bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural Evaluation and Molecular Control of Vacuum-Evaporated Organic Thin Films
Authors: Matsushige Kazumi
Published: August 2016

Recently, organic molecules and their complexes with inorganic or metallic materials have drawn many researchers' interest as candidate materials for nanoscale electronic devices of the next generation, especially since Carter's proposal on molecular electronic devices (MEDs) with the functions of gating, switching, memory, etc. in one molecule. However, in order to build such nanoscopic organic electronic devices to replace conventional silicon-based inorganic devices, one must determine how to produce such nanoscale devices and to recognize the electronic states of a single molecule.

The scanning tunneling microscope (STM) developed by G. Binning and H. Rohrer made it possible to visualize atoms and molecules in real space under various atmospheres. In addition, STMs can be used as nanoscopic tools for manipulation of individual atoms and molecules, thus realizing MEDs and nanotechnology.

In this article, we present our recent achievements concerning the STM as well as in situ x-ray diffraction studies on the molecular structure of ultrathin films prepared by vacuum evaporation. STM observations with atomic resolution reveal the mechanism of nuclei formation and the crystal-growth process in organic molecules. Computer simulations based on STM images of polar organic molecules with electronic dipoles have elucidated the role of electronic interaction for their aggregation structures.

Also, nanometer-sized molecular memory can be created by applying an electronic pulse to the evaporated organic films through the STM tip. Furthermore, we discuss the principle of a newly developed in situ total reflection x-ray diffraction (TRXD) apparatus and its application to the evaluation of crystal structure and molecular orientation in organic thin films during the evaporation process, particularly in regard to the role of the substrate, that is, epitaxial growth on organic molecular crystals.
Materials Science in High Magnetic Fields
Authors: Crow J.E. , Parkin D.M. , Sullivan N.S.
Published: August 2016

The recent rapid growth in the emerging areas of magnetic and magnet-related materials research and applications has led to worldwide recognition of the increased importance of research and technology using high magnetic fields. New high-field magnet facilities and major upgrades of existing facilities are being planned and implemented by a number of countries, among them Japan, Germany, France, the Netherlands, Belgium, Great Britain, Poland, Australia, and the United States. Over the next ten years, these developments will advance the state of the art in magnet-related materials science and technologies by a significant quantum jump. Support by many of the national agencies and a strong corporate commitment to stimulate rapid growth in the development of capabilities at higher magnetic fields and in related technologies results in part from an awareness of the impact these technologies will have in developing the new emerging industrial technologies of the 21st century.

The Francis Bitter National Magnet Laboratory (FBNML) at the Massachusetts Institute of Technology has been one of the pre-eminent facilities in developing and advancing science and technology in high magnetic fields. The new U.S. National High Magnetic Field Laboratory (NHMFL) at Florida State University, at the University of Florida, and at Los Alamos National Laboratory builds on the success of existing facilities. NHMFL will provide the necessary environment to develop the next generation of high magnetic fields: 30–50-tesla continuous fields, 60-tesla quasi-continuous fields, and pulsed fields from 60–1,000 tesla. The ability to develop broad user capabilities at these extreme fields is crucial for the advancement of the frontiers of science and of magnet-related industries.
Highly Correlated Electron Systems
Authors: Fisk Z. , Schrieffer J.R.
Published: August 2016

The study of materials which have electronic phase transitions is a very active area. Such phase transitions include charge and spin density formation, as well the superconducting condensation in a rapidly expanding variety of materials. It is now common to lump these phenomena under the heading of correlated electron physics, involving as they do the essential role of electron-electron interactions in their occurrence. There are also materials in which there is found no electronic phase transition, but whose properties indicate strong electron-electron effects, such as a number of the so-called heavy fermion compounds. The part of condensed matter theory which addresses the particular physics of such materials is generally known as many-body physics. How to effectively treat strong electronic interactions theoretically is very much an unsolved problem, and theory does not give much more than limited guidance to the experimental research in this area. External magnetic fields have proved to be effective experimental probes of the properties of such systems, and the advent of increasingly strong pulsed fields is opening new possibilities for exposing and pulling apart the underlying electronic ground state of many such materials.
Environmental Stability of Materials—Issues and Opportunities
Authors: Clark David E.
Published: August 2016

Professor David Kingery, author of the classic text, Introduction to Ceramics, said it well: “Corrosion, like death and taxes in our existence, is inevitable for all materials.” Metals, ceramics, and polymers all undergo change when exposed to the environment. Metals can exhibit electrochemical corrosion, while ceramics and plastics experience primarily chemical corrosion. Although “corrosion” often is used to describe the environmental stability (or instability) of metals, a host of other definitions have been used to characterize the changes that occur in ceramics and polymers.

Definitions can become an issue when scientists from various disciplines work together to solve a problem of national/international importance. One such example involves the description of the surface changes that occur when nuclear waste forms are exposed to an aqueous environment (as might occur in a geological repository). The observed surface changes have been referred to as corrosion, leaching, weathering, degradation, and alteration, to name a few. In early symposia on nuclear waste management, sponsored by the Materials Research Society and the American Ceramic Society, definitions and technical issues were discussed extensively by materials scientists, chemists, physicists, geologists, nuclear engineers, and other professionals. Because of this interdisciplinary interaction, significant advances were made (in spite of disagreements over terminology) in understanding the aqueous alteration of these materials. Much of this knowledge will be useful in other applications where environmental stability is important.

Although aqueous alteration is an important concept in materials corrosion, the topic of environmental stability is much broader. Other important subtopics are erosion, thermal stability, oxidation and radiation damage, and molten metal, glass, and salt corrosion. Finally, environmental instability need not always be bad. Indeed, there are numerous processes and products that work only because of the material's instability in specific environments.
High-Temperature Stability of Non-Oxide Structural Ceramics
Authors: Tressler Richard E.
Published: August 2016

Oxide-based ceramics have long been used as linings in containment vessels for hot materials (metals, glasses, cement, etc.) and hot gases, at temperatures often in excess of 1500°C, because of their chemical compatibility with these hot materials and with the process ambient—conditions where metals and polymers simply can't perform. However, their low thermal conductivities and generally high thermal expansivities cause poor thermal shock resistance. In addition, their creep resistance (resistance to permanent deformation under load) is generally poorer than the more covalently bonded ceramic materials such as nitrides and carbides which also have excellent thermal shock resistance.
The Photovoltaic Challenge
Authors: Sinke Wim C.
Published: August 2016

The term “solar energy” refers to a wide variety of techniques for using the energy available as sunlight. Well-known examples are active and passive thermal solar energy and photovoltaic solar energy but, strictly speaking, hydropower, wind energy, and biomass are also forms of solar energy. Today, only hydropower is used in significant quantities, covering approximately 6% of the world's energy demand. Traditional use of biomass, mainly in developing countries, accounts for more than 10% of the total energy consumption, but is sometimes left out of statistics because it falls outside the category of organized and commercial use.

The global potential for solar energy is huge, since the amount of energy that reaches the earth's surface every year exceeds the total energy consumption by roughly a factor of 10,000. There are, however, various barriers to the large-scale use of solar energy technologies. Most technologies have in common that the power density of the generator is low; in other words, one needs large areas to generate significant amounts of energy. This is especially true for biomass, with typical conversion efficiencies (solar energy to chemical energy) of 1% or less. Further, many solar energy technologies have proved technically feasible, but have yet to be proved economically feasible. Last, but not least, the large-scale use of solar energy requires substantial modification of our global energy supply system, which is based largely on fossil fuels.
Quantum-Well Solar Cells
Authors: Barnham Keith , Barnes Jenny , Haarpaintner Guido , Nelson Jenny , Paxman Mark , Foxon Tom , Roberts John
Published: August 2016

The best present-day single-bandgap solar cells have efficiencies around 20–25%. However, the Carnot efficiency of the earth-sun system is 95%, so there is considerable potential for improvement. The fundamental efficiency limitation in a conventional solar cell results from the tradeoff between a low bandgap which maximizes light absorption and hence output current and a high bandgap which maximizes output voltage. As a result, the maximum theoretical efficiency of a conventional solar cell is around 30% in unconcentrated sunlight at a bandgap close to that of GaAs.

The quantum-well solar cell is a novel approach to higher efficiency. In its simplest form, shown in Figure 1, it consists of a multiquantum-well (MQW) system in the undoped region of a p-i-n solar cell. For light with energy greater than the band-gap Eg, the quantum-well cell behaves like a conventional cell. However, light with energy below Eg can be absorbed in the quantum wells. Our studies show that if the material quality is good, the electrons and holes escape from the wells and contribute to a higher output current at a voltage between that of the barrier and well material. In AlGaAs/GaAs test devices, we have obtained efficiency enhancements of a factor of more than two when cells with quantum wells are compared with identical cells without wells.

The structure in Figure 1 is, of course, essentially similar to the MQW photodiode or modulator structure that operates in reverse bias, and the quantum-well laser that operates in forward bias beyond flat band.
Phenomenological Modeling of Fusion Welding Processes
Authors: David S.A. , DebRoy T. , Vitek J.M.
Published: August 2016

Welding is utilized in 50% of the industrial, commercial, and consumer products that make up the U.S. gross national product. In the construction of buildings, bridges, ships, and submarines, and in the aerospace, automotive, and electronic industries, welding is an essential activity. In the last few decades, welding has evolved from an empirical art to a more scientifically based activity requiring synthesis of knowledge from various disciplines. Defects in welds, or poor performance of welds, can lead to catastrophic failures with costly consequences, including loss of property and life.

Figure 1 is a schematic diagram of the welding process showing the interaction between the heat source and the base metal. During the interaction of the heat source with the material, several critical events occur: melting, vaporization, solidification, and solid-state transformations. The weldment is divided into three distinct regions: the fusion zone (FZ), which undergoes melting and solidification; the heat-affected zone (HAZ) adjacent to the FZ, that may experience solid-state phase changes but no melting; and the unaffected base metal (BM).

Creating the extensive experimental data base required to adequately characterize the highly complex fusion welding process is expensive and time consuming, if not impractical. One recourse is to simulate welding processes either mathematically or physically in order to develop a phenomenological understanding of the process. In mathematical modeling, a set of algebraic or differential equations are solved to obtain detailed insight of the process. In physical modeling, understanding of a component of the welding process is achieved through experiments designed to avoid complexities that are unrelated to the component investigated.

In recent years, process modeling has grown to be a powerful tool for understanding the welding process. Using computational modeling, significant progress has been made in evaluating how the physical processes in the weld pool influence the development of the weld pool and the macrostructures and microstructures of the weld.
Materials Reliability in Microelectronics
Authors: Lloyd James R. , Thompson Carl V.
Published: August 2016

The 20th century has seen considerable technological achievement that has had far-reaching consequences on the way people live and do business. The first half of the century saw remarkable developments in transportation with the automobile and the airplane and in communications with radio and television. These developments would not have been possible without associated advances in materials technology. The second half of the century has been characterized by the development of the computer (see the cover of this issue).

Nineteenth century futurists equated progress with scale. The bigger the better. One can only speculate on what these savants would say if introduced to what we currently call progress. Progress is now measured by how small you can make a device, how narrow you can make a conductor, and how many circuits you can fit onto the point of a pin (see Figure 1).
Electromigration and IC Interconnects
Authors: Thompson Carl V. , Lloyd James R.
Published: August 2016

A modern integrated circuit (IC) is composed of 106 or more electronic devices. They are connected to form a circuit through the use of metallic films patterned into strips which function as wires to interconnect devices. These wires are usually simply referred to as interconnects. In an IC occupying the surface of a 1 cm2 Si chip, there can be 10 m of total interconnect length. This length is in the form of more than 106 line segments contacting pairs of devices and different segments of the circuit. This enormous number of wires is made possible by their small widths. Interconnect widths as small as 0.55 μm are currently used in commercial circuits, and circuits and processes leading to smaller and smaller widths are continuously in development.

During operation of an IC, interconnects carry current densities as high as 4 × 105 A/cm2. This should be compared with a current density of 102 A/cm2, the maximum allowed for house wiring. Thin-film conductors can carry these high current densities only because of the relatively good heat sinking provided by the Si substrate.
Physical Properties of Si02 and Its Interface to Silicon in Microelectronic Applications
Authors: Weber Werner , Brox Martin
Published: August 2016

The development of microelectronic miniaturization has taken an almost revolutionary course. For more than 20 years, important performance features have doubled every one to one and a half years on a per-chip level and, despite some recent economic worries, most people believe that we will see equally rapid progress for at least another 10 years. CMOS technology is making the fastest advances among the different microelectronic technologies and is pushing forward most powerfully. The acronym CMOS stands for Complementary Metal Oxide Semiconductor (chapter 8 in Reference 1) and means that two complementary types of transistor devices carry a current for complementary bias conditions. A device of this kind often used for switching purposes is drawn schematically in Figure 1. It uses a control electrode, called the gate, to switch a current flow from the terminal source to the terminal drain. The channel can be made conducting depending on the potential applied to the gate which is separated from the semiconductor by an insulating dielectric layer, namely amorphous SiO2. Control is via a field effect; for example, in one of the two complementary types of devices, a positive gate voltage can draw negatively charged electrons toward the interface, which causes conduction from the source to the drain through the otherwise blocked source and drain contacts.
Relaxation in Aqueous Foams
Authors: Durian D.J.
Published: August 2016

Aqueous foams are macroscopically homogeneous complex fluids composed of co-existing gas and liquid phases. A hierarchy of structure and self-organization at progressively smaller length scales is ultimately responsible for the unique material properties of foams, and is shown schematically in Figure 1. A key feature of this microstructure is the continuous random network of liquid which typically occupies 1–10 vol% and separates the tightly packed gas bubbles. As shown by the photographs in Figure 2, the average bubble diameter can vary widely from about 10 μm to 1 cm, while the average bubble shape can vary from nearly spherical to nearly polyhedral, depending on the liquid volume fraction. At the smallest structural scale, surface active molecules are preferentially adsorbed at the gas/liquid interfaces and give rise to several physical-chemical effects that deter the coalescence of neighboring bubbles and thereby lend stability to the foam. However, the delicate structure formed by gas bubbles packed in a continuous liquid phase is not truly stable with either time or applied forces. This article reviews recent progress in understanding the structural response of aqueous foams to temporal and mechanical perturbations.
Structure of Mesoporous Aerogels
Authors: Schaefer Dale W.
Published: August 2016

Several emerging technologies depend on the development of porous materials with pore dimensions in the nanometer range (1 nm = 10 Å). Based on the canonical classification scheme, such materials are defined as “mesoporous materials.” Specialty uses, such as separation applications, require porosities engineered to meet stringent pore-size requirements, particularly for separating high-boiling-temperature or-ganics. In addition, commodity products, such as high-performance thermal insulation, await credible manufacturing methods to produce fine-scale pores. Finally, information discovered during the development of mesoporous materials could be helpful in finding new strategies to generate void-free ceramic materials by reverse engineering.

Although several methods exist to generate nanometer porosity, our ability to tailor porosity for specific applications is still primitive. Because we lack adequate structural data and models for pore formation, the relationship between synthetic protocol and pore structure remains enigmatic.
Photorefractive Materials
Authors: Agulló-López F.
Published: August 2016

There is a growing demand for nonlinear optical materials for a variety of applications—lasers and coherent sources, electrooptic devices, communication technologies, and optical processors and computers. Nonlinear optics is a vast field requiring materials with diverse performance features. Photorefractive (PR) materials, which experience a change in the refractive index under the effect of inhomogeneous illumination, constitute a relevant branch of the field. They behave as third-order nonlinear materials, which can be considered, in general, as photorefractive. However, the materials more commonly designated as photorefractives involve a charge-transport-induced nonlinearity, and it is these materials which are the object of this issue of the MRS Bulletin.

At variance with conventional (often designated as Kerr) nonlinear materials, photorefractives are sensitive not to the local light intensity but to its spatial variation; i.e., they are nonlocal materials. This feature makes them more complicated to deal with than their conventional counterparts, since a χ(3) susceptibility cannot be properly defined (except as a k-dependent function). On the other hand, this sensitivity gives them some unique and interesting features. In particular, an interference light pattern illuminating the crystal and the generated index grating are phase-shifted, leading to remarkable beam coupling and amplification effects. The coupling gain can be markedly enhanced by applying alternating electric fields or by oscillating the interference fringes with a piezoelectric mirror. Efficient image amplifiers have been made using this effect.
Bulk Photorefractive Semiconductors
Authors: Delaye Ph. , Von Bardeleben H.J. , Roosen G.
Published: August 2016

The photorefractive (PR) effect has been studied for more than 25 years and many applications for optical signal processing such as correlation, real-time holography, dynamic interconnections, and optical memories have been developed. The main focus of study for the PR effect has been oxides (ferroelectrics and sillenites) in which the useful spectral range lies in the visible. Applications for telecommunication systems and eye-safe devices have required extending the spectral range into the near infrared (1.0 to 1.5 μm), and so the exploration of different materials. It has been shown that the bulk semi-insulating III-V semiconductors GaAs and InP, and more recently the II-VI compound CdTe, were efficient materials for this spectral range. III-V materials offer the advantage of availability as bulk semiinsulating materials of high crystalline perfection and homogeneity regarding their electrical properties due to their importance as substrate materials in micro and optoelectronic technology. However, these materials have not been optimized for PR applications, so quantitative analyses of PR experiments related to the specific material defect properties are necessary for further developments. It has equally been shown that the PR effect can be used as an efficient tool for materials characterization.
Optical Computing and the Role of Photorefractive Crystals
Authors: Selviah D.R.
Published: August 2016

“Optical computing” is a term which has been used to describe many types of optical systems. This article concentrates on one optical computer design which appears to be particularly promising and competitive with digital electronic systems and which can use photorefractive (PR) crystals. We begin by discussing the motivation for constructing optical and optoelectronic computing systems and go on to describe two approaches to constructing optical computers. The first does not use PR crystals as yet but serves to indicate other approaches. The second approach involves the operation of one type of optical neural network. We discuss in detail the recording of holographic memories in a PR crystal for inclusion in the optical neural network described here.
Pulsed Laser Deposition: Future Directions
Authors: Venkatesan T. , Wu X.D. , Muenchausen R. , Pique A.
Published: August 2016

Despite the discovery of the laser a few decades ago, the potential for pulsed laser deposition (PLD) of thin films has remained unexploited. Despite the sustained pioneering work at Rockwell in laser deposition, it took the development of high-temperature superconductors to fully realize the technique's potential. Early work on PLD of high-temperature superconductors demonstrated for the first time that the composition of rather complex multi-elementary materials can be reproduced in the deposited film under appropriate conditions of laser energy density and deposition angle. These features made PLD unique; and once the recipe for making in-situ crystalline films of proper stoichiometry was known, the technique's popularity was significantly enhanced in the research community.

The features of laser deposition that make the process so unique, and that are discussed throughout this issue, are recapped below:

1. Rather complex multi-elementary materials can be deposited well if a single-phase, homogeneous target can be fabricated. The complexity of the deposition process is translated to the relatively easier process of fabricating a high-quality target.

2. The chamber pressure, target-substrate distance, target orientation with respect to the laser beam, etc. are significantly de-coupled, enabling significant freedom in deposition system design. The target is decoupled from the substrate in the sense that a small target can be used to deposit film over a fairly large area substrate with the appropriate scanning schemes.

3. The efficiency of the target use is superior compared to any other technique since a predominant amount of the evaporated material is forward directed and can be collected with a high degree of efficiency. For example, in a production environment, more than 100 YBCO films (ranging 3,000-4,000 Å thick) on 1 × 1 cm2 substrates have been fabricated from a 0.25-inch-thick one-inch target with a majority of the target still left over. The cost of raw materials in a production environment may become significant, and for toxic elements particularly there is a further advantage in minimizing the spread of contaminants.
Up Close: Centra Nacional de Microelectrónica
Authors: Lora-Tamayo E. , Alvarez M.D.
Published: August 2016

The Spanish National Microelectronics Center (Centra Nacional de Microelectrónica or CNM), a nonprofit R&D institute, was established in 1985 through the joint efforts of the General Directorate of Science (Ministry of Education) and the General Directorate of Electronics and Computer Science (Ministry of Industry and Energy).

As a scientific research center, the CNM belongs to the Spanish Science Research Council (Consejo Superior de Investigaciones Cientifícas, CSIC), but differs from other CSIC centers in two ways. CNM is a direct spinoff of a nationwide scientific and technological research program (Programa Nacional de Microelectrónica), and it has its own board of trustees with representatives from different ministries (Education, Industry and Energy, Defense, and Communications); from the local governments of Catalonia, Andalusia, and Madrid; and from microelectronics-related industries.

CNM's activities are channeled toward promoting microelectronics in Spain through scientific and technological research on the design and fabrication of integrated circuits, electronic devices, and related materials, while providing technological support for industry and university research groups. The global objectives are as follows:

∎ Establishment of stable quasi-industrial technologies in technological niches that permit good interaction between CNM and industry. Among those niches, fixed by Spain's national industrial policy, are application-specific integrated circuits (ASICs), power devices, semiconductor sensors, and molecular beam epitaxy (MBE) technologies and associated devices.

∎ Startup of precise technological processes or new IC design techniques through cooperative research projects with industry and/or university groups that involve carrying out research and technology development tasks, renewing established technologies, and the continuing training of researchers.
Teamwork and Statistical Quality Control at Owens-Corning Fiberglas Corporation
Authors: Choudhary Manoj K.
Published: August 2016

The terms “teamwork” and “statistical quality control” (SQC) have become an established part of U.S. manufacturing vocabulary, though not necessarily of manufacturing practice. Much has been written on these subjects, as even a cursory glance at the literature reveals (e.g., see References 1–11). This article will describe the organization and functioning of an SQC team at Owens-Corning Fiberglas Corporation. My observations are not necessarily novel, but I hope they provide some useful insights into team building, teamwork, and SQC in a U.S. manufacturing environment.

SQC is not a new concept at all, but it was largely ignored in the United States. The contribution of SQC (more accurately, Deming's and Juran's SQC precepts) to Japanese manufacturing quality has by now become a matter of folklore. This does not mean, however, that the SQC “philosophy” is correctly understood by U.S. companies. SQC is often viewed too narrowly as a production tool, or S and C in SQC are given undue attention. SQC is much more than a collection of statistical techniques. Indeed, the major impact of SQC results not from its engineering or technical attributes but from the changes it brings about in attitudes and in a factory's social organization. Drucker has identified SQC as one of the four concepts in the emerging theory of manufacturing.
Quality Architecture: A Concept for Quality Manufacturing
Authors: Bird L. , Frederick S.
Published: August 2016

An engineer or a research scientist developing a new process is not often encouraged to build quality systems into the product or manufacturing process. However, today's market places greater emphasis and focus on stability and reliability of manufactured products. Corning has developed “quality architecture” to help engineers and scientists define and build the system elements that allow quality to be built into a product, rather than rely on inspection. A researcher or engineer can then provide a first-generation prototype of the quality systems, in addition to the first-generation prototypes of equipment and processes.

What is Quality Architecture?

Quality architecture involves designing a system that controls the manufacturing process in a stable and consistent manner, and provides for continuous improvement. The architecture defines and ensures the appropriate interdependence between product specifications, materials used in and by the process, product and process measurements, statistical process control and information systems. This results in a consistent and reliable product—features valued in today's market.
Earth Materials
Authors: Ewing Rodney C. , Navrotsky Alexandra
Published: August 2016

This issue of the MRS Bulletin is devoted to Earth materials — a subject so broad and with such a long history, stretching back to man's first use of materials, that we can offer only a small sample of topics, only a partial review. As our ancestors fashioned the first crude tools from stone, they must have distinguished among materials on the basis of their physical properties. They classified materials by color and density and very early must have wanted more than Nature had provided. They began to synthesize and fashion their own materials. Today's nanoscale engineering of materials is part of this same quest—a continuous evolution of this early toolmaking.

Thus, Earth materials were the first raw materials—and the first subjects of study and classification in materials science. Probably one of the earliest materials scientists to make quantitative observations was Nicolas Steno (1638–1686, actually Nils Stensen, a Dane by birth), who was among the first to note the “law of constancy of angle” in comments which accompany his drawings of quartz and hematite crystals (De Solido intra Solidum Naturaliter Conteno Dissertationis Prodromus, 1669). Such observations were the first clues to understanding the internal structure of solids. Steno was also a keen geological observer. He is given credit for the first statement of the law of superposition of sedimentary strata. The first quantitative experiments on the origin of minerals grew out of studies of glass and ceramics. French mathematician René-Antoine Ferchault de Réaumur (1683–1757) tried to determine the composition of Chinese porcelain by melting minerals and rocks.
Fundamental Concepts of Ion-Solid Interactions: Single Ions, 10−12 Seconds
Authors: Davies J.A.
Published: August 2016

An energetic ion undergoes two major mechanisms of energy loss: (1) screened Coulomb collisions with target atoms (nuclear stopping), and (2) interactions with bound or free electrons in the solid (electronic stopping). This article discusses how these two energy-loss processes—and related quantities such as the ion range, collision cascade behavior, sputtering, and spike effects—depend on the experimental parameters of beam energy, atomic number, and target density. We restrict ourselves to an individual incident ion and a time scale (~10−12 s) sufficient for the cascade to fully develop (Figure 1), but short enough for subsequent quenching or diffusion processes to be ignored. What happens at longer times and higher ion f luences, due to diffusion and cascade overlap phenomena, is treated in the article by Brown and Ourmazd in this issue of the MRS Bulletin.

Energy-Loss Concepts

Figure 2 summarizes the velocity (ε1/2) dependence of the two energy-loss processes, nuclear stopping (dε/dρ)n and electronic stopping (dε/dρ)e, in terms of the dimensionless Thomas-Fermi (TF) energy, ε, and length, ρ, units derived by Lindhard. The energy unit ε is defined as the ratio a/b where a is the TF screening length (typically, ~0.01 nm) and b is the distance of closest approach in an unscreened head on collision. The following simple relationship exists between TF and lab energies.

where M1, Z1, M2, and Z2 are the masses and atomic numbers of projectile and target atoms.
Mechanisms of Stress-Induced and Electromigration-Induced Damage in Passivated Narrow Metallizations on Rigid Substrates
Authors: Korhonen M.A. , Børgesen P. , Li Che-Yu
Published: August 2016

Narrow, passivated metal lines are generally used as interconnects in VLSI microcircuits at the chip level. In most metals, high electric current densities lead to a mass flow of constituent atoms accompanying the current of electrons. Electromigration (EM) has long been considered an important reliability concern in the semiconductor industry because the current-induced atomic fluxes can give rise to void formation and open circuits, or hillock formation and short circuits between nearby interconnects. The problem is exacerbated because of the continued trend of increasing the density of the devices on the chip. This means that the line widths of the interconnects have been reduced and are now in the submicron range; correspondingly, the current densities have increased and may be as high as 106 A/cm2. Recently, thermal-stress-induced damage in metallizations has also been recognized as an important reliability concern, perhaps of the same gravity as EM. Thermal stresses in the metallizations are caused by the different thermal expansion coefficients of the metal and the substrate. Stress-induced void and hillock formation are the main causes of in terconnect failures before service. More recently, concern has been growing that thermal stresses or thermal-stress-induced voids may enhance the subsequent electromigration damage during the service life of the microchips.

For simplicity, this article addresses the case of pure aluminum metallizations on oxidized silicon substrates. However, much of what is said applies to other metal-rigid substrate systems as well, most notably to various aluminum and copper-based metallizations on ceramic substrates. The present treatment emphasizes void formation and growth in the metallizations during nd after cooldown from elevated temperatures, or those due to electromigration in service or testing conditions. Many of the mechanisms we explain are also applicable to hillock formation under compressive stresses, whether due to EM or thermal cycles during manufacturing.
Important Considerations for Processing Bi-Based High-Temperature Superconducting Tapes and Films for Bulk Applications
Authors: Hellstrom Eric E.
Published: August 2016

High-temperature superconductors are brittle oxide ceramics, yet they have been made into wire that has been wrapped into solenoids and used in demonstration magnets and motors. Fabricating wires from these ceramics is an extremely challenging materials science process that requires a precisely engineered microstructure with the correct chemical, mechanical, and electromagnetic properties if these wires are to transport large current densities (Jc) in high magnetic fields. Heine et al. first demonstrated that wires of these materials could carry high Jc in very high magnetic fields. At 4.2 K, the oxide superconducting wires can carry higher Jc at higher magnetic fields than conventional Nb-Ti or Nb3Sn wires (Figure 1), and as shown in the companion article in this issue by Kato et al. they can also have high Jc at 77 K.

Of the three major families of high-temperature superconductors, YBa2Cu3O7-x, Bi-Sr-Ca-Cu-O (BSCCO), and Tl-Ba-Ca-Cu-O, the best wires to date have been made in the BSCCO system. At present, all YBa2Cu3O7-x wires are weak linked and have only small Jc in magnetic fields. In the Tl-based system, the superconducting properties are potentially very interesting, but the toxicity of Tl and the system's complex processing have limited conductor development. For the Bi-based system, the basic processing steps are becoming known, the grains are well connected, and the weak link problem can be controlled. This permits applications in the temperature range 4–77 K, depending on the field and current density requirements of the particular use.
“Materials” Education: The Second Time Around
Authors: Roy Rustum
Published: August 2016

Robert Sproull, the director of AREA (Advanced Research Projects Agency) in the Pentagon, recorded that Pennsylvania State University and Carnegie Institute of Technology first made proposals in 1957 for “interdisciplinary block funding” in what would essentially become “materials” research. But it was the industrial push (by W.O. Baker of AT&T Bell Laboratories and C.G. Suits of General Electric) that helped ARPA start the funding of 12 interdisciplinary materials research laboratories (IDMRLs) between 1960 and 1963. Pennsylvania State University was added in 1963 as a special modest grant limited to materials preparation (synthesis and processing). NASA and the Atomic Energy Commission added six more within two years. The first interdisciplinary degree program in “materials” (then called solid-state technology), administered directly by a graduate school committee drawn from 10 departments, was started under my chairmanship, at Penn State in 1959-60. Probably the first departmental degree program in which a metallurgy department expanded its scope (and changed its name) to include other materials was started at nearly the same time at North western University by Prof. M.E. Fine. It is noteworthy that at least in these two cases the intellectual and curricular argument for integration of degree work preceded the research grants and organization. These two separate patterns have both now permeated the entire national system, and we should clearly distinguish between them. By 1969 the first national colloquy on materials, held at Penn State and published under the title Materials Science and Engineering in the U.S., took an evaluative look at materials education.
Materials Science and Technology: A Model for Achieving National Education Goals
Authors: Hays Irene D.
Published: August 2016

In April 1991, President Bush unveiled “America 2000,” a national strategy for improving the overall performance of students in America's school system. He and the nation's governors developed the strategy as a result of the historical Charlottesville Summit, held in Virginia in 1989.

America 2000 focuses on six national education goals, three directly related to mathematics and science education. Goal 4, in particular, states that “by the year 2000, US. students will be first in the world in science and mathematics achievement.” By the Year 2000, the report of the Federal Coordinating Council for Science, Engineering, and Technology (FCCSET) Committee on Education and Human Resources (CEHR) details the federal government's strategic objectives for meeting this goal.

The primary objectives outlined in the report focus on (1) improving student performance, (2) providing a strong precollege work force, (3) ensuring an adequate pipeline for the science and engineering work force, including increased participation of underrepresented groups, and (4) improving public science literacy. I'll discuss later how a revolutionary materials science and technology curriculum developed by Pacific Northwest Laboratory (PNL) and Northwest teachers has proved to be a model for meeting these objectives.

The FCCSET/CEHR report identified precollege as the educational level receiving the highest priority. At this level, the strategy for achieving the objectives is structured around (1) improving teacher preparation and enhancement, (2) reforming curricula, (3) organizing systemic reform, and (4) providing student incentives and opportunities.
Problems in Engineering and Science Education: Why Do We Have a Weakness in Materials Synthesis and Processing?
Authors: Eagar Thomas W.
Published: August 2016

A 1989 report by the National Research Council (NRC) entitled, Materials Science and Engineering in the 1990s: Maintaining Competitiveness in the Age of Materials, strongly emphasizes that the United States as a nation has devoted insufficient resources to materials synthesis and processing, yet it fails to suggest why. If we are to correct such an imbalance, it is essential that we understand the cause so we can effect a solution.

In my opinion, the cause of our failure to place sufficient emphasis on synthesis and processing is more fundamental than the study of materials science and engineering alone; it is symptomatic of the way we teach all science and engineering. We have failed to instill balanced attitudes of inquiry within our students. They have emulated our academic approach to defining and solving problems, an approach that works very well in academia but unfortunately is not always effective in the world of business and manufacturing. As a result, to be successful in the commercial sector, the young engineer or scientist must “unlearn” much of what has been taught in the universities.
Art-and-Technology: Recent Efforts in Materials and Media
Authors: Piene Otto
Published: August 2016

To avoid misinterpretation, the term “art-and-technology” should be hyphenated because we are looking at an integrated art form which developed, roughly, during the past 70 years (since Naum Gabo's virtual volume, Kinetic Construction, Berlin, 1920). Art-and-technology results from “incorporated” contributions of art, science, and technology or, better, from artists, scientists, and engineers (plus industry, business, government, etc.). Although art-and-technology has frequently been bad-mouthed or even pronouned “dead” by advocates and practitioners of pure art as well as science and technology, it is alive and well and enjoying more vitality, variety, and expansion than ever before. It is currently the only expanding field in the arts; it feeds vitally into technology and industry—most visibly in entertainment but it also provides stimulus beyond fun to areas of science and engineering where “art applications” have abounded since the advent of photography and its vast consequent uses in science.

We can claim an eloquent tradition for art-and-technology in ancient historic, cultural manifestations such as the Egyptian pyramids and their “environmental” scale or the Greek theater with its elaborate stage machines. We are aware of elements of that tradition when we observe contemporary art-and-technology such as sky and space art (Figures 1 and 2), computer-generated virtual reality, performance with medical inquiry and medical apparatus, and art concepts inspired by molecular biology (Figure 3). Emphasis of search—whether artistic/expressive, conceptual/philosophical, or inquisitive/scientific—depends on taste and motivation. However, Leonardo is an undisputed idol to both artists and scientists.
Coulomb's Data on Harpsichord Wire
Authors: Goodway Martha , Savage William R.
Published: August 2016

Charles-Augustin Coulomb published data on the size, strength, and stiffness of harpsichord wire available in Paris in the late 18th century which has not been cited in the literature on musical instruments despite this century's revival of baroque music and the instruments upon which it was played. During an investigation of the internal friction of several antique music wires by means of a torsion pendulum similar to the one invented by Coulomb and first described in the 1784 mémoire (Figure 1), it occurred to us to ask what Coulomb had used as the suspensions in his pendulum. His biographer, C.S. Gillmor, mentioned “harpsichord strings”, and in Coulomb's 1784 Torsion mémoire we found: J'ai pris trois fils de clavcin, tels qu'on les trouve répandus dans le commerce, roulés sur des bobines, et numerotés (“I used three harpsicord wires, such as one finds distributed in commerce, wound up on spools, and numbered”).

The spools of wire recently discovered in the stand drawer of a harpsichord in France fit Coulomb's description. The instrument was built in Paris in 1732 by Antoine Vater, and the wire found with it was wound up on small wooden spools similar to spools for thread. The spool of red brass wire had a mark punched in one end and the spool of iron wire had the gauge size (No 5) written on it in ink, while the spool of yellow brass wire had neither mark nor number. Samples of the wires from these three spools, generally agreed to be of 18th century manufacture, were collected by J. Scott Odell of the Smithsonian Institution as part of a research project which he initiated into the physical properties of antique wire. With these samples in hand it was possible to measure certain of their properties and to compare these properties with those reported in Coulomb's Torsion mémoire in 1784. Since Coulomb's wire was undoubtedly of 18th century manufacture (a degree of confidence that we do not always have with collected samples), and the data were taken not long after the wire was drawn, comparison with the Vater wire allows us to detect if, during two centuries, significant changes occur in highly drawn wire.