Considerations of Operating Conditions of EDS Analytical Microscopy
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For analytical microscopy with EDS technique, the main variables of operation conditions are:
        i) Acceleration voltage.
        ii) Type and condition of electron source.
        iii) Probe size. This affects the EDS spatial resolution and probe current.
        iv) Electron beam current.
        v) Aperture selection. This also affects the EDS spatial resolution and probe current.
        vi) Distance between the specimen and detector. This parameter is critical, especially at long working distances in SEMs. The take-off angle is very large at such a working distance, therefore it is possible that only weak or no X-rays enter the detector. There is always an optimum where the maximum X-rays can be measured. Each microscope has a different geometry, and thus searching the optimum position of the detector is necessary at the installation of the EDS system.
        vii) Column alignment.
        viii) Collimator.
        ix) Specimen thickness.
        x) Maximum count rate. The maximum useful count rate for an EDS system is approximately 2000-3000 counts/s for the total counts collected over the entire spectrum.
        xi) Geometry between specimen and detector, determining X-ray collection efficiency. Two main factors that affect the number of X-ray photons which reach the detector are:
        xi.i) Solid angle(Ω).
        xi.ii) Take-off angle.