bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanowires by Step Decoration
Authors: Himpsel F.J. , Jung T. , Kirakosian A. , Lin J.-L. , Petrovykh D.Y. , Rauscher H. , Viernow J.
Published: August 2016

Recent advances in the control of thin films and surfaces have brought an intriguing question within reach: Is it possible to tailor the electronic properties of solids by controlling them layer by layer or row by row? Customized molecules are commonplace in biochemistry. Can the same idea be brought to bear on solids and electronic materials? Electronic properties of semiconductor devices have been controlled by hetero-structures, quantum wells, and super-lattices. Magnetism as a cooperative phenomenon lends itself to manipulation in small structures, where neighbor atoms can be replaced systematically by species with stronger or weaker magnetism. In fact, a class of magnetic/nonmagnetic multilayers termed spin valves has recently been introduced into commercial read heads for magnetically stored data. The optimum thickness of their active region lies in the single-digit-nanometer regime.

The smallest nanostructures may be viewed as objects consisting only of interfaces with no bulk behind them. More typically, single-digit-nanometer dimensions are sufficient for realizing the benefits of structuring (e.g., operating a quantum-well device at room temperature). This regime is difficult to reach with lithography methods, particularly when macroscopic amounts are to be fabricated. Self-assembly becomes the method of choice.
Display Applications of Rare-Earth-Doped Materials
Authors: Ballato John , Lewis John S. , Holloway Paul
Published: August 2016

The human eye places remarkably stringent requirements on the devices we use to illuminate objects or generate images. Exceedingly small deviations in color or contrast from what we consider natural are easily judged by the brain to be fake. Such cognition drives consumer practice, so great efforts have been made for over a century to synthesize emissive materials that match the response functions associated with the human perception of color. This is an extremely difficult task, given the diverse range of considerations, some of which include whether (1) the display is viewed under artificial light or natural sunlight, (2) the images are stationary or moving, and (3) the rendering of depth in a two-dimensional image is believable.

Established technologies including cathode-ray tubes (CRTs), vacuum fluorescent displays (VFDs), lamps, and x-ray phosphors have made possible a wide variety of display and imaging devices. However, continued advances are required to increase brightness, contrast, color purity, resolution, lifetime, and viewing angle while still lessening the cost, weight, volume, and power consumption. Mature or emerging technologies that address these issues include thin-film electroluminescent (TFEL) displays, liquid-crystal displays (LCDs),8 field-emission displays (FEDs),9 and plasma displays (PDs).10-12 Each of these technologies uses luminescent materials consisting typically of an activator from which light is emitted and a host for low concentrations of the activator (typically >1% activator). The requirements of the host and activator are discussed in a later section. The luminescent material can exhibit either a narrow emission spectrum, useful for color displays, or a broadband emission, which can extend into multiple colors. In addition, with multiple activator/host combinations, a luminescent material can emit several colors and even white light. While LCDs are light valves, which may be used in a reflective mode and therefore do not require a luminescent material, low-light situations require a backlight generated by a luminescent material. Many of the most versatile, efficient activators are rare-earth (RE) elements, for reasons that will be discussed. The ability of RE ions to emit red, green, and blue light make them well suited for application in visible-display technologies. This article reviews dopant and host material systems, excitation mechanisms, and the factors that limit the achievable luminescent intensity and efficiency. Device configurations for modern displays are discussed, as are materials and structures for next-generation technologies. Since each display technology has different performance and operational requirements, only the basic characteristics will be discussed here to enable an appreciation of emission from RE activators. References to the literature are supplied to further direct the reader to more in-depth discussions.
Biomechanical Properties of Fibroblasts
Authors: Thoumine Olivier , Ott Albrecht
Published: August 2016

Cells are a complex topic of study for materials scientists. They are the fundamental building blocks of living organisms, able to sense their environment and act in response to it. In addition to their many biochemical functions, cells also play a mechanical role: They hold organs in place and move to the locations where they are needed in processes like wound healing, metastasis, or embryogenesis. Their mechanical behavior is mostly determined by a meshwork of three types of connected biopolymers (actin microfilaments, microtubules, and intermediate filaments) that compose a structural framework called the cytoskeleton, surrounded by a lipid membrane (Figure 1). In contrast to this simple picture, cells are very different from polymer gels or liposomes: They are active materials, powered by chemically stored energy. Their mechanical condition is closely linked to their biochemical function; for example, they may “commit suicide,” following a well-defined protocol known as apoptosis, which can be triggered by their mechanical state.

The enormous progress of modern cell biology combined with new micromanipulation techniques is leading researchers toward a more global understanding of the mechanical properties of cells and toward finding a functional link between biochemistry, chemical signaling, and cell mechanics, thus crossing the boundaries between these subjects.

The characterization of cell mechanical behavior has been the object of numerous studies. Red blood cells are a simple model system; if deprived of a nucleus while retaining a constant surface area, they have properties reminiscent of lipid vesicles.
Neutron Scattering in Materials Research
Authors: Mason T.E. , Taylor A.D.
Published: August 2016

With materials of ever-increasing complexity becoming key elements of the technologies underpinning industrial and economic development, there is an ongoing need for tools that reveal the microscopic origins of physical, electrical, magnetic, chemical, and biological properties. Neutron scattering is one such powerful tool for the study of the structure and dynamics of materials. Neutrons are well suited to this purpose for several reasons:

∎ Neutrons are electrically neutral, leading to penetration depths of centimeters and thereby enabling in situ studies.

∎ Neutron cross sections exhibit no regular dependence on atomic number and are similar in magnitude across the periodic table, giving rise to sensitivity to light elements in the presence of heavier ones.

∎ Certain large differences in isotopic scattering cross sections (e.g., hydrogen to deuterium, H/D) make neutrons especially useful for the study of light atoms in materials.

∎ The range of momentum transfer available allows probing of a broad range of length scales (0.1–105 Å), important in many different materials and applications.

∎ Thermal and “cold” (longer-wavelength) neutrons cover a range of energies sufficient to probe a wide range of lattice or magnetic excitations, “slow” dynamic processes such as polymer chain reptation, and so forth.

∎ Neutrons have magnetic moments and are thus uniquely sensitive probes of magnetic interactions.

∎ Neutrons can be polarized, allowing the cross sections (magnetic and non-magnetic) to be separated.

∎ The simplicity of the magnetic and nuclear interactions makes interpretation of results straightforward.
Neutrons as a Probe of Magnetization on Atomic to Mesoscopic Scales
Authors: Aeppli G. , Hayden S.M.
Published: August 2016

The neutron is a spin 1/2 particle with a well-specified magnetic dipole moment which interacts with magnetic fields in solids. Because typical neutron wavelengths are comparable to interatomic distances in solids, the fields that can be probed range from the dipoles of individual electron spins to those associated with flux lines in superconductors. In this article, we give a brief introduction to the use of magnetic neutron scattering in materials science.

Progress in materials science typically involves new materials or the improved fabrication of previously known materials, followed by measuring quantities such as electrical resistivity, magnetic susceptibility, or specific heat, typically as a function of variables such as temperature, magnetic field, chemical composition, or pressure. A material is deemed interesting if a simply defined bulk characteristic either undergoes a spectacular evolution as a function of one of the variables—superconductivity comes to mind—or has a range of values that makes it uniquely suited for some predetermined application. Once the material is thought to be interesting, there are natural drives to understand the origin of its interesting properties as well as to improve them. At this point, a microscopic tool such as magnetic neutron scattering provides valuable insights that bulk measurements cannot yield.
Superconductivity and Magnetism in the La2 CuO4-Based Compounds
Authors: Fisk Z. , Cheong S-W. , Johnston D.C.
Published: August 2016

La2CuO4, crystallizes in an orthorhombic distortion of the tetragonal K2NiF4 structure, a so-called layered perovskite. The important question here concerns the stoichiometry of La2CuO4 prepared by various techniques. Regarding the La and Cu sites, recent neutron diffraction studies of powders have shown that the La:Cu ratio can vary from 2:1 by ≳1% in various preparations., Single crystals have been grown variously from CuO, PbO and Li2O-B2O3 fluxes. The last two fluxes incorporate some Pb and Li, respectively, into the crystals, but the cation ratio is found to be 2:1 within the accuracy of x-ray refinement.

It is also known that the oxygen stoichiometry corresponds to La2CuO4 within ≃ 1%. Extensive and precise magnetic susceptibility (χ) and other studies of powder samples showed, however, that the physical properties are extremely sensitive to < 1% changes in the oxygen content. A clear indication from electric and magnetic measurements is that the oxygen stoichiometry is always that, or richer than that, corresponding to a Mott insulator with an exactly half-filled band. Consistent with this, the stoichiometry is more properly written La2-z CuO4-y with small, positive y and z.

Several groups found that bulk superconductivity above 30 K can be produced in La2CuO4 by annealing powders or single crystals at high oxygen pressure. The weight gain in this process corresponds to producing La2CuO4.13, and these authors believe the excess oxygens go in as O-2, based on iodometric titration measurements giving the amount of [Cu-O]⊥ in the sample. Jorgensen et al. found that there is a phase separation below 320 K of La2CuO4 and the O2-loaded phase in oxygen-rich samples; the latter structure is also orthorhombic, but the position of the excess oxygens could not be determined unambiguously.
High Tc Bismuth and Thallium Copper Oxide Superconductors
Authors: Sleight A.W. , Subramanian M.A. , Torardi C.C.
Published: August 2016

The first report of a superconductor in this family came from the laboratory of B. Raveau. The system was Bi/Sr/Cu/O. The Tc's were in the range 10-20 K, and this system therefore did not attract much attention when there was intense effort on 90 K superconductors. Neither the structure nor the composition of the superconductor in the Bi/Sr/Cu/O system was known at the time of the first publication, a common feature with all discoveries of new high Tc superconductors in the past couple of years. We now know that the first discovered member of this new family of superconductors can be represented as Bi2Sr2CuO6. However, the composition and structure of this phase are still not precisely established.

Subsequent to the French work, the Bi/Sr/Ca/Cu/O system was studied in Germany, and higher Tc's were obtained. Although patents were filed; this work was not publicly announced. In January 1988, Maeda announced high Tc in the Bi/Sr/Ca/Cu/O system and Hermann announced high Tc in the Tl/Ba/Ca/Cu/O system.

It is now known that there exists a very large family of compounds of the type (AO)mM2Can-1CunO2n+2. The A cation can be Tl, Pb, Bi or mixtures of these elements. The value of m may be one or two but is only two when A is Bi. The M cation is Ba or Sr, and substitution of Ca by Sr is frequently observed. The number of consecutively stacked CuO2 layers is indicated by n. The highest temperature at which zero resistivity has been obtained in this family is 122 K, and this has been obtained for several distinctly different compositions (Table I).
Science for Art's Sake
Authors: Brunetta Leslie
Published: August 2016

Victorian men placed fig leaves over those parts of classical statues they didn't want their wives and children to see. Yet it's easy for someone looking at those statues today to assume that the leaves play some part in the Roman and Greek concepts of physical beauty.

A fig leaf may be the most blatant breach of an artist's original inspiration you'll encounter in a museum, but it's not likely to be the only one. Other more subtle transgressions are displayed in nearly every gallery and museum in the country—but unmasking them takes more than just a discerning eye. For instance, did the 17th-century painter see the world as quiet and subdued, or have his bright colors been muted by a 19th-century varnish? Did the classical sculptor intend his work to have an even, green patina, or has the Renaissance infatuation with antiquity allowed this corrosion to hide his varying shades of burnished bronze? Did Leonardo conceive the face of the Christ of “The Last Supper” as speaking, or silent, as his overpainters would have it?

“Modern conservators really make us think about objects, says Carol Faill, administrator of college collections at Franklin & Marshall College. “There's been a consciousness raising about objects' own integrity.” Art and science are being used together as never before to gain an understanding of the physical and chemical properties of materials and their role in the fine arts.
Development of Direct Drive, High-Gain Capsules for Inertial Fusion: A Materials Challenge
Authors: Campbell J. H.
Published: August 2016

The application of Inertial Confinement Fusion to power production requires the development of a high-yield fusion capsule. Theoretical design calculations suggest that a single shell capsule with a uniformly distributed deuterium-tritium (DT) fuel layer on the inside surface could give the desired high-gain performance when directly driven with 0.35 μm laser light. This design requires operation at cryogenic temperatures necessary to condense DT (20-30 K) and a means of levitating the fuel layer inside the capsule. On e recently suggested method for making this capsule is to use a rigid foam matrix to support the condensed DT in a spherical shell configuration. For such a capsule to be successfully fielded, a number of critical materials problems must be solved.
Damage Mechanisms in Optical Materials For High-Power, Short-Wavelength Laser Systems
Authors: Haglund Richard F.
Published: August 2016

Damage to optical materials under intense photon irradiation has always been a major problem in the design and operation of high-energy and high-average-power lasers. In short-wavelength lasers, operating at visible and ultraviolet wavelengths, the problem appears to be especially acute; presently attainable damage thresholds seriously compromise the engineering design of laser windows and mirrors, pulsed power trains and oscillator-amplifier systems architecture. Given the present interest in ultraviolet excimer lasers and in short-pulse, high-power free-electron lasers operating at visible and shorter wavelengths, the “optical damage problem” poses a scientific and technological challenge of significantdimensions. The solution of this problem even has significant implications outside the realm of lasers, for example, in large space-borne systems (such as the Hubble Telescope) exposed to intense ultraviolet radiation.

The dimensions of the problem are illustrated by the Large-Aperture krypton-fluoride laser amplifier Module (LAM) shown schematically in Figure 1. This device, now operating at the Los Alamos National Laboratory, is typical of current and planned large excimer lasers for fusion applications. The LAM has an active volume of some 2 m3, and optical surfaces (resonator mirror and windows) exceeding 1 m2 in size; the fabrication of these optical elements was the most expensive and time-consuming single item in the construction of the laser. During laser operation, a population inversion in an Ar-Kr-F2 mix ture is created through electron-beam excitation of the laser gas by two 400 kA beams of 650 keV electrons from a cold cathode discharge. The electron trajectories in the gas are constrained by a 4 kG magnetic field transverse to the optical axis produced by a pair of large Helmholtzcoils.
Point Defects and Diffusion in Nonstoichiometric Metal Oxides
Authors: Dieckmann Rüdiger
Published: August 2016

This article briefly reviews the relationships between point defects and ion diffusion in nonstoichiometric ionic crystals, with special emphasis on cubic oxides. It focuses on crystalline materials with negligibly small concentrations of nonequilibrium defects such as dislocations and grain boundaries. First, the concepts used to analyze the point defect structure and the diffusion of ions in nonstoichiometric crystals will be discussed. Then, specific oxides will be considered as examples. These oxides are manganosite, Mn1−ΔO, and spinels of the type Me3−δO4 with Fe and Mn cations, respectively.
Defect Engineering
Authors: Kimerling Lionel C.
Published: August 2016

The pervasive role of defects in determining the thermal, mechanical, electrical, optical, and magnetic properties of materials is biblical. Thermodynamic control of imperfection under equilibrium conditions dictates, for instance, the high temperatures needed to raise defect content for diffusion processes. Nonequilibrium treatments, such as work hardening, are used to control dislocation and grain boundary density and morphology to enhance mechanical properties. Both approaches represent the practice of defect engineering. Both are examples of a synergistic interaction between science and engineering in which an existing knowledge base is applied to its limits, stirring the development of new knowledge and new applications.

The purpose of this article is to convey the flavor of the defect engineering culture. The invention of the transistor can be traced to a triumph of defect engineering. Original explorations of semiconductor materials had the goal of controlling surface rectification properties to devise rectifiers, oscillators, and amplifier substitutes for vacuum tube counterparts. Schottky barriers, p-n junctions and metal-oxide-semiconductor capacitors—the products of the endeavor—are now the building blocks of today's microcircuits. The commercial success of these applications has fueled a boom in materials physics research during the last two decades. The work-hardening knowledge base can be traced from the Japanese swordmaking ritual to the discovery of dislocations (in theory first, and then by direct observation). Expansion of the dislocation knowledge base was a dominating concern in materials science prior to the transistor. As shown in this article, these two disparate areas are essential components of the defect engineer's tool kit.
Point Defects in Materials Part I: Behavior and Characteristics in Different Material Classes
Authors: Seidman David N. , Shi Donglu
Published: August 2016

In this issue of the MRS Bulletin we present five papers that involve point defect phenomena in a wide variety of materials—metals, conducting ceramic oxides, semiconductors, amorphous alloys, and high Tc superconducting oxides. The unifying theme of this issue is point defects—zero-dimensional defects. Even for the high Tc oxides, where planar defects are discussed, it is the ordering of oxygen/vacancy chains that ultimately gives rise to twins in the famous YBa2Cu3O7.δ (1:2:3) oxide superconductor.

Hillard Huntington, professor emeritus of physics at Rensselaer Polytechnic Institute, is an early and important pioneer in the study of point defects in metals. A theorist, he has also performed many experiments over the years; for example, he performed key early experiments on electromigration effects. Huntington's article presents a historical review of the research on vacancies and self-interstitial atoms in metals during the period that stretches from the mid-1930s to the mid-1960s. He played a crucial role in this field as a result of his seminal theoretical calculations, with Fred Seitz in 1942, on the enthalpies of formation and migration of vacancies or self-interstitial atoms in pure copper. Huntington's and Seitz's calculations indicated that diffusion occurs predominantly by a monovacancy mechanism since the enthalpy of formation of a self-interstitial atom, the [100] split form, also called the dumbbell form, is too large to be compatible with the activation enthalpy for self-diffusion in copper. It is now well established that the latter is given by the sum of the enthalpy of formation and the enthalpy of migration of a monovacancy in many face-centered-cubic (fcc), body-centered-cubic (bec), and hexagonal-close-packed (hcp) metals.
Biomaterials in an Emerging National Materials Science Agenda
Authors: Mueller E.P. , Barenberg S.A
Published: August 2016

In 1988 a biomaterials industry panel was chartered by the National Academy of Sciences and the National Academy of Engineering to address needs and opportunities in materials science and engineering as perceived by the biomaterials industry. This report was subsequently consolidated with similar reports from panels in the other materials science areas into a comprehensive National Research Council (NRC) report, Materials Science and Engineering for the 1990s: Maintaining Competitiveness in the Age of Materials, issued by the National Academy Press in late 1989.

After reading the NRC report, D. Alan Bromley, science adviser to President Bush, decided that materials science would be one of five priorities for research in the current aclministration. In a letter to Frank Press, January 1990, Bromley praised this report and encouraged the Academy to have regional meetings to stimulate action on the local level. It was felt that these regional meetings would offer materials scientists and engineers the opportunity to organize themselves and, cooperating with industry and federal laboratories, take the initiative to address the needs identified in the NRC report. Bromley encouraged structuring these meetings, to the extent possible, to produce items that could be considered for the Office of Science and Technology Policy (OSTP) agenda.
Genetic Engineering of Polymeric Materials
Authors: Tirrell David A. , Fournier Maurille J. , Mason Thomas L.
Published: August 2016

Polymerization reactions are generally divided into two broad classes: step growth or polycondensation reactions (examples would include the synthesis of polyamides and polyesters), and chain growth processes such as those used to prepare polyethylene or polystyrene. These processes are illustrated schematically in Figure 1.

The statistical nature of step and chain growth polymerization processes ensures that the products of such reactions must be heterogeneous. Conventional polymeric materials thus consist of mixtures of chains, often characterized by relatively broad distributions of chain length or composition. In many materials applications, this kind of molecular heterogeneity is advantageous since it suppresses crystallization and helps to preserve desirable properties such as optical clarity or elasticity. On the other hand, synthetic developments that afford improved control of macromolecular architecture have had profound impact on materials science and technology. As examples, one can cite the discovery of Ziegler-Natta polymerization, now used to prepare billions of pounds per year of crystalline polyolefins, or the development of living anionic polymerization of olefins, which led directly to block copolymers and the commercially important thermoplastic elastomers.

The advent of recombinant DNA methods has provided a basis for developing polymeric materials characterized by essentially absolute uniformity of chain length, sequence, and stereochemistry. This article outlines the principles governing the cloning and expression of artificial genes, and examines the potential role of artificial proteins in polymer materials science.
A Materials Scientist in Space: 1990 MRS Fall Meeting Plenary Address
Authors: Dunbar Bonnie J.
Published: August 2016

The following is an edited version of NASA Astronaut Bonnie J. Dunbar's Plenary Address at the 1990 MRS Fall Meeting.

I've often been asked, “Why a materials scientist in space?” I hope my presentation tonight will provide a little more insight on “why.” I don't think it's unusual at all. I look at myself as a continuum between outer space and inner space. I've been equally fascinated looking at the stars as at atomic structures under scanning electron microscopes. So to me it's not an unusual experience. In addition, materials scientists and engineers are needed to operate in space.

Tonight I would like to do several things. I'd like to talk to you about where we've been in space, where we are, and where we hope to go. I'll emphasize the materials aspect of it, not only in how we achieved space, but how we hope to exploit the microgravity environment of space. I have with me “home movies” of a Shuttle Mission I flew on in January 1990. You'Il share with me the experience of performing research as well as retrieving the long-duration exposure facility (LDEF) with a robotic arm.
Designing Interfaces
Authors: Cornie James A.
Published: August 2016

During the 20 years I have been working in the field of metal matrix composites, I have always been drawn to the study of interfaces. Any problems the materials researcher or developer encounters will eventually be tied to some issue involving the interface. The interface controls the in-situ fiber strength and hence the axial strength of the composite. The transverse strength of composites is also controlled directly by the strength of the interface. It follows that in order to optimize a fiber/matrix reinforcement system, one must also optimize the interface. It is no accident, then, that so soon after the two excellent issues on interfaces edited by D. Wolf and S. Yip (MRS Bulletin, September and October 1990), we launch into the subject again. This time, we approach the interface from the point of view of integrating the fields of materials science and engineering, i.e., integrating the structure-processing-properties-materialssynthesis relationships.

The concept of interface design is relatively new. Until recently, we simply controlled damage and limited fiber degradation by controlling processing variables, and contented ourselves with what nature allowed. For the most demanding applications, nature was not permitting reliable structures.

Our emphasis in this issue of the MRS Bulletin is the development of the skills and strategies to design interfaces to a specifie application. In the future, we will be asking materials to perform structurally at temperatures approaching 3000°C in some propulsion applications. The success of such applications will depend on how well we design the interfaces.
In Pursuit of the Lattice Vacancy 1990 MRS Fall Meeting Von Hippel Award Address
Authors: Balluffi R.W.
Published: August 2016

The Von Hippel Award is especially significant to me for several reasons. The name Von Hippel is legendary in the halls of Building 13 at the Massachusetts Institute of Technology, where I have worked for the last 12 years. Professor Von Hippel was one of the first to appreciate the interdisciplinary nature of materials research and engineering, and his insulation laboratory at MIT provided an early prototype for the National Science Foundation-supported system of interdisciplinary materials research laboratories in existence today. These laboratories, both at MIT and earlier at Cornell, have helped me in my research in many ways over the years.

Also I have been a recent councillor of the Materials Research Society and have been privileged to witness the phenomenal growth of MRS at first hand. The stature of the Von Hippel Award must be increasing at least in proportion to this growth. I, therefore, feel very honored and grateful indeed! I would also like to add that much of my work has been done in collaboration with valued colleagues and students. They deserve a substantial share of this award.

Over the years, my research has been devoted mainly to the experimental study of crystal defects and their behavior. These defects can be classified according to their dimensionality as shown in the accompanying table, and they are involved in one way, or another, with a host of phenomena in crystalline materials. Since I address a rather diverse audience, it might be appropriate to discuss some of the history of lattice vacancy research and some of the details of my personal contribution to it.
Molten Polymers in Strong Flows: A Nonclassical Proposal
Authors: de Gennes P.G.
Published: August 2016

In spite of its importance for extrusion and molding, the rheology of polymer melts under high shear rates is not fully explained by the classical theory of Doi and Edwards. In this theory, each polymer chain is trapped in a confining “tube.” When the tube is suddenly stretched, the chain follows at first, but it soon shrinks back to its original length (“retraction process”). I propose a different view: Upon stretching, the tube becomes thinner so the chain is squeezed and tends to span a longer length of tube; there is no retraction.
Pattern Formation in Electrohydrodynamic Convection
Authors: Zimmermann Walter
Published: August 2016

One hundred years after their discovery, we meet liquid crystals everywhere in our daily life. Their most widely known application is the liquid crystal displays (LCDs) in watches, pocket calculators, or gasoline pumps. Applications aside, liquid crystals show many exciting properties, making them highly interesting for fundamental research. For example, electrohydrodynamic convection (EHC) in nematic liquid crystals, which is studied in cells of a configuration similar to liquid crystal displays, serves with its characteristic properties as a model System for investigating central questions of pattern formation and chaos.

Today's liquid crystal displays work on the principle described in 1971 by Martin Schadt and Wolfgang Helfrich (Figure 1). In nematic liquid crystals, organic molecules orient on average along a macroscopic direction, described by the director field n(r), that has neither head nor tail (n = −n). Nematics are therefore anisotropic and for energetic reasons, n(r) orients parallel (perpendicular) to an electric field when the dielectric permittivity (ε∥) along n is larger (smaller) than the perpendicular (ε⊦ one. For positive εa = ε∥ − ε⊦, when an electric field is applied perpendicular to the direction of n, a reorientation of n takes place together with a corresponding change in the optical property of the cell. The controlled change by an electric field in the optic axis (orientation) in well-defined areas of the display then allows the representation of numbers, etc.
Grain Boundary Chemistry and Reactions in Metals
Authors: Briant C.L.
Published: August 2016

An interface can be defined as a surface that serves as a common boundary between two phases. Examples include the boundaries between two solids, two immiscible liquids, a solid and a liquid, a solid and a gas, and a liquid and a gas. Interfaces have been studied for decades by scientists of many different disciplines. One reason for this interest is that the atomic structure and the chemical composition at the interface can differ from that of the bulk material on either side of it. Consequently, the properties of the interface can differ greatly from those of either bulk phase, and chemical reactions can occur more readily at the interface than in the bulk.

All the interfaces listed in the previous paragraph are of interest to materials scientists. However, this article will only consider the grain boundary because it has received the most attention by researchers in materials science. Furthermore, we will only consider grain boundaries in metals; nonmetallic systems will be covered in other articles in this issue.

A grain boundary is an interface that exists where two single crystals are joined in such a way that their crystallographic orientations are not completely matched. Thus, any polycrystalline material contains many grain boundaries. They occur wherever the individual grains meet one another and can usually be observed by etching a polished cross section of the surface as shown in Figure 1. Grain boundaries first form in a metal as a result of the multiple nucleation sites that occur during solidification.
The Emerging Undergraduate Curricula in Materials Science and Engineering
Authors: Liedl G.L.
Published: August 2016

Much attention has again been brought to the question of undergraduate education for the “materials” field. The present reawakening relates to the release last fall of the report by the National Research Council's Committee on Materials Science and Engineering. This far-ranging study, popularly known as the MS&E Study, revealed the vitality, opportunities, challenges, and needs in materials science and engineering for the future. Education was one area that received much attention in this study because it is the enabling aspect for the field: no educated, trained personnel — no progress.

When one considers the breadth of materials science and engineering, the problem of designing a unique undergraduate program becomes a major hurdle. The diversity of the field is, on one hand, a major asset in addressing problems but, on the other, a major obstacle to unifying an educational approach. This problem is not new since we have faced it over time as information and knowledge expands. However, the problem becomes magnified as the time frame for the doubling of information decreases. The explosion of information over the past half-century has drastically altered our outlook on materials, and the educational programs have been evolving with the changes. We are now at one of those crossroads where revolution versus evolution becomes a factor, i.e., the need to change basic philosophy and/or approach becomes the issue. If one doesn't consider a breakdown of the current materials classes into subgroups, then a reunification approach becomes not only desirable but absolutely necessary.
The Undergraduate Physics and Materials Science Connection
Authors: Holcomb D.F.
Published: August 2016

Materials science is fundamentally an interdisciplinary field. For purposes of discussing undergraduate preparation for work in materials science, I think it useful to take chemistry, physics, and materials science and engineering as three more-or-less separate disciplines which combine to form the overall field of materials science. The primary reason for this particular taxonomy is pragmatic rather than philosophical. Undergraduate students choose major fields of study on the basis of disciplinary boundaries. Thus, in thinking about undergraduate preparation for work in the overall field, analysis of the present situation and/or recommendations for change must revolve around that reality.

The recent report entitled Materials Science and Engineering for the 1990s (the MS&E Study), sets forth the four elements of materials science and engineering as “structure and composition, properties, performance, and synthesis and processing.” An examination of these specific elements permits us to make useful distinctions among the three disciplines that combine to form the field of materials science. For example, while input from the point of view of physics certainly can contribute rather directly to expansion of our knowledge in the first three areas, its possible contribution to the last is, at best, indirect. To somewhat belabor the point, the research field of condensed matter physics is certainly contained within the field of materials but arguably not part of the discipline of materials science and engineering.

The MS&E Study includes a chapter entitled “Manpower and Education in Materials Science and Engineering.” Within that chapter is a section called “Undergraduate Education in Materials Science and Engineering.”
Developments and Applications for All-Aluminum Alloy Vacuum Systems
Authors: Ishimaru Hajime
Published: August 2016

Aluminum and aluminum alloys have long been among the preferred materials for ultrahigh vacuum (UHV) systems operating in the 10−10–10−11 torr (10−8–10−11 Pa) range. Pure aluminum and aluminum alloys have an extremely low outgassing rate, are completely nonmagnetic, lack crystal structure transitions at low temperatures, are not sources of heavy metals contamination in semiconductor processing applications, have low residual radioactivity in radiation environments, and are lightweight. Because of aluminum's high thermal conductivity and low thermal emissivity, aluminum components can tolerate high heat fluxes in spite of the relatively low melting point of aluminum.

Recently developed aluminum alloys and new surface finishing techniques allow the attainment of extremely high vacuums (XHV) in the 10−12–10−13 torr (10−10–10−11 Pa) range. XHV technology requires the use of special aluminum alloy flange/gasket/bolt, nut and washer combinations, aluminum alloy-ceramic seals, windows, bellows, right-angle and gate valves, turbomolecular pumps, sputter ion pumps and titanium sublimination pumps, Bayard-Alpert ion gauges, quadrupole mass filters, and related aluminum alloy vacuum components. New surface treatment methods and new techniques in welding and extremely sensitive helium leak testing are required. In short, a whole new technology has been developed to take advantage of the opportunities presented by these new vacuum materials. This article describes some of these newly developed fabrication technologies and vacuum materials.

The TRISTAN electron-positron collider constructed at the National Laboratory for High Energy Physics in Japan is the first all-aluminum alloy accelerator, and the first to use UHV technology.
The Electronic Structure of High Tc Copper-Oxide Superconductors from Photoemission Spectroscopy
Authors: Allen J.W. , Olson C.G.
Published: August 2016

This article will summarize the information gained from photoemission spectroscopy (PES) studies of the electronic structure of high temperature superconductor (HTSC) materials, with emphasis on distinguishing models for the normal state. Inverse photoemission spectroscopy (IPES) is a closely related measurement, and taken together PES and IPES yield the single-particle electronic structure, meaning the the spectrum to remove and add electrons, i.e., the electronic ionization and affinity spectrum. It is assumed that the sudden approximation holds, so that the photon event can be characterized by a photoemission cross section σ. The emission from a particular kind of electronic state i can often be identified because its cross section has a particular photon energy (hv) dependence σ (hv).

We will emphasize a few recent results especially pertinent to the conceptual issues posed by these materials, and we will divide the discussion between angle-integrated spectra and angle-resolved spectra. For angle-integrated spectra, electrons are collected from the sample surface in a large solid angle, while for angle-resolved spectra, electrons are collected in a well-defined direction. Angle resolution can be used to select emitted electrons of a particular value of crystal momentum k.
Infrared Studies of the Superconducting Energy Gap and Normal State Dynamics of Y1Ba2Cu3O7 and Ba0.6K0.4BiO3
Authors: Schlesinger Z. , Collins R. T.
Published: August 2016

The discovery by Bednörz and Müller of superconductivity in La20xBaxCuO4 initiated an intense and fruitful search for additional perovskite-based superconducting compounds. Following the discovery and characterization of a number of important new compounds, and the development of techniques to produce them in pure crystalline form, it becomes relevant to carefully measure the fundamental physical properties of well-characterized samples of these new materials. Ultimately the goal of this work is to illuminate the basic physics of these novel materials.

Traditionally many techniques, including critical field measurements, specific heat, penetration depth, magnetic resonance, and tunneling and infrared spectroscopies, have been useful for the study of superconducting elements and compounds. This article discusses the use of infrared measurements to study both cubic BaBiO3 based compounds and layered cuprates. We emphasize the work on the (ideally) stochiometric compound Y1Ba2Cu3O7, because its infrared properties have been obtained by a number of groups with good reproducibility. Infrared measurements are useful both in terms of their traditional role as a probe of the superconducting energy gap and for their ability to probe the dynamics of the normal state by measuring the conductivity vs. frequency in the crucial infrared range (~1 meV to 2 eV).
Materials Challenges in Integrated Optical Recording Heads
Authors: Weller-Brophy Laura A. , Zelinski Brian J.J. , Birnie Dunbar P.
Published: August 2016

Integrated optical recording head concepts show promise for future light-weight and compact optical heads. Several fundamental issues remain to be explored before fully integrated optical heads. become a reality. This article reviews the basic operating principles of integrated optic heads, focusing on the materials challenges inherent in developing both partially and fully integrated optical heads.

Currently available optical mass storage systems provide a feature unavailable in magnetic direct access storage devices (DASD) — removable and interchangeable media. At present, however, this feature is bought at a price, with magnetic storage devices currently outperforming their optical counterparts in access speed and volumetric storage density. The access time of optical drives is greater than 40 ms, compared to the 10–20 ms typical of magnetic DASD. This is, in large part, a consequence of the 50–100 g moving mass of the optical head. The optical head also limits the maximum volumetric storage density, with current heads ranging from about 0.5 cm to more than 2 cm in height.
Birefringence Properties of Polymeric Substrate Materials
Authors: Pisipati Ramesh M. , Schmid Helmut , Kämpf Günther
Published: August 2016

Depending upon the nature of the application, three materials currently dominate the optical substrate market today. Polycarbonate (PC), the most commonly used material, is typically used in disks with diameters up to 120 mm. For larger diameters, the inherent birefringence exhibited by PC interacts with the read laser and results in errors in the read-back signal. For 200 mm and greater, both polymethylmethacrylate (PMMA) and glass are used. Because PMMA is low in inherent birefringence, it is widely used for 200 mm video disks, an application which takes advantage of the manufacturing economies of the injection molding process. For larger diameter data storage disks, however, glass is used because it does not have the disadvantage of relatively high moisture absorption or the low heat resistance of PMMA.

This article will deal with the state-of-the-art in materials used for polymeric substrates. It will focus primarily on polycarbonate and the most significant substrate property currently confronting the field, namely birefringence. Other constraints placed by optical storage technology on the substrate material will be discussed along with new materials and research activities aimed at circumventing some of the current limitations.
Trends in Optical Disk Mastering
Authors: Put Paul L.M.
Published: August 2016

The commercial life of optical disks started in the late 1970s with prerecorded, read-only video disks. The video information was stored on the disks in the form of pits with varying lengths aligned in a spiral track, a structure which lends itself to easy mass replication. The pits were recorded in a “master” disk by exposing a positive photoresist to a focused beam of blue or UV light from a gas laser and subsequently developing the resist. Now, some 15 years later, mass-replicated, read-only video and audio disks still form the most important application of optical disk technology. Today a large majority of the corresponding masters are recorded using virtually the same technique.

In view of the relative importance of prerecorded disks, it is amazing that so little seems to have changed in the mastering processes. Part of the explanation lies in the fact that the dimensions of the relief structures on the early optical disks were defined by what a player could read using relatively cheap optics, rather than by what could be made in the mastering process. If in the beginning the analog video disk system (Video Long Play or LaserVision) was rather demanding, the digital audio disk (compact disk) (see Figure 1a), introduced later, was a much easier system from a mastering point of view. In that period a trend toward cheaper and faster mastering techniques developed, resulting in a few proposals for direct-effect and direct metal mastering. However, in the meantime very high-quality mastering became necessary for the CD-video system and for preformatted data disks. In the CD-video system, the combination of digital audio and analog video leads in some cases to pits as short as 300 nm (see Figure 1b). On preformatted data disks, wide shallow grooves may have to be combined with narrow deep header pits (Figure 1c).
Magnetic Recording Materials: Present and Future
Authors: Berkowitz Ami
Published: August 2016

For more than 40 years, magnetic recording has been the dominant technology for electronic data storage. During this time, the areal storage density on disks has risen to >108 bits/cm2. On tapes the corresponding figure is 0.2 × 108 bits/cm2. Thus each bit uses about a 1.0 μm2 area. These bits are written and read at data rates that require head-disk relative speeds of tens of meters per second and head-tape relative speeds of several meters per second. All this is accomplished at head-disk spacings of ≈0.2 μm and with contact recording for tapes.

It is truly a wonder that the systems work as well as they do. In fact, for many features in magnetic recording systems it isn't certain why they work as well as they do. However, the demand for storage capacity is estimated to be increasing at about 40% per year. So it is natural to ask whether magnetic recording can maintain its present dominant position in the foreseeable future. The answer is — “Very likely, yes” — but this prediction is based on the assumption that a number of formidable fascinating problems will be solved in order to increase the areal bit density.

The five articles in this special issue present the state-of-the-art in those key areas of magnetic recording that involve materials science, and they define the problems involved in increasing storage density. James U. Lemke discusses the background and outlook for magnetic recording.