Laser‐SNMS investigations on pyrene using Ga+, Bi1+, Bi3+ and Bi5+ as primary ions and different laser wavelengths and laser power densities for photoionization

Abstract

Laser secondary neutral mass spectrometry (Laser‐SNMS) has been used to simultaneously ionize sputtered secondary neutrals in a nonselective way. To investigate the sputtering and photoionization processes, we examined the dependence of the Laser‐SNMS molecular yield on (i) different primary ion bombardment conditions using mono‐ and polyatomic ions and (ii) the laser parameters wavelength and laser power density. The Laser‐SNMS experiments were carried out using Ga+, Bi1+, Bi3+ and Bi5+ as primary ions and two different excimer laser systems for photoionization working at wavelengths of 157 and 193 nm, respectively, with power densities varying between 4 × 106 and 4 × 108 W/cm2. It was found that Bi3+ as primary ion is most suited to investigate organic surfaces. The highest yields could be obtained using a laser wavelength of 157 nm after ionization. Copyright © 2012 John Wiley & Sons, Ltd.