Thin Solid Films 453 – 454 (2004) 16–21 0040-6090/04/$ - see front matter  2003 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2003.11.072 Laser treatment of a steel surface in ambient air A. Pereira *, P. Delaporte , M. Sentis , A. Cros , W. Marine , A. Basillais , A.L. Thomann , a, a a b b c c C. Leborgne , N. Semmar , P. Andreazza , T. Sauvage c c d e LP3, CNRSyUniversite de la Mediterranee, Pole scientifique de Luminy, 163 avenue de Luminy, C.917, 13288, Marseille, Cedex 9, France a ´ ´ ´ GPEC, CNRSyUniversite de la Mediterranee, Pole scientifique de Luminy, 163 avenue de Luminy, C.901, 13288, Marseille, Cedex 9, France b ´ ´ ´ GREMI, CNRSyUniversite d’Orleans, 14 rue d’Issoudun, 45067, Orleans, Cedex 2, France c ´ ´ ´ CRMD, CNRSyUniversite d’Orleans, 1b rue de la Ferollerie, 45071, Orleans, Cedex 2, France d ´ ´ ´ CERI, CNRS, 3a rue de la Ferollerie, 45071, Orleans, Cedex 2, France e ´ Abstract We study the steel surface modifications induced by irradiation of several lasers in air. The surface modifications are found to depend on the laser properties (Krf, 248 nm, 26 ns; XeCl, 308 nm, 25 ns; Nd:YAG, 1064 or 532 nm, 5 or 10 ns). The treated surface features (morphology, chemical composition and crystalline structure) are analysed by complementary techniques, such as X-ray photoelectron spectroscopy, nuclear reactions, scanning electron microscopy and grazing incidence X-ray diffraction. First of all, it is shown that the carbon coming from the machining oils is successfully removed under all the studied conditions. The incorporation of oxygen and nitrogen (beyond 1 mm in depth) to the surface is also shown. In addition to the original ferrite phase, new crystalline compounds are detected after treatment such as austenite, oxides (FeO or Fe O , Fe O ) and nitride (´- 2 3 3 4 Fe N). Depending on the laser characteristics, the main formed crystalline phases are different (oxide or nitride). A discussion 2–3 of the expected surface modification mechanisms is presented. Under some experimental conditions, the formation of a back- deposition layer composed of oxides and hydroxides is observed.  2003 Elsevier B.V. All rights reserved. Keywords: Laser ablation; Heat treatment; Oxidation; Nitrides 1. Introduction A typical metallic surface is composed of complex oxides and atmospheric components like carbon, oils, etc. For some applications of the metal, these polluted layers have to be removed before the final use. Wet chemical, electrolytic and mechanical processes are usu- ally used for surface cleaning in order to achieve new properties of the surface w1x. Many of these processes can generate an environmental risk and there is, there- fore, a definite needs to develop treatments, which use less, or preferably no chemical compounds. A review of the literature indicates that new environment-friendly treatments such as cryoblasting w2,3x, plasma w4x and laser are investigated to replace the polluting processes. In recent years, applications of laser-based processes have been developed. As examples, laser cleaning in *Corresponding author. Tel.: q33-4-91-82-92-86; fax: q33-4-91- 82-92-89. E-mail address: pereira@lp3.univ-mrs.fr (A. Pereira). microelectronic devices w5x and in artworks w6x, laser decontamination in nuclear industry w7x can be men- tioned. Most of these surface modification are achieved with nanosecond lasers in the wavelength range between 193 nm and 10.6 mm. Applications inducing nitrides synthesis connected with an oxidation of the near surface are becoming particularly attractive. The laser nitriding of iron and steel is well known to improve hardness, wear and corrosion resistance of the irradiated surfaces w8,9x. Oxidation layer containing larger amounts of a- Fe O and Fe O produced by CO laser irradiation 2 3 3 4 2 obviously reduces the corrosion rate of the steel against the corrosion w10x. However, the physical processes responsible of the surface modifications are still not clearly understood because of the complicated laser- plasma-surface interactions. In order to get some insight into these complex mechanisms, we study the superficial modifications induced on a steel surface by laser in air. We compare laser treatments performed at different wavelengths and with different pulse durations.