Reflection electron energy‐loss spectroscopy and imaging for surface studies in transmission electron microscopes

Abstract A review is given on the techniques and applications of high‐energy reflection electron energy‐loss spectroscopy (REELS) and reflection electron microscopy (REM) for surface studies in scanning transmission electron microscopes (STEM) and conventional transmission electron microscopes (TEM). A diffraction method is introduced to identify a surface orientation in the geometry of REM. The surface dielectric response theory is presented and applied for studying α‐alumina surfaces. Domains of the α‐alumina (012) surface initially terminated with oxygen can be reduced by an intense electron beam to produce Al metal; the resistance to beam damage of surface domains initially terminated with Al +3 ions is attributed to the screening effect of adsorbed oxygen. Surface energy‐loss near‐edge structure (ELNES), extended energy‐loss fine structure (EXELFS), and microanalysis using REELS are illustrated based on the studies of TiO 2 and MgO. Effects of surface resonances (or channeling) on the REELS signal‐to‐background ratio are described. The REELS detection of a monolayer of oxygen adsorption on diamond (111) surfaces is reported. It is shown that phase contrast REM image content can be significantly increased with the use of a field emission gun (FEG). Phase contrast effects close to the core of a screw dislocation are discussed and the associated Fresnel fringes around a surface step are observed. Finally, an in situ REM experiment is described for studying atomic desorption and diffusion processes on α‐alumina surfaces at temperatures of 1,300—1,400°C.