Enhanced photoelectrochemical performance of bridged ZnO nanorod arrays grown on V-grooved structure

Bridged ZnO nanorod arrays on a V-grooved Si(100) substrate were used as the photoanode of a photoelectrochemical (PEC) cell for water splitting. Photolithography followed by reactive ion etching was employed to create a V-grooved structure on a Si substrate. ZnO nanorod arrays were grown via a hydrothermal method. The light trapping and PEC properties are greatly enhanced using the bridged ZnO nanorod arrays on a V-grooved Si substrate compared with those on a flat one. Increased short circuit photocurrent density (J(SC), 0.73?mA?cm(-2)) and half-life time (1500?s) are achieved. This improved J(SC) and half-life time are 4 times and 10 times, respectively, higher than those of the ZnO nanorod arrays grown on a flat substrate. The overall PEC cell performance improvement for the V-groove grown ZnO array is attributed to the reduced light reflection and enhanced light trapping effect. Moreover, V-groove ZnO showed stronger adhesion between ZnO nanorod arrays and the substrate.     

Structural and magnetic properties of Mn-doped ZnO nanorod arrays grown via a simple hydrothermal reaction

High density Mn-doped ZnO nanorod arrays were vertically grown on ITO substrate via hydrothermal reaction at relatively low temperature of 95 °C. The microstructure and magnetism of the arrays have been examined. Field emission scanning electron microscopy shows that the nanorods of 100 nm diameter and 1 μm length grow along the [001] direction. X-ray photoemission spectroscopy demonstrates that Mn is successfully doped into the nanorods. Meanwhile, all the Mn-doped ZnO nanorod arrays are ferromagnetic at room temperature. It is also found that the value of the saturation magnetization (M_s) of the ZnO nanorod arrays firstly increases with increasing the Mn concentration and then decreases. The higher M_s value is 0.11emu/g, which is obtained in the 5 at.% Mn-doped ZnO nanorod arrays. The ferromagnetism comes from the ferromagnetic interaction between the Mn ions, which partly replace Zn ions.     

Hydrothermal growth of symmetrical ZnO nanorod arrays on nanosheets for gas sensing applications

The hierarchical ZnO nanostructures with 2-fold symmetrical nanorod arrays on zinc aluminum carbonate (ZnAl-CO₃) nanosheets have been successfully synthesized through a two-step hydrothermal process. The primary nanosheets, which serve as the lattice-matched substrate for the self-assembly nanorod arrays at the second-step of the hydrothermal route, have been synthesized by using a template of anodic aluminum oxide (AAO). The as-prepared samples were characterized by XRD, FESEM, TEM and SAED. The nanorods have a diameter of about 100 nm and a length of about 2 μm. A growth mechanism was proposed according to the experimental results. The gas sensor fabricated from ZnO nanorod arrays showed a high sensitivity to ethanol at 230°C. In addition, the response mechanism of the sensors has also been discussed according to the transient response of the gas sensors.     

ZnO nanorod arrays grown on glass substrates below glass transition temperature by metalorganic chemical vapor deposition

High density, well-aligned ZnO nanorods with uniform distributions in their diameters and lengths are successfully prepared on amorphous substrates by metalorganic chemical vapor deposition. The X-ray diffraction measurements indicate that the ZnO nanorods are of wurtzite crystal structure, and are grown preferentially on glass substrates along the [0001]_ZnO direction. The degree of the preferred orientation of the ZnO nanorods is enhanced by increasing the growth temperature, as confirmed by the X-ray diffraction and selected area electron diffraction patterns. Photoluminescence investigations revealed the enhancement of the band edge emission with increasing growth temperature, suggesting the improvement in the optical quality of the ZnO nanorods with increasing temperature.     

Luminescent properties of vertically aligned ZnO nanorod arrays grown on (100) Si substrates

The effect of the dimensions of zinc oxide nanorods on their cathodoluminescence (CL) has been studied in the visible through UV spectral region. The results indicate that hexagonally faceted columnar nanordos grown on (100) Si substrates are aligned almost vertically. The chemistry of point defects in the nanorods is shown to depend on their position in the reactor during growth. The low-temperature CL spectra of the nanorods show peaks due to bound excitons and electron recombination through the nitrogen acceptor level. Electron microscopy results show that the ZnO nanocrystals are highly uniform in shape and size and that these parameters depend on the chemical vapor deposition conditions.     

Highly sensitive hydrogen detection of catalyst-free ZnO nanorod networks suspended by lithography-assisted growth

We have successfully demonstrated a ZnO nanorod-based 3D nanostructure to show a high sensitivity and very fast response/recovery to hydrogen gas. ZnO nanorods have been synthesized selectively over the pre-defined area at relatively low temperature using a simple self-catalytic solution process assisted by a lithographic method. The conductance of the ZnO nanorod device varies significantly as the concentration of the hydrogen is changed without any additive metal catalyst, revealing a high sensitivity to hydrogen gas. Its superior performance can be explained by the porous structure of its three-dimensional network and the enhanced surface reaction of the hydrogen molecules with the oxygen defects resulting from a high surface-to-volume ratio. It was found that the change of conductance follows a power law depending on the hydrogen concentration. A Langmuir isotherm following an ideal power law and a cross-over behavior of the activation energy with respect to hydrogen concentration were observed. This is a very novel and intriguing phenomenon on nanostructured materials, which suggests competitive surface reactions in ZnO nanorod gas sensors.     

Fabrication and characterization of Mg-doped ZnO nanorod arrays

Photoelectronic characteristics are investigated in well-aligned MgO-coated ZnO nanorods (MgO/ZnO nanocables) grown on Si substrates buffered with ZnO film at a low temperature by solution techniques. Transmission electron microscopy shows that a rough surface was observed for the MgO-coated ZnO nanorods due to deposition of MgO nanoparticles on the surface of the ZnO nanorods. However, after annealed at high temperatures, the surface of the MgO-coated ZnO nanorods was flattened to form Mg-doped ZnO nanorods. Photoluminescence spectra of Mg-doped ZnO nanorods displayed a blue shift of the near-band-edge emission with increasing annealing temperature indicative of an increase in the band gap of the MgZnO alloy due to diffusion of the Mg atoms into the ZnO nanorods. In contrast, no blue shift was detected for the samples annealed in H2/N2 (5%/95%) reduction atmosphere but a blue emission was detected at 800 degrees C, indicating that MgO diffusion process may produce a new luminescent center to emit the blue emission in H2/N2 reduction atmosphere.     

Structure and photoluminescence of S-doped ZnO nanorod arrays

Vertically aligned S-doped ZnO nanorod arrays have been successfully synthesized by hydrothermal method at 90 °C for 2 h. The obtained nanorod is ～ 70 nm in diameter and 1.2 μm in length. The XRD pattern and the Raman spectra indicate that the S-doped nanorod arrays are orientated at [001] and are single crystals with hexagonal wurtzite structure. The photoluminescence (PL) spectra show that S-doped ZnO nanorod arrays exhibit a relative weak ultraviolet (UV) emission, a violet emission and a strong green emission. The effects of S-doping on the structure and photoluminescence of ZnO nanorod arrays are discussed in detail.     

Solution grown nanocrystalline ZnO thin films for UV emission and LPG sensing

Nanocrystalline ZnO thin films were successfully deposited by a simple and inexpensive solution growth technique. Photoluminescence (PL) and liquefied petroleum gas (LPG) sensing properties were investigated. Films were found to be uniform, pinhole free, and well adherent. As deposited and heat treated (at 673 K for 2 h) films were characterized by XRD, SEM, and EDAX. The dc electrical resistivity and LPG sensing property were measured. The change in morphology, from spherical particle to rod-like, was observed after air annealing. XRD results revealed that the obtained films were nanocrystalline and had a hexagonal wurtzite structure. The absorption edge was found to be at around 366 nm for the as-deposited film and 374 nm for the annealed film. The band gaps were found to be 3.29 and 2.9 eV for the as-deposited and annealed films, respectively. PL spectra of ZnO thin films showed strong peak at 384 nm, which corresponds to near band edge emission (UV emission) and a relatively weak peak at 471 nm. Further, the annealed film was used for detection of LPG in air. Maximum response was observed at 673 K. The maximum sensitivity of sensor was found to be 4.5 for 0.6 vol.% LPG. Sensing response got saturated after 0.6 vol.% of gas concentration. A possible mechanism of LPG sensing has been explained.     

Periodic ZnO nanorod arrays defined by polystyrene microsphere self-assembled monolayers

We demonstrate a low-cost and effective method to fabricate hexagonally patterned, vertically aligned ZnO nanorod arrays. Selective wet-etching is used to develop the catalyzing gold particle hexagonal pattern with the aid of a polystyrene microsphere self-assembled monolayer. The gold particles have tunable sizes independent of the polystyrene microsphere's diameter and are inherently round in shape. Each ZnO rod is grown individually from a catalyzing site via catalyst-initiated epitaxy, and the original hexagonal periodicity is well-preserved. The rods have flat ends, and the diameters of the rods can be controlled well by the amount of source materials. This method provides a promising way to create ZnO one-dimensional nanostructures for applications as two-dimensional photonic crystal, sensor arrays, nanolaser arrays, and optoelectronic devices.     

Improved UV resistance in wood through the hydrothermal growth of highly ordered ZnO nanorod arrays

In this study, wood materials with significantly improved UV resistance were successfully fabricated by growing highly ordered ZnO nanorod arrays on wood surfaces using a facile one-pot hydrothermal method. The resultant samples were characterized via scanning electron microscopy (SEM), X-ray diffraction, and attenuated total reflectance-Fourier transformation infrared (ATR–FTIR) techniques. The SEM images clearly show the highly ordered and well-aligned ZnO nanorod arrays directly grown onto the wood surface. ATR–FTIR spectra demonstrate that stable chemical bonds between the hydroxyl groups of the ZnO nanorod array film and the wood surface were formed at the interface of the two materials. An accelerated aging test was used to measure the UV resistance of the original wood and the ZnO/wood composite. The experimental results indicate that the ZnO/wood samples exhibited a more superior UV resistance than the original wood. This significantly improved UV resistance is mainly attributed to the excellent UV absorption of the well-aligned ZnO nanorod arrays grown on the wood surface.     

Electrochemical deposition and superhydrophobic behavior of ZnO nanorod arrays

Vertically aligned ZnO nanorod arrays with different heights are grown on the ZnO seeded indium tin oxide substrate by cathodic electrochemical deposition from zinc nitrate at two temperatures of 60 °C and 80 °C. As-grown ZnO nanorods exhibit wurzite crystal structure and their heights can be well controlled by different deposition times. The fluorination coating tends to induce a superhydrophobicity of ZnO nanorods, i.e., the maximal value of contact angle: 166.9°. The super water repellency can be attributed to the fact that an air layer is confined in the nanorod arrays, and thus leads to water droplets sitting on the ZnO surfaces, referring as Cassie state. Interestingly, their water contact angles are found to vary with the heights of ZnO nanorods, ranged from 99.8 to 746 nm. The superhydrophobicity of ZnO surfaces can be well predicted by a proposed model that is capable of determining the wetted fraction of ZnO pillars. This satisfactory result would shed one light on how the variation of rod height would induce the superhydrophobic behavior of ZnO nanorod arrays.     

All-solid,flexible solar textiles based on dye-sensitized solar cells with ZnO nanorod arrays on stainless steel wires

An all-solid, flexible solar textile fabricated with dye-sensitized solar cells (DSSCs) woven into a satin structure and transparent poly(ethylene terephthalate) (PET) film was demonstrated. A ZnO nanorod (NR) vertically grown from fiber-type conductive stainless steel (SS) wire was utilized as a photoelectrode, and a Pt-coated SS wire was used as a counter electrode. A graft copolymer, i.e. poly(vinyl chloride)-graft-poly(oxyethylene methacrylate) (PVC-g-POEM) was synthesized via atom transfer radical polymerization (ATRP) and used as a solid electrolyte. The conditions for the growth of ZnO NR and sufficient dye loading were investigated to improve cell performance. The adhesion of PET films to DSSCs resulted in physical stability improvements without cell performance loss. The solar textile with 10 × 10 wires exhibited an energy conversion efficiency of 2.57% with a short circuit current density of 20.2 mA/cm² at 100 mW/cm² illumination, which is the greatest account of an all-solid, ZnO-based flexible solar textile. DSSC textiles with woven structures are applicable to large-area, roll-to-roll processes.     

PbTiO(3) nanorod arrays grown by self-assembly of nanocrystals

Arrays of ferroelectric lead titanate (PbTiO(3)) nanorods have been grown on a substrate by a novel template-free method. Hydrothermal treatment of an amorphous PbTiO(3) precursor in the presence of a surfactant and PbTiO(3) or SrTiO(3) substrates resulted in the growth of PbTiO(3) nanorod arrays aligned perpendicular to the substrate surface. Two steps in the growth mechanism were demonstrated: first an epitaxial layer was formed on the substrate; this was followed by self-assembly of nanocrystals forming a mesocrystal layer which matured into arrays of PbTiO(3) nanorods.     

Solvothermally grown ZnO nanorod arrays on (101) and (002) single- and poly-crystalline Zn metal substrates

One-dimensional (1D) ZnO nanorod (NR) arrays were grown on (101) and (002) single- and poly-crystalline Zn substrates via direct surface-oxidation in solution, i.e. solvothermal method. The surface-oxidation was done in a solvent mixture of water and 1-propanol with the optimum pH adjusted by adding ammonia. X-ray diffraction patterns revealed that the ZnO NRs grown on the Zn substrates were of single-crystalline with wurtzite structure. The ZnO NRs grown on the (002) single- and poly-crystalline substrates grew in the <001> direction, in contrast to the NRs grown on the (101) single-crystal substrate which were oriented predominantly in the <101> direction. The texture coefficient of the grown ZnO NRs was calculated from the XRD data. Well-aligned NRs that had tips of various shapes were examined by scanning electron microscopy and transmission electron microscopy techniques. The optical properties of the ZnO NRs grown on the Zn substrates were characterized by photoluminescence (PL) spectroscopy.     

ZnO films and nanorod/shell arrays electrodeposited on PET-ITO electrodes

In this work, ZnO films, nanorod and nanorod/shell arrays were synthesized on the surface of PET-ITO electrodes by electrochemical methods. ZnO films with high optical transmittance were prepared from a zinc nitrate solution using a pulsed current technique with a reduced pulse time (3 s). The X-ray diffraction pattern of ZnO film deposited on PET-ITO electrode showed that it has a polycrystalline structure with preferred orientations in the directions [0 0 2] and [1 0 3]. ZnO nanorods were synthesized on electrochemical seeded substrate in an aqueous solution containing zinc nitrate and hexamethylenetetramine. In order to increase the stability of PET-ITO electrode to electrochemical and chemical stresses during ZnO nanorods deposition the surface of the electrode was treated with a 17 wt% NH₄F aqueous solution. Electrochemical stability of PET-ITO electrode was evaluated in a solution containing nitrate ions and hexamethylenetetramine. ZnO nanorod/shell arrays were fabricated using eosin Y as nanostructuring agent. Photoluminescence spectra of ZnO nanorod and ZnO nanorod/shell arrays prepared on the surface of PET-ITO electrode were discussed comparatively. By employing the 1.5 μm-length ZnO nanorod/shell array covered with a Cu₂O film a photovoltaic device was fabricated on the PET-ITO substrate.     

Growth and comparison of different morphologic ZnO nanorod arrays by a simple aqueous solution route

A simple aqueous solution route has been successfully employed to prepare large-scale arrays of ZnO nanorods on the zinc foil without the assistance of any template, oxidant or coating of metal oxide layers. It is found that the growth of ZnO nanorod arrays with different densities, diameters and morphologies is dependent on the ammonia concentration and zinc precursor. The different morphologies of the ZnO nanostructures attained with or without adding Zn²⁺-contained salt in the alkaline solution are compared in the paper. The possible growth mechanism concerning the growth of the different ZnO nanocrystal morphologies is also discussed.     

纳米金刚石表面择优取向生长的氧化锌纳米棒阵列制备及在DNA检测中的应用

研制了基于氧化锌纳米棒阵列的高稳定性和高特异性DNA荧光传感器．首先在纳米金刚石表面制备一层择优取向生长的氧化锌纳米棒，然后通过共缩聚方法在氧化锌表面修饰一层带氨基的硅层．用SEM和XPS对其进行了表征．通过非共价键或共价键方式把探针DNA固定在氧化锌和氨基修饰的氧化锌表面．并对荧光标记DNA进行了检测。实验结果表明共价固定方法比非共价固定方法有更好的特异性。此外，共价固定方法有好的稳定性和较高的灵敏度．     

Microstructural and optical characteristics of solution-grown Ga-doped ZnO nanorod arrays

Highly oriented Ga-doped zinc oxide (ZnO) nanorod arrays have been prepared on a ZnO-buffered silicon substrate in an aqueous solution, which is a mixture of methenamine (C(6)H(12)N(4)), zinc nitrate hexahydrate (Zn(NO(3))(2)·6H(2)O), and gallium nitrate hydrate (Ga(NO(3))(3)·xH(2)O). The microstructure characteristics and optical properties of the nanorod arrays were analyzed using different characterization techniques including field-emission scanning electron microscopy (FESEM), x-ray photoelectron spectroscopy (XPS), and photoluminescence (PL). The experimental results show that the morphology, density, and surface compositions of ZnO nanorod arrays are sensitive to the concentration of gallium nitrate hydrate. The PL spectra of all ZnO nanorod arrays show three different emissions, including UV (ultraviolet), yellow, and NIR (near infrared) emissions. With the increase in the Ga doping level, the luminescence quality of ZnO nanorods has been improved. The peak of UV emission has a small redshift, which can be ascribed to the combined effect of size and Ga doping. Furthermore, Ga doping has caused defects that respond to NIR emission.     

水热法制备掺铝氧化锌纳米棒阵列及其光学特性

采用水热法,在ZnO种子层上制备出不同Al掺杂量的ZnO纳米棒阵列薄膜,利用XRD、SEM、TEM、PL等检测手段对样品进行结构、形貌和发光性能分析.结果表明,纳米棒属于六方纤锌矿结构,具有垂直基底沿[002]方向生长的特征,PL谱上存在强的近紫外辐射峰.随着掺杂量的增加,纳米棒直径略有减小,近紫外辐射峰蓝移,强度先增加后减小,证明掺杂会形成非辐射中心,探讨了Al掺杂ZnO纳米棒阵列的发光机理.