bluuebunny/crossref_metadata_2025 huggingface dataset:
New Carbohydrate-Based Polymeric Materials
Authors: Callstrom Matthew R. , Bednarski Mark D.
Published: August 2016

The total world production of water-soluble polymers is estimated to be greater than five million tons per year. Water-soluble polymers are most conveniently described according to their origin in three classes (see Structures 1-6):

∎ Natural polymers, including starch (1) and cellulose (2);

∎ chemically modified natural polymers, including, for example, hydroxyethyl starch (3) and cellulose acetate (4); and

∎ synthetic polymers, the most important of which are polyacrylamide (5) and polyvinyl alcohol (6), (commonly composed of both alcohol and acetate groups as shown). The widespread use of these materials is due to both their availability and the range of useful physical properties found in the various natural and chemically modified natural polymers.

Of the commercial water-soluble polymers, approximately 50–80% are based on natural polysaccharide materials. One of the primary reasons that these materials find such widespread use is the dramatic response of their properties to changes in their functionality and stereochemistry: chemical modification or the combination of polysaccharides with other polymeric materials has yielded materials whose applications range from explosives to food additives. Although efforts directed at controlling the properties of polysaccharides has resulted in a wide variety of useful materials, we felt control of the composition of carbohydrate-based polymers at the molecular level would provide materials with properties superior to those derived from natural and chemically modified polysaccharide materials.

Our approach for the preparation of new carbohydrate-based materials is to use the carbohydrate as a template for the introduction of desired functionality with complete regiochemical and stereochemical control by both chemical and enzymatic methods (Scheme I).
The Biological Membrane
Authors: Alper Mark
Published: August 2016

All living cells, and many of the structures within these cells (mitochondria, nuclei, chloroplasts) are surrounded by biological membranes which serve to separate the cell contents from the surrounding environment. The biological membrane is an extraordinary material. It controls the highly selective transport of molecules into and out of the cell. It senses the environment outside the cell and transmits information about it to the intracellular machinery. It reports information about the cell to the outside world—its identity and its state of function. It transports electrons, converts sunlight to chemical and electrical energy, pumps small molecules against a concentration gradient, and uses that gradient as a source of energy. The membrane is a generally robust structure, and one that can be modified in a controlled manner, making it adaptable for use in nonbiological applications. It has served as a model for sensors and detectors, for surface modification agents, for drug delivery systems, and for information storage and delivery, as well as other optoelectronic functions.
Simulations of Nanometer-Thick Lubricating Films
Authors: Robbins Mark O. , Thompson Peter A. , Grest Gary S.
Published: August 2016

Hydrodynamics and elastohydrodynamics have been successful in describing lubrication by micron-thick films. However, these continuum theories begin to break down as film thicknesses become comparable to molecular dimensions. An increasing number of applications require an understanding of lubricants in such severely confined geometries. Examples include lubrication of nanoscale bearings in micromachinery or high-density magnetic disk drives, as well as asperity interactions in macroscopic bearings that operate in the mixed lubrication regime.

Development of new experimental and theoretical techniques for studying thin lubricant films has paralleled the growing interest in their properties. The surface force apparatus (SFA) allows normal and shear forces to be measured between atomically flat solid surfaces while their separation is determined to within 0.1 nm using interferometry or capacitance. The contact area in the SFA is typically 100 μm across, much larger than the separation between solid walls. The atomic force microscope (AFM) can be used to explore friction in lubricated contacts whose diameter is comparable to the separation (5 nm). This allows spatial resolution of the frictional force on a molecular scale. Quartz-crystal oscillators have been used to determine the frictional forces between a surface and an adsorbed film of one or more monolayers. Theoretical advances have been aided by the advent of supercomputers that allow thin films to be simulated at the molecular level using molecular dynamics. These new experimental and theoretical techniques reveal a sequence of dramatic changes in the static and dynamic properties of fluid films as their thickness approaches molecular scales.
Atomistic Simulations of Friction at Sliding Diamond Interfaces
Authors: Harrison Judith A. , White Carter T. , Colton Richard J. , Brenner Donald W.
Published: August 2016

Friction, or the resistance to motion of two bodies in contact, and the related phenomenon of wear are two of the more costly problems facing industry today. Despite their importance, a fundamental understanding of friction and wear, especially at the atomic scale, has remained elusive. This is rapidly changing, however, as new scientific instrumentation has been developed that allows, for the first time, the study of friction at the atomic scale. These pioneering efforts have led to the emergence of a rapidly growing field called nanotribology, the subject of this issue of the MRS Bulletin. Some of the contributing techniques include the surface force apparatus, which has been used to study the rheology of molecularly thin liquid layers, a quartz-crystal microbalance, which has been used to measure the sliding friction of molecularly thin adsorbed films, and the atomic force microscope (AFM), which has been used to measure the frictional force between a sharp tip (possibly a single asperity) and a flat surface during sliding. In addition to providing a vast amount of information related to friction on the atomic scale, these innovative experiments have provided the necessary data to test the validity of older theoretical models and have stimulated new theoretical work. For instance, atomic-scale friction has been investigated theoretically using analytic models, first principles calculations, and molecular dynamics simulations.
Copper Etching: New Chemical Approaches
Authors: Hampden-Smith Mark J. , Kodas Toivo T.
Published: August 2016

There is a tremendous demand for improved performance and speed in consumer electronics that is likely to continue as new applications and developments occur. This demand necessitates a reduction in the critical dimensions and an increase in the density of devices in microelectronic circuits. As a result, new materials must be considered for integration into microelectronics technology. In particular, the metal wiring or interconnects that connect different components in silicon-based semiconductor devices is a subject of great interest. As the dimensions of transistors shrink below the 0.5 μm level, their speed will become limited by the delays in the existing interconnect material, Al-Si-Cu alloy (p ~ 3 μΩ cm). Therefore, to avoid problems associated with RC (“resistance/capacitance”) time delays and voltage drops, it will be necessary to construct interconnections of materials that possess lower resistivities, resistance to electromigration and hillock formation, and resistance to diffusion into other materials (see Table I).

A number of materials are possible candidates to replace the Al-Si-Cu alloy, including W, Ag, Au, and Cu. Tungsten has excellent resistance to electromigration and hillock formation, but has higher resistivity compared with the Al-Si-Cu alloy. Thus, applications of W are likely to be found where short interconnection distances are necessary. Silver has the lowest resistivity of all metals, but is easily corroded and diffuses rapidly into many materials used in semiconductor devices. However, some specific applications for silver are viable, such as the formation of contacts on ceramic superconductors. Gold has a lower resistivity than the Al-Si-Cu alloy and is inert to chemical corrosion. As a result Au is used where device reliability is the primary concern-for example, for wiring in GaAs-based semiconductors and electrical contacts in packaging.
Applications of Atom Probe Microanalysis in Materials Science
Authors: Miller M.K. , Smith G.D.W.
Published: August 2016

The atom probe field ion microscope is the most powerful and direct method for the analysis of materials at the atomic level. Since analyses are performed by collecting atoms one at a time from a small volume, it is possible to conduct fundamental characterization of materials at this level. The atom probe technique is applicable to a wide range of materials since its only restriction is that the material under analysis must possess at least some limited electrical conductance. Therefore, since its introduction in 1968, the atom probe field ion microscope has been used in many diverse applications in most branches of materials science. Many of the applications have exploited its high spatial resolution capabilities to perform microstructural characterizations of features such as grain boundaries and other interfaces and ultrafine scale precipitation that are not possible with other microanaly tical techniques. This article briefly outlines some of the capabilities and applications of the atom probe. The details of the atom probe technique are described elsewhere.

The power of the atom probe may be demonstrated by its ability to see and identify a single atom, which is particularly useful in characterizing solute segregation to grain boundaries or other interfaces. An example of a brightly-imaging solute atom at a grain boundary in a nickel aluminide is shown in Figure 1. In order to conclusively determine its identity, its image is aligned with the probe aperture in the center of the imaging screen and then the selected atom is carefully removed by field evaporation and analyzed in the time-of-flight mass spectrometer. This and many other bright spots in this material were shown to be boron atoms. This example also illustrates the light element analytical capability of the atom probe. In fact, the atom probe may to used to analyze all elements in the periodic table and has had applications ranging from characterizing the distribution of implanted hydrogen to phase transformations in uranium alloys.
Atomic-Level Studies of Processes on Metal Surfaces
Authors: Kellogg G.L. , Tsong T.T.
Published: August 2016

An atomic-level understanding of surface phenomena is becoming increasingly important as materials scientists and engineers begin to fabricate new materials by controlling their growth at the nanometer or subnanometer scale. Recent advances in molecular beam epitaxy and chemical vapor deposition make it possible to assemble a crystalline solid or epitaxial overlayer literally one atomic layer at a time. The need to characterize the structure and composition of these complex materials in finer and finer detail has forced the traditional analytical tools (e.g., electron microscopy) to strive for better and better spatial resolution. It has also generated a virtual explosion in the proliferation of scanning probe microscopies inherently capable of viewing surface structure at the atomic level. This same need has recently rekindled an interest in the technique that first allowed scientists to view a solid surface in atomic detail: the field ion microscope (FIM). The unique attributes of this instrument and its successor, the atom probe mass spectrometer, make it possible to observe individual atoms on a solid surface, to remove atoms from the surface one atomic layer at a time, and to determine the chemical identity of the atoms as they are removed. The close match between these capabilities and the requirements of modern-day materials analysis have stimulated renewed efforts to use the FIM to gain fundamental insight into materials problems. This article discusses a few selected applications of the FIM, individually and combined with the atom probe, to phenomena occurring at the surface of solid materials.
Up Close: Laboratoire de Recherche des Musées de France: Materials Science in the Service of Art History
Authors: Bernard Maurice , Dupouy Jean-Michel
Published: August 2016

Until the 18th century, the word “art” meant the product of the artisan (not the artist) and, by extension, also meant the product itself. Objects manufactured by craftsmen had, first of all, a useful function, although they might also have had a symbolic or aesthetic meaning. The concept of aesthetics is actually much older, considering the antiquity of Rome and Greece. And in Egypt, 3,500 years ago, at Saqqara, the first stone pyramid was engraved by scribes expressing their admiration for it.

These artisans were famous for the quality of their work, for their genius in mastering their knowledge. One is reminded of Phidias in Athens, Michelangelo and Julius II, or Leonardo da Vinci and Francois the 1st.

However, the social status of such artists was probably not very different from the status of other exceptional artisans in fields such as jewelry, metallurgy, clothing, music, etc. “Ĺart pour l'art,” a tenet which ignored the function of the object, arose only during the last century. In other words, almost all objects or artifacts in museums were originally devised and built to achieve a very specific and useful function.
Materials Issues in Copper Interconnections
Authors: Harper J.M.E. , Colgan E.G. , Hu C-K. , Hummel P. , Buchwalter L.P. , Uzoh C.E.
Published: August 2016

Significant progress has been made in building multilevel copper interconnection systems for advanced microelectronics. In this article, we examine some of the materials science issues underlying this progress, and indicate where significant materials challenges remain. It is probable that several approaches to process integration will be developed for copper interconnections, as has been the case with aluminum systems. The first successful demonstration of a fully integrated 4-level copper/polyimide (Cu/PI) interconnection system has been described by Luther et al. of IBM. A schematic cross section of this interconnection system is shown in Figure 1, indicating multiple layers of BPDA-PDA polyimide (PI 5810), Cu lines and studs, and layers of Ta and Si3N4 which serve as diffusion barriers, adhesion layers, and stopping layers in the patterning and planarization processes. This system demonstrates excellent planarity, as shown in the SEM cross section in Figure 2. The electromigration lifetime of this Cu/PI system is greatly improved relative to state-of-the-art aluminum-based systems, and the dielectric integrity appears adequate. Signal propagation studies also confirm the performance improvements anticipated for copper as a low-resistivity conductor and the use of Cu may allow significant capacitance reduction (≃ 25%) simply by scaling Cu lines to equal the resistance of Al lines. In parallel with efforts to introduce Cu metallization for its low resistivity, extensive efforts are under way to replace SiO2 with lower dielectric constant insulators.
Materials Engineering Problems in Crystal Growth and Epitaxy of Cuprate Superconductors
Authors: Scheel Hans J.
Published: August 2016

The discovery of superconductivity in yttrium barium cuprate above the boiling point of liquid nitrogen by Wu et al. initiated a race in the search for higher critical temperatures (Tc) which was singular in the history of science. Since the ceramic superconducting pellets could be prepared nearly overnight and superconductivity easily demonstrated with liquid nitrogen and a levitating magnet, a great deal of effort went into garnering funds for a “new technological era.” High Tc superconductivity (HTSC) was expected to have applications in many areas of our life, be it for energy transport and high-power generators, transformers, current limiters, or for ultrafast computers and communication technology, or in medicine for NMR tomography and for SQUIDs in magnetic encephalography. Large-scale uses were also foreseen, such as levitation for trains, magnetohydrodynamic propulsion in ships, and applications for fusion reactors. Thousands of physicists and engineers searched for new materials with high Tc, and explored thin-film preparation by physical vapor deposition. In the early phase only a few scientists recognized that materials engineering problems would greatly hinder the development of applications of the cuprate superconductors. Most early efforts on HTSC went toward physical investigations of samples (crystals, layers, sheets, wires, etc.) which due to their complexity could not be reproducibly prepared, and which were not adequately characterized (see the section on Characterization). The Bi-, Tl-, and Hg-containing cuprates with Tc up to 135 K, for example, were found empirically, not by physical understanding of the HTSC phenomenon. Applications of HTSC have been limited to very specific areas, but a concerted effort should reveal opportunities for the materials research and superconductivity communities. Significant applications could be developed

which in the long run would also benefit fundamental physical investigations of the HTSC phenomenon.
Graphitic Nanoparticles
Authors: Ugarte D.
Published: August 2016

Pure carbon materials, graphite and diamond, possess a wide array of interesting physical properties, and so attract a large spectra of interests and applications. Carbon microparticles (carbon black) and carbon fibers are widely used in practical applications including common materials (paints, inks, polymers, etc.) and high-performance composite materials.

Carbon displays a remarkably rich and complex chemical behavior (three different possible hybridizations: sp1, sp2, and sp3). In particular, the covalent carboncarbon bond is one of the strongest in nature, and induces a high melting temperature (> 4000°C). The phase changes associated with unusually high temperatures and pressures as revealed in the carbon phase diagram, and the fact that the solid sublimates at low pressures before melting, lead to many experimental difficulties in the study of high-temperature properties of carbon materials. Experiments must therefore rely on transient melting, for example, laser vaporization or arc-discharge heating. This explains why fullerenes and related graphitic structures have only recently been discovered.

From a fundamental point of view, the discovery of fullerenes has introduced new ideas about how carbon atoms bond. The curvature and closure of graphitic surfaces has become a standard concept in carbon chemistry, and recently a wide range of structures formed by curved graphitic networks has been observed. A surprising aspect of fullerene research is that these novel graphitic structures were found in well-known experiments, and that they had been overlooked for so many years.

This article will describe recent progress in the generation and physical characterization of graphitic nanoparticles, or multishell fullerenes. The lack of an efficient method for producing, as well as a method for purifying these particles makes it difficult to characterize them and to develop possible applications.
Synroc: A Suitable Waste Form for Actinides
Authors: Vance E.R.
Published: August 2016

Synroc, a ceramic made from a reactive mixture of Al, Ba, Ca, Ti, and Zr oxides, is proving to be a suitable and effective medium for immobilizing nuclear wastes.

Synroc-C, a titanate-based ceramic variant, was initially developed in 1978 by Ringwood et al. for immobilizing high-level nuclear waste (HLW) from nuclear power reactor fuel reprocessing. HLW is essentially a solution of radioactive fission products, actinides, and process contaminants in ~3 mol/L nitric acid. The developers of Synroc-C aimed to immobilize radioactive waste ions by incorporating them in a ceramic. They accomplished this by mixing the HLW solution (liquid waste) with a ceramic precursor, then forming the ceramic by drying, calcining, and hot-pressing the mixture in a metal container for two hours at 1200°C/20 MPa. The result, Synroc-C, is composed of hol-landite, zirconolite, perovskite, and rutile, together with a few percent of minor phases and metal alloys. The Synroc-C precursor has the following composition (wt%): Al203(5.4); BaO(5.6); CaO(11); TiO2(71.4); and ZrO2(6.6). Since 1984, it has been prepared by hydrolyzing a mixture of Al, Ti, and Zr alkoxides with an aqueous slurry of Ba and Ca hydroxide. The abundances of the phases, and the radionuclides contained in them in dilute solid solution, are identified in Table I.
FGMs High-Heat-Flux Environments: Cost/Performance Issues
Authors: Lannutti John J.
Published: August 2016

This article focuses exclusively on the application of functionally gradient materials (FGMs) as structural components in high-heat-flux environments. Preliminary data suggest that FGMs can equal or surpass the properties of fiber-reinforced composites (FRCs) in these applications at a fraction of the material costs. An optimistic value of $1 per foot for 100-μm-diameter Saphikon alumina fiber yields a per-pound cost of $48,000. In contrast, a costly alumina powder used for FGMs might be in the range of .$20 per pound. While many counter-arguments can be advanced, this price differential cannot be easily overcome.

One relative difficulty with FGMs is their inherent compositional flexibility which, ironically, is normally considered an advantage. Determination of the optimum material combination for a given application should precede any effort directed toward determining the “best” processing route. This combination will then specify the processing technique. This would “short circuit” the expensive learning curve historically associated with FRCs.

“Processing for processing's sake” is no longer a viable option in today's composite research market. Without necessary advances in the predictive modeling of structure, composition (and, concurrently, cost) and behavior, FGMs may remain an “on-the-horizon” advanced composite.
FGM Fabrication by Combustion Synthesis
Authors: Stangle Gregory C. , Miyamoto Yoshinari
Published: August 2016

FGMs have been fabricated using the combustion synthesis (or self-propagating high-temperature synthesis (SHS)) process by exploiting a rapid and exothermic chemical reaction, in order to synthesize some (or all) of the constituents in an FGM to simultaneously increase its density. The thermal energy required to drive the process is derived from this internal, chemical source, rather than from an external and usually expensive source (e.g., a furnace). The combustion synthesis process is a powder-based process that has been used to synthesize over 300 compounds, and is particularly useful in preparing materials such as highly refractory ceramics and high-temperature intermetallics that are difficult to prepare by other synthesis methods. In addition, the process can be used to prepare ceramic-metal and ceramic-intermetallic composite materials. As a result, only slight modifications of the combustion synthesis are required to prepare functionally gradient materials from these same combinations of materials.

Sample preparation begins by the creation of a series of mixtures from the powders that will react to form the constituent materials of the FGM sample. Each of these mixtures contains a slightly different percentage of reactants, so that each mixture will yield its own (predetermined) volume fraction of each of its constituents, following the combustion synthesis process. Prior to the combustion step, the samples are assembled by stacking layers of each of the reactant powder mixtures in appropriate amounts, in such a way that the multilayered powder mixture will faithfully produce the composition gradient that is required in the resultant FGM.
Optimization of Mechanical Properties in SiC Control of the Microstructure
Authors: Krstic V.D.
Published: August 2016

The optimization of mechanical properties through microstructural design in metallurgical industries has been used successfully for many years. In comparison, the microstructural design in ceramics has been less successful, mainly due to the complexity and difficulties associated with low diffusivity (in their monolithic form) and to the ability to be sintered at elevated temperatures. For years, many structural ceramics could not be sintered to high densities (>95% of their theoretical density) without large quantities of sintering aids. A typical example is silicon carbide (SiC), which has a unique combination of properties, such as: high hardness and wear resistance, considerable strength at high temperatures, and excellent thermal conductivity, but, due to a high level of covalent bonding and consequently low diffusion rates, it cannot be sintered to high density (without the addition of sintering aids) even at temperatures approaching 3000°C.

Since the first successful sintering of SiC with small additions of boron and carbon in the early 1970s, remarkable progress has been made in developing a wide range of properties for the microstructure, including fracture toughness from 3–4 MPa m½ to 12–14 MPa m½ four-point-bending strength from 300 MPa to over 900 MPa, and thermal conductivity from 60 to 260 W/m K.4

This article presents the most recent developments in SiC ceramics, emphasizing optimization of mechanical properties through microstructure control. The discussion is limited to β-phase SiC pressureless sintering, using oxide additives.
Thermodynamic Calculations as the Basis for CVD Production of Silicide Coatings
Authors: Bernard Claude , Pons Michel , Blanquet Elisabeth , Madar Roland
Published: August 2016

The exponential increase in computing power realized over the past three decades has required devices of ever-decreasing dimensions. With these reductions in feature size, each generation of circuit technology creates a new set of materials-science challenges, as exemplified by the use of silicide-based diffusion barriers.

The use of transition-metal silicides in the semiconductor industry began in the early 1980s with (in retrospect) fairly thick films, simple compositions, and minimal microstructural requirements. The implementation of thin-film binary silicides in integrated circuit (IC) applications required the development of appropriate modeling techniques to select the deposited metal, its gaseous precursor, and the Silicon precursor. These vectors were used to define experimental conditions to yield desired films. Chemical-vapor-deposition (CVD) experiments were simulated and CVD phase diagrams were used to describe the changing film properties with different thermodynamic conditions.

In the early 1990s, research began to focus on CVD of ternary Systems (Ta-Si-N, Ti-Si-N). Modeling these complex Systems required optimization of the thermodynamic data and careful evaluation of the ternary phase diagrams.

Current-generation materials are deposited in extremely thin layers (ULSI, or ultralarge-scale integration), composed of multiple elements from a variety of gas sources, an d have tailored micro-structures. As described in this article, early thermodynamic modeis helped develop deposition techniques for early-generation silicides. As the technological requirements increased, the modeling method s evolved in parallel, yielding continued insight into the relevant processes. Current work on CVD modeling couples thermodynamic calculations with heat and mass transfer. Incorporating both kinetic and thermodynamic effects, these methods provide a more realistic description of the CVD reactor.
Computer Applications in the Development of Steels
Authors: Sundman Bo , Ågren John
Published: August 2016

Despite the fact that thermodynamic calculations, strictly speaking, apply only to equilibrium, they may of ten be used in nonequilibrium situations. If one or several of the stable phases are suppressed in the calculations, we have a metastable equilibrium, which is often of practical interest. For example, one may calculate the driving force available to form the more stable phases and model nucleation.

Thermodynamic calculations may be performed stepwise to predict microseg-regation during solidification by a Scheil-type calculation (no diffusion in the solid State, infinite diffusion in the liquid, and equilibrium at the interface). In such a calculation, no information other than the thermodynamic properties of the System is used.

A more ambitious approach is to com-bine the thermodynamic calculations with kinetic modeis (e.g., diffusion calculations) and thereby predict the rate of reactions. This approach is extremely powerful and may be used to simulate a wide range of different phenomena, including precipitation, homogenization, and diffusional interactionsbetween Substrate and coating.

It is usually assumed that thermodynamic equilibrium holds locally at the migrating phase interface between two phases, and the rate of transformation is calculated at each instant by solving a set of flux-balance equations. The fluxes are obtained from a numerical Solution of the multicomponent diffusion equations (see Reference 3).
Corrosion Science
Authors: Newman R.C. , Sieradzki K.
Published: August 2016

Corrosion is a branch of materials research that is, by its nature, “schmutzy” (dirty). It has a reputation as an unglamorous subject and certainly suffers from an image problem in the materials community: the guest editors would like to have a dollar for every time we sat down and discussed “How can we make corrosion sound positive?” Solving corrosion problems requires an understanding of corrosion mechanisms, and corrosion mechanisms are infinitely subtle and interesting. Corrosion processes can often encompass concepts from a variety of disciplines, including thermodynamics, surface science, electrochemistry, physical metallurgy, and solid-state and statistical physics. While corrosion of metals is the subject of this issue of MRS Bulletin, ceramics, polymers, and geological materials are all greatly affected by corrosion.

Corrosion of metals is an electrochemical process, composed of anodic (metal oxidation) and cathodic (reduction) reactions occurring on a surface. The rates of these reactions are measured as current densities (in units of A m−2). On a single piece of metal, the anodic and cathodic current densities can vary arbitrarily from point to point, as long as the total anodic and cathodic currents are equal. This variation, which is associated with local differences in pH, surface composition, or defects in a surface film, leads to various localized phenomena, such as pitting and stress-corrosion cracking, and also to intriguing oscillatory dynamics.
Materials Engineering of Lipid Bilayers for Drug Carrier Performance
Authors: Needham David
Published: August 2016

The liquid-phase lipid bilayer is a unique engineering material. Biologically, it holds a central position in cellular life, providing the structural basis for the membrane that surrounds every cell on the planet. From a materials perspective, it is essentially a 4-nm-thick, water-insoluble sheet of 2-poise oil. Artificial membranes were “discovered” 35 years ago. It was soon recognized that liposomes could have a range of potential uses, and investigators sought to exploit the obvious capsular and biocompatibility properties of the membrane in applications such as liposome drug delivery. Since 1966, some 18,000 papers on liposomes have appeared in the literature (listed on Medline, and see References 4–7 for reviews), and 260 patents have been issued describing the use of liposomes in the pharmaceutical industry. These patented applications have included the delivery of cancer drugs, intracellular drug delivery, inhalation, topical drugs, gene therapy, proteins, peptides, amino acids, vaccines, targeted liposomes, lipophilic drugs, and liposome production, separation, and analysis. A huge database therefore exists with which to establish boundary conditions for predicting under which circumstances the encapsulation of drugs in liposomes or other carriers may be expected to result in improved therapy. Despite this enormous effort, only a few formulations, principally for amphotericin (an antifungal drug) and anthra-cyclins (anticancer drugs), have been approved and marketed, heralding the promise and potential that these versatile lipid-bilayer materials present. The reasons for this limited success are many, not the least of which is that the cost of developing a new pharmaceutical product can be several hundred million dollars.
Advances in Lithium and Nickel-Metal Hydride Battery Performance
Authors: Oman Henry
Published: August 2016

Traditional batteries stored energy in thick plates made from heavy metals like lead, nickel, and zinc. They delivered from 15 to 20 Wh/kg. Lighter-weight lithium anodes were used in some military batteries. Then came the need for lightweight batteries for powering cellular telephones and laptop computers. Lithiumion batteries were developed, and the worldwide demand, just for use in laptop computers, has grown to 150 million units per year.

The need to reduce air pollution in downtown areas has created a market for battery-powered electric vehicles. Clara Ford chose to drive an electric car, even though her husband, Henry Ford, was making gasoline-powered cars. However, the cost of replacing worn-out leadacid batteries soon ended the electric-car age of the early 1900s. The need for lightweight, long-life batteries for zero-emission cars has produced unprecedented investments in battery technology. The lithium-battery technology used in laptop-computer batteries did not support the requirements of high power and long life for the charge/discharge cycling needed in electric cars. An executive of a lithium-battery manufacturer was asked what he was doing about the cycle life of his batteries. His answer: “The life of a laptop computer is nine months. Then a newer model makes it obsolete. We meet this requirement!”
Neutron-Scattering Measurements of “Soft Matter”
Authors: Lindner Peter , Wignall George
Published: August 2016

Neutron scattering had its origin in 1932, the year that marked the discovery of the neutron by Chadwick, and the first nuclear reactors were successfully operated in Chicago and Oak Ridge, Tenn., in the early 1940s. During its initial stages, neutron scattering was used mainly for the study of “hard” crystalline materials. For example, Shull and Wollan's pioneering research, which led to the 1994 Nobel Prize in physics, began with studies of iron, chromium, and iridium, and was followed by the development of polarization analysis to determine the structure of magnetic materials. Such studies continue to yield important structural information (see the articles on magnetism by Aeppli and Hayden and on crystallography by Radaelli and Jorgensen in this issue of MRS Bulletin), although during the last two decades, the technique has been increasingly used by scientists from other disciplines (chemistry, biology, polymer science), and many of these newer applications have involved “soft” matter such as polymers, colloids, and gels. By definition, these substances are “plastic” or “squishy,” and easy to mold into different shapes; because of this flexibility, they have become some of the most practical and widely used materials today.
Materials Research at Alcoa
Authors: Jarrett Noel
Published: August 2016

The competitive forces that have dominated the aluminum industry over the last decade are similar to those in many other industries. New international competitors, driven primarily by their ability to compete with long-standing U.S. producers on the basis of cost and quality, have made significant inroads into virtually all aluminum markets.

As more emerging nations, driven by the need to create jobs and hard currency rather than profits, entered the primary metal business and exported their output, ingot prices fell. Eventually, ingot became a commodity traded in the international marketplace, with metal prices no longer related to production costs.

While these structural changes in the worldwide aluminum industry are of great concern (particularly in the United States), by no means do they signal the light metal's demise in the materials marketplace. What they have done, however, is to provide the impetus for the development and pursuit of economic and technical strategies designed to ensure long-term, profitable growth.

By the beginning of the 21st century, most monolithic metals will be firmly entrenched as commodities. This will solidify emerging nations as key producers, based upon their access to raw materials, less costly labor and energy resources, and subsidized capital. The ability of companies like Alcoa to compete in this commodity marketplace will be based upon their ability to reduce manufacturing costs and provide technically-based product differentiation, primarily via quality control, through new and improved processing technologies.
Up Close: Northwestern University Materials Research Center
Authors: Carr Stephen H.
Published: August 2016

The Materials Research Center at Northwestern University is an interdisciplinary center that supports theoretical and applied research on experimental advanced materials. Conceived during the post-Sputnik era, it is now in its 26th year.

The Center, housed in the university's Technological Institute, was one of the first three centers funded at selected universities by the federal government in 1960. The federal government, through the National Science Foundation, now supplies $2.4 million annually toward the Center's budget, and Northwestern University supplements this amount. Approximately one third of the money is used for a central pool of essential equipment, and the other two thirds is granted to professors for direct support of their research. Large amounts of time on supercomputers are also awarded to the Materials Research Center from the National Science Foundation and other sources.

The Center's role enables it to provide partial support for Northwestern University faculty working at the frontiers of materials research and to purchase expensive, sophisticated equipment. All members of the Center are Northwestern University investigators in the departments of materials science and engineering, chemical engineering, electrical engineering, chemistry, or physics. The Materials Research Center is a major agent in fostering cross-departmental research efforts, thereby assuring that materials research at Northwestern University includes carefully chosen groups of faculty in physics, chemistry, and various engineering departments.
Infrared Optical Materials: Where Do We Stand?
Authors: Klocek Paul
Published: August 2016

The usefulness of infrared (IR) radiation has been recognized for many years and is today the basisof an expanding technology. The development of the laser, particularly the IR laser, has further fueled this technology expansion. Optical materials have always played a critical role in IR technology, primarily as transmissive and reflective optical components. Often, the lack Of an adequate IR optical material has delayed the implementation of applications Until appropriate materials or quality of materials were developed. While the developed material may satisfy the basic requirements of the application, often its other physical properties and/or cost are not desirable. The limited number of IR optical materials combined with the growing humber of applications has kept their development essential to our technological growth.

This paper reviews some current research and developmen t trend s in IR optical materials primarily for transmissive components. These IR components include geometric optics, windows and domes, optical fibers, high energy laser optics, and coatings. The emphasis is on optical materials for applications involving wavelengths in the 2-14 μm region.

Intrinsic Attenuation

Intrinsic attenuation defines the fundamental limits to light propagation in a transmissive material. It is composed of electronic or bandgap absorption, lattice vibration or multiphonon absorption, and Rayleigh and Brillouin scattering. Bandgap absorption results from the promotion of an electron from the valence to the conduction band by direct absorption of a photon or indirectly involving a phonon and the appropriate change in k-vector. The onset of absorption occurs at photon energies greater than or equal to the bandgap.
Defects in Ceramic Oxides
Authors: Nowick Arthur S.
Published: August 2016

The topic that I am attempting to cover easily requires a whole book to do it justice. To deal with it in a short article, I will focus on a few basic principles that dominate the behavior of defects in oxides and then present some examples taken from well-studied and relatively well-understood materials.

The study of defects in oxides differs from the study of defects in metals and alloys or in semiconductors in several important ways. First, oxides generally have very high melting points so that intrinsic point defect concentrations at temperatures below ~1500°C are usually negligibly small. Second, an oxide does not always maintain the composition at which it was fabricated, as alloys do, but can exchange oxygen with the ambient atmosphere, according to the ambient partial pressure of oxygen, P(O2). Thus, the stoichiometry, and accordingly the defect concentration, can be controlled by annealing in a specific P(O2) atmosphere. Third, and most important, oxides have a high degree of ionicity so that most point defects possess an effective charge. The consequences of this fact are far reaching; some of them are as follows:

1. In a binary oxide, e.g. a metal oxide (MO), there are two sublattices. The diffusion of cations and of anions proceeds each on its own sublattice, involving different point defects. Accordingly, cation and anion diffusion rates can be very different and, in fact, usually are.
Polymer Gels, Materials That Combine Liquid and Solid Properties
Authors: Winter H. Henning
Published: August 2016

We are accustomed to thinking of matter as being in one of three states: solid, liquid, or gas. Nature, however, has provided us with a marvelous intermediate state, the gel. Industrial applications are just beginning to explore the advantageous gel properties as adhesive, superabsorber, damper, membrane, toner, catalyst support, etc. Gels are good adhesives since they combine the surface wetting property of liquids with the cohesive strength of solids. Strong adhesion and damping properties suggest gels as a binder in composite materials. For example, the car of the future may operate at a much reduced noise level due to a thin layer of gel in its body. Widespread technical applications have not yet materialized because, until recently, it was difficult to measure gel behavior. This has changed, and as a consequence, gels can now be manufactured with reproducible properties.

What the many possible types of gelation processes have in common is that molecules connect into a three-dimensional network structure. Junctions between molecules form as chemical bonds (cross-links) or physical associations (such as crystalline or glassy domains, hydrogen bonds, etc.). The molecular architecture determines the gel properties in ways which have yet to be explored. Typical parameters are the monomer building block, molecular size, branching, chain stiffness, cross-link functionality, and solvent content.
Polymer Materials Science: Novel Synthesis and Characterization of Supermolecular Structures
Authors: Frank Curtis W.
Published: August 2016

The two feature articles in this issue present numerous contrasts, but both reflect the vitality of research in polymer science today. David Tirrell and co-authors paint a picture of how the techniques of molecular biology may be applied to the synthesis of novel “proteinlike” polymers with control over molecular weight, composition, and stereoregularity that is unprecedented in the realm of traditional polymer chemistry. Wolfgang Knoll turns his attention to ultrathin polymer films with thicknesses comparable to molecular chain dimensions and demonstrates how evanescent wave optical methods may be used to provide spectroscopic as well as imaging information on the characterization of these “restricted geometry” systems.

Both authors address the issue of supermolecular structure, whether approached from the synthetic or physical chemical viewpoints. Tirrell describes a series of target polymers, expressed by genetically engineered microorganisms, which may provide a fundamental understanding and control over chain folding, a critical morphological feature governing solid-state behavior of synthetic polymers. Knoll analyzes the fundamentals of evanescent wave optical methods for interrogating the molecular organization in polymer films that have considerable potential in electronic or photonic applications.
Environmental Protection: Charting a New Course: 1991 MRS Spring Meeting Plenary Address
Authors: Lingle Stephen A.
Published: August 2016

The U.S. Environmental Protection Agency (EPA) is one of several agencies that serve as members of the Federal Coordinating Council of Science, Engineering, and Technology. In this role, EPA chairs the Environmental, Safety, and Health Work Group of the Committee on Materials. One of the primary purposes of the Committee on Materials is to strengthen the government-industry:university partnership in materials research. Strengthening and building this partnership is also one of the goals of the Materials Research Society. You bring together an interdisciplinary group of scientists and engineers from industry, government, and academia to exchange ideas on the forefront of materials research.

A recent National Research Council report, Materials Science and Engineering for the 1990s: Maintaining Competitiveness in the Age of Materials, identified six major science and engineering initiatives. One of these six initiatives was the environment. I believe that we will see, over the next few years, a major thrust in materials research to develop environmentally benign or “environmentally friendly” materials—materials that are less toxic and less polluting and do not deplete scarce natural resources, materials that have longer useful lives, and materials that can be recycled and require less energy to manufacture.
Load-Bearing Ordered Intermetallic Compounds—A Historical View
Authors: Cahn Robert W.
Published: August 2016

Chemical combination among metals has been studied for a long time. In the early days, chemists had much difficulty in understanding how metals could combine at all among themselves, often in several different proportions, since this often seemed to be at variance with elementary notions of valency. Indeed, in the last century a distinction was proposed between daltonides and berthollides, the former being compounds with simple ratios of the numbers of constituent atoms… consistent with Dalton's atomic theory!… the latter, called after a skeptical French chemist, being the name reserved for compounds with a wide composition range which scarcely seemed explicable on any reasonable atomic model. A few nostalgic souls still employ these distinctions.

An early classic on the subject was a book published by two Italian chemists in 1918. British metallurgist C.H. Desch also wrote a monograph on intermetallic compounds in 1914 (the year when the name “physical metallurgy” was first proposed, and the chemical bias of metallurgy shifted toward a physical one), and he declared that “attempts to form a theory of the constitution of intermetallic compounds… have been comparatively unsuccessful.” When he returned to the subject 20 years later, he felt much more cheerful about the state of the theory because in the meantime Hume-Rothery had introduced the concepts of atomic size factor, electron/atom ratio, and electronegativity (a concept also associated with the name of Linus Pauling) into the discussion of intermetallic phases, or compounds. Today, a battery of sophisticated physical concepts is used to make sense of both binary and multielement intermetallic compounds and they are no longer regarded as chemical anomalies.