Nanometer-film analysis by the laser-induced breakdown spectroscopy method: the effects of laser focus to sample distance

In order to develop a method to analyze metal elements in thin-film samples rapidly, directly and without sample preparation, and to understand the mechanism of laser-film interaction and plasma formation and evolution, a laboratory laser-induced breakdown spectroscopy system was established recently for nanometer-film analysis. ZrO(2) films prepared on silicon chips by a sol-gel process were employed in the following experiment and their thickness was about 40 nm. By the initial investigation that we carried out, the stability of this system was verified and the relative standard deviation of the target peak was found to be lower than 1.6% with the help of a position system. The influences of different experimental parameters, such as laser energy, laser focus to sample distance (LFTSD) settings, and gate delay, were studied under conditions of room temperature and atmospheric pressure. The experimental results show that the LFTSD was one of the most important parameters for plasma formation and spectral collection in comparison with other parameters by means of plasma spectra and images. So the effects of the LFTSD on the spectra, plasma evolution, and craters are specially discussed in this paper. At last, we calculated the plasma temperature and electron density under optimal parameters for quantitative analysis. The result shows that the established system is available for qualitative and quantitative analysis of films under conditions of single pulse and low ablation energy.