Hydrogen interactions with Si(111) and Si(100) surfaces studied by ultraviolet photoemission spectroscopy

H interactions with thermally cleaned Si(111) and Si(100) surfaces at 300-650K have been studied by ultraviolet photoemission spectroscopy. Experimental results are consistent with the existence of weakly adsorbed H atoms at 300K, which revealed surface resonance states around 7 eV below Fermi level. The weakly adsorbed H atoms desorb around 500K from the Si(100) surface to form the monohydride phase, while they are irreversibly transformed into the trihydride phase by annealing at 650K on the Si(111) surface. This indicates the different natures of Si-H chemical reactions on the two surface