An Application of Electron Diffraction to the Study of Gas Adsorption

N the paper by Dr. C. J. Davisson and myself entitled "Diffraction of Electrons by a Crystal of Nickel," 2 we published a variety of information concerning; the gaseous contamination of the surface of our diffracting crystal. This information was obtained from a study of the modifications produced by adsorbed gas in the electron diffraction pattern. We have subsequently succeeded in obtaining some additional facts concerning adsorbed gas from a further study of our original data. Along with the presentation of these new facts, I am taking this opportunity to publish in greater detail the data upon which our original conclusions were based. In our Physical Review paper we showed that the interaction of a beam of electrons with a single crystal of nickel gives rise to phenomena which, in their most essential characteristics, are similar to the diffraction phenomena which would be observed if the beam of electrons of adjustable speed were replaced by a beam of X-rays of adjustable wave-length. The diffraction patterns produced by electron scattering are, however, substantially more complicated than would be the corresponding X-ray diffraction pattern. We showed that electron scattering can give rise to diffraction phenomena of four quite distinct types. The diffraction patterns of two of these types arise from the nickel atoms in the crystal lattice, while the diffraction patterns of the other two types have their origins in the layer of gas adsorbed upon the surface. The relative intensities of the diffraction patterns of these four types are determined by the amount of gaseous contamination on the surface of the crystal, and also by the temperature of the surface.