Interpretation of a Complex Low Energy Electron Diffraction Pattern: Carbonaceous and Sulphur-containing Structures on Ni(111)

Abstract

THE complex low energy electron diffraction pattern shown in Fig. 1, previously described tentatively as Ni(111) (16√(3)×16√(3)) R 30°—C (ref. 1), has been observed during an investigation of the reactions of Ni(111) with various carbon or sulphur-containing gases, including ethylene, carbon monoxide¹, benzene and hydrogen sulphide. The pattern is produced at a variety of surface temperatures, depending on the reactant, from 20° to 350° C and in exposure times from 10 to 1,000 Langmuirs (L=10⁻⁶ torr s). The patterns are not identical in every case but are consistent geometrically and in the grouping of the diffraction beams into two distinct levels of intensity. The strong features predominate at 70 V and above; the weaker spots are more clearly seen at lower voltages (Fig. 2). The differences between the patterns obtained with different reactants are in the relative intensities of the diffraction spots within each category. Both Fig. 1 and Fig. 2 are the products of reaction with ethylene. The action of H₂S produced a series of patterns, one of which was the complex pattern, but diffuse and complicated by the presence of traces of the succeeding patterns. The same strong characteristic features were undoubtedly present, however.