bluuebunny/crossref_metadata_2025 huggingface dataset:
Silicon Nanomembranes
Authors: Lagally Max G.
Published: February 2011

This article is based on the presentation given by Max G. Lagally (University of Wisconsin–Madison) as part of Symposium X: Frontiers of Materials Research on April 18, 2006, at the Materials Research Society Spring Meeting in San Francisco.

Structures with nanoscale dimensions are the essence of nanotechnology. Beginning with quantum dots and buckyballs, nanostructures now include nanotubes, rods, wires, and most recently, nanomembranes: very thin, large, freestanding or freefloating strain-engineered single crystals that can variously be made into tubes or other shapes, cut into millions of identical wires, or used as conformal sheets. This article provides a brief overview of the fabrication and properties of strained-silicon nanomembranes.
Powering the Planet
Authors: Lewis Nathan S.
Published: February 2011

I am humbled and honored to be here to tell you about a topic that is dear to everyone's heart—and vital to the future of our planet. My colleague, Richard Smalley, gave a presentation on this topic several years ago, at a similar MRS plenary session. Over the last few years of Dr. Smalley's life, he and I worked together, traveling across our country to deliver a message about a subject that we—like many others, both scientists and lay people— have come to believe is unequivocally the most important technological problem in the world: our global energy future. That is an incredibly powerful statement, one that during the next hour I hope to ably defend.
Systematic Coarse Graining of Biomolecular and Soft-Matter Systems
Authors: Ayton Gary S. , Noid Will G. , Voth Gregory A.
Published: February 2011

Coarse-grained modeling is a key component in the field of multiscale simulation. Many biomolecular and otherwise complex systems require the characterization of phenomena over multiple length and time scales in order to fully resolve and understand their behavior. These different scales range from atomic to near macroscopic dimensions, and they are generally not independent of one another, but instead coupled. That is, phenomena occurring at atomic length scales have an effect at macroscopic dimensions and vice versa. Systematic transfer of information between these different scales represents a core challenge in the field of multiscale simulation. Coarse-grained modeling works at an intermediate resolution that can bridge the very high resolution (atomic) scale to the very low resolution (macroscopic) scale. As such, a significant challenge is the development of a systematic methodology whereby coarse-grained models can be derived from their high-resolution atomistic-scale counterpart. Here, a systematic theoretical and computational methodology will be described for developing coarse-grained representations of biomolecular and other soft-matter systems. At the heart of the methodology is a variational statistical mechanical algorithm that uses forcematching of atomistic molecular dynamics data to a coarse-grained representation. A theoretical analysis of the coarse-graining methodology will be presented, along with illustrative applications to membranes, peptides, and carbohydrates.
NovelIn SituProbes for Nanocatalysis
Authors: Stierle Andreas , Molenbroek Alfons M.
Published: February 2011

During the past few years, substantial effort has been devoted to developing new experimental techniques capable of delivering atomic-scale information on surfaces and nanoparticles under catalytic reaction conditions. Since the advent of surface science, pioneering experiments under highly idealized conditions have been performed (at very low gas pressures, <10−6mbar), and idealized model material systems (e.g., single crystals) have been investigated. However, understanding chemical reactions on singlecrystal surfaces close to ultrahigh vacuum does not always enable prediction of the performance of nanoparticles operating at gas pressures near or above atmospheric pressure. Therefore, thisMRS Bulletinissue focuses on the capabilities of atomic-scaleresolution, high-gas-pressure- and high-temperature-compatiblein situprobes sensitive to the structure, chemical composition, and dynamical properties of nanomaterials. It will be demonstrated how novelin situtechniques enable one to bridge the combined pressure and materials gaps from ultrahigh vacuum to atmospheric pressures and from metal single-crystal surfaces to nanoparticles or oxides.
In Situ Investigations of Chemical Reactions on Surfaces by X-Ray Diffraction at Atomospheric Pressures
Authors: Ferrer S. , Ackermann M. D. , Lundgren E.
Published: February 2011

Catalytic reactions occurring at metal surfaces and nanoparticles have been an established research field for decades, yielding information on adsorption sites and reaction pathways under ultrahigh-vacuum conditions. Recent experimental developments have made it possible to perform well-controlled in situ surface x-ray diffraction measurements from single-crystal surfaces and nanoparticles under industrially relevant conditions. In this way, a new understanding of atomic-scale processes at surfaces and nanoparticles occurring during catalytic reactions under realistic conditions has been gained. In particular, the identification of the formation of thin oxides on model catalysts and their role in oxidation reactions demonstrates the importance of in situ probes under relevant conditions.
The Reactor-STM: A Real-Space Probe forOperandoNanocatalysis
Authors: Frenken Joost , Hendriksen Bas
Published: February 2011

“Looking” on the other side of the pressure gap in heterogeneous catalysis is an essential step in identifying and understanding differences and similarities between the behavior of catalysts under actual operation conditions (operando) and under the nearvacuum conditions of traditional laboratory experiments. In this article, we demonstrate that real-space, atomic-scale imaging of active catalyst surfaces is possible under realistic or semirealistic reaction conditions with the reactor-STM, a scanning tunneling microscope that is fully integrated with a miniature flow reactor and housed inside an ultrahigh-vacuum system. This special-purpose instrument combines the merits of standard surface-science methods withoperandoSTM observations of model catalysts in action. We illustrate the strength of this microscope with examples of CO oxidation on platinum surfaces.
Sum Frequency Laser Spectroscopy during Chemical Reactions on Surfaces
Authors: Rupprechter Günther
Published: February 2011

The surface specificity of vibrational sum frequency generation (VSFG) spectroscopy allows one to characterize adsorbed and reacting molecules on catalyst surfaces while the catalyst functions at high pressure and high temperature. VSFG spectroscopy can be carried out in different modes, including scanning, broadband, time-resolved, and polarization-dependent, and has been applied to various active surfaces. Single-crystal and nanoparticle model catalysts have mostly been used, which are typically prepared under ultrahigh vacuum, but applications to powder materials have been reported recently. In this article, the fundamentals and technical aspects of VSFG are summarized, and its benefits are illustrated by case studies of elementary processes of heterogeneous catalysis.
Polymer Nanocomposites
Authors: Winey Karen I. , Vaia Richard A.
Published: February 2011

Polymer nanocomposites (PNCs)–that is, nanopar ticles (spheres, rods, plates) dispersed in a polymer matrix–have garnered substantial academic and industrial in terest since their inception, circa 1990. This is due in large part to the incredible promise demonstrated by these early efforts: PNCs will not only expand the per form ance space of traditional filled polymers, but introduce completely new combinations of properties and thus enable new applications for plastics. Low volume additions (1–5%) of nanopar -ticles, such as layered silicates or carbon nanotubes, provide property enhancements with respect to the neat resin that are comparable to those achieved by conventional loadings (15–40%) of traditional fillers. The lower loadings facilitate proc essing and re duce component weight. Most important, though, is the unique value - added properties not normally possible with traditional fillers, such as reduced permeability, optical clarity, self - passivation, and increased re sis tance to oxidation and ablation. These characteristics have been transformed into numerous commercial suc cesses, including automotive parts, coatings, and flame retardants. This issue of theMRS Bulletinprovides a snapshot of these exemplary successes, future opportunities, and the critical scientific challenges still to be addressed for these nanoscale multiphase systems. In addition, these ar ticles provide a perspective on the current status and future directions of polymer nanocomposite science and technology and their potential to move beyond additive concepts to designed ma te rials and devices with prescribed nanoscale composition and morphology.
Strategies for Dispersing Nanoparticles in Polymers
Authors: Krishnamoorti Ramanan
Published: February 2011

Controlling the dispersion of nanoparticles in polymeric matrices is the most significant impediment in the development of high-perform ance polymer nanocomposite ma te rials and results primarily from the strong interpar ticle interactions between the nanopar ticles. This review examines the theoretical and experimental strategies employed in developing appropriate chemical and physical methods to achieve controlled dispersion of nanopar ticles. Methods to characterize the state of dispersion, including force and electron micros copy, and scattering, electrical, and mechanical spectroscopy, are considered with special emphasis on achieving quantitative meas ures of the dispersion. Some of the outstanding issues, such as long-term aging and the implication for the dispersion of nanopar ticles, development of high-throughput methods for rapid screening, and methods for in-line monitoring, are also discussed.
Transparent Conducting Oxides for Photovoltaics
Authors: Fortunato Elvira , Ginley David , Hosono Hideo , Paine David C.
Published: February 2011

Transparent conducting oxides (TCOs) are an increasingly important component of photovoltaic (PV) devices, where they act as electrode elements, structural templates, and diffusion barriers, and their work function controls the open-circuit device voltage. They are employed in applications that range from crystalline-Si heterojunction with intrinsic thin layer (HIT) cells to organic PV polymer solar cells. The desirable characteristics of TCO materials that are common to all PV technologies are similar to the requirements for TCOs for flat-panel display applications and include high optical transmissivity across a wide spectrum and low resistivity. Additionally, TCOs for terrestrial PV applications must use low-cost materials, and some may require device-technology-specific properties. We review the fundamentals of TCOs and the matrix of TCO properties and processing as they apply to current and future PV technologies.
Epitaxial Growth of III-V Nanowires on Group IV Substrates
Authors: Bakkers Erik P. A. M. , Borgström Magnus T. , Verheijen Marcel A.
Published: February 2011

Semiconducting nanowires are emerging as a route to combine heavily mismatched materials. The high level of control on wire dimensions and chemical composition makes them promising materials to be integrated in future silicon technologies as well as to be the active element in optoelectronic devices.

This ar ticle reviews the recent progress in epitaxial growth of nanowires on non-corresponding substrates. We highlight the advantage of using small dimensions to facilitate accommodation of the lattice strain at the surface of the structures. More specifically, we will focus on the growth of III-V nanowires on Group IV substrates. This approach enables the integration of high-perform ance III-V semiconductors monolithically into mature silicon technology, since fundamental issues of III-V integration on Si such as lattice and thermal expansion mismatch can be overcome. Moreover, as there will only be one nucleation site per crystallite, the system will not suffer from antiphase boundaries.

Issues that affect the electronic properties of the heterojunction, such as the crystallographic quality and diffusion of elements across the heterointerface, will be discussed. Finally, we address potential applications of vertical III-V nanowires grown on silicon.
Assembled Semiconductor Nanowire Thin Films for High-Performance Flexible Macroelectronics
Authors: Duan Xiangfeng
Published: February 2011

A new concept of macroelectronics using assembled semiconductor nanowire thin films holds the promise of significant performance improvement. In this new concept, a thin film of oriented semiconductor nanowires is used to produce thin-film transistors (TFTs) with conducting channels formed by multiple parallel single-crystal nanowire paths. There fore, charges travel from source to drain within single crystals, ensuring high carrier mobility. Recent studies have shown that high-performance silicon nanowire TFTs and high-frequency circuits can be readily produced on a variety of substrates including glass and plastics using a solution assembly process. The device performance of these nanowire TFTs not only greatly surpasses that of solution-processed organic TFTs, but is also significantly better than that of conventional amorphous or polycrystalline silicon TFTs, approaching single-crystal silicon-based devices. Furthermore, with a similar frame-work, Group III-V or II-VI nanowire or nanoribbon materials of high intrinsic carrier mobility or optical functionality can be assembled into thin films on flexible substrates to enable new multifunctional electronics/optoelectronics that are not possible with traditional macroelectronics. This can have an impact on a broad range of existing applications, from flat-panel displays to image sensor arrays, and enable a new generation of flexible, wearable, or disposable electronics for computing, storage, and wireless communication.
Nanowire-Based Nanoelectronic Devices in the Life Sciences
Authors: Patolsky Fernando , Timko Brian P. , Zheng Gengfeng , Lieber Charles M.
Published: February 2011

The interface between nanosystems and biosystems is emerging as one of the broadest and most dynamic areas of science and technology, bringing together biology, chemistry, physics, biotechnology, medicine, and many areas of engineering. The combination of these diverse areas of research promises to yield revolutionary advances in healthcare, medicine, and the life sciences through the creation of new and powerful tools that enable direct, sensitive, and rapid analysis of biological and chemical species. Devices based on nanowires have emerged as one of the most powerful and general platforms for ultrasensitive, direct electrical detection of biological and chemical species and for building functional interfaces to biological systems, including neurons. Here, we discuss representative ex amples of nanowire nanosensors for ultrasensitive detection of proteins and individual virus particles as well as recording, stimulation, and inhibition of neuronal signals in nanowire-neuron hybrid structures.
The Mechanics and Physics of Defect Nucleation
Authors: Li Ju
Published: February 2011

The following article is based on the Outstanding Young Investigator Award presentation given by Ju Li on April 19, 2006, at the Materials Research Society Spring Meeting in San Francisco. Li received the award “for his innovative work on the atomistic and first-principles modeling of nanoindentation and ideal strength in revealing the genesis of materials deformation and fracture.”

Defect nucleation plays a critical role in the mechanical behavior of materials, especially if the system size is reduced to the submicron scale. At the most fundamental level, defect nucleation is controlled by bond breaking and reformation events, driven typically by mechanical strain and electronegativity differences. For these processes, atomistic and first-principles calculations are uniquely suited to provide an unprecedented level of mechanistic detail. Several connecting threads incorporating notions in continuum mechanics and explicit knowledge of the interatomic energy landscape can be identified, such as homogeneous versus heterogeneous nucleation, cleavage versus shear-faulting tendencies, chemomechanical coupling, and the fact that defects are singularities at the continuum level but regularized at the atomic scale. Examples are chosen from nano-indentation, crack-tip processes, and grain-boundary processes. In addition to the capacity of simulations to identify candidate mechanisms, the computed athermal strength, activation energy, and activation volume can be compared quantitatively with experiments to define the fundamental properties of defects in solids.
TEM Sample Preparation and FIB-Induced Damage
Authors: Mayer Joachim , Giannuzzi Lucille A. , Kamino Takeo , Michael Joseph
Published: February 2011

One of the most important applications of a focused ion beam (FIB) workstation is preparing samples for transmission electron microscope (TEM) investigation. Samples must be uniformly thin to enable the analyzing beam of electrons to penetrate. The FIB enables not only the preparation of large, uniformly thick, sitespecific samples, but also the fabrication of lamellae used for TEM samples from composite samples consisting of inorganic and organic materials with very different properties. This article gives an overview of the variety of techniques that have been developed to prepare the final TEM specimen. The strengths of these methods as well as the problems, such as FIB-induced damage and Ga contamination, are illustrated with examples. Most recently, FIB-thinned lamellae were used to improve the spatial resolution of electron backscatter diffraction and energy-dispersive x-ray mapping. Examples are presented to illustrate the capabilities, difficulties, and future potential of FIB.
Focused Ion Beam Micro- and Nanoengineering
Authors: Langford Richard M. , Nellen Philipp M. , Gierak Jacques , Fu Yongqi
Published: February 2011

This article discusses applications of focused ion beam micro- and nanofabrication. Emphasis is placed on illustrating the versatility of focused ion beam and dual-platform systems and how they complement conventional processing techniques. The article is divided into four parts: maskless milling, ion beam lithography, ion implantation, and techniques such as in situ micromanipulation.
Sticky Feet: From Animals to Materials
Authors: Creton Costantino , Gorb Stanislav
Published: February 2011

Many insects and some larger animals, such as geckos, skinks, and tree frogs, can easily climb vertical walls and even walk on the ceiling. These abilities require a method to attach the feet strongly but reversibly to a variety of surfaces—smooth or rough, hydrophilic or hydrophobic, clean or containing contaminants. This issue ofMRS Bulletinexamines how fibrils, absorbed water layers, geometry, and other factors make reversible adhesion possible, and how this understanding might be applied to robots and other artificially created structures that can climb walls, walk on ceilings, and get to other hard-to-reach places.
Mechanics of Bioinspired and Biomimetic Fibrillar Interfaces
Authors: Jagota A. , Hui C.-Y. , Glassmaker N. J. , Tang T.
Published: February 2011

Materials that are inspired by or are mimics of natural fibrillar surfaces in lizards and insects aim to achieve enhanced interfacial adhesion and contact properties by means of a fibrillar architecture. Studies of the mechanics of deformation and adhesion of such materials help to explain how they work and are aiding the design of their architecture. This article discusses some of the issues addressed by these studies, such as how can a fibrillar interface be made stronger and tougher than a flat control, and how does one enhance its ability to make contact to a variety of substrates?
Molecular Design of Inorganic-Binding Polypeptides
Authors: Evans John Spencer , Samudrala Ram , Walsh Tiffany R. , Oren Ersin Emre , Tamerler Candan
Published: February 2011

Controlled binding and assembly of peptides onto inorganic substrates is at the core of bionanotechnology and biological-materials engineering. Peptides offer several unique advantages for developing future inorganic materials and systems. First, engineered polypeptides can molecularly recognize inorganic surfaces that are distinguishable by shape, crystallography, mineralogy, and chemistry. Second, polypeptides are capable of self-assembly on specific material surfaces leading to addressable molecular architectures. Finally, genetically engineered peptides offer multiple strategies for their functional modification. In this article, we summarize the details and mechanisms involved in combinatorial-polypeptide sequence selection and inorganic-material recognition and affinity, and outline experimental and theoretical approaches and concepts that will help advance this emerging field.
Molecular Design of β-Hairpin Peptides for Material Construction
Authors: Rughani Ronak V. , Schneider Joel P.
Published: February 2011

Self-assembled materials composed of β-sheet forming peptides hold promise as therapeutics and novel biomaterials. This article focuses on the design and engineering of amphiphilic peptide sequences, especially β-hairpins. Peptides can be designed to intramolecularly fold and then self-assemble on cue, affording hydrogels rich in β-sheet structure. Hydrogels having distinct material properties can be designed at the molecular level by modulating either the peptide's sequence or the environmental stimulus used to trigger folding and assembly, leading to gelation.
Glass-Formers and Viscous Liquid Slowdown since David Turnbull: Enduring Puzzles and New Twists
Authors: Angell C.A.
Published: February 2011

To Turnbull's study of the kinetic problem of nucleation and growth of crystals, we add the further enquiry into what lies behind the slow nucleation kinetics of glass-formers. Our answer to this question leads to the proposal of conditions in which a pure liquid metal, monatomic and elemental, can be vitrified. Using the case of high-pressure liquid germanium, we give electron microscope evidence for the validity of our thinking.

On the question of how liquids behave when crystals do not form, Turnbull pioneered the study of glass transitions in metallic alloys, measuring the heat capacity change at the glass transition Tg for the first time, and developing with Cohen the free volume model for the temperature dependence of liquid transport properties approaching Tg. We extend the phenomenological picture to include networks where free volume does not play a role and reveal a pattern of behavior that provides for a classification of glass-formers (from “strong” to “fragile”). Where Turnbull studied supercooled liquid metals and P4 to the homogeneous nucleation limit using small droplets, we studied supercooled water in capillaries and emulsions to the homogeneous nucleation limit near −40°C. We discuss the puzzling divergences observed that are now seen as part of a cooperative transition that leads to very untypical glass-transition behavior at lower temperatures (when crystallization is bypassed by hyperquenching). Finally, we show how our interpretation of water behavior can be seen as a bridge between the behavior of the “strong” (network) liquids of classical glass science (e.g., SiO2) and the “fragile” behavior of typical molecular glass-formers. The link is made using a “Gaussian excitations” model by Matyushov and the author in which the spike in heat capacity for water is pushed by cooperativity (disorder stabilization of excitations) into a first-order transition to the ground state, at a temperature typically below Tg. In exceptional cases like triphenyl phosphite, this liquid-to-glass first-order transition lies above Tg and can be studied in detail.
Combining Serial Sectioning, EBSD Analysis, and Image-Based Finite Element Modeling
Authors: Spanos G. , Rowenhorst D.J. , Lewis A.C. , Geltmacher A.B.
Published: February 2011

This article first provides a brief review of the status of the subfield of three-dimensional (3D) materials analyses that combine serial sectioning, electron backscatter diffraction (EBSD), and finite element modeling (FEM) of materials microstructures, with emphasis on initial investigations and how they led to the current state of this research area. The discussions focus on studies of the mechanical properties of polycrystalline materials where 3D reconstructions of the microstructure—including crystallographic orientation information—are used as input into image-based 3D FEM simulations. The authors' recent work on a β-stabilized Ti alloy is utilized for specific examples to illustrate the capabilities of these experimental and modeling techniques, the challenges and the solutions associated with these methods, and the types of results and analyses that can be obtained by the close integration of experiments and simulations.
Solution-Processed Organic Solar Cells
Authors: Brabec Christoph J. , Durrant James R.
Published: February 2011

Organic solar cells, based on polymer/fullerene-blend films, are advancing rapidly toward commercial viability. In this article, we review recent progress on two issues critical for technological applications: device photovoltaic efficiencies and processing technologies for high-throughput production. In terms of device efficiencies, we consider advances in low-bandgap polymers, film morphology, and device structure aimed at increasing efficiencies beyond 5%. We then review recent progress in developing high-throughput, solution-printing-based processes for low-cost device fabrication.
Synthetic Aspects of Organic Semiconductors
Authors: Anthony John E. , Heeney Martin , Ong Beng S.
Published: February 2011

This article discusses the importance of the choice of synthetic methodology in the purity, and therefore performance, of both small-molecule and polymeric organic semiconductors. We discuss common methodologies used in the preparation of organic semiconductors, paying particular attention to the impurities and by-products that can arise during these synthetic approaches and how they can have an impact on semiconductor performance.
Progress and Challenges in Commercialization of Organic Electronics
Authors: Loo Yueh-Lin , McCulloch Iain
Published: February 2011

The field of organic electronics is entering its commercial phase. The recent market introduction of the first prototypes based on organic transistors fabricated from solution is set to augment the existing market presence of organic light-emitting diode applications. Organic photovoltaic products are not far behind. In this article, we provide a brief overview of these devices, with our main focus being organic transistor applications. In particular, we examine some of the key performance requirements for working devices. We also review some of the important advances in semiconductor design and device fabrication techniques and discuss some of the technical challenges that remain in the optimization of next-generation products.
Self-Healing Fiber-Reinforced Polymer Composites
Authors: Bond Ian P. , Trask Richard S. , Williams Hugo R.
Published: February 2011

Self-healing is receiving an increasing amount of interest worldwide as a method to address damage in materials. In particular, for advanced high-performance fiber-reinforced polymer (FRP) composite materials, self-healing offers an alternative to employing conservative damage-tolerant designs and a mechanism for ameliorating inaccessible and invidious internal damage within a structure. This article considers in some detail the various self-healing technologies currently being developed for FRP composite materials. Key constraints for incorporating such a function in FRPs are that it not be detrimental to inherent mechanical properties and that it not impose a severe weight penalty.
Electron-Beam Lithographic Studies of the Scaling of Phase-Change Memory
Authors: Raoux Simone , Rettner Charles T. , Chen Yi-Chou , Burr Geoffrey W.
Published: February 2011

Phase-change random-access memory (PCRAM) is a promising technology for future nonvolatile storage with the added potential for possible impact on dynamic random-access memory technologies. To be successful, however, PCRAM must be able to scale to dimensions on the order of a few tens of nanometers, considering the increasingly tiny memory cells that are projected for future technology nodes. The experiments discussed in this article directly address these scaling properties, examining both the materials themselves and the operation of nanoscale devices. One series of experiments is time-resolved x-ray diffraction studies of ultrathin films and nanostructures. Electron-beam lithography was applied to pattern thin films into nanostructures with dimensions down to 20 nm. The article also includes descriptions of prototype PCRAM devices, successfully fabricated and tested down to phase-change material cross sections of 3 nm × 20 nm. The measurements provide a clear demonstration of the excellent scaling potential offered by this technology.
Negative-Index Materials: Optics by Design
Authors: Park Wounjhang , Kim Jinsang
Published: February 2011

Index of refraction, a fundamental optical constant that enters in the descriptions of almost all optical phenomena, has long been considered an intrinsic property of a material. However, the recent progress in negative-index material (NIM) research has shown that the utilization of deep-subwavelength-scale features can provide a means to engineer fundamental optical constants such as permittivity, permeability, impedance, and index of refraction. Armed with new nanofabrication techniques, researchers worldwide have developed and demonstrated a variety of NIMs. One implementation uses a combination of electric and magnetic resonators that simultaneously produce negative permittivity and permeability, and consequently negative refractive index. Others involve chirality, anisotropy, or Bragg resonance in periodic structures. NIM research is the beginning of new optical materials research in which the desired optical properties and functionalities are artificially generated. Clearly, creating negative index materials is not the only possibility, and the most recent developments explore new realms of materials with near-zero indexes and inhomogeneous index profiles that can produce novel phenomena such as invisibility. Furthermore, the concept of controlling macroscopic material properties with a composite structure containing subwavelength-scale features extends to the development of acoustic metamaterials. By providing a review of recent progress in NIM research, we hope to share the excitement of the field with the broader materials research community and also to spur new ideas and research directions.
New Frontiers of Metamaterials: Design and Fabrication
Authors: Chaturvedi Pratik , Hsu Keng , Zhang Shu , Fang Nicholas
Published: February 2011

Artificially engineered metamaterials have emerged with properties and functionalities previously unattainable in natural materials. The scientific breakthroughs made in this new class of electromagnetic materials are closely linked with progress in developing physics-driven design and novel parallel fabrication methods. For example, a smooth superlens has been demonstrated with 30-nm imaging resolution, or 1/12 of the corresponding wavelength, far below the diffraction limit. Similarly, a photoswitchable optical negative-index material has been printed, showing a remarkable tuning range of refractive index in the communication wavelength. New frontiers are being explored as intrinsic limitations challenge the scaling of microwave metamaterial designs to optical frequencies. These novel metamaterials promise an entire new generation of passive and active optical elements, such as paper-thin superlenses and modulators.
In Situ Transmission Electron Microscopy
Authors: Ferreira P.J. , Mitsuishi K. , Stach E.A.
Published: February 2011

The articles in this issue of MRS Bulletin provide a sample of what is novel and unique in the field of in situ transmission electron microscopy (TEM). The advent of improved cameras and continued developments in electron optics and stage designs have enabled scientists and engineers to enhance the capabilities of previous TEM analyses. Currently, novel in situ experiments observe and record the behavior of materials in various heating, cooling, straining, or growth environments. In situ TEM techniques are invaluable for understanding and characterizing dynamic microstructural changes. They can validate static TEM experiments and inspire new experimental approaches and new theories.
Optical Metamagnetism and Negative-Index Metamaterials
Authors: Chettiar Uday K. , Xiao Shumin , Kildishev Alexander V. , Cai Wenshan , Yuan Hsiao-Kuan , Drachev Vladimir P. , Shalaev Vladimir M.
Published: February 2011

A new class of artificially structured materials called metamaterials makes it possible to achieve electromagnetic properties that do not exist in nature. In this article, we review the recent progress made in the area of optical metamaterials, specifically artificial magnetism and negative-index metamaterials. It was predicted that nanostructured metamaterials could provide magnetic responses and negative refractive indexes at optical frequencies. To date, optical metamagnetics have been fabricated to demonstrate magnetic responses in the infrared range and across the entire visible spectrum. Metamaterials showing negative refractive indexes, also called negative-index materials (NIMs), have also been demonstrated in the infrared range and at the border with the visible spectral range. Additionally, we report the results of a sample that displays NIM behavior for red light at a wavelength of 710 nm and another sample that displays double-negative NIM behavior at 725 nm. Both observations represent the shortest wavelengths so far at which NIM behavior has been observed for light. We also discuss the fabrication challenges and the impact of fabrication limitations, specifically the effect of surface roughness of the fabricated structures, on the optical properties of the metamaterials.
Acoustic Metamaterials
Authors: Fok Lee , Ambati Muralidhar , Zhang Xiang
Published: February 2011

The field of engineered materials with designed properties is expected to continue to grow in the future, and metamaterials are instrumental in allowing this freedom of design. Metamaterials, particularly acoustic, are still in the stage of infancy. Acoustic metamaterials are being explored theoretically, but there has been little headway on the experimental front. The design, development, and characterization of acoustic metamaterials will offer many opportunities in materials science. In this article, we review the basic physics of different kinds of acoustic periodic structures with special emphasis on locally resonant acoustic metamaterials. We first survey phononic crystals and then discuss localized resonances in intrinsic and inertial resonating structures of acoustic metamaterials. Finally, we present the ongoing efforts in realizing acoustic metamaterials with negative materials properties and discuss the implications of acoustic metamaterials.
Strongly Correlated Electronic Materials: Present and Future
Authors: Dagotto E. , Tokura Y.
Published: February 2011

In complex transition-metal oxides, the interactions between the electronic spins, charges, and orbitals produce a rich variety of electronic phases. The competition and/or cooperation among these correlated-electron phases can lead to the emergence of surprising electronic phenomena and functionalities and form the basis for a new type of electronics.
Oxide Dilute Magnetic Semiconductors—Fact or Fiction?
Authors: Coey J.M.D. , Chambers S.A.
Published: February 2011

Magnetism in oxides was thought to be well-understood in terms of localized magnetic moments and double-exchange or superexchange rules. This understanding was shaken by the publication of an article in 2001 stating that thin films of anatase TiO2 with only 7 at.% Co substitution had a Curie point in excess of 400 K [Matsumoto et al., Science291, 854 (2001)]. Room-temperature ferromagnetism had previously been predicted for p-type ZnO with 5 at.% Mn [Dietl et al., Science287, 1019 (2000)]. A flood of reports of thin films and nanoparticles of new oxide “dilute magnetic semiconductors” (DMSs) followed, and high-temperature ferromagnetism has been reported for other systems with no 3dcations. The expectation that these materials would find applications in spintronics motivated research in this area. Unfortunately, the data are plagued by instability and a lack of reproducibility. In many cases, the ferromagnetism can be explained by uncontrolled secondary phases; it is absent in well-crystallized films and bulk material. However, it appears that some form of high-temperature ferromagnetism can result from defects present in the oxide films [Coey, Curr. Opin. Solid State Mater. Sci.10, 83 (2007); Chambers, Surf. Sci. Rep.61, 345 (2006)], although they are not DMSs as originally envisaged.
Environmental (S)TEM Studies of Gas–Liquid–Solid Interactions under Reaction Conditions
Authors: Gai Pratibha L. , Sharma Renu , Ross Frances M.
Published: February 2011

We review the development of time-resolved, high-resolution environmental scanning/ transmission electron microscopy [E(S)TEM] for directly probing dynamic gas–solid, liquid–solid, and gas–liquid–solid interactions at the atomic level. Unlike a regular TEM, such a microscope allows us to use high gas pressures (up to 40 mbars) in the sample region. The unique information available from experiments performed using E(S)TEM has enabled visualization of the dynamic nature of nanostructures during reactions. Such information can be directly applied to the development of advanced nanomaterials such as carbon nanotubes, silicon nanowires and processes, including the design of novel routes to polymers synthesis, and has aided in the identification of important phenomena during catalysis, chemical vapor deposition, and electrochemical deposition.
In Situ High-Resolution Transmission Electron Microscopy in the Study of Nanomaterials and Properties
Authors: Howe James M. , Mori Hirotaro , Wang Zhong Lin
Published: February 2011

This article introduces the use of in situ high-resolution transmission electron microscopy (HRTEM) techniques for the study and development of nanomaterials and their properties. Specifically, it shows how in situ HRTEM (and TEM) can be used to understand diverse phenomena at the nanoscale, such as the behavior of alloy phase formation in isolated nanometer-sized particles, the mechanical and transport properties of carbon nanotubes and nanowires, and the dynamic behavior of interphase boundaries at the atomic level. Current limitations and future potential advances in in situ HRTEM of nanomaterials are also discussed.
Observing Interfacial Sliding Processes in Solid–Solid Contacts
Authors: Wahl Kathryn J. , Sawyer W. Gregory
Published: February 2011

Directly seeing into a moving contact is a powerful approach to understanding how solid lubricants develop low-friction, long-lived interfaces. In this article, we present optical microscopy and spectroscopy approaches that can be integrated with friction monitoring instrumentation to provide real-time, in situ evaluation of solid lubrication phenomena. Importantly, these tools allow direct correlation of common tribological events (such as variations in friction and wear) with the responsible sliding-induced mechanical and chemical phenomena. We demonstrate the utility of in situ approaches with applications to a variety of thin-film solid lubricants.
Electroactive Polymer Actuators and Sensors
Authors: Bar-Cohen Yoseph , Zhang Qiming
Published: February 2011

Polymers are highly attractive for their inherent properties of mechanical flexibility, light weight, and easy processing. In addition, some polymers exhibit large property changes in response to electrical stimulation, much beyond what is achievable by inorganic materials. This adds significant benefit to their potential applications.

The focus of this issue of MRS Bulletin is on polymers that are electromechanically responsive, which are also known as electroactive polymers (EAPs). These polymers respond to electric field or current with strain and stress, and some of them also exhibit the reverse effect of converting mechanical motion to an electrical signal.

There are many types of known polymers that respond electromechanically, and they can be divided according to their activation mechanism into field-activated and ionic EAPs. The articles in this issue cover the key material types used in these two groups, review the mechanisms that drive them, and provide examples of applications and current challenges. Recent advances in the development of these materials have led to improvement in the induced strain and force and the further application of EAPs as actuators for mimicking biologic systems and sensors. As described in this issue, the use of these actuators is enabling exciting applications that would be considered impossible otherwise.
Field-Activated Electroactive Polymers
Authors: Cheng Zhongyang , Zhang Qiming
Published: February 2011

Field-activated electroactive polymers (FEAPs) are a class of electroactive polymers that are insulating and exhibit coulombic interaction with and dipole formation in response to external electric signals. There are many polarization mechanisms in insulating polymers, from the molecular to the mesoscopic and even the macroscopic level, which couple strongly with mechanical deformation and can be used to create polymer actuators and sensors. FEAPs feature fast response speed limited by the polymer dielectric and elastic relaxation time, a very large strain level (to more than 100% strain), high electromechanical efficiency, the ability to operate down to micro/nanoelectromechanical devices, and a highly reproducible strain response under electric fields. One challenge in FEAP actuators and electromechanical devices is reducing the operation voltage to below 100 V or even 10 V while achieving an electromechanical conversion efficiency comparable with that of inorganic electroactive materials.
Physical Principles of Ionic Polymer–Metal Composites as Electroactive Actuators and Sensors
Authors: Park Il-Seok , Jung Kwangmok , Kim Doyeon , Kim Sang-Mun , Kim Kwang J.
Published: February 2011

This article introduces and considers the fundamental understanding of ionic polymer–metal composites (IPMCs) functioning as electroactive actuators and sensors. IPMCs consist of ion-exchange polymers acting as base materials and metal layers functioning as electrodes. The actuation and sensing abilities of IPMCs are dependent upon the components of ion-exchange polymers (ionic groups and cations) and electrode materials. In order to improve the bending and sensing performance of the IPMCs, an integral, two-step electroplating technique and a requisite dispersion agent are used during fabrication. Electroding materials also play a key role in determining the properties of IPMCs, and numerous methods in electroding have been tried, making use of various metals, carbon nanotubes, and composites. So far, IPMCs have been adapted as robotic actuators, artificial muscles, and electrical sensors. In the future, it is expected that IPMCs will broadly spread their roles from small-sized biomedical devices to large-scale actuators for aerospace as well as many industrial applications.
The Global Energy Landscape and Materials Innovation
Authors: Arunachalam V.S. , Fleischer E.L.
Published: February 2011

Availability of affordable energy has enabled spectacular growth of industrialization and human development in all parts of the world. With growth now accelerating in developing countries, demands on energy sources and infrastructure are being stretched to new limits. Additional energy issues include the push for renewable resources with reduced greenhouse gas emissions and energy security affected by the uneven distribution of energy resources around the globe. Together, these issues present a field of opportunity for innovations to address energy challenges throughout the world and all along the energy flow. These energy challenges form the backdrop for this special expanded issue of MRS Bulletin on Harnessing Materials for Energy. This article introduces the global landscape of materials issues associated with energy. It examines the complex web of energy availability, production, storage, transmission, distribution, use, and efficiency. It focuses on the materials challenges that lie at the core of these areas and discusses how revolutionary concepts can address them. Cross-cutting topics are introduced and interrelationships between topics explored. Article topics are set in the context of the grand energy challenges that face the world into the middle of this century.
The Economics of Energy Options
Authors: Lave Lester B.
Published: February 2011

Increasing demand for energy, diminishing stocks of oil and natural gas, and the public's desire to enhance environmental quality, particularly by reducing greenhouse gas emissions, all point to the need for improved materials. For example, generating electricity from the most abundant fossil fuel, coal, efficiently and with no environmental damage, presents notable challenges to develop higher performance materials. Technologies exist to transform one fossil fuel to other uses, such as coal to a gas or liquid. New materials that increase the efficiency of the transformation and lower its cost would provide valuable flexibility. Materials should be evaluated in terms of their entire life-cycle in order to discern which will make the greatest contribution. Because society has many pressing needs, both commercial value and contribution to fundamental materials science should guide priorities in materials research.
Materials Challenges in Advanced Coal Conversion Technologies
Authors: Powell Cynthia A. , Morreale Bryan D.
Published: February 2011

Coal is a critical component in the international energy portfolio, used extensively for electricity generation. Coal is also readily converted to liquid fuels and/or hydrogen for the transportation industry. However, energy extracted from coal comes at a large environmental price: coal combustion can produce large quantities of ash and CO2, as well as other pollutants. Advanced technologies can increase the efficiencies and decrease the emissions associated with burning coal and provide an opportunity for CO2 capture and sequestration. However, these advanced technologies increase the severity of plant operating conditions and thus require improved materials that can stand up to the harsh operating environments. The materials challenges offered by advanced coal conversion technologies must be solved in order to make burning coal an economically and environmentally sound choice for producing energy.