Surface Analysis by SNMS: Femtosecond Laser Postionization of Sputtered and Laser Desorbed Atoms

The photoionization efficiency of secondary neutral atoms from metal surfaces has been investigated by very intense (∽1014 W cm‐2) and short‐pulsed (∽200 fs) 248 nm laser radiation. Surface erosion of the samples was performed by Ar+ ion sputtering and by laser desorption (LD) from an N2 gas laser. Five polycrystalline samples (Al, Cu, Zr, In and Au) have been analyzed with respect to their ionization efficiency and LD yields. In order to estimate the desorption yield, we determined the useful yield of our time‐of‐flight (ToF) mass spectrometer by ion sputtering, followed by laser postionization with 193 nm radiation from an ArF excimer laser. The applied femtosecond pulse, high‐intensity 248 nm laser radiation has been found to be an excellent source of non‐selective photoionization. For each material in this study a large fraction of doubly ionized atoms was observed; the measurements on Au have also shown triply ionized atoms. For some spectra, the number of doubly ionized atoms was even higher than for singly ionized atoms. We have estimated that the useful yields for LD are significantly higher than the values observed in ion sputtering