Quantitative analysis of Ge/Si alloys using double-pulse calibration-free laser-induced breakdown spectroscopy

Abstract

In this work, we report the first application of the double-pulse Calibration-Free Laser-Induced Breakdown Spectroscopy (DP-CF-LIBS) to the analysis of Ge-Cu/Si and Ge-Ba/Si alloys. The plasma was produced using two collinear Nd:YAG lasers, operating at 1064 nm. The experimental parameters such as inter-pulse delay, gate delay and energy ratio between the two laser pulses were optimized to maximize the signal to background and signal to noise ratio in the resulting LIBS spectra. The fulfillment of the Local Thermodynamic Equilibrium (LTE) approximation in the time window of the measurement was verified using the McWhirter criterion and considering the relaxation time and diffusion length of the atoms in the plasma. The effect of self-absorption on the lines used in the CF-LIBS analysis was considered and found negligible. The DP-CF-LIBS analysis allowed the determination of the stoichiometric ratio of the elements in the two alloys, an important parameter for industrial quality control and fundamental studies on germanium/silicon alloys.