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.

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.

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.

Bulk metallic glasses (BMGs) are multicomponent alloys with typically three to five components with large atomic size mismatch and a composition close to a deep eutectic. Packing in BMG liquids is very dense, with a low content of free volume resulting in viscosities that are several orders of magnitude higher than in pure metal melts. The dense packing accomplished by structural and chemical atomic ordering also brings the BMG-forming liquid energetically and entropically closer to its corresponding crystalline state. These factors lead to slow crystallization kinetics and consequentially to high glass-forming ability. This article highlights the thermodynamic and kinetic properties of BMGs and their contributions to extraordinarily high glass-forming ability. Some possible links with mechanical properties are also suggested.

The record laboratory cell (∼1 cm2 area) efficiency for thin-film cadmium telluride (CdTe) is 16.5%, and that for a copper indium diselenide (CuInSe2) thin-film alloy is 19.5%. Commercially produced CdTe and CuInSe2 modules (0.5–1 m2 area) have efficiencies in the 7–11% range. Research is needed both to increase laboratory cell efficiencies and to bring those small - area efficiencies to large-area production. Increases in laboratory CdTe cell efficiency will require increasing open-circuit voltage, which will allow cells to harvest more energy from each absorbed photon. This will require extending the minority carrier lifetime from its present τ ≤ 2 ns to τ ≥ 10 ns and increasing hole concentration in the CdTe beyond 1015 cm2, which appears to be limited by compensating defects. Increasing laboratory CuInSe2-based cell efficiency significantly beyond 19.5% will also require increasing the open-circuit voltage, either by increasing the bandgap, the doping level, or the minority carrier lifetime. The photovoltaic cells in commercial modules occupy tens of square centimeters, and both models and experiments have shown that low-performing regions in small fractions of a cell can significantly reduce the overall cell per formance. Increases in commercial module efficiency will require control of materials properties across large deposition areas in a high-throughput environment to minimize such non-uniformities. This article discusses approaches used and research needed to increase the ultimate efficiencies of CdTe- and CuInSe2-based devices and translate these gains to commercial photovoltaic modules.

Nature exhibits a variety of remarkable phenomena that are useful but difficult to imitate in real life. Examples are the “touch me not” plant (Mimosa pudica), which folds up upon being attacked, or microbes that deposit on ocean vessels even under hostile conditions. Understanding the mechanisms governing these phenomena can prove powerful for developing new classes of cosmetic products. This article examines the development of novel materials with functional properties such as controlled delivery and the deposition of sensory attributes (fragrances, flavors, etc.) desirable in cosmetic products. Particularly, systems based on polymer/surfactant chemistry are explored for achieving transport and release of cosmetic and pharmaceutical molecules at desired rates. The hybrid polymers and nanogel particle systems discussed here represent new classes of materials with nanodomains that can be tuned to extract and deliver cosmetic attributes by means of changes in natural parameters such as temperature and pH. While the safety of existing nanomaterials marketed for decades has not been an issue, methods are urgently needed to validate the toxicological safety of future nanomaterials.

A great expansion in the number of alloy compositions known to give bulk metallic glasses (BMGs) has occurred in recent years. This progress is reviewed, and factors contributing to glass-forming ability are discussed. Practical strategies for pinpointing compositions with optimum glass-forming ability are presented, with examples of their use. Consideration is also given to the wide range of possibilities for BMG-based composites.

This article reviews recent developments in laser direct-write addition (LDW+) processes for printing complex materials. Various applications, ranging from small-scale energy storage and generation devices to tissue engineering, require the ability to deposit precise patterns of multicomponent and multiphase materials without degrading desirable properties such as porosity, homogeneity, or biological activity. Structurally complex inorganic materials for the successful fabrication of alkaline and lithium-based microbatteries, micro-ultracapacitors, and dye-sensitized micro solar cells are shown on various low-processing-temperature and flexible substrates using LDW+. In particular, the ability to deposit thick layers while maintaining pattern integrity allows devices produced in this manner to exhibit higher energy densities per unit area than can be achieved by traditional thin-film techniques. We then focus on more complex systems of living and biologically active materials. Patterns of biomaterials such as proteins, DNA, and even living cells can be printed using LDW+ with high spatial and volumetric resolution on the order of a picoliter or less, without compromising the viability of these delicate structures. These results provide for highly selective sensor arrays or cell seeding for tissue engineering. Finally, we review recent work on LDW+ of entire semiconductor circuits, showing the broad range of applications this technique enables.

This article is based on an edited transcript of a presentation given by Frank W. Gayle (National Institute of Standards and Technology) on April 12, 2007, in Symposium X at the Materials Research Society Spring Meeting in San Francisco.

The NIST investigation of the World Trade Center disaster addressed many aspects of the catastrophe, from occupant egress to factors affecting the ability of the Twin Towers to remain standing after being hit by the airplanes, with the goal of gaining valuable information for future best practices in building materials, building design, and emergency response. The presentation addressed the structure of the towers, the analysis of the recovered steel, and special issues faced during the investigation. The probable collapse sequence for each of the towers was also discussed.

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.

Many aspects of materials deformation and failure are controlled by atomic-scale phenomena that can be explored using molecular statics and molecular dynamics simulations. However, many of these phenomena involve processes on multiple length scales with the result that full molecular statics/molecular dynamics simulations of the entire system are too large to be tractable. In this review, we discuss hybrid models that perform molecular statics/molecular dynamics simulations “without all the atoms,” aimed at retaining atomistic detail at a fraction of the computational cost. These methods couple a fully atomistic model in critical regions to regions described by less-expensive continuum methods where they can provide an adequate representation of the important physics. We give an overview of the challenges such models present, with a focus on recent work to address issues of dynamics and finite (non-zero) temperature.

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.

One important application of nanocomposites is their use in engineered structural composites. Among the wide variety of structural applications, fiber-reinforced composites for aerospace structures have some of the most demanding physical, chemical, electrical, thermal, and mechanical property requirements. Nanocomposites offer tremendous po tential to improve the properties of advanced engineered composites with modest additional weight and easy integration into current proc essing schemes. Sig nificant progress has been made in fulfilling this vision. In particular, nanocomposites have been applied at numerous locations within hierarchical composites to improve specific properties and optimize the multifunctional properties of the overall structure. Within this ar ticle, we review the status of nanocomposite incorporation into aerospace composite structures and the need for continued development.

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.

Metal-organic frameworks (MOFs) are an interesting class of molecule-based hybrid materials built from metal-connecting points and bridging ligands. MOFs have received much attention, owing to their potential impact on many technological areas, including gas storage, separation, and heterogeneous catalysis. The modular nature of MOFs endows them with facile tunability, and as a result, properly designed MOFs can yield ideal heterogeneous catalysts with uniform active sites through judicious choice of the building blocks. Homochiral MOFs, which can be prepared by numerous approaches (construction from achiral components by seeding with a chiral single crystal, templating with coordinating chiral co-ligands, and building from metal-connecting nodes and chiral bridging ligands), represent a unique class of materials for the economical production of optically pure compounds, whether through asymmetric catalysis or enantioselective inclusion of chiral guest molecules in their porous frameworks. As such, homochiral MOFs promise new opportunities for developing chirotechnology. This contribution provides a brief overview of recent progress in the synthesis of homochiral porous MOFs and their applications in asymmetric catalysis and chiral separations.

“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 with operando STM observations of model catalysts in action. We illustrate the strength of this microscope with examples of CO oxidation on platinum surfaces.

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.

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 modulus E ≈ 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 with E ≈ 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.

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.

A recent structural model reconciles apparently conflicting features of randomness, short-range order, and medium-range order that coexist in metallic glasses. In this efficient cluster packing model, short-range order can be described by efficiently packed solute-centered clusters, producing more than a dozen established atomic clusters, including icosahedra. The observed preference for icosahedral short-range order in metallic glasses is consistent with the theme of efficient atomic packing and is further favored by solvent-centered clusters. Driven by solute—solute avoidance, medium-range order results from the organization in space of overlapping, percolating (via connected pathways), quasi-equivalent clusters. Cubic-like and icosahedral-like organization of these clusters are consistent with measured medium-range order. New techniques such as fluctuation electron microscopy now provide more detailed experimental studies of medium-range order for comparison with model predictions. Microscopic free volume in the efficient cluster packing model is able to represent experimental and computational results, showing free volume complexes ranging from subatomic to atomic-level sizes. Free volume connects static structural models to dynamic processes such as diffusion and deformation. New approaches dealing with “free” and “anti-free” microscopic volume and coordinated atomic motion show promise for modeling the complex dynamics of structural relaxations such as the glass transition. Future work unifying static and dynamic structural views is suggested.