This article provides a comprehensive review of current research activities that concentrate on one‐dimensional (1D) nanostructures—wires, rods, belts, and tubes—whose lateral dimensions fall anywhere in the range of 1 to 100 nm. We devote the most attention to 1D nanostructures that have been synthesized in relatively copious quantities using chemical methods. We begin this article with an overview of synthetic strategies that have been exploited to achieve 1D growth. We then elaborate on these approaches in the following four sections: i) anisotropic growth dictated by the crystallographic structure of a solid material; ii) anisotropic growth confined and directed by various templates; iii) anisotropic growth kinetically controlled by supersaturation or through the use of an appropriate capping reagent; and iv) new concepts not yet fully demonstrated, but with long‐term potential in generating 1D nanostructures. Following is a discussion of techniques for generating various types of important heterostructured nanowires. By the end of this article, we highlight a range of unique properties (e.g., thermal, mechanical, electronic, optoelectronic, optical, nonlinear optical, and field emission) associated with different types of 1D nanostructures. We also briefly discuss a number of methods potentially useful for assembling 1D nanostructures into functional devices based on crossbar junctions, and complex architectures such as 2D and 3D periodic lattices. We conclude this review with personal perspectives on the directions towards which future research on this new class of nanostructured materials might be directed.

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This article presents an overview of current research activities that center on monodispersed colloidal spheres whose diameter falls anywhere in the range of 10 nm to 1 mm. It is organized into three parts: The first part briefly discusses several useful methods that have been developed for producing monodispersed colloidal spheres with tightly controlled sizes and well-defined properties (both surface and bulk). The second part surveys some techniques that have been demonstrated for organizing these colloidal spheres into two-and three-dimensionally ordered lattices. The third part highlights a number of unique applications of these crystalline assemblies, such as their uses as photonic bandgap (PBG) crystals; as removable templates to fabricate macroporous materials with highly ordered and three-dimensionally interconnected porous structures; as physical masks in lithographic patterning; and as diffractive elements to fabricate new types of optical sensors. Finally, we conclude with some personal perspectives on the directions towards which future research in this area might be directed.

This paper describes a soft, solution-phase approach to the large-scale synthesis of uniform nanowires of bicrystalline silver whose lateral dimensions could be controlled in the range of 30−40 nm, and lengths up to ∼50 µm. The first step of this procedure involved the formation of platinum nanoparticles by reducing PtCl 2 with ethylene glycol heated to ∼160°C. Due to their close match in crystal structure and lattice constants, these platinum nanoparticles could serve as seeds for the heterogeneous nucleation and growth of silver that was produced in the solution via the reduction of AgNO 3 with ethylene glycol. When surfactants such as poly(vinyl pyrrolidone) (PVP) were present in this solution, the silver could be directed to grow into uniform nanowires with aspect ratios as high as ∼1000. Measurements of transport property at room temperature indicated that these nanowires were electrically continuous with a conductivity of approximately 0.8 × 10 5 S/cm.One-dimensional (1D) nanostructures of metals play an important role as both interconnects and active components in fabricating nanoscale electronic devices.1 They also provide an ideal model system to experimentally investigate physical phenomena such as quantized conductance and localization effects. 2 Silver nanowires with well-defined dimensions are particularly interesting to synthesize and study because bulk silver exhibits the highest electrical (or thermal) conductivity among all metals. Silver has also been used in a rich variety of commercial applications, and the performance of silver in these applications could be potentially enhanced by processing silver into 1D nanostructures with well-controlled dimensions and aspect ratios. For instance, the loading of silver in a polymeric composite could be significantly reduced when nanoparticles of silver are replaced by nanowires having higher aspect ratios. 3 A number of chemical approaches have been actively explored to process silver into 1D nanostructures. For example, silver nanowires have been synthesized by reducing AgNO 3 with a developer in the presence of AgBr nanocrystallites, 4 or by arc discharging between two silver electrodes immersed in an aqueous NaNO 3 solution. 5 Silver nanorods have been produced by irradiating an aqueous AgNO 3 solution with ultraviolet light in the presence of poly-(vinyl alcohol). 6 The final products of all these methods are, however, characterized by problems such as low yields, irregular morphologies, polycrystallinity, and low aspect ratios. In contrast, the template-directed synthesis offers a better controlled route to 1D silver nanostructures. 14 Here we wish to report a soft (with temperatures <200°C), solution-phase approach that allows for the production of bicrystalline nanowires of silver with uniform diameters and in bulk quantities.The first step of our synthesis involved the formation of Pt nanoparticles by reducing PtCl 2 with ethylene glycol refluxed at ∼160°C.15 In this so-called polyol process, ethylene glycol served as both solvent and re...

This paper describes a strategy that combines physical templating and capillary forces to assemble monodispersed spherical colloids into uniform aggregates with well-controlled sizes, shapes, and structures. When an aqueous dispersion of colloidal particles was allowed to dewet from a solid surface that had been patterned with appropriate relief structures, the particles were trapped by the recessed regions and assembled into aggregates whose structures were determined by the geometric confinement provided by the templates. We have demonstrated the capability and feasibility of this approach by assembling polystyrene beads and silica colloids (> or =150 nm in diameter) into complex aggregates that include polygonal or polyhedral clusters, linear or zigzag chains, and circular rings. We have also been able to generate hybrid aggregates in the shape of HF or H2O molecules that are composed of polymer beads having different diameters, polymer beads labeled with different organic dyes, and a combination of polymeric and inorganic beads. These colloidal aggregates can serve as a useful model system to investigate the hydrodynamic and optical scattering properties of colloidal particles having nonspherical morphologies. They should also find use as the building blocks to generate hierarchically self-assembled systems that may exhibit interesting properties highly valuable to areas ranging from photonics to condensed matter physics.

Inorganic chemistryInorganic chemistry Z 0100 One-Dimensional Nanostructures: Synthesis, Characterization, and Applications -[238 refs.]. -(XIA*, Y.; YANG*, P.; SUN, Y.; WU, Y.; MAYERS, B.; GATES, B.; YIN, Y.; KIM, F.; YAN, H.; Adv. Mater. (Weinheim, Ger.) 15 (2003) 5, 353-389; Dep. Chem., Univ. Wash., Seattle, WA 98195, USA; Eng.) -Schramke 22-236

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This article describes a soft, solution‐phase approach to the large‐scale synthesis of uniform nanowires of trigonal selenium (t‐Se) with lateral dimensions controllable in the range of ∼10 to ∼800 nm, and lengths up to hundreds of micrometers. These highly anisotropic, one‐dimensional (1D) nanostructures were directly nucleated and grown from aqueous solutions without the help of any physical templates, such as channel‐like structures etched in porous materials, or scaffolds assembled from surfactants or block‐copolymers. The 1D morphology of the product was solely determined by the linear characteristics of the building blocks—i.e., the extended, helical chains of atoms contained in the crystalline lattice of t‐Se. A blue shift was observed for the bandgap and interchain transition of these nanowires when their diameters were reduced from ∼32 to ∼10 nm. The photoconductivity of individual nanowires has also been measured using the four‐probe method, and an increase by ∼150 times was found when the sample was taken from the dark and exposed with ∼3 μW μm–2 tungsten light. Since no exotic seeds were involved in this synthetic process, every nanowire (including both ends) should be made entirely of pure selenium, crystallized in the trigonal phase. We believe the protocol described here can be scaled up for the high‐volume production of t‐Se nanowires that can subsequently serve as the physical or chemical templates to generate 1D nanostructures of various kinds of functional materials. The synthetic strategy itself, may also be extendable to other systems containing chain‐like building blocks. The single crystallinity and absence of kinks and other related defects in these nanowires should make them particularly useful in fabricating nanoscale electronic, optical, or mechanical nanodevices.