Abstracts of Technical Articles from Bell System Sources (01 January 1937)

Electricity in Gases. KARL K. DARROW. The material in this paper was presented as the Joseph W. Richards Memorial Lecture delivered before the Electrochemical Society at Cincinnati, April 23, 1936. This lecture presents in a vividly descriptive manner some of the material published in past issues of the Bell System Technical Journal. 1 Electron Diffraction Experiments Upon Crystals of Galena. L. H. GERMER. Cleaved surfaces of galena crystals yield electron diffraction patterns made up of Kikuchi lines, and spots which are drawn out into streaks by refraction. After etching, the spot pattern predominates and the individual spots are sharp. 

The lines are then rather diffuse and ill-defined. Rocking curves upon various Bragg reflections from the surface plane prove that the imperfection of a certain crystal does not exceed about 15 minutes, and that the projections through which the electrons pass are relatively thick. Estimates of imperfection and thickness made from rocking curves are in approximate agreement with those obtained from widths of Kikuchi lines. A galena crystal which has been filed or ground parallel to a cube face exhibits two different sorts of surfaces. There are smooth "mirror" surfaces from which large blocks of the crystal have been mechanically torn, and there are very deeply scratched portions of the surface. The "mirror" surfaces give diffraction patterns which are qualitatively similar to patterns from cleaved surfaces, although there are notable differences.