Compositional Mapping by Scanning Electron Microscopy With Energy Dispersive X-Ray Spectrometry: Recognizing Facts and Artifacts

Extract

Compositional mapping with energy dispersive x-ray spectrometry (EDS) in the scanning electron microscope (SEM) is one of the most widely used techniques for elemental imaging of microstructures. SEM/EDS maps are usually qualitative presentations of elemental distributions in x-y space. In older implementations of mapping, the x-ray intensity from a single spectral region of interest (ROI) above a threshold was recorded on film as a white “dot” during analog scanning. With modem digital control and data recording, x-ray intensities from many ROIs can be recorded in parallel and true counts stored in memory. For display purposes a gray level or color value is used to represent the stored x-ray intensity at each pixel. For major constituents (arbitrarily, major >10%), it is generally possible to make valid, robust comparisons between regions within an individual compositional map, but comparisons may be problematic among several maps of different constituents within the same field of view, depending on the sophistication of the mapping software.