Analysis

Chemical analysis of solids can be routinely carried out via the use of x-ray spectrometers attached to electron microscopes.

When electrons interact with a specimen, various signals produced are directly related to the chemical composition of the material. With the attachment of special energy or wavelength dispersive spectrometers, the precise elemental composition of materials can be obtained with high spatial resolution.

In some instruments, such as a TEM equipped with an energy dispersive spectrometer (EDS), elemental analyses can be obtained from areas as small as a few nanometres diameter. Because of low count rates, these analyses usually have a relative error between 5% and 10%. On the other hand, very precise accurate chemical analyses (relative error ~ 0.5%) can be obtained from larger areas of the solid (0.5 - 3 micrometer diameter) using an electron microprobe with wavelength dispersive spectrometers (WDS). Analyses at a lower precision and accuracy (1-2% relative) may be obtained from SEMs equipped with ED spectrometers.

Both SEMs and TEMs are often equipped with ED or WD spectrometers to chemically characterise biological or non-biological materials. Another type of spectrometer (EELS), which has maximum sensitivity for light elements, can also be attached to a TEM in order to obtain site-specific information about an element. Thus, the type of element and the nature of its bonding in a crystalline or amorphous solid can be determined with an EEL spectrometer.

In many cases, elements from Boron to Uranium can be identified using these spectroscopic techniques. Because a focussing electron beam often results in a large amount of energy concentrated on a sample during analysis, special cooling stages are available with many microanalytical tools. In the special case of biological tissues, a unique cryo-fixation and molecular distillation drying process is available for those critical chemical analyses of sub-cellular components.

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