Correlation of electron-transfer rates with the surface density of states of native and anodically grown oxide films on titanium (original) (raw)
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The Journal of Chemical Physics, 2009
Introducing a charge into a solid such as a metal oxide through chemical, electrical, or optical means can dramatically change its chemical or physical properties. To minimize its free energy, a lattice will distort in a material specific way to accommodate screen the Coulomb and exchange interactions presented by the excess charge. The carrier-lattice correlation in response to these interactions defines the spatial extent of the perturbing charge and can impart extraordinary physical and chemical properties such as superconductivity and catalytic activity. Here we investigate by experiment and theory the atomically resolved distribution of the excess charge created by a single oxygen atom vacancy and a hydroxyl OH impurity defects on rutile TiO 2 110 surface. Contrary to the conventional model where the charge remains localized at the defect, scanning tunneling microscopy and density functional theory show it to be delocalized over multiple surrounding titanium atoms. The characteristic charge distribution controls the chemical, photocatalytic, and electronic properties of TiO 2 surfaces.
Photoelectrochemical spectroscopy studies of titanium dioxide surfaces: theory and experiment
Surface Science, 1991
We describe experimental and theoretical studies of titanium dioxide. Phot~lectr~he~~l data are presented for surfaces of known structure. The oxides were grown anodically on titanium metal. We report calculations of the electronic densities of states and optical conductivities of r-utile TiO, in finite-size samples disordered by the addition of oxygen vacancies for comparison with experiments. We conclude that in less disordered surfaces the electronic structure exhibited by the photospectra is very close to that of bulk rutile TiO,. In contrast, very thin oxides showed evidence of an electronic structure dominated by localized states near the band edge. More disordered oxides gave photospectra in which transitions associated with direct band gap transitions in bulk TiOZ seem to have been suppressed. Taking the structural information on the oxides into account, we argue that this suppression is probably a matrix element effect. 0039-6028/91/$03.50 0 1991 -Elsevier Science Publishers B.V. All rights reserved Xenon bmp Multiprogrammer
Study of Clean TiO2(110) Surface by Scanning Tunneling Microscopy and Spectroscopy
Langmuir, 1996
The effect of annealing in UHV on the topographic and electronic structure of the TiO2(110) surface was studied by scanning tunneling microscopy and spectroscopy. Different (1×n) reconstructions with domain sizes of 5-10 nm were clearly identified in the crystallographic orientation [001]. Two other types of reconstruction with periodicities of 1.69 and 1.82 nm were detected perpendicular to the [11 h1] and [1 h13] crystallographic shear directions. The comparison of I/V and dI/dV spectra recorded on (1×1) and (1×2) terraces and on a disordered phase suggests a definite difference in the oxidation state of the surface Ti atoms of these arrangements.
Electron Transfer-Induced Dynamics of Oxygen Molecules on the TiO2(110) Surface
Science, 2004
Diffusion of oxygen molecules on transition metal oxide surfaces plays a vital role for the understanding of catalysis and photocatalysis on these materials. By means of time-resolved scanning tunneling microscopy, we provide evidence for a charge transfer-induced diffusion mechanism for O 2 molecules adsorbed on a rutile TiO 2 (110) surface. The O 2 hopping rate depended on the number of surface donors (oxygen vacancies), which determines the density of conduction band electrons. These results may have implications for the understanding of oxidation processes on metal oxides in general.
The Effect of Photoinduced Surface Oxygen Vacancies on the Charge Carrier Dynamics in TiO2 Films
Nano Letters, 2021
Metal-oxide semiconductors (MOS) are widely utilized for catalytic and photocatalytic applications in which the dynamics of charged carriers (e.g., electrons, holes) play important roles. Under operation conditions, photo-induced surface oxygen vacancies (PI-SOV) can greatly impact the dynamics of charge carriers. However, current knowledge regarding the effect of PI-SOV on the dynamics of hole migration in MOS films, such as titanium dioxide, is solely based upon volume-averaged measurements and/or vacuum conditions. This limits the basic understanding of hole-vacancy interactions, as they are
Surface Science, 2006
The titanium dioxide rutile (0 1 1) (equivalent to (1 0 1)) surface reconstructs to a stable (2 · 1) structure upon sputtering and annealing in ultrahigh vacuum. A previously proposed model (T.Phys. Rev. Lett. 93 (2004) 036104/1) containing onefold coordinated oxygen atoms (titanyl groups, Ti@O) is supported by Scanning Tunneling Microscopy (STM) measurements. These Ti@O sites are imaged bright in empty-states STM. A few percent of these terminal oxygen atoms are missing at vacuum-annealed surfaces of bulk-reduced samples. These O vacancies are imaged as dark spots. Their number density depends on the reduction state of the bulk. Double vacancies are the most commonly observed defect configuration; single vacancies and vacancies involving several O atoms are present as well. Formation of oxygen vacancies can be suppressed by annealing a sputtered surface first in vacuum and then in oxygen; annealing a sputtered surface in oxygen results in surface restructuring and a (3 · 1) phase. Anti-phase domain boundaries in the (2 · 1) structure are active adsorption sites. Segregation of calcium impurities from the bulk results in an ordered overlayer that exhibits domains with a centered (2 · 1) periodicity in STM.
Colloids and Surfaces A-physicochemical and Engineering Aspects, 2004
Scanning tunneling microscopy (STM)/scanning tunneling spectroscopy (STS) of titanium dioxide nanoparticulate film on Au(111) surface is carried out yielding topography, I–V, dI/dV versus V and normalized dI/dV versus V. Isolated nanoparticles were found to exhibit semiconducting behavior with a band gap which varies from 1 to >3.0 eV depending on the nature of substrate/nanoparticle/tip junction formation. Increase in the particulate density resulted into change in tunneling behavior from semiconducting to metallic as characterized by decrease in non-linearity in I–V curves and increase in average tunneling conductance. The results are discussed in terms of presence of adsorbed complexes on defect structure of TiO2 surface for low coverage and availability of additional transport paths between the particles at high coverage.
Electronic structure of TiO2(110) surface as a function of surface ligand configuration
Applied Surface Science, 1998
Ž. Electronic structure of TiO 110 surface is studied by a first-principles molecular dynamics calculation with the 2 Ž. Vanderbilt pseudopotential. Three types of the surface are concerned: stoichiometric surface, defect 1 = 1 surface, and Ti O added row surface. STM simulation as well as electronic band structures are presented. The simulated STM images 2 3 show that the surface Ti atom which has less ligand dominates the tunnel current.