RELATIVE ELEMENTAL SENSITIVITY FACTORS IN NONRESONANT LASER-SNMS

Using a reflectron time-of-flight mass spectrometer, the ionization pr ocess in non-resonant Laser postionization Secondary Neutral Mass Spec trometry (SNMS) has been investigated. In particular, the postionizati on efficiencies (PIE) achieved by multi photon and single photon absor ption have been compared by ionizing ten elements sputtered from a NIS T standard reference material by excimer laser radiation of 248 nm, 19 3 nm and 157 nm. Only in the case of single photon ionization (SPI) th e measured laser intensity dependence of the PIE can be understood qua ntitatively in terms of corresponding theory. From the results, absolu te values of the SPI cross sections have been evaluated for atoms of n ine elements, which show a total variation over about two orders of ma gnitude. Furthermore, even in the regime of high laser intensity, wher e the ionization of all atoms is completely saturated, different eleme nts have been detected with relative sensitivity factors which scatter over about one order of magnitude. This has been attributed to elemen t dependent variations of the effective ionization volume which are ca used by the different kinetic energy and angular distributions of diff erent sputtered atoms.