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

Lead is one of few elements that adopts a pseudomorphic structure when deposited on quasicrystalline substrates. We present a structural model of quasiperiodic Pb overlayers formed on the fivefold surface of an icosahedral Al-Pd-Mn quasicrystal at two different coverages close to saturation. The skeleton of the Pb monolayer is formed by a network of ``starfish'' (SF) clusters formed at the initial stages of Pb deposition, as studied in detail in our previous work [Ledieu et al., Phys. Rev. B 79, 165430 (2009)]. The atomic structure of the Pb monolayers can be represented as a decorated pentagonal Penrose P1 tiling. The structural models reproduce also the quasiperiodic superstructure of the layers observed in experimental scanning tunneling microscopy (STM) images which is described by the $\ensuremath{\tau}$-scaled $\ensuremath{\tau}\text{P}1$ tiling ($\ensuremath{\tau}$ is the golden mean). The atomic structure underlying the observed $\ensuremath{\tau}$-scaled ``white flower'' motifs and the origin of irregular bright spots in STM images are discussed. The bright spots appear in the centers of the SF clusters centered at substrate sites occupied by Al atoms. The calculated electronic structure shows that the minimum in the density of states (pseudogap) at the Fermi level which is characteristic for the Al-Pd-Mn quasicrystals appears also in the local density of states of the adsorbed Pb monolayer. However, our analysis demonstrates that the formation of this pseudogap is not due to the quasiperiodic arrangement of the Pb atoms but to the strong hybridization of their orbitals with the substrate.

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Quasiperiodic Pb monolayer on the fivefold i -Al-Pd-Mn surface: Structure and electronic properties

Several surface phases have previously been identified on the five-fold surface of the Al70Pd21Mn9 quasicrystal. Two of these, the clustered and terraced phases, have been discovered by scanning tunnelling microscopy (STM) studies. In this paper, we report STM images showing the existence of a new phase on this surface. This new topography was obtained by annealing the sample close to its melting point for several minutes. A model is presented which exhibits the main features of the structure. The unit-cell dimensions match those of the Al3Mn orthorhombic phase. Mechanical polishing followed by sputtering and annealing restored a pentagonal quasicrystalline surface indicating that the decomposition is a near-surface phenomenon.

Decomposition of the five-fold surface of Al70Pd21Mn9 at elevated temperature

This paper reviews most of the experimental results for the submonolayer adsorption of alkali metals on copper and nickel surfaces, with emphasis on the structural findings. Where possible, comparisons are made between the overlayers on copper and those on nickel. The goal is to point out some of the most interesting recent structural results and to move toward a general understanding of these systems. The few structural results of coadsorption of gases with alkali metals are also described.

Alkali-metal adsorption on copper and nickel surfaces

We present an overview of experimental studies of the structure of adsorbed atomic and molecular species on quasicrystal surfaces with a particular focus on those systems where quasiperiodic ordering of the adsorbate structure occurs. Atomic adsorption is illustrated with examples from studies of Fe and Gd adsorption on the five-fold surface of i-Al–Pd–Mn. Overlayer structure is correlated with several physical parameters to identify trends. It is concluded that the chemical properties of the adsorbate (metallic radius, electronegativity, melting temperature) are important indicators of quasiperiodic structuring of the adsorbate system. These correlations allow predictions of those elements likely to yield pseudomorphic overlayers. Structural effects upon molecular adsorption on clean quasicrystal surfaces have been less successful. A new approach to ordered molecular adsorption is described and illustrated for C60 adsorption on a Pb monolayer film on the ten-fold surface of d-Al–Ni–Co.

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Ordering of adsorbed species on quasicrystal surfaces

The 0.5 ML oxygen-induced reconstruction of the Rh(100) surface has been investigated using surface x-ray diffraction. The rhodium atoms in the surface layer adopt a “clock” reconstruction with an in-plane displacement of the surface-layer Rh atoms of dRhxy=0.19±0.02 A. The oxygen atoms were found to be situated in the “diamond” site rather than the rotated fourfold hollow site, with an in-plane displacement of 0.20±0.05 A on either side of the center. This work supports the conclusions of recent density-functional theory and low-energy-electron-diffraction work.

Ronan McGrath

Papers

Quasiperiodic Pb monolayer on the fivefold i -Al-Pd-Mn surface: Structure and electronic properties

Decomposition of the five-fold surface of Al70Pd21Mn9 at elevated temperature

Alkali-metal adsorption on copper and nickel surfaces

Ordering of adsorbed species on quasicrystal surfaces

A surface X-ray diffraction study of the Rh(100) (2x2)-O reconstruction