The most common questions we get from visitors concern sample preparation. Sample changes take only about 5 minutes, so it is feasible to analyze several polished thin sections during a session. However, many outside users wish to analyze for H in various phases, and hydrogen background signals may take over an hour to decay to baseline conditions after each sample change. Minimizing the hydrogen background. All epoxies will degas somewhat, and this local source of hydrogen seems to represent the most important contribution to the H background.
Backgrounds increase with the volume of epoxy and the type.
Because H sticks to gold, we have found that applying a gold coat immediately prior to insertion into the SIMS also can improve the H background. Because SIMS is a surface analytical technique, sample preparation is extremely important because anything that is left on the sample surface may be analyzed during the session. This includes polishing media, the conducting coat deposited on the sample, and inadvertent contamination. We recommend that visitors consider which elements they want to study before final sample preparation. For example, a carbon coat would be clearly inappropriate for measuring carbon, and polishing with alumina may cause problems in a subsequent analysis for oxygen isotopes, as well as trace aluminum in a low-Al phase such as quartz.