Oxygen coverage effects in SIMS quantitative analysis using a primary rastered probe

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Abstract
The surface oxygen coverage θ has a great influence on positive secondary ion yield. θ must be equal to 1 for optimum quantitative analysis. On SIMS machines (like the CAMECA IMS‐3F) using a rastered high current density probe, instead of a static defocused (hence low current density) beam, there is a danger that this condition is not achieved where bombarding the sample with Ar+ ions while blowing O2 on to the sample. A simple model of the evolution of θ under the rastered probe is proposed; it provides a good frame to interpret surprising experimental results such as: (a) the existence of transients which can last for several seconds (primary Ar+); (b) the existence of cristallographic differential sputtering even though the oxygen back pressure is high; (c) the secondary signal can decrease when the primary beam intensity is increased. An easy and quick way of detecting conditions that would lead to erroneous interpretation is proposed.

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