Color display in electron probe microanalysis

Abstract

The electron probe microanalyzer is used primarily for chemical analysis and for displaying the topography and atomic number distribution of specimens as small as one cubic micron. This is accomplished by first bombarding the sample with a static or scanning beam of fast-moving electrons, causing the sample to give signals resulting from x-rays, or from backscattered, secondary, or absorbed electrons. If any of these signals is collected, discriminated, amplified, and made to modulate a suitable detector, such as an oscilloscope, the topography and atomic number distribution and the elements present in the sample can be displayed. For the former display, electrons (back-scattered, absorbed, or secondary) are used, and for the latter, x-rays. However, the oscilloscope can accept only one signal at a time. If this signal is, for example, that of x-rays representing an element, only the distribution of this element in the sample can be displayed on the CRT. Consequently, if more than one constituent is present, the distribution of these can be attained by repeating the above procedure for as many times as there are elements. The total elemental distribution in a sample is then attained by juxtaposing the individual black and white pictures. However, interpretation might in some cases become ambiguous, since it is not easy to ascertain from these pictures where one elements starts and the other ends, or whether or not elements are together. Color display for electron probe microanalysis has been attempted by using color filters. 1-5 The technique described here is similar to that of Ficca, 6 who attached to the probe a color display computer scope to produce color images. The relatively inexpensive oscilloscope (Telonic Tricolor display model 203) used here is connected to the probe, and no extra attachments or modifications to the mieroanalyzer are needed. This oscilloscope consists of three guns, each having an assigned basic color--blue, green, or red. I f three signals (that is, x-rays from three elements) are used to modulate these guns, one signal per gun, these elements can be displayed concurrently and in color. The resultant image clearly defines the distribution of these elements in the sample, since each one is represented by a different color. In addition, if two or three elements are together, forming an alloy, the resultant color is a mixture of the basic colors, corresponding to the mixture of the pure elements.