BARIUM ADSORPTION ON HYDROGENATED SI(100)2X1 SURFACES

An experimental study of Ba and H adsorption on Si(100)2 x 1 by Auger electron spectroscopy, thermal desorption spectroscopy, low-energy ele ctron diffraction, electron energy loss spectroscopy, and work functio n measurements has been made. Measurements of hydrogen adsorption on a clean silicon surface have been made mainly for reference purposes. H on Si forms two different states, known as monohydride state Si(100)2 x 1:H and dihydride state Si(100)1 x 1::2H. Preadsorption of H made t he surface order more stable without changing the sticking coefficient of Pa on the Si surface. The results supported the double-layer (DL) model for the first Pa layer on the monohydrided Si surface. Ba adatom s up to Theta = 1 ML on the dihydride phase were relaxed at symmetric and equivalent sites following the (1 x 1) symmetry of the restored Si surface. TDS measurements showed that during Ba adsorption on the mon ohydride phase some of the H atoms were removed from their initial ads orption sites, and a new H energy state was formed at 425 degrees C wh ich was attributed to the weakening of the Si-H bond in the presence o f Ba adatoms. When Ba deposition took place on the dihydride phase, tw o new H states were successively developed. The first state at 220 deg rees C was attributed to BaH2 formation, and the subsequent one to a c omplex Ba-H-Si compound near 680 degrees C. The presence of hydrogen c aused a considerable delay of barium overlayer metallization, in contr ast to the early metallization of alkali on hydrogenated surfaces.