Implementation and Optimization of Large Gas Cluster Laser Post-Ionization Secondary Neutral Mass Spectrometry for Molecular Analysis

Abstract

In this study, we describe for the first time a new combined technique for molecular surface analysis using large argon gas clusters as primary ions for laser postionization secondary neutral mass spectrometry (Laser-SNMS). This new technique was investigated on polymer polystyrene (PS) surfaces using pulsed Ar2000+ ions with 20 keV energy and a 157 nm laser beam for postionization. To optimize the ion yield, time-of-flight (ToF) distributions of characteristic sputtered neutral PS fragments were determined. The data could be fitted well with Maxwell–Boltzmann distributions. The data show that the maxima of the individual ToF distributions of the sputtered neutrals move to higher delay time values with increasing mass, which directly correlates to a decrease of velocity of the sputtered neutrals with increasing mass. The delay time dependence on mass could be fitted with a quadratic curve, thus indicating a constant mean kinetic energy for the sputtered molecules. The ion yields obtained with large gas cl...