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Amy Bryant TU Nanomaterials Wokshop Dr. Winton Cornell Dr. Saibal Mitra July 19, 2004 Energy Dispersive X-Ray Analysis (EDX) Energy Dispersive X-ray Analysis (EDX) is one of the most useful accessory features on a Scanning Electron Microscope (SEM). It is useful because it allows simultaneous, non-destructive elemental analysis that is both qualitative and quantitative. The EDX allows the SEM to perform elemental analysis on the portion of the sample being imaged in selected areas as small as ½ a micron in size. When the incident electron beam of the SEM hits atoms of the sample, secondary and backscattered electrons are emitted from the sample’s surface. When the incident beam penetrates the sample, electrons from atoms within the sample are dislodged, creating secondary electrons. As the incident beam passes through the sample, it leaves thousands of the sample atoms with holes in the electron shells where the secondary electrons used to be. If these “holes” are in the inner shells, the atoms stabilize by dropping electrons from the outer shells Source: http://www.seallabs.com/howedx5.html into the inner shells, releasing energy in the form of X-rays. The X-rays then hit the lithium drifted silicon detector generating a photoelectron, which travels through the silicon generating electron-hole pairs. An electric field within the detector attracts the electrons and the holes to opposite ends. The energy of the incoming X-ray determines the number of electron-holes created, which in turn determines the size of the current pulse. An X-ray spectrum can therefore be acquired qualitatively and quantitatively analyzing the elemental composition of the sample. The elements in the sample are identifiable to the detector because each X-ray spectrum is characteristically unique in energy and wavelength. Moreover, the detector can identify the change within the atom because the X-rays from the emitted atom are characteristic in energy and wavelength based on which shells lost electrons and which shells replaced them. The X-rays emitted from each element are characteristic in energy and wavelength and produce a unique X-ray spectrum. Lower atomic number elements have fewer X-ray peaks while higher atomic numbered elements have more X-ray peaks. The area beneath the peak can be calculated to quantitatively analyze each identified element. By analyzing multiple small sections of the sample, it is possible to map the composition of the entire sample, creating an image that mimics the SEM image. Source: http://www.seallabs.com/howedx5.html