Ultralong beltlike (or ribbonlike) nanostructures (so-called nanobelts) were successfully synthesized for semiconducting oxides of zinc, tin, indium, cadmium, and gallium by simply evaporating the desired commercial metal oxide powders at high temperatures. The as-synthesized oxide nanobelts are pure, structurally uniform, and single crystalline, and most of them are free from defects and dislocations. They have a rectanglelike cross section with typical widths of 30 to 300 nanometers, width-to-thickness ratios of 5 to 10, and lengths of up to a few millimeters. The beltlike morphology appears to be a distinctive and common structural characteristic for the family of semiconducting oxides with cations of different valence states and materials of distinct crystallographic structures. The nanobelts could be an ideal system for fully understanding dimensionally confined transport phenomena in functional oxides and building functional devices along individual nanobelts.

https://science.sciencemag.org/content/sci/291/5510/1947.full.pdf

Nanobelts of Semiconducting Oxides

Graphene-Like Two-Dimensional Materials

The surface and materials science of tin oxide

Heavy metal removal from water/wastewater by nanosized metal oxides: a review.

We present a review of current research on the optical properties of ZnO nanostructures. We provide a brief introduction to different fabrication methods for various ZnO nanostructures and some general guidelines on how fabrication parameters (temperature, vapor-phase versus solution-phase deposition, etc.) affect their properties. A detailed discussion of photoluminescence, both in the UV region and in the visible spectral range, is provided. In addition, different gain (excitonic versus electron hole plasma) and feedback (random lasing versus individual nanostructures functioning as Fabry-Perot resonators) mechanisms for achieving stimulated emission are described. The factors affecting the achievement of stimulated emission are discussed, and the results of time-resolved studies of stimulated emission are summarized. Then, results of nonlinear optical studies, such as second-harmonic generation, are presented. Optical properties of doped ZnO nanostructures are also discussed, along with a concluding outlook for research into the optical properties of ZnO.

Optical properties of ZnO nanostructures.

Small-diameter (<5 nm), single-crystalline SnO2 nanorods were synthesized in solution with a mean length of 17 +/- 4 nm (mean aspect ratio of 4:1) with the [001] direction along the major axis. Two characteristic peaks at 576 and 356 cm-1 in the Raman spectrum further confirmed the small crystal size. The SnO2 nanorods exhibit a red emission at 580 nm.

Large-Scale, Solution-Phase Growth of Single-Crystalline SnO2 Nanorods

Oriented silicon carbide nanowires: Synthesis and field emission properties

Silicon is one of the most important electronic materials. Its nanoscale forms, such as nanocrystals, porous silicon, quantum wells, and nanowires, have stimulated great interest among scientists because of their peculiar physical properties, such as light emission, field emission, and quantum confinement effects. The progress made in the synthesis of silicon nanostructures and nanowires in recent years has attracted considerable attention. Today, large quantities of silicon nanowires can be produced by the laser ablation of metalor SiO2-containing silicon targets, [8] and a few properties, such as electric and thermal conductivity and optical properties, have also been studied. However, the experimental characterization and application of silicon nanowires, for example, the measurement of the elastic properties, the realization of efficient field emission of nanoscale silicon, and the fabrication of nanometer field effect transistors and planar displays, have been hampered so far because of the difficulty in growing oriented silicon nanowires. As a result, the production of highly oriented and very long silicon nanowires is a very important and challenging issue. In this communication, we report the successful synthesis of highly oriented, largescale, and very long silicon nanowires on flat silicon substrates by thermal evaporation of silicon monoxide (SiO). The growth mechanism and optical properties of the oriented silicon nanowires are also discussed. To the best of our knowledge, the synthesis of oriented silicon nanowires has not yet been reported. The equipment used for the present work is similar to that described previously. An alumina tube was mounted inside a tube furnace. The SiO powders (Gooodfellow, 99.95 %) were placed near the middle of the high-temperature zone of the furnace. The polished silicon (100) substrates about 5 mm in width and 50 mm in length were ultrasonically cleaned in acetone, ethanol, and deionized water for 20 min each, dipped in 20 % HF for 20 min, and finally rinsed in deionized water for 20 min before they were placed abreast at one end of the alumina tube. The tube had previously been evacuated to a base pressure of 10 torr by a mechanical pump before the starting materials were heated. The carrier gas of argon mixed with 5 % H2 admitted at the other end of the alumina tube flowed at 50 sccm (standard cubic centimeters per minute) at 400 torr. The temperature of the furnace was increased to 1300 C at 6 C/min and kept at this temperature for 7 h. The temperature of the silicon substrate surface where the oriented silicon nanowires grew was found to be approximately 930 C, which differed from that at the center due to the temperature gradient within the tube. The product was first directly examined by scanning electron microscopy (SEM, Philips XL 30 FEG). Microstructural characterization was carried out in a conventional Philips CM 20 transmission electron microscope (TEM) at 200 kV. The high-resolution transmission electron microscopy (HRTEM) study was performed in a Philips CM200 FEG transmission electron microscope, operated at 200 kV accelerating voltage at room temperature. The chemical compositions of the samples were determined by an energy dispersive X-ray (EDX) spectrometer attached to both the SEM and HRTEM instruments. Raman scattering spectra were measured with a Renishaw micro-Raman spectrometer at room temperature. Excitation was by means of the 514 nm line of an Ar laser, and the Raman signals were measured in a backscattering geometry with a spectral resolution of 1.0 cm. The deposited silicon nanowire product is light yellow in color. SEM images at different magnifications of a typical sample in Figures 1a, 1b, 1c, and 1d clearly show the large area of highly oriented nanowires on the surface of the silicon substrate. The low magnification SEM image (Fig. 1a) shows that the area of highly oriented silicon nanowires is about 2 mm ́ 3 mm and the lengths of individual nanowires are up to 1.5±2 mm. The thickness of the oriented nanowire product was about 10 lm, as estimated from the cross-sectional image (Fig. 1d) of the sample prepared by focused ion beam cutting. The highly oriented array of Si nanowires can also be observed from the cross-sectional image. The EDX results show that the nanowires are composed of silicon and oxygen. No metal was found in the sample. Such results are consistent with our previous theory that silicon nanowire growth is enhanced by silicon oxide instead of a metal particle catalyst. Because of local charging effects, the diameters observed from SEM images appear larger than the actual wire diameters. More information about the morphology of silicon nanowires is given by the following TEM characterization Small pieces of oriented silicon nanowire samples were peeled off from a silicon substrate and mounted on a folding grid for TEM and HRTEM observations. Figure 2 shows the typical morphology of silicon nanowires. As reported previously, these nanowires show a better orientation than those synthesized by laser ablation. Silicon nanowires as observed by TEM are quite clean, with very few particles attached to their surfaces, and are relatively homogeneous. Analysis of a number of nanowires shows that the diameters of these silicon nanowires vary from 18 to 46 nm, and the mean value is about 30 nm. The selected-area electron dif-

/pdf/synthesis-of-large-areas-of-highly-oriented-very-long-2c1fjamrcx.pdf

Synthesis of Large Areas of Highly Oriented, Very Long Silicon Nanowires

Silicon carbide (SiC) nanowires were synthesized at 900°C by the laser ablation technique. The growth morphology, microstructure, and defects in SiC nanowires were characterized by scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The Raman scattering study indicated that the Raman peaks corresponding to the TO and LO phonon modes of the SiC nanowires had larger red shifts compared to those of bulk SiC material. The red shift, broadening peak, and the asymmetry of the Raman peak could be explained by the size confinement effect in the radial and growth directions. The growth mechanism of SiC nano-wires was discussed based on the vapor–liquid–solid reaction.

Laser Ablation Synthesis and Optical Characterization of Silicon Carbide Nanowires

Large-scale arrays of highly oriented single-crystal ZnO nanotubes (ZNTs) are successfully fabricated on transparent conductive substrates by a simple method from an aqueous solution at a low temperature (typically 85°C). The tubular morphology of the ZnO nanostructures is formed by a defect-selective chemical etching of the electrodeposited ZnO nanorods. The size of the ZNT arrays is determined by that of ZnO nanorod arrays which can be readily controlled by tuning several electrodeposition parameters. The present method can be employed to prepare ZNT arrays on flexible, conductive substrates, as well as on patterned conductive substrates.

Wensheng Shi

Papers

Large-Scale, Solution-Phase Growth of Single-Crystalline SnO2 Nanorods

Oriented silicon carbide nanowires: Synthesis and field emission properties

Synthesis of Large Areas of Highly Oriented, Very Long Silicon Nanowires

Laser Ablation Synthesis and Optical Characterization of Silicon Carbide Nanowires

Controlled synthesis of oriented single-crystal ZnO nanotube arrays on transparent conductive substrates