Electron beam microanalysis
The electron probe microanalysis (EPMA;. Engl electron probe microanalysis EPMA, or X-ray microanalysis ) is used primarily for non-destructive analysis of solid surfaces with a lateral resolution down to 1 micron .
Procedural principle
The method is based on the wavelength-dispersive analysis (WDS or WDX) or energy-dispersive analysis (EDS or EDX) of the characteristic X-rays emitted by the sample when it is bombarded with an electron beam . Elements from ordinal number 11 ( sodium ) can be quantified, elements from ordinal number 4 ( beryllium ) can only be detected with restrictions. The relative detection limit for elements is 0.01% by weight, which corresponds to an absolute detection limit of 10 −14 to 10 −15 g. By comparing it with known standards, it is possible to quantify the chemical composition, because the signal of the characteristic X-ray lines is proportional to the proportion of the respective element. Thus, the element distributions can be recorded parallel to the surface image. The information obtained comes from a thin surface layer; the analyzed volume per data point is around 0.3 to 3 µm 3 .
Experimental application
The electron beam microanalysis takes place either by additional detectors in regular electron microscopes ( SEM or TEM ) or in electron beam microprobes , also called microprobes for short . The latter are scanning electron microscopes specially equipped for element analysis, which are optimized for a higher sample flow. Although this is undesirable for imaging, it enables a stronger X-ray signal. Electron microprobe are usually multi WDX spectrometers (typically up to five) equipped to a plurality of elements (simultaneously with the accuracy of the WDS to map binders ).
See also
Web links
- MIKROANALYTIK.DE - further information on electron beam microanalysis and EDX
literature
- Frank Eggert: Standard-free electron beam microanalysis with the EDX in the scanning electron microscope. BoD, Norderstedt 2005, ISBN 3-8334-2599-7 .