Surface relaxation and rumpling of TiO2-terminated SrTiO3(001) determined by medium energy ion scattering

The surface relaxation and rumpling of TiO2-terminated SrTiO3(001) were det ermined by medium energy ion scattering (MEIS). A new toroidal electrostati c analyzer with high energy resolution (Delta E/E=1 x 10(-3)) allows direct determination of the displacements of surface atoms by a simple triangulat ion method using the ion shadowing effect. The TiO2-terminated surface was prepared by the chemical treatment with a buffered NH4F-HF solution (pH=3.5 -3.8). Annealing at 600 degrees C for 1 h in an ultrahigh vacuum under O-2 gas flow (5 x 10(-6) Torr) led to a clean surface without carbon contaminat ion and oxygen vacancies, which was confirmed by Auger electron and ultravi olet photoelectron spectroscopy. The present MEIS analysis revealed that th e occupation fraction of the TiO2 face ranged from 85 to 95% and the surfac e relaxation and rumpling were + 2.7 +/- 0.2% and + 3.1 +/- 0.4% respective ly. The present results were compared with other experimental and theoretic al ones. (C) 1999 Elsevier Science B.V. All rights reserved.