In situ deposition of neutral Cs for Secondary Ion Mass Spectrometry

Abstract

The Cation Mass Spectrometer (CMS) is a new instrument allowing to optimize the advantageous quantification technique consisting in analyzing MCsx+ clusters. 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 by Secondary Ion Mass Spectrometry (SIMS). Using this new column, it was possible to introduce an analysis technique consisting of a Xy+ ion bombardment (where X stands for any element except 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 will first describe the new Cs0 column and outline its performances. In a second part, we will focus on the analytical aspect and study the ability to vary the Cs concentration over a complete and continuous range. Experiments using a Ga+ primary bombardment show in particular that the Cs concentration produced during analyses performed with the mentioned technique only depends on the characteristics of the analyzed material and the ratio between the erosion and deposition rates, but not on the individual values of these two rates.