The effect of seed layer thickness on alignment and morphology of ZnO nanorods

Thin films of ZnO of 20, 40,160 and 320 nm thickness were deposited on Si (100) substrates by rf-magnetron sputtering and then nanorods were grown on the seed layer at 95 °C for 2 h. The ZnO nanorods were synthesized in C₆H₁₂N₄ and Zn (NO₃)₂·6H₂O solution by a hydrothermal method and the effect of seed layer thickness on the alignment, diameter, density and growth rate of nanorods was studied.The results revealed that the alignment of nanorods depended on crystallinity, grain size and roughness frequency of the sputtered seed layer, so that, with increase of seed layer thickness, crystallinity improved. In addition the grain size increased and the roughness frequency decreased and hence alignment and diameter of nanorods increased.Finally, we present a model for the effect of seed layer thickness on the alignment and diameter of the nanorods.     

Preparation of nanostructured ZnO nanorods in a hydrothermal-electrochemical process

An array of ZnO nanorods, each nanorod being covered with a shell of porous ZnO was prepared in two steps by hydrothermal-electrochemical processes. The growth of ZnO nanorods was achieved in a zinc nitrate and hexamethylenetetramine aqueous solution on fluorine-doped tin oxide film. The porous ZnO shell was grown from a similar solution in the presence of eosin Y as nanostructuring agent. A dye-sensitized solar cell was assembled using as photoanode an eosin Y sensitized ZnO nanorod/shell layer.     

Growth and optical properties of ZnO nanorods by introducing ZnO sols prior to hydrothermal process

ZnO nanorods of 25 nm with quite homogeneous size and shape have been fabricated by introducing ZnO sols as nucleation centers prior to the hydrothermal reaction. The samples were characterized by scanning electron microscope, transmission electron microscope, X-ray diffraction, photoluminescence and resonant Raman spectra. After ZnO sols are introduced, the width of the resulting nanorods decreases above an order of magnitude and the aspect ratio increases 5 times. The increase of the intensity ratio of ultraviolet to visible emissions in room-temperature photoluminescence spectrum and the decrease of the Raman linewidths show the improvement in the quality of ZnO nanorods. Influences of the number of seed nuclei and the aging time of ZnO sols on the morphology of ZnO nanorods are discussed.     

Effect of ZnO seed layer on the catalytic growth of vertically aligned ZnO nanorod arrays

We have grown vertically aligned ZnO nanorods and multipods by a seeded layer assisted vapor–liquid–solid (VLS) growth process using a muffle furnace. The effect of seed layer, substrate temperature and substrate material has been studied systematically for the growth of high quality aligned nanorods. The structural analysis on the aligned nanorods shows c-axis oriented aligned growth by homoepitaxy. High crystallinity and highly aligned ZnO nanorods are obtained for growth temperature of 850–900 °C. Depending on the thickness of the ZnO seed layer and local temperature on the substrate, some region of a substrate show ZnO tetrapod, hexapods and multipods, in addition to the vertically aligned nanorods. Raman scattering studies on the aligned nanorods show distinct mode at ∼438 cm⁻¹, confirming the hexagonal wurtzite phase of the nanorods. Room temperature photoluminescence studies show strong near band edge emission at ∼378 nm for aligned nanorods, while the non-aligned nanorods show only defect-emission band at ∼500 nm. ZnO nanorods grown without the seed layer were found to be non-aligned and are of much inferior quality. Possible growth mechanism for the seeded layer grown aligned nanorods is discussed.     

从无序到有序ZnO纳米棒的制备

采用3种不同的方法在氧化铟锡玻璃衬底上沉积一层ZnO纳米晶薄膜,然后采用改进的水热法在制备有ZnO纳米晶薄膜的衬底上生长ZnO纳米棒,实现了纳米棒从无序到有序的生长.从XRD和SEM图可得,有序的纳米棒沿(002)择优取向,基本与衬底垂直,平均直径约为40nm.     

种子层对染料敏化ZnO纳米棒光伏电池性能的影响

用射频溅射法在透明导电玻璃上分别沉积了氧化锌（ZnO）和掺铝氧化锌（AZO）薄膜，其可见光透射率达到85％以上。用水热法在不同的薄膜作种子层的导电玻璃上生长了纳米棒，x射线衍射分析（XRD）发现所制得的纳米棒都有（002）择优取向；扫描电子显微镜（SEM）结果表明，采用不同的实验条件和参数可以有效的影响纳米棒的长度、直径、密度等，并得到了垂直于衬底的纳米结构。用所得到的纳米结构制作太阳能电池的效率达到了0．26％。     

Single crystalline ZnO nanorods grown by a simple hydrothermal process

Single crystalline ZnO nanorods with wurtzite structure have been prepared by a simple hydrothermal process. The microstructure and composition of the products were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM, energy dispersive X-ray spectrum (EDS) and Raman spectrum. The nanorods have diameters ranging from 100 nm to 800 nm and length of longer than 10 µm. Raman peak at 437.8 cm^− 1 displays the characteristic peak of wurtzite ZnO. Photoluminescence (PL) spectrum shows a blue light emission at 441 nm, which is related to radiative recombination of photo-generated holes with singularly ionized oxygen vacancies.     

Effect of thickness of ZnO active layer on ZnO-TFT's characteristics

We have investigated the electrical characteristics of ZnO thin film transistors with respect to the thickness of ZnO active layers. The ZnO layers with the thickness of 30 nm to 150 nm were deposited on bottom gate patterned Si substrate by RF sputtering at room temperature. The low-temperature oxide served as gate dielectric. As ZnO channel layer got thicker, the leakage current at V_DS = 30 V and V_G = 0 V greatly increased from 10^− 10 A to 10^− 6 A, while the threshold voltage decreased from 15 V to 10 V. On the other hand, the field effect mobility got around 0.15 cm²/V s except for the 30-nm-thick channel. Overall, the 55-nm-thick ZnO channel layer showed the best performance.     

Highly monodispersed ZnO nanorods: preparation and optical properties

Simple and low cost solution synthesis method was used to synthesise ZnO nanorods. Dodecyl benzene sulfonate was used to control the growth process and monodispersed nanorods with diameters in the range of 25 to 44 nm were obtained. X-ray diffraction, transmission electron microscopy and high resolution transmission electron microscopy measurements demonstrate the structure and morphology of the products. Laser power- and temperature-dependent photoluminescence (PL) experiments confirm the good ultraviolet emission characteristics. Short exciton lifetime feature relevant to thin nanorods was examined by time-resolved PL. Good optical quality and the size characteristics of the obtained products are discussed.     

Growth of compact arrays of optical quality single crystalline ZnO nanorods by low temperature method

We report the synthesis and optical properties of compact and aligned ZnO nanorod arrays (dia, ∼ 50–200 nm) grown on a glass substrate with varying seed particle density. The suspension of ZnO nanoparticles (size, ∼ 15 nm) of various concentrations are used as seed layer for the growth of nanorod arrays via selfassembly of ZnO from solution. We studied the effect of various growth parameters (such as seeding density, microstructure of the seed layer) as well as the growth time on the growth and alignment of the nanorods. We find that the growth, areal density and alignment of the nanorods depend on the density of seed particles which can be controlled. It is observed that there is a critical density of the seed particles at which nanorod arrays show maximum preferred orientation along [002] direction. The minimum and maximum radius of the aligned nanorods synthesized by this method lie in the range 50–220 nm which depend on the seeding density and time of growth. These nanorods have a bandgap of 3.3 eV as in the case of bulk crystals and show emission in the UV region of the spectrum (∼ 400 nm) due to excitonic recombination and defect related emission in the visible region.     

ZnO:Cd纳米棒的制备及其光催化降解性能研究

采用水热法制备了ZnO和不同Cd掺杂浓度的ZnO:Cd纳米棒。通过x射线衍射仪、扫描电子显微镜、紫外-可见-近红外分光光度计和拉曼光谱对ZnO:Cd纳米棒的结构和光学特性进行了系统研究。结果显示,样品为一维纳米棒结构,Cd的掺杂可以减小ZnO纳米棒的晶粒尺寸和光学带隙。利用分光光度计检测ZnO:Cd纳米棒对偶氮结构染料(甲基橙溶液)的光催化降解效率,结果表明Cd掺杂可以改善ZnO的光催化性能,掺杂浓度为16%时ZnO:Cd纳米棒对甲基橙溶液的光催化降解效率最高。     

ZnO单晶堆垒纳米棒的制备与表征

在Au点阵模板上磁控溅射ZnO薄膜,然后在O2气氛下1000℃退火制备了ZnO单晶堆垒纳米棒。采用扫描电子显微镜(SEM)、高分辨透射电子显微镜(HRTEM)、X射线衍射(XRD)和傅立叶变换红外(FTIR)光谱对样品进行分析。结果表明,ZnO纳米棒是由诸多单晶堆垒而成,每个单晶均为六方纤锌矿结构,纳米棒直径在100nm左右。初步探讨了ZnO单晶堆垒纳米棒可能的生长机理。     

Carrier transport mechanism on ZnO nanorods/p-Si heterojunction diodes with various atmospheres annealing hydrothermal seed-layer

Annealing in various atmospheres (vacuum, N₂, and O₂) was employed for a hydrothermal seed-layer. The influence on ZnO nanorods (NRs) and carrier transport of ZnO NRs/p-Si heterojunction diodes (HJDs) was investigated. In this work, a hydrothermal method was employed to prepare a seed-layer on a Si substrate, and then annealing at 450 °C in various atmospheres was carried out to improve the subsequent growth of ZnO NRs according to the same method. Observations indicated that ZnO NRs with an O₂-annealed seed-layer have a higher nucleation density and absorb fewer OH groups or O₂⁻ ions, and hence they have fewer defect-level centres. This leads to a very large rectification ratio of 1.9 × 10⁵ in the ZnO NRs/p-Si HJDs because oxygen atoms compensate for the oxygen vacancy-related defects. More band-gap states are present at the ZnO/p-Si interface for the vacuum annealing sample, and this enables recombination-tunnelling transport with a rather large ideality factor of 7 at forward voltage less than 0.7 V. In contrast, diffusion-recombination transport was obtained in the N₂- and O₂-annealed samples with ideality factors as low as 2.4 and 2.2, respectively.     

Effect of substrate morphology on the nucleation and growth of ZnO nanorods prepared by spray pyrolysis

ZnO nanorods were prepared by a spray pyrolysis technique on both as-received and etched Indium Tin Oxide (ITO)/glass substrates. The morphologies of the ITO substrates, the ZnO nucleation mechanism and the development of ZnO nanorods on both types of ITO substrates were investigated by Atomic Force Microscopy and Scanning Electron Microscopy methods. It was found that the amount of nucleation sites on as-received ITO is significantly higher compared to that on the etched ITO. As a result, well-shaped, elongated, strongly c-axis-oriented ZnO nanorods were obtained on the etched ITO/glass substrates. In contrast, randomly oriented ZnO nanocrystals with different shapes and sizes, as well as low aspect ratios, were obtained on the as-received substrates. It was found that ZnO nucleation follows the grain-boundary nucleation mechanism.     

ZnO纳米棒水热法制备及其发光性能

采用水热法在玻璃基底上成功制备出了ZnO纳米棒.用x射线衍射仪(xRD)和扫描电子显微镜(SEM)对ZnO纳米棒的晶体结构和表面形貌进行了表征,初步探讨了ZnO纳米棒的生长机理;同时对ZnO纳米棒的光致发光性能进行测量,分析了水热温度和反应时间对ZnO纳米棒光致发光性能的影响.结果表明:ZnO纳米棒呈现六方纤锌矿结构,具有沿(002)晶面择优生长特征;随着水热反应温度的升高,ZnO纳米棒的发光强度逐渐增强;随着反应时间的延长,ZnO纳米棒发光强度在1～3 h内增强,而在3～10 h反而减弱.     

Fabrication of ZnO nanorods using metal nanoparticles as growth nuclei

ZnO nanorods were produced by pulsed laser deposition (PLD). Drops of nanoparticle colloid (gold or silver) were placed on silica substrates to form growth nuclei. All nanoparticles were monocrystalline, with well-defined crystal surfaces and a negative electrical charge. The ZnO nanorods were produced in an off-axis PLD configuration at oxygen pressure of 5 Pa. The growth of the nanorods started from the nanoparticles in different directions, as one nanoparticle could become a nucleus for more than one nanorod. The low substrate temperature used indicates the absence of a catalyst during the growth of the nanorods. The diameters of the fabricated 1-D ZnO nanostructures were in the range of 50-120 nm and their length was determined by the deposition time.     

电场辅助溶液法制备氧化锌纳米棒阵列及其形貌研究

在外加电场辅助下用溶液法制备了氧化锌纳米棒阵列,反应过程低温、快速,且在无种子层条件下单步完成.用XRD和SEM表征了不同条件下制备的样品的结构和形貌,制备得到的氧化锌纳米棒尺寸均匀、生长致密,直径在50～200nm之间,长度1.5μm左右.分别研究了添加剂六亚甲基四胺(HMTA)和引入的辅助电场的作用及其对样品形貌的影响.研究了不同反应物浓度和反应时间下的样品形貌,讨论了纳米棒一星状双层氧化锌纳米结构在溶液中的形成和生长机理.     

Zinc vacancies and interstitials in ZnO nanorods

Nominally undoped ZnO nanorods, grown by a chemical method, have been post-treated to intentionally incorporate high concentrations of zinc vacancies and zinc interstitials and were studied with electron microscopy and low temperature photoluminescence spectroscopy. The Zn_i are related to the 3.405 eV peak at 4.2 K, verifying that Zn_i is a shallow donor lying 30 meV below the conduction band minimum, while the acceptors V_Zn are related to the 3.308 eV peak at 4.2 K and have an activation energy of 123 meV.     

基于氧化铝模板的有序ZnO纳米棒的合成及光学特性研究

利用高度有序的多孔氧化铝膜作为模板,使用简单的热蒸发Zn粉的方法,成功地制备出高度有序的ZnO纳米棒束,该方法克服了制备有序纳米结构通常需要的催化剂或复杂的合成过程.利用扫描电镜、透射电镜和X射线衍射研究了样品的形貌及其结构特性,其结果表明模板表面所制备的ZnO纳米棒具有更好的有序度和结晶质量,从而推断出模板表面有序ZnO纳米棒的形成应该同模板表面局域化负电荷的存在有关.同Si基片上所形成无序纳米棒的光致发光谱相比,模板表面所形成的有序ZnO纳米棒束具有更强的紫外峰,表明有序的ZnO纳米棒具有更好的结晶质量和光学特性.     

Fabrication of single-crystal ZnO nanorods and ZnS nanotubes through a simple ultrasonic chemical solution method

A simple and rapid method has been developed for the preparation of rod-like ZnO nanocrystals via ultrasonic irradiation. The as-synthesized ZnO nanocrystals were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The ZnO nanorods had an average diameter of 15-70 nm that varied from the ultrasonic operation mode. The results showed that Zn powder played an important role in the synthesis of ZnO nanorods. Through adding a sulfur source in the reaction system, ZnO/ZnS nanocables and ZnS nanotubes could be obtained with continuous ultrasonic irradiation. The formation mechanism of ZnS nanotubes could be attributed to the Kirkendall effect.