Metallic electronic states on SrTiO3 (110) surface:: An in situ conduction measurement

An in situ conduction measurement of metallic electronic states on the SrTiO3 (110) surface is reported. The electronic states were observed on the SrTiO3 (110) surface in our previous work after annealing in ultrahigh vacuum (UHV) at relatively low temperature. 800 degreesC, based on a sharp Fermi edge detected by ultraviolet photoemission spectroscopy and finite zero-bias differential conductance by scanning tunneling spectroscopy. The electric conductance measurement is performed in order to verify the metallic feature of the surface as a macroscopic property. For the measurement. a sample holder is designed which enables both annealing in UHV by electron beam and four-probe electric conduction measurement with uniform electric field. Conductance contributed by bulk is separated by measuring the decrease of total conductance by adsorption of oxygen at room temperature. which is supposed to modify only the surface electronic states. Surface conductance is deduced between 150 to 300 K and showed a metallic feature. Moreover, the surface conductance during exposure to oxygen is monitored in situ, and shows a reversible-like change depending on the oxygen pressure. This possibly evidences that the oxygen molecules which temporarily stay on the surface suppress the conduction by surface electrons. (C) 2001 American Vacuum Society.