Beryllium Analyses by Secondary Ion Mass Spectrometry

Abstract

Secondary ion mass spectrometry (SIMS, or ion microprobe) represents an extremely sensitive technique for the microanalysis of beryllium. Positive ions of beryllium are readily formed and its analysis by SIMS is not overly complicated. Matrix effects appear to be small (<20%). In this chapter I will describe SIMS instrumentation, the problems facing Be analysis, solutions to these problems, calibrations for Be and limits of detection. As of the writing of this chapter (mid-2000), SIMS instruments broadly useful to geochemists are commercially available from two companies. Australian Scientific Instruments (ASI, at www.anutech.com.au/asi/shrimpii.htm) sells the SHRIMP (Super High Resolution Ion Micro Probe). The SHRIMP was designed to allow high transmission of secondary ions at high mass resolution and permits U-Pb ages on zircons to be determined. Beryllium analyses are possible on the SHRIMP, but none have been obtained to date (Vickie Bennett and Ian Williams, Australian National University, pers. comm.). Cameca Instruments Inc. (www.cameca.fr) markets an instrument (the IMS 3f-6f series) that focuses on the needs of the semiconductor industry, and is also the most common SIMS instrument in earth science laboratories. A second Cameca instrument (IMS 1270) is designed for applications demanding high transmission at high mass resolving power (as in the SHRIMP). A tutorial on SIMS can be found on the world-wide web (www.cea.com), but a brief description follows. In SIMS, a high-energy primary ion beam is directed at a sample. The impacts of these ions with the target result in the ejection of atoms from the top two or three monolayers of the target surface (Dumke et al. 1983). Some of the ejected atoms are ionized during these collisions, and these “secondary ions” can then be accelerated into a mass spectrometer for isotope selection and analysis. Below I describe primary ion beams and the path followed by secondary ions …