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Showing papers in "Nature Materials in 2003"


Journal ArticleDOI
TL;DR: It is demonstrated that DNA-coated carbon nanotubes can be separated into fractions with different electronic structures by ion-exchange chromatography, and opens the door to carbon-nanotube-based applications in biotechnology.
Abstract: Carbon nanotubes are man-made one-dimensional carbon crystals with different diameters and chiralities. Owing to their superb mechanical and electrical properties, many potential applications have been proposed for them. However, polydispersity and poor solubility in both aqueous and non-aqueous solution impose a considerable challenge for their separation and assembly, which is required for many applications. Here we report our finding of DNA-assisted dispersion and separation of carbon nanotubes. Bundled single-walled carbon nanotubes are effectively dispersed in water by their sonication in the presence of single-stranded DNA (ssDNA). Optical absorption and fluorescence spectroscopy and atomic force microscopy measurements provide evidence for individually dispersed carbon nanotubes. Molecular modelling suggests that ssDNA can bind to carbon nanotubes through pi-stacking, resulting in helical wrapping to the surface. The binding free energy of ssDNA to carbon nanotubes rivals that of two nanotubes for each other. We also demonstrate that DNA-coated carbon nanotubes can be separated into fractions with different electronic structures by ion-exchange chromatography. This finding links one of the central molecules in biology to a technologically very important nanomaterial, and opens the door to carbon-nanotube-based applications in biotechnology.

2,620 citations


Journal ArticleDOI
TL;DR: Observations of electromagnetic energy transport from a localized subwavelength source to a localized detector over distances of about 0.5 μm in plasmon waveguides consisting of closely spaced silver rods are presented.
Abstract: Achieving control of light-material interactions for photonic device applications at nanoscale dimensions will require structures that guide electromagnetic energy with a lateral mode confinement below the diffraction limit of light. This cannot be achieved by using conventional waveguides or photonic crystals. It has been suggested that electromagnetic energy can be guided below the diffraction limit along chains of closely spaced metal nanoparticles that convert the optical mode into non-radiating surface plasmons. A variety of methods such as electron beam lithography and self-assembly have been used to construct metal nanoparticle plasmon waveguides. However, all investigations of the optical properties of these waveguides have so far been confined to collective excitations and direct experimental evidence for energy transport along plasmon waveguides has proved elusive. Here we present observations of electromagnetic energy transport from a localized subwavelength source to a localized detector over distances of about 0.5 μm in plasmon waveguides consisting of closely spaced silver rods. The waveguides are excited by the tip of a near-field scanning optical microscope, and energy transport is probed by using fluorescent nanospheres.

2,305 citations


Journal ArticleDOI
TL;DR: Key advances in the understanding and fabrication of surfaces with controlled wetting properties are about to make the dream of a contamination-free (or 'no-clean') surface come true.
Abstract: In the 19th century, Oscar Wilde stated “We live, I regret to say, in an age of surfaces”. Today, we do so even more, and we do not regret it: key advances in the understanding and fabrication of surfaces with controlled wetting properties are about to make the dream of a contamination-free (or 'no-clean') surface come true. Two routes to self-cleaning are emerging, which work by the removal of dirt by either film or droplet flow. Although a detailed understanding of the mechanisms underlying the behaviour of liquids on such surfaces is still a basic research topic, the first commercial products in the household-commodity sector and for applications in biotechnology are coming within reach of the marketplace. This progress report describes the current status of understanding of the underlying mechanisms, the concepts for making such surfaces, and some of their first applications.

2,114 citations


Journal ArticleDOI
TL;DR: The first observations of ferromagnetism above room temperature for dilute (<4 at%) Mn-doped ZnO semiconductors are reported, promising new spintronic devices as well as magneto-optic components.
Abstract: The search for ferromagnetism above room temperature in dilute magnetic semiconductors has been intense in recent years. We report the first observations of ferromagnetism above room temperature for dilute ( 700 °C) methods were used, samples were found to exhibit clustering and were not ferromagnetic at room temperature. This capability to fabricate ferromagnetic Mn-doped ZnO semiconductors promises new spintronic devices as well as magneto-optic components.

1,652 citations


Journal ArticleDOI
TL;DR: The design, formation and testing of QD–protein assemblies that function as chemical sensors that overcomes inherent QD donor–acceptor distance limitations are reported.
Abstract: The potential of luminescent semiconductor quantum dots (QDs) to enable development of hybrid inorganic-bioreceptor sensing materials has remained largely unrealized. We report the design, formation and testing of QD‐protein assemblies that function as chemical sensors. In these assemblies, multiple copies of Escherichia coli maltose-binding protein (MBP) coordinate to each QD by a C-terminal oligohistidine segment and function as sugar receptors. Sensors are selfassembled in solution in a controllable manner. In one configuration, a β-cyclodextrin-QSY9 dark quencher conjugate bound in the MBP saccharide binding site results in fluorescence resonance energy-transfer (FRET) quenching of QD photoluminescence. Added maltose displaces the β-cyclodextrin-QSY9, and QD photoluminescence increases in a systematic manner. A second maltose sensor assembly consists of QDs coupled with Cy3-labelled MBP bound to β-cyclodextrin-Cy3.5. In this case, the QD donor drives sensor function through a two-step FRET mechanism that overcomes inherent QD donor‐acceptor distance limitations. Quantum dot‐biomolecule assemblies constructed using these methods may facilitate development of new hybrid sensing materials.

1,600 citations


Journal ArticleDOI
TL;DR: A DSC with unprecedented stable performance under both thermal stress and soaking with light, matching the durability criteria applied to silicon solar cells for outdoor applications is shown, fostering widespread practical application of dye-sensitized solar cells.
Abstract: Dye-sensitized nanocrystalline solar cells (DSC) have received considerable attention as a cost-effective alternative to conventional solar cells. One of the main factors that has hampered widespread practical use of DSC is the poor thermostability encountered so far with these devices. Here we show a DSC with unprecedented stable performance under both thermal stress and soaking with light, matching the durability criteria applied to silicon solar cells for outdoor applications. The cell uses the amphiphilic ruthenium sensitizer cis-RuLL'(SCN)(2) (L = 4,4'-dicarboxylic acid-2,2'-bipyridine, L' = 4,4'-dinonyl-2,2'-bipyridine) in conjunction with a quasi-solid-state polymer gel electrolyte, reaching an efficiency of >6% in full sunlight (air mass 1.5, 100 mW cm(-2)). A convenient and versatile new route is reported for the synthesis of the heteroleptic ruthenium complex, which plays a key role in achieving the high-temperature stability. Ultramicroelectrode voltammetric measurements show that the triiodide/iodide couple can perform charge transport freely in the polymer gel. The cell sustained heating for 1,000 h at 80 degrees C, maintaining 94% of its initial performance. The device also showed excellent stability under light soaking at 55 degrees C for 1,000 h in a solar simulator (100 mW cm(-2)) equipped with a ultraviolet filter. The present findings should foster widespread practical application of dye-sensitized solar cells.

1,541 citations


Journal ArticleDOI
TL;DR: This review discusses combinatorial biological protocols, that is, bacterial cell surface and phage-display technologies, in the selection of short sequences that have affinity to (noble) metals, semiconducting oxides and other technological compounds.
Abstract: Proteins, through their unique and specific interactions with other macromolecules and inorganics, control structures and functions of all biological hard and soft tissues in organisms. Molecular biomimetics is an emerging field in which hybrid technologies are developed by using the tools of molecular biology and nanotechnology. Taking lessons from biology, polypeptides can now be genetically engineered to specifically bind to selected inorganic compounds for applications in nano- and biotechnology. This review discusses combinatorial biological protocols, that is, bacterial cell surface and phage-display technologies, in the selection of short sequences that have affinity to (noble) metals, semiconducting oxides and other technological compounds. These genetically engineered proteins for inorganics (GEPIs) can be used in the assembly of functional nanostructures. Based on the three fundamental principles of molecular recognition, self-assembly and DNA manipulation, we highlight successful uses of GEPI in nanotechnology.

1,533 citations


Journal ArticleDOI
TL;DR: It is demonstrated that polytypism, or the existence of two or more crystal structures in different domains of the same crystal, coupled with the manipulation of surface energy at the nanoscale, can be exploited to produce branched inorganic nanostructures controllably.
Abstract: Nanoscale materials are currently being exploited as active components in a wide range of technological applications in various fields, such as composite materials1,2, chemical sensing3, biomedicine4,5,6, optoelectronics7,8,9 and nanoelectronics10,11,12. Colloidal nanocrystals are promising candidates in these fields, due to their ease of fabrication and processibility. Even more applications and new functional materials might emerge if nanocrystals could be synthesized in shapes of higher complexity than the ones produced by current methods (spheres, rods, discs)13,14,15,16,17,18,19. Here, we demonstrate that polytypism, or the existence of two or more crystal structures in different domains of the same crystal, coupled with the manipulation of surface energy at the nanoscale, can be exploited to produce branched inorganic nanostructures controllably. For the case of CdTe, we designed a high yield, reproducible synthesis of soluble, tetrapod-shaped nanocrystals through which we can independently control the width and length of the four arms.

1,407 citations


Journal ArticleDOI
TL;DR: This work reports 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.
Abstract: 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.

1,396 citations


Journal ArticleDOI
TL;DR: A new technique for fabricating silicon oxide nanopores with single-nanometre precision and direct visual feedback, using state-of-the-art silicon technology and transmission electron microscopy is reported.
Abstract: Single nanometre-sized pores (nanopores) embedded in an insulating membrane are an exciting new class of nanosensors for rapid electrical detection and characterization of biomolecules. Notable examples include α-hemolysin protein nanopores in lipid membranes1,2 and solid-state nanopores3 in Si3N4. Here we report a new technique for fabricating silicon oxide nanopores with single-nanometre precision and direct visual feedback, using state-of-the-art silicon technology and transmission electron microscopy. First, a pore of 20 nm is opened in a silicon membrane by using electron-beam lithography and anisotropic etching. After thermal oxidation, the pore can be reduced to a single-nanometre when it is exposed to a high-energy electron beam. This fluidizes the silicon oxide leading to a shrinking of the small hole due to surface tension. When the electron beam is switched off, the material quenches and retains its shape. This technique dramatically increases the level of control in the fabrication of a wide range of nanodevices.

1,375 citations


Journal ArticleDOI
TL;DR: It is demonstrated that both structural features of nacre and bones can be reproduced by sequential deposition of polyelectrolytes and clays, and their nanoscale nature enables elucidation of molecular processes occurring under stress.
Abstract: Finding a synthetic pathway to artificial analogs of nacre and bones represents a fundamental milestone in the development of composite materials. The ordered brick-and-mortar arrangement of organic and inorganic layers is believed to be the most essential strength- and toughness-determining structural feature of nacre. It has also been found that the ionic crosslinking of tightly folded macromolecules is equally important. Here, we demonstrate that both structural features can be reproduced by sequential deposition of polyelectrolytes and clays. This simple process results in a nanoscale version of nacre with alternating organic and inorganic layers. The macromolecular folding effect reveals itself in the unique saw-tooth pattern of differential stretching curves attributed to the gradual breakage of ionic crosslinks in polyelectrolyte chains. The tensile strength of the prepared multilayers approached that of nacre, whereas their ultimate Young modulus was similar to that of lamellar bones. Structural and functional resemblance makes clay– polyelectrolyte multilayers a close replica of natural biocomposites. Their nanoscale nature enables elucidation of molecular processes occurring under stress.

Journal ArticleDOI
TL;DR: The aim here is to discuss the usability of conducting polymers in both types of electronic applications in light of these two parameters: conductivity and work function.
Abstract: Conducting organic polymers have found two main kinds of application in electronics so far: as materials for construction of various devices and as selective layers in chemical sensors. In either case, interaction with ambient gases is critical. It may compromise the performance of a device based on conducting polymers, whereas it is beneficial in a sensor. Conductivity has been the primary property of interest. Work function--related to conductivity, but in principle a different property--has received only scant attention. Our aim here is to discuss the usability of conducting polymers in both types of electronic applications in light of these two parameters.

Journal ArticleDOI
TL;DR: A prototype of such 'gecko tape' is reported on, made by microfabrication of dense arrays of flexible plastic pillars, the geometry of which is optimized to ensure their collective adhesion.
Abstract: The amazing climbing ability of geckos has attracted the interest of philosophers and scientists alike for centuries1,2,3 However, only in the past few years2,3 has progress been made in understanding the mechanism behind this ability, which relies on submicrometre keratin hairs covering the soles of geckos Each hair produces a miniscule force ≈10−7 N (due to van der Waals and/or capillary interactions) but millions of hairs acting together create a formidable adhesion of ≈10 N cm−2: sufficient to keep geckos firmly on their feet, even when upside down on a glass ceiling It is very tempting3 to create a new type of adhesive by mimicking the gecko mechanism Here we report on a prototype of such 'gecko tape' made by microfabrication of dense arrays of flexible plastic pillars, the geometry of which is optimized to ensure their collective adhesion Our approach shows a way to manufacture self-cleaning, re-attachable dry adhesives, although problems related to their durability and mass production are yet to be resolved

Journal ArticleDOI
TL;DR: These findings indicate that heat transport in a nanotube composite material will be limited by the exceptionally small interface thermal conductance and that the thermal conductivity of the composite will be much lower than the value estimated from the intrinsic thermal conductivities of the nanotubes and their volume fraction.
Abstract: The enormous amount of basic research into carbon nanotubes has sparked interest in the potential applications of these novel materials. One promising use of carbon nanotubes is as fillers in a composite material to improve mechanical behaviour, electrical transport and thermal transport. For composite materials with high thermal conductivity, the thermal conductance across the nanotube-matrix interface is of particular interest. Here we use picosecond transient absorption to measure the interface thermal conductance (G) of carbon nanotubes suspended in surfactant micelles in water. Classical molecular dynamics simulations of heat transfer from a carbon nanotube to a model hydrocarbon liquid are in agreement with experiment. Our findings indicate that heat transport in a nanotube composite material will be limited by the exceptionally small interface thermal conductance (G approximately 12 MW m(-2) K(-1)) and that the thermal conductivity of the composite will be much lower than the value estimated from the intrinsic thermal conductivity of the nanotubes and their volume fraction.

Journal ArticleDOI
TL;DR: The distribution of Tgs across polystyrene films has been obtained by a fluorescence/multilayer method, revealing that the enhancement of dynamics at a surface affects Tg several tens of nanometres into the film.
Abstract: Despite the decade-long study of the effect of nanoconfinement on the glass-transition temperature (Tg) of amorphous materials, the quest to probe the distribution of Tgs in nanoconfined glass formers has remained unfulfilled. Here the distribution of Tgs across polystyrene films has been obtained by a fluorescence/multilayer method, revealing that the enhancement of dynamics at a surface affects Tg several tens of nanometres into the film. The extent to which dynamics smoothly transition from enhanced to bulk states depends strongly on nanoconfinement. When polymer films are sufficiently thin that a reduction in thickness leads to a reduction in overall Tg, the surface-layer Tg actually increases with a reduction in overall thickness, whereas the substrate-layer Tg decreases. These results indicate that the gradient in Tg dynamics is not abrupt, and that the size of a cooperatively rearranging region is much smaller than the distance over which interfacial effects propagate.

Journal ArticleDOI
TL;DR: Both redox stability and operation in low steam hydrocarbons have been demonstrated, overcoming two of the major limitations of the current generation of nickel zirconia cermet SOFC anodes.
Abstract: Solid-oxide fuel cells (SOFCs) promise high efficiencies in a range of fuels. Unlike lower temperature variants, carbon monoxide is a fuel rather than a poison, and so hydrocarbon fuels can be used directly, through internal reforming or even direct oxidation. This provides a key entry strategy for fuel-cell technology into the current energy economy. Present development is mainly based on the yttria-stabilized zirconia (YSZ) electrolyte. The most commonly used anode materials are Ni/YSZ cermets, which display excellent catalytic properties for fuel oxidation and good current collection, but do exhibit disadvantages, such as low tolerance to sulphur and carbon deposition when using hydrocarbon fuels, and poor redox cycling causing volume instability. Here, we report a nickel-free SOFC anode, La0.75Sr0.25Cr0.5Mn0.5O3, with comparable electrochemical performance to Ni/YSZ cermets. The electrode polarization resistance approaches 0.2 Omega cm2 at 900 degrees C in 97% H2/3% H2O. Very good performance is achieved for methane oxidation without using excess steam. The anode is stable in both fuel and air conditions, and shows stable electrode performance in methane. Thus both redox stability and operation in low steam hydrocarbons have been demonstrated, overcoming two of the major limitations of the current generation of nickel zirconia cermet SOFC anodes.

Journal ArticleDOI
TL;DR: These controls of the size and shape of inorganic nanomaterials are discussed and it is shown that nanoparticles can be considered to be efficient nanoreactors.
Abstract: In the past decade, colloidal solutions have been assumed to be very efficient templates for controlling particle size and shape A large number of groups have used reverse micelles to control the size of spherical nanoparticles This makes it possible to determine the various parameters involved in such processes, and demonstrates that nanoparticles can be considered to be efficient nanoreactors However, some discrepancies arise There are few reports concerning the control of particle shape, and it is still rather difficult to determine the key parameters, such as the adsorption of salts and other molecules, and the synthesis procedure Here, we discuss these controls of the size and shape of inorganic nanomaterials

Journal ArticleDOI
TL;DR: The mechanical deformation of proteins and nucleic acids may provide key insights for understanding the changes in cellular structure, response and function under force, and offer new opportunities for the diagnosis and treatment of disease.
Abstract: Living cells can sense mechanical forces and convert them into biological responses. Similarly, biological and biochemical signals are known to influence the abilities of cells to sense, generate and bear mechanical forces. Studies into the mechanics of single cells, subcellular components and biological molecules have rapidly evolved during the past decade with significant implications for biotechnology and human health. This progress has been facilitated by new capabilities for measuring forces and displacements with piconewton and nanometre resolutions, respectively, and by improvements in bio-imaging. Details of mechanical, chemical and biological interactions in cells remain elusive. However, the mechanical deformation of proteins and nucleic acids may provide key insights for understanding the changes in cellular structure, response and function under force, and offer new opportunities for the diagnosis and treatment of disease. This review discusses some basic features of the deformation of single cells and biomolecules, and examines opportunities for further research.

Journal ArticleDOI
TL;DR: A solid-state nanopore microscope capable of observing individual molecules of double-stranded DNA and their folding behaviour is demonstrated and extensions of the nanopore telescope concept to alternative probing mechanisms and applications are discussed, including the study of molecular structure and sequencing.
Abstract: A nanometre-scale pore in a solid-state membrane provides a new way of electronically probing the structure of single linear polymers, including those of biological interest in their native environments. Previous work with biological protein pores wide enough to let through and sense single-stranded DNA molecules demonstrates the power of using nanopores, but many future tasks and applications call for a robust solidstate pore whose nanometre-scale dimensions and properties may be selected, as one selects the lenses of a microscope. Here we demonstrate a solid-state nanopore microscope capable of observing individual molecules of double-stranded DNA and their folding behaviour. We discuss extensions of the nanopore microscope concept to alternative probing mechanisms and applications, including the study of molecular structure and sequencing.

Journal ArticleDOI
TL;DR: This work fabricated fully dense nanocomposites of single-wall carbon nanotubes with nanocrystalline alumina (Al2O3) matrix at sintering temperatures as low as 1,150 °C by spark-plasma sintered, demonstrating their potential use in reinforcing nanocrystaline ceramics.
Abstract: The extraordinary mechanical, thermal and electrical properties of carbon nanotubes have prompted intense research into a wide range of applications in structural materials, electronics, chemical processing and energy management. Attempts have been made to develop advanced engineering materials with improved or novel properties through the incorporation of carbon nanotubes in selected matrices (polymers, metals and ceramics). But the use of carbon nanotubes to reinforce ceramic composites has not been very successful; for example, in alumina-based systems only a 24% increase in toughness has been obtained so far. Here we demonstrate their potential use in reinforcing nanocrystalline ceramics. We have fabricated fully dense nanocomposites of single-wall carbon nanotubes with nanocrystalline alumina (Al2O3) matrix at sintering temperatures as low as 1,150 degrees C by spark-plasma sintering. A fracture toughness of 9.7 MPa m 1/2, nearly three times that of pure nanocrystalline alumina, can be achieved.

Journal ArticleDOI
TL;DR: In this article, the authors demonstrate that hole transport and electron transport are both generic properties of organic semiconductors and combine the organic ambipolar transistors into functional CMOS-like inverters.
Abstract: There is ample evidence that organic field-effect transistors have reached a stage where they can be industrialized, analogous to standard metal oxide semiconductor (MOS) transistors. Monocrystalline silicon technology is largely based on complementary MOS (CMOS) structures that use both n-type and p-type transistor channels. This complementary technology has enabled the construction of digital circuits, which operate with a high robustness, low power dissipation and a good noise margin. For the design of efficient organic integrated circuits, there is an urgent need for complementary technology, where both n-type and p-type transistor operation is realized in a single layer, while maintaining the attractiveness of easy solution processing. We demonstrate, by using solution-processed field-effect transistors, that hole transport and electron transport are both generic properties of organic semiconductors. This ambipolar transport is observed in polymers based on interpenetrating networks as well as in narrow bandgap organic semiconductors. We combine the organic ambipolar transistors into functional CMOS-like inverters.

Journal ArticleDOI
TL;DR: A non-viral gene-delivery system based on multisegment bimetallic nanorods that can simultaneously bind compacted DNA plasmids and targeting ligands in a spatially defined manner is presented, which allows precise control of composition, size and multifunctionality of the gene-Delivery system.
Abstract: The goal of gene therapy is to introduce foreign genes into somatic cells to supplement defective genes or provide additional biological functions, and can be achieved using either viral or synthetic non-viral delivery systems. Compared with viral vectors, synthetic gene-delivery systems, such as liposomes and polymers, offer several advantages including ease of production and reduced risk of cytotoxicity and immunogenicity, but their use has been limited by the relatively low transfection efficiency. This problem mainly stems from the difficulty in controlling their properties at the nanoscale. Synthetic inorganic gene carriers have received limited attention in the gene-therapy community, the only notable example being gold nanoparticles with surface-immobilized DNA applied to intradermal genetic immunization by particle bombardment. Here we present a non-viral gene-delivery system based on multisegment bimetallic nanorods that can simultaneously bind compacted DNA plasmids and targeting ligands in a spatially defined manner. This approach allows precise control of composition, size and multifunctionality of the gene-delivery system. Transfection experiments performed in vitro and in vivo provide promising results that suggest potential in genetic vaccination applications.

Journal ArticleDOI
TL;DR: It was found that fracture in human cortical bone is consistent with strain-controlled failure, and the influence of microstructure can be described in terms of several toughening mechanisms, such as uncracked-ligament bridging.
Abstract: A mechanistic understanding of fracture in human bone is critical to predicting fracture risk associated with age and disease. Despite extensive work, a mechanistic framework for describing how the underlying microstructure affects the failure mode in bone is lacking.

Journal ArticleDOI
TL;DR: The use of water vapour in place of hydrogen gas gives highly uniform, conformal films of metal oxides, including lanthanum oxide, and it is proposed that these ALD layers grow by a hydrogenation mechanism that should also operate during the ALD of many other metals.
Abstract: Atomic layer deposition (ALD) is a process for depositing highly uniform and conformal thin films by alternating exposures of a surface to vapours of two chemical reactants. ALD processes have been successfully demonstrated for many metal compounds, but for only very few pure metals. Here we demonstrate processes for the ALD of transition metals including copper, cobalt, iron and nickel. Homoleptic N,N'-dialkylacetamidinato metal compounds and molecular hydrogen gas were used as the reactants. Their surface reactions were found to be complementary and self-limiting, thus providing highly uniform thicknesses and conformal coating of long, narrow holes. We propose that these ALD layers grow by a hydrogenation mechanism that should also operate during the ALD of many other metals. The use of water vapour in place of hydrogen gas gives highly uniform, conformal films of metal oxides, including lanthanum oxide. These processes should permit the improved production of many devices for which the ALD process has previously not been applicable.

Journal ArticleDOI
TL;DR: This work presents a new in situ-formed nanostructured matrix/ductile dendritic phase composite microstructure for Ti-base alloys, which exhibits up to 14.5% compressive plastic strain at room temperature.
Abstract: Single-phase nanocrystalline materials undergo inhomogeneous plastic deformation under loading at room temperature, which results in a very limited plastic strain (smaller than 0–3%). The materials therefore display low ductility, leading to catastrophic failure, which severely restricts their application. Here, we present a new in situ-formed nanostructured matrix/ductile dendritic phase composite microstructure for Ti-base alloys, which exhibits up to 14.5% compressive plastic strain at room temperature. The new composite microstructure was synthesized on the basis of the appropriate choice of composition, and by using well-controlled solidification conditions. Deformation occurs partially through dislocation movement in dendrites, and partially through a shear-banding mechanism in the nanostructured matrix. The dendrites act as obstacles restricting the excessive deformation by isolating the highly localized shear bands in small, discrete inter-dendritic regions, and contribute to the plasticity. We suggest that microscale ductile crystalline phases might therefore be used to toughen nanostructured materials.

Journal ArticleDOI
TL;DR: It is envisaged that 3D microvascular networks will provide an enabling platform for a wide array of fluidic-based applications.
Abstract: The creation of geometrically complex fluidic devices is a subject of broad fundamental and technological interest. Here, we demonstrate the fabrication of three-dimensional (3D) microvascular networks through direct-write assembly of a fugitive organic ink. This approach yields a pervasive network of smooth cylindrical channels (approximately 10-300 microm) with defined connectivity. Square-spiral towers, isolated within this vascular network, promote fluid mixing through chaotic advection. These vertical towers give rise to dramatic improvements in mixing relative to simple straight (1D) and square-wave (2D) channels while significantly reducing the device planar footprint. We envisage that 3D microvascular networks will provide an enabling platform for a wide array of fluidic-based applications.

Journal ArticleDOI
TL;DR: This work follows in real time the evolution of individual clusters, and compares their development with simulations incorporating the basic physics of electrodeposition during the early stages of growth, to analyse dynamic observations—recorded in situ using a novel transmission electron microscopy technique—of the nucleation and growth of nanoscale copper clusters during electro Deposition.
Abstract: Dynamic processes at the solid–liquid interface are of key importance across broad areas of science and technology. Electrochemical deposition of copper, for example, is used for metallization in integrated circuits, and a detailed understanding of nucleation, growth and coalescence is essential in optimizing the final microstructure. Our understanding of processes at the solid–vapour interface has advanced tremendously over the past decade due to the routine availability of real-time, high-resolution imaging techniques yielding data that can be compared quantitatively with theory1,2,3. However, the difficulty of studying the solid–liquid interface leaves our understanding of processes there less complete. Here we analyse dynamic observations—recorded in situ using a novel transmission electron microscopy technique—of the nucleation and growth of nanoscale copper clusters during electrodeposition. We follow in real time the evolution of individual clusters, and compare their development with simulations incorporating the basic physics of electrodeposition during the early stages of growth. The experimental technique developed here is applicable to a broad range of dynamic phenomena at the solid–liquid interface.

Journal ArticleDOI
TL;DR: In March 2003, ionic liquids came of age with the announcement of BASIL, the first industrial process based on room-temperature ionic liquid technology.
Abstract: In March 2003, ionic liquids came of age with the announcement of BASIL, the first industrial process based on room-temperature ionic liquid technology.

Journal ArticleDOI
TL;DR: MOROF-1 shows a reversible and highly selective solvent-induced 'shrinking–breathing' process involving large volume changes that strongly influence the magnetic properties of the material, which could be the first stage of a new route towards magnetic solvent sensors.
Abstract: A nanoporous molecular magnet with reversible solvent-induced mechanical and magnetic properties

Journal ArticleDOI
TL;DR: Multicolour photochromism of TiO2 films loaded with silver nanoparticles by photocatalytic means is reported, and the apparently uniform Ag–TiO2 film can be almost any colour.
Abstract: Photochromic materials, which change their colours reversibly in response to light, can be applied to smart windows, displays and memories1,2,3. Conventional photochromic materials respond in a monochromatic way, so that multicolour photochromism has required several different materials or filters combined appropriately. If multicolour photochromism could be achieved with a simple material, photochromic devices would be find a greater number of applications, including a rewritable colour copy paper or electronic paper4 and a high-density multi-wavelength optical memory. Here we report multicolour photochromism of TiO2 films loaded with silver nanoparticles by photocatalytic means. Its colour, initially brownish-grey, changes under monochromatic visible light to almost the same colour as that of the light; the apparently uniform Ag–TiO2 film can be almost any colour. Behaviour similar to persistent hole-burning effects5,6 is also observed. The colour reverts to brownish-grey under ultraviolet light, and these processes are repeatable.