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Electronic properties of disordered anodic TiO 2 (001) surfaces: Application of the equation‐of‐motion method
Author(s) -
Tit Nacir,
Halley J. W.,
Michalewicz M. T.
Publication year - 1992
Publication title -
surface and interface analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.52
H-Index - 90
eISSN - 1096-9918
pISSN - 0142-2421
DOI - 10.1002/sia.740180204
Subject(s) - condensed matter physics , rutile , vacancy defect , local density of states , density of states , materials science , electronic structure , scanning tunneling microscope , impurity , band gap , chemistry , nanotechnology , physics , organic chemistry
We report calculations of the electronic properties for rutile TiO 2 (001) surfaces using the equation‐of‐motion (EOM) method. We use a full tight‐binding Hamiltonian developed by Vos to describe the electronic structure. In contrast to the Green's‐function (GF) method which is traditionally used for such a problem, the EOM method gives excellent results with large systems and any number of defects, and puts no restriction on the range of the impurity potential. There is experimental evidence that the observed gap state at 0.7 eV below the conduction‐band edge is due to an oxygen vacancy. For this reason we study the electronic properties of disordered surfaces as a function of oxygen vacancy concentrations (up to 10%). Our results are applied to the interpretation of recent scanning tunneling Microscopy (STM) experiments on anodic rutile TiO 2 (001) films (whose thickness is ∼ 150 Å), and the density of surface defects is estimated. Special care was paid to the study of the nature of gap states. Our results show that these states are localized and play the role of trapping centers which impede the conduction in the films and that no impurity band exists for the studied surfaces. We use both conductivity and local density of states (LDOS) calculations to draw this conclusion. In agreement with experiments, no contribution from gap states in the transport was confirmed in our work. We also report the LDOS calculations on a few sites around the defect at the surface. This in turn gives information about both the spatial decay of the bound‐state wave function (localization) and the existence of the impurity band.