X-Ray Excited Fluorescence Spectroscopy Within SEM for Trace Analysis

Abstract

Within the scanning electron microscope (SEM) the electron beam scans line by line across the sample. The reflected electrons which emerge from the primary beam and the secondary electrons which are knocked out of the surface of the sample are used to produce the electron optical picture. The X-rays generated at the corresponding points of electron impact enable a chemical analysis of the surface of the sample within a depth of information of about 1 μm. The positionable fine electron beam with its diameter of nearly 0.1 μm produces a clear X-ray signal on particles of 1 μm, e.g. 10⁻¹² g. More limited is the detectability of uniformly spread material traces, as alloy ingredients. Here the Bremsstrahlung, generated by the stopping of primary electrons hides in its statistical fluctuations the weak signals of trace elements. This is the case especially for energy dispersive spectrometers with their relatively poor energy dispersion, as they are commonly used at the SEM.