Uniform surface elemental analysis using sputtering and photoionization mass spectrometry with a 6 ns pulse length Nd:YAG laser

Abstract

The feasibility of performing a uniform surface elemental analysis was investigated by using high laser power to postionize sputtered neutrals. Model calculations and experiments were performed for situations where a 6 ns high power Nd:YAG laser operating at 532 nm was applied to photoionization. Photoionization mass spectra of Ar+ sputtered alloys containing common metals were measured as a function of laser power density and the relative sensitivity factor of each element was determined. The results show uniform ionization of the elements sputtered from the alloys and, therefore, quantitative measurement of the surface elemental composition at the maximum laser output power. For comparison, the same calculations and experiments were performed using a 35 ps, 532 nm mode-locked, high power Nd:YAG laser. The comparison showed that the 6 ns laser reaches uniform ionization at a lower power density. The capabilities of this technique and its operating parameters relevant to sensitive and quantitative surface analysis are discussed from a practical analysis perspective.