Microanalysis with the X-ray scanning microscope

Abstract

In the normal method of X-ray emission microanalysis, developed by Castaing (1, 2), the specimen surface is positioned optically under a fixed electron probe. With the present equipment (3, 4), the electron probe may be scanned over the specimen and the emitted X-rays collected to form an image of the surface on a cathode-ray tube, which is scanned in synchronism with the probe. An accelerating voltage of about 25 kV is used, and the probe, of diameter 0.1–1 µ, may be scanned over an area up to 0.4 mm square. X-rays may be detected either with or without wavelength discrimination; the crystal spectrometer (or proportional counter and pulse analyser) on the right of the column (Fig. 1) selects a particular characteristic emission line, whereas the scintillation counter on the left accepts the total X-ray emission. In the former case the surface distribution of one element is obtained and, in the latter, contrast is chiefly due to the variation of atomic number over the surface. For specimens thicker than the electron penetration depth, the resolving power is limited to about 1 µ by lateral electron diffusion.