  We investigated the influences charge writing on the surface work function
and resistance of the LaAlO3/SrTiO3 (LAO/STO) heterointerface in several gas
environments (air, O2, N2, and H2/N2). Charge writing decreased the surface
work function and resistance of the LAO/STO sample quite a lot in air but
slightly in O2.The interface carrier density was extracted from the measured
sheet resistance and compared with that obtained from the proposed
charge-writing mechanisms, such as carrier transfer via surface adsorbates and
surface redox. Such quantitative analyses suggested that additional processes
(e.g., electronic state modification and electrochemical surface reaction) were
required to explain charge writing on the LAO/STO interface.
