c(6x2)and c(4x2)reconstruction of SrTiO3(001)

In this paper we report centered 6 x 2 [c(6 x 2)] and centered 4 x 2 [c(4 x 2)] reconstructions of SrTiO3(001) surfaces observed consistently using low energy electron diffraction and high resolution scanning tunneling microscopy. We find that the final ordering of the SrTiO3(001) surface depends not only on the annealing conditions, but also critically on the surface condition before ultra-high vacuum annealing. Auger electron spectroscopy measurements revealed a systematic correlation of AES intensity ratio I(Sr)/I(Ti) and I(O)/I(Ti) with various types of reconstructed surface [1 x 1, 2 x 1, c(4 x 2), and c(6 x 2)]. It also shows roughly a linear dependence of O-to-Ti ratio on the Sr-to-Ti ratio. Therefore, the change in stoichiometry drives the surface to different superstructures. We discuss the surface electronic states associated with the oxygen vacancies, and their effect on the electron tunneling. The c(6 x 2) surface is found to be extremely stable in ultra-high vacuum, even during atomic resolution scanning tunneling microscopic imaging. A single domain c(6 x 2) reconstruction can be stabilized on a vicinal (001) surface. (C) 1999 Elsevier Science B.V. All rights reserved.