Multiple Reflection Phenomena in Electron Diffraction

Abstract

A diffraction phenomenon that is rare for X-rays but very common for 50- to 100-kv electrons is a principal source of difference between X-ray and electron diffraction intensities. Workers at our laboratory first became aware of this effect and its extent after examining electron diffraction patterns of cuprite (Cu2O) in a Phillips EM 100A electron microscope at an accelerating potential of 100 kv. The powder pattern (Fig. 1) contains every possible reflection from a primitive cubic lattice. The strongest lines are those of a face-centered cubic lattice—that is, the Miller indices are all even or all odd. Lines having mixed indices with even sums are of intermediate intensity, while those having one odd and two even indices are the weakest set. There are only a few spots on each Debye ring of the latter set.