atoms density profile.…”

“…The fluorescence emitted by the laser-excited atomic state in the plasma is collected perpendicularly to the laser beam, using a 10-cm-focal-length lens, in a 4f configuration, and a photomultiplier tube. A complete description of the experimental TALIF setup used, and thorough validity verification can be found in Remigy et al [17].…”

“…It should be mentioned that a map of the N atoms density at 30 mbar uniform pressure in figure 5(a) would have been more appropriate for quantitative comparison with the MHCD-jet configuration. In our previous paper [17], we performed a parametric study of N atoms density in the discharge configuration of figure 5(a). TALIF measurements were made at (x = 0 mm, y = 4 mm), 20% N 2 in Ar/N 2 and I d = 1 mA.…”

Influence of the pulse polarity on micro-hollow cathode helium plasma jet

“…The characteristics of APPJ are influenced by discharge configuration, working gas, and driving scheme. Typical APPJs are generated by needle electrode, dielectric barrier discharge or micro-hollow cathode configuration within gas He/Ar [1,[6][7][8]. Some temporal evolution photographs of the plasma jet obtained by intensified charge-coupled device (ICCD) camera show that a continuous plasma jet observed by the naked eye is actually composed of a moving plasma bullet or a guided ionization wave [9][10][11][12][13][14][15].…”

A pulsed hollow cathode discharge operated in an Ar/N2/O2 gas mixture and the formation of nitric oxide.

“…The discharge is sustained by electrons undergoing a pendulum motion inside the HC [2][3][4][5][6][7]. Hollow cathode discharges are employed in many applications, e.g., in atomic spectroscopy [1, [8][9][10], mass spectrometry [11], and laser technology [12], as UV generators [13,14] and propulsion thrusters [15,16], for the generation of neutral and ion beams [17,18], surface processing [19], thin film deposition [20][21][22][23][24][25][26][27], and in plasma chemical investigations [28][29][30][31][32][33][34].…”