Field Emission Enhancement of Carbon Nanotubes by Surface Modification

By employing a multi-walled carbon nanotube （MWCNT） film as the substrate, we obtain Fe tipped carbon nanorods or carbon nanoparticles grown on the outer walls of MWCNTs by combining sputtering deposition of Fe films and rf plasma enhanced chemical vapour deposition at high temperature. Scanning electron microscopy and high-resolution transmission electron microscopy are used to examine the structure of carbon nanorods and carbon nanoparticles. In addition, the formation mechanism is discussed briefly. The electron field emission tests indicate that the turn-on field （at 10μA/cm^2） of the treated MWCNT films decreases from 2.4 V/μm to O. 79 V/μm and the field emission current is relatively stable. The enhanced field enhancement factor, increasing emission densities coming from the grown nanorods and nanoparticles, and H terminated by H plasma a11 are responsible for the enhancement of the field enhancement factor.     

Fabrication of GaN Nanorods in a Large Scale on Si（111）Substrate by Ammoniating Technique

GaN nanorods in a large scale have been synthesized on Si （111） substrates by ammoniating Ga2O3/Mg films under flowing ammonia atmosphere at the temperature of 1000℃ for 15 min. The as-synthesized GaN nanorods are characterized by scanning electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and highresolution transmission electron microscopy. The results demonstrate that these straight nanorods are hexagonal wurtzite GaN single crystals in diameters ranging from 200 nm to 600 nm.     

Synthesis and Growth Mechanism： A Novel Fishing Rod-Shaped GaN Nanorods

A novel fishing rod-shaped GaN nanorod is successfully fabricated through a new method by using the two-step growth technology. This growth method is applicable to continuous synthesis and is able to produce a large number of single-crystalline GaN nanorods with a relatively high purity and at a low cost. X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy are used to characterize the as- synthesized nanorods. The results show that most of the nanorods consist of a main rod and a top curved thread. It is single-crystal GaN with hexagonal wurtzite structure. The representative photoluminescence spectrum at room temperature exhibits a strong UV light emission band centered at 370.8nm. Furthermore, a possible two-stage growth mechanism of the fishing rod-shaped GaN nanorod is also briefly discussed.     

Fabrication of Syringe-Shaped GaN Nanorods

Syringe-shaped GaN nanorods are synthesized on Si（111） substrates by annealing sputtered Ga2O3/BN films under flowing ammonia at temperature of 950℃. Most of the nanorods consist of a main rod and a top needle, looking like a syringe. X-ray diffraction and selected-area electron diffraction confirm that the syringe-shaped nanorods are hexagonal wurtzite GaN. Scanning electron microscopy and high-resolution transmission electron microscopy reveal that these nanorods are as long as several micrometres, with diameters ranging from 100 to 300nm. In addition to the BN intermediate layer, the proper annealing temperature has been demonstrated to be a crucial factor for the growth of syringe-shaped nanorods by this method.     

Photoluminescence of Nanoporous GaN Films Prepared by Electrochemical Etching

Nanoporous （NP） CaN is prepared by electrochemical etching on a CaN epilayer grown on a sapphire substrate by metal-organic chemical vapor deposition. Scanning electron microscopy reveals that the average pore diameter and inter-pore spacing are approximately 25 and 45 nm, respectively. The photoluminescence （PL） spectra show that in contrast to the initial as-grown CaN epilayer, the NP CaN exhibits a high near-band-edge UV intensity, significant relaxation of compressive strain, and a lower yellow luminescence intensity. Both the line shape and line width of the PL spectra are almost the same for these two samples. The high quality of the NP CaN can be explained by the enhancement of the PL extraction efficiency and the decrease of impurity and defect density after etching.     

Growth of β-Ga2O3 nanorods by ammoniating Ga2O3/V thin films on Si substrate

This paper reports that/3-Ga2O3 nanorods have been synthesized by ammoniating Ga2O3 films on a V middle layer deposited on Si（111） substrates. The synthesized nanorods were confirmed as monoclinic Ga2O3 by x-ray diffraction,Fourier transform infrared spectra. Scanning electron microscopy and transmission electron microscopy reveal that the grown β-Ga2O3 nanorods have a smooth and clean surface with diameters ranging from 100 nm to 200 nm and lengths typically up to 2μm. High resolution TEM and selected-area electron diffraction shows that the nanorods are pure monoclinic Ga2O3 single crystal. The photoluminescence spectrum indicates that the Ga2O3 nanorods have a good emission property. The growth mechanism is discussed briefly.     

Comparative Characterization of InGaN/GaN Multiple Quantum Wells by Transmission Electron Microscopy, X-Ray Diffraction and Rutherford Backscattering

The composition, elastic strain and structural defects of InCaN/CaN multiple quantum wells （MQWs） are comparatively investigated by using x-ray diffraction （XRD）, transmission electron microscopy and Rutherford backscattering/channelling. The InGaN well layers are fully strained on CaN, i.e. the degree of relaxation is zero. The multilayered structure has a clear defined periodic thickness and abrupt interfaces. The In composition is deduced by XRD simulation. We show how the periodic structure, the In composition, the strain status and the crystalline quality of the InGaN/GaN MQ, Ws can be determined and cross-checked by various techniques.     

A study of transition from n-to p-type based on hexagonal WO3 nanorods sensor

Hexagonal WO3 nanorods are fabricated by a facile hydrothermal process at 180 ℃ using sodium tungstate and sodium chloride as starting materials. The morphology, structure, and composition of the prepared nanorods are studied by scanning electron microscopy, X-ray diffraction spectroscopy, and energy dispersive spectroscopy. It is found that the agglomeration of the nanorods is strongly dependent on the PH value of the reaction solution. Uniform and isolated WO3 nanorods with diameters ranging from 100 nm-150 nm and lengths up to several micrometers are obtained at PH = 2.5 and the nanorods are identified as being hexagonal in phase structure. The sensing characteristics of the WO3 nanorod sensor are obtained by measuring the dynamic response to NO2 with concentrations in the range 0.5 ppm-5 ppm and at working temperatures in the range 25 ℃-250 ℃. The obtained WO3 nanorods sensors are found to exhibit opposite sensing behaviors, depending on the working temperature. When being exposed to oxidizing NO2 gas, the WO3 nanorod sensor behaves as an n-type semiconductor as expected when the working temperature is higher than 50 ℃, whereas, it behaves as a p-type semiconductor below 50 ℃. The origin of the n- to p-type transition is correlated with the formation of an inversion layer at the surface of the WO3 nanorod at room temperature. This finding is useful for making new room temperature NO2 sensors based on hexagonal WO3 nanorods.     

Growth of Indium Nanorods by Magnetron Sputtering

Indium nanorods are grown on silicon substrates by using magnetron-sputtering technique. Film morphologies and nanorod microstructure are investigated by using scanning electron microscopy, high-resolution transmission electron microscopy （HRTEM）, and x-ray diffraction. It is found that the mean diameter of the nanorods ranges from 30nm to 100nm and the height ranges from 30nm to 200nm. The HRTEM investigations show that the indium nanorods are single crystals and grow along the [100] axis. The nanorods grow from the facets near the surface undulation that is caused by compressive stress in the indium grains generated during grain coalescence process. For low melting point and high diffusivity metal, such as bismuth and indium, this spontaneous nanorod growth mechanism can be used to fabricate nanostructures.     

Luminescence Properties of Nanostructure ZnO-Covered Carbon Fibers Prepared by Thermal Oxidation

We report on ZnO nanosheets and nanorods synthesized by thermal oxidation of zinc films deposited on carbon fiber surfaces. The structure and optical properties are characterized by x-ray diffraction, scanning electron microscopy and photoluminescence spectrum. An orange-red emission around 683 nm is found in the PL spectrum when the sample prepaxs at 400℃ for four hours in air. With annealing temperature increasing from 400℃ to 500℃, the blue shift is observed.