HYDROGEN-INDUCED REORDERING OF THE SI(111)-ROOT-3X-ROOT-3-AL SURFACE STUDIED BY ERDA LEED

Using elastic recoil detection analysis and low-energy electron diffraction we have investigated the adsorption process of hydrogen on the Si(111)- square-root 3 x square-root 3-Al surface. We have found that (1) hydrogen adsorption of 0.5 ML induces a structural transformation from the Si(111)-square-root 3 x square-root 3-Al to Si(111)-1 x 1-Al(H) at room temperature, (2) the saturation coverage of hydrogen on the square-root 3 x square-root 3 -Al surface is 1.6 ML, which almost coincides with that on a clean 7 x 7 surface, (3) the 1 x 1-Al(H) LEED pattern still persists after almost all hydrogen has desorbed from the 1 x 1-Al(H) surface on heating to 400-degrees-C, and that (4) the original square-root 3 x square-root 3 -Al surface is recovered after heating at 700-degrees-C.