Electron Microprobe Analysis (EMA) is an x-ray spectrometry based quantitative determination of elemental composition of solid samples. The electron microprobe is similar to a scanning electron microscope and includes electron imaging capabilities, however, it is optimized for chemical determination. Individual sample volumes can range from tens to hundreds of cubic micrometers.
In EMA, the instrument focuses an electron beam onto the sample which among other interactions ionizes the atoms of the sample. As the sample recovers x-ray photons characteristic for each element the sample is composed of are generated. The x-rays can be detected with either an energy dispersive spectrometer (EDS) or a wavelength dispersive spectrometer (WDS). With EMA, wavelength dispersive spectrometers are used because they have better resolution of the x-rays than EDS systems. Additionally, the WDS systems have detectors that allow for longer time acquisition which allows for detection of elements at lower concentrations.
Importantly, EMA is a standards-based analytical method. Standard reference materials with analyze elements in concentrations and in a matrix similar to the unknown are required. The composition of the unknown sample is determined by comparing the WDS intensities of the unknown with those of the standard reference material(s).
Analyses can be made at individual points the diameter of the electron beam, for volumes under rastered electron beams, or for areas up to several centimeters using an automated sample stage under a stationary electron beam.
McCrone Associates utilizes a JEOL electron microprobe with five WDS spectrometers and an EDS spectrometer. The WDS spectrometers have multiple diffraction crystals to minimize sample acquisition time as much as possible.
The all digital JXA-8200 is equipped with a new silicon drift EDS detector system. A Probe Software control system is also installed offering the largest variety of data quantification options.
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