ZnO纳米线阵列修饰对材料表面浸润性调控

采用溶胶-凝胶法制备了ZnO薄膜,利用溶剂热沉积法获得大面积均匀ZnO纳米线阵列。通过对水在ZnO材料表面的浸润性研究,发现薄膜材料表面的粗糙度对ZnO膜亲水性有增强作用,而周期性ZnO阵列微结构表面可以实现其疏水性质增强效果。同时从理论上分析了这两种现象的物理机制,讨论了空气填隙对ZnO纳米线阵列表面的浸润性质的敏感性。制备出ZnO纳米线阵列的表观接触角约为103°,具有较强的疏水性质,可为进一步的ZnO光流控研究提供实验基础。     

High efficiency dye-sensitized solar cells based on three-dimensional multilayered ZnO nanowire arrays with "caterpillar-like" structure

A 3D ZnO nanowire-based dye-sensitized solar cell (DSSC) with unique "caterpillar-like" structure was designed. Because of the significant improvement of the total ZnO nanowire surface area, the amount of light absorption was substantially increased. This increase in the light harvesting efficiency enables us to achieve an overall power conversion efficiency as high as 5.20%, which is the highest reported value to date for ZnO nanowire-based DSSCs. A branched-multilayered design of ZnO nanowire arrays grown from ZnO nanofiber seed layers proves to be very successful in fabricating 3D ZnO nanowire arrays. Practically, electrospun ZnO nanowires were used as the seeds in multilayer growth of ZnO nanowire arrays with a unique "caterpillar-like" structure. This unique structure significantly enhances the surface area of the ZnO nanowire arrays, leading to higher short-circuit currents. Additionally, this design resulted in closer spacing between the nanowires and more direct conduction pathways for electron transfer. Thus, the open-circuit voltage was so significantly improved as a direct result of the reduction in electron recombination.     

Manipulation of Crawling Growth for the Formation of Sub-millimeter Long ZnO Nanowalls

Vapor-phase growth of ZnO nanowires based on gold catalyst is usually accompanied with lateral crawling growth on the substrate surface. We present results from our systematic experiments where the growth temperature and catalyst size are controlled. The data corroborate that it is possible to obtain clean vertical nanowire arrays while avoiding the crawling growth. 0% the other hand, crawling growth can be manipulated to obtain root-interconnected nanowire arrays, which could be useful for certain applications. Our results also imply that the previously suggested growth mechanism for the wire-on-wall hybridstructure might be incorrect. Finally, we show the formation of sub-millimeter long, straight ZnO nanowalls by combining a gold-catalyzed epitaxial growth of vertical nanowires and their mergence due to a confined crawling growth. These unconventional nanostructures might have unique electric or optical transport properties.     

A facile chemical route to synthesize ZnO nanoarrays: one-dimensional nanowire arrays and two-dimensional porous nanosheet arrays

A facile chemical route is presented to synthesize ZnO nanoarrays including one-dimensional nanowire arrays and two-dimensional porous nanosheet arrays. Large-scale ZnO nanowire arrays with the length of 5 microm and aspect ratio of 42 were achieved by cyclic growth in aqueous solution. After being immerged in the zinc acetate solution for 24 h, the ZnO nanowire arrays converted to sheet-like Zn5(OH)8(CH3COO)2 arrays. Subsequently, the sheet-like Zn5(OH)8(CH3COO)2 arrays converted to the porous ZnO nanosheet arrays by annealing treatment. As demonstrated by the performance of dye-sensitized solar cells (DSC), the porous ZnO nanosheet arrays can improve the efficiency of DSC effectively. In addition, the synthesized ZnO nanoarrays have potential applications in solar cells, catalysis, sensors and other nanodevices.     

Structure, photoluminescence and wettability properties of well arrayed ZnO nanowires grown by hydrothermal method

Well aligned ZnO nanowire arrays with high crystal quality were grown on Si substrates at a low temperature (50 degrees C) by hydrothermal method using a pre-formed ZnO seed layer. ZnO seeds were prepared via radio-frequency magnetron sputtering onto Si substrates. The morphologies of the ZnO nanowire arrays were shown by field emission scanning electron microscopy. X-ray diffraction spectra showed that the full width at the half maximum of the (0002) peak of the nanowire arrays without any heat treatment was only 0.07 degrees, indicating very high crystal quality. Furthermore, the room-temperature photoluminescence spectra of the ZnO nanowire arrays exhibited excellent UV emission. The special micro/nano surface structure of the ZnO nanowire arrays can enhance the dewettability for surfaces modified via low surface energy materials such as long chain fluorinated organic compounds. The surface of the ZnO nanowire arrays is also found to be superhydrophobic with a contact angle of 165 degrees +/- 1 degrees, while the sliding angle is 3 degrees.     

Facile route to well-aligned ZnO nanowire arrays

Well-aligned ZnO nanowire arrays were fabricated on the photoresist SPR6112-B coated (111) Si substrates by a facile vapor transport and condensation method. The structure and growth mechanism of the ZnO nanowire arrays were investigated in detail. It is found that the immiscibility of the zinc oxide-carbon system is responsible for the self-catalysis vapor-liquid-solid (VLS) growth of nanowire arrays. The photoluminescence measurement only presents a strong near-band-edge ultraviolet (UV) emission band centered at 379.6 nm (3.266 eV), exhibiting that the nanowire arrays are of stoichiometric composition and have good optical performance.     

Fabrication of ZnO nanowire arrays by cycle growth in surfactantless aqueous solution and their applications on dye-sensitized solar cells

Large-scale ZnO nanowire arrays vertically aligned on the substrates were achieved from cycle growth without surfactants. The 8 μm long ZnO nanowire arrays were prepared by 20 cycles. The aspect ratio of ZnO nanowire can be increased with increasing the growth cycle. As displayed by microstructures and photoluminescence (PL) analysis, the ZnO nanowire was good single crystal and the defects in the as-prepared ZnO nanowire arrays were controlled at a low concentration. By increasing the length and aspect ratio of ZnO nanowire, the performances of dye-sensitized solar cells based on the ZnO nanowire arrays were improved. As-prepared ZnO nanowire arrays have potential applications in fabricating next generation nanodevices.     

Reshaping the tips of ZnO nanowires by pulsed laser irradiation

Vertically aligned ZnO nanowires have been synthesized by a hydrothermal method. After being irradiated by a short laser pulse, the tips of the as-synthesized ZnO nanowires can be tailored into a spherical shape. Transmission electron microscopy revealed that the spherical tip is a single-crystalline piece connected to the body of the ZnO nanowire, and that the center of the sphere is hollow. The growth mechanism of the hollow ZnO nanospheres is proposed to involve laser-induced ZnO evaporation immediately followed by re-nucleation in a temperature gradient environment. The laser-irradiated ZnO nanowire array shows hydrophobic properties while the original ZnO nanowire array shows hydrophilicity. The as-grown ZnO nanowire arrays with hollow spherical tips can serve as templates to grow ZnO nanowire arrays with very fine tips, which may be a good candidate material for use in field emission and scanning probe microscopy.      

反应源温度对ZnO纳米线阵列定向性及发光性能的影响

以Au薄膜为催化剂、ZnO与碳混合粉末为反应源,采用碳热还原法在单晶Si衬底上制备了ZnO纳米线阵列.通过扫描电子显微镜( SEM)、X射线衍射仪(XRD)、荧光分光光度计对样品的表征,研究了反应源温度对ZnO纳米线阵列的定向性和光致发光性能的影响.样品在源温度920℃条件下沿(002)方向择优生长,定向性最好,温度过低不利于ZnO纳米线阵列密集生长,而温度过高导致Zn原子二次蒸发,因而也不利于纳米线阵列的定向和择优生长;样品在源温度880℃有最强的近紫外带边发射,表明温度过高和过低都不利于ZnO晶体结构的优化;由于ZnO纳米线在缺氧氛围下生长,氧空位是缺陷存在的主要形式,因此所有样品都有较强的绿光发射.温度升高导致纳米线生长速度提高而增加了氧空位缺陷数量,从而使样品绿峰强度增强并在源温度920℃时达最大值,但温度的进一步升高可导致ZnO纳米线表面Zn元素的蒸发而降低氧空位缺陷的数量,从而抑制绿峰强度.     

Layer-by-layer assembly synthesis of ZnO/SnO2 composite nanowire arrays as high-performance anode for lithium-ion batteries

A layer-by-layer approach has been developed to synthesize ZnO/SnO₂ composite nanowire arrays on copper substrate. ZnO nanowire arrays have been first prepared on copper substrate through seed-assisted method, and then, the surface of ZnO nanowires have been modified by the polyelectrolyte. After oxidation-reduction reaction, SnO₂ layer has been deposited onto the surface of ZnO nanowires. The as-synthesized ZnO/SnO₂ composite nanowire arrays have been applied as anode for lithium-ion batteries, which show high reversible capacity and good cycling stability compared to pure ZnO nanowire arrays and SnO₂ nanoparticles. It is believed that the improved performance may be attributed to the high capacity of SnO₂ and the good cycling stability of the array structure on current collector.     

ZnO纳米线的制备及场发射特性的研究进展

从ZnO纳米线的生长机制出发,重点讨论了催化剂在制备过程中的作用,比较了采用VLS和VS不同机制生长ZnO纳米线的优缺点,并结合二者特点发现采用金属自催化将是制备高质量ZnO纳米线阵列的一种有效方法.分析了几种有利于提高其场发射性能的后处理方法,经过适当的后处理ZnO纳米线晶体的结构将更加完善,场发射开启场、阈值场将进一步降低,电流密度和场增强因子也将随之大大提高.     

Electrodeposition of ZnO nanowires with controlled dimensions for photovoltaic applications: Role of buffer layer

The role of a ZnO buffer layer on the electrodeposition of ZnO nanowire arrays was analyzed. ZnO buffer layers were deposited on conducting glass substrates by spray pyrolysis and electrodeposition. The electrodeposited ZnO buffer layer resulted in a collection of open-packed small grains (∼ 20 nm), while the sprayed layers were comprised of close-packed grains with size in the range of 15-100 nm. The ZnO nanowire arrays electrodeposited on ZnO buffer layers exhibited increased nanowire density (by factors of 6× and 3×, for electrodeposited and sprayed buffer layers, respectively) compared to arrays deposited directly on naked substrates, demonstrating that ZnO nanocrystalline layers can be used to increase nucleation sites for nanowire growth. On the other hand, nanowire diameters were tailored from 45 to 160 nm as a function of the size of the grains in the buffer layer. The influence of crystallographic orientation of the buffer layer was also analyzed.     

Ultra-fast microwave-assisted hydrothermal synthesis of long vertically aligned ZnO nanowires for dye-sensitized solar cell application

Long vertically aligned ZnO nanowire arrays were synthesized using an ultra-fast microwave-assisted hydrothermal process. Using this method, we were able to grow ZnO nanowire arrays at an average growth rate as high as 200?nm?min(-1) for maximum microwave power level. This method does not suffer from the growth stoppage problem at long growth times that, according to our investigations, a normal microwave-assisted hydrothermal method suffers from. Longitudinal growth of the nanowire arrays was investigated as a function of microwave power level and growth time using cross-sectional FESEM images of the grown arrays. Effect of seed layer on the alignment of nanowires was also studied. X-ray diffraction analysis confirmed c-axis orientation and single-phase wurtzite structure of the nanowires. J-V curves of the fabricated ZnO nanowire-based mercurochrome-sensitized solar cells indicated that the short-circuit current density is increased with increasing the length of the nanowire array. According to the UV-vis spectra of the dyes detached from the cells, these increments were mainly attributed to the enlarged internal surface area and therefore dye loading enhancement in the lengthened nanowire arrays.     

ZnO nanowire arrays with and without cavity tops

We report a new bubble-assisted growing and etching method for constructing ZnO nanowire (NW) arrays with cavity tops. Firstly, a ZnO NW array structure was formed on a ZnO-seed-layer-patterned Si substrate by combining e-beam lithography and a wet chemical method. Secondly, a new kind of ZnO NW array with cavity tops could be formed by a subsequent bubble-assisted growing and etching. These ZnO NW array structures with different morphologies exhibited different photoluminescence properties, showing their potential applications in lasing cavities, stimulated emitters, nanogenerator, photocatalysis and light-emitting diodes. The bubble-assisted etching method will open a new door for morphology design of ZnO and other semiconductor nanowire arrays at special sites.     

Comparison of optical properties of Si and ZnO/CdTe core/shell nanowire arrays

The systematic computations of the short-circuit current density have been performed for Si and ZnO/CdTe core shell nanowire arrays of 1 μm height in order to optimize the structural morphology in terms of nanowire diameter and period. It is found that the best structural configuration for Si leading to the ideal short-circuit current density of 19.6 mA/cm² is achieved for a nanowire diameter and period of 315 nm and 350 nm, respectively. In case of ZnO/CdTe, the ideal short circuit current density is of 24.0 mA/cm², the nanowire diameter and period is of 210 nm and 350 nm, respectively. It is shown that the optimal configuration is more compact in the case of Si nanowire arrays than in the case of ZnO/CdTe nanowire arrays. Since Si has a smaller absorption coefficient than CdTe, a larger amount of material is needed and thus more compact nanowire arrays are required. It is also revealed that core–shell nanowire arrays made of ZnO/CdTe more efficiently absorb light than that of Si, making this device a good candidate for the next generation of nanostructured solar cells.     

MBE法生长ZnO纳米线阵列的结构和光学性能

在氧等离子体辅助的MBE系统中, 以1 nm厚的Au薄膜为催化剂, 基于气?液?固(VLS)机制实现了低温ZnO纳米线阵列在Si(111)衬底表面的生长. 通过场发射扫描电子显微镜(FE-SEM)可以观察到, ZnO纳米线阵列垂直生长在衬底上, 直径为20~30 nm. X射线衍射(XRD)和高分辨透射电镜(HRTEM)结果表明: ZnO纳米线为六方纤锌矿结构, 具有沿c轴方向的择优取向. 光致发光(PL)谱显示在380 nm附近有强烈ZnO本征发射峰, 475~650 nm可见光区域有较强的缺陷导致的发射峰.     

Capillary-driven assembly of ZnO nanowire arrays into micropatterns

The vertically aligned ZnO nanowire arrays prepared by vapor transport process can be assembled into complex micropatterns under capillary force. The deflection of the flexible ceramic nanowire is closely related to the liquid tension coefficient, mechanical and structural properties of the ZnO nanowires. The bended nanowires are adhesive together because the solid adhesion energy is sufficient to withstand the restoring elastic force of the deformed nanowires. The size of the bundling pattern can be controlled by varying the aspect ratio of the nanowire. The deflection of the ZnO nanostructure composed of a nanowire and a base is multifarious.     

An advanced fabrication method of highly ordered ZnO nanowire arrays on silicon substrates by atomic layer deposition

In this work, the controlled fabrication of highly ordered ZnO nanowire (NW) arrays on silicon substrates is reported. Si NWs fabricated by a combination of phase shift lithography and etching are used as a template and are subsequently substituted by ZnO NWs with a dry-etching technique and atomic layer deposition. This fabrication technique allows the vertical ZnO NWs to be fabricated on 4 in Si wafers. Room temperature photoluminescence and micro-photoluminescence are used to observe the optical properties of the atomic layer deposition (ALD) based ZnO NWs. The sharp UV luminescence observed from the ALD ZnO NWs is unexpected for the polycrystalline nanostructure. Surprisingly, the defect related luminescence is much decreased compared to an ALD ZnO film deposited at the same time ona plane substrate. Electrical characterization was carried out by using nanomanipulators. With the p-type Si substrate and the n-type ZnO NWs the nanodevices represent p–n NW diodes.The nanowire diodes show a very high breakthrough potential which implies that the ALD ZnO NWs can be used for future electronic applications.     

Formation of novel homojunction device using p-type ZnO:Co shell coating on n-type ZnO nanowires

P-type ZnO:Co thin film was spin coated onto n-type ZnO nanowire arrays to form a novel ZnO homojunction device using a fully solution-based process. The optoelectronic and structural properties of the homojunction device were extensively characterized by using scanning electron microscopy, X-ray diffraction, energy dispersive spectroscopy and photoluminescence emission measurement and current voltage measurement. It was found that the applied ZnO:Co coating bundles the nanowires together and suppress surface defects on the nanowire. Dark and illuminated device confirms the pn junction formation and its light sensitivity properties.     

Improved seedless hydrothermal synthesis of dense and ultralong ZnO nanowires

Seedless hydrothermal synthesis has been improved by introducing an adequate content of ammonia into the nutrient solution, allowing the fabrication of dense and ultralong ZnO nanowire arrays over large areas on a substrate. The presence of ammonia in the nutrient solution facilitates the high density nucleation of ZnO on the substrate which is critical for the nanowire growth. In order to achieve an optimal growth, the growth conditions have been studied systematically as a function of ammonia content, growth temperature and incubation time. The effect of polyethyleneimine (PEI) has also been studied but shown to be of no benefit to the nucleation of ZnO. Ultradense and ultralong ZnO nanowires could be obtained under optimal growth conditions, showing no fused structure at the foot of the nanowire arrays. Due to different reaction kinetics, four growth regimes could be attributed, including the first fast growth, equilibrium phase, second fast growth and final erosion. Combining this simple method with optical lithography, ZnO nanowires could be grown selectively on patterned areas. In addition, the as-grown ZnO nanowires could be used for the fabrication of a piezoelectric nanogenerator. Compared to the device of ZnO nanowires made by other methods, a more than twice voltage output has been obtained, thereby proving an improved performance of our growth method.