Electron Diffraction Pattern of Mica of Various Thicknesses

Abstract

N-PATTERNS of spots from thin crystals, and Kikuchi-lines from comparatively thick ones, have been observed by several workers¹ as electron diffraction patterns from mica. In this study a flake of mica having various thicknesses was stuck on a mesh of 0.1 mm. diameter by means of methyl alcohol and was then placed on the projection lens of an electron microscope so that electron micrographs and electron-diffraction patterns of the mica might be taken. First the electron image of the mica (Fig. la) was observed, then the incident electron beam was converged on it (the least area illuminated by the electrons was a circle of about 0.01 mm. diameter), and was moved horizontally to the part of the mica to be observed having the desired thickness. Then the electric current through the projection lens was switched off, and afterwards the electron diffraction pattern of one part of the mica (Fig. 1 b) was observed. The thickness of each part of the mica was determined relatively by comparing the intensities of the transmitted electrons.