Study of photo-induced electron transport phenomena on oxide semiconductor surfaces

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We studied electronic structure and carrier dynamics of oxide semiconductor surfaces that are significant in applied chemistry of photocatalysis and in physics of strongly correlated electronic system. Experiments were carried out with high-resolution angle-resolved photoemission spectroscopy and newly developed time-resolved photoemission spectroscopy at SPring-8 BL07LSU.Surfaces of SrTiO3 and ZnO crystals are metalized with quite strong electron correlation by adsorbing hydrogen atoms and introducing surface defects.The carrier dynamics was studied by tracking relaxation of the surface photovoltage in real time. For the photocatalysts of TiO2 nanoparticles, chemical reactivity has been reported better on the anatase-type crystal than on the rutile-type. The photo-excited carriers were found to have 10 times longer lifetime on the anatase-type than on the rutile type, as evaluated from the experimentally determined time constants from the two crystal surfaces.