Showing papers in "Nature Materials in 2011"
15 Dec 2011-Nature Materials
TL;DR: The energy that can be stored in Li-air and Li-S cells is compared with Li-ion; the operation of the cells is discussed, as are the significant hurdles that will have to be overcome if such batteries are to succeed.
Abstract: Li-ion batteries have transformed portable electronics and will play a key role in the electrification of transport. However, the highest energy storage possible for Li-ion batteries is insufficient for the long-term needs of society, for example, extended-range electric vehicles. To go beyond the horizon of Li-ion batteries is a formidable challenge; there are few options. Here we consider two: Li-air (O(2)) and Li-S. The energy that can be stored in Li-air (based on aqueous or non-aqueous electrolytes) and Li-S cells is compared with Li-ion; the operation of the cells is discussed, as are the significant hurdles that will have to be overcome if such batteries are to succeed. Fundamental scientific advances in understanding the reactions occurring in the cells as well as new materials are key to overcoming these obstacles. The potential benefits of Li-air and Li-S justify the continued research effort that will be needed.
TL;DR: The thermal properties of carbon materials are reviewed, focusing on recent results for graphene, carbon nanotubes and nanostructured carbon materials with different degrees of disorder, with special attention given to the unusual size dependence of heat conduction in two-dimensional crystals.
Abstract: Recent years have seen a rapid growth of interest by the scientific and engineering communities in the thermal properties of materials. Heat removal has become a crucial issue for continuing progress in the electronic industry, and thermal conduction in low-dimensional structures has revealed truly intriguing features. Carbon allotropes and their derivatives occupy a unique place in terms of their ability to conduct heat. The room-temperature thermal conductivity of carbon materials span an extraordinary large range--of over five orders of magnitude--from the lowest in amorphous carbons to the highest in graphene and carbon nanotubes. Here, I review the thermal properties of carbon materials focusing on recent results for graphene, carbon nanotubes and nanostructured carbon materials with different degrees of disorder. Special attention is given to the unusual size dependence of heat conduction in two-dimensional crystals and, specifically, in graphene. I also describe the prospects of applications of graphene and carbon materials for thermal management of electronics.
01 Oct 2011-Nature Materials
TL;DR: The Co₃O₄/N-doped graphene hybrid exhibits similar catalytic activity but superior stability to Pt in alkaline solutions, making it a high-performance non-precious metal-based bi-catalyst for both ORR and OER.
Abstract: Catalysts for oxygen reduction and evolution reactions are at the heart of key renewable-energy technologies including fuel cells and water splitting. Despite tremendous efforts, developing oxygen electrode catalysts with high activity at low cost remains a great challenge. Here, we report a hybrid material consisting of Co₃O₄ nanocrystals grown on reduced graphene oxide as a high-performance bi-functional catalyst for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Although Co₃O₄ or graphene oxide alone has little catalytic activity, their hybrid exhibits an unexpected, surprisingly high ORR activity that is further enhanced by nitrogen doping of graphene. The Co₃O₄/N-doped graphene hybrid exhibits similar catalytic activity but superior stability to Pt in alkaline solutions. The same hybrid is also highly active for OER, making it a high-performance non-precious metal-based bi-catalyst for both ORR and OER. The unusual catalytic activity arises from synergetic chemical coupling effects between Co₃O₄ and graphene.
TL;DR: Plasmon-enhanced water splitting on composite photocatalysts containing semiconductor and plasmonic-metal building blocks is focused on, and recently reported plasMon-mediated photocatallytic reactions on plAsmonic nanostructures of noble metals are discussed.
Abstract: Recent years have seen a renewed interest in the harvesting and conversion of solar energy. Among various technologies, the direct conversion of solar to chemical energy using photocatalysts has received significant attention. Although heterogeneous photocatalysts are almost exclusively semiconductors, it has been demonstrated recently that plasmonic nanostructures of noble metals (mainly silver and gold) also show significant promise. Here we review recent progress in using plasmonic metallic nanostructures in the field of photocatalysis. We focus on plasmon-enhanced water splitting on composite photocatalysts containing semiconductor and plasmonic-metal building blocks, and recently reported plasmon-mediated photocatalytic reactions on plasmonic nanostructures of noble metals. We also discuss the areas where major advancements are needed to move the field of plasmon-mediated photocatalysis forward.
TL;DR: The direct synthesis of three-dimensional foam-like graphene macrostructures, which are called graphene foams (GFs), by template-directed chemical vapour deposition is reported, demonstrating the great potential of GF/poly(dimethyl siloxane) composites for flexible, foldable and stretchable conductors.
Abstract: [Chen, Zongping; Ren, Wencai; Gao, Libo; Liu, Bilu; Pei, Songfeng; Cheng, Hui-Ming] Chinese Acad Sci, Shenyang Natl Lab Mat Sci, Inst Met Res, Shenyang 110016, Peoples R China.;Cheng, HM (reprint author), Chinese Acad Sci, Shenyang Natl Lab Mat Sci, Inst Met Res, Shenyang 110016, Peoples R China;firstname.lastname@example.org
01 Sep 2011-Nature Materials
TL;DR: A lithium superionic conductor, Li(10)GeP(2)S(12) that has a new three-dimensional framework structure that exhibits an extremely high lithium ionic conductivity of 12 mS cm(-1) at room temperature, which represents the highest conductivity achieved in a solid electrolyte, exceeding even those of liquid organic electrolytes.
Abstract: Batteries are a key technology in modern society. They are used to power electric and hybrid electric vehicles and to store wind and solar energy in smart grids. Electrochemical devices with high energy and power densities can currently be powered only by batteries with organic liquid electrolytes. However, such batteries require relatively stringent safety precautions, making large-scale systems very complicated and expensive. The application of solid electrolytes is currently limited because they attain practically useful conductivities (10(-2) S cm(-1)) only at 50-80 °C, which is one order of magnitude lower than those of organic liquid electrolytes. Here, we report a lithium superionic conductor, Li(10)GeP(2)S(12) that has a new three-dimensional framework structure. It exhibits an extremely high lithium ionic conductivity of 12 mS cm(-1) at room temperature. This represents the highest conductivity achieved in a solid electrolyte, exceeding even those of liquid organic electrolytes. This new solid-state battery electrolyte has many advantages in terms of device fabrication (facile shaping, patterning and integration), stability (non-volatile), safety (non-explosive) and excellent electrochemical properties (high conductivity and wide potential window).
TL;DR: This work demonstrates a TaO(x)-based asymmetric passive switching device with which it was able to localize resistance switching and satisfy all aforementioned requirements, and eliminates any need for a discrete transistor or diode in solving issues of stray leakage current paths in high-density crossbar arrays.
Abstract: Numerous candidates attempting to replace Si-based flash memory have failed for a variety of reasons over the years. Oxide-based resistance memory and the related memristor have succeeded in surpassing the specifications for a number of device requirements. However, a material or device structure that satisfies high-density, switching-speed, endurance, retention and most importantly power-consumption criteria has yet to be announced. In this work we demonstrate a TaO(x)-based asymmetric passive switching device with which we were able to localize resistance switching and satisfy all aforementioned requirements. In particular, the reduction of switching current drastically reduces power consumption and results in extreme cycling endurances of over 10(12). Along with the 10 ns switching times, this allows for possible applications to the working-memory space as well. Furthermore, by combining two such devices each with an intrinsic Schottky barrier we eliminate any need for a discrete transistor or diode in solving issues of stray leakage current paths in high-density crossbar arrays.
TL;DR: This work focuses on the interplay between the mechanisms that individually contribute to strength and toughness, noting that these phenomena can originate from very different lengthscales in a material's structural architecture.
Abstract: The attainment of both strength and toughness is a vital requirement for most structural materials; unfortunately these properties are generally mutually exclusive. Although the quest continues for stronger and harder materials, these have little to no use as bulk structural materials without appropriate fracture resistance. It is the lower-strength, and hence higher-toughness, materials that find use for most safety-critical applications where premature or, worse still, catastrophic fracture is unacceptable. For these reasons, the development of strong and tough (damage-tolerant) materials has traditionally been an exercise in compromise between hardness versus ductility. Drawing examples from metallic glasses, natural and biological materials, and structural and biomimetic ceramics, we examine some of the newer strategies in dealing with this conflict. Specifically, we focus on the interplay between the mechanisms that individually contribute to strength and toughness, noting that these phenomena can originate from very different lengthscales in a material's structural architecture. We show how these new and natural materials can defeat the conflict of strength versus toughness and achieve unprecedented levels of damage tolerance within their respective material classes.
TL;DR: A highly active photocathode for solar H(2) production is presented, consisting of electrodeposited cuprous oxide, which was protected against photocathodic decomposition in water by nanolayers of Al-doped zinc oxide and titanium oxide and activated for hydrogen evolution with electroDeposited Pt nanoparticles.
Abstract: A clean and efficient way to overcome the limited supply of fossil fuels and the greenhouse effect is the production of hydrogen fuel from sunlight and water through the semiconductor/water junction of a photoelectrochemical cell, where energy collection and water electrolysis are combined into a single semiconductor electrode. We present a highly active photocathode for solar H(2) production, consisting of electrodeposited cuprous oxide, which was protected against photocathodic decomposition in water by nanolayers of Al-doped zinc oxide and titanium oxide and activated for hydrogen evolution with electrodeposited Pt nanoparticles. The roles of the different surface protection components were investigated, and in the best case electrodes showed photocurrents of up to -7.6 mA cm(-2) at a potential of 0 V versus the reversible hydrogen electrode at mild pH. The electrodes remained active after 1 h of testing, cuprous oxide was found to be stable during the water reduction reaction and the Faradaic efficiency was estimated to be close to 100%.
TL;DR: By rational design of a core-shell structure with a set of lanthanide ions incorporated into separated layers at precisely defined concentrations, efficient upconversion emission can be realized through gadolinium sublattice-mediated energy migration for a wide range of Lanthanide activators without long-lived intermediary energy states.
Abstract: Photon upconversion is promising for applications such as biological imaging, data storage or solar cells. Here, we have investigated upconversion processes in a broad range of gadolinium-based nanoparticles of varying composition. We show that by rational design of a core-shell structure with a set of lanthanide ions incorporated into separated layers at precisely defined concentrations, efficient upconversion emission can be realized through gadolinium sublattice-mediated energy migration for a wide range of lanthanide activators without long-lived intermediary energy states. Furthermore, the use of the core-shell structure allows the elimination of deleterious cross-relaxation. This effect enables fine-tuning of upconversion emission through trapping of the migrating energy by the activators. Indeed, the findings described here suggest a general approach to constructing a new class of luminescent materials with tunable upconversion emissions by controlled manipulation of energy transfer within a nanoscopic region.
TL;DR: On the bicentenary of the publication of Poisson's Traité de Mécanique, the continuing relevance of Poissons's ratio in the understanding of the mechanical characteristics of modern materials is reviewed.
Abstract: In comparing a material's resistance to distort under mechanical load rather than to alter in volume, Poisson's ratio offers the fundamental metric by which to compare the performance of any material when strained elastically. The numerical limits are set by ½ and -1, between which all stable isotropic materials are found. With new experiments, computational methods and routes to materials synthesis, we assess what Poisson's ratio means in the contemporary understanding of the mechanical characteristics of modern materials. Central to these recent advances, we emphasize the significance of relationships outside the elastic limit between Poisson's ratio and densification, connectivity, ductility and the toughness of solids; and their association with the dynamic properties of the liquids from which they were condensed and into which they melt.
01 Oct 2011-Nature Materials
TL;DR: An atomic ligand strategy is established that makes use of monovalent halide anions to enhance electronic transport and successfully passivate surface defects in PbS CQD films that shows up to 6% solar AM1.5G power-conversion efficiency.
Abstract: Colloidal-quantum-dot (CQD) optoelectronics offer a compelling combination of solution processing and spectral tunability through quantum size effects. So far, CQD solar cells have relied on the use of organic ligands to passivate the surface of the semiconductor nanoparticles. Although inorganic metal chalcogenide ligands have led to record electronic transport parameters in CQD films, no photovoltaic device has been reported based on such compounds. Here we establish an atomic ligand strategy that makes use of monovalent halide anions to enhance electronic transport and successfully passivate surface defects in PbS CQD films. Both time-resolved infrared spectroscopy and transient device characterization indicate that the scheme leads to a shallower trap state distribution than the best organic ligands. Solar cells fabricated following this strategy show up to 6% solar AM1.5G power-conversion efficiency. The CQD films are deposited at room temperature and under ambient atmosphere, rendering the process amenable to low-cost, roll-by-roll fabrication.
TL;DR: It is shown that grain boundaries give a significant Raman 'D' peak, impede electrical transport, and induce prominent weak localization indicative of intervalley scattering in graphene, opening a route towards scalable fabrication of single-crystal graphene devices without grain boundaries.
Abstract: Chemical vapour deposition is a promising route for large-scale graphene growth. It is now shown that—through the use of seeds—high-quality, large, single-crystal domains can be grown on a patterned arrangement, and can be used to carefully study the transport across grain boundaries.
TL;DR: In this article, the authors describe localized surface plasmon resonances arising from p-type carriers in vacancy-doped semiconductor quantum dots (QDs) and demonstrate that doped QDs allow realization of LSPRs and quantum-confined excitons within the same nanostructure.
Abstract: Localized surface plasmon resonances (LSPRs) typically arise in nanostructures of noble metals resulting in enhanced and geometrically tunable absorption and scattering resonances. LSPRs, however, are not limited to nanostructures of metals and can also be achieved in semiconductor nanocrystals with appreciable free carrier concentrations. Here, we describe well-defined LSPRs arising from p-type carriers in vacancy-doped semiconductor quantum dots (QDs). Achievement of LSPRs by free carrier doping of a semiconductor nanocrystal would allow active on-chip control of LSPR responses. Plasmonic sensing and manipulation of solid-state processes in single nanocrystals constitutes another interesting possibility. We also demonstrate that doped semiconductor QDs allow realization of LSPRs and quantum-confined excitons within the same nanostructure, opening up the possibility of strong coupling of photonic and electronic modes, with implications for light harvesting, nonlinear optics, and quantum information processing.
TL;DR: It is shown that conducting polymers might be capable of meeting the demands of electricity production from waste heat (co-generation) and natural heat sources and to generate electricity from large volumes of warm fluids, heat exchangers must be functionalized with TEGs.
Abstract: Thermoelectric generators (TEGs) transform a heat flow into electricity. Thermoelectric materials are being investigated for electricity production from waste heat (co-generation) and natural heat sources. For temperatures below 200 °C, the best commercially available inorganic semiconductors are bismuth telluride (Bi(2)Te(3))-based alloys, which possess a figure of merit ZT close to one. Most of the recently discovered thermoelectric materials with ZT>2 exhibit one common property, namely their low lattice thermal conductivities. Nevertheless, a high ZT value is not enough to create a viable technology platform for energy harvesting. To generate electricity from large volumes of warm fluids, heat exchangers must be functionalized with TEGs. This requires thermoelectric materials that are readily synthesized, air stable, environmentally friendly and solution processable to create patterns on large areas. Here we show that conducting polymers might be capable of meeting these demands. The accurate control of the oxidation level in poly(3,4-ethylenedioxythiophene) (PEDOT) combined with its low intrinsic thermal conductivity (λ=0.37 W m(-1) K(-1)) yields a ZT=0.25 at room temperature that approaches the values required for efficient devices.
TL;DR: The discovery of a Ag(2)S inorganic synapse is reported, which emulates the synaptic functions of both STP and LTP characteristics through the use of input pulse repetition time and indicates a breakthrough in mimicking synaptic behaviour essential for the further creation of artificial neural systems that emulate characteristics of human memory.
Abstract: The electronic properties of inorganic devices such as memristors can be used to simulate neurological behaviour. In particular, ionic and electronic effects in a silver sulphide device are now shown to mimic short- and long-term synaptic functions. Memory is believed to occur in the human brain as a result of two types of synaptic plasticity: short-term plasticity (STP) and long-term potentiation (LTP; refs 1, 2, 3, 4). In neuromorphic engineering5,6, emulation of known neural behaviour has proven to be difficult to implement in software because of the highly complex interconnected nature of thought processes. Here we report the discovery of a Ag2S inorganic synapse, which emulates the synaptic functions of both STP and LTP characteristics through the use of input pulse repetition time. The structure known as an atomic switch7,8, operating at critical voltages, stores information as STP with a spontaneous decay of conductance level in response to intermittent input stimuli, whereas frequent stimulation results in a transition to LTP. The Ag2S inorganic synapse has interesting characteristics with analogies to an individual biological synapse, and achieves dynamic memorization in a single device without the need of external preprogramming. A psychological model related to the process of memorizing and forgetting is also demonstrated using the inorganic synapses. Our Ag2S element indicates a breakthrough in mimicking synaptic behaviour essential for the further creation of artificial neural systems that emulate characteristics of human memory.
TL;DR: The emergence of a new trend in the design of adaptive materials that involves the use of reversible chemistry to programme a response that originates at the most fundamental (molecular) level is described.
Abstract: In chemistry, some dynamic bonds can be selectively and reversibly broken and reformed in response to an environmental stimulus. This Review article discusses the incorporation of dynamic bonds, or interactions, in polymeric materials and the structural changes and macroscopic responses observed in the presence of different stimuli.
01 Feb 2011-Nature Materials
TL;DR: The formation of SkX close to room temperature in thin-films of the helimagnet FeGe with magnetic chirality inversion of the SkX across lattice twin boundaries will pave a new path to designing quantum-effect devices based on the controllable skyrmion dynamics.
Abstract: Skyrmions are vortex-like arrangements of spin magnetic moments, which so far have been observed in only a few compounds, and only at low temperatures. The discovery that skyrmions can be stabilized by thin magnetic films close to room temperature promises their use in spintronic devices.
01 Apr 2011-Nature Materials
TL;DR: Scanning tunnelling microscopy is used to show that graphene conforms to hBN, as evidenced by the presence of Moiré patterns, but contrary to predictions, this conformation does not lead to a sizeable band gap because of the misalignment of the lattices.
Abstract: Using boron nitride as a substrate for graphene has been suggested as a promising way to reduce the disorder in graphene caused by space fluctuations. It is now shown by scanning tunnelling microscopy that graphene conforms perfectly to boron nitride and the charge fluctuations are minimal compared with the conventionally used substrate, silica. Boron nitride could really be the natural graphene substrate. Graphene has demonstrated great promise for future electronics technology as well as fundamental physics applications because of its linear energy–momentum dispersion relations which cross at the Dirac point1,2. However, accessing the physics of the low-density region at the Dirac point has been difficult because of disorder that leaves the graphene with local microscopic electron and hole puddles3,4,5. Efforts have been made to reduce the disorder by suspending graphene, leading to fabrication challenges and delicate devices which make local spectroscopic measurements difficult6,7. Recently, it has been shown that placing graphene on hexagonal boron nitride (hBN) yields improved device performance8. Here we use scanning tunnelling microscopy to show that graphene conforms to hBN, as evidenced by the presence of Moire patterns. However, contrary to predictions9,10, this conformation does not lead to a sizeable band gap because of the misalignment of the lattices. Moreover, local spectroscopy measurements demonstrate that the electron–hole charge fluctuations are reduced by two orders of magnitude as compared with those on silicon oxide. This leads to charge fluctuations that are as small as in suspended graphene6, opening up Dirac point physics to more diverse experiments.
01 Apr 2011-Nature Materials
TL;DR: The development of porphysomes; nanovesicles formed from self-assembled porphyrin bilayers that generated large, tunable extinction coefficients, structure-dependent fluorescence self-quenching and unique photothermal and photoacoustic properties demonstrate the multimodal potential of organic nanoparticles for biophotonic imaging and therapy.
Abstract: Optically active nanomaterials promise to advance a range of biophotonic techniques through nanoscale optical effects and integration of multiple imaging and therapeutic modalities. Here, we report the development of porphysomes; nanovesicles formed from self-assembled porphyrin bilayers that generated large, tunable extinction coefficients, structure-dependent fluorescence self-quenching and unique photothermal and photoacoustic properties. Porphysomes enabled the sensitive visualization of lymphatic systems using photoacoustic tomography. Near-infrared fluorescence generation could be restored on dissociation, creating opportunities for low-background fluorescence imaging. As a result of their organic nature, porphysomes were enzymatically biodegradable and induced minimal acute toxicity in mice with intravenous doses of 1,000 mg kg^(−1). In a similar manner to liposomes, the large aqueous core of porphysomes could be passively or actively loaded. Following systemic administration, porphysomes accumulated in tumours of xenograft-bearing mice and laser irradiation induced photothermal tumour ablation. The optical properties and biocompatibility of porphysomes demonstrate the multimodal potential of organic nanoparticles for biophotonic imaging and therapy.
TL;DR: Combustion processing is now reported as a new low-temperature route for the deposition of diverse metal oxide films, and high-performance transistors are demonstrated using this method as discussed by the authors.
Abstract: Solution-deposited metal oxides show great potential for large-area electronics, but they generally require high annealing temperatures, which are incompatible with flexible polymeric substrates. Combustion processing is now reported as a new low-temperature route for the deposition of diverse metal oxide films, and high-performance transistors are demonstrated using this method.
TL;DR: Electrochemical processes are confirmed to be an accurate route to precisely investigate in a continuous way such a complex system and provide a new way to synthesize materials with a very narrow existence range.
Abstract: Sodium layered oxides NaxCoO2 form one of the most fascinating low-dimensional and strongly correlated systems; in particular P2–NaxCoO2 exhibits various single-phase domains with different Na+/vacancy patterns depending on the sodium concentration. Here we used sodium batteries to clearly depict the P2–NaxCoO2 phase diagram for x≥0.50. By coupling the electrochemical process with an in situ X-ray diffraction experiment, we identified the succession of single-phase or two-phase domains appearing on sodium intercalation with a rather good accuracy compared with previous studies. We reported new single-phase domains and we underlined the thermal instability of some ordered phases from an electrochemical study at various temperatures. As each phase is characterized by the position of its Fermi level versus the Na+/Na couple, we showed that the synthesis of each material, even in large amounts, can be carried out electrochemically. The physical properties of the as-prepared Na1/2CoO2 and Na2/3CoO2 ordered phases were characterized and compared. Electrochemical processes are confirmed to be an accurate route to precisely investigate in a continuous way such a complex system and provide a new way to synthesize materials with a very narrow existence range.
TL;DR: The formation of atomically flat quasi-two-dimensional colloidal CdSe, CdS and CdTe nanoplatelets with well-defined thicknesses ranging from 4 to 11 monolayers with electronic properties of two-dimensional quantum wells formed by molecular beam epitaxy are demonstrated.
Abstract: The syntheses of strongly anisotropic nanocrystals with one dimension much smaller than the two others, such as nanoplatelets, are still greatly underdeveloped. Here, we demonstrate the formation of atomically flat quasi-two-dimensional colloidal CdSe, CdS and CdTe nanoplatelets with well-defined thicknesses ranging from 4 to 11 monolayers. These nanoplatelets have the electronic properties of two-dimensional quantum wells formed by molecular beam epitaxy, and their thickness-dependent absorption and emission spectra are described very well within an eight-band Pidgeon-Brown model. They present an extremely narrow emission spectrum with full-width at half-maximum less than 40 meV at room temperature. The radiative fluorescent lifetime measured in CdSe nanoplatelets decreases with temperature, reaching 1 ns at 6 K, two orders of magnitude less than for spherical CdSe nanoparticles. This makes the nanoplatelets the fastest colloidal fluorescent emitters and strongly suggests that they show a giant oscillator strength transition.
01 Jul 2011-Nature Materials
TL;DR: A promising flat-panel solar thermal to electric power conversion technology based on the Seebeck effect and high thermal concentration is demonstrated, thus enabling wider applications and opening up a promising new approach which has the potential to achieve cost-effective conversion of solar energy into electricity.
Abstract: The conversion of sunlight into electricity has been dominated by photovoltaic and solar thermal power generation. A highly efficient solar to electric energy conversion device based on nanostructured thermoelectric materials and high solar concentration is now demonstrated. The results show potential for cost effective solar thermoelectric generation.
TL;DR: P porous nanoparticle-supported lipid bilayers (protocells) that synergistically combine properties of liposomes and nanoporous particles are reported that allow a single protocell loaded with a drug cocktail to kill a drug-resistant HCC cell, representing a 106-fold improvement over comparable liposome.
Abstract: Encapsulation of drugs within nanocarriers that selectively target malignant cells promises to mitigate side effects of conventional chemotherapy and to enable delivery of the unique drug combinations needed for personalized medicine. To realize this potential, however, targeted nanocarriers must simultaneously overcome multiple challenges, including specificity, stability and a high capacity for disparate cargos. Here we report porous nanoparticle-supported lipid bilayers (protocells) that synergistically combine properties of liposomes and nanoporous particles. Protocells modified with a targeting peptide that binds to human hepatocellular carcinoma exhibit a 10,000-fold greater affinity for human hepatocellular carcinoma than for hepatocytes, endothelial cells or immune cells. Furthermore, protocells can be loaded with combinations of therapeutic (drugs, small interfering RNA and toxins) and diagnostic (quantum dots) agents and modified to promote endosomal escape and nuclear accumulation of selected cargos. The enormous capacity of the high-surface-area nanoporous core combined with the enhanced targeting efficacy enabled by the fluid supported lipid bilayer enable a single protocell loaded with a drug cocktail to kill a drug-resistant human hepatocellular carcinoma cell, representing a 10(6)-fold improvement over comparable liposomes.
TL;DR: This work places a single palladium nanoparticle near the tip region of a gold nanoantenna and detects the changing optical properties of the system upon hydrogen exposure, demonstrating antenna-enhanced hydrogen sensing at the single-particle level.
Abstract: Plasmonic resonances are widely used for sensing applications. The plasmon resonance of a single nanoantenna structure is now used to detect changes in the dielectric properties of a nearby palladium nanoparticle exposed to hydrogen gas, enabling highly sensitive sensing in ultrasmall volumes. The approach can be easily extended to other sensing and catalysis schemes.
TL;DR: The formation of amorphous metal oxide semiconducting thin-films using a ‘sol–gel on chip’ hydrolysis approach from soluble metal alkoxide precursors affords unprecedented high field-effect mobilities, reproducible and stable turn-on voltages Von≈0 V and high operational stability at maximum process temperatures as low as 230 °C.
Abstract: A low-temperature, solution-based preparation of amorphous, metal oxide semiconducting thin-films is reported. This ‘sol–gel on chip’ hydrolysis approach yields thin-film transistors with high field-effect mobilities, reproducible and stable turn-on voltages and high operational stability.
01 Mar 2011-Nature Materials
TL;DR: Developments towards applications as emissive and photovoltaic materials; as optical limiters; in nanoelectronics, information storage, nanopatterning and sensing; as macromolecular catalysts and artificial enzymes; and as stimuli-responsive materials are illustrated.
Abstract: Synthetic polymers containing metal centres are emerging as an interesting and broad class of easily processable materials with properties and functions that complement those of state-of-the-art organic macromolecular materials. A diverse range of different metal centres can be harnessed to tune macromolecular properties, from transition- and main-group metals to lanthanides. Moreover, the linkages that bind the metal centres can vary almost continuously from strong, essentially covalent bonds that lead to irreversible or 'static' binding of the metal to weak and labile, non-covalent coordination interactions that allow for reversible, 'dynamic' or 'metallosupramolecular', binding. Here we review recent advances and challenges in the field and illustrate developments towards applications as emissive and photovoltaic materials; as optical limiters; in nanoelectronics, information storage, nanopatterning and sensing; as macromolecular catalysts and artificial enzymes; and as stimuli-responsive materials. We focus on materials in which the metal centres provide function; although they can also play a structural role, systems where this is solely their purpose have not been discussed.
TL;DR: A strong composition gradient in the absorber layer is identified as the main reason for inferior performance and it is shown that, by adjusting it appropriately, very high efficiencies can be obtained.
Abstract: Solar cells based on polycrystalline Cu(In,Ga)Se(2) absorber layers have yielded the highest conversion efficiency among all thin-film technologies, and the use of flexible polymer films as substrates offers several advantages in lowering manufacturing costs. However, given that conversion efficiency is crucial for cost-competitiveness, it is necessary to develop devices on flexible substrates that perform as well as those obtained on rigid substrates. Such comparable performance has not previously been achieved, primarily because polymer films require much lower substrate temperatures during absorber deposition, generally resulting in much lower efficiencies. Here we identify a strong composition gradient in the absorber layer as the main reason for inferior performance and show that, by adjusting it appropriately, very high efficiencies can be obtained. This implies that future manufacturing of highly efficient flexible solar cells could lower the cost of solar electricity and thus become a significant branch of the photovoltaic industry.
TL;DR: In an ultrathin Co nanowire, integrated in a trilayer with structural inversion asymmetry (SIA), the high spin-torque efficiency facilitates the depinning and leads to high mobility, while the SIA-mediated Rashba field controlling the domain-wall chirality stabilizes the Bloch domain- wall structure.
Abstract: The propagation of magnetic domain walls induced by spin-polarized currents has launched new concepts for memory and logic devices. A wave of studies focusing on permalloy (NiFe) nanowires has found evidence for high domain-wall velocities (100 m s(-1); refs,), but has also exposed the drawbacks of this phenomenon for applications. Often the domain-wall displacements are not reproducible, their depinning from a thermally stable position is difficult and the domain-wall structural instability (Walker breakdown) limits the maximum velocity. Here, we show that the combined action of spin-transfer and spin-orbit torques offers a comprehensive solution to these problems. In an ultrathin Co nanowire, integrated in a trilayer with structural inversion asymmetry (SIA), the high spin-torque efficiency facilitates the depinning and leads to high mobility, while the SIA-mediated Rashba field controlling the domain-wall chirality stabilizes the Bloch domain-wall structure. Thus, the high-mobility regime is extended to higher current densities, allowing domain-wall velocities up to 400 m s(-1).