LATERALLY RESOLVED CHEMICAL-ANALYSIS OF SOLID-SURFACES BY LASER-SNMS

The prospects of laser-based secondary neutral mass spectrometry (SNMS ) as a technique for quantitative and fast imaging of the chemical com position of a solid surface are evaluated on a model sample consisting of different nickel grids pressed into a silver substrate. In the exp eriment, neutral atoms sputtered from the sample surface by a finely f ocused Ga+ ion beam are post-ionized by non-resonant two-photon absorp tion from a pulsed 248 nm excimer laser and detected by a reflectron-t ype time-of-flight spectrometer. Particular emphasis is put on the int errelation between image acquisition time and detection sensitivity. I t is demonstrated that multiple mass images taken with only one single laser shot per pixel allow the safe detection of 0.1 at. % impurities at a lateral resolution of 1 mu m, the total image acquisition time b eing only of the order of minutes. In order to convert the measured si gnals into element concentrations, a quantitation scheme is described that allows correction of the acquired images for influences of surfac e topography, fluctuations and drift of primary ion current, etc.