Two-dimensional TiO x nanostructures on Au(111): a scanning tunneling microscopy and spectroscopy investigation (original) (raw)

Scanning Tunneling Microscopy Study of Titanium Oxide Nanocrystals Prepared on Au(111) by Reactive-Layer-Assisted Deposition

ACS Nano, 2008

We report on an scanning tunneling microscopy study of the nanocrystallite phases of TiO 2 formed via reactive-layer-assisted deposition in ultrahigh vacuum. The synthesis used reaction of a thin layer of water, on a Au(111) substrate at 130 K, with low-coverage vapor-deposited Ti. The effects of annealing temperature and reactant coverage were investigated. Large-scale (>20 nm) patterns in the surface distribution of nanoparticles were observed with the characteristic length-scale of the pattern correlating with the thickness of the initial layer of H 2 O. The phenomenon is explained as being due to the formation of droplets of liquid water at temperatures between 130 and 300 K. After the surface was annealed to 400 K, the individual titania nanoparticles formed by this process had diameters of 0.5؊1 nm.

Synthesis of TiO[sub 2] nanoparticles on the Au(111) surface

The Journal of Chemical Physics, 2005

The growth of titanium oxide nanoparticles on reconstructed Au(111) surfaces was investigated by scanning tunneling microscopy and X-ray photoelectron spectroscopy. Ti was deposited by physical vapor deposition at 300 K. Regular arrays of titanium nanoparticles form by preferential nucleation of Ti at the elbow sites of the herringbone reconstruction. Titanium oxide clusters were synthesized by subsequent exposure to O 2 at 300 K. Two-and three-dimensional titanium oxide nanocrystallites form during annealing in the temperature range from 600 to 900 K. At the same time, the Au(111) surface assumes a serrated, <110> oriented step-edge morphology, suggesting step-edge pinning by titanium oxide nanoparticles. The oxidation state of these titanium oxide nanoparticles varies with annealing temperature. Specifically, annealing to 900 K results in the formation of stoichiometric TiO 2 nanocrystals as judged by the observed XPS binding energies. Nano-dispersed TiO 2 on Au(111) is an ideal system to test the various models explaining the enhanced catalytic reactivity of supported Au nanoparticles.

STM/STS investigations of titanium oxide nanostructures on au substrate

Materials Letters, 2007

Au substrate was prepared by Au evaporation on Si(111) surface. Au surface was composed of Au grains with typical diameter of about 50 nm with atomically flat terraces. TiO 2 nanostructures were created by electron gun evaporation of Ti while simultaneous dosing of high purity O 2 gas. The pressure of oxygen was kept at 5 • 10 − 8 mbar and controlled by means of residual gas analyzer (RGA). Scanning tunneling microscopy (STM) images showed that TiO 2 nanocrystallites had grown between Au grains in cavities between them. This may suggest that such spots are preferred TiO 2 nucleation sites. I-V curves measured above Au showed metallic properties while those measured above TiO 2 exhibit energy gap characteristics for semiconducting material.

Scanning tunneling microscopy/spectroscopy of titanium dioxide nanoparticulate film on Au() surface

Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2004

Using ultrahigh-vacuum low-temperature scanning tunneling microscopy and spectroscopy combined with first principles density functional theory calculations, we have investigated structural and electronic properties of pristine and potassium (K)-deposited picene thin films formed in situ on a Ag(111) substrate. At low coverages, the molecules are uniformly distributed with the long axis aligned along the [112] direction of the substrate. At higher coverages, ordered structures composed of monolayer molecules are observed, one of which is a monolayer with tilted and flatlying molecules resembling a (110) plane of the bulk crystalline picene. Between the molecules and the substrate, the van der Waals interaction is dominant with negligible hybridization between their electronic states; a conclusion that contrasts with the chemisorption exhibited by pentacene molecules on the same substrate. We also observed a monolayer picene thin film in which all molecules were standing to form an intermolecular π stacking. Two-dimensional delocalized electronic states are found on the K-deposited π stacking structure. © 2014 AIP Publishing LLC.

Scanning tunneling microscopy/spectroscopy of titanium dioxide nanoparticulate film on Au( 1 1 1 ) surface

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.

Preparation and structure of a single Au atom on the TiO2(110) surface: control of the Au–metal oxide surface interaction

Faraday Discussions, 2013

Three-dimensional Au structures on bare and organic-compound-modified TiO 2 (110) surfaces were interrogated by Au L 3-edge polarization dependent total reflection fluorescence X-ray absorption fine structure (PTRF-XAFS) spectroscopy. On the bare TiO 2 (110) surface, icosahedral Au 55 nanoclusters were the main product found. When the surfaces were modified with ortho or meso mercapto benzoic acid (o-MBA or m-MBA), Au was atomically dispersed. Sulfur atoms in the o-and m-MBA formed strong covalent bonds with Au to produce stable Au-MBA (o-and m-forms) surface complexes. On the other hand, only oxygen atoms on the surface did not make a strong enough interaction to stabilize the Au species. We discuss how the Au species formed on the modified TiO 2 (110) surface and the possibility to control the Au structure by the surface modification method.

Growth of TiO2(B)(001) on Au(111) by chemical vapor deposition

Surface Science, 2015

This study presents how a TiO 2 (B) film exposing the (001) face can be grown on Au(111) by chemical vapor deposition. Identification and characterization of the TiO 2 (B)(001) layer are carried out with low-energy electron diffraction (LEED), synchrotron radiation photoelectron spectroscopy (PES), scanning tunneling microscopy (STM) and X-ray absorption spectroscopy (XAS). Formation of the TiO 2 (B) film requires a two-step preparation procedure: deposition at 280°C followed by annealing to 500°C. This suggests that the interaction between a substrate and an overlayer stabilizes the TiO 2 (B) film, preventing the formation of thermodynamically more stable rutile islands. The study thus gives insight into how the morphology and the atomic structure of the titania overlayer can be controlled.

Au nanoparticles on a templating TiOx/Pt(111) ultrathin polar film: a photoemission and photoelectron diffraction study

Physical Chemistry Chemical Physics, 2009

We present an in-depth investigation of Au nanoparticles self-assembled on a zigzag-like TiO x /Pt(111) ultrathin polar film, whose structure is known in great detail. The peculiar pattern of defects (picoholes) templates a linear array of size-selected (ca. 1 nm) Au nanoparticles without disruption of the titania layer, as observed by scanning tunneling microscopy. Their structure and electronic properties have been investigated by several large-area spectroscopic tools, i.e. high-resolution core and valence level photoemission and angle-scanned and energy-scanned photoelectron diffraction. The comparison between experimental data and density functional theoretical calculations indicates that the Au atoms landing on the oxide film are rather mobile, and that the picoholes can act as effective trapping and nucleation centers for the growth of the Au nanoparticles. All the experimental results are in concord in indicating that the Au NPs are flat islands with a maximum thickness of 2-3 layers exposing the (111) surface.

Mobility of Au on TiO x Substrates with Different Stoichiometry and Defectivity

2008

Au nanoparticles deposited on titania films, where two nanophases of different stoichiometry and defectivity are co-present, were imaged on the same spot by scanning tunneling microscopy. The observed sizes are rather dissimilar as a consequence of the different mobility of Au on the two surfaces. The role of the stoichiometry, which can influence the Au-substrate interaction, and of the defects, which can trap the metal atoms, is discussed on the basis of theoretical calculations of diffusion energy barriers on the two surfaces.