Synthesis, Composition, and Electronic Structure of Cr−Si−N Thin

J. Phys. Chem. C 2008, 112, 1589-1593

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Synthesis, Composition, and Electronic Structure of Cr-Si-N Thin Films Formed by Reactive Ion Beam Mixing of Cr/Si Interfaces A. Arranz and C. Palacio* Departamento de Fı´sica Aplicada, Facultad de Ciencias, C-XII, UniVersidad Auto´ noma de Madrid, Cantoblanco, 28049-Madrid, Spain ReceiVed: July 3, 2007; In Final Form: October 30, 2007

Cr-Si-N thin films have been synthesized by 3 keV N2+ reactive ion beam mixing (IBM) of Cr/Si interfaces. The kinetics of growth, composition, and electronic structure of the films formed have been analyzed using X-ray photoelectron spectroscopy, angle-resolved X-ray photoelectron spectroscopy (ARXPS), ultraviolet photoelectron spectroscopy, factor analysis, and Monte Carlo TRIDYN simulations. ARXPS results show that the composition of the films formed by reactive IBM is rather uniform in the near-surface region. The comparison of experimental results with those obtained from TRIDYN, which uses pure ballistic mechanisms, suggests that the processes driven by residual defects are the rate-controlling mechanisms during the reactive IBM of Cr/Si interfaces. The reactive IBM kinetic is characterized by two stages: below ∼3 × 1016 ions/ cm2, a strong decrease of the Cr concentration along with a fast nitrogen incorporation is observed. This behavior can be explained mainly by Cr sputtering and nitrogen implantation. During this first stage, the formation of chromiun nitride and a small Si incorporation in the near-surface region are also observed, suggesting the formation of a CrNx/SiNx nanocomposite film. For ion doses above ∼3 × 1016 ions/cm2, the Cr/Si ratio can be varied in a broad range with nearly constant nitrogen concentration, as a consequence of sputtering, nitruration, and strong intermixing effects taking place simultaneously. Furthermore, during this second stage, chromium nitride is tranformed into a ternary (Cr-Si)N compound due to the strong Si incorporation in the near-surface region.

Introduction The synthesis and characterization of Cr-based ternary nitride coatings have recently attracted great interest because these compounds also display the outstanding wear and corrosion behavior of chromium nitride.1-16 It has been recently reported by several authors that the addition of silicon can improve considerably the mechanical properties and oxidation resistance of chromium nitride.11-16 Cr-Si-N thin films containing small silicon amounts have been grown by reactive sputtering (RSP)11-15 and a combination of RSP and arc ion plating.16 However, low temperature processes such as reactive ion beam mixing (IBM) of Cr/Si interfaces have not been explored, even though IBM of bilayers and multilayer structures is a feasible technique not only to grow thin films at low temperatures, but also to form new phases otherwise impossible to be produced using conventional techniques.10,17,18 In addition to that, the mechanical and tribological properties of the ternary films have been extensively studied as a function of the Si content, relating the hardness increase to the morphology and nanostructure of the films. Because of the great technological interest of CrSi-N coatings, the above-mentioned works have focused on their mechanical and tribological properties;11-16 however, the information available in the literature about the electronic structures of these materials is very scarce and rather limited.16 The above-mentioned reasons justify the interest in studying the room temperature (RT) synthesis of Cr-Si-N thin films by reactive ion beam mixing (IBM) of Cr/Si interfaces using 3 keV N2+ ion beams. * Corresponding author. Fax: [email protected].

++ 34 91 4974949. E-mail:

In order to avoid oxygen or carbon contamination characteristic of RSP films, especially if they are analyzed “ex situ” of the preparation chamber after exposition to atmospheric pressure, the synthesis and subsequent characterization of the films have been carried out in an ultrahigh vacuum (UHV) chamber. To characterize “in situ” the formation and electronic structures of such ultrathin Cr-Si-N films, surface-sensitive techniques such as X-ray photoelectron spectroscopy (XPS), angle-resolved X-ray photoelectron spectroscopy (ARXPS), and ultraviolet photoelectron spectroscopy (UPS) have been used. Special attention has been paid to the Cr 2p core level peak, analyzing the evolution of this band during reactive IBM by means of factor analysis (FA) in order to obtain a more complete description of the chemical composition of the films formed. In addition to that, the experimental results have been compared with those obtained from TRIDYN19,20 simulations in order to elucidate whether the reactive IBM of Cr/Si interfaces can be explained using only pure ballistic mixing mechanisms. The purpose of our study was not only to explore an alternative way to synthesize Cr-Si-N ternary compounds, but also to understand the kinetics of formation of such compounds, and above all to obtain information on the conditions leading either to the formation of a ternary compound or to a nanocomposite structure, since this point is of great relevance for the tribological applications of these films. Experimental Section The experiments were performed in an UHV system at a base pressure better than 8 × 10-8 Pa. Si(100) single crystals (ntype, 3.5 Ω‚cm) manufactured by Virginia Semiconductors Inc.

10.1021/jp0751615 CCC: $40.75 © 2008 American Chemical Society Published on Web 01/11/2008

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Arranz and Palacio below 2.7 × 10-7 Pa. The Cr deposition rate was estimated to be ∼0.19 nm/min. The Cr/Si interfaces were nitrogen implanted at room temperature in the preparation chamber using a Penning ion source (SPECS IQP 10/63). The ion bombardment was carried out using an ion beam energy of 3 keV, raising the pressure to 2 × 10-2 Pa of 5 N N2. The ion beam current density, measured with a Faraday cup that could be placed in the position of the sample holder, was 7.5 µA/cm2. Those experimental conditions lead to an ion beam with a flat profile greater than ∼10 × 10 mm2. The angle between the ion beam and the surface normal was 0°. Results and Discussion

Figure 1. Cr 2p, Si 2p, and N 1s core level spectra of Cr(8 nm)/Si interface exposed to different N2+ ion doses for an ion beam energy of 3 keV.

Figure 2. Cr, Si, and N concentrations obtained from experimental data (symbols + thin lines) and TRIDYN simulations (continuous, dashed, and dotted thick lines) for an ion beam energy of 3 keV, as a function of ion dose.

have been used as substrates throughout this work. They were degreased by successively boiling in carbon tetrachloride, acetone, and ethanol, and rinsed in deionized water. Then the samples were introduced into the UHV chamber. The substrates were sputter-cleaned “in situ” using a 3 keV Ar+ beam until no impurities were detected by XPS. XPS spectra were measured using a hemispherical analyzer (SPECS EA-10 Plus). The pass energy was 15 eV, giving a constant resolution of 0.9 eV. The Ag 3d5/2 line at 367.9 eV was used to calibrate binding energies. A twin anode (Mg and Al) X-ray source was operated at a constant power of 300 W using Mg KR radiation for the XPS measurements. For UPS, the He I line at 21.2 eV produced by a differentially pumped discharge lamp (SPECS UVS 10/35) was used. UPS valence band spectra were measured using the hemispherical analyzer operating in the constant relative resolution mode with a constant retardation ratio of 10. The Cr/Si interfaces were formed evaporating Cr layers 8 nm thick on the silicon substrates at room tempeature (RT) in a preparation chamber, with a base pressure better than 8 × 10-8 Pa, attached to the main analysis chamber. It should be pointed out that the sum of the ion projected range and the range straggling calculated using SRIM simulations is 56 Å for 3 keV N2+ ions on Cr and therefore the energy of the impinging ions is mainly deposited within the thickness of the deposited film. Chromium evaporation was carried out by electron bombardment at constant heating power of a 99.7% pure Cr rod target manufactured by Goodfellow, in such a way that the Crevaporated amount was controlled by the deposition time. During the evaporation, the residual pressure was always kept

Synthesis. Figure 1 shows the evolution of the Cr 2p, Si 2p, and N 1s core level spectra of the Cr(8 nm)/Si interface during 3 keV N2+ implantation, as a function of the ion dose. The spectra have been measured with a takeoff angle, θ ) 0°, and the background has been subtracted using a modified Shirley method.22 The upper spectra, labeled as 0 ions/cm2, are representative of metallic Cr because the Si 2p signal is completely attenuated by the Cr deposited layer. As the ion dose increases, several changes can be observed in Figure 1 that can be associated with the formation of Cr-N and Si-N bonds, sputtering effects, and intermixing of Cr and Si at the interface, which occur simultaneously. The binding energies of metallic Cr0 and Si0 species at 574.0 and 99.1 eV, respectively, and those at 574.5 and 101.8 eV observed for CrNx and SiNx thin films formed by 3 keV nitrogen implantation up to saturation on Cr and Si substrates, respectively, have been indicated in Figure 1 by dashed lines.18 Likewise, the N 1s binding energies, observed for CrNx (396.6 eV) and SiNx (397.6 eV) thin films formed by the same procedure, have been also indicated. Figure 2 shows the Cr, Si, and N average concentrations (symbols + thin lines) determined using sensitivity factors23 as a function of the ion dose. A strong decrease of the Cr concentration along with a fast nitrogen incorporation in the near-surface region is observed for ion doses up to ∼3 × 1016 ions/cm2. Above this dose the Cr/Si ratio varies in a broad range, whereas the nitrogen concentration remains practically constant because nitrogen implantation and nitrogen removal rates are similar, which leads to nitrogen saturation in the near-surface region. The changes observed during the first stage (up to ∼3 × 1016 ions/cm2) are mainly associated with Cr sputtering and nitrogen implantation. For higher ion doses, sputtering, nitrogen implantation, and a strong intermixing between Cr and Si at the interface are taking place simultaneously, in such a way that it is not straightforward to isolate the contribution of every mechanism in the overall process. To get further insight into the whole process, the reactive IBM of Cr/Si interfaces has been simulated using the dynamic Monte Carlo TRIDYN code. Further details about TRIDYN simulations can be found elsewhere.10,17,19,20,25 The Cr, Si, and N concentration depth profiles obtained using TRIDYN simulations show that a strong intermixing between Cr and Si is taking place, in such a way that the near-surface Cr/Si concentration ratio can be tailored by variation of the ion dose. The nitrogen profile reaches the saturation in the near-surface region at an ion dose of 8 × 1016 ions/cm2, and above this ion dose only changes in the Cr/Si ratio are observed. Simulations also show that the composition of the thin film formed by reactive IBM is rather uniform in the near-surface region for ion doses above 8 × 1016 ions/cm2. It should be pointed out that the concentrations of Cr, Si, and N obtained using angle-resolved X-ray photoelectron spectros-

Cr-Si-N Thin Films by Reactive IBM

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copy (ARXPS) are practically independent of the takeoff angle, therefore suggesting that the composition of the Cr-Si-N films formed by reactive IBM is rather uniform within the sampled depth (∼50 Å). Moreover, the Cr 2p, Si 2p, and N 1s bands do not show shape changes with increasing takeoff angle, supporting the uniform composition of the Cr-Si-N films in the nearsurface region. In order to compare experimental results of Figure 2 (symbols + thin lines) with those simulated using TRIDYN, the average concentration of element X (X ) Cr, Si, or N) in the formed film as a function of the ion dose has been calculated integrating every simulated depth profile, CX(z), using eq 1:

CX )

1 λX cos θ

(

∫0∞ CX(z) exp λX -z cos θ

)

dz

(1)

Here, the experimental takeoff angle is θ ) 0° and the attenuation lengths of Cr 2p, Si 2p, and N 1s photoelectrons are estimated to be λCr ≈ 14 Å, λSi ≈ 18.5 Å, and λN ≈ 21 Å.24 The results of such an integration are shown in Figure 2 by continuous, dashed, and dotted thick lines, for Cr, Si, and N, respectively. As can be observed, a considerable disagreement is found between the simulated and experimental concentrations in the near-surface region as a function of the ion dose. Moreover, simulations of reactive IBM of Cr/Si interfaces involving Cr thicknesses of (15% the nominal thickness have been also carried out; however, a strong disagreement is still found. Such a disagreement suggests that pure ballistic mixing mechanisms alone cannot explain the reactive IBM process of Cr/Si interfaces produced by 3 keV N2+ ions. Likewise, the results of Figure 2 clearly show that the experimental ion dose needed to obtain a specific Cr-Si-N film composition is much lower than that predicted with TRIDYN simulations, which uses pure ballistic mechanisms. As previously discussed in detail for the reactive IBM of other interfaces,17,25 the disagreement observed in Figure 2 between experimental and TRIDYN results suggests that, in addition to nitrogen implantation and pure ballistic atomic mixing mechanisms at the Cr/Si interface, simulated by the TRIDYN code, processes driven by residual defects26 should be the main mechanism responsible for the high mixing rate observed at the Cr/Si interface during low-energy reactive IBM at RT. Composition and Electronic Structure. As can be observed in Figure 1, for ion doses between 2.5 × 1016 and 8 × 1016 ions/cm2, the N 1s band shifts from 396.8 to 397.3 eV, and the Si 2p band shifts from 101.2 to 101.5 eV, with increasing Si content, whereas no metallic Cr0 and Si0 species are observed, therefore indicating that all Cr and Si atoms are bonded to nitrogen within the sampled depth. It should be pointed out that both the binding energy and the shape of the Cr 2p band at intermediate ion doses (∼3 × 1016 ions/cm2) are the same as those observed in a CrNx film formed by 3 keV nitrogen implantation of a Cr substrate.18 However, for higher ion doses, the Cr 2p band shifts to ∼575.2 eV, that is, 0.7 eV above the value observed for a CrNx film (∼574.5 eV). In addition to that, the Si 2p binding energy is lower than that observed in a SiNx film formed by 3 keV nitrogen implantation of a Si substrate.18 This behavior suggests that within the Cr-Si-N films formed, Cr atoms are more ionic whereas Si atoms are more covalent, than in single binary CrNx and SiNx nitrides, respectively. The reason should be attributed to the changes in the charge transfer from Cr and Si atoms to the nitrogen in the ternary nitride compound with respect to the binary nitrides. Moreover, for ion doses above ∼8 × 1016 ions/cm2, the shape and binding energy of Cr 2p, Si 2p, and N 1s bands do not display further

Figure 3. UPS valence band spectra of Cr-Si-N thin films as a function of Cr concentration, CCr. The atomic chromium concentration, CCr, and the ratio between the nitrogen concentration, CN, and those of Cr plus Si, CM ) CCr + CSi, are also indicated. The spectra labeled as CrNx and SiNx correspond to Cr and Si nitride films grown by 3 keV nitrogen implantation up to saturation of high-purity Cr and Si substrates, respectively. For the other spectra, the ion dose in ions/cm2 is also indicated parenthetically.

changes, therefore suggesting that they should be attributed to a (Cr-Si)N ternary nitride and not to a combination of binary nitrides. To get additional information on this point, the UPS valence band (VB) of the Cr-Si-N films formed has been measured. Figure 3 shows the UPS VB spectra of Cr-Si-N ternary nitride thin films after background subtraction based on a modified Shirley method.22 The atomic chromium concentration, CCr, and the ratio between the nitrogen concentration, CN, and those of Cr plus Si, CM ) CCr + CSi, calculated from Cr 2p, Si 2p, and N 1s bands using sensitivity factors22 are also indicated. The spectra labeled as CrNx and SiNx correspond to Cr and Si nitride films grown by 3 keV nitrogen implantation up to saturation of high-purity Cr and Si substrates, respectively. For the other spectra, the corresponding ion dose (in parentheses) is also indicated. The VB spectrum of the SiNx film is characterized by a broad band peaking at ∼4.6 and 6.6 eV formed by the strong hybridization of N 2p and Si 3p and 3s atomic orbitals due to a charge transfer from silicon to nitrogen atoms,18 and does not show occupied states at the Fermi level, EF, due to the insulating character of the film. On the other hand, the VB spectrum of the CrNx film is characterized by two broad peaks at ∼0.6 and 4.8 eV below EF. The first peak is mainly of Cr 3d character, whereas the second peak is formed by the strong hybridization of N 2p and Cr 3d atomic orbitals as a consequence of the charge transfer from Cr to N atoms. In this case, the high density of states at EF indicates the metallic character of this nitride,18,27 since CrNx films formed by 3 keV nitrogen implantation are formed by a mixture of 30% Cr2N and 70% CrN phases.28 With decreasing Cr concentration, the VB spectra show a gradual change from the CrNx VB spectrum to that of SiNx. Since the nitrogen concentration remains practically constant, no remarkable changes are observed in the density of states (DOS) intensity between ∼2 and 8 eV, but only a gradual shape change with decreasing Cr content. In a Cr-Si-N ternary nitride, this VB region is formed by the strong hybridization of N 2p, Cr 3d, and Si 3sp atomic orbitals. However, the occupied states at EF are mainly of Cr 3d character,18,27 and therefore the

1592 J. Phys. Chem. C, Vol. 112, No. 5, 2008 decrease of the Cr concentration causes a strong decrease of the DOS at the Fermi level along with the appearance of new occupied states at ∼1.6 eV (feature (a)), which suggests a metalto-insulator transition with decreasing Cr content. Occupied states at ∼1.5 eV of nearly pure Cr 3d character have been observed in the XPS VB of Cr1-xAlxN ternary nitrides by Sanjine´s et al.5 According to the XPS VB spectra reported by these authors, the DOS intensity at EF in those Cr-based ternary nitrides is very low, suggesting a shift of the Fermi level to higher binding energies. Therefore, the changes observed in Figure 3 strongly support the formation of a (Cr-Si)N ternary compound at higher ion doses, as previously suggested by the evolution of Cr 2p and Si 2p bands. In such a ternary compound, the Cr bond seems to change to a more insulating one than that observed in CrNx films. In a similar way, Martinez et al.11 have also found by electrical resistivity measurements that the addition of silicon to the Cr-N system also produces changes in the electronic properties of the films, leading to a more nonmetallic character. A more complete description of the evolution of the chemical composition of the ultrathin Cr-Si-N films formed by reactive IBM can be obtained by application of factor analysis (FA) to the Cr 2p data set of Figure 1. FA is a mathematical technique for the analysis of systems where a property can be represented as a linear combination of several variables. The use of FA to evaluate spectroscopic data is well documented, and the mathematical details will not be repeated here.29,30 In a first step, known as principal component analysis (PCA), the number of principal components, that is, the different phases present in the analyzed data set, is determined. It should be pointed out that spectra of the Cr 2p data set have been scaled to constant area before FA application to take into account the Cr loss because of sputtering. The application of the IND criterion29-31 to the Cr 2p data of Figure 1 gives three principal factors. If only the Cr 2p spectra measured for ion doses below ∼3 × 1016 ions/cm2 are analyzed, only two factors are detected. These factors can be associated with metallic chromium and chromium nitride, respectively, since according to previous discussion of Cr 2p evolution no (Cr-Si)N ternary nitride seems to be formed for such low ion doses. Likewise, if only the Cr 2p spectra for ion doses above ∼3 × 1016 ions/cm2 are analyzed, only two factors are also detected. In this case, these factors should be attributed to chromium nitride and (Cr-Si)N ternary nitride, respectively, since in this ion dose range metallic chromium has completely disappeared. In a second step, known as target testing (TT), the abstract components, in which the data matrix has been decomposed during PCA, are transformed into the spectra of the pure components and their respective concentrations (relative fractions) in each experimental spectrum.29,30 To carry out this task, a TT transformation with reliable target spectra has been carried out.29,30 The Cr 2p spectrum measured for a zero ion dose has been taken as the target spectrum for the principal factor related to metallic chromium. Likewise, the Cr 2p spectrum measured at saturation for a CrNx film formed by 3 keV nitrogen implantation of a pure Cr substrate18 has been used as the target spectrum for the chromium nitride component. As discussed previously, no changes in the binding energy and shape of the Cr 2p band have been observed for ion doses above ∼8 × 1016 ions/cm2; therefore, the experimental spectrum measured for an ion dose of 1.0 × 1017 ions/cm2 has been used as a reliable target spectrum for the principal factor associated with the (Cr-Si)N ternary compound. Once reliable target spectra are available for the three principal factors, they are used to obtain their respective

Arranz and Palacio

Figure 4. Evolution of Cr 2p pure component concentrations during reactive IBM of Cr(8 nm)/Si interface obtained using target testing transformation as explained in the text.

Figure 5. Cr 2p target spectra of different Cr phases formed during reactive IBM of Cr(8 nm)/Si interface (dotted lines). Continuous lines are the reproduction of these target spectra after TT transformation.

concentrations or weight factors in every experimental spectrum by TT transformation with spectra.29,30 It should be mentioned that the selected target spectra have been also scaled to constant area as for the Cr 2p data, before carrying out the TT transformation. Figure 4 shows the evolution of the three Cr principal factor concentrations as a function of the ion dose obtained after TT transformation with the above-mentioned target spectra. These target spectra, labeled as Cr0, CrNx, and (Cr-Si)N, respectively, are shown in Figure 5 by dotted lines, whereas the continuous lines are the reproduction of these target spectra after TT transformation. As can be seen the agreement is very good, supporting again the validity of the chosen target spectra as representative of the principal factors. Moreover, an excellent reproduction of all experimental spectra is obtained by combination of the pure component spectra weighted by their respective concentrations, therefore supporting the FA study carried out. Two stages can be observed for the concentration evolutions of Figure 4. In a first stage, a strong attenuation of the Cr0 signal is observed due not only to Cr sputtering but also to the formation of chromium nitride species up to ion doses of ∼3 × 1016 ions/cm2. During this first stage, only a small Si incorporation is observed in Figure 1 in the near-surface region, and even a part of this Si is still in metallic form. This behavior could be related to the formation of a CrNx/SiNx nanocomposite film as previously reported by other authors for RSP Cr-Si-N films with low Si contents.12-14,16 For ion doses above ∼3 × 1016 ions/cm2, metallic chromium has completely disappeared

Cr-Si-N Thin Films by Reactive IBM and the binary chromium nitride is transformed progressively in a ternary (Cr-Si)N compound as a consequence of the strong intermixing taking place between Cr and Si. During this second stage, a strong Si incorporation is observed in Figure 1 in the near-surface region, and no metallic Si species are observed. The above proposed change from a two-phase nanocomposite structure to a single-phase ternary nitride with increasing Si content in the film should be a consequence of the decrease in the average CrNx crystallite size upon increasing Si content as previously reported for RSP Nb-Si-N and Zr-Si-N films.32 Conclusions Cr-Si-N thin films have been grown by 3 keV N2+ reactive IBM of Cr/Si interfaces. The synthesis procedure, kinetics of growth, composition, and electronic structure of the films formed have been analyzed using XPS, ARXPS, UPS, FA, and TRIDYN simulations. ARXPS results show that the composition of the films formed by reactive IBM is rather uniform in the near-surface region. The comparison of experimental results with those obtained from TRIDYN, which uses pure ballistic mechanisms, suggests that processes driven by residual defects are the rate-controlling mechanisms during the reactive IBM of Cr/Si interfaces. Two stages have been found for the reactive IBM kinetic. A first stage, below ∼3 × 1016 ions/cm2, is characterized by a strong decrease of the Cr concentration along with a fast nitrogen incorporation, which can be explained mainly by Cr sputtering and nitrogen implantation. In this first stage, the formation of chromiun nitride and a small Si incorporation in the near-surface region are observed, suggesting the formation of a CrNx/SiNx nanocomposite film. In a second stage, for ion doses above ∼3 × 1016 ions/cm2, the Cr/Si ratio can be varied in a broad range with a rather constant nitrogen concentration, as a consequence of sputtering, nitruration, and strong intermixing effects taking place simultaneously. During this stage, chromiun nitride is tranformed into a ternary (CrSi)N compound due to the strong Si incorporation in the nearsurface region. Acknowledgment. The authors thank D. Dı´az and D. Alonso for technical assistance. This work was financially supported by the Spanish Ministerio de Ciencia y Tecnologı´a (Project No. MAT2005-05669-C03-01). Likewise, the authors gratefully acknowledge Dr. M. Posselt (Institute of Ion Beam Physics and Materials Research. Forschungszentrum Rossendorf, Dresden, Germany) for licensing the use of the TRIDYN program.

J. Phys. Chem. C, Vol. 112, No. 5, 2008 1593 References and Notes (1) Hones, P.; Sanjine´s, R.; Le´vy, F.; Shojaei, O. J. Vac. Sci. Technol., A 1999, 17, 1024. (2) C ˇ ekada, M.; Panjan, P.; Navinsˇek, B.; Cvelbar, F. Vacuum 1999, 52, 461. (3) Hones, P.; Diserens, M.; Sanjine´s, R.; Le´vy, F. J. Vac. Sci. Technol., B 2000, 18, 2851. (4) Aouadi, S. M.; Maeruf, T.; Twesten, R. D.; Mihut, D. M.; Rohde, S. L. Surf. Coat. Technol. 2006, 200, 3411. (5) Sanjine´s, R.; Banakh, O.; Rojas, C.; Schmid, P. E.; Le´vy, F. Thin Solid Films 2002, 420-421, 312. (6) Kawate, M.; Hashimoto, A. K.; Suzuki, T. Surf. Coat. Technol. 2003, 165, 163. (7) Hones, P.; Sanjine´s, R.; Le´vy, F. Thin Solid Films 1998, 332, 240. (8) Aouadi, S. M.; Wong, K. C.; Mitchell, K. A. R.; Namavar, F.; Tobin, E.; Mihut, D. M.; Rohde, S. L. Appl. Surf. Sci. 2004, 229, 387. (9) Lee, K. H.; Park, C. H.; Yoon, Y. S.; Lee, J. J. Thin Solid Films 2001, 385, 167. (10) Palacio, C.; Arranz, A. Surf. Sci. 2006, 600, 2385. (11) Martinez, E.; Sanjine´s, R.; Banakh, O.; Le´vy, F. Thin Solid Films 2004, 447-448, 332. (12) Martinez, E.; Sanjine´s, R.; Karimi, A.; Esteve, J.; Le´vy, F. Surf. Coat. Technol. 2004, 180-181, 570. (13) Mercs, D.; Bonasso, N.; Naamane, S.; Bordes, J. M.; Coddet, C. Surf. Coat. Technol. 2005, 200, 403. (14) Mercs, D.; Briois, P.; Demange, V.; Lamy, S.; Coddet, C. Surf. Coat. Technol. 2007, 16-17, 6970. (15) Lee, S. Y.; Kim, B.; Kim, S. D.; Kim, G.; Hong, Y. S. Thin Solid Films 2006, 506-507, 192. (16) Park, J. H.; Chung, W. S.; Cho, Y.; Kim, K. H. Surf. Coat. Technol. 2004, 188-189, 425. (17) Palacio, C.; Arranz, A. Surf. Sci. 2005, 578, 71. (18) Arranz, A.; Palacio, C. Surf. Sci. 2006, 600, 2510. (19) Mo¨ller, W.; Eckstein, W. Nucl. Instrum. Methods Phys. Res. B 1984, 2, 814. (20) Mo¨ller, W.; Eckstein, W.; Biersack, J. P. Comput. Phys. Commun. 1988, 51, 355. (21) Ziegler, J. F.; Biersack, J. B.; Littmark, U. The Stopping and Range of Ions in Matter; Pergamon: New York, 1985; Vol. 1. Ziegler, J. F. SRIM2000; 1201 Dixona Drive, Edgewater, MD, 21037; http://www.SRIM.org. (22) Proctor, A.; Sherwood, M. P. A. Anal. Chem. 1982, 54, 13. (23) Handbook of X-Ray Photoelectron Spectroscopy; Wagner, C. D., Riggs, W. M., Davis, L. E., Moulder, J. F., Muilenberg, G. E., Eds.; PerkinElmer Corp.: Eden Prairie, MN, 1979. (24) Seah, M. P.; Dench, W. A. Surf. Interface Anal. 1979, 1, 2. (25) Arranz, A.; Palacio, C. Thin Solid Films 2007, 515, 3426. (26) Kelly, R.; Miotello, A. Appl. Phys. Lett. 1994, 64, 2649. (27) Sanjine´s, R.; Hones, P.; Le´vy, F. Thin Solid Films 1998, 332, 225. (28) Palacio, C.; Arranz, A.; Dı´az, D. Thin Solid Films 2006, 513, 175. (29) Malinowski, E. R.; Howery, D. C. Factor Analysis in Chemistry; Krieger: Malabar, FL, 1989. (30) Palacio, C.; Mathieu, H. J. Surf. Interface Anal. 1990, 16, 178. (31) Arranz, A.; Palacio, C. Surf. Interface Anal. 1994, 22, 93. (32) Sandu, C. S.; Sanjine´s, R.; Benkahoul, M.; Medjani, F.; Le´vy, F. Surf. Coat. Technol. 2006, 201, 4083.