Influence of molybdenum layer on the laser plasma generated from interfacing copper layer

The results for laser-induced breakdown spectroscopy (LIBS) measurement of thin Cu films (1 μm) on soda-lime glass (SLG) substrates with and without a supporting thin Mo layer (1 μm) are reported. The ablation was carried out using a nanosecond Q-switched Nd:YAG laser (λ=1064 nm, τ=4 ns, spot diameter=50  μm, top-hat profile) in the laser fluence range of 19.16-65.97 J/cm(2). It was found that, under the same laser irradiance conditions, the depth and morphology of ablation craters produced with and without the Mo layer were completely different. The electron number densities of the plasma from the two samples calculated from the measured LIBS spectra differed by a factor of 4 as 4.1×10(17) cm(-3) (Cu/Mo/SLG) and 17.7×10(17) cm(-3) (Cu/SLG), which was attributed to the matrix effects resulting from ionization of Na atoms diffused into the Mo layer. It is demonstrated that a nanosecond-laser-based LIBS is applicable for the characterization and composition analysis of thin film layers of a few micrometer thickness on glass substrates, especially for the measurement of Na contents of each layer.