The surface science of titanium dioxide

Zinc oxide is a unique material that exhibits semiconducting and piezoelectric dual properties. Using a solid–vapour phase thermal sublimation technique, nanocombs, nanorings, nanohelixes/nanosprings, nanobelts, nanowires and nanocages of ZnO have been synthesized under specific growth conditions. These unique nanostructures unambiguously demonstrate that ZnO probably has the richest family of nanostructures among all materials, both in structures and in properties. The nanostructures could have novel applications in optoelectronics, sensors, transducers and biomedical sciences. This article reviews the various nanostructures of ZnO grown by the solid–vapour phase technique and their corresponding growth mechanisms. The application of ZnO nanobelts as nanosensors, nanocantilevers, field effect transistors and nanoresonators is demonstrated.

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Zinc oxide nanostructures: growth, properties and applications

The Interaction of Water with Solid Surfaces: Fundamental Aspects Revisited

Surface Science Studies of the Photoactivation of TiO2New Photochemical Processes

S. Pillai would like to acknowledge the UNSW Faculty
of Engineering Research Scholarship. K.R. Catchpole
acknowledges the support of an Australian Research Council fellowship.

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Surface plasmon enhanced silicon solar cells

The tiling and covering of images derived from the experimental technique of high-resolution transmission electron microscopy (HRTEM) has been a fruitful avenue in studies of bulk quasicrystal structures. In particular, the quasi-unit-cell model has been successfully applied to the 2-dimensional decagonal AlNiCo (d-AlNiCo) quasicrystal (see Sect. 8.3.1). However, HRTEM is a bulk technique and can only be used to observe the average structure over the thickness of the sample. On the other hand, scanning tunneling microscopy (STM) is a purely surface technique. Hence, if high-quality images of quasicrystal surfaces can be obtained, then the possibility arises of applying tiling and covering methodologies to these surfaces, with a view to elucidating their structure and determining whether or not they are terminations of the bulk. A corollary of this approach is that such studies would provide independent verification of current bulk tiling and covering models. In this chapter, we describe our attempts to apply tilings and coverings to images of surfaces of quasicrystals obtained using STM [1, 2, 3, 4, 5, 6, 7].

Tilings and Coverings of Quasicrystal Surfaces

Overlayer ordering induced by carbon monoxide adsorption on potassium pre-covered Ni(100)

Surface ordering of pentacene molecules adsorbed on an aperiodic Cu surface has been studied with density functional theory (DFT) and scanning tunnelling microscopy as a function of coverage. Below 0.73 ML (5.3 × 1013 molecules cm−2), the adsorbate structure is row-like with the molecular axes aligned with the rows in the Cu structure. Between this coverage and 1 ML (7.3 × 1013 molecules cm−2), a structural phase with a checkerboard structure is seen. At this coverage region, the molecules are very close to each other which leads to unusual bending. At higher coverages, a further phase transition to a high-density row structure is seen for most of the film. DFT with van der Waals functionals is employed to study how the molecule-molecule and molecule-surface interactions evolve as a function of coverage.

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Coverage-dependent structural phase transformations in the adsorption of pentacene on an aperiodically modulated Cu film

Metal adsorption upon the 3-fold and 5-fold symmetric surfaces of the i-Ag-In-Yb quasicrystal has led to the observation of unique growth modes Here, we present a study of the growth of Pb upon the 2-fold i-Ag-In-Yb surface, where the growth mechanism is found to be different from those observed on the other, higher symmetry surfaces of the same system Initial Pb atoms occupy non-chemically-specific surface sites before forming a row structure At higher coverages, the Pb atoms form a dense wetting layer before 1D Pb chains of limited size are self-assembled as a second layer We therefore consider the Pb atoms to exhibit a type of Stranski-Krastanov growth mode Substrate-adsorbate interaction is favoured in the wetting layer, before adsorbate-adsorbate interaction promotes chain growth The difference in growth modes upon the three high symmetry surfaces is discussed with respect to their respective atomic densities

Influence of differences in orientational planar density on the growth of Pb on the i-Ag-In-Yb quasicrystal.

Medium energy ion scattering (MEIS) is employed to characterize the composition and structure of the five-fold surface of the icosahedral Ag42In42Yb16 quasicrystal. The composition of the surface after sputtering is dominated by Ag and In, and when the surface is annealed at temperatures approaching 430°C, Yb is restored at the surface. The composition is that expected from the bulk structure if the surface is formed at bulk planes involving the centre of rhombic triacontahedral clusters, the building blocks of the system. Structural analysis of MEIS results are also consistent with a surface after annealing that is in close agreement with bulk truncation intersecting the cluster centre.

Ronan McGrath

Papers

Tilings and Coverings of Quasicrystal Surfaces

Overlayer ordering induced by carbon monoxide adsorption on potassium pre-covered Ni(100)

Coverage-dependent structural phase transformations in the adsorption of pentacene on an aperiodically modulated Cu film

Influence of differences in orientational planar density on the growth of Pb on the i-Ag-In-Yb quasicrystal.

Medium energy ion scattering (MEIS) study from the five-fold surface of icosahedral Ag-In-Yb quasicrystal