Diffraction of Low-Speed Electrons by Single Crystals of Copper and Silver

Abstract

Diffraction beams for normal incidence on the (100) faces of copper and silver crystals.—Previous results for a copper crystal are checked and extended, by using another crystal of exceptionally pure copper. All of the expected diffraction beams which are x-ray analogues in the two principal azimuths and in the range below 325 volts are found. These beams require values of refractive index greater than unity, but the associated values of inner potential are not constant. Another class of weak beams is found characteristic of the copper lattice, but which require a refractive index of approximately unity for the first order beams of the two principal azimuths. These weak beams accompany the main beams on the high voltage side as satellites. Conditions for orders higher than the 1st are more complicated and indicate that the above method of classification is not sufficient. For a silver crystal the number of experimental maxima is considerably greater than the number of theoretical beams in the low-voltage range. These maxima cannot be classified as main beams requiring a refractive index greater than unity, and weak satellites requiring unit refractive index as in case of a copper crystal, but whenever two or more experimental maxima are to be associated with a given theoretical beam, they are, in general, grouped as components of fine structure of a single diffraction beam.