More Than One Ever Wanted To Know About X-ray Detectors

Extract

A combination of electron microscope and x-ray spectrometer is a very powerful tool. Not only can one see a sample in great detail, but one can determine, and even map, the chemical elements. In Part 1, I discussed some of the basics of energy dispersive x-ray spectroscopy (EDS or EDX). The heart of the spectrometer is a small piece of single crystal silicon about the size and shape of a shirt button, and about twice as thick. It has been selected for high purity, and then lithium drifted to compensate the remaining impurities.

The lithium is carefully drifted into the crystal button in order to exactly compensate the impurities in the crystal that would create leakage current. This is done at about 60° C under an electric field. It is then evaluated and re-drifted for a final clean up of any uncompensated impurity atoms that remain.