Beugung langsamer Elektronen an kugelförmigen oxydierten Kupfer-Einkristallen

Abstract

The surfaces of spherical copper monocrystals were investigated with slow electron diffraction. The crystals were grown in the UHV of the diffraction apparatus by cooling-down molten droplets of the metal according to MENZEL'S method. By turning the crystal the diffraction pattern of an arbitrary crystallographic pole may be observed some minutes after crystal growth. On the untreated crystal only the interferences of the copper lattice appear. The patterns have the character of space lattice diffraction if the incident beam strikes a larger spherical calotte of the surface (focussing on the fluorescence screen). If the beam is focussed on the crystal surface (diameter 0.3 mm) the spots on the screen are enlarged and weaker, but the diffraction resembles more the usual two-dimensional type. These facts are explained by taking account of the shape transform of the irradiated spherical surface region. — By heating the crystal flat regions may be produced to some extent at low index poles, giving sharp diffraction spots surrounded by diffuse halos. — The main subject of this work is the study of structure produced by weak oxidation (10^-4 Torr O₂, 150°C, 30 min.). A c (2 x 2) superstructure developer at the (001)-pole, a c (2 x 6) structure at the (110)-pole. The most remarkable effect of oxygen chemisorption is a very pronounced facetting of the surface: In the neighbourhood of (001) the surface is built up by four macroscopic facets of the type {410}, showing no superstructure. Other types of facetting appear near the (011) - and (111)-pole; in the surrounding of the latter facets of the type {011} appear. — Reduction with hydrogen produces firstly {113} facets near the (001) -pole. After complete reduction this pole is transformed again to a small flat region surrounded by a spherical surface without any facets.