Depth profiling characterisation of the surface layer obtained by pulsed Nd:YAG laser irradiation of titanium in nitrogen

We investigated the composition of the surface layer obtained by pulsed Nd:YAG laser (λ=1.064 μm, τ∼120 ns, ν=1 kHz) irradiation of Ti targets in high pressure nitrogen. The surface morphology, the crystalline state, and the depth distribution of the elements were analysed by scanning electron microscopy, X-ray diffractometry, secondary ion mass spectrometry, X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy. The chemical binding states were studied by deconvolution of the XPS spectra. The layer has a uniform surface, and mainly consists of the tetragonal δ′-TiNx crystalline phase. The nitrogen concentration increases firstly in the depth until approximately 0.15 μm, and then decreases until the greatest measured depth of 2 μm. The TiNx stoichiometry changes from x≈0.8 close to the surface to x≈0.5 at a depth of approximately 0.2 μm, it remains around this value until approximately 0.5 μm, and for greater depths decreases until 0.1 at 1.6 μm. Furthermore, the oxygen concentration decreases quickly and reaches the concentration of bulk Ti at approximately 0.2 μm.