Self-assembly of FeCl3-S nanotrees and their application in directed growth of nanofibers

Nanoscale tree-like FeCl₃-S structures have been assembled. Their unique characteristics, based on the high reactivity of FeCl₃ moiety and the branched thread morphology of sulfur moiety, endow them multiple excellent functions, particularly acting as reactive seeds or templates to directly induce organic polymerization reaction and guide the growth of polymer nanofibers. Using the excellent ability of these tree-like nanostructures, we have synthesized long and flexible polycyclopentadiene nanofibers in one-step process. This result may lead to a new technical way to control the formation of organic polymer nanofibers and to tailor the growth of microstructures by using reactive nanostructures as structure-directing objects.     

Complex and oriented ZnO nanostructures

Extended and oriented nanostructures are desirable for many applications, but direct fabrication of complex nanostructures with controlled crystalline morphology, orientation and surface architectures remains a significant challenge. Here we report a low-temperature, environmentally benign, solution-based approach for the preparation of complex and oriented ZnO nanostructures, and the systematic modification of their crystal morphology. Using controlled seeded growth and citrate anions that selectively adsorb on ZnO basal planes as the structure-directing agent, we prepared large arrays of oriented ZnO nanorods with controlled aspect ratios, complex film morphologies made of oriented nanocolumns and nanoplates (remarkably similar to biomineral structures in red abalone shells) and complex bilayers showing in situ column-to-rod morphological transitions. The advantages of some of these ZnO structures for photocatalytic decompositions of volatile organic compounds were demonstrated. The novel ZnO nanostructures are expected to have great potential for sensing, catalysis, optical emission, piezoelectric transduction, and actuations.     

Soft solution processing of ZnO nanoarrays by combining electrophoretic deposition and hydrothermal growth

The use of seeded or pretreated substrates has been reported as a feasible way to control the morphology, texture and orientation of ZnO structures during hydrothermal growth. However, in a typical seeding procedure, high energy-consumption, high-cost, complexity and/or specific substrates are by now required. Electrophoretic deposition (EPD) is a soft solution process that may allow avoiding such problems of classical seeding procedures. In this work, the combination of these two soft solution processing techniques, EPD and hydrothermal growth, has been studied for growing ZnO nanostructures onto stainless steel substrates. The use of ZnO seed layers deposited by EPD as a way to control the evolution of ZnO structures during hydrothermal growth is discussed, showing that the seeding and its nature have an effect on the number of nucleation sites and consequently on the size and morphology of the obtained structures.     

Microwave-controlled facile synthesis of well-defined PbS hexapods

Controlled synthesis of well-defined PbS nanostructures in terms of size and shape has been strongly motivated by their potential applications ranging from solar photovoltaics to near-infrared optics. Hereby, we report a facile microwave-assistant method for ultrafast fabrication of PbS nanostructures, by which uniform PbS hexapods with six arms stretching along six (100) directions of the crystal seeds have been easily synthesized within minutes. Various morphologies including rectangle plates, uniform cubes as well as nanoparticles were obtained by tuning the parameters for the formation of PbS nanocrystals. The results reveal that both concentration and feed ratio of precursors determine the growth of PbS nanocrystals significantly. And higher initial precursor concentration favors the formation of the hexapod structures. The process of crystal growth is monitored through scanning electron microscopy of PbS from different durations of the reaction. This controlled ultrafast synthesis of PbS structures at nanometer and micrometer scale with various morphologies may be promising in large scale fabrication of nanostructures. Based on the systematically study of the growth process, a possible mechanism for the formation of the hexapod-like structure is discussed.     

Formation of chiral branched nanowires by the Eshelby Twist

Manipulating the morphology of inorganic nanostructures, such as their chirality and branching structure, has been actively pursued as a means of controlling their electrical, optical and mechanical properties. Notable examples of chiral inorganic nanostructures include carbon nanotubes, gold multishell nanowires, mesoporous nanowires and helical nanowires. Branched nanostructures have also been studied and been shown to have interesting properties for energy harvesting and nanoelectronics. Combining both chiral and branching motifs into nanostructures might provide new materials properties. Here we show a chiral branched PbSe nanowire structure, which is formed by a vapour-liquid-solid branching from a central nanowire with an axial screw dislocation. The chirality is caused by the elastic strain of the axial screw dislocation, which produces a corresponding Eshelby Twist in the nanowires. In addition to opening up new opportunities for tailoring the properties of nanomaterials, these chiral branched nanowires also provide a direct visualization of the Eshelby Twist.     

控制O2流量生长结状 ZnO微纳米棒及其特性研究

采用热蒸发法以锌粉和二水醋酸锌作为源材料在Si（111）衬底上制备了高密度的ZnO微纳米棒，制得的每根ZnO棒明显分为直径不同的四段．利用X射线衍射、扫描电镜、透射电镜、拉曼光谱和光致发光谱等测试手段对制备的样品进行了形貌、结构和光学性能的分析，结果表明制备的ZnO棒晶体质量良好，仅存在很少量的缺陷.通过讨论该结构的生长机理，发现O2分压对制备的ZnO微纳米棒的形貌有显著的影响，调节O2流量可控制ZnO纳米结构的形貌．     

Reactive oxygen plasma-enabled synthesis of nanostructured CdO: tailoring nanostructures through plasma-surface interactions

Plasma-assisted synthesis of nanostructures is one of the most precise and effective approaches used in nanodevice fabrication. Here we report on the innovative approach of synthesizing nanostructured cadmium oxide films on Cd substrates using a reactive oxygen plasma-based process. Under certain conditions, the surface morphology features arrays of crystalline CdO nano/micropyramids. These nanostructures grow via unconventional plasma-assisted oxidation of a cadmium foil exposed to inductively coupled plasmas with a narrow range of process parameters. The growth of the CdO pyramidal nanostructures takes place in the solid-liquid-solid phase, with the rates determined by the interaction of plasma-produced oxygen atoms and ions with the surface. It is shown that the size of the pyramidal structures can be effectively controlled by the fluxes of oxygen atoms and ions impinging on the cadmium surface. The unique role of the reactive plasma environment in the controlled synthesis of CdO?nanopyramidal structures is discussed as well.     

Hyperbranched lead selenide nanowire networks

Lead chalcogenide nanostructures are good potential candidates for applications in multiexciton solar cells, infrared photodetectors, and electroluminescence devices. Here we report the synthesis and electrical measurements of hyperbranched PbSe nanowire networks. Hyperbranched PbSe nanowire networks are synthesized via a vapor-liquid-solid (VLS) mechanism. The branching is induced by continuously feeding the PbSe reactant with the vapor of a low-melting-point metal catalyst including In, Ga, and Bi. The branches show very regular orientation relationships: either perpendicular or parallel to each other. The diameter of the individual NWs depends on the size of the catalyst droplets, which can be controlled by the catalyst vapor pressure. Significantly, the hyperbranched networks can be grown epitaxially on NaCl, a low-cost substrate for future device array applications. Electrical measurements across branched NWs show the evolution of charge carrier transport with distance and degree of branching.     

Hybrid epitaxial-colloidal semiconductor nanostructures

We present a growth technique which combines wet-chemical growth and molecular beam epitaxy (MBE) to create complex semiconductor nanostructures with nanocrystals as active optical material. The obtained results show that wet-chemically prepared semiconductor nanocrystals can be incorporated in an epitaxally grown crystalline cap layer. As an exemplary system we chose CdSe nanorods and CdSe(ZnS) core-shell nanocrystals in ZnSe and discuss the two limits of thin (d approximately 2R) and thick (d>2R) ZnSe cap layers of thickness d for CdSe nanorods and nanodots of radii R between 2 and 4 nm. In contrast to the strain-induced CdSe/ZnSe Stranski-Krastanow growth of a quantum dot layer in a semiconductor heterostructure, the technique proposed here does not rely on strain and thus results in additional degrees of freedom for choosing composition, concentration, shape, and size of the nanocrystals. Transmission electron microscopy and X-ray diffractometry show that the ZnSe cap layer is of high crystalline quality and provides all parameters for a consecutive growth of Bragg structures, waveguides, or diode structures for electrical injection.     

Nanopatterning the electronic properties of gold surfaces with self-organized superlattices of metallic nanostructures

The self-organized growth of nanostructures on surfaces could offer many advantages in the development of new catalysts, electronic devices and magnetic data-storage media. The local density of electronic states on the surface at the relevant energy scale strongly influences chemical reactivity, as does the shape of the nanoparticles. The electronic properties of surfaces also influence the growth and decay of nanostructures such as dimers, chains and superlattices of atoms or noble metal islands. Controlling these properties on length scales shorter than the diffusion lengths of the electrons and spins (some tens of nanometres for metals) is a major goal in electronics and spintronics. However, to date, there have been few studies of the electronic properties of self-organized nanostructures. Here we report the self-organized growth of macroscopic superlattices of Ag or Cu nanostructures on Au vicinal surfaces, and demonstrate that the electronic properties of these systems depend on the balance between the confinement and the perturbation of the surface states caused by the steps and the nanostructures' superlattice. We also show that the local density of states can be modified in a controlled way by adjusting simple parameters such as the type of metal deposited and the degree of coverage.     

Synthesis and size-dependent properties of zinc-blende semiconductor quantum rods

Dimensionality and size are two factors that govern the properties of semiconductor nanostructures. In nanocrystals, dimensionality is manifested by the control of shape, which presents a key challenge for synthesis. So far, the growth of rod-shaped nanocrystals using a surfactant-controlled growth mode, has been limited to semiconductors with wurtzite crystal structures, such as CdSe (ref. 3). Here, we report on a general method for the growth of soluble nanorods applied to semiconductors with the zinc-blende cubic lattice structure. InAs quantum rods with controlled lengths and diameters were synthesized using the solution-liquid-solid mechanism with gold nanocrystals as catalysts. This provides an unexpected link between two successful strategies for growing high-quality nanomaterials, the vapour-liquid-solid approach for growing nanowires, and the colloidal approach for synthesizing soluble nanocrystals. The rods exhibit both length- and shape-dependent optical properties, manifested in a red-shift of the bandgap with increased length, and in the observation of polarized emission covering the near-infrared spectral range relevant for telecommunications devices.     

Palladium urchin-like nanostructures and their H2 sorption properties

Urchin-like palladium nanostructures were synthesized by slow radiolytic reduction of Pd(II) in cetylpyridinium chloride (CPCl) micellar solution. They were formed by polycrystalline nanowires originating from the same core. The growth process leading to these urchin-like structures has been studied. These three-dimensional (3D) nanostructures were obtained at high Pd concentration (0.1 M) which led to a relatively large quantity of nanomaterials. These nanostructures show very interesting cycling sorption properties for hydrogen storage.     

Convenient synthesis of twin-Christmas tree-like PbWO<Subscript>4</Subscript> microcrystals and their photocatalytic properties

Novel twin-Christmas tree-like PbWO₄ microcrystals have been prepared via a convenient aqueous solution route at room temperature under the assistance of β-cyclodextrin (β-CD). The product was characterized by XRD, EDX, SEM, TEM, UV-vis and PL and BET techniques. It was found that β-CD plays an important role in the forming of twin-Christmas tree-like PbWO4 microcrystals. A five-step growth mechanism was proposed to explain the formation of such twin-Christmas tree-like structures. The photocatalytic performance of PbWO₄ microcrystals was evaluated by measuring the decomposition rate of methylene blue (MB) and malachite green (MG) solution under the UV irradiation, and the photocatalytic results indicated that as-prepared PbWO₄ microcrystals exhibit good and versatile photocatalytic activity as well as excellent recyclability.     

Kinetically controlled fabrication of C60 1-dimensional crystals

Considering the current application of fullerenes in the field of organic semiconductor devices, the highly crystalline or single crystal fullerene nanostructures with controlled shape and size contains some breakthrough for improved efficiency. Recently, fullerene 1-dimensional nanostructures, including nanowhiskers and nanotubes, become attractive kind of materials since the development of liquid-liquid interface precipitation (LLIP) process. The LLIP process has critical advantage; the fabrication of highly crystalline, even single crystal, fullerene 1-dimensional nanostructures with simple apparatus. However, the fabrication fullerene 1-dimensional structures by LLIP process requires long process time from one day to several days. In order to overcome this drawback, a modified process from conventional LLIP process is suggested. In the modified LLIP process, the nucleation step and growth step were divided. For the nucleation step, saturated fullerene solution is mixed with small amount of alcohols such as 2-propanol or ethanol. For the controlled growth step, the fullerenes in the nucleated solution are precipitated by addition of alcohol, which is injected to the bottom of the solution with controlled flow rate. In this modified process, the shape of the precipitated fullerene crystals is critically dependent on the nucleation steps and the size is dependent on the precipitation rate. By combination of proper nucleation step and growth rate, a well defined fullerene 1-dimensional structures, of 200-500 nm width and of hundreds microm length can be fabricated within two hours. In addition, by controlling injection rate and degree of supersaturation, several types of 1-dimensional structures including micro-tubes can be prepared and, by changing solvent and alcohol, several shape of C60 crystals including polyhedral particles and plates can be prepared.     

Graphene Emerges as a Versatile Template for Materials Preparation

Graphene and its derivatives are emerging as a class of novel but versatile templates for the controlled preparation and functionalization of materials. In this paper a conceptual review on graphene‐based templates is given, highlighting their versatile roles in materials preparation. Graphene is capable of acting as a low‐dimensional hard template, where its two‐dimensional morphology directs the formation of novel nanostructures. Graphene oxide and other functionalized graphenes are amphiphilic and may be seen as soft templates for formatting the growth or inducing the controlled assembly of nanostructures. In addition, nanospaces in restacked graphene can be used for confining the growth of sheet‐like nanostructures, and assemblies of interlinked graphenes can behave either as skeletons for the formation of composite materials or as sacrificial templates for novel materials with a controlled network structure. In summary, flexible graphene and its derivatives together with an increasing number of assembled structures show great potentials as templates for materials production. Many challenges remain, for example precise structural control of such novel templates and the removal of the non‐functional remaining templates.     

Controlled AFM manipulation of small nanoparticles and assembly of hybrid nanostructures

We demonstrate controlled manipulation of semiconductor and metallic nanoparticles (NPs) with 5-15 nm diameters and assemble these NPs into hybrid structures. The manipulation is accomplished under ambient environment using a commercial atomic force microscope (AFM). There are particular difficulties associated with manipulating NPs this small. In addition to spatial drift, the shape of an asymmetric AFM tip has to be taken into account in order to understand the intended and actual manipulation results. Furthermore, small NPs often attach to the tip via electrostatic interaction and modify the effective tip shape. We suggest a method for detaching the NPs by performing a pseudo-manipulation step. Finally, we show by example the ability to assemble these small NPs into prototypical hybrid nanostructures with well-defined composition and geometry.     

Effects of alkali on the morphologies and photoluminescence properties of ZnO nanostructures

ZnO nanostructures were fabricated in the ethanol solution of different alkali by a surfactant-free solvothermal method. ZnO nanoparticles, nanowires and nanorods were obtained depending on the experimental conditions. The corresponding growth mechanism follows a typical self-assembly growth process. The effects of various alkalis on the structures and morphologies of ZnO nanostructures were investigated. Moreover, the photoluminescence (PL) properties of the ZnO nanostructures were studied and exhibited some new features. It is found that the surface defects should be responsible for the green emission observed in the as-prepared ZnO nanostructures. The higher the specific surface area of ZnO nanostructures, the stronger the green emission and the weaker the ultraviolet (UV) emission are.     

Potential-induced copper periodic micro-/nanostructures by electrodeposition on silicon substrate

We demonstrate the fabrication of large scale nano-?and micropatterned copper periodic structures on a silicon substrate without imposed templates. In the electrodeposition process, we employ a periodic variation voltage in an ultrathin layer of concentrated CuSO(4) electrolyte. The pattern can be controlled by varying the frequency of the applied potential. We suggest that the observed periodic micro-/nanostructures are caused by the lag of the migrating ion concentration profile versus the applied voltage profile near the tip of the growth.     

Stability of DNA origami nanoarrays in cell lysate

Scaffolded DNA origami, a method to create self-assembled nanostructures with spatially addressable features, has recently been used to develop water-soluble molecular chips for label-free RNA detection, platforms for deterministic protein positioning, and single molecule reaction observatories. These applications highlight the possibility of exploiting the unique properties and biocompatibility of DNA nanostructures in live, cellular systems. Herein, we assembled several DNA origami nanostructures of differing shape, size and probes, and investigated their interaction with lysate obtained from various normal and cancerous cell lines. We separated and analyzed the origami-lysate mixtures using agarose gel electrophoresis and recovered the DNA structures for functional assay and subsequent microscopic examination. Our results demonstrate that DNA origami nanostructures are stable in cell lysate and can be easily separated from lysate mixtures, in contrast to natural, single- and double-stranded DNA. Atomic force microscope (AFM) and transmission electron microscope (TEM) images show that the DNA origami structures are fully intact after separation from cell lysates and hybridize to their targets, verifying the superior structural integrity and functionality of self-assembled DNA origami nanostructures relative to conventional oligonucleotides. The stability and functionality of DNA origami structures in cell lysate validate their use for biological applications, for example, as programmable molecular rafts or disease detection platforms.