Investigation of the SrTiO3 (110) surface by means of LEED, scanning tunneling microscopy and Auger spectroscopy

We prepared SrTiO3 (110) surfaces by reducing and sputtering in UHV at high temperatures of around 1000 degrees C. The as-prepared samples were characterized using low energy electron diffraction (LEED), Auger electron spectroscopy and scanning tunneling microscopy (STM). LEED experiments revealed the existence of a variety of reconstructed surfaces of the type (n x m). In some cases we attributed missing LEED spots to an incommensurability of the surface structure in the [110] direction. These results were confirmed by STM measurements. STM images of the as-prepared SrTiO3 (110) surfaces showed stripe-like surface structures running in the [1(1) over bar0$] direction consisting of individual building blocks. These blocks were frequently found to be uncorrelated between adjacent stripes. SrTiO3 (110)samples, only slightly annealed, yielded a different surface structure. The STM measurements revealed a micro-faceted surface. Our STM measurements allowed direct observation of the (1 x 1) surface periodicity of the SrTiO3 (110) surface due to tunneling into empty states of Ti2+/Ti3+ sites at the surface. Our results suggest the necessity of special treatments of the SrTiO3 (110) surfaces in order to get the smooth, homogeneous surfaces, imperative for growing high quality (110)- or (103)/(013)-oriented RBa3Cu3O7-delta thin films. Auger measurements showed that the surface concentration of strontium increases with respect to titanium with increasing annealing temperature. This behavior is different from other SrTiO3 surfaces. The surface concentration of oxygen with respect to titanium is almost independent of the annealing temperature. (C) 1997 Elsevier Science B.V.