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

A method for growing vertical ZnO nanowire arrays on arbitrary substrates using either gas-phase or solution-phase approaches is presented. A ∼10 nm-thick layer of textured ZnO nanocrystals with their c axes normal to the substrate is formed by the decomposition of zinc acetate at 200−350 °C to provide nucleation sites for vertical nanowire growth. The nanorod arrays made in solution have a rod diameter, length, density, and orientation desirable for use in ordered nanorod−polymer solar cells.

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General Route to Vertical ZnO Nanowire Arrays Using Textured ZnO Seeds

Semiconducting zinc oxide nanowires (NWs) and nanobelts (NBs) are a unique group of quasi-one-dimensional nanomaterial. This review mainly focuses on the rational synthesis, structure analysis, novel properties and unique applications of zinc oxide NWs and NBs in nanotechnology. First, we will discuss rational design of synthetic strategies and the synthesis of NWs via vapor phase and chemical growth approaches. Secondly, the vapor–solid process for synthesis of oxide based nanostructures will be described in details. We will illustrate the polar surface dominated growth phenomena, such as the formation of nanosprings, nanorings and nanohelices of single-crystal zinc oxide. Third, we will describe the unique and novel electrical, optoelectronic, field emission, and mechanical properties of individual NWs and NBs. Finally, we will illustrate some novel devices and applications made using NWs as ultra-sensitive chemical and biological nanosensors, solar cell, light emitting diodes, nanogenerators, and nano-piezotronic devices. ZnO is ideal for nanogenerators for converting nano-scale mechanical energy into electricity owing to its coupled piezoelectric and semiconductive properties. The devices designed based on this coupled characteristic are the family of piezotronics, which is a new and unique group of electronic components that are controlled by external forces/pressure.

ZnO nanowire and nanobelt platform for nanotechnology

Growth of (0001) facet-dominated, free-standing, piezoelectric zinc oxide (ZnO) nanostructures is challenged by the divergence of the surface energy due to intrinsic polarization. By controlling gr...

http://www.nanoscience.gatech.edu/zlwang//paper/2003/03_NL_1.pdf

Spontaneous Polarization-Induced Nanohelixes, Nanosprings, and Nanorings of Piezoelectric Nanobelts

http://www.ruhr-uni-bochum.de/pc1/sfb/publikationen/Abstract_97.pdf

The chemistry and physics of zinc oxide surfaces

The structures of the polar surfaces of ZnO are studied using ab initio calculations and surface x-ray diffraction. The experimental and theoretical relaxations are in good agreement. The polar surfaces are shown to be very stable; the cleavage energy for the (0001)-Zn and (0001;)-O surfaces is 4.0 J/m(2) comparable to 2.32 J/m(2) for the most stable nonpolar (1010) surface. The surfaces are stabilized by an electronic mechanism involving the transfer of 0.17 electrons between them. This leads to 2D metallic surface states, which has implications for the use of the material in gas sensing and catalytic applications.

/pdf/stability-of-polar-oxide-surfaces-fkn2gp8wgy.pdf

Stability of polar oxide surfaces

The structures of the polar surfaces of ZnO are studied using ab initio calculations and surface x-ray diffraction. The experimental and theoretical relaxations are in good agreement. The polar surfaces are shown to be very stable; the cleavage energy for the (0001)-Zn and (0001 )-O surfaces is 4.0J/m2 comparable to 2.32J/m2 for the most stable nonpolar (1010) surface. The surfaces are stabilized by an electronic mechanism involving the transfer of 0.17 electrons between them. This leads to 2D metallic surface states, which has implications for the use of the material in gas sensing and catalytic applications.

The Stability of Polar Oxide 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 ${d}_{\mathrm{Rh}\mathrm{xy}}=0.19\ifmmode\pm\else\textpm\fi{}0.02 \AA{}.$ 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 $0.20\ifmmode\pm\else\textpm\fi{}0.05 \AA{}$ on either side of the center. This work supports the conclusions of recent density-functional theory and low-energy-electron-diffraction work.

Surface x-ray diffraction study of the Rh ( 100 ) ( 2 × 2 ) − O reconstruction

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.

A.G. Norris

Papers

Stability of polar oxide surfaces

The Stability of Polar Oxide Surfaces

Surface x-ray diffraction study of the Rh ( 100 ) ( 2 × 2 ) − O reconstruction

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

An STM study of the potassium-induced removal of the Ni(100)(2×2)p4g-N reconstruction