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 composition of a solid surface are evaluated on a model sample consisting of different nickel grids pressed into a silver substrate. In the experiment, neutral atoms sputtered from the sample surface by a finely focused Ga + ion beam are post‐ionized by non‐resonant two‐photon absorption from a pulsed 248 nm excimer laser and detected by a reflectron‐type time‐of‐flight spectrometer. Particular emphasis is put on the interrelation between image acquisition time and detection sensitivity. It 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 μm, the total image acquisition time being only of the order of minutes. In order to convert the measured signals into element concentrations, a quantitation scheme is described that allows correction of the acquired images for influences of surface topography, fluctuations and drift of primary ion current, etc.