Laboratory 25 X-Ray Microanalysis in the AEM Purpose The aim of this laboratory is to introduce the principles and practice of quantitative x-ray microanalysis in the AEM using an energy-dispersive spectrometer (EDS). Since it is important to recognize the limitations of the technique as well as the relative ease of quantification, some effects due to spurious x-rays in the EDS spectrum will be identified in the first experiment. More details may be found in PAEM, Chapters 4 and 5. Equipment 1. STEM equipped with an EDS system. 2. Software for quantitative thin-film analysis by the Cliff-Lorimer ratio method including an absorption correction. 3. Low-background specimen holder with beryllium or graphite specimen cup. Specimens 1. Cr thin film evaporated onto a carbon film partially covering a heavy metal grid (e.g., 400-mesh gold) or heavy metal aperture (e.g., molybdenum). 2. Fe-Ni thin foil (or any alloy containing elements of similar z) fabricated by electropolishing or ion-beam milling. 3. Ni-AI thin foil (or any alloy containing elements of widely differing z) fabricated by electropolishing or ion-beam milling. 4. Biotite mica crystals (or any multielement specimen) ground and dispersed onto a carbon film. 5. Copper or nickel thin foil (or any simple metal/alloy foil with large grain size) fabricated by electropolishing or ion-beam milling. Time for this lab session Two to three hours. 25.1 Sources of Spurious X-Rays Ideally the x-rays reaching the detector should be generated only from the volume of the thin foil illuminated by the electron probe. Unfortunately, unwanted x-rays can also be generated. For example, spurious x-rays from locations on the specimen remote from the electron beam may be generated by high-energy continuum x-rays or uncollimated electrons from the illumination system of the microscope (the "hole count"), or as the result of electron probe-specimen interactions. These sources of spurious x-rays must be understood and minimized before quantitative analysis is attempted. Experiment 25.1: The "Hole Count." Using the chromium film on the molybdenum aperture or gold grid specimen in the low background holder, observe the presence (or 143 C. E. Lyman et al., Scanning Electron Microscopy, X-Ray Microanalysis, and Analytical Electron Microscopy © Plenum Press, New York 1990