Optimization of an analytical electron microscope for X-ray microanalysis: Instrumental problems

The addition of an energy dispersive x-ray spectrometer to a modern transmission or scanning transmission electron microscope can provide a powerful tool in the characterization of materials. Unfortunately this seemingly simple modification can lead to a host of instrumental problems with respect to the accuracy, validity, and quality of the recorded information. This tutorial reviews the complications which can arise in performing x-ray microanalysis in current analytical electron microscopes. The first topic treated in depth is fluorescence by uncollimated radiation. The source, distinguishing characteristics, effects on quantitative analysis and schemes for elimination or minimization as applicable to TEM/STEMs, D-STEMs and HVEMs are discussed. The local specimen environment is considered in the second major section where again detrimental effects on quantitative analysis and remedial procedures, particularly the use of 'low-background' specimen holders, are highlighted. Finally, the detrimental aspects of specimen contamination, insofar as they affect x-ray microanalysis, are discussed. It is concluded that if the described preventive measures are implemented, reliable quantitative analysis is possible.