 
Ralf Thomann |
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-elemental analysis - |
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An electron beam strikes the surface of the sample. The energy of the beam is 120 keV. This causes X-rays to be emitted. The energy of the X-rays emitted depend on the material under examination. The X-rays are generated in the whole section. The detector used in EDX is the Lithium drifted Silicon detector. This detector must be operated at liquid nitrogen temperatures. When an X-ray strikes the detector, it will generate a photoelectron within the body of the Si. As this photoelectron travels through the Si, it generates electron-hole pairs. The electrons and holes are attracted to opposite ends of the detector with the aid of a strong electric field. The size of the current pulse thus generated depends on the number of electron-hole pairs created, which in turn depends on the energy of the incoming X-ray, which depends on the composition of the sample. Thus, an X-ray spectrum can be acquired giving information on the elemental composition of the material under examination. By moving the electron beam across the material an image of each element in the sample can be acquired. |
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If an electron beam strikes the surface X-rays (hν) were emitted, which energy depends on the elemental compostion of the sample. Vice versa the energy of the electrons is reduced. Analysis of the X-rays is called EDX; analysis of the energy loss of the electrons is called ESI. |
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Example for an EDX spectra. By choosing characteristic elemental peaks an elemental mapping is possible by analysing the sample point by point.
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