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Effect of excitation states of nitrogen on the surface nitridation of iron and steel in d.c. glow discharge plasma
Author(s) -
Sato Shigeo,
Hirai Hirokazu,
Araki Sawa,
Wagatsuma Kazuaki
Publication year - 2011
Publication title -
surface and interface analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.52
H-Index - 90
eISSN - 1096-9918
pISSN - 0142-2421
DOI - 10.1002/sia.3673
Subject(s) - nitriding , glow discharge , auger electron spectroscopy , nitrogen , chemistry , nitride , x ray photoelectron spectroscopy , iron nitride , analytical chemistry (journal) , sputtering , noble gas , inorganic chemistry , plasma , materials science , layer (electronics) , thin film , chemical engineering , environmental chemistry , nanotechnology , physics , organic chemistry , quantum mechanics , nuclear physics , engineering
The plasma nitriding phenomena that occur on the surfaces of iron and steel were investigated. In particular, the correlation between the kinds of nitrogen radicals and the surface nitriding reaction was investigated using a glow‐discharge apparatus. To control the excitation of nitrogen radicals, noble gas mixtures were used for the plasma gas. The highly populated metastables of noble gases selectively produce excited nitrogen molecules (N 2 *) or nitrogen molecule ions (N 2 + ). The optical emission spectra suggested that the formation of N 2 *‐rich or N 2 + ‐rich plasma was successfully controlled by introducing different kinds of noble gases. Auger electron spectroscopy and XPS were used to characterize the depth profile of the elements and chemical species on the nitrided surface. The nitride layer formed by a N 2 + ‐rich plasma had a much higher nitrogen concentration than that by a N 2 *‐rich plasma, likely due to the larger chemical activity of the N 2 + species as well as the N 2 + sputtering bombardment to the cathode surface. The strong reactivity of the N 2 + species was also confirmed from the chemical shift of N 1s spectra for iron nitrides. An iron nitride formed by the N 2 + ‐rich plasma has higher stoichiometric quantity of nitrogen than that formed by the N 2 *‐rich plasma. Besides the effect of nitrogen radicals on surface nitridation, the contribution of the chromium in steel to the nitriding reaction was also examined. This chromium can promote a nitriding reaction at the surface, which results in an increase in the nitrogen concentration and the formation of nitride with high nitrogen coordination. Copyright © 2010 John Wiley & Sons, Ltd.