New Spectrometers and Accessories for the Electron Microprobe

Abstract

Several new types of spectrometers have been developed for use with the EMX which will become available within the next year.

Two compact semi-scanning curved crystal monochromators of limited range have been designed to be mounted on either side of the microscope of the EMX spectrometer. One is designed to utilize the ARL standard 4" radius curved crystals, the other the 11" radius curved crystals. By choosing a crystal of the proper material and radius of curvature, most X-ray wavelengths of interest can be reached with one or the other of these two monochromators. Thus up to five curved crystal monochromators become available for the EMX.

The second is a grazing incidence grating spectrometer utilizing a gold grating with low blaze angle developed specially for work in the long wavelength X-ray region. By operating this scanning grating instrument at increased input angles for increased wavelengths, optimum performance can be achieved for first order diffraction, while discriminating against second and higher orders. Good performance from 20–170 A has been achieved with efficiencies from two to six times as great as obtainable from crystals or pseudo-crystals working in this range. The use of gold replica gratings provides good service life for this type of spectrometer when operated in the low contamination environment of the EMX spectrometer.

A new accessory which further reduces contamination in the microprobe has been developed. This consists of a means of cooling the large lower plate of the objective lens to –40°C by the use of a Freon refrigeration system. This accessory reduces the contamination rate of the EMX by a large factor. By controlling the temperature of the objective lens to very close limits, this markedly improves the stability of the electron beam position on the sample.

We wish to report three developments applicable to the EMX electron microprobe which we believe will be of general interest.