Selective growth of ZnO nanorods in aqueous solution

ZnO nanorod arrays find applications in solar energy conversion, light emission and other promising areas. One approach to generate ZnO nanorods is the cost efficient aqueous chemical growth (ACG). Usually the ACG process is based on a nucleation step followed by growth of ZnO nanorods in aqueous solution at temperatures below 95 C.We report on the fabrication of homogeneous, large scale arrays of nanorods on various substrate materials (Si, glass, polymer) by ACG. PL-measurements show surprisingly good optical quality although the rods were grown at low temperature.Even though we have developed patterning of these arrays with photolithographic techniques, a bottom up approach for lateral patterning is important concerning further applications especially for mass-production. The substrates with patterned metal layers were employed to realize selective growth of nanorods. The experiments were carried out on Ti-, Ag- and Pt-patterned substrates. Selective growth on metal structured glass substrates was developed and is described.     

Shape alterations of ZnO nanocrystal arrays fabricated from NH3·H2O solutions

Well-aligned crystalline ZnO nanorod arrays were synthesized via an aqueous solution route with ammonia and zinc nitrate as inorganic precursors. ZnO crystalline seed films were firstly coated on ITO substrates for epitaxial growth of rods through sol-gel processing and heat treatment. SEM, TEM, SAED and XRD were utilized to characterize morphologies and structures of ZnO crystals. Heterogeneous nucleation is crucial for rod growth. A broad scope of pH favorable for heterogeneous nucleation was disclosed at zinc concentration from 0.04 to 0.1 M in the inorganic system due to the complex reaction of ammonia with Zn²⁺. Elevation of initial zinc concentration or pH promoted growth rate of rods and enlarged rod size. ZnO nanorods were transformed to nanotubes, nanosheets and rods with blanket-like shaped surface mainly by secondary pH adjustment. All ZnO nanocrystals are wurtzite structure preferentially oriented in c-axis direction.     

Growth of ZnO nanorods by aqueous solution method with electrodeposited ZnO seed layers

ZnO nanorod arrays on ZnO-coated seed layers were fabricated by aqueous solution method using zinc nitrate and hexamethylenetetramine at low temperature. The seed layers were coated on ITO substrates by electrochemical deposition technique, and their textures were dominated by controlling the deposition parameters, such as deposition potential and electrolyte concentration. The effects of the electrodeposited seed layers and the growing parameters on the structures and properties of ZnO nanorod arrays were primarily discussed. The orientation and morphology of both the seed layer and successive nanorods were analyzed by using X-ray diffraction (XRD), SEM and TEM. The results show that the seed layer deposited at −700 mV has evenly distributed crystallites and (0 0 2) preferred orientation; the density of resultant nanorods is high and ZnO nanorods stand completely perpendicular onto substrates. Meanwhile, the size of nanorods quite also depends on the growth solution, and the higher concentration of growth solution primary leads to a large diameter of the ZnO nanorods.     

水热法合成ZnO纳米棒图案及其场增强效应

利用水热合成方法在图案化的Au岛上合成了ZnO纳米棒图案,采用的溶液体系为六次甲基四胺和硝酸锌溶液,ZnO纳米棒的基底是ITO导电玻璃上的有序Au岛. 由于ZnO的异相成核速度在Au和ITO基底上具有不同的成核速度,因此ZnO优先生长在成核速度快的Au岛上,同时由于受到了溶液中前驱物种扩散的限制,纳米棒继续生长也被受到了约束. 通过调控六次甲基四胺和硝酸锌的浓度,可以调整不同的图案. 此外,利用X射线衍射、光致发光谱和场发射特性性能对水热合成的ZnO纳米棒图案进行了研究. ZnO纳米棒表现出良好的场增强性     

Fabrication of needle-like ZnO nanorods arrays by a low-temperature seed-layer growth approach in solution

Uniform, large-scale, and well-aligned needle-like ZnO nanorods with good photoluminescence and photocatalysis properties on Zn substrates, have been successfully fabricated using a simple low-temperature seed-layer growth approach in solution (50 °C). The formation of ZnO seed-layer by the anodic oxidation technique (AOT) plays an important role in the subsequent growth of highly oriented ZnO nanorods arrays. Temperature also proved to be a significant factor in the growth of ZnO nanorods and had a great effect on their optical properties. X-ray diffraction (XRD) analysis, selected-area electron diffraction (SAED) pattern and high-resolution TEM (HRTEM) indicated that the needle-like ZnO nanorods were single crystal in nature and that they had grown up preferentially along the [0001] direction. The well-aligned ZnO nanorods arrays on Zn substrates exhibited strong UV emission at around 380 nm at room temperature. To investigate their potential as photocatalysts, degradation of pentachlorophenol (PCP) in aqueous solution was carried out using photocatalytic processes, with comparison to direct photolysis. After 1 h, the degradation efficiencies of PCP by direct photolysis and photocatalytic processes achieved 57% and 76% under given experimental conditions, respectively. This improved degradation efficiency of PCP illustrates that ZnO nanorods arrays on Zn substrates have good photocatalytic activity. This simple low-temperature seed-layer growth approach in solution resulted in the development of an effective and low-cost fabrication process for high-quality ZnO nanorods arrays with good optical and photocatalytic properties that can be applicable in many fields such as photocatalysis, photovoltaic cells, luminescent sensors, and photoconductive sensors. PACS 81.07.Bc; 81.10.Dn; 81.15.Pq; 82.50.Hp; 85.60.Jb     

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.     

Synthesis and optical properties of ZnO nanorods on indium tin oxide substrate

ZnO nanorods with uniform diameter and length have been synthesized on an indium-tin oxide (ITO) substrate by using a simple thermal evaporation method which is suitable to larger scale production and without any catalyst or additives. The samples were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-vis (UV-vis) absorption spectrum, photoluminescence (PL) spectrum and Raman spectrum. The single-phase ZnO nanorods grow well-oriented along the c-axis of its wurtzite structure on ITO substrate. The ZnO nanorods shows sharp and strong UV emission located at 380 nm without notable visible light emission in the PL spectrum, which suggests the good crystallinity of the nanorods, which was also testified by their Raman spectrum. The photodegradation of methylene orange (MO) in aqueous solution reveals that the well-arranged c-axis growth of ZnO nanorods possess evidently improved photocatalytic performance and these properties enable the ZnO nanorods potential application in UV laser.     

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。     

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.     

Characterisation of ZnO nanorod arrays grown by a low temperature hydrothermal method

In this paper, growth steps of well defined ZnO nanorod arrays deposited on seeded substrates were investigated. To obtain ZnO seed layer on glass substrates, a successive ionic layer adsorption and reaction (SILAR) method was used and then ZnO nanorods were grown on seed layer using a chemical bath deposition (CBD) method. The effects of seed layer and deposition time on morphology, crystallographic structure (e.g. grain size, microstrain and dislocation density) and electrical characteristics of ZnO nanorods were studied. From the SEM micrographs, it could be seen that the ZnO nanorods densely covered the substrate and were nearly perpendicular to the substrate surface. The XRD patterns showed that the ZnO nanorod arrays had a hexagonal wurtzite structure with a preferred orientation along the (002) plane. An increase in deposition time resulted in an increase in the intensity of the preferred orientation and grain size, but a decrease in microstrain and dislocation density. Electrical activation energies of the structures were calculated as 0.15–0.85?eV from current–temperature characteristics. It was concluded that the morphologies of the structures obtained in this study via a simple and fast solution method can provide high surface areas which are important in area-dependent applications, such as solar cells, hydrogen conversion devices, sensors, etc.     

Room temperature magnetic properties of ZnO nanostructured films

The ZnO nanorod array films have been epitaxially deposited on indium tin oxide (ITO) glass along 〈0001〉 direction. It is found that the film is grown in a two-step process including nanoparticle film nucleation and oriented rod growth. The as-prepared ZnO film shows a dominant diamagnetic signal and a weak ferromagnetic signal at room temperature. The room temperature ferromagnetism deteriorated by annealing in air or N₂. The photoluminescent spectra revealed that the intensity of ZnO defect band decreases after annealing. Thus, the decreased ferromagnetism is likely to have resulted from the decrease of oxygen vacancies and defects in the as-prepared film. Moreover, ZnO deposited at various times showed that defects located at or near the interface between the substrate and the film play a major role in ferromagnetism. It suggests that ferromagnetism can be tuned by changing the defects in ZnO.     

Thermo-electrochemical selective growth of ZnO nanorods on any noble metal electrodes

Selective growth of ZnO nanorods has been successfully performed on the patterned Au/Ti metal electrode regions on a glass substrate by using a seeded thermo-electrochemical method in an acidic growth solution. The selective growth mechanism of the thermo-electrochemical method was proposed by using a series of chemical reactions for the first time. The thermo-electrochemical selective ZnO growth was performed on the cathode electrode at a temperature below 90 °C. A ZnO seed layer was precoated and selectively etched away from the non-metal regions in order to create the patterned selective nucleation sites on which the precursors are transferred and crystallized into ZnO nanorods. Both the dimensions and the placements of the ZnO nanorods have been simultaneously controlled. Energy dispersive X-ray spectrometry showed that the selectively grown ZnO nanorods consist of only Zn and O, indicating that the selectively grown ZnO nanorods are pure and contamination free. XRD and electron diffraction patterns revealed that the obtained ZnO nanorods have a wurtzite single-crystal structure.     

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.     

Seed layer-free synthesis and characterization of vertically grown ZnO nanorod array via the stepwise solution route

A novel stepwise method was developed for the deposition of ZnO nanorod array (NRA) from the simple inorganic aqueous solution. Different from the traditional one-pot synthesis route, merely a thin liquid precursor layer adsorbed on the substrate instead of the bulk solution underwent the reaction at elevated temperature in a typical deposition cycle. Sparse and vertically grown wurtzite ZnO NRA was deposited on seed layer-free glass substrate after 20 cycles (in typically 20 min). Each individual ZnO rod possessed the well-defined hexagonal facet, the side length of about 150 nm, the aspect ratio of 2:3, and the small size dispersity. Also the overall ZnO NRA exhibited high ultraviolet photoluminescence and weak blue emission, indicating its good optical properties. Mechanism analysis indicated that, the decrease of the supersaturation degree in solution after the climax in the reaction period of each deposition cycle is the root cause of the sparse nucleation and the vertical growth of ZnO nanorods. The work has opened up a novel stepwise approach toward high quality ZnO NRA, being valuable for extending the synthetic methods of semiconductor nanostructures in mild solutions.     

Growth of ZnO nanorods by a simple chemical method

ZnO nanorods were grown by a near-room-temperature, simple, chemical solution method on large-area Zn foils and substrate materials such as silicon, and zinc oxide thin films on silicon and glass. Study of the ZnO nanorods on the different substrates by electron microscopy methods shows that the morphology and size of the ZnO nanorods can be tuned varying the growth parameters and the substrates used. The growth mechanism is briefly discussed. Photoluminescence experiments at room temperature reveal a major emission peak of the nanorods at around 385 nm, which is attributed to the band edge transition of ZnO and weaker defect-related visible band peaks. PACS 81.05.Dz; 78.55.Et; 81.07.-b     

Growth and investigation of antifungal properties of ZnO nanorod arrays on the glass

In this study, we have investigated the antifungal activity of ZnO nanorods prepared by the chemical solution method against Candida albicans. In the study, Zinc oxide nanorods have been deposited on glass substrates using the chemical solution method. The as-grown samples are characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). X-ray diffraction (XRD) showed zinc oxide nanorods grown in (0 0 2) orientation. The antifungal results indicated that ZnO nanorod arrays exhibit stable properties after two months and play an important role in the growth inhibitory of Candida albicans.     

GaN衬底的腐蚀程度对ZnO纳米棒阵列光学性能的调控

研究了在湿法腐蚀Ga N衬底上生长的Zn O纳米棒阵列的微结构和光学性能。相比于未经腐蚀及腐蚀5 min、10 min的Ga N上生长的Zn O纳米棒阵列,在腐蚀8 min的Ga N上生长的Zn O纳米棒阵列最细密,光学性能最好,其相应PL光谱峰强积分比IUV/Ivis最大(70.92)。因为此时Ga N衬底中的位错基本全部在表面露头,Zn O容易附着而形成更多的形核种子,并且衬底的位错在表面的边缘有助于诱导Zn O晶体的外延生长,所以Zn O棒更加细密,晶体质量更高,从而光学性能更好。     

聚乙烯亚胺对氧化锌纳米阵列形貌的影响

采用化学沉淀法,以硝酸锌和六次亚甲基四胺的水溶液为生长溶液,在涂覆氧化锌晶种层的玻璃衬底上制备了定向生长的氧化锌纳米棒阵列,并研究了添加剂聚乙烯亚胺的浓度对氧化锌纳米棒形貌和结构的影响。X射线衍射和场发射扫描电镜的结果表明,合成的氧化锌纳米棒阵列较为均匀致密,具有六方纤锌矿结构,且有沿(002)晶面择优生长的特性;随着聚乙烯亚胺浓度的增加,氧化锌纳米棒的直径减小,直径分布趋于均匀,且氧化锌纳米棒的形貌也从锥状转变为柱状结构;另外,聚乙烯亚胺的加入对氧化锌的生长速度具有抑制作用,当聚乙烯亚胺的浓度增加至0.012 mol·L-1时,无氧化锌阵列生长。对氧化锌纳米棒阵列进行了拉曼光谱表征,结果表明,随着溶液中聚乙烯亚胺浓度的增加,氧化锌纳米棒的氧空位缺陷减少。最后,对聚乙烯亚胺浓度对氧化锌纳米阵列影响的机理进行了探讨。     

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     

Growth and interconversion of ZnO nanostructure films on different substrates

Hexagonal c-axis oriented ZnO nanorod (NR) arrays were grown on ZnO-coated glass substrates by chemical bath deposition (CBD). By varying the concentration of the precursor solutions, NRs’ mean diameter was controlled from about 100-400 nm. With increasing the growing time, the morphology of as-synthesized ZnO NRs evolved: the top center of the ZnO NRs was eroded into volcano-like structures which developed into ZnO nanotubes (NT) and finally the ZnO NTs split to form ZnO nanosheets (NS). We have also introduced Al to the fabrication of some different ZnO nanostructures: on Al substrate, freestanding ZnO NSs formed a flower-like structure at the early growing period and these ZnO NSs reassembled into ZnO NTs as growing time increased; while on ZnO-coated glass substrate with an Al foil dipped in the growing precursor solution ZnO NR-NS composited arrays were synthesized.