Plasma chemistry and diagnostic in an Ar–N₂–H₂ microwave expanding plasma used for nitriding treatments

Abstract

This paper reports on mass spectrometry analysis performed downstream a microwave discharge in Ar-N 2-H 2 gas mixture in nitriding conditions. Investigations are focused on the main simple radicals NH 2 , NH and N, and on the molecular species NH 3 and N 2 H 2 produced. Because of wall desorptions due to catalytic effects, we must develop a specific method taking into account both wall desorption and dissociative ionization effects, in order to correct the mass spectrometer signal intensity. The relative concentrations of the previous species are studied in various gas mixtures. Correlations are made between the plasma chemistry and plasma parameters (electron density and energy electron distribution function), measured by means of Langmuir probes spatially resolved within the plasma expansion. These results show the efficiency of ternary gas mixtures (Ar-N 2-H 2) to produce electrons and N x H y species used in plasma nitriding process. 1. introduction. Microwave discharge sustained in Ar-N 2-H 2 gas mixtures are used in a wide range of industrial applications. Like ammonia synthesis /1/, nitriding processes for surface treatment of metallic or polymer pieces /2,3,4/ and for the elaboration of optical or electronic devices /5/. The efficiency of such plasma processes depends on the knowledge of the various elementary mechanisms involved in the gas phase and at the surface of the reactor wall or of the work pieces. In previous papers /6, 7/, we have shown that the surface oxide reduction of thin molybdenum films, in the nitriding treatment, depends on the gas composition in the plasma expansion and on the distance between the work piece surface and the discharge centre. We confirm correlations between nitrided layers characteristics, discharge expansion

Plasma-assisted catalytic formation of ammonia in N2–H2plasma on a tungsten surface

“…Plasma catalysis has thus the potential to provide improved energy efficiency, decreased capital costs, and extended catalyst lifetime. 14 Over the years, the formation of ammonia from nitrogen and hydrogen feed gases has been studied for a wide variety of plasmas from high pressure thermal plasmas [15][16][17][18][19][20][21][22] (lower electron and ion temperatures than in low-pressure plasmas but high gas temperature) to low pressure plasmas [23][24][25][26][27][28][29] (high electron and ion energy).…”

Measurement and modeling of neutral, radical, and ion densities in H2-N2-Ar plasmas

“…Jang and Lee 29 previously examined a few aspects in an inductively coupled H 2 -N 2 plasma by measuring n e , T e and ion signal intensities. In addition, there exists a variety of studies about H 2 -N 2 plasmas in which the densities of background gas species 13,20,[30][31][32][33] , radicals 7,8,20,32,34 , electrons 34,35 and ion signals 7,36 as well as the surface loss probability of H and N (see Ref. 7 ) were reported.…”

“…Argon admixtures to hydrogen and nitrogen containing plasmas were examined in the studies of Refs. 20,26,31,35,36 .…”

Plasma Catalysis as an Alternative Route for Ammonia Production: Status, Mechanisms, and Prospects for Progress

“…Jauberteau et al 76 provided estimated reaction coefficients for important recombination processes of atomic and molecular hydrogen with surface-adsorbed NH x species such as NH and NH 2 ; these are important for plasma modeling. Touimi et al 77 reported detailed measurements of N atoms, NH x radicals, and NH 3 and N 2 H 2 molecules in a Ar−N 2 −H 2 plasma used for nitriding. Correlations were examined between the plasma chemistry and plasma parameters (electron density and energy electron distribution function) obtained using spatially resolved Langmuir probe measurements.…”