The key strength of hard x-ray full-field microscopy is the large penetration depth of hard x-rays into matter, which allows one to image the interior of opaque objects. Combined with tomographic techniques, the three-dimensional inner structure of an object can be reconstructed without the need for difficult and destructive sample preparation. Projection microscopy and microtomography are now routinely available at synchrotron radiation sources. The resolution of these techniques is limited by that of the detector to 1 µm or slightly less. X-ray images and tomograms at higher spatial resolution can be obtained by x-ray optical magnification, for example, by using parabolic refractive x-ray lenses as a magnifying optic. Combining magnifying x-ray imaging with tomography allows one to reconstruct the three-dimensional structure of an object, such as a microprocessor chip, with resolution well below 1 µm. In x-ray scanning microscopy, the sample is scanned through a small-diameter beam. The great advantage of scanning microscopy is that x-ray analytical techniques such as fluorescence analysis, diffraction, and absorption spectroscopy can be used as contrast mechanisms in the microscope. In combination with tomography, fluorescence analysis makes it possible to reconstruct the distribution of different chemical elements inside an object (fluorescence microtomography), while combining absorption spectroscopy with tomography yields the distribution of different oxidation states of atomic species.

In order to meet technology scaling in the field of solid-state memory and data storage, the mainstream transistor-based flash technologies will start evolving to incorporate material and structural innovations. Dielectric scaling in nonvolatile memories is approaching the point where new approaches will be required to meet the scaling requirements while simultaneously meeting the reliability and performance requirements of future products. High-dielectric-constant materials are being explored as possible candidates to replace the traditional SiO2 and ONO (oxide/nitride/oxide) films used today in memory cells. Likewise, planar-based memory cell scaling is approaching the point where scaling constraints force exploration of new materials and nonplanar, three-dimensional scaling alternatives. This article will review the current status and discuss the approaches being explored to provide scaling solutions for future transistor floating-gate-based nonvolatile memory products. Based on the introduction of material innovations, it is expected that the planar transistor-based flash memory cells can scale through at least the end of the decade (2010) using techniques that are available today or projected to be available in the near future. More complex, structural innovations will be required to achieve further scaling.

In conventional solid-state electronic devices, junctions and interfaces play a significant if not dominant role in controlling charge transport. Although the emerging field of molecular electronics often focuses on the properties of the molecule in the design and understanding of device behavior, the effects of interfaces and junctions are often of comparable importance. This article explores recent work in the study of metal–molecule–metal and semiconductor–molecule–metal junctions. Specific issues include the mixing of discrete molecular levels with the metal continuum, charge transfer between molecules and semiconductors, electron-stimulated desorption, and resonant tunneling. By acknowledging the consequences of junction/interface effects, realistic prospects and limitations can be identified for molecular electronic devices.

The atomic force microscope (AFM) allows biomolecules to be observed and manipulated under native conditions. It produces images with an outstanding signal-to-noise ratio and addresses single molecules while the sample is in a buffer solution. Progress in sample preparation and instrumentation has led to topographs that reveal subnanometer details and the surface dynamics of biomolecules. Tethering single molecules between a support and a retracting AFM tip produces force–extension curves, giving information about the mechanical stability of secondary structural elements. For both imaging and force spectroscopy, the cantilever and its tip are critical:the mechanical properties of the cantilever dictate the force sensitivity and the scanning speed, whereas the tip shape determines the achievable lateral resolution.

This article describes the use of an electronic nose (the Cyranose 320) to sense and identify three species of bacteria responsible for ear, nose, and throat (ENT) infections. Gathered data were a complex mixture of different chemical compounds. An innovative approach for classifying the bacteria data was investigated by using a combination of several clustering algorithms. The best results suggest that the three classes of bacteria examined can be predicted with up to 98% accuracy, allowing more precise diagnosis of ENT infection in patients. This type of bacteria data analysis and feature extraction is difficult, but it can be concluded that combined use of the analysis methods described here can solve the feature extraction problem with very complex data and enhance the performance of electronic noses.

This article focuses on nanocrystalline-matrix ceramic composites specifically designed for applications requiring improved fracture toughness. While the models and theory of toughening mechanisms for microcrystalline composites are well developed, the same cannot be said for their nanocrystalline counterparts. The difficulty in producing fully consolidated ceramic composites that retain a nanocrystalline structure is the main hurdle to thorough investigations in this area. Thus, much of the research on so-called nanocomposites has been on materials with microcrystalline matrices and nanometric second phases. In this article, we present the general principles of toughness mechanisms in microcrystalline ceramic composites, and then extend these ideas to consider how they should apply to ceramics with nanocrystalline matrices. While work in this area is still quite limited, we review current research focused on the production and testing of composites with nanocrystalline matrices and second phases, and we recap the results of some promising fracture toughness reports.

This article provides an overview of the fabrication of epitaxial, biaxially aligned buffer layers on rolling-assisted biaxially textured substrates (RABiTS) as templates for YBCO films carrying high critical current densities.The RABiTS technique uses standard thermomechanical processing to obtain long lengths of flexible, biaxially oriented substrates with smooth surfaces.The strong biaxial texture of the metal is conferred to the superconductor by the deposition of intermediate metal and/or oxide layers that serve both as a chemical and a structural buffer.Epitaxial YBCO films with critical current densities exceeding 3 106A/cm2at 77K in self-field have been grown on RABiTS using a variety of techniques and demonstrate magnetic-field-dependent critical current values that are similar to those of epitaxial films on single-crystal ceramic substrates.The RABiTS architecture most commonly used consists of a CeO2 (sputtered)/YSZ (sputtered)/Y203 (e-beam)/Ni-W alloy.

The desired texture of the base metal has been achieved in 100 m lengths and 10cm widths.Scaleable and cost-effective techniques are also being pursued to deposit the epitaxial multilayers.The results discussed here demonstrate that this technique is a viable route for the fabrication of long lengths of high-critical-current-density wire capable of carrying high currents in magnetic fields and at temperatures accessible by cooling with relatively inexpensive liquid nitrogen (up through the 77K range).

Understanding current flow through molecular conductors involves simulating the contact surface physics, the molecular chemistry, the device electrostatics, and the quantum kinetics of nonequilibrium transport, along with more sophisticated processes such as scattering and many-body effects.We summarize our current theoretical understanding of transport through such nanoscale devices. Our approach is based on self-consistently combining the nonequilibrium Green's function (NEGF) formulation of transport with an electronic structure calculation of the molecule.We identify the essential ingredients that go into such a simulation. While experimental data for many of the inputs required for quantitative simulation are still evolving, the general framework laid down in this treatment should still be applicable.We use these concepts to examine a few prototype molecular devices, such as wires, transistors, and resonant-tunneling diodes.

When liquids solidify, the interface between a crystal and its melt often forms branching structures (dendrites), just as frost spreads across a window. The development of a quantitative understanding of dendritic evolution continues to present a major theoretical and experimental challenge within the metallurgical community. This article looks at key parameters that describe the interface—excess free energy and mobility—and discusses how these important properties relate to our understanding of crystal growth and other interfacial phenomena such as wetting and spreading of droplets and nucleation of the solid phase from the melt. In particular, two new simulation methods have emerged for computing the interfacial free energy and its anisotropy:the cleaving technique and the capillary fluctuation method. These are presented, along with methods for extracting the kinetic coefficient and a comparison of the results to several theories of crystal growth rates.

Magnetoresistive random-access memory (MRAM) is a new memory technology that is nearing commercialization. MRAM integrates a magnetic tunnel junction (MTJ) device with standard silicon-based microelectronics, resulting in a combination of qualities not found in other memory technologies. For example, MRAM is nonvolatile, has unlimited read and write endurance, and is capable of high-speed read and write operations. In this article, we will describe the fundamentals of an MTJ-based MRAM as well as recent important technology developments in the areas of magnetic materials and memory cell architecture. In addition, we will compare the present and future capabilities of MRAM to those of existing memory technologies such as static RAM and flash memory.

Unlike other porous materials such as sandstone, brick, or porous glass, the interatomic bonding continuity of cement-based materials like concrete is far from obvious. When scrutinized at the micro- or nanoscopic level, the continuity of the ionic–covalent bonding in the solid phase is interrupted almost everywhere by water molecules or liquid water films. The same situation is found in set plaster.Yet, plaster and cementitious materials are able to withstand stresses of the same order of magnitude as rocks. Molecular simulation studies and direct-force measurements by atomic force microscopy provide strong arguments for predicting that short- and medium-range surface forces mediated by partially or totally hydrated calcium ions are the essential components of cement strength, with additional contributions from van der Waals and capillary forces. This provides a clue for understanding the nano- and mesostructure of cement-based materials and new levers for improving their properties.

An effective way to build ordered materials with micrometer- or submicrometer-sized features is to pack together monodisperse (equal-sized) colloidal particles. But most monodisperse particles in this size range are spheres, and thus one problem in building new micrometer-scale ordered materials is controlling how spheres pack. In this article, we discuss how this problem can be approached by constructing and studying packings in the few-sphere limit. Confinement of particles within containers such as micropatterned holes or spherical droplets can lead to some unexpected and diverse types of polyhedra that may become building blocks for more complex materials. The packing processes that form these polyhedra may also be a source of disorder in dense bulk suspensions.

Three-dimensional x-ray diffraction (3DXRD) microscopy is a tool for fast and nondestructive characterization of the individual grains, subgrains, and domains inside bulk materials. The method is based on diffraction with very penetrating hard x-rays (E ≥ 50 keV), enabling 3D studies of millimeter-to-centimeter-thick specimens.The position, volume, orientation, and elastic and plastic strain can be derived for hundreds of grains simultaneously. Furthermore, by applying novel reconstruction methods, 3D maps of the grain boundaries can be generated. The 3DXRD microscope in use at the European Synchrotron Radiation Facility in Grenoble, France, has a spatial resolution of ∼5 μm and can detect grains as small as 150 nm. The technique enables, for the first time, dynamic studies of the individual grains within polycrystalline materials. In this article, some fundamental materials science applications of 3DXRD are reviewed: studies of nucleation and growth kinetics during recrystallization, recovery, and phase transformations, as well as studies of polycrystal deformation.

Magnetic force microscopy (MFM) is a well-established technique for imaging the magnetic structures of small magnetic particles. In cooperation with external magnetic fields, MFM can be used to study the magnetization switching mechanism of submicrometer-sized magnetic particles. Various MFM techniques allow the measurement of a hysteresis curve of an individual particle, which can then be compared to ensemble measurements. The advantage of using MFM-constructed hysteresis loops is that one can in principle understand the origin of dispersion in switching fields. It is also possible to directly observe the correlation between magnetic particles through careful imaging and control of the external magnetic field. In all of these measurements, attention needs to be paid to avoid artifacts that result from the unavoidable magnetic tip stray field. Control can be achieved by optimizing the MFM operation mode as well as the tip parameters. It is even possible to use the tip stray field to locally and reproducibly manipulate the magnetic-moment state of small particles. In this article, we illustrate these concepts and issues by studying various lithographically patterned magnetic nanoparticles, thus demonstrating the versatility of MFM for imaging, manipulation, and spectroscopic measurements of small particles.

The following article is an edited transcript based on the MRS Medalist presentation given by C. Jeffrey Brinker (Sandia National Laboratories and the University of New Mexico) on December 3, 2003, at the Materials Research Society Fall Meeting in Boston. Brinker received the Medal for “his pioneering application of principles of sol-gel chemistry to the self-assembly of functional nanoscale materials.” Nature combines hard and soft materials, often in hierarchical architectures, to obtain synergistic, optimized properties with proven, complex functionalities. Emulating natural designs in robust engineering materials using efficient processing approaches represents a fundamental challenge to materials chemists. This presentation reviews progress on understanding so-called evaporation-induced silica/surfactant self-assembly (EISA) as a simple, general means of preparing porous thin-film nanostructures. Such porous materials are of interest for membranes, low-dielectric-constant (low-k) insulators, and even ‘“nano-valves” that open and close in response to an external stimulus. EISA can also be used to simultaneously organize hydrophilic and hydrophobic precursors into hybrid nanocomposites that are optically or chemically polymerizable, patternable, or adjustable.

The problems posed by the synthesis and purification of single-walled carbon nanotubes (SWNTs) have inhibited progress in the field. In this article, we review the methods available for measuring the purity of SWNTs and the current status of processes designed to purify them.We emphasize the hierarchy of the purification steps that must be developed in order to obtain high-quality material suitable for the full range of advanced applications that are envisioned for the ultimate carbon nanofiber.We review two strategies for SWNT purification, the assessment of SWNT purity by use of near-IR spectroscopy and its application to the thermal oxidation of thin films of SWNTs, as well as recent advances in the separation of metallic and semiconducting SWNTs. While substantial progress has been made in the purification and separation of SWNTs, we note the need for quality control and quality assurance within the industry. Much work remains before pure SWNTs of specific lengths, diameters, and chirality can be made available for applications.

The current status of ferroelectric random-access memory (FeRAM) technology is reviewed in this article. Presented first is the status of conventional FeRAM, in which the memory cells are composed of ferroelectric capacitors to store the data and cell-selection transistors to access the selected capacitors. Discussed next are recent developments in the field. Pb(Zrx, Ti1–x)O3 (PZT) and SrBi2Ta2O9 (SBT) films are being used to produce 0.13 mμ and 0.18 μm FeRAM cells, respectively, with a stacked capacitor configuration; these cells are easily embedded into logic circuits. A new class of FeRAM called 6T4C—containing static RAM (SRAM) cells composed of six transistors (6T) and four ferroelectric capacitors (4C)—has been commercially produced. This type of FeRAM features a nondestructive readout operation, unlimited read/write cycling, and a fast access time of less than 10 ns. Lastly, the status of field-effect-transistor (FET)-type FeRAM is reviewed, emphasizing that the data retention time of a ferroelectric-gate FET has been improved to more than a month in recent studies.

Ion-beam-assisted deposition (IBAD) has been used to prepare biaxially textured templates necessary to realizing high superconducting performance in coated conductors.The IBAD method is characterized by the direct deposition of sharply aligned templates on nontextured metal substrates using fluorite-like oxide films (yttrium-stabilized zirconia, Gd2Zr2O7, etc.).Recent progress in vacuum technology for IBAD has made it possible to reproducibly fabricate long lengths (100 m) of IBAD-GZO templates.Continuous deposition of YBCO films on these templates has been achieved by pulsed laser deposition (PLD).Furthermore, a new approach to improving the texture of IBAD templates was found by using CeO2 films grown by PLD.Trifluoroacetate-based metalorganic deposition has also been used instead of PLD to produce superconducting layers on IBAD buffered tapes, aiming at a low-cost process.This article reviews progress in the research and development of biaxially textured templates produced using IBAD and their subsequent use in fabricating superconducting tapes and wires by means of several processes.

This article reviews recent advances in understanding amorphous glassy states in dense colloidal suspensions with or without short-range interparticle attractions. Experiments, theory, and simulation show that two kinds of glassy states are possible, dominated respectively by repulsion and attraction. Under suitable conditions, a small change in the interparticle potential can lead to a transition between these two kinds of colloidal glasses that entails sharp changes in material properties such as the shear modulus. This may provide novel routes for fine-tuning the properties of industrial pastes and slurries.

An electronic nose that uses an array of 32 polymer–carbon black composite sensors has been developed, trained, and tested. By selecting a variety of chemical functionalities in the polymers used to make sensors, it is possible to construct an array capable of identifying and quantifying a broad range of target compounds, such as alcohols and aromatics, and distinguishing isomers and enantiomers (mirror-image isomers). A model of the interaction between target molecules and the polymer–carbon black composite sensors is under development to aid in selecting the array members and to enable identification of compounds with responses not stored in the analysis library.