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Showing papers in "Advanced Materials in 2003"


Journal ArticleDOI
TL;DR: A comprehensive review of 1D nanostructures can be found in this article, where the authors provide a comprehensive overview of current research activities that concentrate on one-dimensional (1D) nanostructure (wires, rods, belts and tubes).
Abstract: 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.

8,259 citations



Journal ArticleDOI
TL;DR: In this article, a template-less and surfactant-free aqueous method is proposed to generate metal oxide thin films with controlled complexity. But the synthesis involves a templateless and a surfactent-free approach, which enables the generation of, at large-scale, low-cost, and moderate temperatures, advanced metal oxide particle-to-particle thin films.
Abstract: A novel approach to the rational fabrication of smart and functional metal oxide particulate thin films and coatings is demonstrated on the growth of ZnO nanowires and oriented nanorod arrays The synthesis involves a template-less and surfactant-free aqueous method, which enables the generation of, at large-scale, low-cost, and moderate temperatures, advanced metal oxide thin films with controlled complexity The strategy consists of monitoring of the nucleation, growth, and aging processes by means of chemical and electrostatic control of the interfacial free energy It enables the control of the size of nano-, meso-, and microcrystallites, their surface morphology, orientations onto various substrates, and crystal structure

2,619 citations



Journal ArticleDOI
TL;DR: A general view of the underlying self-assembly mechanisms leading to vesicles and the control of size, shape, and other vesicular properties by physicochemical means is presented in this paper.
Abstract: This Progress Report describes the latest advances in vesicles and liposomes. Recent work on the self-assembly of complex polymer systems shows that the formation of polymer vesicles or closed hull structures is archetypal, leading to fascinating new possibilities and applications in materials science. A general view of the underlying self-assembly mechanisms leading to vesicles and the control of size, shape, and other vesicular properties by physicochemical means is presented, as background. This is followed by an overview of the recently described new classes of polymer and supramolecular tectons that make vesicle formation a more general phenomenon going beyond just lipids. Finally, the potential applications of vesicles, including non-lipid vesicles, are outlined.

1,278 citations


Journal ArticleDOI
TL;DR: In this paper, the authors review the motivation for using conjugated polymers, the types of devices that have been fabricated, and some of the biomedical applications that are being developed.
Abstract: Conjugated polymers are electroactive and have found applications as artificial muscles. Actuators that have been developed over the last decade have now reached the early stages of commercialization, particularly for use in biomedical devices. This article reviews the motivation for using this class of actuator, the types of devices that have been fabricated, and some of the biomedical applications that are being developed. Recommendations are presented for future work on understanding the actuation mechanisms, on actuator design, and on the measurement of metrics.

1,149 citations


Journal ArticleDOI
TL;DR: Amorphous calcium carbonate (ACC) in its pure form is highly unstable, yet some organisms produce stable ACC, and cases are known in which ACC functions as a transient precursor of more stable crystalline aragonite or calcite.
Abstract: Amorphous calcium carbonate (ACC) in its pure form is highly unstable, yet some organisms produce stable ACC, and cases are known in which ACC functions as a transient precursor of more stable crystalline aragonite or calcite. Studies of biogenic ACC show that there are significant structural differences, including the observation that the stable forms are hydrated whereas the transient forms are not. The many different ways in which ACC can be formed in vitro shed light on the possible mechanisms involved in stabilization, destabilization, and transformation of ACC into crystalline forms of calcium carbonate. We show here that ACC is a fascinating form of calcium carbonate that may well be of much interest to materials science and biomineralization.

1,144 citations




Journal ArticleDOI
TL;DR: In this article, a replacement reaction between the surface of a nanoscale template and the solution of an appropriate salt precursor is used to synthesize metal nanostructures with well-defined hollow interiors.
Abstract: We have recently developed a simple and versatile route to the large-scale synthesis of metal nanostructures with well-defined hollow interiors. The key step of this process involves a replacement reaction between the surface of a nanoscale template and the solution of an appropriate salt precursor. The capability and feasibility of this method have been demonstrated by preparing hollow nanostructures of gold with a range of different morphologies (e.g., triangular rings, prism-shaped boxes, cubic boxes, spherical capsules, and tubes). In addition to gold, this method also worked well for other metals such as platinum and palladium (see Figure for an SEM image of Pd nanotubes). These metal nanostructures with hollow interiors are useful as fillers for generation of ultralight composites; they are also interesting for new types of applications that include use as components for highly sensitive colorimetric sensors and as effective, recoverable catalysts.

947 citations


Journal ArticleDOI
TL;DR: In this paper, the authors show a clear correlation between the field effect mobility of RR P3HT and its molecular weight (MW) with mobility values increasing from 1.7 to 9.4 cm 2 V ± 1 s ± 1.5 kD.
Abstract: Semiconducting conjugated polymers are being developed for light-emitting diodes, [1,2] photovoltaic cells, [3,4] and thin-film transistors [5±7] because they can readily be deposited from solution onto almost any substrate. Clearly, it is important to maximize the charge carrier mobilities for all of these applications , especially for transistors and photovoltaic cells. Most conjugated polymers have hole mobilities in the range of 10 ±7 ±10 ±5 cm 2 V ±1 s ±1. The electron mobility is usually even lower because of traps with energies slightly below the lowest unoccupied molecular orbital (LUMO) level of the polymer. Poly(9,9¢-dioctylfluorene-co-2,2¢-bithiophene) (F8T2) has a higher hole mobility (as high as 10 ±2 cm 2 V ±1 s ±1) because of its liquid crystalline character. [8,9] Regioregular poly(3-hexyl-thiophene) (RR P3HT) has an even higher mobility (with quoted values as high as 10 ±1 cm 2 V ±1 s ±1) [10±12] because the regular arrangement of its side chains allows efficient p-stacking of the conjugated backbones. [11] Despite the achievements that have been made towards improving the mobility of conjugated polymers, much is still not known about how charge moves through the films and how the chain packing can be optimized to obtain even higher mobilities. Reported values for the mobilities in RR P3HT vary by orders of magnitude. [10±12] We now show a clear correlation between the field-effect mobility of RR P3HT and its molecular weight (MW) with mobility values increasing from 1.7 ” 10 ±6 to 9.4 ” 10 ±3 cm 2 V ±1 s ±1 as the MW is increased from 3.2 to 36.5 kD. These variations in MW are also accompanied by significant changes in film morphology. These observations probably explain why the mobility values obtained in different labs vary so widely and suggest that optimizing the MW of conjugated polymers could lead to significant improvements in device performance. Our studies were performed both on batches of RR P3HT that were synthesized in our laboratory by a modified McCul-lough route [13±15] and also with a commercial sample purchased from Aldrich, which was said to be prepared through the Rieke route. [16] MW control in our samples prepared by the modified McCullough route was achieved by adjusting the polymerization time. Since the commercial sample had a large polydispersity, we separated it into several low polydispersity fractions with different MWs through a series of Soxhlet extractions with solvents of increasing solvency (hexane, dichloromethane, and chloroform). …

Journal ArticleDOI
TL;DR: A brief overview on the preparation and properties of resorcinol-formaldehyde organic and carbon gels reveals very interesting features about their structural and performance characteristics as mentioned in this paper, which leads to a remarkable potential for designing and tailoring these materials to fit specific applications.
Abstract: A brief overview on the preparation and properties of resorcinol–formaldehyde organic and carbon gels reveals very interesting features about their structural and performance characteristics. The resulting nanostructure was very sensitive to the various synthesis and processing conditions. This leads to a remarkable potential for designing and tailoring these materials to fit specific applications. Based on step-by-step comparisons of the published studies, approximate generalizations on the specific roles the synthesis and processing conditions play on the final properties are provided. Overall, resorcinol–formaldehyde organic gels undergo two main stages during synthesis. The first stage is associated with the preparation of the sol mixture, and the subsequent gelation and curing of the gel. The second stage is associated with the drying of the wet gel. The most important factors that affect the properties of the organic gel during the first stage are the catalyst concentration, the initial gel pH, and the concentration of the solids in the sol. The most important factors that affect the properties of the organic gel during the second stage are the drying procedure (e.g., super- or subcritical drying), and the difference between the surface tensions of the solvent before and after drying. The corresponding resorcinol–formaldehyde carbon gels are produced from the organic gels during a third stage, which is associated with carbonization or activation. Depending on the conditions, carbonization and activation both impact the structural and performance characteristics significantly.

Journal ArticleDOI
TL;DR: In this article, a general perspective is presented on the state of the art in photonic crystals (PCs) providing a broad audience-oriented description of fundamentals and properties, as well as a broad overview of photonic bandgap (PBG) materials.
Abstract: Photonics, the technology of photons (as electronics is the technology of electrons), promises to be the new century's driving force in the advancement of, mainly but not only, information technology, such as communications and computing. This technology was initiated with the advent of lasers and optical fibers that, for various reasons, embody the best choice of source and channel of the information carrier: the photon. If the parallel with electronics is to be further pursued, one soon realizes that many more components are needed not only in the transport section of the technology but also, and principally, in the logic section: signal processing. An answer is promised to many of these demands by the potentiality of the new photonics era: photonic bandgap (PBG) materials, otherwise known as photonic crystals (PCs). In the present review a general perspective is presented on the state of the art in PC technology providing a broad audience-oriented description of fundamentals and properties.

Journal ArticleDOI
TL;DR: An overview of the electrochemistry of poly(3,4-alkylenedioxythiophene)s (PXDOTs) is presented in this article.
Abstract: An overview of the electrochemistry of poly(3,4-alkylenedioxythiophene)s (PXDOTs) is presented. As a class of conducting and electroactive polymers that can exhibit high and quite stable conductivities, a high degree of optical transparency as a conductor, and the ability to be rapidly switched between conducting doped and insulating neutral states, PXDOTs have attracted attention across academia and industry. Numerous fundamental aspects are addressed here in detail, ranging from the electrochemical synthesis of PXDOTs, a variety of in-situ characterization techniques, the broad array of properties accessible, and morphological aspects. Finally, two electrochemically-driven applications, specifically electrochromism and chemical sensors of PXDOTs are discussed.

Journal ArticleDOI
TL;DR: Functional hybrids are nanocomporie umterials lying at the interfoce of organic and inorganic realnts, whose high sersatility offers a wide range of possibilities to eloborate tailor-made materials in terms of chemical and physical properties as discussed by the authors.
Abstract: Functional hybrids are nanocomporie umterials lying at the interfoce of organic and inorganic realnts, whose high sersatility offers a wide range of possibilities to eloborate tailor-made materials in terms of chemical and physical properties. Because they present several advantogys for derigning materialy for opticol applications (versatile and relativrly facite chemistry, easy shaping and patierning, materials having good mechanical integrity and cacrdlent optical quality), numerous silica or/and silaxane tussed hytirid orgunic-inorganic materiois imve been developed in the past few years. The men striking examples of fonctional hybrids exhibiting emission properties (solid-state dye lasers rare-carth doped hybridslads, electronuminescent devices), absorption properties (photockiomic), nonlinear optical (NLO) porperties (second-order NLO properties, phoiochemical hole burning (PHB), photorefractivity), and sensing are sunimorized in this review.

Journal ArticleDOI
TL;DR: In this article, experimental results on low bias, room-temperature currents through orgnaic molecules obtained in different electrode-molecule-electrode test-beds are discussed.
Abstract: We compile, compare, and discuss experimental results on low bias, room-temperature currents through orgnaic molecules obtained in different electrode-molecule-electrode test-beds. Currents are normalized to single-molecule values for comparison and are quoted at 0.2 and 0.5 V junction bias. Emphasis is on currents through saturated alkane chains where many comparable measurements have been reported, but comparison to conjugated molecules is also made. We discuss factors that affect the magnitude of the measured current, such as tunneling attenuation factor, molecular energy gap and conformation, molecule/electrode contacts, and electrode material.



Journal ArticleDOI
TL;DR: In this paper, the alternating copolymer with a C-60 derivative (PCBM) was used for solar cells with a power conversion efficiency of 2.2 % under simulated solar light.
Abstract: Solar cells prepared using the alternating copolymer shown in the Figure blended with a C-60 derivative (PCBM) are demonstrated to have a high performance, with a power conversion efficiency of 2.2 % under simulated solar light. The molecular weight of the polymer is low due to limited solubility, and films of the polymer exhibit red-shifted absorption.

Journal ArticleDOI
TL;DR: In this paper, the authors reviewed ionic self-assembly, i.e., the coupling of structurally different buildings blocks by electrostatic interactions, a powerful tool to create new material nanostructures and chemical objects.
Abstract: The technique of ionic self-assembly, i.e., the coupling of structurally different buildings blocks by electrostatic interactions, a powerful tool to create new material nanostructures and chemical objects, is reviewed. The excellent availability of the starting products (charged tectonic units) and the simplicity of synthesis, by neat addition and cooperative stoichiometric precipitation with high purity, allow the recombinatorial synthesis of a whole range of functional materials and hybrids with interesting and versatile functions. Diverse combinations between polyelectrolytes, surfactants, clusters, and extended rigid organic scaffolds are discussed in detail, and the underlying principles of nanostructure formation are illustrated.

Journal ArticleDOI
TL;DR: In this paper, the authors highlight developments in the fields of microporous and mesoporous materials that were published mostly during the year 2002, and illustrate new zeolite structures, porous coordination materials, mesopore solids with new compositions, controlled morphologies, and increased hydrothermal and thermal stabilities.
Abstract: This report highlights developments in the fields of microporous and mesoporous materials that were published mostly during the year 2002. Selected examples are provided to illustrate new zeolite structures, porous coordination materials, mesoporous solids with new compositions, controlled morphologies, and increased hydrothermal and thermal stabilities, as well as porous solids with tunable pore openings or other structural features that can be dynamically modified. A number of applications are discussed, including stabilization of reactive guests, separations, electronic materials, and sensors.



Journal ArticleDOI
TL;DR: In this article, the authors present a concise, although admittedly non-exhaustive, but hopefully didactic review and discussion of some of the central and basic concepts related to the energetics of surfaces and interfaces of solids.
Abstract: We present a concise, although admittedly non-exhaustive, but hopefully didactic review and discussion of some of the central and basic concepts related to the energetics of surfaces and interfaces of solids. This is of particular importance for surfaces and interfaces that involve organic molecules and molecular films. It attempts to pull together different views and terminologies used in the solid state, electrochemistry, and electronic device communities, regarding key concepts of local and absolute vacuum level, surface dipole, work function, electron affinity, and ionization energy. Finally, it describes how standard techniques like photoemission spectroscopy can be used to measure such quantities.

Journal ArticleDOI
TL;DR: The shape of CdSe and other semiconductor nanocrystals is controlled, producing dots, rods, rice-shaped particles, tetrapods, or other elongated shapes as discussed by the authors.
Abstract: The shape of CdSe and other semiconductor nanocrystals is controlled, producing dots, rods, rice-shaped particles, tetrapods, or other elongated shapes. Monomer concentration in the growth solution is the determining factor in shape-control and shape-evolution. The elongated shapes could be transformed into more spherical shapes if the monomer concentration in the solution was lowered to a certain level, and spherically shaped nanocrystals could grow to elongated shapes by simply increasing the monomer concentration. The precursors are stable, inexpensive, and relatively non-toxic, and therefore good choices for the growth of nearly monodisperse and shape-controlled nanocrystals.


Journal ArticleDOI
TL;DR: In this paper, the self-assembling properties and supramolecular structures of liquid crystals can be tailored to improve the electroluminescence properties of organic light emitting devices.
Abstract: Ordered molecular materials are increasingly used in active electronic and photonic organic devices. In this progress report we discuss whether the self-assembling properties and supramolecular structures of liquid crystals can be tailored to improve such devices. Recent developments in charge-transporting and luminescen(t liquid crystals are discussed in the context of material requirements for organic llight-emitting devices, photovoltaics, and thin film transistors. We identify high carrier mobility, polarized emission, and enhanced output-coupling as the key advantages of nematic and smectic liquid crystals for electroluminescence. The formation of anisotropic polymer networks gives the added benefits of multilayer capability and photoparternability. The anisotropic transport and high carrier mobilities of columnar liquid crystals make them promising candidates for photovoltaics and transistors. We also outline some of the issues in material design and processing that these applications demand. The photonic properties of chiral liquid crystals and their use as mirror-less lasers are also discussed.

Journal ArticleDOI
TL;DR: In this paper, the oxide-assisted growth (OAG) technique was proposed for the growth of nanostructured materials. But the OAG technique is not suitable for high-purity silicon nanowires.
Abstract: In this contribution, we outline oxide-assisted growth (OAG) (distinct from the conventional metal-catalytic vapor-liquid-solid (VLS) process) for the growth of nanostructured materials. This synthesis technique, in whichoxides instead of metals play an important role in inducing the nucleation and growth of nanowires, is capable of producing large quantities of high-purity silicon nanowires with a preferential growth direction, uniform size, and long length, without the need for a metal catalyst. The OAG 1D nanomaterials synthesis is complementary to, and coexistent with, the conventional metal-catalyst VLS approach, and can be utilized to produce nanowires from a host of materials other than Si including Ge nanowires, carbon nanowires, silicon and SnO 2 nanoribbons, and Group III-V and II-VI compound semiconductor nanowires.

Journal ArticleDOI
TL;DR: In this article, it is shown that nanobelts, nanowires, and nanodiskettes of materials such as zinc oxide, gallium oxide, silica, and tin oxide can be fabricated using a vapor phase evaporation method.
Abstract: novel nanostructures of semiconducting oxides are reviewed here It is shown that nanobelts, nanowires, and nanodiskettes of materials such as zinc oxide, gallium oxide, silica, and tin oxide can be fabricated using a vapor-phase evaporation method Two applications of these materials - in field effect transistors and as gas sensors - are highlighted

Journal ArticleDOI
TL;DR: In this paper, the shape control of colloidal nanocrystals including one-dimensional (1D) nanorods remains a key issue in the bottom-up approach of nanoscience.
Abstract: The systematic shape control of colloidal nanocrystals including one-dimensional (1D) nanorods remains a key issue in the “bottom–up” approach of nanoscience. Here, we examine the anisotropic structural evolution of various semiconductor nanocrystals and systematically elucidate the key growth parameters for their shape control. The crystalline phase of nucleating seeds and kinetic growth regimes controlled by changing growth parameters are crucial for the determination of the 1D nanocrystal geometry.