Depth profile analysis of copper coating on steel using laser ablation inductively coupled plasma mass spectrometry

Abstract

A commercial highly focused (Gaussian) nanosecond UV (266 nm) Nd:YAG laser ablation system coupled to an inductively coupled plasma quadrupole mass spectrometer was examined as a tool for depth profile analysis of copper coating on steel. The studied samples were Standard Reference Materials 1361b and 1362b from NIST, which consist of a set of eight coupons of an AISI 1010 cold rolled sheet steel substrate with a uniform coating of copper (certified copper coating thickness: 5.9, 12.3, 25.3, 40.6, 52.0, 77, 130, and 199 μm). Depth resolution was determined from the normalized depth profiles as a function of irradiance, which was varied by changing the laser pulse energy and the focusing conditions, as well as coating thickness. At lower irradiances, depth resolution values were higher for irradiances obtained by changing the laser pulse energy, whereas at higher irradiances this parameter was higher for irradiances obtained by changing the focusing conditions. At moderate irradiance levels, the results obtained were quite similar, and, in addition, the best depth resolution was attained in this irradiance range, which was obtained by using a moderate laser energy (about 2 mJ per pulse) and by focusing the laser beam below the sample surface (approximately 2000 μm). Depth resolution increased linearly with coating thickness. For the eight studied samples the ablation rate was approximately 1 μm per pulse and the depth resolution values were between 0.8 μm for the thinnest coating and 26 μm for the thickest one.