Resolution of Electron Probe Microanalyzers

摘要

In microanalysis using x‐ray emission excited on the surface of a thick specimen by an electron probe, the minimum volume element which can be analyzed is limited by the size of the electron probe, by fluorescence excitation, and by the penetration and diffusion of the electrons in the specimen. With an electron accelerating voltage of about 30 kv the electrons have an energy of the order of 3 times the critical excitation energy of the K or L x‐ray levels of the target and the minimum volume which can be analyzed (in the absence of strong fluorescence effects) is of the order of 8 cubic microns for a copper target, and is considerably larger than this for targets of low atomic number or density. It is shown that the resolution in this method of analysis can be improved without loss of statistical accuracy or increase in the time of measurement by (1) improving the quality of the electron optics and by (2) selecting the accelerating voltage and electron probe size. The minimum volume element for practical quantitative analysis can thereby be made as small as about 0.2 cubic microns in a copper target. This is obtained by using slightly larger electron probes and lower accelerating voltages than those representative of current practice.