bluuebunny/crossref_metadata_2025 huggingface dataset:
Assessment of New High-Performance Fibers for Advanced Applications
Authors: Sikkema Doetze J. , Northolt Maurits G. , Pourdeyhimi Behnam
Published: February 2011

High-performance fibers, used in fabric applications ranging from bulletproof vests to trampolines, must have a sufficient number of chemical and physical bonds for transferring the stress along the fiber. To limit their deformation, the fibers should possess high stiffness and strength. Stiffness is brought about by the degree to which the chemical bonds are aligned along the fiber axis. In fiber-reinforced composites, the fibers are the load-bearing element in the structure, and they must adhere well to the matrix material. An ideal reinforcing fiber must have high tensile and compressive moduli, high tensile and compressive strength, high damage tolerance, low specific weight, good adhesion to the matrix materials, and good temperature resistance. This article reviews and compares the properties and behavior of novel high-performance fiber materials including polyethylene, aramid, polybenzobisoxazole, M5, and carbon fibers.
Low-Cost Wafer-Level Vacuum Packaging for MEMS
Authors: Gooch Roland , Schimert Thomas
Published: February 2011

Vacuum packaging of high-performance surface-micromachined uncooled microbolometer detectors and focal-plane arrays (FPAs) for infrared imaging and nonimaging applications, inertial MEMS (microelectromechanical systems) accelerometers and gyroscopes, and rf MEMS resonators is a key issue in the technology development path to low-cost, high-volume MEMS production. In this article, two approaches to vacuum packaging for MEMS will be discussed. The first is component-level vacuum packaging, a die-level approach that involves packaging individual die in a ceramic package using either a silicon or germanium lid. The second approach is wafer-level vacuum packaging, in which the vacuum-packaging process is carried out at the wafer level prior to dicing the wafer into individual die. We focus the discussion of MEMS vacuum packaging on surface-micromachined uncooled amorphous silicon infrared microbolometer detectors and FPAs for which both component-level and wafer-level vacuum packaging have found widespread application and system insertion. We first discuss the requirement for vacuum packaging of uncooled a-Si microbolometers and FPAs. Second, we discuss the details of the component-level and wafer-level vacuum-packaging approaches. Finally, we discuss the system insertion of wafer-level vacuum packaging into the Raytheon 2000AS uncooled infrared imaging camera product line that employs a wafer-level-packaged 160 × 120 pixel a-Si infrared FPA.
New Materials for Spintronics
Authors: Chambers Scott A. , Yoo Young K.
Published: February 2011

This article introduces the October 2003 issue of MRS Bulletin on “New Materials for Spintronics.” As a result of quantum mechanics, the carriers in ferromagnetic metals such as Fe, Co, and Ni are spin-polarized due to an imbalance at the Fermi level in the number of spin-up and spin-down electrons. A carrier maintains its spin polarization as long as it does not encounter a magnetic impurity or interact with the host lattice by means of spin-orbit coupling. The discovery of optically induced, long-lived quantum coherent spin states in semiconductors has created a range of possibilities for a new class of devices that utilize spin. This discovery also points to the need for a wider range of spin-polarized materials that will be required for different device configurations. In this issue of MRS Bulletin, we focus on three classes of candidate spintronic materials and review the current state of our understanding of them: III–V and II–VI semiconductors, oxides, and Heusler alloys. The field of spin-polarized materials is growing very rapidly, and the search for new magnetic semiconductors and other suitable spin-injection materials with higher Curie temperatures is bringing spintronics closer to the realm of being practical.
Ferromagnetic III–V and II–VI Semiconductors
Authors: Dietl Tomasz , Ohno Hideo
Published: February 2011

Recent years have witnessed extensive research aimed at developing functional, tetrahedrally coordinated ferromagnetic semiconductors that could combine the resources of semiconductor quantum structures and ferromagnetic materials systems and thus lay the foundation for semiconductor spintronics. Spin-injection capabilities and tunability of magnetization by light and electric field in Mn-based III–V and II–VI diluted magnetic semiconductors are examples of noteworthy accomplishments. This article reviews the present understanding of carrier-controlled ferromagnetism in these compounds with a focus on mechanisms determining Curie temperatures and accounting for magnetic anisotropy and spin stiffness as a function of carrier density, strain, and confinement. Materials issues encountered in the search for semiconductors with a Curie point above room temperature are addressed, emphasizing the question of solubility limits and self-compensation that can lead to precipitates and point defects. Prospects associated with compounds containing magnetic ions other than Mn are presented.
Epitaxial Heusler Alloys: New Materials for Semiconductor Spintronics
Authors: Palmstrøm Chris
Published: February 2011

Ferromagnetic materials that have Curie temperatures above room temperature, crystal structures and lattice matching compatible with compound semiconductors, and high spin polarizations show great promise for integration with semiconductor spintronics. Heusler alloys have crystal structures (fcc) and lattice parameters similar to many compound semiconductors, high spin polarization at the Fermi level, and high Curie temperatures. These properties make them particularly attractive for injectors and detectors of spin-polarized currents. This review discusses the progress and issues related to integrating full and half Heusler alloys into ferromagnetic compound semiconductor heterostructures.
Inkjet Printing of Highly Loaded Particulate Suspensions
Authors: Derby Brian , Reis Nuno
Published: February 2011

Inkjet printing is an attractive method for patterning and fabricating objects directly from design or image files without the need for masks, patterns, or dies. In order to achieve this with metals or ceramics, it is often necessary to print them as highly concentrated suspensions of powders in liquids. Such liquid suspensions must have physical properties appropriate to the inkjet delivery mechanism. These properties are presented using a nondimensional formalism to illustrate the requirements for both drop formation and spreading on impact. Further critical issues relevant to inkjet printing of particulate suspensions are discussed and illustrated with experiments on a model alumina-containing colloidal suspension.
Inkjet Printing of Polymer Thin-Film Transistor Circuits
Authors: Burns Seamus E. , Cain Paul , Mills John , Wang Jizheng , Sirringhaus Henning
Published: February 2011

We present a process for manufacturing printable thin-film transistors (TFTs) that is based on solution processing and direct inkjet printing of polymer semiconductors, dielectrics, and conductors, as well as inorganic nanoparticle conductors. We show that the high device yield, uniformity, and resolution required for thin-film electronic applications can be achieved by using a substrate that contains a surface energy pattern to control the flow and spreading of inkjet droplets. This technique overcomes many of the limitations of current inkjet printing technology related to its limited droplet placement accuracy. We demonstrate the potential of this printing-based TFT manufacturing process with the fabrication of 50 dpi active-matrix, polymer dispersed liquid-crystal and Gyricon Smartpaper electronic paper displays.
Characterizing Complex Fluids
Authors: Magid L. J. , Schurtenberger P.
Published: February 2011

Among the experimental techniques used to characterize complex fluids, neutron scattering has played a unique and successful role, primarily for two reasons: (1) neutrons access the proper length and time scales, especially small-angle neutron scattering and reflectometry for structural and kinetic studies and neutron spin echo for dynamic investigations; and (2) for hydrogen-containing substances, the exchange of hydrogen by deuterium facilitates labeling on a molecular scale, an extremely important method for deciphering complex structures in multicomponent materials. In this short review, we give a number of examples for successful neutron studies of dense particle suspensions, including aggregation phenomena, in situ kinetic studies on shape transformations, shear-induced surfactant self-assembly phenomena near surfaces, and dynamics of complex fluids. Finally, we give an outlook on future developments.
Neutron Scattering Studies of Dynamics: A New Frontier in Materials Science
Authors: Richter Dieter , Neumann Dan A.
Published: February 2011

Knowledge of the dynamic dimension of materials is an extremely important ingredient for understanding their properties. Neutron scattering is uniquely capable of revealing aspects of the atomic and molecular geometry of motions over a wide range of time scales. To illustrate this fact, we give a number of examples from different areas of materials science. We discuss the diffusion of hydrogen in protonic conductors; the hydration of portland cement; and aspects of the molecular rheology of polymers, emphasizing in particular the effect of branching. All of these experiments have added important basic information to the understanding of the respective systems. With the advent of the new megawatt neutron spallation sources, the role of neutron scattering in revealing the dynamical properties of materials is expected to increase substantially.
Single-Event Upsets in Microelectronics: Fundamental Physics and Issues
Authors: Tang Henry H.K. , Rodbell Kenneth P.
Published: February 2011

We review the current understanding of single-event upsets (SEUs) in microelectronic devices. In recent years, SEUs have been recognized as one of the key reliability concerns for both current and future technologies. We identify the major sources of SEUs that impact many commercial products: (1) alpha particles in packaging materials, (2) background radiation due to cosmic rays, and (3) thermal neutrons in certain device materials. The origins of SEUs are examined from the standpoint of the fundamental atomic and nuclear interactions between the intruding particles (alpha particles, cosmic rays, and thermal neutrons) and semiconductor materials. We analyze field funneling, which is a key mechanism of charge collection in a device struck by an ionizing particle. Next, we formulate how SEU cross sections and SEU rates are calculated and discuss how these basic quantities are related to experiments. Finally, we summarize the major SEU issues regarding modeling, bulk complementary metal oxide semiconductor technologies, and research on future, exploratory technologies.
Relations Between Basic Nuclear Data and Single-Event Upsets Phenomena
Authors: Blomgren Jan , Granbom Bo , Granlund Thomas , Olsson Nils
Published: February 2011

This article approaches single-event upset (SEU) problems from the standpoint of experimental nuclear physics, with a focus on certain neutron experiments and neutron data essential for SEU studies. A review is given of some research programs, both basic and applied, that are strongly motivated by SEU applications. Some specific examples are presented from the The (short for Theodor) Svedberg Laboratory (TSL) in Uppsala, Sweden: First, using the quasi-monoenergetic neutron beam, SEU cross sections (of chips) are measured over the neutron energy range of 20–150 MeV. Data from the same technology generation, in general, can be fitted into a simple curve. Second, the particle origins of SEUs are discussed from the framework of neutron–nucleus spallation reactions.
Superhard Ceramic Oxides
Authors: Lowther J. E.
Published: February 2011

Oxide-based ceramic materials are rapidly proving to have exciting potential for application as hard coatings. The most commonly known oxide material is silica, with a well-known variety of polytypes. Many other oxides, especially those involving metals, are now also proving to be important for a variety of applications where, because of the chemical role played by metal d electrons, large oxygen coordinations can be sustained. Properties of a variety of oxides—from silica to metal-based oxides—are discussed, and the role of predictive computer modeling is shown to be valuable in guiding the search for potentially new superhard oxides.
Cellular Solids
Authors: Gibson L. J.
Published: February 2011

This brief article describes the content of this issue of MRS Bulletin on Cellular Solids. Cork, wood, sponge, and bone are all examples of cellular solids in nature. Engineered honeycombs and foams are now made from polymers, metals, ceramics, and glasses, and their structure gives them unique properties that can be exploited in a variety of applications. The articles in this issue provide an overview of the fabrication, structure, properties, and applications of such porous solids as cellular ceramics, aluminum and other metallic foams, and scaffolds for tissue engineering, as well as discussions of techniques for understanding, modeling, and measuring their behavior and properties.
Aluminum Foams: On the Road to Real Applications
Authors: Banhart John
Published: February 2011

Metallic foams have become an attractive research field both from a scientific viewpoint and the prospect of industrial applications. Various methods for making such foams are available. Some techniques start from specially prepared molten metals with adjusted viscosities. Such melts can be foamed by injecting gases or by adding gas-releasing blowing agents that decompose in situ, causing the formation of bubbles. Another method is to prepare supersaturated metal–gas systems under high pressure and initiate bubble formation by pressure and temperature control. Yet a further class of techniques begins with solid precursors containing a blowing agent. These can be prepared by mixing metal powders with a blowing agent, compacting the mix, and then foaming the compacted mix by melting. Alternatively, casting routes can be used to make such precursors. The unique properties of foams offer promise in a variety of applications ranging from lightweight construction and impact-energy absorption to various types of acoustic damping and thermal insulation.
III–V Nitrides: A New Age for Optoelectronics
Authors: Hangleiter Andreas
Published: February 2011

With the advent of bright-blue light-emitting diodes in 1994, violet laser diodes in 1996, and vertical-cavity surface-emitting lasers at telecommunications wavelengths in 2000, all based on nitride-containing III–V compounds, a new age for optoelectronics began. Despite their technological success, III-nitride materials still hold some mysteries. Compared with conventional III–V semiconductors, even commercial nitride devices are of poor material quality. Due to their heteroepitaxial origin, their crystals are full of dislocations. Electrical properties, particularly in the case of p-type material, are fairly unsatisfactory. Still, light-emitting diodes with extremely high brightness and lasers with high power and good lifetime can be produced with III–V nitride compounds. In this review, we will give an overview of the essential properties of nitride materials for optoelectronic devices, their current development status, open questions, and recent device achievements.
Our Earthen Architectural Heritage: Materials Research and Conservation
Authors: Houben Hugo , Balderrama Alejandro Alva , Simon Stefan
Published: February 2011

Earth construction is the oldest and most universal architectural expression on our planet. The most ancient human settlements were built with raw earth, and even today at least 30% of the world's population still lives in earthen homes. The conservation of earthen architecture depends of two aspects of a global strategy. One part involves intervention to preserve existing structures, and the second involves continuing to use the construction methods and materials in contemporary and future building practices. Traditionally, earth construction has been approached in an empirical way. Only recently have those involved in the field felt it necessary to develop a specific materials research attitude. This has resulted in major technological progress over the last 20 years. The wide range of building systems emphasizes the technological diversity of earth construction. This article presents a historical perspective, along with a review of the characteristics of earth as a building material, stabilization processes, and construction methods, and a report on an ongoing research program aimed at identifying and characterizing the fundamental binding mechanisms responsible for cohesion properties in earthen construction.
Nanocrystalline-Matrix Ceramic Composites for Improved Fracture Toughness
Authors: Kuntz Joshua D. , Zhan Guo-Dong , Mukherjee Amiya K.
Published: February 2011

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.
Charge Transport through Molecular Junctions
Authors: Hersam M.C. , Reifenberger R.G.
Published: February 2011

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.
Carbon Nanotube Electronics and Optoelectronics
Authors: Avouris Phaedon
Published: February 2011

Carbon nanotubes (CNTs) are one-dimensional nanostructures with unique properties. This article discusses why CNTs provide an ideal basis for a future carbonbased nanoelectronic technology, focusing specifically on single-carbon-nanotube fieldeffect transistors (CNT-FETs). Results of transport experiments and theoretical modeling will be used to address such issues as the nature of the switching mechanism, the role of the metal contacts, the role of the environment, the FET scaling properties, and the use of these findings to produce high-performance p-type, n-type, and ambipolar CNT-FETs and simple intra-nanotube circuits. CNTs are also direct-gap nanostructures that show promise in the field of optoelectronics. This article briefly reviews their optical behavior and presents results that show that ambipolar CNT-FETs can be used to produce electrically controlled light sources based on radiative electron–hole recombination. The reverse process—that is, the generation of photocurrents by the irradiation of single CNT—FETs—and photoconductivity spectra of individual CNTs are also demonstrated.
Scanning Probe Microscopy in Materials Science
Authors: Meyer Ernst , Jarvis Suzanne P. , Spencer Nicholas D.
Published: February 2011

This brief article introduces the July 2004 issue of MRS Bulletin, focusing on Scanning Probe Microscopy in Materials Science.Those application areas of scanning probe microscopy (SPM) in which the most impact has been made in recent years are covered in the articles in this theme.They include polymers and semiconductors, where scanning force microscopy is now virtually a standard characterization method; magnetism, where magnetic force microscopy has served both as a routine analytical approach and a method for fundamental studies;tribology, where friction force microscopy has opened entirely new vistas of investigation;biological materials, where atomic force microscopy in an aqueous environment allows biosystems to be imaged and measured in a native (or near-native) state;and nanostructured materials, where SPM has often been the only approach capable of elucidating nanostructures.
Nanostructured p–n Junctions for Printable Photovoltaics
Authors: Brabec Christoph J. , Nann Thomas , Shaheen Sean E.
Published: February 2011

By controlling the morphology of organic and inorganic semiconductors on a molecular scale, nanoscale p–n junctions can be generated in a bulk composite. Such a composite is typically called a bulk heterojunction composite, which can be considered as one virtual semiconductor combining the electrical and optical properties of the individual components. Solar cells are one attractive application for bulk heterojunction composites. Conjugated polymers or oligomers are the favorite p-type semiconducting class for these composites, while for the n-type semiconductor, inorganic nanoparticles as well as organic molecules have been investigated. Due to the solubility of the individual components, printing techniques are used to fabricate them.
Metalorganic Deposition of YBCO Films for Second-Generation High-Temperature Superconductor Wires
Authors: Rupich Martin W. , Verebelyi Darren T. , Zhang Wei , Kodenkandath Thomas , Li Xiaoping
Published: February 2011

Metalorganic deposition (MOD) is an attractive process for low-cost, high-rate deposition of YBa2Cu3O7– (YBCO) films on continuous lengths of biaxially textured metallic templates for second-generation (2G) high-temperature superconductor (HTS) wires.MOD of YBCO films involves four steps:precursor synthesis, coating, decomposition, and reaction.The final films must meet stringent requirements, including high critical current, uniformity across the width and along the length of the textured substrate, and excellent mechanical properties.Achieving these properties has required the development of a metalorganic precursor that produces an intermediate BaF2-based film, which in turn is converted to a high-quality YBCO film.Understanding and controlling the deposition of the metalorganic precursor and its conversion to YBCO are critical to reproducibly manufacturing uniform, high-performance, HTS wires required for commercial applications.This article reviews the issues that must be addressed in the use of MOD for low-cost YBCO film fabrication and summarizes the performance of 2G HTS wires prepared by this manufacturing process.
Nanoscale Structures: Lability, Length Scales, and Fluctuations
Authors: Williams Ellen D.
Published: February 2011

This article is an edited transcript based on the David Turnbull Lecture given by Ellen D. Williams of the University of Maryland on December 2, 2003, at the Materials Research Society Fall Meeting in Boston.Williams received the award for “groundbreaking research on the atomic-scale science of surfaces and for leadership, writing, teaching, and outreach that convey her deep understanding of and enthusiasm for materials research.” This article focuses on the special properties of small structures that provide much of the exciting potential of nanotechnology.One aspect of small structures—their susceptibility to thermal fluctuations—may create or necessitate new ways of exploiting nanostructures.The advent of scanned probe imaging techniques created new opportunities for observing and understanding such structural fluctuations and the related evolution of nanostructure.Direct observations show that it is relatively easy for large numbers of atoms—the kinds of numbers that are present in nanoscale structures—to pick up and move about on the surface cooperatively with substantial impact on nano-to micron-scale structures.Such labile evolution of structure can be predicted quantitatively by using length-scale bridging techniques of statistical mechanics coupled with scanned probe observations of structural and temporal distributions.The same measurements also provide direct information about the stochastic paths of structural fluctuations that can be used outside of the traditional thermodynamic framework.Future work involves moving beyond the classical thermodynamic picture to assess the impact that the stochastic behavior has on the physical properties of individual nanostructures.
Electronic Properties of Inorganic and Organic Semiconductors and Their Application to National Security Needs
Authors: Smith Darryl L.
Published: February 2011

The following article is based on the plenary presentation given by Darryl L.Smith of Los Alamos National Laboratory on December 1, 2003, at the Materials Research Society Fall Meeting in Boston.The presentation contrasted the electronic structure of inorganic semiconductors with that of organic semiconductors, examined how the differences in electronic structure lead to complementary physical properties, and discussed applications of these materials—including infrared detectors and sources, gamma-ray detectors, and chemical/biological sensors—that are of interest to issues of national security.
Electronic Tongues
Authors: Winquist F. , Krantz-Rülcker C. , Lundström I.
Published: February 2011

The use of multivariate data analysis combined with sensors with partially overlapping selectivities has become a very powerful tool in measurement technology. These systems are often referred to as artificial senses, because they function in a way similar to the human senses. One such system is the electronic nose. This article focuses on similar concepts as the electronic nose, but for use in aqueous solutions. Because these systems are related to the human sense of taste in the same way the electronic nose is related to olfaction, they have been termed taste sensors, or “electronic tongues.” Various measurement principles that can be used in electronic tongues are described and discussed in this article. These include electrochemical techniques such as potentiometry, voltammetry, and conductometry. Also, optical techniques based on light absorption at specific wavelengths or the use of surface plasmon resonance are described. Mass-sensitive devices based on piezoelectric crystals have also been used and are described here. A special emphasis is given to the voltammetric electronic tongue.
Nonvolatile Magnetoresistive Random-Access Memory Based on Magnetic Tunnel Junctions
Authors: Grynkewich G. , Åkerman J. , Brown P. , Butcher B. , Dave R.W. , DeHerrera M. , Durlam M. , Engel B.N. , Janesky J. , Pietambaram S. , Rizzo N.D. , Slaughter J.M. , Smith K. , Sun J.J. , Tehrani S.
Published: February 2011

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.
Current Status of Ferroelectric Random-Access Memory
Authors: Arimoto Yoshihiro , Ishiwara Hiroshi
Published: February 2011

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.
Crystal–Melt Interfaces and Solidification Morphologies in Metals and Alloys
Authors: Hoyt J.J. , Asta M. , Haxhimali T. , Karma A. , Napolitano R.E. , Trivedi R. , Laird B.B. , Morris J.R.
Published: February 2011

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.
Colloids under External Control
Authors: van Blaaderen Alfons
Published: February 2011

The ability of colloids to self-organize through a minimization of their free energy is a direct consequence of their well-defined thermodynamic temperature that manifests itself through the Brownian motion they perform. In this article, it will be shown that through the use of external fields such as electric and magnetic fields, gravity, structured or confining walls, and shear, this self-organization can be directed to make new advanced materials. Moreover, a start has been made toward colloidal model systems to study fundamental questions relating to materials science such as defect structure and dynamics, grain boundaries, wall and confinement effects, and tribology. Finally, we predict that the enhanced insights on how to use external fields will also lead to “smart” materials with properties that can be changed dynamically.
Colloidal Glasses
Authors: Poon Wilson C.K.
Published: February 2011

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.
The Role of Nanoscale Forces in Colloid Dispersion Rheology
Authors: Wagner Norman J. , Bender Jonathan W.
Published: February 2011

Advances in our fundamental understanding of and control over interparticle colloidal forces have enhanced our ability to formulate stable, complex fluids with colloidal and/or nano-sized particles with specific rheological properties. This understanding stems from advances in experimental methods that probe these forces, either directly or indirectly, as well as theoretical treatments and simulation methods linking macroscopic suspension properties to the dynamics and interactions between colloidal particles. This article highlights recent experimental developments in the structure—property relationships for colloidal dispersions, with emphasis on the sensitivity of colloid rheology to nanometer-scale interactions. Examples of applications are used to illustrate these relationships.
High-Resolution 3D Imaging Microscopy Using Hard X-Rays
Authors: Schroer Christian G. , Cloetens Peter , Rivers Mark , Snigirev Anatoly , Takeuchi Akahisa , Yun Wenbing
Published: February 2011

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.
Turning Peapods into Double-Walled Carbon Nanotubes
Authors: Bandow S. , Hirahara K. , Hiraoka T. , Chen G. , Eklund P.C. , Iijima S.
Published: February 2011

The formation pathway to double-walled carbon nanotubes (DWNTs) from C60 encased within single-walled carbon nanotubes (peapods) is introduced in this article. Onedimensionally arranged C60 molecules coalesce gradually within the nanotube and change the structure to C60 dimers, trimers, tetramers, and so on as intermediates. In addition to these interesting structural transformations visualized in the nanotube space, the nanotube itself is very stable, and this structural stability is very important when using the interior of the nanotube as the reaction field or the space for molecular storage. In terms of optical absorption, the lowest energy absorption band for DWNTs, ∼0.65 eV, shows broadened and downshifted features as compared with that of SWNTs.We expect that this opticalabsorption feature will lead to the use of DWNTs in absorbing devices for optical-fiber communications. The Raman experiments give new information about the frequency of the C-C stretching-mode vibration for nanotubes with diameters of less than ∼1 nm, which shows a decrease in vibration frequency with decreasing tube diameter. This diameter dependence can be explained by an admixture of sp3 character in the C-C interaction. Therefore, the electronic and mechanical properties of nanotubes with diameters of <1 nm are expected to be different from nanotubes of the ∼1-nm-diameter class, and we anticipate that new phenomena will occur in small-diameter tubes.
Construction Materials: From Innovation to Conservation
Authors: Scrivener Karen , Van Damme Henri
Published: February 2011

This article serves to introduce the May 2004 issue of MRS Bulletin on Construction Materials: From Innovation to Conservation. By volume, building materials are by far the most widely used type of materials. The most common construction materials—concrete and wood—are paradigms of complex and hierarchical materials, with a microstructure extending quasi-continuously down to the nanoscale. In the past, most improvements have been obtained by modifying the microstructure at the largest scales, for instance, by reducing the macroporosity. Recent advances in our understanding of the interactions and microstructure development show that the major levers for improvement from now on will rely on surface and colloid science and the science of complex materials, often at the nanoscale. This can lead to remarkable properties, such as self-compaction and ultrahigh strength, and even new functionality, such as self-cleaning through photocatalysis. Construction materials face a wide range of challenges today, many of which are linked to the need for more sustainable development: reducing the consumption of raw materials, reducing the energy used in processing, and increasing service life. In many parts of the world, there is also an increasing need to repair, rehabilitate, and conserve old buildings. The articles in this issue touch on these challenges as well as the advances being made in construction materials through materials research.
Optically and Chemically Encoded Nanoparticle Materials for DNA and Protein Detection
Authors: Thaxton C. Shad , Rosi Nathaniel L. , Mirkin Chad A.
Published: February 2011

Nanoscale materials are beginning to have an impact in the field of molecular diagnostics. In particular, gold nanoparticles surface-functionalized with DNA have garnered much recent interest. Due to the unusual optical and catalytic properties of gold nanoparticle labels, several distinct advantages for assay readout have been realized. This review focuses on the progress made in our group over the past seven years in the development of particle surface chemistry and ultrasensitive protein and nucleic acid assays based upon DNA-functionalized gold nanoparticles. For DNA targets, experiments demonstrate that assays based upon gold nanoparticle labels have enhanced target specificity and in certain cases the sensitivity of polymerase chain reaction (PCR), without the need for target amplification. For protein targets, similar experiments demonstrate that assays based upon gold nanoparticles are up to one million times more sensitive than conventional protein detection methods. Recent data using human samples demonstrate the utility of such assays.
“Wave-Function Imaging” Studies of High-Tc Superconductivity
Authors: Slezak James A. , Lee Jinho , Davis J. C.
Published: February 2011

High-temperature superconductivity in the cuprates emerges when the localized electrons of a Mott insulator become mobile due to carrier doping. Understanding both the electronic ground state and the excited states of these systems are key challenges in physics today. Angle-resolved photoemission spectroscopy (ARPES) and inelastic neutron-scattering (INS) studies have been remarkably successful in mapping the momentum-space characteristics of the cuprate electronic structure. However, since cuprate superconductivity develops from atomically localized electrons and exhibits nanoscale disorder, a pure momentum-space description is unlikely to be sufficient. Instead, simultaneous information on electronic structure at the nanoscale in real space, and throughout momentum space, is required. Here, we describe a combination of novel spectroscopic imaging scanning tunneling microscopy (SI-STM) techniques that we have developed to achieve these apparently contradictory aims, along with the outcome of a series of SI-STM studies of the electronic structure of Bi2Sr2CaCu2O8+x.
From Transistors to Lasers and Light-Emitting Diodes
Authors: Holonyak Nick
Published: February 2011

This article is based on the 2004 Von Hippel Award address by Nick Holonyak Jr. (University of Illinois at Urbana-Champaign). Holonyak received the award for “his many contributions to research and development in the field of semiconductors, not least for the first development of semiconductor lasers in the useful visible portion of the optical spectrum.” The talk was presented on Holonyak's behalf by Russell Dupuis on December 1, 2004, at the Materials Research Society Fall Meeting in Boston.

With the discovery of the transistor by Bardeen and Brattain in 1947, and as a consequence of carrier injection and collection, the hole indeed became equal to the electron. The semiconductor took on new importance, as did the study of electron–hole recombination, first in the transistor materials Ge and Si, and then in III–V crystals (e.g., GaAs and GaP). Beyond Si and its indirect-gap and heterojunction limitations, the directgap III–V materials, particularly III–V alloys, made possible lasers and light-emitting diodes (LEDs)—and thus optoelectronics.

The direct-gap III–V alloy LED after four decades of development exceeds in performance the incandescent lamp (as well as other forms of lamps) in much of the visible range. Beyond growing display applications, it has put conventional lighting under longrange threat with a semiconductor lamp—an “ultimate lamp” that promises unusual performance and energy savings. In principle, the LED or laser, basically a p–n junction, is an ultimate lamp that cannot be exceeded.
Biomaterials for Regenerative Medicine
Authors: Stupp Samuel I.
Published: February 2011

The following article is based on a presentation given by Samuel I. Stupp of Northwestern University as part of Symposium X—Frontiers of Materials Research on April 13, 2004, at the Materials Research Society Spring Meeting in San Francisco. Materials designed at the molecular and supramolecular scales to interact with cells, biomolecules, and pharmaceuticals will have a profound impact on technologies targeting the regeneration of body parts. Materials science is a great partner to stem cell biology, genomics, and proteomics in crafting the scaffolds that will effectively regenerate tissues lost to trauma, disease, or genetic defects. The repair of humans should be minimally invasive, and thus the best scaffolds would be liquids programmed to create materials inside our bodies. In this regard, self-assembling materials will play a key role in future technologies. This article illustrates how molecules are designed to assemble into cell scaffolds for human repair and provides examples relevant to brain damage, fractures of the skeleton, spinal cord injuries leading to paralysis, and diabetes.
Fuel Cells: The Next Evolution
Authors: Lashway Robert W.
Published: February 2011

The articles in this issue of MRS Bulletin highlight the enormous potential of fuel cells for generating electricity using multiple fuels and crossing a wide range of applications. Fuel cells convert chemical energy directly into electrical energy, and as a powergeneration module, they can be viewed as a continuously operating battery.They take in air (or pure oxygen, for aerospace or undersea applications) and hydrocarbon or hydrogen fuel to produce direct current at various outputs. The electrical output can be converted and then connected to motors to generate much cleaner and more fuelefficient power than is possible from internal combustion engines, even when combined with electrical generators in today's hybrid engines. The commercialization of these fuel cell technologies is contingent upon additional advances in materials science that will suit the aggressive electrochemical environment of fuel cells (i.e., both reducing an oxidizing) and provide ionic and electrical conductance for thousands of hours of operation.
An All-Ceramic Interconnect for Use in Solid-Oxide Fuel Cell Stacks
Authors: Morris Thomas A. , Barringer Eric A. , Kung Steven C. , McKain Rodger W.
Published: February 2011

This article summarizes a unique approach in which all-ceramic interconnects are used in place of metal interconnects in solid-oxide fuel cell (SOFC) stacks. The approach combines advanced SOFC materials with the manufacturing technology and infrastructure established for multilayer ceramic (MLC) packaging for the microelectronics industry. The MLC interconnect is fabricated using multiple layers of yttria-stabilized zirconia (YSZ) tape, with each layer containing conductive vias to provide for electrical current flow through the interconnect. The all-ceramic interconnect design facilitates uniform distribution of air and fuel gas to the respective electrodes of adjacent cells. The multilayer interconnects are fabricated using traditional MLC manufacturing processes. A detailed description of the processes for fabricating the all-ceramic interconnect is presented.To aid in moving from prototype fabrication to commercialization of these fuel cell systems, a detailed cost model has been used as a roadmap for commercial stack development. Cost model projections are presented for three different interconnect footprint sizes. These projections show an SOFC stack cost of less than $150 per kilowatt for the optimized SOFC stack design produced at high volume.
Carbonate Fuel Cell Technology and Materials
Authors: Farooque M. , Yuh C. , Maru H.C.
Published: February 2011

High-temperature carbonate fuel cells are recognized as the cleanest and most efficient power generation option for commercial and industrial customers. The firstgeneration carbonate fuel cell plants have shown an electrical efficiency of 45–48%.The electrolyte in this fuel cell is a mixture of alkali carbonates, and it operates at a highenough temperature that the heat by-product can be used for cogeneration applications such as district heating, hot water, process steam, and absorption chilling for air conditioning. Alternatively, the heat by-product can be used with an unfired gas turbine for additional electrical generation. Depending on location, application, and load size, carbonate fuel cells are expected to achieve an overall energy efficiency of 65–80% in cogeneration and combined cycle applications. The cell hardware uses commonly available stainless steels. Electrode materials are nickel-based. Furthermore, standard, well-established manufacturing processes are employed. Therefore, carbonate fuel cells are well positioned to be cost-competitive with alternative technologies. Significant progress has been made in the development, manufacturing, product engineering, and field operation of carbonate fuel cell technology. Megawatt and submegawatt units are operating worldwide. A comprehensive review of carbonate fuel cell technology and materials are presented in this article.
Nanotechnology and DNA Delivery
Authors: Luo Dan
Published: February 2011

Nonviral DNA delivery systems have great therapeutic and prophylactic potential, but their clinical utility has been limited by three major barriers: (1) inefficient uptake by the cell, (2) insufficient release of DNA within the cell, and (3) ineffective nuclear targeting and transport. Since the size of most cells is in the micrometer regime and the space inside a cell is extremely crowded, ideal DNA delivery systems must be in the nanometer range. Advancements in nanoscale science and nanotechnology have provided us with novel nanoparticles that may overcome all of these barriers, leading to higher-efficiency DNA delivery. This review article will focus on the recent developments in nanoscale DNA delivery systems that consist of chemical dendrimers, DNA dendrimers, nanospheres, nanolayers, nanorods, and nanotubes. The future of DNA delivery systems that interface with nanotechnology is also discussed.