Scanning Microscopy


Mass spectrometric detection of neutral surface particles released by ion bombardment has become an important method for surface and depth profile analysis. Its fundamental difference to secondary ion mass spectrometry SIMS is the separation of the formation of the analyzed particles and their ionization. Hence, matrix and selectivity effects influencing SIMS signals in a mostly unknown manner via the ionization process in secondary ion emission are avoided in general.

The different techniques being presently employed for the necessary postionization of the sputtered neutrals are reviewed and discussed with respect to their potentialities. Secondary Neutral Mass Spectrometry (SNMS) using efficient postionization by the electron component of a special tow pressure high frequency plasma is the presently most elaborated technique. The quantifiability of SNMS signals is discussed and illustrated by various examples. Depth resolution in the subnanometer range is shown to be obtained with the direct bombardment mode of SNMS in which the sample is bombarded with noble gas ions from the SNMS-plasma at energies in the order of only 102 eV.

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