O2浓度对纳米氧化锌形貌、产量和发光性质的影响

目的研究不同O_2体积浓度下,双管管式炉内不同沉积位置处纳米ZnO形貌、产量和发光性质的变化规律。方法采用化学气相沉积法,在双管管式炉的三个不同沉积位置制备了具有不同形貌、产量和性质的纳米ZnO产物。采用扫描电子显微镜(SEM)、X-射线衍射仪(XRD)和荧光分光光度计(PL)等对产物的形貌、结构和光致发光性能进行表征和测试。结果 SEM表明O_2体积浓度较小时,有利于形成针状的多脚结构。O_2体积浓度较大时,有利于生成棒状的多脚状结构。通过对比沉积产物产量发现,当O_2体积浓度较低时,沉积反应主要发生在内管外。随着O_2体积浓度的增大,沉积产物逐渐向内管内部转移,内管口附近的沉积产物增多。XRD结果表明所有产物均为六方纤锌矿结构,当O_2体积浓度为0.0625%时,产物沿c轴择优生长。随着O_2体积浓度的增加,无明显择优取向。PL结果表明,紫外发射峰与绿光发射峰强度的比值随着O_2体积浓度的增加而增大,说明绿光发射峰主要由氧空位引起,随着O_2体积浓度的增加,氧空位逐渐减少。结论通过调节O_2体积浓度可以制备出不同形貌和发光性质的纳米ZnO,从而应用于不同领域,并且在适当的沉积位置可以获得最大产量。     

Low-temperature synthesis and photoluminescence of ZnO nanostructures by a facile hydrothermal process

We reported a facile route to large-scale ZnO nanostructures by a poly (styrene-alt-maleic acid sodium) (PSMA)-assisted hydrothermal process. Various nanostructures including nanowires, nanobelts and nanorod arrays were fabricated depending on the experimental conditions. The structural studies reveal that all the nanostructures are single crystal with hexagonal phase and preferentially grow along [0 0 0 1]. The organic additive PSMA offers a spatial template for the one-dimensional (1D) growth of ZnO. The photoluminescence (PL) spectra of these nanostructures exhibit coexistence properties of ultraviolet (UV) and green emission. The nanorod arrays and nanobelts exhibit the strongest UV performance and green emission, respectively. We deduce that quantity of surface defects should be responsible for the difference in PL properties of these nanostructures.     

Comparative study of ZnO nanostructures grown on silicon (1 0 0) and oxidized porous silicon substrates with and without Au catalyst by chemical vapor transport and condensation

ZnO tetrapods and rods were grown on silicon and thermally oxidized porous silicon substrates with and without Au catalyst layer by carbothermal reduction of ZnO powder through chemical vapor transport and condensation method (CVTC). Porous silicon was fabricated by electrochemical etching of silicon in HF solution. The effect of substrates on morphology, structure and photoluminescence spectra of ZnO nanostructures has been studied. The texture coefficient (TC) of each sample was calculated from XRD data that demonstrated random orientation of ZnO nanostructures on the oxidized porous silicon substrate. Moreover, TC indicates the effect of Au catalyst layer on formation of more highly oriented ZnO nanorods. The morphology of the samples was investigated by SEM which confirms formation of ZnO nanostructures on oxidized porous silicon substrates with and without catalyst. A blue-green emission has been observed in ZnO nanostructures grown on Si and the oxidized PS substrates without Au catalyst layer by PL measurements.     

Absorption-emission study of hydrothermally grown Al:ZnO nanostructures

The preparation, structural characterization and optical properties of aluminum doped ZnO (Al:ZnO) nanostructures grown under hydrothermal method are reported. One-dimensional (1-D) growth is achieved by the controlled addition of metal nitrate as precursors in the presence of long chain surfactant, poly-ethylene glycol (PEG) at 160 °C for 20 h. The as-synthesized ZnO rods are single crystalline, exhibiting an oriented growth along [001] direction. The Al6 rod has an aspect ratio of 3.2, which can be effectively applied in optoelectronic devices. Comprehensive structural analysis using X-ray diffraction method (XRD) and Energy dispersive X-ray analysis (EDX) indicate that the dopant Al atom occupies Zn sites in ZnO and the elemental composition of Al is consistent with the amount utilized in the hydrothermal synthesis. XRD shows that the Al:ZnO nanostructures from 1 to 9 atomic percent (at.%) has hexagonal wurtzite structure of ZnO. The Al dopant effects on lattice vibration and electronic transitions of the ZnO nanostructures have been investigated by Fourier transform Infrared spectroscopy (FT-IR), Ultraviolet-visible (UV-vis) absorption spectroscopy and photoluminescence (PL) emission recorded at room temperature. The correlation existing between absorption and emission study tell that their characteristic band edge peak of doped ZnO shifts towards higher wavelength side for 3-9 at.% with respect to Al0 thus, exhibiting a red shift phenomenon with decrease in optical bandgap. The observed PL reveals two emission peaks centered at 374 nm and 530 nm. The near band edge (NBE) to defect emission ratio increases with dopant concentration indicating the linear enhancement in crystal quality and declination in zinc vacancies from 3 to 9 at.% of Al.     

Novel pulsed electron deposition route to ZnO nanowire arrays

Well aligned ZnO nanowire arrays with uniform size are grown on Au-coated indium tin oxide substrates via a novel pulsed electron deposition (PED) technique. These nanowires have single-crystal hexagonal wurtzite structure and are grown along [0 0 0 1]. Au nanoparticles are found at the tip of the nanowires, indicating the growth process follows a typical vapor-liquid-solid mechanism. It is also found that the aligned ZnO nanowire arrays can be grown on Au-coated 6H-SiC and Si substrates, revealing that the PED technique is applicable for growth of ZnO nanowires on some common substrates. All the photoluminescence spectra of the ZnO nanowires reveal strong ultraviolet emission bands, indicating that the high-quality ZnO nanowires can be fabricated via the novel PED technique.     

ZnO nanocoral reef grown on porous silicon substrates without catalyst

Porous silicon (PS) technology is utilized to grow coral reef-like ZnO nanostructures on the surface of Si substrates with rough morphology. Flower-like aligned ZnO nanorods are also fabricated directly onto the silicon substrates through zinc powder evaporation using a simple thermal evaporation method without a catalyst for comparison. The characteristics of these nanostructures are investigated using field-emission scanning electron microscopy, grazing-angle X-ray diffraction (XRD), and photoluminescence (PL) measurements of structures grown on both Si and porous Si substrates. The texture coefficient obtained from the XRD spectra indicates that the coral reef-like nanostructures are highly oriented on the porous silicon substrate with decreasing nanorods length and diameter from 800-900 nm to 3.5-5.5 μm and from 217-229 nm to 0.6-0.7 μm, respectively. The PL spectra show that for ZnO nanocoral reefs the UV emission shifts slightly towards lower frequency and the intensity increase with the improvement of ZnO crystallization. This non-catalyst growth technique on the rough surface of substrates may have potential applications in the fabrication of nanoelectronic and nanooptical devices.     

Characterization of ZnO needle-shaped nanostructures grown on NiO catalyst-coated Si substrates

ZnO nanostructures were synthesized over NiO-coated Si substrate by a thermal evaporation of Zn powders in a vertical chemical vapor deposition (CVD) reactor. The ZnO nanostructures had a needle-like morphology and the diameter of the structures decreased linearly from the bottom to the top. The bottom diameters of the ZnO nano-needles normally ranged from 20 to 100 nm and the lengths were in the range of 2–3 μm. The clear lattice fringes in HRTEM image indicated the growth of good quality hexagonal single-crystal ZnO. Field emission (FE) characteristics of the ZnO nano-needles showed that the turn-on field was about 8.87 V/μm with a field enhancement factor of about 1099. The growth mechanism of the ZnO nano-needles was proposed on the basis of experimental data.     

Temperature-dependant non-catalytic growth of ultraviolet-emitting ZnO nanostructures on silicon substrate by thermal evaporation process

Needle-like nanowires, nanorods, and nanosheets containing nanowires of ZnO have been synthesized on silicon substrate by the thermal evaporation of metallic zinc powder in the presence of oxygen without the use of any catalyst or additives. It was observed that a particular type of ZnO nanostructure can be obtained in a specific temperature zone and morphology can be well controlled simply by adjusting the substrate temperature. Detailed structural analysis revealed that the formed ZnO nanostructures are single-crystalline with wurtzite hexagonal phase, grown along the [0 0 0 1] direction in preference. Raman scattering and room-temperature photoluminescence spectra showed the good crystallinity with hexagonal wurtzite phase and excellent optical properties, respectively for all the deposited ZnO nanostructures.     

Defect mediated photocatalytic activity in shape-controlled ZnO nanostructures

Shape-controlled ZnO nanostructures were synthesized through a facile soft-chemical approach by varying the concentration of OH⁻ ions. X-ray diffraction and Raman spectra reveal the formation of highly crystalline single-phase hexagonal wurtzite nanostructure. It has been observed that the concentration of OH⁻ ions plays an important role in controlling the shape of ZnO nanostructures. TEM micrographs indicate that well-spherical particles of size about 8 nm were formed at lower concentration of OH⁻ ions whereas the higher concentration of OH⁻ ions favor the formation of nanorods of length 30-40 nm. The optical studies confirmed that the band gap and near band edge emission of ZnO nanostructures are strongly dependent on the shape of particles. Furthermore, the decrease in the intensity of green emission as shape of particles changes from sphere to rod indicates the suppressing of defect density, which in turn influences the photocatalytic activity and ferromagnetic-like behavior of ZnO nanostructures.     

Rapid growth of ZnO hexagonal prism crystals by direct microwave heating

ZnO hexagonal prism crystals were synthesized from ZnO powders by microwave heating in a short time (within 20 min) without any metal catalyst or transport agent.Zinc oxide raw materials were made by evaporating from the high-temperature zone in an enclosure atmosphere and crystals were grown on the self-source substrate.The inherent asymmetry in microwave heating provides the temperature gradient for crystal growth.Substrate and temperature distribution in the oven show significant effects on the growth of the ZnO crystal.The morphologies demonstrate that these samples are pure hexagonal prism crystals with maximum 80 μm in diameter and 600 μm in length,which possess a well faceted end and side surface.X-ray diffraction (XRD) reveals that these samples are pure crystals.The photoluminescence (PL) exhibits strong ultraviolet emission at room temperature,indicating potential applications for short-wave light-emitting photonic devices.     

Synthesis of cadmium oxide doped ZnO nanostructures using electrochemical deposition

Ternary ZnCdO alloy semiconductor nanostructures were grown using electrochemical deposition. Crystalline nanostructures/nanorods with cadmium concentration ranging from 4 to 16 at% in the initial solution were electrodeposited on tin doped indium oxide (ITO) conducting glass substrates at a constant cathodic potential −0.9 V and subsequently annealed in air at 300 °C. X-ray diffraction measurements showed that the nanostructures were of wurtzite structure and possessed a compressive stress along the c-axis direction. The elemental composition of nanostructures was confirmed by energy dispersive spectroscopy (EDS). ZnO nanostructures were found to be highly transparent and had an average transmittance of 85% in the visible range of the spectrum. After the incorporation of Cd content into ZnO the average transmittance decreased and the bandgap tuning was also achieved.     

Oriented growth of ZnO nanostructures on Si and Al substrates

Aligned ZnO nanorod arrays and oriented ZnO nanoplates were synthesized on Si and Al substrates, respectively, using a hydrothermal method without any surfactant. The process involved the deposition of ZnO seeds on the substrate and the oriented growth of ZnO nanostructure in aqueous solution. The ZnO seeds were indispensable for the alignment of ZnO nanorods and TEM and XRD analysis confirmed that the ZnO rods are single crystalline grown along [001] direction. Al substrate caused formation of (001) surface dominated ZnO nanoplates, in which ZnO preferential growth direction was suppressed. The photoluminescence spectra of the as-grown ZnO products were measured to indicate their structural and optical quality. These oriented ZnO nanostructures are expected to be prospectively applied in nanodevices fabrication.     

ZnO nanoneedles fabricated by a simple approach and their optical properties

Spoke-like ZnO nanoneedles have been successfully synthesized at the ambient pressure through thermally oxidizing Zn powders containing Au nanoparticles. X-ray diffraction analysis indicates that the ZnO nanoneedles have a hexagonal wurtzite structure of the crystalline ZnO. The morphology of the products was examined by FESEM. The photoluminescenee(PL) spectrum under 325 nm exhibits both an UV emission and a green emission. It is interesting to note that the heating rate plays a key role in the synthesis of ZnO nanoneedles. Based on this discovery we propose to explain the special growth behavior as novel mechanism that a large temperature gradient and Au nanoparticles simultaneously result in the spoke-like ZnO nanoneedles growth.     

Effect of ammonia solution on properties of sprayed ZnO thin films consisting of nano-pyramids

Hexagonal wurtzite zinc oxide (ZnO) thin films were deposited at substrate temperatures from 300 to 500 °C with surfactant of ammonia solution. The effect of ammonia on the structural, surface morphology, compositional, optical and electrical properties of ZnO thin films was studied. X-ray diffraction shows that the all films are polycrystalline in nature and have a hexagonal wurtzite structure with a high preferential orientation (002) plane for ammonia solution. High-resolution SEM studies reveal the formation of ZnO films consisting of nano-pyramids with uniformly distributed grains over the entire surface of the substrates. Photoluminescence studies indicate the presence of two emission peaks: (a) a sharp ultra-violet near band edge ～392 nm, (b) a sharp visible deep-level green emission peak ～564 nm. The optical properties show that the direct band gap energy values increase with increasing substrate temperatures.     

Control of morphology and orientation of electrochemically grown ZnO nanorods

We report the direct electrochemical deposition of ZnO nanorods on an indium tin oxide substrate. The morphology and orientation of the grown ZnO nanorods were investigated as functions of the current density. It is likely that the concentrations of OH^? and Zn²⁺ ions, which could be controlled by varying the current density, determine the shape and alignment of the ZnO nanorods. The nanorods were tilted, hexagonal, and prismatic at a low current density (0.1 mA/cm²) and vertically aligned and obelisk-shaped at high current densities (greater than 0.6 mA/cm²). By using the low and high current densities sequentially in a two-step growth process, vertically aligned, hexagonal, and prismatic ZnO nanorods could be grown successfully. The underlying mechanism responsible for the growth of the ZnO nanorods is also discussed.     

Effects of supply time of Ar gas current on structural properties of Au-catalyzed ZnO nanowires on silicon (1 0 0) grown by vapor–liquid–solid process

ZnO nanowires were grown on Au-coated Si (1 0 0) substrates by the method of vapor–liquid–solid (VLS) growth processing technique. The effects of supply time of Ar gas current on morphology and microstructure of Au-catalyzed ZnO nanowires were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy. The results showed that the morphologies of ZnO nanostructures strongly depended on the time of flowing Ar gas. When the time of flowing Ar gas was 90 s, ZnO showed nanowires with hexagonal structure. Their diameters and lengths were 160 nm and 20 μm, respectively, on average, and the Raman scattering peak located at 438 cm⁻¹ reached maximum intensity. The results also showed that the ZnO growth could be patterned by controlling the initial position of Au-coated area on the Si substrates.     

基于氧化钛纳米管模板电沉积氧化锌纳米棒

研究了氧化锌纳米棒在用二次阳极氧化法制备的二氧化钛纳米管模板表面的电沉积生长。与一次阳极氧化法对比,以二次阳极氧化法获得的氧化钛纳米管薄膜为模板,更有利于形貌均一、取向一致的ZnO纳米棒的电沉积生长,并且在电解质溶液中添加六次甲基四胺(HMT)、适当延长沉积时间均可提高ZnO纳米棒的结晶度和择优生长趋势。当沉积电压为1.0~1.5 V时,可获得形貌规则的ZnO纳米棒;而电压继续增大时,ZnO沿c轴择优生长趋势消失,电沉积产物氧化锌纳米棒由六边形氧化锌纳米片取代。     

单晶ZnO六棱锥的PEG400辅助热分解合成及其光致发光性能(英文)

将由Zn(CH3COO)2·2H2O和Na2CO3通过室温研磨反应获得的前驱体在PEG400存在下于240°C热分解获得大量的ZnO六棱锥产物。用X射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和高分辨透射电子显微镜(HRTEM)表征产物的晶体结构和形貌。进一步的实验结果表明:PEG400在ZnO六棱锥形成过程中发挥着重要作用,单六棱锥和双六棱锥的结构差异来自于热分解反应。光致发光谱(PL)测试表明:ZnO六棱锥在386nm处展示强的近带隙发射,在550nm处展示较弱的绿光发射。435cm-1处的拉曼振动表明ZnO六棱锥具有良好的晶体质量。     

High-density arrays of low-defect-concentration zinc oxide nanowire grown on transparent conducting oxide glass substrate by chemical vapor deposition

High-density ZnO nanowire arrays with low defect concentrations were directly grown on transparent conducting oxide glass substrates under catalyst-free and low temperature conditions by chemical vapor deposition (CVD). A possible growth mechanism of the nanowires is studied. The experiments indicate that correct levels of supersaturation and evaporation temperature are beneficial to the growth of ZnO nanowires. Photoluminescence exhibits a weak ultraviolet emission at 380 nm and a strong green emission at 495 nm. While using a double-tube growth system, the visible light emission diminishes and the 380 nm emission is the only emission, suggesting that ZnO nanowires with few defects can be prepared using the present CVD technique at low temperature.     

ZnO／Ga2O3膜的氨化温度对制作硅基GaN纳米材料的影响

通过在不同温度下氨化ZnO／Ga2O3膜，在Si衬底上成功制备了GaN纳米结构材料。氨化前，ZnO层和Ga2O3膜分别通过射频磁控溅射法依次溅射到Si衬底上。用X射线衍射(XRD)、红外傅里叶变换光谱(FTIR)分析了GaN晶体的结构和组分，利用扫描电子显微镜(SEM)观察了样品的形貌。通过对测试结果的分析可知在Si衬底上由ZnO挥发辅助生长出六方纤锌矿GaN纳米结构晶体，并且ZnO／Ga2O3的氨化温度对形成GaN纳米材料具有明显的影响。