Surface of sputtered and annealed polar SrTiO3(111):: TiOx-rich (n x n) reconstructions

SrTiO3(111) samples, doped with Nb, are Ar+ ion sputtered and annealed in ultrahigh vacuum (UHV) and in varying pressures of oxygen and investigated using scanning tunneling microscopy (STM) and Auger electron spectroscopy (AES). STM images show that a number of reconstructions constituting a family of (n x n) surfaces are able to form on the surface by varying the sputtering conditions and O-2 annealing pressures. The family of (n x n) reconstructions is due to variations in the oxygen stoichiometry, with (3 x 3) the most oxygen-rich, followed by (4 x 4), (6 x 6), and finally (5 x 5). Annealing in atmospheric pressure of air causes a (9/5 x 9/5) reconstruction to form. Highly reducing the surface, through extended UHV annealing, produces a TiO (111)-(2 x 2) nanophase. Step heights are always found to be equivalent to integer multiples of the distance between two similar (111) planes (the d(111) lattice parameter). AES analysis indicates no detectable impurities and shows all the surfaces to be Ti-enriched and either stoichiometric or deficient with respect to Sr. The concentration of Ti at the surface increases as the surface becomes more reduced.