Reflection High Energy Electron Diffraction

Abstract

Reflection high energy electron diffraction (RHEED) was first used in the study of a cleaved calcite crystal by Nishikawa and Kikuchi in 1928 [12.1]. They observed diffraction spots, and lines attributed to diffuse scattering. Other early workers included Germer (1936) [12.2] who took diffraction patterns from galena and Miyake (1936) [12.3] who examined oxide surfaces. Uyeda et al. [12.4] used RHEED with metal films in 1940 and with adsorbed organic molecules in 1950. Commercial RHEED equipment was developed through the 1950s but this operated at 10−4 to 10−6 Ton and hence only on dirty surfaces. However its application was as an alternative to X-ray diffraction. RHEED’s forward scattering nature and comparatively high scattering cross section (108:1) made it competitive. As ultra high vacuum equipment became common in the 1960s, systems were equipped with RHEED guns, but good LEED was then possible, and LEED largely displaced RHEED as a diffraction technique for clean single crystal surfaces. The main reasons for this neglect was that RHEED gives quantitative results only on extremely flat surfaces which were not easily prepared and offered no theoretical advantages over LEED in the central surface science question of the surface atomic structure. Also the LEED apparatus was easily constructed and much cheaper than the traditional magnetically focussed RHEED guns. A good review of RHEED and LEED before 1970 is given by Bauer [12.5]. The growth technique of molecular beam epitaxy (MBE) brought about a renaissance in RHEED in the 1980s. For this reason the applications of RHEED discussed in this chapter will be drawn from MBE.