Showing papers in "Nature Materials in 2002"
TL;DR: It is shown that controlled cation non-stoichiometry combined with solid-solution doping by metals supervalent to Li+ increases the electronic conductivity of LiFePO4 by a factor of ∼108, which may allow development of lithium batteries with the highest power density yet.
Abstract: Lithium transition metal phosphates have become of great interest as storage cathodes for rechargeable lithium batteries because of their high energy density, low raw materials cost, environmental friendliness and safety. Their key limitation has been extremely low electronic conductivity, until now believed to be intrinsic to this family of compounds. Here we show that controlled cation non-stoichiometry combined with solid-solution doping by metals supervalent to Li+ increases the electronic conductivity of LiFePO4 by a factor of approximately 10(8). The resulting materials show near-theoretical energy density at low charge/discharge rates, and retain significant capacity with little polarization at rates as high as 6,000 mA x g(-1). In a conventional cell design, they may allow development of lithium batteries with the highest power density yet.
2,707 citations
TL;DR: Terahertz spectroscopy and imaging provide a powerful tool for the characterization of a broad range of materials, including semiconductors and biomolecules, as well as novel, higher-power terahertz sources.
Abstract: Terahertz spectroscopy systems use far-infrared radiation to extract molecular spectral information in an otherwise inaccessible portion of the electromagnetic spectrum. Materials research is an essential component of modern terahertz systems: novel, higher-power terahertz sources rely heavily on new materials such as quantum cascade structures. At the same time, terahertz spectroscopy and imaging provide a powerful tool for the characterization of a broad range of materials, including semiconductors and biomolecules.
2,673 citations
TL;DR: This work shows the stabilization of blue phases over a temperature range of more than 60 K including room temperature (260–326 K), and demonstrates an electro-optical switching with a response time of the order of 10−4 s for the stabilized blue phases at room temperature.
Abstract: Blue phases are types of liquid crystal phases that appear in a temperature range between a chiral nematic phase and an isotropic liquid phase. Because blue phases have a three-dimensional cubic structure with lattice periods of several hundred nanometres, they exhibit selective Bragg reflections in the range of visible light corresponding to the cubic lattice. From the viewpoint of applications, although blue phases are of interest for fast light modulators or tunable photonic crystals, the very narrow temperature range, usually less than a few kelvin, within which blue phases exist has always been a problem. Here we show the stabilization of blue phases over a temperature range of more than 60 K including room temperature (260–326 K). Furthermore, we demonstrate an electro-optical switching with a response time of the order of 10−4 s for the stabilized blue phases at room temperature.
1,876 citations
TL;DR: A redshift that is strongly dependent on pump power supports the idea that the electron–hole plasma mechanism is primarily responsible for the gain at room temperature and is a considerable advance towards the realization of electron-injected, nanowire-based ultraviolet–blue coherent light sources.
Abstract: There is much current interest in the optical properties of semiconductor nanowires, because the cylindrical geometry and strong two-dimensional confinement of electrons, holes and photons make them particularly attractive as potential building blocks for nanoscale electronics and optoelectronic devices, including lasersand nonlinear optical frequency converters. Gallium nitride (GaN) is a wide-bandgap semiconductor of much practical interest, because it is widely used in electrically pumped ultraviolet-blue light-emitting diodes, lasers and photodetectors. Recent progress in microfabrication techniques has allowed stimulated emission to be observed from a variety of GaN microstructures and films. Here we report the observation of ultraviolet-blue laser action in single monocrystalline GaN nanowires, using both near-field and far-field optical microscopy to characterize the waveguide mode structure and spectral properties of the radiation at room temperature. The optical microscope images reveal radiation patterns that correlate with axial Fabry-Perot modes (Q approximately 10(3)) observed in the laser spectrum, which result from the cylindrical cavity geometry of the monocrystalline nanowires. A redshift that is strongly dependent on pump power (45 meV microJ x cm(-2)) supports the idea that the electron-hole plasma mechanism is primarily responsible for the gain at room temperature. This study is a considerable advance towards the realization of electron-injected, nanowire-based ultraviolet-blue coherent light sources.
1,207 citations
TL;DR: In this article, high-kappa (approximately 25) zirconium oxide thin-films (approximately 8 nm) are formed on top of individual single-walled carbon nanotubes by atomic-layer deposition and used as gate dielectrics for nanotube field effect transistors.
Abstract: The integration of materials having a high dielectric constant (high-kappa) into carbon-nanotube transistors promises to push the performance limit for molecular electronics. Here, high-kappa (approximately 25) zirconium oxide thin-films (approximately 8 nm) are formed on top of individual single-walled carbon nanotubes by atomic-layer deposition and used as gate dielectrics for nanotube field-effect transistors. The p-type transistors exhibit subthreshold swings of S approximately 70 mV per decade, approaching the room-temperature theoretical limit for field-effect transistors. Key transistor performance parameters, transconductance and carrier mobility reach 6,000 S x m(-1) (12 microS per tube) and 3,000 cm2 x V(-1) x s(-1) respectively. N-type field-effect transistors obtained by annealing the devices in hydrogen exhibit S approximately 90 mV per decade. High voltage gains of up to 60 are obtained for complementary nanotube-based inverters. The atomic-layer deposition process affords gate insulators with high capacitance while being chemically benign to nanotubes, a key to the integration of advanced dielectrics into molecular electronics.
1,052 citations
TL;DR: In this report, the in vitro biosynthesis of silver nanoparticles using silver-binding peptides identified from a combinatorial phage display peptide library is described.
Abstract: The creation of nanoscale materials for advanced structures has led to a growing interest in the area of biomineralization. Numerous microorganisms are capable of synthesizing inorganic-based structures. For example, diatoms use amorphous silica as a structural material, bacteria synthesize magnetite (Fe3O4) particles and form silver nanoparticles, and yeast cells synthesize cadmium sulphide nanoparticles. The process of biomineralization and assembly of nanostructured inorganic components into hierarchical structures has led to the development of a variety of approaches that mimic the recognition and nucleation capabilities found in biomolecules for inorganic material synthesis. In this report, we describe the in vitro biosynthesis of silver nanoparticles using silver-binding peptides identified from a combinatorial phage display peptide library.
1,008 citations
TL;DR: The free-standing SWNT/polyelectrolyte membranes delaminated from the substrate were found to be exceptionally strong with a tensile strength approaching that of hard ceramics.
Abstract: The mechanical failure of hybrid materials made from polymers and single-wall carbon nanotubes (SWNT) is primarily attributed to poor matrix–SWNT connectivity and severe phase segregation. Both problems can be successfully mitigated when the SWNT composite is made following the protocol of layer-by-layer assembly. This deposition technique prevents phase segregation of the polymer/SWNT binary system, and after subsequent crosslinking, the nanometre-scale uniform composite with SWNT loading as high as 50 wt% can be obtained. The free-standing SWNT/polyelectrolyte membranes delaminated from the substrate were found to be exceptionally strong with a tensile strength approaching that of hard ceramics. Because of the lightweight nature of SWNT composites, the prepared free-standing membranes can serve as components for a variety of long-lifetime devices.
966 citations
TL;DR: High-efficiency anti-reflection coatings are created from phase-separated polyelectrolyte multilayer films that undergo a reversible pH-induced swelling transition, which has potential for pH-responsive biomaterial and membrane applications.
Abstract: For nearly two centuries, researchers have sought novel methods to increase light transmission in optical systems, as well as to eliminate unwanted reflections and glare. Anti-reflection coatings and surfaces have enabled the increasing performance demands of optical components fabricated from glass-based optical materials. With the current trend of technology moving towards optically transparent polymeric media and coatings, the need for anti-reflection technology and environmentally benign processing methods for polymeric materials independent of shape or size has become quite apparent. We describe an economical, aqueous-based process controlled at the molecular level that simultaneously coats all surfaces of almost any material. Systematically designed nanoporous polymer films are used, which are suitable for optical applications operating at both visible and near-infrared wavelengths. These high-efficiency anti-reflection coatings are created from phase-separated polyelectrolyte multilayer films that undergo a reversible pH-induced swelling transition. Furthermore, such films, easily patterned by an inkjet printing technique, possess potential for pH-responsive biomaterial and membrane applications.
841 citations
TL;DR: This review focuses on the nature of the non-thermal transitions in semiconductors under femtosecond laser excitation.
Abstract: Soon after it was discovered that intense laser pulses of nanosecond duration from a ruby laser could anneal the lattice of silicon, it was established that this so-called pulsed laser annealing is a thermal process. Although the radiation energy is transferred to the electrons, the electrons transfer their energy to the lattice on the timescale of the excitation. The electrons and the lattice remain in equilibrium and the laser simply 'heats' the solid to the melting temperature within the duration of the laser pulse. For ultrashort laser pulses in the femtosecond regime, however, thermal processes (which take several picoseconds) and equilibrium thermodynamics cannot account for the experimental data. On excitation with femtosecond laser pulses, the electrons and the lattice are driven far out of equilibrium and disordering of the lattice can occur because the interatomic forces are modified due to the excitation of a large (10% or more) fraction of the valence electrons to the conduction band. This review focuses on the nature of the non-thermal transitions in semiconductors under femtosecond laser excitation.
837 citations
TL;DR: It is demonstrated that, in contrast to coarse-grained Al, mechanical twinning may play an important role in the deformation behaviour of nanocrystalline Al, and large-scale molecular-dynamics simulations are used to elucidate this intricate interplay during room-temperature plastic deformation of model nanocrystaline Al microstructures.
Abstract: The mechanical behaviour of nanocrystalline materials (that is, polycrystals with a grain size of less than 100 nm) remains controversial. Although it is commonly accepted that the intrinsic deformation behaviour of these materials arises from the interplay between dislocation and grain-boundary processes, little is known about the specific deformation mechanisms. Here we use large-scale molecular-dynamics simulations to elucidate this intricate interplay during room-temperature plastic deformation of model nanocrystalline Al microstructures. We demonstrate that, in contrast to coarse-grained Al, mechanical twinning may play an important role in the deformation behaviour of nanocrystalline Al. Our results illustrate that this type of simulation has now advanced to a level where it provides a powerful new tool for elucidating and quantifying--in a degree of detail not possible experimentally--the atomic-level mechanisms controlling the complex dislocation and grain-boundary processes in heavily deformed materials with a submicrometre grain size.
823 citations
TL;DR: It is shown that nanocrystalline diamond thin-films covalently modified with DNA oligonucleotides provide an extremely stable, highly selective platform in subsequent surface hybridization processes, suggesting that diamond thin -films may be a nearly ideal substrate for integration of microelectronics with biological modification and sensing.
Abstract: Diamond, because of its electrical and chemical properties, may be a suitable material for integrated sensing and signal processing. But methods to control chemical or biological modifications on diamond surfaces have not been established. Here, we show that nanocrystalline diamond thin-films covalently modified with DNA oligonucleotides provide an extremely stable, highly selective platform in subsequent surface hybridization processes. We used a photochemical modification scheme to chemically modify clean, H-terminated nanocrystalline diamond surfaces grown on silicon substrates, producing a homogeneous layer of amine groups that serve as sites for DNA attachment. After linking DNA to the amine groups, hybridization reactions with fluorescently tagged complementary and non-complementary oligonucleotides showed no detectable non-specific adsorption, with extremely good selectivity between matched and mismatched sequences. Comparison of DNA-modified ultra-nanocrystalline diamond films with other commonly used surfaces for biological modification, such as gold, silicon, glass and glassy carbon, showed that diamond is unique in its ability to achieve very high stability and sensitivity while also being compatible with microelectronics processing technologies. These results suggest that diamond thin-films may be a nearly ideal substrate for integration of microelectronics with biological modification and sensing.
TL;DR: The first observations of lasing in three-dimensional photonic crystals, in the cholesteric blue phase II are reported, showing that distributed feedback is realized in three dimensions, resulting in almost diffraction-limited lasing with significantly lower thresholds than in one dimension.
Abstract: Photonic-bandgap materials, with periodicity in one, two or three dimensions, offer control of spontaneous emission and photon localization. Low-threshold lasing has been demonstrated in two-dimensional photonic-bandgap materials, both with distributed feedback and defect modes. Liquid crystals with chiral constituents exhibit mesophases with modulated ground states. Helical cholesterics are one-dimensional, whereas blue phases are three-dimensional self-assembled photonic-bandgap structures. Although mirrorless lasing was predicted and observed in one-dimensional helical cholesteric materials and chiral ferroelectric smectic materials, it is of great interest to probe light confinement in three dimensions. Here, we report the first observations of lasing in three-dimensional photonic crystals, in the cholesteric blue phase II. Our results show that distributed feedback is realized in three dimensions, resulting in almost diffraction-limited lasing with significantly lower thresholds than in one dimension. In addition to mirrorless lasing, these self-assembled soft photonic-bandgap materials may also be useful for waveguiding, switching and sensing applications.
TL;DR: Innovation in high-pressure research is examined that might be harnessed to develop new materials for technological applications, including condensed rare gases, and ionic compounds such as CsI.
Abstract: High-pressure synthesis on an industrial scale is applied to obtain synthetic diamonds and cubic boron nitride (c-BN), which are the superhard abrasives of choice for cutting and shaping hard metals and ceramics. Recently, high-pressure science has undergone a renaissance, with novel techniques and instrumentation permitting entirely new classes of high-pressure experiments. For example, superconducting behaviour was previously known for only a few elements and compounds. Under high-pressure conditions, the 'superconducting periodic table' now extends to all classes of the elements, including condensed rare gases, and ionic compounds such as CsI. Another surprising result is the newly discovered solid-state chemistry of light-element 'gas' molecules such as CO2, N2 and N2O. These react to give polymerized covalently bonded or ionic mineral structures under conditions of high pressure and temperature: the new solids are potentially recoverable to ambient conditions. Here we examine innovations in high-pressure research that might be harnessed to develop new materials for technological applications.
TL;DR: This approach preserves the fundamental semiconducting properties of the conjugated wires, and is effective at both increasing the photoluminescence efficiency and blue-shifting the emission of the Conjugated cores, in the solid state, while still allowing charge-transport.
Abstract: Control of intermolecular interactions is crucial to the exploitation of molecular semiconductors for both organic electronics and the viable manipulation and incorporation of single molecules into nano-engineered devices. Here we explore the properties of a class of materials that are engineered at a supramolecular level by threading a conjugated macromolecule, such as poly(para-phenylene), poly(4,4'-diphenylene vinylene) or polyfluorene through alpha- or beta-cyclodextrin rings, so as to reduce intermolecular interactions and solid-state packing effects that red-shift and partially quench the luminescence. Our approach preserves the fundamental semiconducting properties of the conjugated wires, and is effective at both increasing the photoluminescence efficiency and blue-shifting the emission of the conjugated cores, in the solid state, while still allowing charge-transport. We used the polymers to prepare single-layer light-emitting diodes with Ca and Al cathodes, and observed blue and green emission. The reduced tendency for polymer chains to aggregate allows solution-processing of individual polyrotaxane wires onto substrates, as revealed by scanning force microscopy.
TL;DR: A method for optically encoding micrometre-sized nanostructured particles of porous silicon using a periodic electrochemical etch and a simple antibody-based bioassay using fluorescently tagged proteins demonstrates the encoding strategy in biologically relevant media.
Abstract: Strategies to encode or label small particles or beads for use in high-throughput screening and bioassay applications focus on either spatially differentiated, on-chip arrays or random distributions of encoded beads. Attempts to encode large numbers of polymeric, metallic or glass beads in random arrays or in fluid suspension have used a variety of entities to provide coded elements (bits)--fluorescent molecules, molecules with specific vibrational signatures, quantum dots, or discrete metallic layers. Here we report a method for optically encoding micrometre-sized nanostructured particles of porous silicon. We generate multilayered porous films in crystalline silicon using a periodic electrochemical etch. This results in photonic crystals with well-resolved and narrow optical reflectivity features, whose wavelengths are determined by the etching parameters. Millions of possible codes can be prepared this way. Micrometre-sized particles are then produced by ultrasonic fracture, mechanical grinding or by lithographic means. A simple antibody-based bioassay using fluorescently tagged proteins demonstrates the encoding strategy in biologically relevant media.
TL;DR: This work has demonstrated repeatable sorption–desorption with high selectivity on the basis of size, shape and functional group of the sorbate by a microporous metalloporphyrin solid in analogy to zeolites.
Abstract: The assembly of molecular building blocks with metal ions genera-ting microporous network solids has been the focus of intense activity1,2,3,4,5,6,7,8,9,10,11,12. Because of their potential applications associated with channels and cavities, such materials have been examined for size- and shape-selective catalysis, separations, sensors, molecular recognition and nanoscale reactors. Within this context, assemblies of robust and chemically versatile porphyrin and metalloporphyrin building blocks remain rare. Supramolecular architectures of porphyrin solids based on weak van der Waals interactions13,14, hydrogen bonding15,16 and metal-ligand coordination networks17,18,19,20,21,22,23 have been reported. Although there are frequent allusions to zeolite-like microporosity from crystallography and loss of initial guest solvent molecules, evidence of functional microporous behaviour is scarce. We have demonstrated repeatable sorption–desorption with high selectivity on the basis of size, shape and functional group of the sorbate by a microporous metalloporphyrin solid in analogy to zeolites.
TL;DR: Here it is shown that an in situ process in which MgB2 is formed directly on the substrate is desirable and can be achieved by hybrid physical–chemical vapour deposition, and this advance removes a major barrier for superconducting electronics using M gB2.
Abstract: The newly discovered 39-K superconductor MgB2 holds great promise for superconducting electronics. Like the conventional superconductor Nb, MgB2 is a phonon-mediated superconductor, with a relatively long coherence length. These properties make the prospect of fabricating reproducible uniform Josephson junctions, the fundamental element of superconducting circuits, much more favourable for MgB2 than for high-temperature superconductors. The higher transition temperature and larger energy gap of MgB2 promise higher operating temperatures and potentially higher speeds than Nb-based integrated circuits. However, success in MgB2 Josephson junctions has been limited because of the lack of an adequate thin-film technology. Because a superconducting integrated circuit uses a multilayer of superconducting, insulating and resistive films, an in situ process in which MgB2 is formed directly on the substrate is desirable. Here we show that this can be achieved by hybrid physical-chemical vapour deposition. The epitaxially grown MgB2 films show a high transition temperature and low resistivity, comparable to the best bulk samples, and their surfaces are smooth. This advance removes a major barrier for superconducting electronics using MgB2.
TL;DR: It is demonstrated that quantum dots can be manipulated using modified chaperonins and organized into arrays for use in next-generation electronic and photonic devices.
Abstract: Traditional methods for fabricating nanoscale arrays are usually based on lithographic techniques. Alternative new approaches rely on the use of nanoscale templates made of synthetic or biological materials. Some proteins, for example, have been used to form ordered two-dimensional arrays. Here, we fabricated nanoscale ordered arrays of metal and semiconductor quantum dots by binding preformed nanoparticles onto crystalline protein templates made from genetically engineered hollow double-ring structures called chaperonins. Using structural information as a guide, a thermostable recombinant chaperonin subunit was modified to assemble into chaperonins with either 3 nm or 9 nm apical pores surrounded by chemically reactive thiols. These engineered chaperonins were crystallized into two-dimensional templates up to 20 microm in diameter. The periodic solvent-exposed thiols within these crystalline templates were used to size-selectively bind and organize either gold (1.4, 5 or 10nm) or CdSe-ZnS semiconductor (4.5 nm) quantum dots into arrays. The order within the arrays was defined by the lattice of the underlying protein crystal. By combining the self-assembling properties of chaperonins with mutations guided by structural modelling, we demonstrate that quantum dots can be manipulated using modified chaperonins and organized into arrays for use in next-generation electronic and photonic devices.
TL;DR: Generic tests have been performed to check the viability of Escherichia coli bacteria in silica gels and it is found that more bacteria remain culturable in the gel than in an aqueous suspension.
Abstract: The encapsulation of enzymes within silica gels has been extensively studied during the past decade for the design of biosensors and bioreactors. Yeast spores and bacteria have also been recently immobilized within silica gels where they retain their enzymatic activity, but the problem of the long-term viability of whole cells in an inorganic matrix has never been fully addressed. It is a real challenge for the development of sol-gel processes. Generic tests have been performed to check the viability of Escherichia coli bacteria in silica gels. Surprisingly, more bacteria remain culturable in the gel than in an aqueous suspension. The metabolic activity of the bacteria towards glycolysis decreases slowly, but half of the bacteria are still viable after one month. When confined within a mineral environment, bacteria do not form colonies. The exchange of chemical signals between isolated bacteria rather than aggregates can then be studied, a point that could be very important for 'quorum sensing'.
TL;DR: This work proposes and demonstrates for an industrially relevant system, polyethylene and polyamide, that hitherto inaccessible co-continuous morphologies can be produced over a wide range of compositions by reactive blending and presents a unique combination of properties impossible to achieve with classical blends.
Abstract: With an annual production of hundreds of millions of tons, the few commodity polymers that dominate the plastics market cannot satisfy all the applications and expectations. In this context, the fabrication of thermodynamically stable polymer blends structured on submicrometre scales raises much hope, but poses significant scientific and industrial challenges. Here, we propose and demonstrate for an industrially relevant system, polyethylene and polyamide, that hitherto inaccessible co-continuous morphologies can be produced over a wide range of compositions by reactive blending. Paradoxically, the self-assembled structures are thermodynamically stable because of the molecular polydispersity inherent in the production method. These nanostructured materials present a unique combination of properties impossible to achieve with classical blends. This versatile, low-cost and simple strategy should be widely applicable.
TL;DR: Looking through a window on a rainy day may generate feelings other than melancholy: curiosity, for example: isn't it remarkable that water droplets stick to the pane rather than sliding down?
Abstract: Looking through a window on a rainy day may generate feelings other than melancholy Curiosity, for example: isn't it remarkable that water droplets stick to the pane rather than sliding down?
TL;DR: This work has studied the elastic properties of the myosin coiled-coil at the single molecule level and found that this protein undergoes a massive structural transition at forces between 20 and 25 pN where the coil extends to about 2.5 times its original length.
Abstract: Coiled-coils occur in a variety of proteins involved in mechanical and structural tasks in the cell. Their mechanical properties are important in various contexts ranging from hair elasticity1 to synaptic fusion2. Beyond their importance in biology, coiled-coils have also attracted interest as programmable protein sequences for the design of novel hydrogels and materials3. We have studied the elastic properties of the myosin coiled-coil at the single molecule level. The coiled-coil undergoes a massive structural transition at forces between 20 and 25 pN where the coil extends to about 2.5 times its original length. Unlike all other proteins investigated mechanically so far, this transition is reversible on a timescale of less than a second, making the coiled-coil a truly elastic protein.
TL;DR: This work shows that substituents attached to a conjugated bridge connecting two triarylamine redox centres have a marked influence on the near-infrared absorption spectra of the corresponding cations of mixed-valence radical cations.
Abstract: Hopping and superexchange are generally considered to be alternative electron-transfer mechanisms in molecular systems. In this work we used mixed-valence radical cations as model systems for the investigation of electron-transfer pathways. We show that substituents attached to a conjugated bridge connecting two triarylamine redox centres have a marked influence on the near-infrared absorption spectra of the corresponding cations. Spectral analysis, followed by evaluation of the electron-transfer parameters using the Generalized Mulliken-Hush theory and simulation of the potential energy surfaces, indicate that hopping and superexchange are not alternatives, but are both present in the radical cation with a dimethoxybenzene bridge. We found that the type of electron-transfer mechanism depends on the bridge-reorganization energy as well as on the bridge-state energy. Because superexchange and hopping follow different distance laws, our findings have implications for the design of new molecular and polymeric electron-transfer materials.
TL;DR: In this article, the Ni catalyst has a surface layer rich in carbon, consistent with the formation of a eutectic Ni-C droplet as a nucleation site for the carbon nanofibres, so that the carbon diffuses across the surface.
Abstract: Carbon nanotubes, first identified by Iijima1, require for their production a source of elemental carbon and a transfer of energy that is specific to the type of source and the growth environment. Methods developed so far involve arc discharge2, and vaporization using laser3,4, pyrolysis5,6 and chemical vapour deposition of hydrocarbons7. Here, we show growth of carbon nanofibres from radio-frequency plasma-enhanced chemical vapour deposition at room temperature, which was made possible by substituting the thermal energy requirements for the growth with plasma decomposition of methane on the Ni catalyst. Electron microscopy analysis provides evidence for a 'tip' growth model8, with the Ni catalyst particle attached to the tip of the nanofibre. Energy-filtered imaging shows the Ni catalyst has a surface layer rich in carbon, consistent with the formation of a eutectic Ni–C droplet as a nucleation site for the carbon nanofibres9, so that the carbon diffuses across the surface. The reduced distortion of the catalyst particles at low temperatures leads to a more uniform growth of the carbon nanofibres over large areas. The lower growth temperature allows for the removal of the silicon dioxide barrier layer associated with catalytic growth, and should allow in situ growth of nanofibres on relatively large areas of temperature-sensitive substrates, such as plastics, organics and even paper.
TL;DR: Experiments with colloidal systems, combined with theoretical predictions, may lead to the design of novel soft materials and to a deeper understanding of the glass and gel states of matter.
Abstract: The ability to tune the properties of disordered materials is reaching new levels. Experiments with colloidal systems, combined with theoretical predictions, may lead to the design of novel soft materials and to a deeper understanding of the glass and gel states of matter.
TL;DR: The discovery that the electronic conductivity of LiFePO4 can be increased by eight orders of magnitude may have a profound impact on the next generation of lithium-ion batteries.
Abstract: The discovery that the electronic conductivity of LiFePO4 can be increased by eight orders of magnitude may have a profound impact on the next generation of lithium-ion batteries.
TL;DR: This work demonstrates the long-range ordering of nanoparticle assemblies that adopt the helical configuration of the cholesteric liquid crystalline phase and demonstrates how such an assembly process could be modulated, providing a versatile route to new materials systems.
Abstract: Patterning nano-objects is an exciting interdisciplinary research area in current materials science, arising from new optical and optoelectronic properties and the need to miniaturize electronic components. Many techniques have been developed for assembling nanoparticles into two- and three-dimensional arrays. Most studies involving liquid crystals as templates have dealt with colloidal particles and nematic and smectic phases. Here, we demonstrate the long-range ordering of nanoparticle assemblies that adopt the helical configuration of the cholesteric liquid crystalline phase. Because we used glass-forming cholesterics, the nanostructures could be examined by transmission electron microscopy. The platinum nanoparticles form periodic ribbons that mimic the well-known 'fingerprint' cholesteric texture. Surprisingly, the nanoparticles do not decorate the original cholesteric texture but create a novel helical structure with a larger helical pitch. By varying the molar fraction of cholesterol-containing mesogen in the liquid crystal host, we show that the distance between the ribbons is directly correlated to the pitch. Therefore this inherent lengthscale becomes a simple control parameter to tune the structuring of nanoparticles. These results demonstrate how such an assembly process could be modulated, providing a versatile route to new materials systems.
TL;DR: This work has discovered a class of materials that become highly fluorescent on multiphoton absorption of pulses of 800-nm light from a Ti:sapphire oscillator, making them excellent candidate storage media for three-dimensional data storage.
Abstract: Efficient and robust multiphoton data storage in molecular glasses and highly crosslinked polymers
TL;DR: This work proposes devices that control the motion of flux quanta in superconductors and could address a central problem in many superconducting devices; namely, the removal of trapped magnetic flux that produces noise.
Abstract: A new generation of microscopic ratchet systems is currently being developed for controlling the motion of electrons and fluxons, as well as for particle separation and electrophoresis. Virtually all of these use static spatially asymmetric potential energies to control transport properties. Here we propose completely new types of ratchet-like systems that do not require fixed spatially asymmetric potentials in the samples. As specific examples of this novel general class of ratchets, we propose devices that control the motion of flux quanta in superconductors and could address a central problem in many superconducting devices; namely, the removal of trapped magnetic flux that produces noise. In layered superconductors there are two interpenetrating perpendicular vortex lattices consisting of Josephson vortices (JVs) and pancake vortices (PVs). We show that, owing to the JV‐PV mutual interaction and asymmetric driving, the a.c. motion of JVs and/or PVs can provide a net d.c. vortex current. This controllable vortex motion can be used for making pumps, diodes and lenses of quantized magnetic flux. These proposed devices sculpt the microscopic magnetic flux profile by simply modifying the time dependence of the a.c. drive, without the need for samples with static pinning—for example, without lithography or irradiation.
TL;DR: The synthesis and characterization of microbial polythioesters (PTEs), a novel class of biopolymers of general technological relevance, are reported, which open up new avenues in the field of biomaterials.
Abstract: The development of non-petrochemical sources for the plastics industry continues to progress as large multinationals focus on renewable resources to replace fossil carbon1. Many bacteria are known to accumulate polyoxoesters as water-insoluble granules in the cytoplasm. The thermoplastic and/or elastomeric behaviour of these biodegradable polymers holds promise for the development of various technological applications2,3. Here, we report the synthesis and characterization of microbial polythioesters (PTEs), a novel class of biopolymers of general technological relevance. Biosynthesis of PTE homopolymers was achieved using a recombinant strain of Escherichia coli that expressed a non-natural pathway consisting of a butyrate kinase, a phosphotransbutyrylase, and a PHA synthase. Different homopolymers were produced, consisting of either 3-mercaptopropionate, 3-mercaptobutyrate, or 3-mercaptovalerate repeating units, if the respective mercaptoalkanoic acids were provided as precursor substrates to the fermentative process. The PTEs contributed up to 30% (w/w) of the cellular dry weight and were identified as hydrophobic inclusions in the cytoplasm. The chemical and stereochemical homogeneity of the purified PTEs were identified by different methods, and the estimated physical properties were compared to the oxypolyester equivalents, revealing low crystalline order and, for the poly(3-mercaptopropionate) improved thermal stability. The ability to produce PTEs through a biosynthetic route opens up new avenues in the field of biomaterials.