Low Temperature Growth of One-Dimensional Al and Al2O3 Nano/Micro-Structures Using Al and SnO2 Powder Mixture

One-dimensional Al and Al2O3 nano/microstructures were fabricated via thermal oxidation of Al and SnO2 powder mixtures at temperatures below the melting point of Al (660 oC). Furthermore, the synthesis process was carried out in air at atmospheric pressure, which made the process very simple and easy. Sn metal particles with spherical shape were observed on the tips of the Al and Al2O3 nano/microstructures, suggesting that the nano/microstructures were grown via a catalyst-assisted growth mechanism. The Sn acted as a catalyst for growing the Al and Al2O3 nano/microstructures. The Sn with low melting point (232 oC) was produced via the reduction of SnO2 by Al, and formed catalyst droplets at the growth temperatures. Al atoms diffused and dissolved into the Sn liquid droplets, leading to the nucleation and then the growth of the Al and Al2O3 nano/microstructures. At 400 oC, the diffusion of Al atoms into the Sn liquid droplets was associated with high stress generated at the Al2O3/Al interface. At 600 oC close to the melting point of Al, Al atoms were diffused from the thin Al liquid layer, which was formed on the surface of the Al powder, to the Sn liquid droplets. Simultaneously, the Al atoms reacted with oxygen in air and formed solid Al2O3 nuclei. A relatively strong ultraviolet emission band centered at 330 nm was observed in the sample prepared at 600 oC.

CATALYST–FREE GROWTH OF WELL–ALIGNED ZnO NANOWIRES ON GRAPHENE/Si SUBSTRATEBY THERMAL EVAPORATION

Vertically well–aligned ZnO nanowire (NW) arrays with high density were directly synthesized on graphene/Si substrate by thermal evaporation of zinc powder without catalysts or additives. The ZnO NWs were characterized by field emission scanning electron microscopy (FE–SEM), high resolution transmission electron microscopy (HRTEM), X–ray diffraction (XRD), photoluminescence (PL), and Raman spectroscopy. The results showed that the obtained ZnO NWs have diameters in the range of 300–350 nm with lengths of several tens micrometers. The prepared ZnO NWs are of a single crystal, which have a hexagonal wurtzite crystal structure with c–axis (002) orientation growth perpendicular to the substrate surface. The NW arrays had a good crystal quality with excellent optical properties, indicating a sharp and strong ultraviolet emission at 380 nm, and a weak visible emission at around 516 nm.

Ultraviolet emission from high-quality crystalline ultra-long AlN whiskers

We report here the fabrication and characterization of ultra-long AlN whiskers by physical vapor transport method. The obtained whiskers are 1–3 µm in diameter and up to millimeters in length. The whiskers grow along the [0001] crystallographic direction and are well crystallized. They exhibit a strong ultraviolet emission at 345 nm, the shortest wavelength reported in AlN whiskers or nanowires. Our results indicate that these large scales of AlN whiskers are less contaminated by oxygen and other impurities compared with the previously reported ones, which may find wide applications in fabricating ultraviolet optoelectronic devices.

Low Temperature Synthesis and Characterization of Flower-Like ZnO Nanostructures

Flower-like ZnO nanostructures have been synthesized via solution process using zinc nitrate and sodium hydroxide at very low temperature of 70 °C in 1h. The structure, morphology and optical properties of the product were characterized by scanning electron microscopy, X-ray diffraction, Raman spectroscopy and photoluminescence. The flower-like ZnO nanostructures were composed of uniform nanorods, they were well crystallized with a hexagonal wurtzite structure, and showed a strong ultraviolet emission at 385 nm and a weak and broad yellow emission in the photoluminescence spectrum.

Growth Mechanism, Structural and Optical Properties of ZnO Nanoparticles

This paper using an electric field-assisted direct precipitation method synthesize the ZnO nanosheets with zinc nitrate hexahydrate and sodium carbonate. The synthesis processes with and without an electric field were compared. The morphology of the ZnO nanosheets was investigated by scanning electron microscopy (SEM) measurements. The SEM results show that the application of an electric field caused the morphology transformation from flake-like to flower-like. It was found that an electric field had an effect on the crystal structure，the particle size and morphology. The photoluminescence spectrum of the synthesized ZnO nanosheets shows a strong ultraviolet emission at 249 nm. In addition，the formation mechanism of the ZnO nanosheets is discussed.

Fabrication of ZnO Nanodot Arrays by Sol-Gel within AAO Template

ZnO nanodot arrays were fabricated by using AAO template combining with sol-gel method. Structure and optical properties of ZnO/AAO composite structure were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL). The SEM results indicated that the pores in the template were arranged in a regular hexagonal lattice and ZnO nanodots were assembled into the AAO template. The XRD patterns demonstrated that the AAO template had an amorphous structure, and the ZnO nanodots had wurtzite structures. The PL spectrum revealed that ZnO/AAO composite structure had a strong ultraviolet emission at 390 nm.

Ultraviolet Photoluminescence on Nano-Crystalline 6H-SiC

SiC films were prepared by HFCVD technique on (111) Si substrate. The composition and the structure of the films were investigated using EDX, XRD and transient fluorescence. Results indicated the films deposited were nanocrystalline and the calculation of the grain size gave a further confirmation. PL measurement of the present films showed that there existed a strong ultraviolet emission at room temperature.

Synthesis of Disarrayed and Arrayed ZnO Nanowires by Physical Evaporation Deposition Approach without Catalysts

Large-scaled ZnO nanowires have been successfully synthesized by heating and evaporating zinc powders directly without the assistance of any catalysts or additives. We acquired disarrayed and arrayed ZnO nanowires respectively on Si(100) substrates and c-oriented ZnO thin film. The disarrayed ZnO nanowires are about 40nm in diameter and 10μm in length, evenly and randomly distributed on the substrate; while the arrayed nanowires are about 60nm in diameter and 3-4μm in length, well aligned along the normal direction of the substrate. XRD and TEM results reveal that in both kinds of the products, most of the synthesized ZnO nanowires are single crystalline in a hexagonal structure and grow along the [001] direction. During the growth process of arrayed ZnO nanowires, the c-oriented ZnO thin film control the growth direction. Photoluminescence spectrums were measured showing that both of the disarrayed and arrayed ZnO nanowires have a strong ultraviolet emission around 380nm. Such results suggest the synthesized ZnO nanowires, especially arrayed nanowires can be applied to excellent optoelectronic devices.