It is well known that the use of Cs + primary ions results in an important increase of the negative ionization probability during SIMS analyses. Moreover, Cs + bombardment allows working in the MCs x + mode, which is a widely used technique to reduce the matrix effect. A major drawback of Cs + primary ion bombardment is that the Cs + beam serves both for the incorporation of Cs and for the sputtering of the surface. Therefore, the sputtering yield, and consequently the cesium surface concentration, are constricted by the primary bombardment conditions.To overcome this problem, the Cation Mass Spectrometer (CMS), equipped with an evaporator delivering a collimated and adjustable stream of neutral Cs onto the sample, has been developed at the SAM department. By continuous Cs 0 deposition during the SIMS analysis, optimal Cs surface concentrations, and thus optimal ionization probabilities are obtained. [1] In order to make the Cs 0 deposition technique available for other analysis instruments, a standalone UHV instrument for Cs evaporation prior to SIMS analyses has been developed. Furthermore, a suitcase for the transfer under UHV conditions of the samples in-between the Cs 0 evaporation chamber and the analysis instruments has been designed, to avoid any contaminations. In this work, we present this new Cs 0 evaporation chamber, as well as our new UHV suitcase in terms of their characteristics and handling.
In SIMS, the emission of negative secondary ions is strongly enhanced by the introduction of electropositive elements into the system. In our group, we have extensively studied SIMS analyses either performed with simultaneous cesium (Cs) deposition or with Cs deposition prior to the analysis. These studies were mainly performed on inorganic samples, focusing both on steady-state and pre-equilibrium conditions. The interest of Cs deposition prior to the SIMS analysis has been presented for inorganic as well as organic samples on the Cameca Sc-Ultra and NanoSIMS50 instruments. The present work has been carried out on different organic samples including PTCDA and C 60 , which were covered with a layer of Cs prior to SIMS analysis. The diffusion of Cs into the sample as well as the change in emission of positive and negative secondary ions have been monitored by SIMS depth profiling by using Cs + primary ions. Furthermore, the effect of air exposure on the obtained results has been investigated. The study on the same organic samples is completed by Cs deposition performed simultaneously to primary ion bombardment.
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