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Electron-irradiation damage in chromium nitrides and chromium oxynitride thin films
Micron 37 (2006) 385–388 www.elsevier.com/locate/micron
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 Cr0.47N0.53) were prepared on silicon wafers by reactive magnetron sputtering of a metallic chromium target in nitrogen plasma. In addition, a CrON sample (Cr0.5O0.2N0.3) 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 Cr0.47N0.53 and Cr0.5O0.2N0.3 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). * Corresponding author. Current address: Department of Chemical Engineering 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: [email protected] (C. Mitterbauer).
0968-4328/$ - see front matter q 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.micron.2006.01.006
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 (Cr0.5O0.2N0.3) 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 Cr0.47N0.53) were prepared by reactive magnetron sputtering of a metallic chromium target in nitrogen plasma. For the CrON film sample (Cr0.5O0.2N0.3, 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 LaB6-cathode. This
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Fig. 1. Morphology of the investigated specimens. (A) Focused ion beam thinned CrN specimen. (B) Ar ion milled Cr0.5O0.2N0.3 specimen.
microscope was equipped with a Gatan Imaging Filter (GIF 200), corrected for the major spectral aberrations up to second order (Krivanek et al., 1995). The EELS spectra were recorded from thin specimen regions (t/l!0.8) in TEM image mode (diffraction coupling) with a collection angle of 7 mrad and a spectrometer dispersion of 0.05 eV/channel (core loss spectra) and 0.5 eV/channel for the low loss spectra, respectively. All spectra were corrected for dark current and intrinsic channel to channel gain variations of the CCD. The background below the ionization edges was subtracted by using the power-law model and was corrected for the effect of thickness by means of the Fourier-ratio deconvolution (Egerton, 1996). In order to acquire an N–K edge spectrum of an ‘undamaged’ specimen, a non-irradiated area of the sample was selected and a moderate current density (in the order of 104 A/m2) was used. The time evolution of the N–K ELNES was obtained by collecting EELS spectra with 30 s exposure time during the irradiation period. The final spectrum in each series was acquired after irradiating the specimen for 300 s at maximum current density (w2!106 A/m2). Additionally, EELS spectra were collected at low temperature (w100 K)
by cooling the specimen in a liquid-nitrogen-cooled holder in order to minimize beam-induced specimen heating. 3. Results and discussion Fig. 2A shows the N–K edge in the reference spectrum from a thin section (approximately 35 nm) of a CrN powder sample (purityO99%; Alfa Aesarw). The powder was crushed in an agate mortar, dispersed in ethanol and placed on holey carbon grid. This spectrum was acquired under above experimental conditions with an exposure time of 30 s. The N–K edge ELNES remained unaffected by electron irradiation, therefore, only the first spectrum is displayed in Fig. 2A. The selected region of the N–K edge exhibits two features at energy-losses of 399.0 and 401.1 eV, respectively. The octahedral coordination of the N surrounding the Cr ions affects crystal field splitting and which results in a branching of the N–K edge (Mitterbauer et al., 2004). Peak I corresponds to the electronic transitions to unoccupied N 2p orbitals hybridized to Cr 3d-t2g orbitals while the peak II results from hybridized N 2p and Cr 3d-eg states. However, peak II is
Fig. 2. (A) Reference spectrum of the N–K ELNES from a CrN powder sample (purityO99%; Alfa Aesarw). (B) Time resolved N–K ELNES of a CrN film specimen measured at room temperature. All spectra are Fourier-ratio deconvoluted.
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Fig. 3. Time resolved N–K ELNES of a Cr0.47N0.53 film specimen measured at (A) low temperature (100 K) and (B) at room temperature (295 K). All spectra are Fourier-ratio deconvoluted.
hardly visible at the given energy resolution (0.8 eV full width at half maximum (FWHM) at the zero loss peak (ZLP)). A detailed description of the N–K ELNES, a comparison to monochromated EELS data, and theoretical calculations of
the N–K ELNES for CrN can be found in Mitterbauer et al. (2004). Contrary to the findings in this paper the investigated stoichiometric CrN film was more sensitive to radiation damage. Fig. 2B presents a series of EELS spectra from the
Fig. 4. Time resolved N–K ELNES of a Cr0.5O0.2N0.3 film specimen measured at (A) low temperature (100 K) and (B) at room temperature (295 K). All spectra are Fourier-ratio deconvoluted.
Fig. 5. (A) Low loss spectra (Fourier-log deconvoluted): (1) reference spectrum from a CrN powder sample (purityO99%; Alfa Aesarw), (2) CrN-, (3) Cr0.47N0.53-, and (4) Cr0.5O0.2N0.3-sample. (B) Time resolved O–K ELNES of a Cr0.5O0.2N0.3 film specimen measured at room temperature (295 K). All spectra are Fourier-ratio deconvoluted.
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CrN film measured at room temperature. By increasing the electron dose, a feature II at 401.4 eV emerges in the EEL spectra (indicated by arrow in Fig. 2B). In Cr0.47N0.53, the increase of intensity of the peak II with the accumulated electron dose was more distinct and the feature was sharper. The first spectra in Fig. 3 (0 min; nonirradiated Cr0.47N0.53 sample) show a significant effect due to the deposited electron dose. Comparing the EEL spectra of Cr0.47N0.53 at different temperatures, the increase of intensity (peak II) is less distinct at low temperatures (100 K, cf. Fig. 3A and B) but there is no distinct difference in peak intensity (feature II) after high-current-density irradiation, compared to the findings at room temperature. A similar behavior was also noticed in Cr0.5O0.2N0.3. The spectra series (Fig. 4B) of the Cr0.5O0.2N0.3 specimen at room temperature show a strong rise of the peak II. This can be attributed to the formation of an intermediate species which finally leads to a reversed peak ratio after high-current density irradiation. The narrow peak width of 1.4 eV FWHM precludes the possibility that the feature results from an orbital that is hybridized to an orbital of Cr. The occurrence of feature II presumably arises from a 1s–p*-transition of molecular nitrogen, which is formed in the interstitial positions of chromium oxynitride. Esaka et al. (1996) observed the formation of molecular nitrogen due to surface oxidation of CrN thin films monitored by X-ray absorption spectroscopy. Chung et al. (2005) were able to directly observe interstitial molecular N2 in SiON by using vibrationally resolved N–K edge absorption spectroscopy and X-ray photoelectron spectroscopy. N–K ELNES investigations of TiN also showed that peak I progressively decrease with respect to that of peak II as the number of nitrogen vacancies increases (Tsujimoto et al., 2005). Considering the experimental energy resolution in our EELS investigations, no electron irradiation-induced effects could be detected in the low loss region (Fig. 5A) and the Cr–L2,3 ELNES (not shown here; cf. Mitterbauer et al., 2004; Fig. 6) from all analyzed samples as well as the O–K ELNES of the Cr0.5O0.2N0.3 (Fig. 5B) specimen. 4. Concluding remarks We have shown that the N–K edge ELNES of chromium nitride and chromium oxynitride show changes in the peak ratio of the low-energy features during high-electron irradiation in a TEM. The O–K ELNES of the Cr0.5O0.2N0.3 sample, the Cr–L2,3 ELNES and the low loss region of all analyzed samples show no electron irradiation-induced effects. The N–K ELNES of the stoichiometric CrN film sample remains nearly unaffected. By changing the composition, however a sharp feature emerges at 401.4 eV. The relative intensity of the features further increases from Cr0.47N0.53 to Cr0.5O0.2N0.3. Therefore, the rise of the second peak could be used as an indicator for the composition of the chromium
(oxy)nitride. The feature in question (peak II) presumably arises from a 1s–p*-transition of molecular nitrogen located in interstitial positions. Acknowledgements We wish to thank the Austrian Science Foundation (FWF) within the Special Research Program ‘Electroactive Materials’ (project F00923) for financial support of C. Mitterbauer and M. Dienstleder and A. Brunegger (FELMI, Graz University of Technology) for sample preparation. References Chung, Y., Lee, C.H., Shin, H.J., 2005. Direct observation of interstitial molecular N2 in Si oxynitrides. Applied Physics Letters 86, 022901-1– 022901-3. Craven, A.J., 1995. The electron energy-loss near-edge structure (ELNES) on the N K-edges from the transition metal mononitrides with the rock-salt structure and its comparison with that on the C K-edges from the corresponding transition metal monocarbides. Journal of Microscopy 180, 250–262. Egerton, R.F., 1996. Electron Energy-loss Spectroscopy in the Electron Microscope, second ed. Plenum Press, New York. Egerton, R.F., Li, P., Malac, M., 2004. Radiation damage in the TEM and SEM. Micron 35, 399–409. Esaka, F., Furuya, K., Shimada, H., Imamura, M., Matsubayashi, N., Sato, T., Nishijima, A., Kawana, A., Ichimura, H., Kikuchi, T., 1996. X-ray absorption and X-ray photoelectron spectroscopic studies of air-oxidized chromium nitride thin films. Thin Solid Films 281–282, 314–317. Esaka, F., Furuya, K., Shimada, H., Imamura, M., Matsubayashi, N., Sato, T., Nishijima, A., Kawana, A., Ichimura, H., Kikuchi, T., 1997. Comparison of surface oxidation of titanium nitride and chromium nitride films studied by x-ray absorption and photoelectron spectroscopy. Journal of Vacuum Science and Technology 15, 2521–2528. Hofer, F., Golob, P., 1987. New examples for near-edge fine structures in electron energy-loss spectroscopy. Ultramicroscopy 21, 379–383. Krivanek, O.L., Kundmann, M.K., Trevor, C., Leapman, R.D., 1995. Improved EELS performance with an imaging filter. Proceedings of the 29th Annual Conference of the Microbeam Analysis Society, Breckenridge, pp. 305–306. MacKenzie, M., Craven, A.J., Parkin, I., Nartowski, A., 1997. ELNES in Metal Nitrides. Institute of Physics Conference Series No. 153. IOP Publishing Ltd, Cambridge, MA, pp. 323–326. Mitterbauer, C., He´bert, C., Kothleitner, G., Hofer, F., Schattschneider, P., Zandbergen, H.W., 2004. Electron energy loss-near edge structure as a fingerprint for identifying chromium nitrides. Solid State Communications 130, 209–213. Paxton, A.T., van Schilfgaarde, M., MacKenzie, M., Craven, A.J., 2000. The near-edge structure in energy-loss spectroscopy: many-electron and magnetic effects in transition metal nitrides and carbides. Journal of Physics Condensed Matter 12, 729–750. Tsujimoto, M., Kurata, H., Nemoto, T., Isoda, I., Terada, S., Kaji, K., 2005. Influence of nitrogen vacancies on the N K-ELNES spectrum of titanium nitride. Journal of Electron Spectroscopy and Related Phenomena 143, 159–165. Wilhartitz, P., Dreer, S., Ramminger, P., 2004. Can oxygen stabilize chromium nitride?—characterization of high temperature cycled chromium oxynitride. Thin Solid Films 447–448, 289–295.
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 Cr0.47N0.53) were prepared on silicon wafers by reactive magnetron sputtering of a metallic chromium target in nitrogen plasma. In addition, a CrON sample (Cr0.5O0.2N0.3) 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 Cr0.47N0.53 and Cr0.5O0.2N0.3 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). * Corresponding author. Current address: Department of Chemical Engineering 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: [email protected] (C. Mitterbauer).
0968-4328/$ - see front matter q 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.micron.2006.01.006
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 (Cr0.5O0.2N0.3) 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 Cr0.47N0.53) were prepared by reactive magnetron sputtering of a metallic chromium target in nitrogen plasma. For the CrON film sample (Cr0.5O0.2N0.3, 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 LaB6-cathode. This
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Fig. 1. Morphology of the investigated specimens. (A) Focused ion beam thinned CrN specimen. (B) Ar ion milled Cr0.5O0.2N0.3 specimen.
microscope was equipped with a Gatan Imaging Filter (GIF 200), corrected for the major spectral aberrations up to second order (Krivanek et al., 1995). The EELS spectra were recorded from thin specimen regions (t/l!0.8) in TEM image mode (diffraction coupling) with a collection angle of 7 mrad and a spectrometer dispersion of 0.05 eV/channel (core loss spectra) and 0.5 eV/channel for the low loss spectra, respectively. All spectra were corrected for dark current and intrinsic channel to channel gain variations of the CCD. The background below the ionization edges was subtracted by using the power-law model and was corrected for the effect of thickness by means of the Fourier-ratio deconvolution (Egerton, 1996). In order to acquire an N–K edge spectrum of an ‘undamaged’ specimen, a non-irradiated area of the sample was selected and a moderate current density (in the order of 104 A/m2) was used. The time evolution of the N–K ELNES was obtained by collecting EELS spectra with 30 s exposure time during the irradiation period. The final spectrum in each series was acquired after irradiating the specimen for 300 s at maximum current density (w2!106 A/m2). Additionally, EELS spectra were collected at low temperature (w100 K)
by cooling the specimen in a liquid-nitrogen-cooled holder in order to minimize beam-induced specimen heating. 3. Results and discussion Fig. 2A shows the N–K edge in the reference spectrum from a thin section (approximately 35 nm) of a CrN powder sample (purityO99%; Alfa Aesarw). The powder was crushed in an agate mortar, dispersed in ethanol and placed on holey carbon grid. This spectrum was acquired under above experimental conditions with an exposure time of 30 s. The N–K edge ELNES remained unaffected by electron irradiation, therefore, only the first spectrum is displayed in Fig. 2A. The selected region of the N–K edge exhibits two features at energy-losses of 399.0 and 401.1 eV, respectively. The octahedral coordination of the N surrounding the Cr ions affects crystal field splitting and which results in a branching of the N–K edge (Mitterbauer et al., 2004). Peak I corresponds to the electronic transitions to unoccupied N 2p orbitals hybridized to Cr 3d-t2g orbitals while the peak II results from hybridized N 2p and Cr 3d-eg states. However, peak II is
Fig. 2. (A) Reference spectrum of the N–K ELNES from a CrN powder sample (purityO99%; Alfa Aesarw). (B) Time resolved N–K ELNES of a CrN film specimen measured at room temperature. All spectra are Fourier-ratio deconvoluted.
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Fig. 3. Time resolved N–K ELNES of a Cr0.47N0.53 film specimen measured at (A) low temperature (100 K) and (B) at room temperature (295 K). All spectra are Fourier-ratio deconvoluted.
hardly visible at the given energy resolution (0.8 eV full width at half maximum (FWHM) at the zero loss peak (ZLP)). A detailed description of the N–K ELNES, a comparison to monochromated EELS data, and theoretical calculations of
the N–K ELNES for CrN can be found in Mitterbauer et al. (2004). Contrary to the findings in this paper the investigated stoichiometric CrN film was more sensitive to radiation damage. Fig. 2B presents a series of EELS spectra from the
Fig. 4. Time resolved N–K ELNES of a Cr0.5O0.2N0.3 film specimen measured at (A) low temperature (100 K) and (B) at room temperature (295 K). All spectra are Fourier-ratio deconvoluted.
Fig. 5. (A) Low loss spectra (Fourier-log deconvoluted): (1) reference spectrum from a CrN powder sample (purityO99%; Alfa Aesarw), (2) CrN-, (3) Cr0.47N0.53-, and (4) Cr0.5O0.2N0.3-sample. (B) Time resolved O–K ELNES of a Cr0.5O0.2N0.3 film specimen measured at room temperature (295 K). All spectra are Fourier-ratio deconvoluted.
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CrN film measured at room temperature. By increasing the electron dose, a feature II at 401.4 eV emerges in the EEL spectra (indicated by arrow in Fig. 2B). In Cr0.47N0.53, the increase of intensity of the peak II with the accumulated electron dose was more distinct and the feature was sharper. The first spectra in Fig. 3 (0 min; nonirradiated Cr0.47N0.53 sample) show a significant effect due to the deposited electron dose. Comparing the EEL spectra of Cr0.47N0.53 at different temperatures, the increase of intensity (peak II) is less distinct at low temperatures (100 K, cf. Fig. 3A and B) but there is no distinct difference in peak intensity (feature II) after high-current-density irradiation, compared to the findings at room temperature. A similar behavior was also noticed in Cr0.5O0.2N0.3. The spectra series (Fig. 4B) of the Cr0.5O0.2N0.3 specimen at room temperature show a strong rise of the peak II. This can be attributed to the formation of an intermediate species which finally leads to a reversed peak ratio after high-current density irradiation. The narrow peak width of 1.4 eV FWHM precludes the possibility that the feature results from an orbital that is hybridized to an orbital of Cr. The occurrence of feature II presumably arises from a 1s–p*-transition of molecular nitrogen, which is formed in the interstitial positions of chromium oxynitride. Esaka et al. (1996) observed the formation of molecular nitrogen due to surface oxidation of CrN thin films monitored by X-ray absorption spectroscopy. Chung et al. (2005) were able to directly observe interstitial molecular N2 in SiON by using vibrationally resolved N–K edge absorption spectroscopy and X-ray photoelectron spectroscopy. N–K ELNES investigations of TiN also showed that peak I progressively decrease with respect to that of peak II as the number of nitrogen vacancies increases (Tsujimoto et al., 2005). Considering the experimental energy resolution in our EELS investigations, no electron irradiation-induced effects could be detected in the low loss region (Fig. 5A) and the Cr–L2,3 ELNES (not shown here; cf. Mitterbauer et al., 2004; Fig. 6) from all analyzed samples as well as the O–K ELNES of the Cr0.5O0.2N0.3 (Fig. 5B) specimen. 4. Concluding remarks We have shown that the N–K edge ELNES of chromium nitride and chromium oxynitride show changes in the peak ratio of the low-energy features during high-electron irradiation in a TEM. The O–K ELNES of the Cr0.5O0.2N0.3 sample, the Cr–L2,3 ELNES and the low loss region of all analyzed samples show no electron irradiation-induced effects. The N–K ELNES of the stoichiometric CrN film sample remains nearly unaffected. By changing the composition, however a sharp feature emerges at 401.4 eV. The relative intensity of the features further increases from Cr0.47N0.53 to Cr0.5O0.2N0.3. Therefore, the rise of the second peak could be used as an indicator for the composition of the chromium
(oxy)nitride. The feature in question (peak II) presumably arises from a 1s–p*-transition of molecular nitrogen located in interstitial positions. Acknowledgements We wish to thank the Austrian Science Foundation (FWF) within the Special Research Program ‘Electroactive Materials’ (project F00923) for financial support of C. Mitterbauer and M. Dienstleder and A. Brunegger (FELMI, Graz University of Technology) for sample preparation. References Chung, Y., Lee, C.H., Shin, H.J., 2005. Direct observation of interstitial molecular N2 in Si oxynitrides. Applied Physics Letters 86, 022901-1– 022901-3. Craven, A.J., 1995. The electron energy-loss near-edge structure (ELNES) on the N K-edges from the transition metal mononitrides with the rock-salt structure and its comparison with that on the C K-edges from the corresponding transition metal monocarbides. Journal of Microscopy 180, 250–262. Egerton, R.F., 1996. Electron Energy-loss Spectroscopy in the Electron Microscope, second ed. Plenum Press, New York. Egerton, R.F., Li, P., Malac, M., 2004. Radiation damage in the TEM and SEM. Micron 35, 399–409. Esaka, F., Furuya, K., Shimada, H., Imamura, M., Matsubayashi, N., Sato, T., Nishijima, A., Kawana, A., Ichimura, H., Kikuchi, T., 1996. X-ray absorption and X-ray photoelectron spectroscopic studies of air-oxidized chromium nitride thin films. Thin Solid Films 281–282, 314–317. Esaka, F., Furuya, K., Shimada, H., Imamura, M., Matsubayashi, N., Sato, T., Nishijima, A., Kawana, A., Ichimura, H., Kikuchi, T., 1997. Comparison of surface oxidation of titanium nitride and chromium nitride films studied by x-ray absorption and photoelectron spectroscopy. Journal of Vacuum Science and Technology 15, 2521–2528. Hofer, F., Golob, P., 1987. New examples for near-edge fine structures in electron energy-loss spectroscopy. Ultramicroscopy 21, 379–383. Krivanek, O.L., Kundmann, M.K., Trevor, C., Leapman, R.D., 1995. Improved EELS performance with an imaging filter. Proceedings of the 29th Annual Conference of the Microbeam Analysis Society, Breckenridge, pp. 305–306. MacKenzie, M., Craven, A.J., Parkin, I., Nartowski, A., 1997. ELNES in Metal Nitrides. Institute of Physics Conference Series No. 153. IOP Publishing Ltd, Cambridge, MA, pp. 323–326. Mitterbauer, C., He´bert, C., Kothleitner, G., Hofer, F., Schattschneider, P., Zandbergen, H.W., 2004. Electron energy loss-near edge structure as a fingerprint for identifying chromium nitrides. Solid State Communications 130, 209–213. Paxton, A.T., van Schilfgaarde, M., MacKenzie, M., Craven, A.J., 2000. The near-edge structure in energy-loss spectroscopy: many-electron and magnetic effects in transition metal nitrides and carbides. Journal of Physics Condensed Matter 12, 729–750. Tsujimoto, M., Kurata, H., Nemoto, T., Isoda, I., Terada, S., Kaji, K., 2005. Influence of nitrogen vacancies on the N K-ELNES spectrum of titanium nitride. Journal of Electron Spectroscopy and Related Phenomena 143, 159–165. Wilhartitz, P., Dreer, S., Ramminger, P., 2004. Can oxygen stabilize chromium nitride?—characterization of high temperature cycled chromium oxynitride. Thin Solid Films 447–448, 289–295.