Analysis of Growing Films of Complex Oxides by RHEED

Abstract

The majority of sophisticated ultra-high-vacuum (UHV) systems for deposition of thin films, such as molecular beam epitaxy (MBE) machines, contain some kind of electron diffraction apparatus which is used to scrutinize the surface structure of the film while it is grown. Reflection high energy electron diffraction (RHEED) is probably the most frequently employed configuration. An excellent introduction to RHEED, including a treatment of electron diffraction, reciprocal-space description, reflection from imperfect surfaces, etc., was recently published in the MRS Bulletin by Lagally and Savage. Hence, we will not review these basics here. Rather, we will assume the reader to be familiar with that article, and will refer to it as LS.The materials discussed in LS include Si, Ge on Si, and GaAs. The applications of MBE for synthesis of semiconductor thin films and heterostructures are widely recognized. MRS has recently bestowed its greatest honor, the Von Hippel Award, to Alfred Y. Cho for his pioneering work on MBE synthesis of GaAs and its application to new devices.In contrast, here we focus on complex oxides—cuprates, titanates, manganates, etc. This is a relatively new area of application for both MBE and RHEED. Actually, it was only after the discovery of high-temperature superconductivity (HTS) that many MBE systems were designed and built specifically for metallic oxide deposition. More recently, some of these machines have also been employed to synthesize other interesting oxides, for example, ferroelectrics and ferromagnets. In all these studies, RHEED has been the principal diagnostic tool and source of information about the growing film surface.