Optimization of SIMS analyses performed in the MCsx+ mode by using an in situ deposition of neutral Cs

To optimize the advantageous quantification technique consisting in analyzing MCsx+ clusters, the Laboratoire dʹAnalyse des Matériaux (LAM) has developed the Cation Mass Spectrometer (CMS), a new instrument specially dedicated to perform this kind of analysis. To further enhance the potential of this instrument, we have developed a column that delivers a collimated and adjustable stream of neutral Cs atoms to be deposited on the surface of the sample while this one is being analyzed. Using this new column, it was possible to introduce an analysis technique consisting of an Xy+ ion bombardment (where `Xʹ stands for any element excepting Cs) accompanied by a simultaneous deposition of Cs0 at the surface of the sample. This experimental technique permits a successful decoupling of the sputtering and Cs introduction processes by avoiding the constraints imposed by an energetic Cs+ ion bombardment. As a consequence, it becomes possible to optimize simultaneously the sensitivity of the analysis, by carefully adjusting the Cs concentration to its optimum value, and the depth resolution of the analysis, by choosing adequate primary bombardment conditions. In this paper, we investigate numerous aspects of the mentioned analytical technique by using a Ga+ ion bombardment and by performing analyses on three different samples (Al, Si, Ni). We study in detail the behavior of the measured MCsx+ signals as well as of the corresponding useful yields. In this context, the observed evolutions are discussed in terms of ionization probabilities, number of available atoms participating in the formation mechanisms and recombination probabilities. We show in particular that the useful yields only depend on the ratio between the erosion and deposition rates, but not on the individual values of these two rates.