Microchemical Analysis in the HB5 STEM

Abstract

The microchemical analysis of small extracted precipitates well dispersed on thin carbon support films has been carried out in a vacuum generators HB5 STEM, Particles in the size range ∼ 2 nm to several microns have been analyzed by a combination of simultaneous EDX and microdiffraction techniques. The major significance of this precipitate characterization is the high spatial resolution ∼ 5 nm and low detectability limit 5.10-20 g demonstrated by the EDX technique. However, a disturbing and frequently recurring feature of precipitate microanalysis was the detection of steep concentration gradients even within ∼ 10 nm precipitates.The McMaster HB5 is equipped with a virtual objective aperture, a modified x-ray collimator(1) and a double tilt berylium specimen holder, which minimize continuum and instrumental contributions to EDX spectra and have allowed high precision microchemical analysis. EDX data was obtained from a region of interest by first imaging at 25.106 to attain thermal stability, then stopping the probe and simultaneously monitoring the microdiffraction pattern during EDX acquisition.