Effects of Adsorption and Thermal Desorption of Atomic Hydrogen on Electronic and Atomic Structures of Si(111)(√3×√3)-Al Surface

The adsorption and thermal desorption of atomic hydrogen induce electronic and atomic structural changes on the Si(111)(√3×√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 (√3×√3) surface structure changes into a hydrogen-induced (1×1) in the LEED pattern. Simultaneously, the characteristic loss peaks of the Si(√3×√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 (√3×√3) LEED pattern reappears and a new loss peak emerges at 1.5 eV. The Al-LVV Auger peak is observed on the Si(√3×√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 (√3×√3) surface structure is proposed to be induced by the Si adatoms substituting for Al in the T4 adatom geometry.