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.

In his visionary 1959 lecture at Caltech, Richard P. Feynman foresaw the potential of the ability to manipulate matter at the atomic scale. In this article, adapted from Integrated Nanosensors, MRS Symposium Proceedings Volume 952E, edited by I.K. Schuller, Y. Bruynseraede, L.M. Lechuga, and E. Johnson (2007), Jozef T. Devreese (University of Antwerp) discusses implementations of Feynman's vision in the field of nanosensors and perspectives of its further development and applications.

Nanoparticles are unique tools as sensors. Particles with sizes at the nanoscale reveal physical properties that do not exist in bulk materials; these properties can operate well inside living cells. Nanosensors possess unique physical characteristics. Their sensitivity can be orders of magnitude better than that of conventional devices. Nanosensors possess such performance advantages as fast response and portability. State-of-the-art nanosensors are based on various advanced materials (quantum dots, nanoshells, nanopores, carbon nanotubes, etc.). Nanosensors furthermore allow for building an entirely new class of integrated devices that provide the elemental base for “intelligent sensors” capable of data processing, storage, and analysis. Advances can open unprecedented perspectives for the application of nanosensors in various fields, for example, as molecular-level diagnostic and treatment instruments in medicine and as networks of nanorobots for real-time monitoring of physiological parameters of a human body.

Three-dimensional structures of selected materials can be written directly to the precise locations required using laser exposure of suitable gaseous precursor mixtures. Writing speeds exceeding 50 μm/s can be achieved. Examples presented in this work include the creation of a tiny time-of-flight laser ionization mass spectrometer, laserdriven movable micro-objects, and an ac electric-field microcage for storage, handling, and transferring small neutral objects in aqueous solution. The impact for lasercontrolled site-selective growth of carbon nanotube cables is demonstrated.

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.

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.

Cosmetics are products that are designed to maintain or improve visual appearance when applied to skin. Skin is a mechanically flexible substrate that changes in chemical and surface properties during the course of the day. Sebum (an oily substance secreted by the sebaceous glands) and perspiration (a secretion of mostly salt water by the eccrine glands) as well as environmental insults work counter to the desired benefits of cosmetics on physical appearance. Recent advances in the ability to control morphology and chemical properties have led to novel materials that in turn have enabled the development of cosmetics that provide, on the one hand, a more natural look, and on the other, unique and unprecedented visual effects. Progress in understanding skin biomechanics and surface properties lead to product formulations with unprecedented wear and performance characteristics. This article reviews recent advances in the ability to control the optical, bulk, and surface properties of materials, and their application to improved cosmetic formulations.

The efficiency of a solar cell can be increased by stacking multiple solar cells with a range of bandgap energies, resulting in a multijunction solar cell with a maximum the oretical efficiency limit of 86.8% III–V compound semiconductors are good candidates for fabricating such multijunction solar cells for two reasons: they can be grown with excellent material quality; and their bandgaps span a wide spectral range, mostly with direct bandgaps, implying a high absorption coefficient. These factors are the reason for the success of this technology, which has achieved 39% efficiency, the highest solar-to-electric conversion efficiency of any photovoltaic device to date. This article explores the materials science of today's high-efficiency multijunction cells and describes challenges associated with new materials developments and how they may lead to next-generation, multijunction solar cell concepts.

Magnetic ordering that typically occurs for extended three-dimensional structured inorganic materials has also been established for several organic- and molecule-based materials. In addition to the characterization of new magnetic materials, new phenomena and combinations of phenomena have been observed for molecule-based materials. An overview of the new materials and phenomena is presented.

Semiconductor quantum dots may be used in so-called third-generation solar cells that have the potential to greatly increase the photon conversion efficiency via two effects: (1) the production of multiple excitons from a single photon of sufficient energy and (2) the formation of intermediate bands in the bandgap that use sub-bandgap photons to form separable electron–hole pairs. This is possible because quantization of energy levels in quantum dots produces the following effects: enhanced Auger processes and Coulomb coupling between charge carriers; elimination of the requirement to conserve crystal momentum; slowed hot electron–hole pair (exciton) cooling; multiple exciton generation; and formation of minibands (delocalized electronic states) in quantum dot arrays. For exciton multiplication, very high quantum yields of 300–700% for exciton formation in PbSe, PbS, PbTe, and CdSe quantum dots have been reported at photon energies about 4–8 times the HOMO–LUMO transition energy (quantum dot bandgap), respectively, indicating the formation of 3–7 excitons/photon, depending upon the photon energy. For intermediate-band solar cells, quantum dots are used to create the intermediate bands from the con fined electron states in the conduction band. By means of the intermediate band, it is possible to absorb below-bandgap energy photons. This is predicted to produce solar cells with enhanced photocurrent without voltage degradation.

We describe the production of hierarchical branched nanowire structures by the sequential seeding of multiple wire generations with metal nanoparticles. Such complex structures represent the next step in the study of functional nanowires, as they increase the potential functionality of nanostructures produced in a self-assembled way. It is possible, for example, to fabricate a variety of active heterostructure segments with different compositions and diameters within a single connected structure. The focus of this work is on epitaxial III-V semiconductor branched nanowire structures, with the two materials GaP and In As used as typical examples of branched structures with cubic (zinc blende) and hexagonal (wurtzite) crystal structures. The general morphology of these structures will be described, as well as the relationship between morphology and crystal structure.

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?

Current technology trends imply that further miniaturization and integration of systems are anticipated, and one approach to realizing the next generation of systems integration is the development of materials that are protean, or capable of taking on various properties; in essence, the materials properties can be selectively altered via laser excitation. The objective is that a common substrate material can be used for multiple functions. Laser direct-write material processing, because of its maskless patterning flexibility, is inherently suitable for producing localized changes in materials properties and thereby fabricating linked, integrated devices on a common substrate. The enabling of this new form of materials processing requires a light-activated protean material along with a scheme for the dynamic regulation of the laser energy for optimum laser processing on the scale of the laser spot size and for patterning speeds on the order of meters per second. The “protean material” concept and a high-fidelity laser amplitude-modulation scheme are the focus of this article.

A cosmetic product is often a complex non-homogeneous mixture of physicochemical units including polymers, small molecules, surface-active species, and particles. In use, it is applied to an equally heterogeneous substrate, skin. Consequently, materials structure as well as composition and the nature of the surfaces are relevant to a clear understanding of any technologically important product property or process. No longer is it sufficient to answer the classical questions of analysis—what and how much?—for many applications; we must now ask the additional questions of where, how organized, and how is it manifest to the customer? Although analytical sciences have, for many years, been applied to the problem of characterizing what is in chemical systems, the need to understand spatial and interfacial interactions has received much less attention. The explosive growth, however, in electronics, computing, biology, mathematical methodologies, microscopy, and optics now present the cosmetic industry with a new set of tools that can be utilized to address this issue. It is the objective of this article to highlight some of these measurement advances and how they might have relevance in the cosmetics industry in the coming years.

With the guidance offered by nonequilibrium statistical thermodynamics, simulation techniques are elevated from brute-force computer experiments to systematic tools for extracting complete, redundancy-free, and consistent coarse-grained information for dynamic systems. We sketch the role and potential of Monte Carlo, molecular dynamics, and Brownian dynamics simulations in the thermodynamic approach to coarse graining. A melt of entangled linear polyethylene molecules serves us as an illustrative example.

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.

In the absence of dislocation-mediated crystallographic slip, room-temperature deformation in metallic glasses occurs in thin shear bands initially only ∼10 nm thick. A sharp drop in viscosity (shear softening) occurs in deformed glassy matter and facilitates additional flow in existing shear bands. This further localization of plastic flow leads to shearing-off failure without any significant macroscopic plasticity.

However, whereas most bulk metallic glasses fail in this manner, some undergo surprisingly extensive plastic deformation (in some cases, up to 50% or more) in compression or bending. When this occurs, the flow is “jerky,” as indicated by serrated stress–strain curves. Each serration may correspond to the emission of a shear band that then ceases to operate, at least temporarily, despite the predicted shear softening. As elastic energy is converted to heat during shear, temperatures rise sharply at or near shear bands. This heating may lead to the growth of nanocrystals that then block propagation of shear bands and cracks. The understanding of the dependence of mechanical response of metallic glasses on intrinsic (elastic constants, chemistry) and extrinsic factors (shapes, flaws) is the subject of intense current interest.

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.

The self-assembly of small molecules into large, functional nanostructures has led to the construction of supramolecular systems, both in solution and on solid substrates, with defined dimensions that display unique properties through collective interactions, much like natural systems. In this article, we show how one assembles photo- and electroluminescent molecules through coordination chemistry for the purpose of producing novel materials that can be used for displays and lighting applications. In a stepwise process, we discuss the design and synthesis of the components, their spectroscopic behavior, and finally the properties arising from the assembly. We then move from molecules to more complex systems such as zeolite L nano-objects that can be used as nanocontainers and functionalized in different ways. We show how it is possible to organize rods of micron length in a geometrically controlled manner in solution and on surfaces. The assemblies are built by coordinative bonds and are luminescent materials that can be constructed from fluorescent building blocks, with potential applications as optoelectronic materials, in analogy to their molecular counterparts.

This article considers the fundamentals of what happens in a solid when it is impacted by a medium-energy gallium ion. The study of the ion/sample interaction at the nanometer scale is applicable to most focused ion beam (FIB)–based work even if the FIB/sample interaction is only a step in the process, for example, micromachining or microelectronics device processing. Whereas the objective in other articles in this issue is to use the FIB tool to characterize a material or to machine a device or transmission electron microscopy sample, the goal of the FIB in this article is to have the FIB/sample interaction itself become the product. To that end, the FIB/sample interaction is considered in three categories according to geometry: below, at, and above the surface. First, the FIB ions can penetrate the top atom layer(s) and interact below the surface. Ion implantation and ion damage on flat surfaces have been comprehensively examined; however, FIB applications require the further investigation of high doses in three-dimensional profiles. Second, the ions can interact at the surface, where a morphological instability can lead to ripples and surface self-organization, which can depend on boundary conditions for site-specific and compound FIB processing. Third, the FIB may interact above the surface (and/or produce secondary particles that interact above the surface). Such ion beam–assisted deposition, FIB–CVD (chemical vapor deposition), offers an elaborate complexity in three dimensions with an FIB using a gas injection system. At the nanometer scale, these three regimes—below, at, and above the surface—can require an interdependent understanding to be judiciously controlled by the FIB.