Useful yields of MCs x+ clusters: a cesium concentration-dependent study on the Cation Mass Spectrometer (CMS)

Abstract

To optimize the advantageous quantification technique consisting in analyzing MCs x + clusters, the Laboratoire d’Analyse des Matériaux (LAM) has developed a new instrument specially dedicated to performing this kind of analysis. The Cation Mass Spectrometer (CMS) instrument leads to high MCs x + useful yields by allowing to reach an optimum value of the stationary Cs surface concentration, which is known to be a very critical parameter in MCs x + analysis due to its strong influence on the probability of secondary Cs + ionization. The present work focuses on the potential of the CMS instrument to vary the stationary Cs concentration over a large range and the benefits concerning the MCs x + useful yields resulting from this possibility. Analyses were performed on three different samples (Al, Si, Ni) while modifying the impact angle of the primary Cs + beam and in the Cs +–Ga + cobombardment mode. These techniques are shown to be complementary with respect to the covered ranges of cesium concentrations resulting in a complete range going from quasi 0 to some 30%. The observed variations of the useful yields are discussed in terms of the stationary Cs concentration produced during the analysis and the consequent variations of the Cs + ionization probability provoked by work function shifts which were determined by in-situ measurements. A comparison between the performances of the CMS and those of classic Cameca instruments shows, depending on the element, useful yield enhancements up to a factor 90 mainly due to work function conditions resulting in high Cs + ionization probabilities.