EFFECT OF NH3 ON SI(100) VICINAL SURFACES

The structural and electronic properties of clean vicinal surfaces of Si(100) upon interaction with NH3 have been studied using low energy electron diffraction (LEED), Auger electron spectroscopy (AES), and photoemission yield spectroscopy (PYS) in situ, under ultrahigh vacuum (UHV). Two cases of vicinal surfaces were compared to the nominal (100) face, namely one with a 6-degrees angle towards the [011] direction, the other with a 5-degrees angle towards the [010] direction. It is shown that the rougher the surface, the faster the common saturation coverage theta-s is reached, where theta-s corresponds to one NH3 molecule per two surface Si dimers. The dipole formed upon adsorption leads to a similar decrease of the work function, which can reach 0.9 eV at saturation. The best ordered surfaces (here 6-degrees vicinal) show upon NH3 saturation a well pronounced electronic structure near the valence band edge, the origin of which is discussed.