A method for the investigation of primary beam parameters in SIMS microprobes is presented. An exact measurement of the primary beam shape over several decades of intensity is possible by observation of the secondary ion signal during the motion of the primary beam across a strip structure of a suitable combination of materials. A special mathematical method is used for the modelling of the measured primary beam shapes. It is shown that the well known approximation of the primary current density distribution by a Gaussian function is not appropriate in the case considered (ARL-IMMA).
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