Links in this section:

Introduction
Fundamentals of the TEM technique
Beam-sample interaction
The Analytical TEM
Detector Protection
Qualitative Analysis
Quantitative Analysis
Microanalysis Examples (1)
Microanalysis Examples (2)
Microanalysis Examples (3)
Summary

Qualitative Analysis in the AEM

Many analytical observations in the AEM are qualitative. Often, it is only necessary to distinguish between phases and it is not necessary to calculate elemental concentrations. Spectra may be collected at up to 0 - 40 keV range as this aids in the identification of K lines of elements that may have overlapping L or M peaks in a lower range e.g. Pb and Mo. It is easier to detect small peaks from minor elements when the background is smooth. Counting for longer periods of time increases total counts, which reduces statistical scatter in the background. Increased counts can also be achieved by increasing probe current or analyzing thicker parts of the specimen, although this involves some sacrifice in spatial resolution. Peak visibility is improved by having good detector resolution, which improves peak to background. To avoid false identifications, spurious peaks need to be eliminated by good collimation and design of sample holder.

The limit of detectability for an element, expressed as the minimum mass fraction (MMF), depends on the other elements present in the sample, microscope kV, detector resolution and the number of counts recorded in the spectrum. The MMF is usually calculated as the largest concentration that could be attributed to statistical fluctuations alone. By reducing statistical fluctuations, the MMF is improved. In a TEM, the total volume of material analyzed is determined by the probe diameter and specimen thickness. Therefore the total mass of material excited by the probe can be very small and masses as small as 10^-19g can be measured with EDS.

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