Amplification of raman scattering by localized plasmons in silver nanoparticles on the surface of zinc oxide nanorods

The magnetron sputtering of Ag nanoparticles onto ZnO nanorod arrays is studied. The lateral faces of the nanorods are coated with nanoparticles at a much lower density as compared to the flat faces at comparable sputtering times. The silver density is high on the edges of the lateral faces of the nanorods. The plasmon absorption in the synthesized arrays of nanorods coated with individual Ag nanoparticles is maximal at 450?C500 nm. The appearance of local plasmon excitations increases the intensity of the multiphonon processes with the participation of ZnO polar modes in Raman spectra. The cross section of resonance Raman scattering for A ₁(LO) phonon overtones increases with the equivalent Ag film thickness.     

Effect of heat and time-period on the growth of ZnO nanorods by sol–gel technique

Sol–gel routes to metal oxide nanoparticles in organic solvents under exclusion of water have become a versatile alternative to aqueous methods. We focus on the preparation of well-aligned ZnO nanorod arrays using non-aqueous sol–gel synthesis route, where ZnO nanorods arrays have been grown on glass substrates. This work provides a systematic study of controlled morphology and crystallinity of ZnO nanorod arrays. The investigation demonstrates that the synthesis process conditions of ZnO thin film have strong influences on the morphology and crystallinity of the ZnO nanorod arrays grown thereon, where non-aqueous process offers the possibility of better understanding and controlling the reaction pathways on the molecular level, enabling the synthesis of nanomaterials with high crystallinity and well-defined, uniform particle morphologies. Here the annealing temperature plays an important role on the growth of nanostructures of the ZnO grains and nanorod arrays. The scanning electron microscopy (SEM) image shows that the growth of ZnO nanorod arrays are high-quality single crystals growing along the c-axis perpendicular to the substrates. A detailed analysis of the growth characteristics of ZnO nanostructures as functions of growth time is also reported.     

The SERS response of semiordered Ag nanorod arrays fabricated by template oblique angle deposition

Semiordered Ag nanorod arrays are fabricated by template oblique angle deposition (OAD) using regular Au nano‐post arrays with different diameters as seed patterns. The Au nano‐post arrays do not give an observable surface‐enhanced Raman scattering (SERS) activity under our detection configuration, whereas the patterned Ag nanorod arrays can produce a very strong SERS signal. These SERS intensities increase monotonically with the decrease in the diameter and separation of the Ag nanorods, which demonstrates that one can improve the SERS detection by tuning the diameter and separation of the Ag nanorods, and the template OAD method can help produce more uniform, reproducible, and sensitive Ag nanorod SERS substrates. Copyright © 2010 John Wiley & Sons, Ltd.     

AFM analysis of piezoelectric nanogenerator based on n-diamond/n-ZnO heterojunction

We have demonstrated a high performance piezoelectric nanogenerator by scanning a diamond-coated conductive tip on ZnO nanorod arrays in an AFM system with contact-mode. About 95% ZnO nanorods generate piezoelectric current due to the excellent mechanical and electrical properties of the tip. The tip's nitrogen-doped diamond coating is the key factor to maintain effective physical contact and electrical contact to ZnO nanorods, leading to efficient piezoelectric generation. Rectifying n⁺-n heterojunction is formed when the nitrogen-doped diamond tip contacted with a ZnO nanorod, which plays an important role in accumulating and releasing piezoelectric charges of the piezoelectric nanogenerator. Our research indicates that conductive diamond film is an ideal electrode for this type of piezoelectric nanogenerator.     

两步法制备空间取向高度一致的ZnO纳米棒阵列

采用两步法,即先用磁控溅射在Si(100)表面生长一层ZnO籽晶层、再利用液相法制备空间取向高度一致的ZnO纳米棒阵列.用扫描电子显微镜、X射线衍射、高分辨透射电子显微镜和选区电子衍射对样品形貌和结构特征进行了表征.结果表明,ZnO纳米棒具有垂直于衬底沿c轴择优生长和空间取向高度一致的特性和比较大的长径比,X射线衍射的(XRD)(0002)峰半高宽只有0.06°,选区电子衍射也显示了优异的单晶特性.光致发光谱表明ZnO纳米棒具有非常强的紫外本征发光和非常弱的杂质或缺陷发光特性. 关键词： ZnO纳米棒阵列 ZnO籽晶层 两步法 液相生长     

A template-free sol-gel technique for controlled growth of ZnO nanorod arrays

The growth of ZnO nanorod arrays via a template-free sol-gel process was investigated. The nanorod is single-crystalline wurtzite structure with [0 0 0 1] growth direction determined by the transmission electron microscope. The aligned ZnO arrays were obtained directly on the glass substrates by adjusting the temperatures and the withdrawal speeds, without seed-layer or template assistant. A thicker oriented ZnO nanorod arrays was obtained at proper experimental conditions by adding dip-coating layers. Room temperature photoluminescence spectrum exhibits an intensive UV emission with a weak broad green emission as well as a blue double-peak emission located at 451 and 468 nm, respectively. Further investigation results show that the difference in the alignment of nanorods ascribes to the different orientations of the nanoparticles-packed film formed prior to nanorods on the substrate. Well ordered ZnO nanorods are formed from this film with good c-axis orientation. Our study is expected to pave a way for direct growth of oriented nanorods by low-cost solution approaches.     

Controlled synthesis of oriented ZnO nanorod arrays by seed-layer-free electrochemical deposition

Oriented ZnO nanorod arrays were successfully prepared on transparent conductive substrates by seed-layer-free electrochemical deposition in solution of Zn(NO₃)₂ at a low temperature of 70 °C without using any catalysts, additives, and additional seed crystals. The effects of the Zn(NO₃)₂ concentration, deposition time and applied current on the localized nanorod arrays are investigated. X-ray powder diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) were used to characterize the structures and the morphologies of ZnO nanorod arrays. The heights and diameters of ZnO nanorods can be tuned by controlling the electrodeposition parameters.     

Controllable synthesis of Ag nanorods using a porous anodic aluminum oxide template

This paper describes a new approach to the synthesis of Ag nanorods. A solvothermal method was used to make Ag nanoparticles inside anodic aluminum oxide (AAO) templates. The nanoparticles were then annealed at 300 °C to produce Ag nanorods. The size of AAO templates, which is focused on in this study, would determine the diameter of Ag nanorods. The product was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In this study, a nanorod growth mechanism is deduced, and understanding of the growth of nanorods inside AAO templates is furthered. This work demonstrates that it is possible to make crystalline nanorods that the size can be varied.     

Aligned ZnO nanorod arrays fabricated on Si substrate by solution deposition

Aligned ZnO nanorod arrays were fabricated by chemical solution deposition based on Si substrate which was spin coated with ZnO colloid as nucleation seeds. Their microstructures were characterized by X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. The results indicated that ZnO nanorods nucleated and grew vertically on Si substrates along the [0 0 1] direction with single-crystalline structure. The diameter of ZnO nanorods was greatly affected by the grain size of ZnO seeds. Room-temperature photoluminescence of nanorods has a strong emission band at about 384 nm.     

Controllable synthesis of highly ordered Ag nanorod arrays by chemical deposition method

Highly ordered Ag nanorod arrays were successfully fabricated using a simple chemical deposition method with the assistance of porous alumina membrane (PAM) template. The products were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Ag⁺ ions in the PAM nanochannels were reduced by acetaldehyde reagent and resulting in the formation of rod array structures. It is found that the diameter of the Ag nanorods is determined by the PAM template, and the length of the Ag nanorods is depended on the reaction temperature. The growth mechanism of the Ag nanorod arrays is investigated in the study.     

Synthesis and characterization of ZnO-Ag core-shell nanocomposites with uniform thin silver layers

This paper presents an investigation on the synthesis and characterization of ZnO-Ag core-shell nanocomposites. ZnO nanorods were employed as core material for Ag seeds, and subsequent nucleation and growth of reduced Ag by formaldehyde formed the ZnO-Ag core-shell nanocomposites. The ZnO-Ag nanocomposites were annealed at different temperature to improve the crystallinity and binding strength of Ag nanoparticles. The morphology, microstructure and optical properties of the ZnO-Ag core-shell nanocomposites were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, ultraviolet-visible (UV-vis) absorption and photoluminescence measurement. It was demonstrated that very small face-center-cubic Ag nanoparticles were coated on the surface of ZnO nanorods. The ultraviolet absorption and surface plasmon absorption band of ZnO-Ag core-shell nanocomposites exhibited some redshifts relative to pure ZnO nanorods and monometallic Ag nanoparticles. The coating of Ag nanocrystals onto the ZnO nanorods completely quenched the photoluminescence. These observations reflected the strong interfacial interaction between ZnO nanorods and Ag nanoparticles. The effect of Ag coating thickness on the morphology and optical properties of ZnO-Ag core-shell nanocomposites was also investigated. Moreover, the growth mechanism of ZnO-Ag core-shell nanocomposites was also proposed and discussed in detail.     

水热法制备Co掺杂ZnO纳米棒及其光学性能

采用水热法在石英衬底上以Zn(CH3COO)2.2H2O和Co(NO3)2.6H2O水溶液为源溶液,以C6H12N4(HMT)溶液作为催化剂,在较低温度下制备了Co掺杂的ZnO纳米棒。采用X射线衍射(XRD)和扫描电子显微镜(SEM)对所生长ZnO纳米棒的晶体结构和表面形貌进行了表征,考察了Co掺杂对ZnO纳米棒微观结构和对发光性能影响的机制。结果表明:Co掺杂的ZnO纳米棒呈六方纤锌矿结构,具有沿(002)面择优生长特性,Co掺杂使ZnO纳米棒的直径变细;同时室温光致发光(PL)谱检测显示Co掺杂ZnO纳米棒具有很强的近带边紫外发光峰,而与深能级相关的缺陷发光峰则很弱。本研究采用水热法在石英衬底上于较低温度下生长出了具有较高光学质量的Co掺杂ZnO纳米棒。     

电沉积法制备ZnO纳米柱及其机制研究

采用阴极还原方法,以Zn(NO₃)₂水溶液为电解液制备ZnO纳米柱。分析了不同沉积电位和不同沉积时间的缓冲层对ZnO纳米柱的密度、形貌及取向的影响。通过分析缓冲层在不同沉积时间下的电流密度变化,研究了缓冲层对ZnO纳米柱密度影响的机理。利用扫描电子显微镜(SEM)和X射线衍射(XRD)分析了样品的表面形貌及结构。研究结果表明,缓冲层能够增加ZnO纳米柱的密度及c轴的取向性,当缓冲层的沉积时间为60 s时,可以得到密度最大、取向最好的ZnO纳米柱。     

Controllable growth of well-aligned ZnO nanorod arrays by low-temperature wet chemical bath deposition method

Well-aligned ZnO nanorod arrays were synthesized by low-temperature wet chemical bath deposition (CBD) method on Si substrate under different conditions. Results illustrated that dense ZnO nanorods with hexagonal wurtzite structure were vertically well-aligned and uniformly distributed on the substrate. The effects of precursor concentration, growth temperature and time on nanorods morphology were investigated systematically. The mechanism for the effect of preparation parameters was elucidated based on the chemical process of CBD and basic nucleation theory. It is demonstrated that the controllable growth of well-aligned ZnO nanorods can be realized by readily adjusting the preparation parameters. Strong near-band edge ultraviolet (UV) emission were observed in room temperature photoluminescence (PL) spectra for the samples prepared under optimized parameters, yet the usually observed defect related deep level emissions were nearly undetectable, indicating high optical quality ZnO nanorod arrays could be achieved via this easy process chemical approach at low temperature.     

Controllable vertical growth onto anatase TiO2 nanoparticle films of ZnO nanorod arrays and their photoluminescence and superhydrophilic characteristics

Well-aligned ZnO nanorod arrays have been successfully fabricated directly on anatase TiO₂ nanoparticle films via low-temperature hydrothermal processes. The effects of the reactive time, temperature and reactant concentration on the growth of the as-prepared ZnO crystals are investigated in detail, and the possible mechanisms of crystal ZnO nanorod growth are also suggested. The results show that the low reactant concentration is in favor of the increase in the aspect ratio of crystal ZnO nanorods with weak orientation, while the long reactive time and high reactant concentration are useful to prepare well-aligned crystal ZnO nanorod arrays. Interestingly, the typically constructed composite films exhibit superhydrophilic characteristic without UV irradiation. Moreover, a strong near-ultraviolet PL band centering at about 385 nm and a weak green PL band centering at about 525 nm can appear at the room temperature.     

Efficient one-pot synthesis of Ag nanoparticles loaded on N-doped multiphase TiO2 hollow nanorod arrays with enhanced photocatalytic activity

The simultaneous Ag loaded and N-doped TiO₂ hollow nanorod arrays with various contents of silver (Ag/N-THNAs) were successfully synthesized on glass substrates by one-pot liquid phase deposition (LPD) method using ZnO nanorod arrays as template. The catalysts were characterized by Raman spectrum, field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscope (HRTEM), ultraviolet-vis (UV-vis) absorption spectrum and X-ray photoelectron spectroscopy (XPS). The results suggest that AgNO₃ additive in the precursor solutions not only can promote the anatase-to-rutile phase transition, but also influence the amount of N doping in the samples. The photocatalytic activity of all the samples was evaluated by photodegradation of methylene blue (MB) in aqueous solution. The sample exhibited the highest photocatalytic activity under UV light illumination when the AgNO₃ concentration in the precursor solution was 0.03 M, due to Ag nanoparticles acting as electron sinks; When the AgNO₃ concentration was 0.07 M, the sample performed best under visible light illumination, attributed to the synergetic effects of Ag loading, N doping, and the multiphase structure (anatase/rutile).     

Controlled growth of standing Ag nanorod arrays on bare Si substrate using glancing angle deposition for self-cleaning applications

A facile approach to manipulate the hydrophobicity of surface by controlled growth of standing Ag nanorod arrays is presented. Instead of following the complicated conventional method of the template-assisted growth, the morphology or particularly average diameter and number density (nanorods cm^?2) of nanorods were controlled on bare Si substrate by simply varying the deposition rate during glancing angle deposition. The contact angle measurements showed that the evolution of Ag nanorods reduces the surface energy and makes an increment in the apparent water contact angle compared to the plain Ag thin film. The contact angle was found to increase for the Ag nanorod samples grown at lower deposition rates. Interestingly, the morphology of the nanorod arrays grown at very low deposition rate (1.2 Å?sec^?1) results in a self-cleaning superhydrophobic surface of contact angle about 157° and a small roll-off angle about 5°. The observed improvement in hydrophobicity with change in the morphology of nanorod arrays is explained as the effect of reduction in solid fraction within the framework of Cassie–Baxter model. These self-cleaning Ag nanorod arrays could have a significant impact in wide range of applications such as anti-icing coatings, sensors and solar panels.     

掺银氧化锌纳米棒的水热法制备研究

利用水热法在直流磁控溅射制备的掺铝氧化锌 (AZO) 种子层上制备了不同形貌和光学性能的掺银ZnO纳米棒, 并采用XRD、扫描电镜、透射谱、光发射谱和EDS谱详细研究了Ag离子与Zn离子的摩尔百分比 (R_Ag/Zn) 及AZO种子层对掺银ZnO纳米棒的结构和光学性质的影响. 随着R_Ag/Zn的增加, 掺银ZnO 纳米棒的微结构和光学性质的变化与银掺杂诱导的纳米棒的端面尺寸变化有关. 平均端面尺寸的变化归结于种子层颗粒大小和颗粒数密度不同导致掺入的Ag离子的相对比例不同. 溅射15 min的AZO种子层上生长的ZnO纳米棒由于缺陷增多导致在可见光区的发光峰明显强于溅射10 min 的AZO种子层上、相同R_Ag/Zn 条件下生长的ZnO纳米棒. Ag掺杂产生的点缺陷增多导致可见光区PL波包较宽. 纯ZnO纳米棒的微结构与种子层厚度导致的结晶度和颗粒大小有关. 关键词： ZnO纳米棒 水热法 Ag掺杂 直流磁控溅射     

Alignment-controlled hydrothermal growth of well-aligned ZnO nanorod arrays

ZnO nanorod arrays (ZNAs) were prepared via a two-step seeding and solution hydrothermal growth process. Effects of preparing parameters such as seed layer, colloid concentration, substrate and precursor concentration, on the alignment control of ZNAs were systematically investigated. The deviation angle of ZnO nanorods was measured to evaluate the alignment of arrays. Results show that seed layer not only controls the vertical orientation of ZNAs, but also the compactness of ZNAs. Altering colloid concentration and substrate can influence the microstructure of ZnO seed layer and affect the ordered alignment of ZNAs. The precursor concentration has an insignificant effect on the alignment of ZNAs but has great impact on the morphology of ZNAs. Alignment-controlled and well-aligned ZnO nanorods with different diameter and aspect ratio can be obtained by properly controlling the preparing parameters. A growth mechanism was proposed for the growth of ZnO nanorods.     

ZnO nanorod arrays fabrication via chemical bath deposition: Ligand concentration effect study

A new ligand, N,N,N′,N′-tetramethylethylenediamine, has been used to grow ZnO nanorods on silicon substrates via a two steps approach. A preliminary seeding on silicon substrates has been combined with chemical bath deposition using a Zinc acetate–N,N,N′,N′-tetramethylethylenediamine aqueous solution. The used diamino ligand has been selected as Zn²⁺ complexing agent and the related hydrolysis generates the reacting ions (Zn²⁺ and OH⁻) responsible for the ZnO growth. The seed layer has been annealed at low temperature (<200 °C) and the ZnO nanorods have been grown on this ZnO amorphous layer. There is experimental evidence that the ligand concentration (ranging from 5 to 50 mM) strongly affects the alignment of ZnO nanorods on the substrate, their lateral dimension and the related surface density. Length and diameter of ZnO nanorods increase upon increasing the ligand concentration, while the nanorod density decreases. Even more important, it has been demonstrated, as proof of concept, that chemical bath deposition can be usefully combined with colloidal lithography for selective ZnO nanorod deposition. Thus, by patterning the ZnO seeded substrate with polystyrene microsphere colloidal lithography, regular Si hole arrays, spatially defined by hexagonal ZnO nanorods, have been successfully obtained.