EFFECTS OF ADSORPTION AND THERMAL-DESORPTION OF ATOMIC-HYDROGEN ON ELECTRONIC AND ATOMIC STRUCTURES OF SI(111)(SQUARE-ROOT 3 X SQUARE-ROOT 3)-AL SURFACE

The adsorption and thermal desorption of atomic hydrogen induce electronic and atomic structural changes on the Si(111)(square-root 3 x square-root 3)-Al surface. These changes have been studied using low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and angle-resolved electron-energy-loss spectroscopy (AR-EELS). Upon exposure to atomic hydrogen, the (square-root 3 x square-root 3) surface structure changes into a hydrogen-induced (1 x 1) in the LEED pattern. Simultaneously, the characteristic loss peaks of the Si(square-root 3 x square-root 3)-Al surface completely disappear and a new loss peak appears at 8 eV. We ascribe this new peak to a Si-H bonding state. After thermal desorption of atomic hydrogen, a (square-root 3 x square-root 3) LEED pattern reappears and a new loss peak emerges at 1.5 eV. The Al-LVV Auger peak is observed on the Si(square-root 3 x square-root 3)-Al surface, but not on this hydrogen-desorbed surface. The new loss peak at 1.5 eV is ascribed to the transition due to the Si-adatom-induced surface state. The reappeared (square-root 3 x square-root 3) surface structure is proposed to be induced by the Si adatoms substituting for Al in the T4 adatom geometry.