Electric field influenced ZnO growth on nanoscale etched Si surface by continuous spray pyrolysis

This work reports ZnO growth by electric field influenced continuous spray pyrolysis reactor over seed layer assisted nanoscale etched Si surface. The comparative studies of ZnO growth in the presence and absence electric field on anisotropically etched Si surface are supported by XRD, SEM, EDX, FTIR and reflectance measurements. XRD measurements confirm preferable (002) oriented ZnO growth by certain amount of etching which is reduced with further anisotropic etching. The chlorine incorporation in ZnO thin film measured by EDX and FTIR may be attributed to the seed layer effect. This present investigation show that anisotropic etch pits surface energy profile has played an important role in deciding ZnO nanorods alignment and coalescence amongst ZnO species during self assembly at nucleation sites. It is observed that additional electric field force in spray droplets is enhancing population density, homogeneous growth and surface coverage of Si surface by ZnO nanorods for particular amount of etched Si surface and improved light coupling is confirmed by reflectance measurement. The relevant growth mechanisms for ZnO nanostructure layers comprising nanorods are also discussed.     

Water molecule-induced stiffening in ZnO nanobelts

We report the observation of remarkable water molecule-induced stiffening in ZnO nanobelts using atomic force microscopy three-point bending test. It was found that the elastic modulus of ZnO nanobelts could increase significantly from 40 GPa under ambient condition up to 88 GPa at the relative humidity level of 80%. The physical mechanism for this phenomenon was explained in terms of increasing surface stress induced by water molecule adsorption on ZnO nanobelt surface. Our first-principles density functional theory calculations revealed that the water molecules adsorbed on the ZnO surface would attract surface Zn atoms to move outward and hence increase the value of surface stress of ZnO surface.     

Solution-processed ZnO-chemically converted graphene gas sensor

We report a solution-processed gas sensor based on vertically aligned ZnO nanorods (NRs) on a chemically converted graphene (CCG) film. The prepared sensor device effectively detected 2 ppm of H₂S in oxygen at room temperature. A high sensitivity of the gas sensor resulted from the growth of highly dense vertical ZnO NRs on the CCG film with numerous tiny white dots on its surface, which may provide a sufficient number of sites for the nucleation and growth of the ZnO NRs. The adsorption of oxygen on the surface of the ZnO NRs was found to be crucial for obtaining an excellent gas sensing performance of the ZnO NRs-CCG sensor.     

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.     

Integration of metal organic chemical vapour deposition and wet chemical techniques to obtain highly ordered porous ZnO nanoplatforms

Large-area, highly ordered ZnO micropores-arrays consisting of ZnO nanotubes delimited by ZnO nanorods have been successfully fabricated and tested for protein sensing applications. ZnO seed layers have been deposited by Metal Organic Chemical Vapour Deposition and readily patterned by Colloidal Lithography to attain ZnO nanorods growth at selective sites by Chemical Bath Deposition. The used synthetic approach has been proven effective for the easy assembly of ZnO nanoplatforms into high-density arrays. Both patterned and unpatterned ZnO nanorods have been morphologically and compositionally characterised and, thus, tested for model studies of protein mobility at the interface. The patterned layers, having a higher contribution of surface polar moieties than the corresponding unpatterned surfaces, exhibit a reduced lateral diffusion of the adsorbed protein. This evidence is related to the intrinsic porous nature of the ZnO hemispherical arrays characterised by a nanotube-nanorod hybrid networks. The present study gives a great impetus to the fabrication of tunable ZnO nanoplatforms having multiple morphologies and exceptionally high surface areas suitable for application in sensing devices.     

Impact of interfacial interactions on optical and ammonia sensing in zinc oxide/polyaniline structures

Zinc oxide/polyaniline (ZnO/PANI) hybrid structures have been investigated for their optical and gas sensing properties. ZnO nanoparticles, prepared by the sol–gel method, pressed in the form of pellets were used for gas sensing. The hybrid ZnO/PANI structure was obtained by the addition of PANI on the surface of ZnO. The UV–Vis absorption of the modified pellets show band edge at 363 nm corresponding to ZnO, while a change in the absorption peaks for PANI was observed. The possible interaction between Zn^2?+? of ZnO and NH-group of PANI was confirmed using Raman spectroscopy studies. The results reveal that the hybrid structures exhibit much higher sensitivity to NH $_{{3}}$ gas at room temperature than blank ZnO, which is sensitive to NH₃ gas at higher temperature. This enhancement has been attributed to the creation of active sites on the ZnO surface due to the presence of PANI.     

Spectroscopic ellipsometry studies on various zinc oxide films deposited by ion beam sputtering at room temperature

Various zinc oxide films were deposited by ion-beam sputter deposition (IBSD) under different oxygen partial pressures (P(O2)) at room temperature. The as-deposited ZnO films fabricated at P(O2)>1.0×10(-4) Torr had poly-crystalline structures to absorb water on the surface at ambient condition. Simultaneously, the film surfaces were covered and smoothed by the surface layers formed with the water, hydroxyl (OH(-)) groups, and ZnO materials investigated by X-ray photoelectron spectroscopy (XPS). When the compositions of the surface layers were used in a multilayer fitting model of spectroscopic ellipsometry, the actual optical refractive index of the ZnO film deposited at P(O2)=1.2×10(-4) Torr was found to be about 1.9618 at λ=550 nm.     

Circular patterns of calcium oxalate monohydrate induced by defective Langmuir–Blodgett film on quartz substrates

The defective Langmuir–Blodgett (LB) film of dipalmitoylphosphatidylcholine (DPPC) on quartz injured by potassium oxalate (K₂C₂O₄) was used as a model system to induce growth of calcium oxalate crystals. Atomic force microscopy (AFM) indicated that circular defective domains with a diameter of 1–200 μm existed in the LB film. Scanning electron microscopy (SEM) showed circular patterns of aggregated calcium oxalate monohydrate (COM) crystallites were induced by these defective domains. It was ascribed to that the interaction between the negatively-charged oxalate ions and the phosphatidyl groups in DPPC headgroups makes the phospholipid molecules rearranged and exist in an out-of-order state in the LB film, especially at the boundaries of liquid-condensed (LC)/liquid-expanded (LE) phases, which provide much more nucleating sites for COM crystals.     

Electron field emission characteristics of different surface morphologies of ZnO nanostructures coated on carbon nanotubes

The optimal carbon nanotube (CNT) bundles with a hexagonal arrangement were synthesized using thermal chemical vapor deposition (TCVD). To enhance the electron field emission characteristics of the pristine CNTs, the zinc oxide (ZnO) nanostructures coated on CNT bundles using another TCVD technique. Transmission electron microscopy (TEM) images showed that the ZnO nanostructures were grown onto the CNT surface uniformly, and the surface morphology of ZnO nanostructures varied with the distance between the CNT bundle and the zinc acetate. The results of field emissions showed that the ZnO nanostructures grown onto the CNTs could improve the electron field emission characteristics. The enhancement of field emission characteristics was attributed to the increase of emission sites formed by the nanostructures of ZnO grown onto the CNT surface, and each ZnO nanostructure could be regarded as an individual field emission site. In addition, ZnO-coated CNT bundles exhibited a good emission uniformity and stable current density. These results demonstrated that ZnO-coated CNTs is a promising field emitter material.     

Physicochemical studies on ZnO-Al2O3 system

Several mixed ZnO-Al₂O₃ systems were prepared by the impregnation method and calcined for 5 h at 300, 600 and 1000 ° C. The crystal structure, surface acidity, surface basicity, surface area, catalytic decomposition of H₂O₂ and the electrical conductivity of the samples prepared were studied. It was found that the decomposition of H₂O₂ is catalysed by the acidic sites formed on the catalyst surface at composition less than 50 mol% ZnO and by basic sites for oxides having composition higher than 50 mol% ZnO. ZnAl₂O₄-spinel was found to be formed at temperatures 600 ° C and it has a catalytic activity and electrical conductivity lower than each of the pure ZnO and the oxide mixtures. The results obtained were correlated together and discussed.     

Au/ZnO nanocomposites: Facile fabrication and enhanced photocatalytic activity for degradation of benzene

Au nanoparticles supported on highly uniform one-dimensional ZnO nanowires (Au/ZnO hybrids) have been successfully fabricated through a simple wet chemical method, which were first used for photodegradation of gas-phase benzene. Compared with bare ZnO nanowires, the as-prepared Au/ZnO hybrids were found to possess higher photocatalytic activity for degradation of benzene under UV and visible light (degradation efficiencies reach about 56.0% and 33.7% after 24 h under UV and visible light irradiation, respectively). Depending on excitation happening on ZnO semiconductor or on the surface plasmon band of Au, the efficiency and operating mechanism are different. Under UV light irradiation, Au nanoparticles serve as an electron buffer and ZnO nanowires act as the reactive sites for benzene degradation. When visible light is used as the light irradiation source, Au nanoparticles act as the light harvesters and photocatalytic sites alongside of charge-transfer process, simultaneously.     

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.     

Plasmonic ZnO/Ag Embedded Structures as Collecting Layers for Photogenerating Electrons in Solar Hydrogen Generation Photoelectrodes

A new fabrication strategy in which Ag plasmonics are embedded in the interface between ZnO nanorods and a conducting substrate is experimentally demonstrated using a femtosecond‐laser (fs‐laser)‐induced plasmonic ZnO/Ag photoelectrodes. This fs‐laser fabrication technique can be applied to generate patternable plasmonic nanostructures for improving their effectiveness in hydrogen generation. Plasmonic ZnO/Ag nanostructure photoelectrodes show an increase in the photocurrent of a ZnO nanorod photoelectrodes by higher than 85% at 0.5 V. Both localized surface plasmon resonance in metal nanoparticles and plasmon polaritons propagating at the metal/semiconductor interface are available for improving the capture of sunlight and collecting charge carriers. Furthermore, in‐situ X‐ray absorption spectroscopy is performed to monitor the plasmonic‐generating electromagnetic field upon the interface between ZnO/Ag nanostructures. This can reveal induced vacancies on the conduction band of ZnO, which allow effective separation of charge carriers and improves the efficiency of hydrogen generation. Plasmon‐induced effects enhance the photoresponse simultaneously, by improving optical absorbance and facilitating the separation of charge carriers.     

Towards Perfectly Ordered Novel ZnO/Si Nano‐Heterojunction Arrays

The fabrication of a highly ordered novel ZnO/Si nano‐heterojuntion array is introduced. ZnO seed layer is first deposited on the Si (P<111>) surface. The nucleation sites are then defined by patterning the surface through focused ion beam (FIB) system. The ZnO nanorods are grown on the nucleation sites through hydrothermal process. The whole fabrication process is simple, facile and offers direct control of the space, length and aspect ratio of the array. It is found that ZnO/Si nanojunctions show an improved interface when subjected to heat treatment. The recrystallization of ZnO and the tensile lattice strain of Si developed during the heating process contribute the enhancement of their photoresponses to white light. The photoluminescence (PL) measurement result of nano‐heterojunction arrays with different parameters is discussed.     

The growth and the ultraviolet photoresponse properties of the horizontal growth ZnO nanorods

The horizontal ZnO nanorods (NRs) were grown by using a low temperature hydrothermal method between the lithographic ZnO interdigital electrodes. In order to horizontally grow the ZnO nanorods, the vertical growth was restrained by coating with the photoresist on the surface nucleation sites. By controlling the distance between the electrodes, only the electrodes for an interval of 7 μm can be connected by the horizontal nanorods to form device. The electrical property of the device was measured. The detector showed a narrow ultraviolet photoresponse with a response peak at 379 nm, which was according with the peak of the photoluminescence. The mechanism of photoresponse was discussed.     

晶格空位ZnO纳米棒的制备及其在镍锌电池中的应用

作为绿色、高功率密度的二次电池, 镍锌电池的应用往往受限于负极材料性能的不足。本工作以乌洛托品(HMT)为模板剂, 通过溶胶-凝胶法合成与热退火处理制备了高性能ZnO纳米棒。透射电子显微镜(TEM)、X射线衍射(XRD)和红外光谱(FT-IR)数据分别揭示了ZnO纳米棒的微观形貌、晶型结构和表面官能团。X射线光电子能谱(XPS)和电子顺磁共振(EPR)结果表明ZnO纳米棒中存在表层碳和晶格空位。Tafel曲线和电化学阻抗等测试表明: 与ZnO商品相比, ZnO纳米棒电极的腐蚀电流和电荷转移电阻分别降低了40%和62%。进一步研究发现, ZnO纳米棒构筑的镍锌电池具有更好的循环性能, 在1 A·g^-1下循环100圈后, ZnO纳米棒的容量保持率为92%, 显著优于市售的ZnO粉末(32%)。     

Annealing effects on the photocatalytic activity of ZnO nanoparticles

This paper describes the development of ZnO nanoparticles by a chemical method, to test them in the photocatalysis of the degradation of textile dyes, using Rhodamine B (RhB) as a probe reaction. The samples were submitted to different heat treatments in order to observe the annealing effects on the photocatalytical properties, surface decontamination and the consequent particle change, in terms of crystallinity. The as-prepared samples (ZOA) correspond to a metastable phase (oxy or hydroxy zinc acetate) and post annealing leads to ZnO crystallization. In spite of the XRD patterns showing only the ZnO phase for heat treatment at 100 degrees C, FTIR data show that carboxylate groups remains attached to the ZnO surface up to 300 degrees C. Up to 300 degrees C the presence of these carboxylate groups, provided by the synthesis method, showed to be more relevant to photoactivity than the specific surface area. At higher temperatures, crystallinity becomes the dominant factor and an increasing of crystallinity favors the photoactivity.     

Morphology tailored surface plasma emission of titanium capped ZnO films

Titanium (Ti)-capped ZnO samples with different roughness were prepared to investigate the effect of ZnO morphology on surface plasma energy of ZnO/Ti interface. ZnO nanoparticle samples with diverse particle shapes, sizes and filling factors were obtained by annealing at different temperatures. Ti-capped ZnO films annealed at 700 °C exhibit excellent photoluminescence property, which can attribute to the high degree of crystallinity (DC) and appropriate surface roughness. Tuning the microcrystalline structure and the ratio of inter-particle distance to the nanoparticle diameter of ZnO can facilitate the surface plasma resonance energy at ZnO/Ti interface close to the near-band-gap emission energy of ZnO, leading to an enhancement of the near-band-gap emission.     

硬脂酸改性纳米ZnO的研究

采用酯化反应法,以水为溶剂,采用硬脂酸对纳米ZnO的表面进行改性,对改性效果进行测试表征。其最佳工艺条件为:硬脂酸质量分数为6%,反应温度为90℃,反应时间为90 min。结果表明,改性后的ZnO粒子呈纳米级的分散,亲油化度值达到72.31%,吸水率达到3.04%;经表面改性的纳米ZnO表现了很好的亲油疏水性;改性后的纳米ZnO表面引入了硬脂酸的官能团,使其表面羟基的数目明显减少,其改性机理为纳米ZnO表面羟基与硬脂酸分子中的羧基发生了类似醇和酸的酯化反应。     

Facile synthesis of Au/ZnO nanoparticles and their enhanced photocatalytic activity for hydroxylation of benzene

Au/ZnO nanocomposites have been prepared by a simple chemical method. For the first time, the nanocomposites were directly used as photocatalysts for hydroxylation of aromatic hydrocarbons under UV and visible light irradiation. The results show that the as-prepared photocatalysts display high photocatalytic activity for UV and visible catalytic hydroxylation of benzene. Without the assistance of any solvent or additive, high selectivity and high conversion efficiency were still obtained. Different photocatalytic mechanisms were proposed depending on whether excitation happens on ZnO semiconductor or on the surface plasmon band of Au. The former is Au nanoparticles act as electron buffer due to irradiation by UV light and ZnO nanoparticles as reactive sites for hydroxylation of benzene, the latter is that Au nanoparticles act as light harvesters and inject electrons into ZnO conduction band and as photocatalytic sites under visible light irradiation.