Electron-irradiation damage in chromium nitrides and chromium oxynitride thin films Christoph Mitterbauer a, * , Werner Grogger a , Peter Wilhartitz b , Ferdinand Hofer a a Research Institute for Electron Microscopy, Graz University of Technology, Steyrergasse 17, A-8010 Graz, Austria b Plansee Aktiengesellschaft, Thin Film Technology, A-6600 Reutte, Austria Abstract The aim of this work is to monitor changes of the N–K electron energy-loss near-edge structure (ELNES) of chromium nitride layers (CrN) introduced by electron irradiation in a transmission electron microscope (TEM). These changes are different for each sample material and seem to give an indication for a particular composition. The CrN samples (CrN and Cr 0.47 N 0.53 ) were prepared on silicon wafers by reactive magnetron sputtering of a metallic chromium target in nitrogen plasma. In addition, a CrON sample (Cr 0.5 O 0.2 N 0.3 ) was also investigated. This sample was prepared by the addition of oxygen to the plasma during film deposition. The ELNES of the N–K ionization edge of stoichiometric CrN shows a typical fine structure (peaks at 399.0 and 401.1 eV) and remains nearly unaffected even after high-current-density irradiation. On the other hand the N–K fine structures of Cr 0.47 N 0.53 and Cr 0.5 O 0.2 N 0.3 show a change of the ELNES with irradiation dose. This presumably arises from a 1s–p*- transition of molecular nitrogen located at interstitial positions in these samples. q 2006 Elsevier Ltd. All rights reserved. Keywords: Chromium nitride; Electron energy-loss spectrometry; Analytical transmission electron microscopy 1. Introduction The ability to damage organic and inorganic samples by electron irradiation in a TEM is well known (Egerton et al., 2004). The degree of radiation damage thereby depends on the accumulated radiation dose as well as to the amount of deposited energy. Electron energy-loss spectrometry (EELS) is an appropriate tool to investigate these subtle changes of structure and/or chemical composition changes induced by electron irradiation by means of the ELNES, which contains information about the local bonding and environment of atoms in solids. ELNES arises because the final states of the excitation process are unoccupied states above the Fermi level which may be appreciably modified by chemical bonding (Hofer and Golob, 1987). Detailed studies of the N–K ELNES of CrN were published by Craven (1995), MacKenzie et al. (1997), Paxton et al. (2000) and Mitterbauer et al. (2004). Additionally, X-ray absorption spectroscopy measurements were done by Esaka et al. (1996, 1997). In this paper, we investigate the damage effect in different chromium nitride and chromium oxynitride thin films by time resolved EELS in order to trace changes in the N–K ELNES under the electron beam. Chromium nitride (CrN) as well as chromium oxynitride (Cr 0.5 O 0.2 N 0.3 ) crystallize in the rock salt structure (fcc) and are antiferromagnetic with a Ne ´el point of about 273 K. CrN is widely used in decorative application as a substitute for electroplated hard Cr or as chemically and thermally resistant hard coating on forming tools, moulds, and dies. 2. Experimental The CrN film samples (CrN and Cr 0.47 N 0.53 ) were prepared by reactive magnetron sputtering of a metallic chromium target in nitrogen plasma. For the CrON film sample (Cr 0.5 O 0.2 N 0.3 , isostructural with CrN), a controlled amount of oxygen was added to the plasma gas (Wilhartitz et al., 2004). Silicon wafers were selected as the proper substrate material for subsequent analysis. The chemical composition of each film was determined by quantitative electron probe micro analysis (EPMA) and Rutherford backscattering (RBS). Cross-sectional TEM specimens were prepared by standard metallographical methods and final Ar ion milling under a low angle (Fig. 1B). For our investigations we used a 200 kV Philips CM20 (S)TEM (twin lens) with a thermionic LaB 6 -cathode. This Micron 37 (2006) 385–388 www.elsevier.com/locate/micron 0968-4328/$ - see front matter q 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.micron.2006.01.006 * Corresponding author. Current address: Department of Chemical Engin- eering and Materials Science, University of California-Davis, Davis, CA 95616, U.S.A. Tel.: C1 530 754 6891; fax: C1 530 752 9554. E-mail address: cjmitterbauer@ucdavis.edu (C. Mitterbauer).