Surface morphologies of SnO2(110)

Scanning tunneling microscopy (STM), ion scattering spectroscopy (ISS), and low energy electron diffraction (LEED) was used to investigate the surface morphology of SnO2(110) for different preparation conditions. Annealing in 10(-3) mbar oxygen results in a 1 x 1 diffraction pattern. Such surfaces exhibit terraces separated predominantly by straight step edges along low index crystallographic directions. The terraces exhibit a high density of defects. Annealing to 8 10 K results in the loss of surface oxygen but the surface retains a 1 x 1 periodicity. Steps of less than monolayer-height, however, indicate that a significant reordering of the surface atoms occurs already at this temperature. Annealing to higher temperature or preparation of the surface by sputtering and vacuum annealing always results in a superstructure in the diffraction pattern and a low [O]/[Sn] ratio in ISS. For annealing temperatures between 920 and 1050 K co-existence of c(2 x 2) and 4 x 1 reconstructed domains is observed. In this regime small adislands are always present at the surface; extended terraces were imaged by STM with a 4 x 1 periodicity. This implies that the c(2 x 2)structure is associated with adislands at the surface. Annealing to 1100 K resulted in the formation of a 4 x 1 surface only. This surface exhibits terraces with meandering step edges and antiphase domain boundaries of the 4 x 1 surface structure. A new model for this reconstruction is proposed including Sn atoms occupying interstitial surface sites. Annealing to 1180 K results in the fragmentation of the 4 x 1 structure and the surface looses its long-range order. This causes a 1 x 1 LEED pattern originating from the underlying substrate. Surface undulations with sub-interlayer step heights are explained by the frequent presence of stacking faults and other bulk defects that are also accompanied by variations in the electronic structure due to a locally altered Sn/O stoichiometry. (C) 2003 Elsevier Science B.V. All rights reserved.