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XeCl laser treatment of steel surface
Applied Surface Science 197±198 (2002) 845±850
XeCl laser treatment of steel surface A. Pereiraa,*, A. Crosb, Ph. Delaportea, W. Marineb, M. Sentisa a
Lasers, Plasmas and Photonic Processes Laboratory (LP3), FRE 2165 CNRS, Universite de la MeÂditerraneÂe, Pole Scienti®que et Technologique de Luminy, 163, Avenue de Luminy, C. 917, 13288 Marseille Cedex 9, France b Groupe de Physique des Etats CondenseÂs (GPEC), UMR 6631 CNRS, Universite de la MeÂditerraneÂe, Pole Scienti®que et Technologique de Luminy, 163, Avenue de Luminy, C. 901, 13288 Marseille Cedex 9, France
Abstract Due to the UV radiation properties such as high surface adsorption and high photon energies, excimer laser are well adapted for surface treatment. UV laser irradiation of a surface with a ¯uence high enough induces the ejection of particles from the surface (through ablation process). In many cases, laser treatment results are more complex than simple ablation. We studied the effects of excimer laser (XeCl) irradiation of steel surface on its chemical properties. To investigate the induced surface changes, we have used Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). XPS and AES analyses show that the laser treatment induces the apparition of a Fe2O3 layer at the surface instead of FeOOH for an untreated surface. The evolution of the chemical properties of the surface has been studied as a function of the air exposure duration after the laser treatment. # 2002 Elsevier Science B.V. All rights reserved. Keywords: UV laser; Surface treatment; XPS and AES analysis
1. Introduction Motivated by economic and environment necessity, the industry has developed alternative cleaning processes, especially in many ®elds related to surface preparation like cleaning, dust or paint removal, etc. The laser treatment of metals and alloys has emerged as a novel surface modi®cation technique, and laser application in the surface treatment has grown rapidly in recent years. For example, it has been shown that high-power laser irradiation may modify the surface of metal and alloys to obtain a better resistance to wear and corrosion [1±3]. Moreover, in the case of iron, it has been shown that excimer laser irradiation in air or *
Corresponding author. Tel.: 33-4-91-82-92-86; fax: 33-4-91-82-92-89. E-mail address: [email protected] (A. Pereira).
nitrogen atmosphere can lead to signi®cative surface nitration, which is known to improve the hardness and corrosion resistance of the surface materials [4±6]. Due to the short pulse duration and rapid heating and cooling of the irradiation area, excimer laser ablation modi®es the chemical and physical properties of the surface without changing the properties of the bulk. The aim of this work is to study the effects of excimer laser XeCl irradiations on the chemical properties of a steel surface. The chemical property studies have been achieved with X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). These analysis techniques allow the analysis of the samples surface on depths of several nanometers depending on the escape length of the photoelectron. XPS is a powerful method for the study of oxidation processes and allows to identify the oxidation state and chemical environment of Fe atoms [7±12]. We have
0169-4332/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 9 - 4 3 3 2 ( 0 2 ) 0 0 4 6 0 - 9
846
A. Pereira et al. / Applied Surface Science 197±198 (2002) 845±850
also used AES and argon sputtering gun to perform a depth pro®le.
3. Results and discussion
2. Experimental
At ®rst, the XPS spectrum of the untreated steel surface shows the presence of Fe, O, C and other species Mn, Zn, Ca. XPS data on iron oxide and oxyhydroxide layers have been used for Fe 2p and O 1s spectra shape and binding energy analysis [8± 12]. The Fe 2p spectrum obtained from the untreated samples are shown in Fig. 1. Binding energy of the Fe 2p3/2 satellites allows to determine the Fe oxidation state. For iron in oxidation state II or III, the satellite of Fe 2p3/2 appears clearly as a shoulder in the photoelectron peak, while in mixed oxides of Fe(II) and Fe(III) the overlap of both structures make the satellite indistinguishable [10,11]. For the spectra of Fig. 1, the satellite of the Fe 2p3/2 peak can be observed at 719.5 eV and suggests the presence of Fe(III), in the form of Fe2O3 and/or FeOOH, with binding energies of 711.4 and 724.7 eV for Fe 2p3/2 and Fe 2p1/2, respectively. Furthermore, the shoulder at 707.4 eV indicates the presence of pure iron (Fe0) in the probed layer (10 nm) [9,11,13]. This spectrum does not allow to separate the constitution of FeOOH and Fe2O3 to the Fe 2p signal, so we used the O 1s spectra (Fig. 2) to gain further information. It suggests, the O 1s peak is composed of three peaks located at 530.4, 531.7 and 533.3 eV. These peaks can be assigned, respectively, to oxygen in the Fe±O bond of Fe2O3 and FeOOH, to oxygen in the OH bond of FeOOH and to adsorbed water [7±10]. The atomic concentration of the elements (Fe, O, C) calculated from the corresponding peak areas and the corresponding photoemission cross-section [13] are given in Table 1. We note an important carbon contamination of the untreated steel surface. Furthermore, the contributions of Fe±O, OH and H2O in the O 1s peak are, respectively, 41.3, 44.6 and 14.1%. The important OH concentration suggests in addition to the native oxide layer (2±3 nm), the formation of an oxyhydroxide layer [8,9,18]. For the samples treated at 2 and 10 J/cm2, the same study has been realized. For both ¯uences, the survey scan shows only the presence of Fe, O and C, and the Mn, Zn, Ca removal con®rms the cleaning effect of the laser irradiation. The peak shape of Fig. 1(b) and (c) are similar to the one obtained for the untreated
The tests were carried out on DD 11 steel (C, 0.12 wt.%; Mn, 0.30 wt.%; P, 0.045 wt.%; S, 0.045 wt.%, and balance of Fe). Samples of 10 10 mm2 and 3 mm thickness were irradiated with the laser in air. The laser source was a 80 W excimer laser from Lambda Physics (EMG 203 MSC, l 308 nm, t 25 ns). An optical system allowed to irradiate the sample with a uniform ¯uence from 2 to 10 J/cm2. The samples were ®xed on a X±Y table and translated in front of the beam. They were irradiated in a scanning mode to cover all the area. The table speed and the laser pulse repetition rate were set to obtain 10 pulses at each point of the surface. The chemical composition of the untreated and laser-treated specimens were analysed by XPS and AES. The XPS measurement were performed using a non-monochromatized Al Ka X-ray source at 1486.6 eV. The photoelectrons were collected and analysed using a hemispherical analyser with pass energies of 50 and 20 eV for the general scans and the high resolution core levels scans, respectively. Quantitative analyses were performed by ®tting the XPS spectra with a mixed Gaussian±Lorentzian pro®le after subtraction of a Shirley-background [17]. Depth pro®le was recorded by AES equipped with an argon sputtering gun. The spectra were collected from an area of approximately 1 1 mm2 in the centre of the sputtered region. 2.1. Procedure Oxide, hydroxide and oxyhydroxide coatings are naturally formed on steel in air at room conditions. For the comprehension of laser irradiation effects on surface steel, we studied the chemical composition of the surface and its evolution as a function of air exposure duration after the laser treatment. So, some samples were analysed (XPS) as soon as possible after the treatment and the air exposure was limited to 5 min. For other samples, delays of 24 h and 1 month in room atmosphere have been used between the laser treatment and the XPS analyses.
3.1. XPS analysis
A. Pereira et al. / Applied Surface Science 197±198 (2002) 845±850
847
Fig. 1. The Fe 2p photoelectron peak of treated and untreated sample: (a) untreated sample, (b) 2 J/cm2 in air and (c) 10 J/cm2 in air.
sample (Fig. 1(a)). The peaks binding energy of 711.4 and 724.7 eV are due to Fe 2p3/2 and Fe 2p1/2, respectively. We note the absence of metallic iron at 707.4 eV in (b) and (c) indicating that the thickness of oxide and oxyhydroxide layer is larger than the probed depth (10 nm) on the laser-irradiated samples. The laser irradiation induces both surface cleaning and iron oxide formation. The O 1s spectra, shown in Fig. 2, is composed of two peaks originating from oxygen in the oxide (O2 ) at 530.4 eV and oxygen in hydroxyl group (OH ) at 532.1 eV. Besides, an important concentration of carbon in the steel surface (Table 1), the quantitative analysis reveal that the
contribution of OH is less important than in the case of the untreated sample: 37% for OH against 63% for Fe±O at 2 J/cm2 and 77% for Fe±O against 23% for OH at 10 J/cm2. So, the laser irradiation induces the creation of Fe2O3 oxide layer instead of FeOOH oxyhydroxide layer. This effect is more pronounced at higher ¯uence. The evolution of the chemical properties of the surface has been studied as a function of the air exposure after the laser treatment. The O 1s spectra, after 1 month, are shown in Fig. 2(d) and (e). As expected the contamination by carbon increases with the air exposure (Table 1) and we can see that the
Table 1 Composition of the treated and untreated surface steel analysed by XPS Sample
C 1s (%)
Fe 2p (%)
O 1s (%)
Fitting O 1s peak Fe±O (%)
Untreated Air, 2 J/cm2 Air, 10 J/cm2 Air, 2 J/cm2 in 1 month Air, 10 J/cm2 in 1 month
47.9 48.4 29.6 82.9 70.9
6.8 10.2 14.3 1.6 4.1
45.3 41.4 56.1 15.5 25.0
41.3 63.3 77.3 30.1 46.8
OH (%) 44.6 36.7 22.7 52.4 39.4
H2O (%) 14.1 0 0 17.5 13.8
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A. Pereira et al. / Applied Surface Science 197±198 (2002) 845±850
Fig. 2. The O 1s photoelectron peak of treated and untreated sample: (a) untreated sample, (b) 2 J/cm2 in air, (c) 10 J/cm2 in air, (d) 10 J/cm2 after 1 month and (e) 2 J/cm2 after 1 month.
carbon contribution is more important for the laserirradiated samples after 1 month of air exposure than for the untreated samples. This difference can be explained by carbon diffusion during the laser treatment. As shown in AES analysis and in Fig. 3, the necessary time for carbon removal, 30 min, suggests that this carbon is not only a pollution layer. The hydration of the oxide layer can also be observed in Fig. 2(d) and (e) and in Table 1 which show an increase of the OH and H2O concentration after 1 month. These effects are less pronounced for high laser ¯uence. 3.2. AES analysis Metallic iron gives rise to a Fe(MNN) peak at 47 eV and two oxide-related peaks at 43±46 and 51±52.5 eV [14±16]. These binding energies and the measurement of O(KLL)/Fe(LMM) ratio [14], permit us to
determine the iron oxidation states. An analysis of the untreated surface before sputtering shows a large amount of carbon (48%) (Fig. 3) which prevents any detection of the Fe(MNN) peak. This carbon pollution disappears quickly with sputtering: 8 and 4% after 2 and 6 min of sputtering, respectively. The analysis realized after 2 min of sputtering, has shown a single Fe(MNN) peak at 47 eV indicating the presence of metallic iron in spite of 35% of oxygen. Sputtering time of 2 min is suf®cient to remove the oxide layer and most of the carbon contamination. Qualitative results obtained for 2 and 10 J/cm2 treated sample are similar. The analysis before sputtering shows two peaks for Fe(MNN) at 44.6 and 52.5 eV associated to oxidized iron in the form of either a-Fe2O3 or gFeOOH. The O(KLL)/Fe(LMM) ratio is about 4.40, in agreement with the literature for Fe2O3 (ratio of 4.38) [14]. After 2 min of sputtering and in spite of a small shoulder at 54.5 eV, metallic iron is prevailing.
A. Pereira et al. / Applied Surface Science 197±198 (2002) 845±850
849
Fig. 3. Composition of the treated and untreated steel surface versus sputtering time.
At this stage, the percentage of oxygen, as shown in Fig. 3, is important (49%) and will remain the same during all the sputtering. If we estimate a sputtering Ê s 1 (measurements done with Si permitted rate of 1 A Ê s 1 by the Ar to estimate an etching rate of 1 A sputtering in spot mode), the thickness of the Fe2O3 oxide layer is estimated to about 12 nm and the zone of high oxygen content to be about 300 nm on treated sample. These observations are similar to what is observed in cast steel [19]. 4. Conclusion In summary, we have demonstrated the importance of the excimer laser treatment for a steel surface. XPS and AES experiments clearly show that the laser irradiation of steel has a cleaning effect and results in the formation of Fe3 oxides (10 nm), mainly Fe2O3. It has been found that higher ¯uence promote the formation of Fe2O3 oxide instead of FeOOH. This Fe2O3 layer permits to improve the resistance to corrosion and so protect the surface before following the treatment. At the same time, the AES analysis has shown an important diffusion of oxygen in the bulk.
References [1] A.C. Aggudelo, J.R. Gancedo, J.F. Marco, M.F. Creus, E. Gallego-Lluesma, J. Desimoni, R.C. Mercader, Appl. Surf. Sci. 148 (1999) 171±182. [2] T.M. Yue, J.K. Yu, H.C. Man, Surf. Coat. Technol. 137 (2001) 65±71. [3] A. Conde, R. Colaco, R. Vilar, J. de Damborenea, Mater. Des. 21 (2000) 441±445. [4] P. Schaaf, A. Emmel, C. Illgner, K.P. Lieb, E. Schubert, H.W. Bergmann, Mater. Sci. Eng. A 197 (1995) L1. [5] E. Carpene, F. Landry, P. Schaaf, J. Appl. Phys. 77 (2000) 2412. [6] A. Conde, I. Garcia, J. de Damborenea, Corros. Sci. 43 (2001) 817. [7] J.B. Metson, M.M. Hyland, A. Gillespie, M. HemmingsenJensen, Colloids Surf. A 93 (1994) 173±180. [8] G. Kurbatov, E. Darque-Ceretti, M. Aucouturier, Surf. Interf. Anal. 20 (1996) 402±406. [9] S. Suzuki, K. Yanagihara, K. Hirokawa, Surf. Interf. Anal. 30 (2000) 372±376. [10] T.C. Lin, G. Seshadri, J.A. Kelber, Appl. Surf. Sci. 119 (1997) 83±92. [11] M. Descotes, F. Mercier, N. Thromat, C. Beaucaire, M. Gautier-Soyer, Appl. Surf. Sci. 165 (2000) 288±302. [12] I.D. Wesh, P.M.A. Sherwood, Phys. Rev. B 40 (1989) 6386. [13] C.D. Wagner, W.M. Riggs, L.E. Davis, J.F. Moulder, Handbook of X-Ray Photoelectron Spectroscopy, Perkin Elmer Corp., Physical Electronics Division, Eden Prairie, Minnesota, 1979.
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A. Pereira et al. / Applied Surface Science 197±198 (2002) 845±850
[14] A.G. Sault, Appl. Surf. Sci. 74 (1994) 249±262. [15] M. Seo, J.B. Lumsden, R.W. Staehle, Surf. Sci. 50 (1975) 541±552. [16] Handbook of Auger Electron Spectroscopy. [17] P.M.A. Sherwood, J. Vac. Sci. Technol. A 14 (1996) 1424± 1432.
[18] P. Landolt, in: Corrosion et Chimie de Surfaces des MeÂtaux, Eds. Presses Polytechniques et Universitaires Romandes, 1997. [19] A. Fontes, Refusion micromeÂtrique super®cielle par laser aÁ exciplexes de la matrice de fontes pour l'ameÂlioration des proprieÂteÂs tribologiques, TheÁse de doctorat, Ecole Nationale SupeÂrieure des Mines de Paris, 1994.
XeCl laser treatment of steel surface A. Pereiraa,*, A. Crosb, Ph. Delaportea, W. Marineb, M. Sentisa a
Lasers, Plasmas and Photonic Processes Laboratory (LP3), FRE 2165 CNRS, Universite de la MeÂditerraneÂe, Pole Scienti®que et Technologique de Luminy, 163, Avenue de Luminy, C. 917, 13288 Marseille Cedex 9, France b Groupe de Physique des Etats CondenseÂs (GPEC), UMR 6631 CNRS, Universite de la MeÂditerraneÂe, Pole Scienti®que et Technologique de Luminy, 163, Avenue de Luminy, C. 901, 13288 Marseille Cedex 9, France
Abstract Due to the UV radiation properties such as high surface adsorption and high photon energies, excimer laser are well adapted for surface treatment. UV laser irradiation of a surface with a ¯uence high enough induces the ejection of particles from the surface (through ablation process). In many cases, laser treatment results are more complex than simple ablation. We studied the effects of excimer laser (XeCl) irradiation of steel surface on its chemical properties. To investigate the induced surface changes, we have used Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). XPS and AES analyses show that the laser treatment induces the apparition of a Fe2O3 layer at the surface instead of FeOOH for an untreated surface. The evolution of the chemical properties of the surface has been studied as a function of the air exposure duration after the laser treatment. # 2002 Elsevier Science B.V. All rights reserved. Keywords: UV laser; Surface treatment; XPS and AES analysis
1. Introduction Motivated by economic and environment necessity, the industry has developed alternative cleaning processes, especially in many ®elds related to surface preparation like cleaning, dust or paint removal, etc. The laser treatment of metals and alloys has emerged as a novel surface modi®cation technique, and laser application in the surface treatment has grown rapidly in recent years. For example, it has been shown that high-power laser irradiation may modify the surface of metal and alloys to obtain a better resistance to wear and corrosion [1±3]. Moreover, in the case of iron, it has been shown that excimer laser irradiation in air or *
Corresponding author. Tel.: 33-4-91-82-92-86; fax: 33-4-91-82-92-89. E-mail address: [email protected] (A. Pereira).
nitrogen atmosphere can lead to signi®cative surface nitration, which is known to improve the hardness and corrosion resistance of the surface materials [4±6]. Due to the short pulse duration and rapid heating and cooling of the irradiation area, excimer laser ablation modi®es the chemical and physical properties of the surface without changing the properties of the bulk. The aim of this work is to study the effects of excimer laser XeCl irradiations on the chemical properties of a steel surface. The chemical property studies have been achieved with X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). These analysis techniques allow the analysis of the samples surface on depths of several nanometers depending on the escape length of the photoelectron. XPS is a powerful method for the study of oxidation processes and allows to identify the oxidation state and chemical environment of Fe atoms [7±12]. We have
0169-4332/02/$ ± see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 9 - 4 3 3 2 ( 0 2 ) 0 0 4 6 0 - 9
846
A. Pereira et al. / Applied Surface Science 197±198 (2002) 845±850
also used AES and argon sputtering gun to perform a depth pro®le.
3. Results and discussion
2. Experimental
At ®rst, the XPS spectrum of the untreated steel surface shows the presence of Fe, O, C and other species Mn, Zn, Ca. XPS data on iron oxide and oxyhydroxide layers have been used for Fe 2p and O 1s spectra shape and binding energy analysis [8± 12]. The Fe 2p spectrum obtained from the untreated samples are shown in Fig. 1. Binding energy of the Fe 2p3/2 satellites allows to determine the Fe oxidation state. For iron in oxidation state II or III, the satellite of Fe 2p3/2 appears clearly as a shoulder in the photoelectron peak, while in mixed oxides of Fe(II) and Fe(III) the overlap of both structures make the satellite indistinguishable [10,11]. For the spectra of Fig. 1, the satellite of the Fe 2p3/2 peak can be observed at 719.5 eV and suggests the presence of Fe(III), in the form of Fe2O3 and/or FeOOH, with binding energies of 711.4 and 724.7 eV for Fe 2p3/2 and Fe 2p1/2, respectively. Furthermore, the shoulder at 707.4 eV indicates the presence of pure iron (Fe0) in the probed layer (10 nm) [9,11,13]. This spectrum does not allow to separate the constitution of FeOOH and Fe2O3 to the Fe 2p signal, so we used the O 1s spectra (Fig. 2) to gain further information. It suggests, the O 1s peak is composed of three peaks located at 530.4, 531.7 and 533.3 eV. These peaks can be assigned, respectively, to oxygen in the Fe±O bond of Fe2O3 and FeOOH, to oxygen in the OH bond of FeOOH and to adsorbed water [7±10]. The atomic concentration of the elements (Fe, O, C) calculated from the corresponding peak areas and the corresponding photoemission cross-section [13] are given in Table 1. We note an important carbon contamination of the untreated steel surface. Furthermore, the contributions of Fe±O, OH and H2O in the O 1s peak are, respectively, 41.3, 44.6 and 14.1%. The important OH concentration suggests in addition to the native oxide layer (2±3 nm), the formation of an oxyhydroxide layer [8,9,18]. For the samples treated at 2 and 10 J/cm2, the same study has been realized. For both ¯uences, the survey scan shows only the presence of Fe, O and C, and the Mn, Zn, Ca removal con®rms the cleaning effect of the laser irradiation. The peak shape of Fig. 1(b) and (c) are similar to the one obtained for the untreated
The tests were carried out on DD 11 steel (C, 0.12 wt.%; Mn, 0.30 wt.%; P, 0.045 wt.%; S, 0.045 wt.%, and balance of Fe). Samples of 10 10 mm2 and 3 mm thickness were irradiated with the laser in air. The laser source was a 80 W excimer laser from Lambda Physics (EMG 203 MSC, l 308 nm, t 25 ns). An optical system allowed to irradiate the sample with a uniform ¯uence from 2 to 10 J/cm2. The samples were ®xed on a X±Y table and translated in front of the beam. They were irradiated in a scanning mode to cover all the area. The table speed and the laser pulse repetition rate were set to obtain 10 pulses at each point of the surface. The chemical composition of the untreated and laser-treated specimens were analysed by XPS and AES. The XPS measurement were performed using a non-monochromatized Al Ka X-ray source at 1486.6 eV. The photoelectrons were collected and analysed using a hemispherical analyser with pass energies of 50 and 20 eV for the general scans and the high resolution core levels scans, respectively. Quantitative analyses were performed by ®tting the XPS spectra with a mixed Gaussian±Lorentzian pro®le after subtraction of a Shirley-background [17]. Depth pro®le was recorded by AES equipped with an argon sputtering gun. The spectra were collected from an area of approximately 1 1 mm2 in the centre of the sputtered region. 2.1. Procedure Oxide, hydroxide and oxyhydroxide coatings are naturally formed on steel in air at room conditions. For the comprehension of laser irradiation effects on surface steel, we studied the chemical composition of the surface and its evolution as a function of air exposure duration after the laser treatment. So, some samples were analysed (XPS) as soon as possible after the treatment and the air exposure was limited to 5 min. For other samples, delays of 24 h and 1 month in room atmosphere have been used between the laser treatment and the XPS analyses.
3.1. XPS analysis
A. Pereira et al. / Applied Surface Science 197±198 (2002) 845±850
847
Fig. 1. The Fe 2p photoelectron peak of treated and untreated sample: (a) untreated sample, (b) 2 J/cm2 in air and (c) 10 J/cm2 in air.
sample (Fig. 1(a)). The peaks binding energy of 711.4 and 724.7 eV are due to Fe 2p3/2 and Fe 2p1/2, respectively. We note the absence of metallic iron at 707.4 eV in (b) and (c) indicating that the thickness of oxide and oxyhydroxide layer is larger than the probed depth (10 nm) on the laser-irradiated samples. The laser irradiation induces both surface cleaning and iron oxide formation. The O 1s spectra, shown in Fig. 2, is composed of two peaks originating from oxygen in the oxide (O2 ) at 530.4 eV and oxygen in hydroxyl group (OH ) at 532.1 eV. Besides, an important concentration of carbon in the steel surface (Table 1), the quantitative analysis reveal that the
contribution of OH is less important than in the case of the untreated sample: 37% for OH against 63% for Fe±O at 2 J/cm2 and 77% for Fe±O against 23% for OH at 10 J/cm2. So, the laser irradiation induces the creation of Fe2O3 oxide layer instead of FeOOH oxyhydroxide layer. This effect is more pronounced at higher ¯uence. The evolution of the chemical properties of the surface has been studied as a function of the air exposure after the laser treatment. The O 1s spectra, after 1 month, are shown in Fig. 2(d) and (e). As expected the contamination by carbon increases with the air exposure (Table 1) and we can see that the
Table 1 Composition of the treated and untreated surface steel analysed by XPS Sample
C 1s (%)
Fe 2p (%)
O 1s (%)
Fitting O 1s peak Fe±O (%)
Untreated Air, 2 J/cm2 Air, 10 J/cm2 Air, 2 J/cm2 in 1 month Air, 10 J/cm2 in 1 month
47.9 48.4 29.6 82.9 70.9
6.8 10.2 14.3 1.6 4.1
45.3 41.4 56.1 15.5 25.0
41.3 63.3 77.3 30.1 46.8
OH (%) 44.6 36.7 22.7 52.4 39.4
H2O (%) 14.1 0 0 17.5 13.8
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A. Pereira et al. / Applied Surface Science 197±198 (2002) 845±850
Fig. 2. The O 1s photoelectron peak of treated and untreated sample: (a) untreated sample, (b) 2 J/cm2 in air, (c) 10 J/cm2 in air, (d) 10 J/cm2 after 1 month and (e) 2 J/cm2 after 1 month.
carbon contribution is more important for the laserirradiated samples after 1 month of air exposure than for the untreated samples. This difference can be explained by carbon diffusion during the laser treatment. As shown in AES analysis and in Fig. 3, the necessary time for carbon removal, 30 min, suggests that this carbon is not only a pollution layer. The hydration of the oxide layer can also be observed in Fig. 2(d) and (e) and in Table 1 which show an increase of the OH and H2O concentration after 1 month. These effects are less pronounced for high laser ¯uence. 3.2. AES analysis Metallic iron gives rise to a Fe(MNN) peak at 47 eV and two oxide-related peaks at 43±46 and 51±52.5 eV [14±16]. These binding energies and the measurement of O(KLL)/Fe(LMM) ratio [14], permit us to
determine the iron oxidation states. An analysis of the untreated surface before sputtering shows a large amount of carbon (48%) (Fig. 3) which prevents any detection of the Fe(MNN) peak. This carbon pollution disappears quickly with sputtering: 8 and 4% after 2 and 6 min of sputtering, respectively. The analysis realized after 2 min of sputtering, has shown a single Fe(MNN) peak at 47 eV indicating the presence of metallic iron in spite of 35% of oxygen. Sputtering time of 2 min is suf®cient to remove the oxide layer and most of the carbon contamination. Qualitative results obtained for 2 and 10 J/cm2 treated sample are similar. The analysis before sputtering shows two peaks for Fe(MNN) at 44.6 and 52.5 eV associated to oxidized iron in the form of either a-Fe2O3 or gFeOOH. The O(KLL)/Fe(LMM) ratio is about 4.40, in agreement with the literature for Fe2O3 (ratio of 4.38) [14]. After 2 min of sputtering and in spite of a small shoulder at 54.5 eV, metallic iron is prevailing.
A. Pereira et al. / Applied Surface Science 197±198 (2002) 845±850
849
Fig. 3. Composition of the treated and untreated steel surface versus sputtering time.
At this stage, the percentage of oxygen, as shown in Fig. 3, is important (49%) and will remain the same during all the sputtering. If we estimate a sputtering Ê s 1 (measurements done with Si permitted rate of 1 A Ê s 1 by the Ar to estimate an etching rate of 1 A sputtering in spot mode), the thickness of the Fe2O3 oxide layer is estimated to about 12 nm and the zone of high oxygen content to be about 300 nm on treated sample. These observations are similar to what is observed in cast steel [19]. 4. Conclusion In summary, we have demonstrated the importance of the excimer laser treatment for a steel surface. XPS and AES experiments clearly show that the laser irradiation of steel has a cleaning effect and results in the formation of Fe3 oxides (10 nm), mainly Fe2O3. It has been found that higher ¯uence promote the formation of Fe2O3 oxide instead of FeOOH. This Fe2O3 layer permits to improve the resistance to corrosion and so protect the surface before following the treatment. At the same time, the AES analysis has shown an important diffusion of oxygen in the bulk.
References [1] A.C. Aggudelo, J.R. Gancedo, J.F. Marco, M.F. Creus, E. Gallego-Lluesma, J. Desimoni, R.C. Mercader, Appl. Surf. Sci. 148 (1999) 171±182. [2] T.M. Yue, J.K. Yu, H.C. Man, Surf. Coat. Technol. 137 (2001) 65±71. [3] A. Conde, R. Colaco, R. Vilar, J. de Damborenea, Mater. Des. 21 (2000) 441±445. [4] P. Schaaf, A. Emmel, C. Illgner, K.P. Lieb, E. Schubert, H.W. Bergmann, Mater. Sci. Eng. A 197 (1995) L1. [5] E. Carpene, F. Landry, P. Schaaf, J. Appl. Phys. 77 (2000) 2412. [6] A. Conde, I. Garcia, J. de Damborenea, Corros. Sci. 43 (2001) 817. [7] J.B. Metson, M.M. Hyland, A. Gillespie, M. HemmingsenJensen, Colloids Surf. A 93 (1994) 173±180. [8] G. Kurbatov, E. Darque-Ceretti, M. Aucouturier, Surf. Interf. Anal. 20 (1996) 402±406. [9] S. Suzuki, K. Yanagihara, K. Hirokawa, Surf. Interf. Anal. 30 (2000) 372±376. [10] T.C. Lin, G. Seshadri, J.A. Kelber, Appl. Surf. Sci. 119 (1997) 83±92. [11] M. Descotes, F. Mercier, N. Thromat, C. Beaucaire, M. Gautier-Soyer, Appl. Surf. Sci. 165 (2000) 288±302. [12] I.D. Wesh, P.M.A. Sherwood, Phys. Rev. B 40 (1989) 6386. [13] C.D. Wagner, W.M. Riggs, L.E. Davis, J.F. Moulder, Handbook of X-Ray Photoelectron Spectroscopy, Perkin Elmer Corp., Physical Electronics Division, Eden Prairie, Minnesota, 1979.
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A. Pereira et al. / Applied Surface Science 197±198 (2002) 845±850
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