INSITU FORMATION OF MGO2 THIN-FILMS ON MGO SINGLE-CRYSTAL SURFACES AT HIGH-TEMPERATURES

Structures on MgO(100) surfaces heated to high temperatures have been comprehensively studied in-situ using the combined electron microscopy techniques of imaging (REM, HREM), diffraction (RHEED, THEED) and spectroscopy (REELS, TEELS, EDS) in both reflection and transmission geometries. A thin film, less than about 10 atomic layers in thickness. is formed on the surface after heating to 1500 K inside a conventional electron microscope. The newly formed film consists of mainly MgO2 and small amounts of calcium and chromium impurities produced by surface segregation at high temperature. The film covers the entire surface in patches of a few tens of nanometers in size; the [110] direction and the (001) plane of each MgO2 patch are parallel to the [110] direction and the {111} plane of the MgO matrix, respectively. This MgO2 film is stable at high temperature (1500 K), room temperature. and even after being exposed to air for two weeks, and can be produced on surfaces other than (100) such as irregularly shaped MgO fragments. It has been found that multiple-diffraction effects may create additional "rods" in RHEED patterns, leading to possibly incorrect structural interpretation. The combination of RHEED with imaging techniques is important for solving the surface structures.