Showing papers in "Annual Review of Materials Research in 2013"
TL;DR: Flexoelectricity is a universal effect allowed by symmetry in all materials as discussed by the authors and has been studied in many nanoscale systems, and potential applications of this electromechanical phenomenon have been discussed.
Abstract: Flexoelectricity—the coupling between polarization and strain gradients—is a universal effect allowed by symmetry in all materials. Following its discovery several decades ago, studies of flexoelectricity in solids have been scarce due to the seemingly small magnitude of this effect in bulk samples. The development of nanoscale technologies, however, has renewed the interest in flexoelectricity, as the large strain gradients often present at the nanoscale can lead to strong flexoelectric effects. Here we review the fundamentals of the flexoelectric effect in solids, discuss its presence in many nanoscale systems, and look at potential applications of this electromechanical phenomenon. The review also emphasizes the many open questions and unresolved issues in this developing field.
767 citations
TL;DR: A review of the current needs and key aspects of the conversion process is given in this paper, where the authors describe some currently used families of phosphors and consider why they are suitable for solid-state lighting.
Abstract: Since the mid-1990s, phosphors have played a key role in emerging solid-state white-lighting technologies that are based on combining a III-nitride-based near-UV or blue solid-state light source with downconversion to longer wavelengths. Almost all widely used phosphors comprise a crystalline oxide, nitride, or oxynitride host that is appropriately doped with either Ce3+ or Eu2+. These ions, with [Xe] 4fn5d0 configurations (n = 1 for Ce3+ and 7 for Eu2+) have proximal excited states that are [Xe] 4fn−15d1. Optical excitation into these states and concomitant reemission can be tuned into the appropriate regions of the visible spectrum by the crystal these ions are hosted in. In this article, we review the current needs and key aspects of the conversion process. We describe some currently used families of phosphors and consider why they are suitable for solid-state lighting. Finally, we describe some empirical rules for new and improved host materials.
646 citations
TL;DR: In this paper, the authors proposed a method known as optical sectioning SIM (OSSIM) to remove the out-of-focus blur caused by the Moire effect in a wide-field fluorescence microscope.
Abstract: The resolution of an optical microscope is fundamentally limited by diffraction. In a conventional wide-field fluorescence microscope, the resolution limit is at best 200 nm. However, modern superresolution methods can bypass this limit. Pointillistic imaging techniques like PALM (photoactivated localization microscopy) and STORM (stochastic optical reconstruction microscopy) do so by precisely localizing each individual molecule in a sample. In contrast, STED uses the stimulated emission process driven to saturation to dramatically reduce the size of the region in the sample that is capable of spontaneously emitting fluorescence. Structured illumination microscopy (SIM) illuminates the sample with a pattern, typically the image of a grating. This computationally removes the out-of-focus blur, a method known as optical sectioning SIM. Furthermore, frequency mixing of the illumination pattern with the sample caused by the moire effect results in a downmodulation of fine sample detail into the frequency-sup...
387 citations
TL;DR: In this article, a phase field model for spinodal decomposition and ripening in Ag-Cu with realistic thermodynamic and kinetic data from a database is presented, and the model is applied to spinodic decomposition.
Abstract: This review presents a phase-field model that is generally applicable to homogeneous and heterogeneous systems at the mesoscopic scale. Reviewed first are general aspects about first- and second-order phase transitions that need to be considered to understand the theoretical background of a phase field. The mesoscopic model equations are defined by a coarse-graining procedure from a microscopic model in the continuum limit on the atomic scale. Special emphasis is given to the question of how to separate the interface and bulk contributions to the generalized thermodynamic functional, which forms the basis of all phase-field models. Numerical aspects of the discretization are discussed at the lower scale of applicability. The model is applied to spinodal decomposition and ripening in Ag-Cu with realistic thermodynamic and kinetic data from a database.
210 citations
TL;DR: In this paper, a review outlines the interactions in ionic liquids that are responsible for the advantageous properties of these solvents in electroplating and summarizes recent research in which these properties have been analyzed or exploited and highlights fundamental issues in research and technology that need to be addressed.
Abstract: Electroplating is a key technology in many large-scale industrial applications such as corrosion-resistant and decorative coatings. Issues with current aqueous processes, such as toxicity of reagents and low current efficiencies, can often be overcome by using ionic liquids, and this approach has turned ionometallurgy into a fast-growing area of research. This review outlines the interactions in ionic liquids that are responsible for the advantageous properties of these solvents in electroplating. It summarizes recent research in which these properties have been analyzed or exploited and highlights fundamental issues in research and technology that need to be addressed.
208 citations
TL;DR: A review of the development of hard X-ray microscopy techniques for materials characterization at the nanoscale can be found in this article, where the authors review the current state of synchrotron-based, hard Xray nanoscopy techniques.
Abstract: This review discusses recent progress in the development of hard X-ray microscopy techniques for materials characterization at the nanoscale. Although the utility of traditionally ensemble-based X-ray techniques in materials research has been widely recognized, the utility of X-ray techniques as a tool for local characterization of nanoscale materials properties has undergone rapid development in recent years. Owing to a confluence of improvements in synchrotron source brightness, focusing optics fabrication, detection, and data analysis, nanoscale X-ray imaging techniques have moved beyond proof-of-principle experiments to play a central role in synchrotron user programs worldwide with high-impact applications made to materials science questions. Here, we review the current state of synchrotron-based, hard X-ray nanoscale microscopy techniques—including 3D tomographic visualization, spectroscopic elemental and chemical mapping, microdiffraction-based structural analysis, and coherent methods for nanomate...
152 citations
TL;DR: This review describes molecular elements inside and outside of the cell that establish labile physical connections, and how forces regulate their interplay, namely formation, reinforcement, breakage, and reconfiguration of these elements.
Abstract: According to the Chinese yin-yang concept, seemingly opposing forces give rise and respond to each other. Opposing forces, whether passive or active, are also at work when cells adhere to a substrate or extracellular matrix, sense environmental properties, and finally respond to them. In this review, we describe molecular elements inside and outside of the cell that establish labile physical connections, and how forces regulate their interplay, namely formation, reinforcement, breakage, and reconfiguration of these elements. What a cell locally feels thus depends not only on the displacement of materials, but also on the stability of molecular interactions, on the conversion of mechanical forces to biochemical signals by stretching proteins into structural intermediates (mechano-chemical signal conversion), and on the micro- and nanoscopic features of the extracellular material. Current methodologies for quantifying forces in the cellular context at different length scales are also critically assessed.
118 citations
TL;DR: In this paper, the authors describe some recent advances in crystal morphology engineering, with a special focus on a new mechanistic model for spiral growth, which is a surface-controlled phenomenon in which solute molecules are incorporated into surface lattice sites to yield the bulk long-range order that characterizes crystalline materials.
Abstract: Crystallization is an important separation and particle formation technique in the manufacture of high-value-added products. During crystallization, many physicochemical characteristics of the substance are established. Such characteristics include crystal polymorph, shape and size, chemical purity and stability, reactivity, and electrical and magnetic properties. However, control over the physical form of crystalline materials has remained poor, due mainly to an inadequate understanding of the basic growth and dissolution mechanisms, as well as of the influence of impurities, additives, and solvents on the growth rate of individual crystal faces. Crystal growth is a surface-controlled phenomenon in which solute molecules are incorporated into surface lattice sites to yield the bulk long-range order that characterizes crystalline materials. In this article, we describe some recent advances in crystal morphology engineering, with a special focus on a new mechanistic model for spiral growth. These mechanist...
114 citations
TL;DR: In this paper, the authors discuss salient issues concerning uncertainty quantification from a variety of fields and review the sparse literature on UQ in materials simulations, identifying needs for conceptual advances, needs for the development of best practices, and needs for specific implementations.
Abstract: Simulation has long since joined experiment and theory as a valuable tool to address materials problems. Analysis of errors and uncertainties in experiment and theory is well developed; such analysis for simulations, particularly for simulations linked across length scales and timescales, is much less advanced. In this prospective, we discuss salient issues concerning uncertainty quantification (UQ) from a variety of fields and review the sparse literature on UQ in materials simulations. As specific examples, we examine the development of atomistic potentials and multiscale simulations of crystal plasticity. We identify needs for conceptual advances, needs for the development of best practices, and needs for specific implementations.
105 citations
TL;DR: In this article, the authors present a review of water vapor-mediated volatilization in high-temperature materials during processing and in service, and the significance of these processes.
Abstract: Volatilization in water vapor–containing atmospheres is an important and often unexpected mechanism of degradation of high-temperature materials during processing and in service. Thermodynamic properties data sets for key (oxy)hydroxide vapor product species that are responsible for material transport and damage are often uncertain or unavailable. Estimation, quantum chemistry calculation, and measurement methods for thermodynamic properties of these species are reviewed, and data judged to be reliable are tabulated and referenced. Applications of water vapor–mediated volatilization include component and coating recession in turbine engines, oxidation/volatilization of ferritic steels in steam boilers, chromium poisoning in solid-oxide fuel cells, vanadium transport in hot corrosion and degradation of hydrocracking catalysts, Na loss from Na β″-Al2O3 tubes, and environmental release of radioactive isotopes in a nuclear reactor accident or waste incineration. The significance of water vapor–mediated volati...
103 citations
TL;DR: Density functional theory models have been developed over the past decade to provide unique information about the structure of nanoscale defects produced by irradiation and about the nature of short-range interaction between radia- tion defects, clustering of defects, and their migration pathways as discussed by the authors.
Abstract: Density functional theory models developed over the past decade provide unique information about the structure of nanoscale defects produced by irradiation and about the nature of short-range interaction between radia- tion defects, clustering of defects, and their migration pathways. These ab initio models, involving no experimental input parameters, appear to be as quantitatively accurate and informative as the most advanced experimental techniques developed for the observation of radiation damage phenomena. Density functional theory models have effectively created a new paradigm for the scientific investigation and assessment of radiation damage effects, offering new insight into the origin of temperature- and dose-dependent response of materials to irradiation, a problem of pivotal significance for applications.
TL;DR: In this paper, a review summarizes recent advancements in the application of PFM to a number of ferroelectric relaxors and provides a tentative explanation of the peculiar polarization distributions related to the intriguing physical phenomena in these materials.
Abstract: Ferroelectric relaxors continue to be one of the most mysterious solid-state materials. Since their discovery by Smolenskii and coworkers, there have been many attempts to understand the properties of these materials, which are exotic, yet useful for applications. On the basis of the numerous experimental data, several theories have been established, but none of them can explain all the properties of relaxors. The recent advent of piezoresponse force microscopy (PFM) has allowed for polarization mapping on the surface of relaxors with subnanometer resolution. This development thus leads to the question of whether the polar nanoregions that contribute to diffuse X-ray scattering and a range of macroscopic properties can be visualized. This review summarizes recent advancements in the application of PFM to a number of ferroelectric relaxors and provides a tentative explanation of the peculiar polarization distributions related to the intriguing physical phenomena in these materials.
TL;DR: In this paper, the authors discuss opportunities and challenges of recently developed computational strategies to predict the dynamics of self-assembly of polymeric materials on the basis of the underlying free-energy landscape.
Abstract: Polymeric materials can assemble into a multitude of intricate nanoscale morphologies whose free energy differs by only a fraction of the thermal energy per molecule. Such small free-energy differences pose a challenge for modeling and simulation but also offer exciting opportunities to direct the assembly of such materials into morphologies that do not correspond to those of equilibrium bulk structures. Over the past decade, significant progress has been achieved in our ability to guide their self-assembly through the use of confinement, topographical or chemical patterns, and electric fields. In contrast, approaches to guide self-assembly by tailoring the dynamics of structure formation have received less attention. This review discusses opportunities and challenges of recently developed computational strategies to predict the dynamics of self-assembly of polymeric materials on the basis of the underlying free-energy landscape.
TL;DR: In this article, the theoretical description of charge transport and charge injection from electrodes in organic semiconductors is presented at the density functional theory level, with an emphasis on the work-function modifications induced by the organic layer and on the interfacial energy-level alignments.
Abstract: We focus this review on the theoretical description, at the density functional theory level, of two key processes that are common to electronic devices based on organic semiconductors (such as organic light-emitting diodes, field-effect transistors, and solar cells), namely charge transport and charge injection from electrodes. By using representative examples of current interest, our main goal is to introduce some of the reliable theoretical methodologies that can best depict these processes. We first discuss the evaluation of the microscopic parameters that determine charge-carrier transport in organic molecular crystals, i.e., electronic couplings and electron-vibration couplings. We then examine the electronic structure at interfaces between an organic layer and a metal or conducting oxide electrode, with an emphasis on the work-function modifications induced by the organic layer and on the interfacial energy-level alignments.
TL;DR: In this paper, the authors demonstrate that electro-optic imaging combined with the brightness of recently developed intense terahertz sources permits the imaging of subwavelength-size samples without compromising spatial resolution or acquisition time.
Abstract: The fields of biosensing, nanospectroscopy, and plasmonics have great potential for near-field terahertz (THz) technology. In this work, we demonstrate that electro-optic (EO) imaging combined with the brightness of recently developed intense THz sources permits the imaging of subwavelength-size samples without compromising spatial resolution or acquisition time. We report on recent advances in this field and current achievements in optimizing spatial resolution and acquisition time. Near-field imaging demonstrations on field enhancement in metallic-based resonators and metamaterials are also discussed. This development will accelerate our comprehension of subwavelength light-matter interactions at THz frequencies and enable new spectroscopic applications.
TL;DR: In this article, a review of the capabilities of bionanomaterials and bio-inspired nanostructures for selective vapor sensing is presented, where the authors demonstrate that these sensing materials with new performance properties can be coupled with the suitable physical transducers.
Abstract: At present, monitoring of air at the workplace, in urban environments, and on battlefields; exhaled air from medical patients; air in packaged food containers; and so forth can be accomplished with different types of analytical instruments. Vapor sensors have their niche in these measurements when an unobtrusive, low-power, and cost-sensitive technical solution is required. Unfortunately, existing vapor sensors often degrade their vapor-quantitation accuracy in the presence of high levels of interferences and cannot quantitate several components in complex gas mixtures. Thus, new sensing approaches with improved sensor selectivity are required. This technological task can be accomplished by the careful design of sensing materials with new performance properties and by coupling these materials with the suitable physical transducers. This review is focused on the assessment of the capabilities of bionanomaterials and bioinspired nanostructures for selective vapor sensing. We demonstrate that these sensing m...
TL;DR: In this paper, the authors review recent advances in nonlinear optical (NLO) microscopy studies of single nanostructures and discuss NLO modalities based on harmonic generation, multiphoton photoluminescence, four-wave mixing, and pump-probe processes.
Abstract: We review recent advances in nonlinear optical (NLO) microscopy studies of single nanostructures. NLO signals are intrinsically sensitive to the electronic, vibrational, and structural properties of such nanostructures. Ultrafast excitation allows for mapping of energy relaxation pathways at the single-particle level. The strong nonlinear response of nanostructures makes them highly attractive for applications as novel NLO imaging agents in biological and biomedical research. NLO modalities based on harmonic generation, multiphoton photoluminescence, four-wave mixing, and pump-probe processes are discussed in detail.
TL;DR: In this paper, high-pressure chemical vapor deposition (HPCVD) is used to create conformal layers and void-free wires of precisely doped crystalline unary and compound semiconductors inside the micro-to-nanoscale-diameter pores of microstructured optical fibers.
Abstract: Chemical deposition is a powerful technology for fabrication of planar microelectronics. Optical fibers are the dominant platform for telecommunications, and devices such as fiber lasers are forming the basis for new industries. High-pressure chemical vapor deposition (HPCVD) allows for conformal layers and void-free wires of precisely doped crystalline unary and compound semiconductors inside the micro-to-nanoscale-diameter pores of microstructured optical fibers (MOFs). Drawing the fibers to serve as templates into which these semiconductor structures can be fabricated allows for geometric design flexibility that is difficult to achieve with planar fabrication. Seamless coupling of semiconductor optoelectronic and photonic devices with existing fiber infrastructure thus becomes possible, facilitating all-fiber technological approaches. The deposition techniques also allow for a wider range of semiconductor materials compositions to be exploited than is possible by means of preform drawing. Gigahertz bandwidth junction-based fiber devices can be fabricated from doped crystalline semiconductors, for example. Deposition of amorphous hydrogenated silicon, which cannot be drawn, allows for the exploitation of strong nonlinear optical function in fibers. Finally, crystalline compound semiconductor fiber cores hold promise for high-power infrared light-guiding fiber devices and subwavelength-resolution, large-area infrared imaging.
TL;DR: In this article, the authors review the strengths and limitations of simulation techniques that are most commonly used to model the mechanical behavior of ceramics and discuss specific application areas of simulations, focusing on the effects of high strain rate, confined deformation volume, altered material chemistry, and high temperature.
Abstract: The mechanical behavior of ceramics in extreme environments can be qualitatively different from that observed at ambient conditions and at typical loading rates. For instance, during shock loading the fracture of ceramics is not controlled by the largest flaw. Computer simulations play an increasingly important role in understanding and predicting material behavior, in particular under conditions in which experiments might be challenging or expensive. Here, we review the strengths and limitations of simulation techniques that are most commonly used to model the mechanical behavior of ceramics. We discuss specific application areas of simulations, focusing on the effects of high strain rate, confined deformation volume, altered material chemistry, and high temperature. We conclude by providing examples of future opportunities for modeling studies in this field.