Exploration of Cs-O co-adsorption on GaAs(100) β2 (2x 4) surface at different sites from first-principles calculation

( )The micro-mechanism of Cs-O co-adsorption on GaAs(100) beta(2) (2 x 4) surface is clarified through first-principles calculation. In Cs-O adsorption models, several different adsorption sites including D, D', T2, T2', T3, T3', T4, T4', H and H' are respectively considered to research the influence of adsorption sites on photoemission. Related crucial properties including adsorption energy, work function, charge transfer and dipole moment are analyzed. The calculation results show that the uppermost As-dimer D site has the maximum work function reduction, but its adsorption energy is not the lowest, while the hollow site H is considered to be the most undesirable site because of its minimum work function reduction and higher adsorption energy. Although T3 site is the most stable adsorption site, its weaker dipole moment resulting in smaller work function reduction is not favorable for photoemission. Moreover, it is inferred from Mulliken charge distribution that the Cs atom can transfer electrons to Ga atoms in the upper bilayer, especially for the sites D, D', H and H'. Meanwhile, Cs-O adsorption at the lowest hollow H site promotes the formation of gallium oxide while the arsenic oxide tends to form for adsorption at the sites D, D' and H' nearby the As-dimers.