bluuebunny/crossref_metadata_2025 huggingface dataset:
Trends in Advanced Materials Data: Regularities and Predictions
Authors: Rodgers John R. , Villars Pierre
Published: August 2016

Recently, there have been a number of reports identifying technologies of strategic importance. These technologies, which reflect the full range of national critical technology needs, are: materials, manufacturing, informatics and computing, biotechnology/life sciences, aeronautics/surface transport and energy/environment. In support of these technologies there has been much discussion on their research infrastructure, e.g., instrumentation, telecommunication networks, and supercomputing facilities. With the exception of biotechnology/life sciences, however, there has been little discussion on the uses of evaluated numeric and factual databases at the research level. The uses of databases are more advanced in biotechnology and life science research than in other fields, and this has been driven by the needs of genetic research, protein engineering, and drug design, where researchers need data and models for the design of new products. The needs of databases and their manipulation tools in materials science research are also essential in developing an intelligent research infrastructure. Given the present financial constraints, there is a need to use existing funds more efficiently and effectively. One way to achieve this is to use all available experimental data from various intersecting disciplines and bind them together with knowledge which will aid in the design of new materials.
Data Compilation, Analysis, and Access: The Role of the Computer
Authors: Westbrook J.H.
Published: August 2016

History is replete with examples of the enormous impact of data compilations in all fields of science and technology. The advantages and opportunities such aggregations confer include:

• convenience of access,

• condensation and homogenization of raw data,

• formats tailored for the application,

• perception of patterns,

• detection of errors,

• definition of gaps and inconsistencies, and

• basis for formulating and testing theories.

The opportunities in materials science, and specifically in the subfield of alloy design, are no fewer than in other fields of science. Indeed, as I have remarked in a review of the history of the development of understanding and application of intermetallic compounds, breakthroughs in this field have usually come about not from “a new technique, a unique experimental observation, or an abstruse theory… Rather it was the amassing of a critical volume of experimental data in the literature which permitted an individual with great insight to perceive an underlying pattern not previously apparent.”
Portuguese-Spanish Collaboration on LiNbO3
Authors: Soares J.C. , Agulló-Lopez F.
Published: August 2016

Since 1987, an intensive Portuguese-Spanish collaboration program has been developed on microstructural characterization of LiNbO3 by nuclear (ion-beam and hyperfine interaction) techniques. The collaboration involves the Department of Applied Physics of the Universidad Autónoma de Madrid, on the Spanish side, and the Center of Nuclear Physics and the Department of Physics of LNETI, on the Portuguese side. The combined effort of the two latter institutions is now channeled through the recently created Center for Materials Characterization and Processing.

LiNbO3 is an important material for optoelectronic applications, including light modulation, microwave filters, frequency doublers, and those applications based on the photorefractive effect. Photorefractive applications, still at the laboratory level, include holographic information storage, coherent beam amplification, beam deflectors, and applications relying on the production of phase-conjugated beams by four-wave mixing. LiNb03 is particularly useful for optical information processing, optical interconnects, associative memories, and neural net implementations. These applications involve bulk LiNbO3, but mostly waveguide structures fabricated in LiNbO3 substrates. Recently the development of efficient waveguide lasers on ion-implanted and proton-exchanged waveguides has opened a new field whose final objective is the fabrication of integrated laser modulators and frequency doublers on the same “chip.” The mastering and optimization of all these applications rely on an adequate microstructural characterization of the material with particular reference to both intrinsic and extrinsic point defects. The knowledge and control of this microstructure should permit the fabrication of well-characterized and reproducible devices.
Research on Cement-Based Materials: Expanding Our Horizons
Authors: Young J. Francis
Published: August 2016

Concrete is the most widely used man-made product; in the United States we use about two tons per year per person. It has been estimated that the replacement value of concrete structures is over six trillion dollars, and that over one trillion dollars needs to be spent in the repair and rehabilitation of these structures over a 20-year period. By contrast, the resources devoted to the materials issues of the industry have been meager. This neglect may in part explain why the development of the science of cementitious materials had lagged behind that of other materials. The situation has been changing rapidly in recent years, however, and the articles in this issue have been selected to illustrate some of the advances that are being made.

One key to the resurgence in research in cement-based materials is the realization of the pressing need to upgrade our deteriorating infrastructure. Another is the realization that a materials science and engineering approach is needed to provide a solid knowledge base to underpin new technologies. Chemistry took us a long way in the 1950s and 1960s, but an appreciation of how chemistry and processing could combine to create desirable micro-structures that would achieve desirable bulk properties came much later. It is significant that, with the noticeable exception of the Pennsylvania State University, cement research in universities in the United States previously was funded through civil engineering departments. Similarly, in Europe and Japan, research was conducted primarily in engineering faculties, although there were programs in a few chemistry departments. Now, however, on both sides of the Atlantic Ocean, research groups are well established in materials science departments. It is noteworthy that on an NSF Science and Technology Center devoted to advanced cement-based materials is funded through the Division of Materials Research.
Material Considerations in Musical Strings
Authors: Pickering Norman C.
Published: August 2016

Strings for musical instruments seem to be among the simplest of devices. Textbooks on acoustics commonly use them as the most elementary example of a vibrating system. However, the assumptions often made to simplify mathematics are far from the conditions that exist in real strings made of even the most suitable materials available.

Consider what a musician wants in any instrument: as wide a frequency range as practical; considerable acoustic power with a significant difference between loud and soft notes; and, if possible, the ability to play several notes at once. The last requirement dictates the presence of multiple oscillators. Long, thin strings in closely-spaced groups fit the bill, but they are inherently deficient in meeting the other criteria without help from additional devices.

Direct acoustic output from a vibrating string is negligible because it alone cannot move enough air. This deficiency has been corrected in hundreds of ingenious ways over thousands of years by mechanical coupling to a light, stiff structure large enough to radiate the lowest pitch being produced, often incorporating air-cavity resonators tuned to enhance low-frequency output. In this electronic era, unlimited power can be obtained using transducers to detect string motion as electrical voltages that can be amplified and directed to loud-speakers.
Graphite-Epoxy Acoustic Guitar Technology
Authors: Decker John A.
Published: August 2016

We have successfully developed an acoustic guitar (Figure 1) composed of graphite. Trademarked the RainSong® graphite guitar, this instrument uses no endangered tropical tonewoods. The instrument's sound quality is equal to that of a fine wooden guitar. At high frequencies, the clarity, sustain, and play-ability surpasses that of wooden guitars. Because of its construction, the instrument is sturdy and is impervious to humidity, heat, and water.

The development of this guitar required analysis of the theory of anisotropic sound propagation in the guitar soundboard and body, and resulted in two patents. We designed prototype guitars in collaboration with Pimentel & Sons, Guitar Makers, and used combinations of unidirectional and woven graphite and aramid fibers in an epoxy-resin matrix.

The goal of our project was to accurately duplicate—panel by panel—the acoustic properties of a fine wooden guitar. We had the resulting acoustic modes and frequencies verified in the laboratory. We then developed and constructed open-mold and resin-transfer molding tooling for a family of classical, steel-string acoustic and hollow-body electric guitars, which are now in commercial production.

Possibly the first all-composite acoustic guitar, the RainSong® represents a fundamental change in stringed-instrument construction, perhaps the first since the 17th Century Italian masters.

The RainSong® technology allows musicians to skirt the effects of climate and transport damage on their instruments. The instrument contains essentially no wood, and hence negates environmental concerns about rapid depletion of the virgin-forest woods, from which stringed instruments have traditionally been made.
Why In Situ, Real-Time Characterization of Thin-Film Growth Processes?
Authors: Auciello Orlando , Krauss Alan R.
Published: August 2016

It is anticipated that a new generation of advanced electronic and optical devices will involve the synthesis of diverse materials in single or multielement thin-film form, or in layered heterostructures. These devices will most likely involve diverse materials such as high-temperature superconductors, ferroelectric, electrooptic, and optical materials; diamond; nitrides; semiconductors; insulators; and metals in the form of ultra-thin layers with sharp interfaces in which the layer thickness may reach atomic dimensions. Therefore, it becomes increasingly important to be able to monitor the deposition process in situ and in real time, particularly for complex multicomponent oxides or nitrides, in which the production of the desired phase is a highly sensitive function of the growth conditions, often requiring relatively high-pressure oxygen or nitrogen environments up to several hundred mTorr, and in some cases, several Torr. Consequently, the growth environment for many of these materials is incompatible with conventional surface-analytic methods, which are typically restricted to high-or ultrahigh-vacuum conditions. New deposition and analytical methods, or adaptation of those already established, will be required.

Since thin-film growth occurs at the surface, the analytical methods should be highly surface-specific, although sub-surface diffusion and chemical processes also affect film properties. Sampling depth and ambient-gas compatibility are key factors which must be considered when choosing in situ probes of thin-film growth phenomena. In most cases, the sampling depth depends on the mean range of the exit species (ion, photon, or electron) in the sample.
Time-of-Flight, Ion-Beam Surface Analysis for In Situ Characterization of Thin-Film Growth Processes
Authors: Krauss Alan R. , Auciello Orlando , Schultz J. Albert
Published: August 2016

Low-energy (5–15 keV) ion scattering spectroscopy (ISS) and direct recoil spectroscopy (DRS) are well-established analysis techniques that have been used for several years to characterize surfaces of materials. ISS utilizes a beam of ions in the 1–15 keV range which are scattered by a surface atom at an angle θ1 relative to the direction of incidence. In this energy range, the collisions are elastic and are described by classical two-body collision kinematics. The kinetic energy E1 of the scattered primary ion is given by

where E0 is the primary ion kinetic energy and α = M2/M1. Note that Equation 1 has real values only if M2 > M1, and ISS is not able to detect surface atoms which are lighter than the primary ion beam.

The kinetic energy of the backscattered primary particle may be measured either by using an electrostatic energy analyzer (ESA) or by pulsing the beam and using a time-of-flight (TOF) detection scheme. The ESA only detects the ion fraction (typically 10 2−10−4) of the scattered primary beam and transmits only a narrow portion of the energy distribution of these ions, whereas the TOF detection scheme simultaneously detects the full energy range of both ions and neutrals. Consequently, the required beam dose for TOF detection is 3–4 orders of magnitude smaller than that required by the ESA. A typical analysis beam dose for TOF detection is ∼1011−1012 ions/cm2, removing or displacing one part in 103−104 of the near-surface atoms and making the TOF scheme essentially nondestructive.
Laser-Reflectance Interferometry Measurements of Diamond-Film Growth
Authors: Zuiker Christopher D. , Gruen Dieter M. , Krauss Alan R.
Published: August 2016

The remarkable properties of diamond, including its hardness, chemical inertness, high thermal conductivity, low coefficient of friction, optical transparency, and semiconducting properties, have led to considerable research in the area of diamond thin-film deposition. Diamond films have been characterized ex situ by a large number of diagnostic techniques including Raman spectroscopy, x-ray diffraction, SEM, and TEM. In situ diagnostics, which can provide information in real time as the film is growing, are less common.

Laser-reflectance interferometry (LRI) has been used to monitor the growth of diamond films in situ. The technique involves measuring the intensity of a laser beam reflected from the substrate surface on which the film is growing. The reflected beam is the sum of beams reflected by the gas-diamond interface and the diamond-silicon interface. Oscillations in the reflectivity are observed as the film grows because of interference between the reflected beams. Each oscillation indicates an increase in film thickness of λ/2n, where λ is the laser wavelength and n is the index of refraction of the film. If the index of refraction of the film is known, the thickness and growth rate can be determined in situ. For LRI measurements with 632.8-nm-wavelength HeNe lasers, the index of refraction of diamond films has been found to be within 10% of the bulk diamond value of 2.4. Each oscillation therefore indicates an increase in film thickness of 0.13 μm.

The reflectivity measured by LRI is also affected by scattering because of surface roughness.
Total-Reflection X-Ray Fluorescence Spectroscopy for In Situ, Real-Time Analysis of Growing Films
Authors: Roberts T.A. , Gray K.E.
Published: August 2016

For many thin-film applications it is useful or necessary to accurately monitor and control the film's physical properties. Particularly important are composition and structure, which determine most of the material's properties. Examples include the semiconducting properties of SixGe1−x, the ferroelectric properties of BaTiO, and the superconducting properties of Bi2Sr2CaCu2Oy, all of which depend strongly on composition. The development of in situ analyses not only provides the possibility of feedback control during deposition, but also assists in a more efficient evaluation of the best processing conditions to achieve particular properties. Control of the film structure and composition during film growth has not been easy, and in situ analyses during film nucleation and growth has been a goal of many investigators.

Our interest in in situ monitoring of film deposition was motivated by sputter growth of Bi2Sr2CaCu2Oy from a composite target. These studies found that the film composition was a strong function of deposition parameters, particularly the substrate temperature. Investigating these complex relationships required the growth and ex situ analysis of many films. It was clear that a technique to determine the composition of films during growth could efficiently unravel the complex relationships between composition and processing parameters.

An important consideration for an in situ analysis technique is that it not interfere with the growth process either by altering the film surface or by changing the deposition dynamics. During deposition, the substrate temperature, gas flow, and deposition rate all must be maintained; any interruptions for the analysis may alter the growth irreversibly.
Real-Time Monitoring of Epitaxial Processes by Parallel-Polarized Reflectance Spectroscopy
Authors: Dietz Nikolaus , Bachmann Klaus J.
Published: August 2016

The engineering of advanced micro-electronic circuits, optoelectronic devices, and integrated optical circuits requires precise control of the lateral dimensions and thicknesses of device features and of the stoichiometry and doping of epitaxial semiconductor regions. This is preferably achieved by real-time monitoring and control of the individual deposition and etching processes that constitute the processing sequence. The use of optical probe techniques for the real-time monitoring of etching and/or growth processes is favored because of their nondestructive character and their potential use in real-time feedback control. Some of these methods are ideal in monitoring the overall growth process and/or substrate temperature in industrial applications, requiring low cost and maintenance. For example, in situ reflectance-spectroscopy methods, such as dynamic optical reflectivity (DOS), spectral-resolved normal incidence reflectance spectroscopy (MRS), or pyrometric interferometry (PI), are successfully applied to various deposition processes and provide information on both the growth rate and the composition of the deposits. However, small changes in the reflectance (because of chemical interactions at the surface of the films with the reactants supplied from the vapor phase) are of the order of 10−3 to 10−4 and are hardly observable with normal-incidence reflectance techniques because of the high reflectivity of substrate/film interface, which is typically of the order of 40%–60% for many semiconductors.

In order to increase the sensitivity to surface- and interface-related growth properties, alternative optical-observation methods such as reflectance difference spectroscopy (RDS), surface photoabsorption (SPA), and spectral ellipsometry (SE) have been developed.
The Coolidge Process for Making Tungsten Ductile: The Foundation of Incandescent Lighting
Authors: Briant C.L. , Bewlay Bernard P.
Published: August 2016

Try to imagine a world without incandescent lamps. We light our homes with 20-200-watt lamps, which are routinely purchased in local stores. These lamps are made at the rate of millions per week and their manufacture represents a large global industry. The consumer expects them to last approximately 1,000 hours and to be energy efficient and inexpensive.

Many types of incandescent lamps exist. Figure 1 shows several examples. The most common types are A-line (the general household lamp), automotive lamps, and reflector lamps for floodlight or projector applications. We also have many thousands of specialty lamps, which have a broad range of applications, such as audio-visual projectors, fiberoptic systems, video-camera lights, airport-runway markers, photoprinters, medical/scientific instruments, and stage/studio systems. They can have power ratings from a few watts to several thousand watts, but they all have at least one feature in common. They contain a filament made of tungsten wire. The diameter of the wire will vary, depending on the power rating and application of the lamp, but for most common household lamps it is less than 100 μm.
Magnetism on a Microscopic Scale
Authors: Krishnan Kannan M.
Published: August 2016

Tremendous progress has been made in the field of magnetic-materials research and technology over the past few years. Superior properties and novel scientific questions arise from our ability to either synthesize artificial structures or tailor microstructures at the appropriate length scale. The development of enhanced macroscopic properties in such materials requires, in addition to synthesis, that the magnetic microstructure be quantitatively determined and its dependence on the physical/chemical microstructure at the appropriate length scale be understood. Such studies are also motivated by the technologies of information storage, magnetic and magnetooptic recording, sensors, and magnetic devices. While these applications have been the focus of earlier issues of the MRS Bulletin, here we emphasize the physics, materials science, novel magnetic measurements, and micromagnetics, as well as the implications of this work on emerging technologies.

Magnetism, subtle in its manifestations, is electronically driven but weak compared to electrostatic interactions. It is quantum-mechanical in nature with its origins in the Pauli exclusion principle and the existence of electron spin. However, it is known for a variety of both classical and quantum-mechanical effects stemming from both short- and long-range forces. It has a wide association with what is traditionally known as “microstructure” or the morphological arrangement of phases, grains, or individual atoms themselves. These factors are in part the reason for the richness of structures and properties encountered in magnetic systems from which many useful engineering and technical applications arise. They are also in part the reason why magnetism remains poorly understood and why many fundamental questions remain unanswered.
Magnetic Microstructures of Perpendicular Magnetic-Recording Media
Authors: Lodder J. Cock
Published: August 2016

Magnetic recording has been the dominant recording technology for information storage since the invention of the computer. Currently, 1-Gbit/in. longitudinal magnetic recording (LMR) systems have been realized and densities of 10 Gbit/in., having bit areas less than 0.1 μm, are being developed. To reach this goal, a drastic scaling down of the track pitch, bit-cell length, head gap, medium thickness, and head-medium spacing is required. If this trend of increasing densities continues, an areal density of more than 300 Gbit/in. is predicted in the 21st century, based on computer simulation using the perpendicular magnetic recording (PMR) mode instead of the current LMR scheme. Magnetic-recording technologies and related materials have already been discussed in another issue of the MRS Bulletin, and hence in this paper, we concentrate on Co-Cr-X material used as a medium for PMR.

The PMR mode has been studied since 1975 and at present, Co-Cr-X (e.g., X = Ta) films with perpendicular anisotropy are the most promising media material. In general, such media should have the following properties: easy axis of magnetization perpendicular to the film plane, suitable coercivity (Hc) and remanent magnetization (Mr) for storing the information and reading it at a high signal-to-noise (S/N) level, uniform columnar size with a small diameter, magnetically uncoupled columns having a magnetization reversal based on rotation instead of a domain-wall motion, chemical stability under various environmental conditions, and a small surface roughness. In order to achieve the desired magnetic anisotropy and coercivity, a columnar morphology (small diameter) with an hep [0001] texture and exchange-decoupled, columnar boundaries—to create a magnetic microstructure for single domain switching columns with high coercivity—should be obtained. An overview of the preparation, microstructure, and magnetic properties of Co-Cr thin films is given in Reference 8. Depending on the deposition parameters, a so-called initial layer (with an in-plane magnetization) can be present.
Collimated Sputtering of Titanium and Titanium Nitride Films
Authors: Ryan James G. , Brodsky Stephen B. , Katata Tomio , Honda Makoto , Shoda Naohiro , Aochi Hideaki
Published: August 2016

Collimated sputtering is a physical vapor deposition (PVD) method where a collimator is inserted between a conventional “full-face-erosion” sputtering target and a substrate (Figure 1). The collimator is a plate of hexagonal cells that acts as a filter to remove obliquely incident atoms before they arrive at the substrate. Only material with a nearly normal incidence trajectory may pass through the collimator and deposit on the substrate. Collimated sputtering was initially evaluated for conductor-level depositions in order to improve the filling of recessed features. Although the method has been successfully used to fill damascene structures, depositing thick conductor films is inefficient because most of the sputtered material is captured by the collimator, causing the collimator to clog quickly, necessitating frequent replacement.

A more common use of collimated sputtering is associated with the deposition of thin “liner” films. For example, thin, collimated aluminum alloy films have been used as underlayers for aluminum reflow processes. Also, collimated Ti/TiN films are used as contact/adhesion layers for chemically vapor-deposited (CVD) W metallization. Collimation provides better bottom and sidewall coverage for small, high aspect-ratio features than conventionally sputtered films do.

Coliimated sputtered films often exhibit unique properties because the angle of incidence of depositing atoms is controlled. Collimated AlMg alloys have superior electromigration resistance compared to noncollimated AlMg films. Collimated TiN films appear to exhibit denser grain structures when compared to films deposited with higher amounts of obliquely incident flux (Figure 2).
Chemical-Vapor-Deposited Tungsten for Vertical Wiring
Authors: Ohba Takayuki
Published: August 2016

As the feature size of ULSI (ultralarge-scale integration) circuit devices shrinks, interconnects need to be scaled to maximize the wiring density and wire ability. This increased density leads to smaller contacts or via holes connecting the wires. The reduction in size increases the aspect ratio of these features for the same dielectric thickness. Conventional physical vapor deposition (PVD) techniques such as sputtering are unable to fill high aspect-ratio contacts/vias with aluminum conformally, as shown in Figure 1. This poor conformity is attributed to the shadowing effect by already-deposited nondirectional sputtering atoms and leads to void formation and open failures. Chemical vapor deposition (CVD) is a solution for achieving conformal filling.

This is a prime reason why CVD has been investigated since the 1980s and why a large number of metals have been proposed. Above all, because tungsten as a refractory metal has high resistance to electromigration (EM) failures and tungsten hexafluoride (WF6) as a source gas has some advantages in manufacturing, for example, high vapor pressure (boiling point = 17.4°C) and purity, W-CVD with WF6 based on H2 or SiH4 reduction has been widely studied. Blanket W-CVD has been used for actual via-hole filling for 0.5-μm devices. Figure 2 shows a cross-sectional view of five-level interconnects using W plugs in 0.35-μm devices. Another advantage of W-CVD is that W deposits selectively into via holes if a low flow-rate ratio of reductants to WF6 is used.
Aluminum Reflow Sputtering
Authors: Kikuta Kuniko
Published: August 2016

The scaling of integrated-circuit device dimensions in the horizontal direction has caused an increase in aspect ratios of contact holes and vias without a corresponding scaledown in vertical dimensions. Conventional sputtering has become unreliable for handling higher aspect-ratio via/contact holes because of its poor step coverage. Several studies have attempted to overcome this problem by using W-CVD and reflow technology. The W-CVD is used for practical device fabrications. However, this technique has several problems such as poor adhesion to SiO2, poor W surface morphology, greater resistivity than Al, and the need of an etch-back process.

Al reflow technology using a conventional DC magnetron sputtering system can simplify device-fabrication processes and achieve high reliability without Al/W interfaces. In particular, the Al reflow technology is profitable for multi-level interconnections in combination with a damascene process by using Al chemical mechanical polishing (CMP). These interconnections are necessary for miniaturized and high-speed devices because they provide lower resistivity than W and simplify fabrication processes, resulting in lower cost.

This article describes recent Al reflow sputtering technologies as well as application of via and interconnect metallization.
Chemical-Mechanical Planarization of Aluminum-Based Alloys for Multilevel Metallization
Authors: Fury M.A. , Scherber D.L. , Stell M.A.
Published: August 2016

As recently as 1993, the prevailing presumption among the semiconductor technical community was that then-current development efforts associated with aluminum lines and tungsten damascene vias needed to shift rapidly to copper multilevel interconnect schemes. This is exemplified by the June 1993 issue of the MRS Bulletin, which featured copper metallization as its theme. In the intervening years, however, that same technical community revised the Semiconductor Industry Association (SIA) roadmap and placed renewed emphasis on the use of an all-aluminum interconnect scheme. This was done largely in deference to the costs associated with converting existing semiconductor lines to copper-compatible facilities. In addition to tooling costs, there is a learning curve for copper systems that remains to be established for device reliability, field failures, yield learning, and process maturation. On the other hand, existing fabs are already compatible with aluminum metallurgies, and there is a rich history of reliability and yield data.

This change in direction creates two immediate needs: (1) the need to fill small-diameter vertical interconnects (vias) with void-free aluminum and (2) the need to remove the top surface aluminum resulting from its blanket deposition (overburden) following the metal fill. In addition, for high circuit-density applications, it may be desirable, if not necessary, to form the metal lines using the same damascene fill method as is used for the vias. This process strategy replaces metal etching and insulator gap fill with insulator (usually silicon oxide) etching and metal gap fill.
Technological Applications of Ion Tracks in Insulators
Authors: Fleischer Robert L.
Published: August 2016

Natural nuclear tracks in solids have existed since close to the beginning of the solar system, billions of years ago. Only during the last few decades have we learned how to employ tracks practically. Uses now range from radiation dosimetry to microchemical analysis, virus counting, oil and uranium exploration, and aiding earthquake prediction. The key to these applications is track etching, which in insulators allows tracks to be revealed simply and then enlarged. Etching also makes it possible to produce minute holes with clean, geometric shapes.
Design of High-Strength, High-Conductivity Alloys
Authors: Miyake J. , Ghosh G. , Fine M.E.
Published: August 2016

Computer-aided design of alloys is becoming increasingly useful, replacing the completely experimental approach. The computer-aided approach significantly reduces the cost of alloy design and more easily leads to optimum properties by reducing the amount of experimentation. Design of high-strength, high-conductivity alloys is a good example of the efficacy of using the computer to design experimental alloys.

Alloys that have both high strength and high electrical conductivity are needed for many applications such as lead frames, connectors, conducting springs, and sliding contacts. Figure 1 shows the strength and conductivity of some commercially available copper-based alloys. Since dissolved solutes in an otherwise pure metal rapidly reduce the electrical conductivity (as well as the thermal conductivity), solid solution strengthening is not suitable for designing this class of alloys. Such alloys must be designed on the basis of precipitation or dispersion hardening. The theory of the yield stress of alloys with precipitates or dispersed phases has been well-formulated and may be used for alloy design. The solubility of the hardening phase in the matrix must be very small. Otherwise the conductivity will be degraded too much. Nordheim's rule relates conductivity to dissolved solute in alloys and is also available for alloy design. Decreasing the dissolved solute increases the conductivity and strength due to an increase in the volume fraction of the precipitate.
Interatomic Potentials for Atomistic Simulations
Authors: Voter Arthur F.
Published: August 2016

Atomistic simulations are playing an increasingly prominent role in materials science. From relatively conventional studies of point and planar defects to large-scale simulations of fracture and machining, atomistic simulations offer a microscopic view of the physics that cannot be obtained from experiment. Predictions resulting from this atomic-level understanding are proving increasingly accurate and useful. Consequently, the field of atomistic simulation is gaining ground as an indispensable partner in materials research, a trend that can only continue. Each year, computers gain roughly a factor of two in speed. With the same effort one can then simulate a system with twice as many atoms or integrate a molecular-dynamics trajectory for twice as long. Perhaps even more important, however, are the theoretical advances occurring in the description of the atomic interactions, the so-called “interatomic potential” function.

The interatomic potential underpins any atomistic simulation. The accuracy of the potential dictates the quality of the simulation results, and its functional complexity determines the amount of computer time required. Recent developments that fit more physics into a compact potential form are increasing the accuracy available per simulation dollar.

This issue of MRS Bulletin offers an introductory survey of interatomic potentials in use today, as well as the types of problems to which they can be applied. This is by no means a comprehensive review. It would be impractical here to attempt to present all the potentials that have been developed in recent years. Rather, this collection of articles focuses on a few important forms of potential spanning the major classes of materials bonding: covalent, metallic, and ionic.
Diamond Synthesis: The Russian Connection
Authors: DeVries R.C. , Badzian A. , Roy R.
Published: August 2016

Several 40-year anniversaries of the modern area of the synthesis of diamond at high pressures and temperatures (HPHT) have come and gone. If you are a proponent of the Norton Company, this first synthesis would be somewhere between 1948 and 1950. ASEA's Feb. 15, 1953, accomplishment was noted at an international meeting in 1993 on high pressure (AIRAPT) with a small session that included papers by ASEA and General Electric (GE) representatives. The GE success in the Hall experiment of Dec. 16, 1954 (announced in February 1955), was marked only in the personal memories of the remaining members of that diamond team. DeBeers recognizes the ASEA date, but if it celebrates the 40th anniversary of its own in-house accomplishment, it will do so late in 1998; the Russians will do so on or about the year 2000. In any case, the basic, muchcopied GE HPHT process is repeated thousands of times each day at sites all over the world (Figure 1) to make a product that has replaced 90% of natural diamond as an abrasive and has given to technology new superhard products in forms unavailable from the earth (Figure 2). All manufacturers are in fierce competition for a total business that probably is in the range of $1 billion per year, and engineers spend their time primarily in finer tuning for faster growth, greater yields, lower costs, and higher quality crystals. The HPHT process seems to have survived the threat of the low-pressure chemical vapor deposition (CVD) process with respect to abrasive grain and gem-quality stones. However, the low-pressure process has some unique capabilities that obviously cannot be achieved by HPHT, and the product is finding niches in specialized applications (Figures 3 and 4).
Biology and Materials? Part I
Authors: Alper Mark
Published: August 2016

Poets and philosophers have, through the ages, viewed organisms as the embodiment of the mysterious “Vital Force,” a unique non-earthly element required for the functioning of life processes.

Biologists have seen, in living organisms, an adaptive, self-reproducing, evolving collection of molecules acting solely according to the laws of chemistry and physics.

Historians speak of the iron or bronze ages and, more recently of the plastics (polymers) and the silicon ages. Materials science departments speak of metals, alloys, ceramics, and perhaps polymers—but not of genes.

The “common man” has, it must be admitted, seen living organisms as a source of useful and important materials—wood for building; cotton, silk, and other fibers for textiles; horn, shell, and bone for tools and weapons; fats for lubricants; fur for clothing

But, in fact, few of us now think of materials when we think of living things. Neither do we think of DNA, protein, and carbohydrates when we think of materials.

No, biologists have not been blackballed by materials scientists, chemists, and physicists. Until recently, they neither understood the processes by which life produces its materials nor even conceived of manipulating those processes to tailor the properties of the materials to our needs. Only within the past few years has the “biological revolution” expanded our understanding of the molecular basis for biological phenomena and our ability to control them. It is only now, for the first time, that one can point to a legitimate field of science based on mimicking, adapting, and controlling biological systems with the goal of producing novel materials with important, unique, and useful properties.
Eggshell Mineralization: A Case Study of a Bioprocessing Strategy
Authors: Fink David J. , Caplan Arnold I. , Heuer Arthur H.
Published: August 2016

Product Concept: Fluid packaging device.

Description: A package is required to contain approximately 50 ml (55–60 grams) of a viscous, 2-phase, thermally labile, aqueous medium containing proteins, carbohydrates, salts, nucleic acids and fats. A seamless ellipsoidal container is anticipated having a maximum radial dimension of 45 mm and a maximum axial dimension of 60 mm. The container wall must be permeable to respiratory gases and water vapor. External surface texture must be minimal. White coloration is acceptable, but the ability to incorporate solid or patterned surface coloration is desirable. The package wall must weigh approximately 5 g, the material must contain at least 0.3 g of bioavailable calcium, and it must be recyclable and biodegradable. The container must withstand 400-g drop test impacts.

Processing: All materials must be maintained and the container fabricated by aseptic processing in neutral-pH, aqueous medium at less than 40°C and with a unit production time of less than 24 hours.

Unit cost: Filled unit containers must be produced for approximately $4.00/100 units, with approximately $1.00/100 units allocated to container components and assembly.

Laboratory Solution: Not achievable in the laboratory.

Biological Solution: The eggshell.

In its composition, architecture, and function, the eggshell is an elegant solution to the design problem posed above—a multilayered bioceramic composite, consisting of a mineral phase (primarily calcite, CaCO3) deposited on and within a complex organic phase (the matrix). The eggshell provides a unique microenvironment for housing embryonic development. It protects the embryo, regulates respiratory gases, water and ions, and provides calcium for embryonic skeletal development.
Genetic Production of Synthetic Protein Polymers
Authors: Cappello Joseph
Published: August 2016

A goal of polymer chemistry is to control the final properties of a processed material by controlling the chemistry and physics of the polymer chain. Since the final formulated materials' properties are a complex function of chemical and physical interactions at both the micro and macro scales, it would be desirable to influence those interactions at the level of the molecular chemistry of the chain. However, in order to affect those macromolecular associations that occur via chemical functionalities separated over long distances, a chemistry is needed that can specify not only variability in chemical composition along the chain but can also specify the positions at which this chemical variability must occur over the entire length of the chain—several hundred nanometers.

Protein-based materials in nature are formulated from protein chains which have evolved chemical compositions that through the specific sequence of their amino acid monomer constituents can result in diverse materials such as ultrahigh strength fibers, silks and collagens, and soft, ultradurable elastomers, elastin. As described in the article by Kaplan in this issue, the fundamental six amino acid repeat of the crystalline fraction of Bombyx mori silk fibroin is composed of essentially three amino acids, glycine (G), alanine (A), and serine (S), in a 3:2:1 ratio. The strength of the fiber is derived from these crystallized peptide blocks. They are positioned to a great extent as tandem repeats of the sequence GAGAGS.
Self-Assembled and Langmuir-Blodgett Organic Thin Films As Functional Materials
Authors: Charych Deborah H. , Bednarski Mark D.
Published: August 2016

Biological membranes provide numerous functions for the survival of cells, ranging from molecular recognition to signal transduction and energy conversion. The spacial organization of proteins, enzymes, glycoproteins, and glycolipids in the membrane is provided by the lipid bilayer matrix. The lipids of the membrane are small molecules which have the common characteristic of having both a hydrophilic and a hydrophobic moiety. In aqueous media, they are entropically driven to self-organize in bimolecular sheets (see the article by Alper in this issue). These sheets, in addition to providing a fluid matrix for a wide variety of biomolecules, also serve to impede the flow of molecules across the membrane.
Quantitative Structural and Chemical Analysis of Thin Films Part I
Authors: Bruynseraede Y. , Schuller Ivan K.
Published: August 2016

Thin-film materials are playing an ever-increasing role in basic and applied research and are the basis for a large number of devices. In many cases, thin films are used in multilayered configurations so that the interfaces between different materials play a key role in their properties. The thicknesses of thin films being investigated approach interatomic spacing, so interfacial structure and chemistry become dominant. The field is now at a stage where it is no longer sufficient to only obtain qualitative information; it is also necessary to understand the structure and chemistry quantitatively and to determine limits on the accuracy of the various characterization tools. The present and next issues of the MRS Bulletin bring together a number of experts in the most commonly used characterization tools. To highlight and encourage international collaboration, the articles presented here are jointly written by scientific groups in the United States and Europe.

The first issue of this series is dedicated to the most commonly used techniques: electron microscopy, x-ray diffraction, and surface analysis. The article on electron diffraction by Ourmazd, Scheffler, Heinemann, and Rouviere presents studies of atomic resolution microscopy and their limitations. Aspects highlighted are the importance of comparing simulations to the images obtained in the electron microscope, and the importance of theoretical studies to obtain quantitative information. The article by Fullerton, Bruynseraede, and Schuller describes recent developments in the field of x-ray diffraction. This article focuses on a refinement technique capable of quantitative determination of interfacial roughness, interdiffusion, and crystal structure changes in a variety of novel multilayer configurations.
Quantitative X-Ray Diffraction From Superlattices
Authors: Fullerton Eric E. , Schuller Ivan K. , Bruynseraede Y.
Published: August 2016

The physical properties of superlattices have been the subject of considerable interest because a wide range of phenomena associated with very thin films, interfaces, and coupling effects can be studied. Recent areas of activity in metallic superlattices include antiferromagnetic coupling of ferromagnetic layers across nonmagnetic spacer layers, giant magnetoresistance, magnetic surface anisotropy, low-dimensional superconductivity, and anomalous mechanical properties. All of these phenomena are strongly affected by the chemical and physical properties of the individual layers and by the superlattice structure. Therefore, a detailed understanding of the properties of superlattices requires a nondestructive, quantitative determination of the superlattice structure.

Because superlattices are not in thermodynamic equilibrium, their structure is sensitive to preparation methods and growth conditions. A dramatic example of superlattice structural dependence on growth conditions is shown in Figure 1, for sputtered Nb/Si superlattices. Increasing the Ar pressure during sputtering decreases the kinetic energy of the deposited atoms, thereby changing their surface mobility, and thus altering growth dynamics. Figure 1 shows the low-angle x-ray diffraction and cross-sectional transmission electron microscopy (TEM) images of [Nb(35 Å)/Si(25 Å)]40, superlattices sputtered in, respectively, 3 and 15 mTorr of Ar. The TEM image of the 3 mTorr superlattice clearly shows the smooth and continuous layering across the entire cross section of the image (≈5 μm). This is characteristic of sputtered metal/semiconductor superlattices used for x-ray optics.
Use of the Atomic Force Microscope to Study Mechanical Properties of Lubricant Layers
Authors: Salmeron Miquel B.
Published: August 2016

Advances in our understanding of the phenomena of adhesion, friction, and lubrication are facilitated by the recent development of new tools that allow the study of contacts in close-to-ideal conditions. These new tools are the surface force spparatus (SFA) and the atomic force microscope (AFM). The first was developed by Israelachvili in the 1970s. In this device, contact between two atomically flat surfaces of mica occurs over an area of several micrometers in diameter after the mica sheets, glued onto two perpendicular cylindrical lenses, are compressed. Force, area of contact, and separation distance can be controlled at the atomic scale. The second device, the AFM, was developed by Binnig et al. in 1986. The sharp tip of the AFM is a convenient idealization of a single asperity. In addition, the AFM can be used to image the surface in the weak repulsive or in the attractive modes so that minimum perturbation is introduced by the imaging process itself. These two devices have the necessary sensitivity to allow the application of forces weak enough not to dislodge atoms from their sites during contact. The order of magnitude of the force that can lead to the rupture of chemical bonds is a convenient figure to keep in mind in this context. A simple estimate of this force is obtained by considering a bond-length increase of 1 Å as leading to dissociation. For a bond energy of ≈1 eV, Fb ≈ 1 eV/1 Å ≈ 1 × 10−9 N.