bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling Deformation and Flow of Disordered Materials
Authors: Barrat Jean-Louis , de Pablo Juan J.
Published: February 2011

Disordered, glassy materials are arguably one of the least understood states of condensed matter. Yet, they are ubiquitous in everyday life (polymers, “soft” glasses such as toothpaste, various emulsions, pastes, and foams) and in demanding applications (metallic glasses). Much of what is known about this important class of materials has been the result of truly concerted experimental and molecular modeling efforts. It is now generally accepted that amorphous materials exhibit dynamic and mechanical heterogeneities, but efforts to incorporate these into truly multiscale modeling approaches have been limited. This article describes the current state of affairs, along with many of the challenges that must be met to arrive at a fundamental understanding of amorphous materials and their response to external stresses.
The New Paradigm of Transmission Electron Microscopy
Authors: Urban Knut W.
Published: February 2011

The following article is based on the Von Hippel Award address given by Knut W. Urban, chair of experimental physics at RWTH Aachen University and director of the Institute of Microstructure Research within the Department of Solid-State Research at the Jülich Research Center. Urban presented his award talk on November 29, 2006, during the 2006 Materials Research Society Fall Meeting in Boston. He was recognized with MRS's highest honor, the Von Hippel Award, for his “sustained contributions to the development and use of electron microscopy, and for major discoveries in the defect physics of quasicrystals and high-temperature superconductors.” The Von Hippel Award honors those qualities most prized by materials scientists and engineers—brilliance and originality of intellect, combined with vision that transcends the boundaries of conventional scientific disciplines, as exemplified by the life of Arthur von Hippel (http://vonhippel.mrs.org).

In this article, Urban describes the advances in spherical-aberration-corrected electron optics that have set transmission electron microscopy on an entirely new track in materials science. The new imaging theory for aberration-corrected instruments is based on exploiting both lens focus and spherical aberration as variable parameters to optimize contrast, resolution, and point spread. The novel negative-spherical-aberration imaging technique makes it possible to image low-nuclear-charge atoms, which were previously inaccessible directly by electron microscopy. This technique has proven particularly successful for research on oxides. Due to negligible point spread, quantitative measurements of atomic-site occupancies, which are equivalent to local concentrations, have become feasible. These improvements are dramatically expanding the potential of electron microscopy for quantitative studies in materials science.
In SituX-Ray Photoelectron Spectroscopy Studies of Gas-Solid Interfaces at Near-Ambient Conditions
Authors: Bluhm Hendrik , Hävecker Michael , Knop-Gericke Axel , Kiskinova Maya , Schlögl Robert , Salmeron Miquel
Published: February 2011

X-ray photoelectron spectroscopy (XPS) is a quantitative, chemically specific technique with a probing depth of a few angstroms to a few nanometers. It is therefore ideally suited to investigate the chemical nature of the surfaces of catalysts. Because of the scattering of electrons by gas molecules, XPS is generally performed under vacuum conditions. However, for thermodynamic and/or kinetic reasons, the catalyst's chemical state observed under vacuum reaction conditions is not necessarily the same as that of a catalyst under realistic operating pressures. Therefore, investigations of catalysts should ideally be performed under reaction conditions, that is, in the presence of a gas or gas mixtures. Using differentially pumped chambers separated by small apertures, XPS can operate at pressures of up to 1 Torr, and with a recently developed differentially pumped lens system, the pressure limit has been raised to about 10 Torr. Here, we describe the technical aspects of high-pressure XPS and discuss recent applications of this technique to oxidation and heterogeneous catalytic reactions on metal surfaces.
In SituEXAFS Characterization of Nanoparticulate Catalysts
Authors: Evans John , Puig-Molina Anna , Tromp Moniek
Published: February 2011

X-ray absorption fine structure (XAFS) spectroscopy probes the structure and electronic properties of metal centers. Because it can be applied to noncrystalline materials, it is a key technique for probing nanoparticulate materials, such as colloidal and heterogeneous metal catalysts. The high brilliance of modern synchrotron radiation x-ray sources facilitatesin situstudies, which provide direct structure–function relationships with both spatial and time resolution; this is especially effective when applied in combination with complementary techniques such as x-ray diffraction, mass spectrometry, and optical or vibrational spectroscopies. Tracking the particle formation of platinum-group metal catalysts, their behavior under reaction conditions, and the distribution of sites within a catalyst bed shows that this approach is essential for understanding the chemistry of these nanoparticles. Rather than behave as monolithic entities, nanoparticulate catalysts undergo rapid structural transformations induced by the gas environment and reaction conditions, and their lifetimes as catalysts depend on the reversibility of these changes.
Processing and Properties of Polymers Modified by Clays
Authors: Hunter Douglas L. , Kamena Karl W. , Paul Donald R.
Published: February 2011

Layered smectite nanoclays are being developed for incorporation into a variety of host polymer systems. Nanoscopic phase distribution can impart enhanced stiffness at low addition levels and improve barrier and flame-retardant properties. When combined with other inorganic and organic modifiers, nanoclays can provide synergies to generate the desired formulation properties and cost/per form ance characteristics. Developments with existing nanoclay products using conventional amine chemistries are described for thermoplastic, thermoset, and rubber formulations. Nanoclays are demonstrating unique, multidimensional per form ance and proc essing capabilities. Commercial applications are emerging in a variety of diverse markets ranging from automotive to packaging.
Designed Interfaces in Polymer Nanocomposites: A Fundamental Viewpoint
Authors: Schadler Linda S. , Kumar Sanat K. , Benicewicz Brian C. , Lewis Sarah L. , Harton Shane E.
Published: February 2011

Using nanocomposites in design-critical applications requires an understanding of their structure–property–function relationships. Despite many reports of highly favorable properties, the behavior of polymer nanocomposites is not generally predictable. The ability to tailor the filler/matrix interaction and an understanding of the impact of the inter face on macroscopic properties are key to designing their properties. Tailoring can be achieved by grafting short mole cules or polymer chains from the surface with precise control over their chain length (1–1000 mers), graft density (0.01–1 chains/nm2), and chemical architecture. The challenge is understanding the impact of the modified surfaces on the properties of the interfacial polymer, which can be more than 50% of the volume of the polymer matrix and, hence, can exert significant control over the macroscopic behavior of the nanocomposite. This ar ticle highlights the fundamental technical challenges that need to be overcome before spherical nanopar ticle or nanotube composites can be designed. In particular, we discuss results from the recent literature that have significantly advanced our ability to predict and control nanocomposite properties through the use of designed interfaces.
Improving Electrical Conductivity and Thermal Properties of Polymers by the Addition of Carbon Nanotubes as Fillers
Authors: Winey Karen I. , Kashiwagi Takashi , Mu Minfang
Published: February 2011

The remarkable electrical and thermal conductivities of isolated carbon nanotubes have spurred worldwide interest in using nanotubes to enhance polymer properties. Electrical conductivity in nanotube/polymer composites is well described by percolation, where the presence of an interconnected nanotube network corresponds to a dramatic increase in electrical conductivity ranging from 10−5 S/cm to 1 S/cm. Given the high aspect ratios and small diameters of carbon nanotubes, percolation thresholds are often reported below 1 wt% although nanotube dispersion and alignment strongly influence this value. Increases in thermal conductivity are modest (∼3 times) because the inter facial thermal re sis tance between nanotubes is considerable and the thermal conductivity of nanotubes is only 104 greater than the polymer, which forces the matrix to contribute more toward the composite thermal conductivity, as compared to the contrast in electrical conductivity, >1014. The nanotube network is also valuable for improving flame-retardant efficiency by producing a protective nanotube residue. In this ar ticle, we highlight published research results that elucidate fundamental structure–property relationships pertaining to electrical, thermal, and/or flammability properties in numerous nanotube-containing polymer composites, so that specific applications can be targeted for future commercial success.
Pb-Free Solder: New Materials Considerations for Microelectronics Processing
Authors: Borgesen Peter , Bieler Thomas , Lehman L. P. , Cotts E. J.
Published: February 2011

A single printed circuit board includes thousands, sometimes even hundreds of thousands, of solder joints. The failure of even a single solder joint is usually enough to compromise the functionality of an electronic device or system. PbSn solder had been the standard ma te rial for these joints until various regulations around the world began to limit Pb use. SnAgCu and related alloys are quickly replacing PbSn, but much still needs to be understood and controlled. None of the paradigms for understanding the mechanical response of PbSn alloys is applicable to lead-free alloys. Much of the surprising behavior of SnAgCu solder arises from the complex and fascinating nature of its solidification behavior. In this ar ticle, the impact of solidification on the microstruc ture and therefore the mechanical properties of these solder joints will be addressed in the context of microelectronics proc essing. The need for better simulations of SnAgCu solder behavior will also be examined. Notably, modelers will have to account for a variety of new parameter dependencies not previously considered.
Reconstruction of Historical Alloys for Pipe Organs Brings True Baroque Music Back to Life
Authors: Baretzky B. , Friesel M. , Straumal B.
Published: February 2011

The pipe organ is the king of musical instruments. No other instrument can compare with the pipe organ in power, timbre, dynamic range, tonal complexity, and sheer majesty of sound. The art of organ building reached its peak in the Baroque Age (∼1600–1750); with the industrial revolution in the 19th century, organ building shifted from a traditional artisans' work to factory production, changing the aesthetic concept and design of the organ so that the profound knowledge of the organ masters passed down over generations was lost.

This knowledge is being recreated via close collaborations between research scientists, musicians, and organ builders throughout Europe. Dozens of metallic samples taken from 17th- to 19th-century organ pipes have been investigated to determine their composition, microstructure, properties, and manufacturing processes using sophisticated methods of materials science. Based upon these data, technologies for casting, forming, hammering, rolling, filing, and annealing selected leadtin pipe alloys and brass components for reed pipes have been reinvented and customized to reproduce those from characteristic time periods and specific European regions. The new materials recreated in this way are currently being processed and used by organ builders for the restoration of period organs and the manufacture of new organs with true Baroque sound.
Functional Nanowires
Authors: Lieber Charles M. , Wang Zhong Lin
Published: February 2011

Nanotechnology offers the promise of enabling revolutionary advances in diverse areas ranging from electronics, optoelectronics, and energy to healthcare. Underpinning the realization of such advances are the nanoscale ma te rials and corresponding nanodevices central to these application areas. Semiconductor nanowires and nanobelts are emerging as one of the most powerful and diverse classes of functional nanoma terials that are having an impact on science and technology. In this issue of MRS Bulletin, several leaders in this vibrant field of research present brief reviews that highlight key aspects of the underlying materials science of nanowires, basic device functions achievable with these materials, and developing applications in electronics and at the interface with biology. This article introduces the controlled synthesis, patterned and designed self-assembly, and unique applications of nanowires in nanoelectronics, nano-optoelectronics, nanosensors, nanobiotechnology, and energy harvesting.
Growth of Binary Oxide Nanowires
Authors: Wang Jiangxiong , Xie Sishen , Zhou Weiya
Published: February 2011

One-dimensional (1D) semiconducting oxide nanostructures such as ZnO, SnO2, and In2O3 have been extensively studied due to their excellent optical and electrical properties. Growth of 1D nanostructures with precisely controlled size, phase purity, crystallinity, and chemical composition still presents numerous challenges. In this review, we report the recent progress on the synthesis of binary oxide nanostructures consisting of different oxides through a simple and effective vapor transport approach in our research. By controlling the experimental conditions, this approach enables the synthesis of various multicomponent binary oxide nanowires.
Three-Dimensional Microstructural Characterization Using Focused Ion Beam Tomography
Authors: Uchic Michael D. , Holzer Lorenz , Inkson Beverley J. , Principe Edward L. , Munroe Paul
Published: February 2011

This article reviews recent developments and applications of focused ion beam (FIB) microscopes for three-dimensional (3D) materials characterization at the microscale through destructive serial sectioning experiments. Precise ion milling—in combination with electron-optic—based imaging and surface analysis methods—can be used to iteratively section through metals, ceramics, polymers, and electronic or biological materials to reveal the true size, shape, and distribution of microstructural features. Importantly, FIB tomographic experiments cover a critical size-scale gap that cannot be obtained with other instrumentation. The experiments encompass material volumes that are typically larger than 1000 μm3, with voxel dimensions approaching tens of nanometers, and can contain structural, chemical, and crystallographic information. This article describes the current state of the art of this experimental methodology and provides examples of specific applications to 3D materials characterization.
Gecko Adhesion: Structure, Function, and Applications
Authors: Autumn Kellar
Published: February 2011

Geckos attach and detach their adhesive toes in milliseconds while running with reckless abandon on nearly any surface. The adhesive on gecko toes differs dramatically from that of conventional adhesives. Conventional pressure-sensitive adhesives (PSAs) are soft viscoelastic polymers that degrade, foul, self-adhere, and attach accidentally to inappropriate surfaces. In contrast, gecko toes bear angled arrays of branched, hair-like fibers (setae) formed from stiff, hydrophobic keratin that act as a bed of angled springs with an effective stiffness similar to that of PSAs. Setae are selfcleaning and maintain function for months during repeated use in dirty conditions. Setae are an anisotropic “frictional adhesive” in that adhesion requires maintenance of a proximally directed shear load. Thus, gecko setae resist inappropriate bonding and are capable of easy and rapid attachment and detachment. Engineered adhesive nanostructures inspired by geckos may become the glue of the future—and perhaps the screw of the future as well.
Functional Morphology and Design Constraints of Smooth Adhesive Pads
Authors: Barnes W. Jon. P.
Published: February 2011

Smooth adhesive pads are found among the arthropods, amphibians (particularly tree frogs), and in some mammals. They are used for dynamic adhesion when an animal is climbing steep or overhanging smooth surfaces. There is a need for strong attachment to avoid falling and easy detachment to enable the animal to move. This article describes the morphology and physical properties of smooth adhesive pads, stressing how there is little variation in structure, within tree frogs at least, even among pads that have evolved independently. This is clear evidence of an optimum design; best adhesion occurs when there is a continuous, thin film of fluid between the pad and the surface. Smooth adhesive pads adhere by wet adhesion, the main force component being capillarity, produced by the air/liquid interface (meniscus) around the edge of each pad. Smooth adhesive pads also produce substantial friction forces, probably because of actual contact between the pad surface and substrate (tree frogs) or non-Newtonian properties of the secreted fluid (insects). This is possible because the fluid layer beneath the pad has an average thickness of only a few nanometers. The article also discusses the scaling of adhesive force with size and, finally, implications for biomimetics.
Biological Adhesion for Locomotion on Rough Surfaces: Basic Principles and A Theorist's View
Authors: Persson B. N. J.
Published: February 2011

Surface roughness is the main reason why macroscopic solids usually do not adhere to each other with any measurable strength, and a root-mean-square roughness amplitude of only 1 μm is enough to completely remove the adhesion between normal rubber (with an elastic modulusE≈ 1 MPa) and a hard, nominally flat substrate. Biological adhesion systems used by insects and geckos for locomotion are built from a relatively stiff material (keratin or chitin–protein composite withE≈ 1 GPa). Nevertheless, strong adhesion is possible even to very rough substrate surfaces by using noncompact solid structures consisting of fibers (setae) and plates (spatulae). Biological systems use a hierarchical building principle, where the thickness of the fibers or plates decreases as one approaches the outer surface of the attachment pad, to optimize the binding to rough surfaces while simultaneously avoiding elastic instabilities, for example, lateral bundling of fibers.
Designing Model Systems for Enhanced Adhesion
Authors: Chan Edwin P. , Greiner Christian , Arzt Eduard , Crosby Alfred J.
Published: February 2011

Nature provides inspiration for enhanced control of adhesion through numerous examples ranging from geckos to jumping spiders. The primary strategy in these examples is the incorporation of patterns, specifically high-aspect-ratio topographic features, to ingeniously maximize adhesion forces while maintaining ease of release. Recently, considerable research efforts have been devoted toward the understanding, development, and optimization of synthetic analogues to these examples in nature. In this article, we provide insight into the mechanisms that lead to enhanced control of interfacial properties through patterning, the strategies that can be used for fabricating synthetic patterns, and an overview of experimental results that have been used to gain understanding and guidance in this emerging field.
Microstructured Polymer Adhesive Feet for Climbing Robots
Authors: Daltorio Kathryn A. , Gorb Stanislav , Peressadko Andrei , Horchler Andrew D. , Wei Terence E. , Ritzmann Roy E. , Quinn Roger D.
Published: February 2011

Novel insect-foot–inspired materials may enable future robots to walk on surfaces regardless of the direction of gravity. Mini-Whegs™, a small robot that uses four wheel-legs for locomotion, was converted to a wall-walking robot with compliant, adhesive feet. First, the robot was tested with conventional adhesive feet. Then a new, reusable insect-inspired adhesive was tested on the robot. This structured polymer adhesive has less adhesive strength than conventional pressure-sensitive adhesives, but it has two important advantages: the foot material maintains its properties for more walking cycles before becoming contaminated, and the feet can then be washed and reused with similar results, which is not feasible with conventional adhesives. After the addition of a tail and widening the feet, the robot is capable of ascending vertical smooth glass surfaces using the structured polymer adhesive.
Next-Generation Fibrous Media for Water Treatment
Authors: Kaur Satinderpal , Gopal Renuga , Ng Wun Jern , Ramakrishna Seeram , Matsuura Takeshi
Published: February 2011

Fibrous media in the form of nonwoven filters have been used extensively in water treatment as pre-filters or to support the medium that does the separation. Nonwoven media are composed of randomly oriented micron-size fibers and provide a one step separation as a substitute for conventional processes comprising chemical addition, flocculation, sedimentation, and sand filtration. At present the use of nonwoven filter media is limited to pre-filters and is not used further downstream as high performance filters. However it is expected that by reducing the fiber size in the nanometer range, higher filtration efficiency can be achieved. With the advent of nanotechnology, the ease of producing high quality nano scaled fibers is now a reality. Recent advancements in nanofibrous media through surface modifications have shown that nonwoven media can be used beyond the prefilter stage. Furthermore the pore size of the filter media can be controlled through modification of fiber size and thickness of membranes. These nanofibrous membranes possess high surface area and large porosity leading to high flux, low pressure membranes. This article highlights important opportunities and challenges associated with developing nanofibrous media for water treatment. In addition, we have attempted to capture a snapshot of this rapidly developing new area of fibrous media for water treatment for the benefit of the wider membrane community.
Functional-DNA–Based Nanoscale Materials and Devices for Sensing Trace Contaminants in Water
Authors: Wernette Daryl P. , Liu Juewen , Bohn Paul W. , Lu Yi
Published: February 2011

Trace contaminant detection in water represents both a grand challenge and great opportunity for materials scientists and engineers. The recent discovery that functional DNA can be obtained to bind selectively to a wide range of contaminants makes it possible to interface these molecules with nanoscale materials, such as gold nanoparticles and quantum dots, to transform the molecular reorganization between functional DNA and contaminants into physically detectable colorimetric and fluorescent signals. Micro- and nanofluidic devices have also played a critical role in lowering the detection limits of functional-DNA sensors, promoting sensor regeneration and thus improving sensor performance and allowing long-term unattended monitoring of water quality.
Analysis of Complex Microstructures: Serial Sectioning and Phase-Field Simulations
Authors: Kammer D. , Voorhees P. W.
Published: February 2011

With the emergence and evolution of serial sectioning techniques that allow for three-dimensional data collection and the continuing increase in computational power, it is now possible to analyze and compute the evolution of three-dimensional nano- and microstructures. Structures can be accurately characterized, and it is possible to correlate processing paths with materials properties with great precision. Examples of the analysis and computations of the evolution of three-dimensional microstructures are discussed. The focus is on experiments that use serial sectioning methods to determine three-dimensional structure and on phase-field simulations of microstructural evolution that employ experimental three-dimensional data as initial conditions.
3DXRD Characterization and Modeling of Solid-State Transformation Processes
Authors: Jensen D. Juul , Offerman S.E. , Sietsma J.
Published: February 2011

Three-dimensional x-ray diffraction (3DXRD) allows nondestructive characterization of grains, orientations, and stresses in bulk microstructures and, therefore, enables in situ studies of the structural dynamics during processing. The method is described briefly, and its potential for providing new data valuable for validation of various models of microstructural evolution is discussed. Examples of 3DXRD measurements related to recrystallization and to solid-state phase transformations in metals are described. 3DXRD measurements have led to new modeling activity predicting the evolution of metallic microstructures with much more detail than hitherto possible. Among these modeling activities are three-dimensional (3D) geometric modeling, 3D molecular dynamics modeling, 3D phase-field modeling, two-dimensional (2D) cellular automata, and 2D Monte Carlo simulations.
A Molecular Basis for Advanced Materials in Water Treatment
Authors: Cygan Randall T. , Brinker C. Jeffrey , Nyman May D. , Leung Kevin , Rempe Susan B.
Published: February 2011

A molecular-scale interpretation of interfacial processes is often downplayed in the analysis of traditional water treatment methods; however, such a fundamental approach is perhaps critical for the realization of enhanced performance in traditional desalination and related treatments, and in the development of novel water treatment technologies. Specifically, we examine in this article the molecular-scale processes that affect water and ion selectivity at the nanopore scale as inspired by nature, the behavior of a model polysaccharide as a biofilm, and the use of cluster-surfactant flocculants in viral sequestration.
Organic Light-Emitting Devices for Solid-State Lighting
Authors: So Franky , Kido Junji , Burrows Paul
Published: February 2011

Organic light-emitting devices (OLEDs) have been widely developed for flat-panel displays, but only recently the efficiency of white OLEDs has risen to the point where they can be considered for solid-state lighting (SSL) applications. In this review, we discuss the requirements of solid-state lighting as they relate to OLEDs. We focus on how the color, efficiency, and cost requirements of general illumination differ from those of displays and how these differences might have an impact on the design of organic SSL. We then present some recent developments in large-area fabrication techniques that might be appropriate for solid-state lighting applications. Finally, we review recent results in the development of organic materials, device architectures, light extraction schemes, and fabrication techniques that can lead to cost-effective OLED lighting.
Connecting Electrical and Molecular Properties of Semiconducting Polymers for Thin-Film Transistors
Authors: Chabinyc Michael L. , Jimison Leslie H. , Rivnay Jonathan , Salleo Alberto
Published: February 2011

An overview of recent work on the connection between electrical and molecular properties of semiconducting polymers for thin-film transistors (TFTs) is presented. A description of the molecular packing and microstructure of amorphous to semicrystalline semiconducting polymers is presented. The features of basic models for electrical transport in TFTs are discussed. These studies indicate that defect states and traps are as important as ordered domains for understanding transport in semiconducting polymers. Advanced methods, such as electric force microscopy, useful for measuring the characteristics of defect states and charge traps, are briefly reviewed.
Organic Semiconductor Devices with Enhanced Field and Environmental Responses for Novel Applications
Authors: Someya Takao , Pal Bholanath , Huang Jia , Katz Howard E.
Published: February 2011

We discuss some recent advances in the use of organic semiconductor devices with additional or enhanced functionality beyond simple electrical switching. These include diodes that act as local temperature sensors or that filter reverse-bias currents at tens of megahertz frequency. Transistors are described with a range of sensing and reporting functions, for such properties as pressure, magnetic field, and chemical vapor. Because these devices will likely be employed in arrays and assemblies, we also present concepts of some larger, integrated components such as artificial skin, sensor arrays, and wireless power systems. The common theme of these devices is that they build on an extensive and growing understanding of the parent transistors and diodes, but represent a departure into new physical phenomena and application areas.
Superhydrophobicity and Contact-Line Issues
Authors: Gao Lichao , Fadeev Alexander Y. , McCarthy Thomas J.
Published: February 2011

The wettability of several superhydrophobic surfaces that were prepared recently by simple, mostly single-step methods is described and compared with the wettability of surfaces that are less hydrophobic. We explain why two length scales of topography can be important for controlling the hydrophobicity of some surfaces (the lotus effect). Contact-angle hysteresis (difference between the advancing, θA, and receding, θR, contact angles) is discussed and explained, particularly with regard to its contribution to water repellency. Perfect hydrophobicity (θA/θR = 180°/180°) and a method for distinguishing perfectly hydrophobic surfaces from those that are almost perfectly hydrophobic are described and discussed. The Wenzel and Cassie theories, both of which involve analysis of interfacial (solid/liquid) areas and not contact lines, are criticized. Each of these related topics is addressed from the perspective of the three-phase (solid/liquid/vapor) contact line and its dynamics. The energy barriers for movement of the three-phase contact line from one metastable state to another control contact-angle hysteresis and, thus, water repellency.
Design Parameters for Superhydrophobicity and Superoleophobicity
Authors: Tuteja Anish , Choi Wonjae , McKinley Gareth H. , Cohen Robert E. , Rubner Michael F.
Published: February 2011

Recent experiments have revealed that the wax on the lotus leaf surface, by itself, is weakly hydrophilic, even though the lotus leaf is known to be superhydrophobic. Conventional understanding suggests that a surface of such waxy composition should not be able to support superhydrophobicity and high contact angles between a liquid and the surface. Here, we show that the unexpected superhydrophobicity is related to the presence of “reentrant texture” (that is, a multivalued surface topography) on the surface of the lotus leaf. We exploit this understanding to enable the development of superoleophobic surfaces (i.e., surfaces that repel extremely low-surface-tension liquids, such as various alkanes), where essentially no naturally oleophobic materials exist. We also develop general design parameters that enable the evaluation of the robustness of the composite interface on a particular surface. Based on these design parameters, we also rank various superhydrophobic and superoleophobic substrates discussed in the literature, with particular emphasis on surfaces developed from inherently hydrophilic or oleophilic materials.
The Underlying Chemistry of Self-Healing Materials
Authors: Williams Kyle A. , Dreyer Daniel R. , Bielawski Christopher W.
Published: February 2011

Over the past ten years, a broad range of self-healing materials, systems that can detect when they have been damaged and heal themselves either spontaneously or with the aid of a stimulus, has emerged. Although many unique compositions and components are used to create these materials, they all employ basic chemical reactions to facilitate repair processes. Kinetically controlled ring-opening reactions and reversible metal–ligand interactions have proven useful in autonomic self-healing materials, which require no stimulus (other than the formation of damage) for operation. In contrast, nonautonomic self-healing materials, which require some type of externally applied stimulus (such as heat or light) to enable healing functions, have capitalized on chemistries that utilize either reversible covalent bonds or various types of noncovalent interactions. This review describes the underlying chemistries used in state-of-the-art self-healing materials, as well as those currently in development.
Nanostructured Materials in Information Storage
Authors: Bandić Zvonimir Z. , Litvinov Dmitri , Rooks M.
Published: February 2011

The ever-increasing demand for information storage has pushed research and development of nonvolatile memories, particularly magnetic disk drives and silicon-based memories, to areal densities where bit sizes are approaching nanometer dimensions. At this level, material and device phenomena make further scaling increasingly difficult. The difficulties are illustrated in the examples of magnetic media and flash memory, such as thermal instability of sub-100-nm bits in magnetic memory and charge retention in flash memory, and solutions are discussed in the form of patterned media and crosspoint memories. The materials-based difficulties are replaced by nanofabrication challenges, requiring the introduction of new techniques such as nanoimprinting lithography for cost-effective manufacturing and self-assembly for fabrication on the sub-25-nm scale. Articles in this issue describe block-copolymer lithographic fabrication of patterned media, materials studies on the scaling limits of phase-change-based crosspoint memories, nanoscale fabrication using imprint lithography, and biologically inspired protein-based memory.
Patterned Magnetic Media Made by Self-Assembled Block-Copolymer Lithography
Authors: Ross C.A. , Cheng J.Y.
Published: February 2011

Patterned magnetic recording media, in which data bits are stored in discrete single-domain magnetic particles, have been proposed for the next generation of recording media. To achieve high densities, features with periodicities on the order of 25 nm and below are required over large areas, which is a challenging task for any lithography process. Block copolymers (BCPs), which phase-separate into ordered periodic nanoscale structures, might provide a path to accomplish such patterning. In this article, we describe BCP lithography and show how the self-assembled patterns can be templated to make large-area arrays of nanoscale structures with long-range order.
Nanoscale Manufacturing Enabled by Imprint Lithography
Authors: Sreenivasan S.V.
Published: February 2011

Imprint lithography has a remarkable patterning resolution of less than 5 nm, and it is simultaneously capable of patterning over large areas with long-range order. This combination enables a broad range of potential applications including terabit-density magnetic storage, CMOS integrated circuits, and nanowire molecular memory. This article provides a review of the status of imprint lithography for nanoscale manufacturing. First, representative nanoscale devices and their manufacturing requirements are reviewed, along with key patterning challenges that have to be overcome to enable these nanoscale applications. Two classes of top–down nanopatterning techniques, namely, photon-based lithography and proximity mechanical nanopatterning (including imprint lithography), are described, followed by the three primary building blocks of imprint lithography: imprint masks, tools, and materials. Theresults of the lithography process are detailed in terms of process data such as long-range order in the placement and size of the nanostructures, process throughput, and overall cost considerations.
Protein-Based Disk Recording at Areal Densities beyond 10 Terabits/in.2
Authors: Khizroev S. , Ikkawi R. , Amos N. , Chomko R. , Renugopalakrishnan V. , Haddon R. , Litvinov D.
Published: February 2011

The concept of optical protein-based memory has been of interest since the early 1970s. Yet, no commercially available protein-based memory devices exist. This review presents an analysis of the main challenges associated with the practical implementation of such devices. In addition, the discussion includes details on the potential of using the unparalleled properties of photochromic proteins by creating an optical data storage disk drive with unmatched features and, particularly, record-high data densities and rates.
Negative Refraction in Photonic Crystals
Authors: Baba Toshihiko , Asatsuma Tomohiko , Matsumoto Takashi
Published: February 2011

Photonic crystals are multidimensional periodic gratings, in which the light propagation is dominated by Bragg diffraction that appears to be refraction at the flat surfaces of the crystals. The refraction angle from positive to negative, perfectly or only partially obeying Snell's law, can be tailored based on photonic band theory. Negative refraction enables novel prism, collimation, and lens effects. Because photonic crystals usually consist of two transparent media, these effects occur at absorption-free frequencies, affording significant design flexibility for free-space optics. The photonic-crystal slab, a high-index membrane with a two-dimensional airhole array, must be carefully designed to avoid unwanted reflection and diffraction. Light focusing based on negative refraction forms a parallel image of a light source, facilitating optical couplers and condenser lenses for wavelength demultiplexing. A compact wavelength demultiplexer can be designed by combining the prism and lens effects.
Two-Dimensional Electron Gases at Oxide Interfaces
Authors: Mannhart J. , Blank D.H.A. , Hwang H.Y. , Millis A.J. , Triscone J.-M.
Published: February 2011

Two-dimensional electron gases (2DEGs) based on conventional semiconductors such as Si or GaAs have played a pivotal role in fundamental science and technology. The high mobilities achieved in 2DEGs enabled the discovery of the integer and fractional quantum Hall effects and are exploited in high-electron-mobility transistors. Recent work has shown that 2DEGs can also exist at oxide interfaces. These electron gases typically result from reconstruction of the complex electronic structure of the oxides, so that the electronic behavior of the interfaces can differ from the behavior of the bulk. Reports on magnetism and superconductivity in oxide 2DEGs illustrate their capability to encompass phenomena not shown by interfaces in conventional semiconductors. This article reviews the status and prospects of oxide 2DEGs.
Tribology in Full View
Authors: Marks Laurence D. , Warren Oden L. , Minor Andrew M. , Merkle Arno P.
Published: February 2011

For many years, a fundamental problem in contact mechanics, both tribology and indentation problems, has been the inability to see what is taking place—the buried-interface problem. Over the past few years, there have been developments whereby it has become possible to perform contact mechanics experimentsin situwithin a transmission electron microscope. These new experiments have been enabled by both the miniaturization of sensors and actuators and improvements in their mechanical stability and force sensitivity. New information is now becoming available about the nanoscale processes of sliding, wear, and tribochemical reactions, as well as microstructural evolution during nanoindentation such as dislocation bursts and phase transformations. This article provides an overview of some of these developments, in terms of both the advances in technical instrumentation and some of the novel scientific insights.
Visualizing the Behavior of Dislocations—Seeing is Believing
Authors: Robertson Ian M. , Ferreira Paulo J. , Dehm Gerhard , Hull Robert , Stach Eric A.
Published: February 2011

The spatial resolution of the transmission electron microscope makes it an ideal environment in which to continuously track the real-time response of a system to an external stimulus and to discover and quantify the rate-limiting fundamental microscopic processes and mechanisms governing the macroscopic properties. Advances in instrumentation, stage design, recording media, computational power, and image manipulation software are providing new opportunities for not only observing the microscopic mechanisms but also measuring concurrently the macroscopic response. In this article, the capability of this technique as applied to mechanical properties of materials is highlighted.
Gel Sensors and Actuators
Authors: Calvert Paul
Published: February 2011

Gels, soft polymeric or composite materials that have a high fraction of water, are often found as structural materials and actuators in nature but have so far not found many uses when fabricated synthetically. We first examine some natural systems such as jellyfish, sea anemones, starfish, legumes, and human tissue, all having interesting ways of moving or otherwise reacting to the surrounding environment. Then we discuss swelling and cross-linking of hydrogels, followed by a look at actuation by electrically, thermally, and chemically stimulated gels, noting that electrical stimulation needs a chemical intermediary to show substantial actuation (comparable to human muscle, for instance). Electroactive gels have great potential as sensors and actuators but their actual uses are mainly restricted to passive drug delivery and matrices for sensors. For most applications as artificial muscles, electrically driven actuators are too weak, but chemically driven actuators look very promising. Better ways of coupling electrical energy to chemically driven gels are needed.
Materials Challenges in Present and Future Wind Energy
Authors: Hayman Brian , Wedel-Heinen Jakob , Brøndsted Povl
Published: February 2011

The main concept currently in use in wind energy involves horizontal-axis wind turbines with blades of fiber composite materials. This turbine concept is expected to remain as the major provider of wind power in the foreseeable future. However, turbine sizes are increasing, and installation offshore means that wind turbines will be exposed to more demanding environmental conditions. Many challenges are posed by the use of fiber composites in increasingly large blades and increasingly hostile environments. Among these are achieving adequate stiffness to prevent excessive blade deflection, preventing buckling failure, ensuring adequate fatigue life under variable wind loading combined with gravitational loading, and minimizing the occurrence and consequences of production defects. A major challenge is to develop cost-effective ways to ensure that production defects do not cause unacceptable reductions in equipment strength and lifetime, given that inspection of large wind power structures is often problematic.
The 3 GW Initiative
Authors: Palucka Tim
Published: February 2011

California continues its tradition of leading the United States in environmental stewardship through the California Solar Initiative (CSI), a $3.3 billion program established in January 2006. The goal is to generate 3 GW of electricity by 2017 through photovoltaic methods by installing solar cells on the roofs of existing and new residential and commercial buildings (see Figure 1). CSI will “reduce our output of greenhouse gases by 3 million tons,” California Governor Arnold Schwarzenegger said in a speech given in October 2006. “That is equivalent to taking one million cars off the road.”
Bioenergy Research Needs for Heat, Electricity, and Liquid Fuels
Authors: Farrell Alexander E. , Gopal Anand R.
Published: February 2011

Biomass remains a key energy source for several billion people living in developing countries, and the production of liquid biofuels for transportation is growing rapidly. However, both traditional biomass energy and crop-based biofuels technologies have negative environmental and social impacts. The overall research challenge for bioenergy is to develop the technologies to produce useful products at low costs while minimizing the use of scarce resources such as arable land and water. This requires substantial advancements in modern biomass power generation and the success of liquid biofuel technologies that permit the use of lignocellulosic feedstocks or possibly algae. With such technologies, biomass resources could meet a significant fraction (over 10%) of global energy demand. Both improved policies and technologies are needed to ensure that bioenergy contributes significantly to economic, social, and environmental goals.
Hydropower, Geothermal, and Ocean Energy
Authors: Sims Ralph E.H.
Published: February 2011

Some forms of renewable energy have long contributed to electricity generation, whereas others are just emerging. For example, large-scale hydropower is a mature technology generating about 16% of global electricity, and many smaller scale systems are also being installed worldwide. Future opportunities to improve the technology are limited but include upgrading of existing plants to gain greater performance efficiencies and reduced maintenance. Geothermal energy, widely used for power generation and direct heat applications, is also mature, but new technologies could improve plant designs, extend their lifetimes, and improve reliability. By contrast, ocean energy is an emerging renewable energy technology. Design, development, and testing of a myriad of devices remain mainly in the research and development stage, with many opportunities for materials science to improve design and performance, reduce costly maintenance procedures, and extend plant operating lifetimes under the harsh marine environment.
The Electric Power Grid: Today and Tomorrow
Authors: Amin Massoud , Stringer John
Published: February 2011

In the coming decades, electricity's share of total global energy is expected to continue to grow, I and more intelligent processes will be introduced into the electric power delivery (transmission and distribution) networks. It is envisioned that the electric power grid will move from an electromechanically controlled system to an electronically controlled network in the next two decades. A key challenge is how to redesign, retrofit, and upgrade the existing electromechanically controlled system into a smart self-healing grid that is driven by a well-designed market approach. Revolutionary developments in both information technology and materials science and engineering promise significant improvements in the security, reliability, efficiency, and cost effectiveness of electric power delivery systems. Focus areas in materials and devices include sensors, smart materials and structures, microfabrication, nanotechnology, advanced materials, and smart devices.
The Hydrogen Fuel Alternative
Authors: Crabtree G.W. , Dresselhaus M.S.
Published: February 2011

The cleanliness of hydrogen and the efficiency of fuel cells taken together offer an appealing alternative to fossil fuels. Implementing hydrogen-powered fuel cells on a significant scale, however, requires major advances in hydrogen production, storage, and use. Splitting water renewably offers the most plentiful and climate-friendly source of hydrogen and can be achieved through electrolytic, photochemical, or biological means. Whereas presently available hydride compounds cannot easily satisfy the competing requirements for on-board storage of hydrogen for transportation, nanoscience offers promising new approaches to this challenge. Fuel cells offer potentially efficient production of electricity for transportation and grid distribution, if cost and performance challenges of components can be overcome. Hydrogen offers a variety of routes for achieving a transition to a mix of renewable fuels.