The surface structure of α-Al2O3 determined by low-energy electron diffraction: aluminum termination and evidence for anomolously large thermal vibrations

The temperature dependence of the first three interlayer distances of the Ag(111) surface was studied by low-energy electron diffraction (LEED) over the temperature range 128K to 723 K. The first three interlayer spacings and the effective Debye temperatures were extracted from the LEED analysis. At the lowest temperature, the first two interlayer spacings are slightly (0.5 percent) contracted. All three interlayer spacings increase with temperature, finally reaching expansions relative to the bulk of about 0.8 percent at the highest temperature studied. The effective surface Debye temperature is lowest for the outermost layer, increasing toward the bulk value for successive layers.