Description and Applications fo a New Design Cs⁺ Ion Source on the COALA Ion Microprobe for Negative Ion SIMS

Abstract

In any mass spectrometric system, one of the key instrumentation components is the ion source, or stated similarly, the method of ionization. Apart from influencing the level at which the sought-for constituents can be quantitatively ionized, the ionization process should also preserve the native chemical integrity of the sample, that is, without inducing decomposition, compound formation, or falsifying sample structure. In the SIMS method, the practicing spectroscopist can often select a primary ion projectile species which affords advantages when sputtering into certain materials or when profiling specific elements. For example, negative primary ions can reduce the accumulation of electrostatic charge on the surface of poor-conducting samples [1]; molecular ions were used in one study to obtain information relative to damage density effects in the collision cascade [2]; and bombardment by 0 and Cs promotes ion yield enhancements for positive secondary ions [3] and negative secondary ions [4], respectively. The latter aspect — Cs bombardment SIMS — is of active interest in several research groups [5–7], including this laboratory [8]. We have recently designed and brought into operation a compact, microbeam Cs⁺ source for SIMS [9]. This brief report is intended to describe the source, and present first results of its coupling to a scanning ion microprobe mass analyzer developed at IPP.