The growth of porous ZnO nanowires by thermal oxidation of ZnS nanowires

The growth of porous ZnO nanowires (NWs) via phase transformation of ZnS NWs at 500-850 degrees C in air was studied. The ZnS NWs were first synthesized by thermal evaporation of ZnS powder at 1100 degrees C in Ar. On subsequent annealing at 500 degrees C in air, discrete ZnO epilayers formed on the surface of ZnS NWs. At 600 degrees C, polycrystalline ZnO and the crack along the (0001) interface between the ZnO epilayer and ZnS NW were observed. At 700-750 degrees C ZnS NWs transformed to ZnO NWs, meanwhile nanopores and interfacial cracks were observed in the ZnO NWs. Two factors, the evaporation of SO2 and SO3 and the stress induced by the incompatible structure at the interface of ZnO epilayer and ZnS NW, can be responsible for the formation of porous ZnO NWs from ZnS NW templates on annealing at 700-750 degrees C in air. Rapid growth of ZnO at 850 degrees C could heal the pores and cracks and thus resulted in the well-crystallized ZnO NWs.     

Self-assembled tungsten oxide nanowires by electron beam assisted rapid thermal annealing

We report on the fabrication of WO₃ nanowires on Si (100) substrate using nickel catalyzed electron beam assisted rapid thermal annealing process. A 7 nm thick W layer deposited on the nickel coated substrate was annealed under high vacuum using electron beam (3 keV) for 30, 60 and 90 s. The nickel activates the growth of tungsten nanowires with a high aspect ratio and subsequently is oxidized due to the high refractory nature of tungsten under exposure to oxygen gas. The resulting changes in surface morphology, oxidization state and elemental composition of WO₃ nanowires were investigated systematically. The oxidization of metallic tungsten nanowire was found to depend on the annealing time.     

无催化热蒸发ZnS粉末制备半导体ZnO纳米带

通过无催化物理热蒸发ZnS粉末的方法首次制备了互相平行交叉的纤锌矿ZnO纳米带,X射线衍射分析和扫描电镜检测显示所制得的ZnO纳米带沿着它们的长度是平滑而单一的纤锌矿结构.合成的纳米带长度数十微米,宽度几百纳米.同时对纳米带的生长机制作了详细讨论.     

ZnO sputter coating on SnO2 nanowires: Effects of thin coating and subsequent thermal annealing

The structural and optical properties of SnO₂–ZnO core–shell nanowires were studied and the effects of thermal annealing were investigated. As-prepared SnO₂–ZnO core–shell nanowires exhibited a smooth and continuous shell layer along the nanowire, with a thickness in the range of 5–10 nm. While the thin ZnO shell layer disappeared after annealing at 800 °C, this did not occur after annealing at 600 °C. The as-fabricated SnO₂–ZnO core–shell nanowires exhibited yellow emission, presumably from the core SnO₂ nanowires. The UV emission from ZnO shell layer was obtained by annealing at 600 °C, whereas it was removed by annealing at 800 °C.     

Rapid thermal annealing of sputter-deposited ZnO/ZnO:N/ZnO multilayered structures

Rapid thermal annealing (RTA) of sputter-deposited ZnO/ZnO:N/ZnO multilayered structures formed by a combination of radio-frequency magnetron sputtering and a microwave plasma source was investigated for the fabrication of highly-crystallized ZnO:N films. The assistance of the microwave plasma source resulted in the enhancement of nitrogen incorporation into the ZnO films and the deterioration of film crystallization. On the other hand, crystallization of the ZnO:N layer was improved by RTA with no significant effusion and diffusion of N atoms using a ZnO/ZnO:N/ZnO multilayered structure. The role of the front and bottom ZnO layers during RTA of ZnO/ZnO:N/ZnO multilayered structures is demonstrated.     

Low-temperature synthesis and photocatalytic properties of ZnO nanotubes by thermal oxidation of Zn nanowires

A low-cost and catalyst-free two-step approach has been developed to produce ZnO nanotubes (ZNTs) by simple thermal oxidation of Zn nanowires under 20?Pa at a low temperature of 400?°C. The growth mechanism of ZNTs is discussed in detail. The formation of these tubular structures is closely linked to the oxidation pressure and temperature, which involves a process consisting of the deposition of Zn nanowires, cracking of the Zn nanowires and sublimation of the Zn cores, and subsequent oxidation to ZNTs. The optical properties were studied by using Raman and photoluminescence spectra, where a strong green emission related to the single ionized oxygen vacancy appears. The photocatalytic activity measurement indicates an enhanced photocatalytic activity of the prepared ZNTs due to their high surface-to-volume ratios and abundant oxygen vacancies near the surfaces of the ZNTs. This type of high surface area structural ZNTs could find promising potential for optoelectronic and environmental applications.     

Effect of rapid thermal annealing on Zn/ZnO layers

Zn/ZnO layers were deposited on SiO₂/Si substrate by magnetron sputtering at room temperature, and then these layers were annealed at various temperatures from 200 to 400 °C in nitrogen atmosphere for 1 min. The structural and electrical properties of the Zn/ZnO layers before and after annealing are systematically investigated by X-ray diffraction, scanning electron microscopy, current–voltage measurement system, and Auger electron spectroscopy. Current–voltage measurements show that the Zn/ZnO layers exhibit an Ohmic contact behavior. It is shown that, initially, the specific contact resistivity decreases with the increase of the annealing temperature and reaches a minimum value of 9.76 × 10^?5 Ω cm² at an annealing temperature of 300 °C. However, with a further increase of the annealing temperature, the Ohmic contact behavior degrades. This phenomenon can be explained by considering the diffusion of zinc interstitials and oxygen vacancies. It is also shown that Zn-rich ZnO thin films can be obtained by annealing Zn on the surface of ZnO film and that good Ohmic contact between Zn and ZnO layers can be observed when the annealing temperature was 300 °C.     

Rapid thermal annealing of rare earth implanted ZnO epitaxial layers

Zinc oxide epilayers grown by metal organic vapour phase epitaxy on (0 0 0 1) sapphire substrates were doped with Praseodymium and Europium by ion implantation. The as-implanted samples were either annealed in air for 20 min in a tube furnace or rapid thermal annealing (RTA) was performed, for 2 min, in a nitrogen atmosphere. The samples were characterized by Rutherford Backscattering Spectrometry/Channelling and photoluminescence. The presented results indicate that in the as-implanted samples the majority of the rare earth (RE) ions are incorporated into substitutional Zn-sites. Furnace annealing at 1000 °C recovers the crystal quality of the samples but leads to an out-diffusion of the RE. RTA suppresses diffusion but lattice damage is not fully recovered at 1000 °C. More importantly, during RTA the RE ions are driven from the substitutional site and are now found mainly on random interstitial sites and no optical activation could be achieved.     

Growth and thermal annealing of amorphous germanium carbide obtained by X-ray chemical vapor deposition

The growth of amorphous hydrogenated germanium carbide (a-GeCx:H) alloys was performed with high deposition rates by radiolysis chemical vapor deposition (X-ray) of germane/allene (GeH₄/C₃H₄, 70/30 %) mixtures at different irradiation times. The experimental deposition parameters were correlated to the composition, the structural features, and the optical coefficients of the films, as studied by different spectroscopic techniques, namely, IR, Raman, and UV–Vis. It was observed that the increase of irradiation time yields a more hydrogenated and more disordered material, with abundant formation of sp³ CH₂ groups, characterized by high band-gap values. In addition, we report the effects of thermal annealing on bonding structures and optical properties of the amorphous germanium carbon alloys. The decrease of hydrogen extent, together with the enhancement of sp² C bonds present and amorphous-to-crystalline germanium phase transition, contribute to a larger structural order of the material and to the reduction of the optical gap at higher temperatures.     

Silica-coated ZnO nanowires

ZnO-core/SiO_x shell nanowires were successfully fabricated and their morphology, structure, Raman and photoluminescence properties were examined. Not only the sputter-coated product had an one-dimensional morphology, but the tubular structure of SiO_x shell was also continuous, smooth, and uniform, along the core nanowires. It was found that two fundamental modes (334, 437 cm⁻¹) and 2 s order modes (1106, 1156 cm⁻¹) of hexagonal ZnO appeared in the Raman spectrum of ZnO-core/SiO_x shell nanowires. The photoluminescence (PL) spectrum of the core-shell nanowires were deconvoluted into three Gassian functions, centered at 382, 500, and 758 nm, whether the subsequent thermal annealing was performed or not. The integrated intensities of UV (382 nm) and green (758 nm) emissions were changed by means of the shell-coating and thermal annealing. We have discussed the possible emission mechanisms.     

Effects of precursor concentrations and thermal annealing on ZnO nanorods grown by hydrothermal method

ZnO nanorods were grown on spin-coated ZnO seed layers by hydrothermal method. The ZnO nanorods were grown with various precursor concentrations ranging from 0.01 to 0.3 M. Field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and photoluminescence (PL) were carried out to investigate the structural and optical properties of the ZnO nanorods. The average diameter and length of the ZnO nanorods is increased as the precursor concentration increased from 0.01 to 0.3 M. From XRD, the intensity of ZnO (002) peak is increased and full width at half maximum (FWHM) of ZnO (002) decreased as the precursor concentration increased. The FWHM of near-band-edge emission (NBE) decreased and intensity ratio of the NBE to the deep-level emission (DLE) increased as the precursor concentration increased which indicated the optical property is improved. The DLE is red-shifted from yellow- to red-emission and its intensity is increased as the annealing temperature increased due to thermal diffusion process.     

离子络合法制备ZnO纳米线

通过高聚物PAM与锌盐发生离子络合反应 ,将络合溶液涂膜在单晶硅片上 ,再通过烧结使之生长出ZnO纳米线。用场发射扫描电子显微镜 (FE SEM )、X射线衍射 (XRD)、红外光谱 (IR)对所得样品的结构与形貌进行分析表征 ,结果表明ZnO纳米线直径约 6 0～ 80nm、长度约 1～ 2 μm ,单晶 ,为六方晶系 ,且沿c轴方向优先生长。     

Microstructural changes in CdSe-coated ZnO nanowires evaluated by in situ annealing in transmission electron microscopy and x-ray diffraction

We report on the crystallite growth and phase change of electrodeposited CdSe coatings on ZnO nanowires during annealing. Both in situ transmission electron microscopy (TEM) and x-ray diffraction (XRD) reveal that the nanocrystal size increases from ～3?to ～10?nm upon annealing at 350?°C for 1?h and then to more than 30?nm during another 1?h at 400?°C, exhibiting two distinct growth regimes. Nanocrystal growth occurs together with a structural change from zinc blende to wurtzite. The structural transition begins at 350?°C, which results in the formation of stacking faults. Increased crystallite size, comparable to the coating thickness, can improve charge separation in extremely thin absorber solar cells. We demonstrate a nearly two-fold improvement in power conversion efficiency upon annealing.     

The effect of annealing on properties of europium doped ZnO nanopowders obtained by a microwave hydrothermal method

Europium doped ZnO nanopowders made by microwave hydrothermal method are investigated. As zinc oxide precursor zinc nitrate(V) hexahydrate (Zn(NO₃)₂·6H₂O) was used. Two types of nanopowder samples are examined: as grown and annealed at 750 °C in air atmosphere. We investigate the structural, morphological and optical prosperities of europium doped ZnO. Results of scanning electron microscopy, X-ray diffraction, photo- and cathodoluminescence investigations and also CIE1961 chromaticity diagram are presented.     

Diamond nanocrystals and amorphous SiOx nanowires formed by rapid thermal annealing of carbon film

Rapid thermal annealing (RTA) has been performed on the carbon films prepared by radio frequency plasma-enhanced chemical vapor deposition on Si substrate. The RTA at 800 °C for 60 s leads to the formation of many diamond nanocrystallites agglomerating on the film surface. Higher temperature RTA at 1100 °C for 60 s induces the high-density amorphous SiO_x (x = 1.2) nanowires on the film surface without diamond nanocrystallites. At both the RTA temperatures, a well-oriented SiC interlayer is also formed simultaneously. The sp³ sites in the carbon film and the oxygen during the RTA treatment as well as the RTA temperature are considered to play important roles in determining the final reaction products.     

Detector-grade CdZnTe:In crystals obtained by annealing

A method for successfully obtaining detector-grade CdZnTe:In (CZT:In) crystals by annealing is described in this article. Pure Te is used as annealing source, which can provide sufficient deep-level Te antisites. Characterizations reveal that the resistivity is greatly enhanced by more than five orders after this annealing, thus the crystals can be use for radiation detectors. This is due to introduce efficient Te antisites to pin the Fermi level to the middle of the band gap. The EPD of dislocation reduces because the star-like Cd inclusions are eliminated by annealing. Investigation of annealing time shows that 240 h annealed CZT:In crystal with 7.8% energy resolution and 2.01×10⁻³ cm²/V μτ value has the best detector performance.     

脉冲激光沉积ZnO及其掺杂薄膜的研究

本文用脉冲激光沉积（PLD）法在SiO2基片上制备了ZnO薄膜和Zn1-xMnxO薄膜。X射线衍射、原子力显微镜、紫外-可见分光光度计对ZnO薄膜的测试结果表明：薄膜具有（103）面的择优取向，表面比较平坦；SiO2基片上制备的薄膜在387nm附近存在明显的吸收边，且薄膜的吸收对基片温度变化不明显。通过对Zn1-xMnxO薄膜的吸收光谱分析得出：Mn离子的掺杂改变了ZnO薄膜的禁带宽度，随Mn离子的掺杂量的增加，薄膜禁带宽度增加；薄膜的光吸收也从直接跃迁过渡为间接跃迁过程。     

Characterization of Ni nanowires after annealing

The effect of Ni nanowires, fabricated by electrodeposition in self-ordered AAO templates, was studied. NiO and Ni₂O₃ nanofibers were fabricated by simple heat-treatment in air and in an atmosphere of pure O₂. Ni nanowires after vacuum annealing exhibit pronounced preferential orientation of Ni (111) at 600 °C. Grain growth resulted in size effects and induced the transformation of NiO to Ni₂O₃ during annealing in air. Ni was oxidized to Ni₂O₃ (∼ 500 °C) in an atmosphere of pure O₂. The stable Ni-oxides Ni₂O₃ are formed during annealing at a higher temperature (∼ 900 °C) in air and in an atmosphere of pure O₂.     

Influence of rapid thermal annealing on surface texture-etched Al-doped ZnO films prepared by various magnetron sputtering methods

The influence of rapid thermal annealing (RTA) on surface texture formation as well as the light management obtainable by wet-chemically etching was investigated for transparent conducting Al-doped ZnO (AZO) thin films prepared by various types of magnetron sputtering deposition (MSD) with an oxide target. Texture-etched AZO films prepared by an r.f. (13.56 MHz) power-superimposed d.c. magnetron sputtering deposition (rf + dc-MSD) exhibited a higher haze value than found in equivalent films prepared by d.c. MSD. The order that the RTA treatment and the etching were conducted considerably affected the obtainable surface texture. Conducting the etching after a heat treatment with RTA in air resulted in larger etch pits as well as higher haze values than were obtained in AZO films that were etched before the RTA. A high haze value generally above 70% in the range from visible to near infrared (at wavelengths up to 1200 nm) was obtained in texture-etched AZO thin films that were prepared by rf + dc-MSD and etched after RTA at a temperature of 500 °C for 3 min.