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TiO2 (110) theory

The task of fully characterizing transition metal oxide surfaces is complicated substantially by the ability of many of these compounds to accommodate high degrees of nonstoichiometry.  As a result, a large variety of stable or metastable surface structures, many with large unit cells and low symmetry, have been observed.

stmtheory1_part1
15 nm x 22 nm

stmtheory2_part1
6.5 nm x 9.0 nm


G. S. Rohrer, V. Henrich, D. A. Bonnell Science 250 (1991).

Oxides Adopt Complex Surface Structures

Reconstruction or Surface Stabilized Phases!!!

Constant current STM images of crystallographic shear structures on Ti02 (110)

 

stmtheory1_part3

srti16c


Y. Liang, D. Bonnell J. Am. Cer. Soc. 78 (1995), Surf. Sci. 310 (1994) 128

Constant current STM imaging of the stabilization of Ruddleson Popper Phases on SrTiO3 (100

One successful approach to the interpretation of images of TiO2 (110) is the use of first principles pseudo-potential calculations of spatially resolved surface electronic structure of states relevant to tunneling.  However, the ability to perform first principle calculations is often removed from the experimentalist and the formidable cost and slow running time of such calculations make them impractical as a tool for in-situ image interpretation of complex surfaces.

STM Theory

The approach shown here makes use of first principles results for ideal or unreconstructed surfaces to develop a basis that is then extended to the much larger number of relatively complex reconstructed surfaces. Since Hamiltonian diagonalizations are avoided for all reconstructions, it extends the applicability of image simulation techniques to arbitrarily complex surfaces. This method is applied to the case of TiO2(110) 2x3 for which several atomic structures can be invoked to explain STM image contrast.

STM Theory