Excimer laser treatments of iron, aluminum and silicon substrates in nitrogen and methane atmospheres

Abstract

Materials processing by laser irradiation is an expanding field with attractive technological applications. Among all laser-based treatments, the irradiation of metals and semiconductors in controlled reactive atmospheres can successfully lead to important modifications on the surface of the irradiated targets. When the reactive gas contains nitrogen or carbon, the process is called laser nitriding and laser carburising, respectively. In the present work, iron, aluminium and silicon substrates have been treated in controlled nitrogen (N2) and methane (CH4) atmospheres with a pulsed XeCl excimer laser (wavelength=308 nm, pulse duration=55 ns FWHM) in order to incorporate nitrogen and carbon into the substrates. The modifications induced by the laser are analysed as a function of the various experimental parameters (gas pressure, laser fluence, number of laser pulses) and the mass transport mechanisms during the laser treatment are studied in detail. Solid solutions (Fe(N), Fe(C)) as well as stoichiometric phases (AlN, SiC) can be synthesized on the surface, forming coatings with enhanced adhesion to the underlying substrates. The experimental analysis is carried out by a number of techniques (Rutherford Backscattering Spectrometry, Resonant Nuclear Reaction Analysis, Mössbauer Spectroscopy, X-ray Absorption Fine Structure, X-ray Diffraction, Nanoindentation Hardness) in order to achieve information on the elemental distribution, the phase formation, the local atomic environment and the mechanical properties of the treated targets. By investigating the modification of the materials after the laser treatment we can also obtain a valuable insight into the mass incorporation mechanisms and the plume-surface interaction during the laser irradiation.