bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel Approaches for Assessing the Preservation of Historic Silks: A Case Study of the First Ladies' Gowns
Authors: Becker Mary , Tuross Noreen
Published: August 2016

Friable natural products are often used in articles of personal adornment, and the perishable nature of these materials presents a unique challenge to museums. At the Smithsonian's National Museum of American History, a collection of gowns worn by the First Ladies of the United States is a popular display of historical and sentimental import. Opened to the public on February 1, 1914, fifteen gowns were displayed as part of a “Period Costumes“ exhibit in the U.S. National Museum (now known as the Arts and Industries Building). Within just a few years, the exhibit was recognized as “one of the most interesting and popular in the Museum.” A First Ladies' Hall was created in the mid-1950s to exhibit the gown collection in period room settings. This design theme continued when the Hall moved to the Museum of American History and Technology (now the National Museum of American History) in 1964. The First Ladies' Hall was closed for renovation in 1987, allowing the curatorial staff to reassess the collection's use and conservators to perform long overdue examinations and treatments. Reinstallation of the exhibit is scheduled for spring 1992.

The First Ladies' conservation project includes a history of each gown's use and exhibition as related to its physical condition and also includes stabilization treatments to meet the demands of future display. The current conservation project provided an unusual opportunity for extensive research into fabric deterioration of a popular and important collection. The goals of the research are twofold: first, to determine each object's state of preservation by studying the effectivenss of several analytical approaches with minimal destructive sampling and, second, to begin investigating the mechanisms involved in the degradation of silk, the material predominant in this collection.
Materials in Musical Instruments: Romance of Art and Science
Authors: Hansen Uwe J.
Published: August 2016

A few years ago, I surprised my wife by asking for a guitar for Christmas. Our budget was limited in those days, so I started at the low-cost end and remember being disappointed with the tone quality of the guitar we purchased. Even with my poorly trained ear, I could tell the difference between a $50 guitar and a $100 instrument. The jump from $100 to $200 was also easily detectable. I could even make out the difference in tone quality between a $200 and a $500 guitar. One hand-crafted instrument with a $1000 price tag had a lovely tone. However, the limitations of my ear made it difficult to detect significant improvement in tone quality beyond that stage. At any rate, I realized that an instrument manufacturer would clearly not waste precious select woods on a “cigar-box” instrument. Since then, while trying to unlock the secrets of fine tone quality, the importance of materials in crafting fine musical instruments has become apparent during my investigations of various musical instruments in the laboratory.
Measurable Characteristics of Violin-Family Instruments in Relation to the Sound of a High-Quality Violin
Authors: Hutchins Carleen M.
Published: August 2016

The extreme variations in the mechanical as well as acoustical properties of wood, not only within a given species, but even within the same tree, have plagued violin researchers for nearly 100 years and violin makers for more than 300 years. The lore of violin making tells us that a spruce tree growing on the north side of a mountain should be cut in the spring when the water is moving up in the wood cells, and that the first six or eight feet of the trunk should be discarded because the twisting and the weight of the big trunk cause increased density in the wood with a less even grain structure. The wood should then be cut into lengths, free of knots and sap cracks, and split into so-called flitches that can be used for various violin-family instruments, depending on size. When a flitch is properly cut and joined for a violin top, the annual-ring spacing, or grain, ideally should be narrow in the center of the violin top, gradually becoming wider toward the edges. Also, the grain should be vertical to the bottom surface of the top plate. The more researchers study the desirable parameters of spruce for the proper tuning of violin top and back free plates and the effects they have on the finished instrument, the more the seemingly unsupported lore of violin making makes very good sense.
The Caribbean Steel Pan: Tuning and Mode Studies
Authors: Hansen Uwe J. , Rossing Thomas D. , Mannette Ellie , George Kaethe
Published: August 2016

The evolution of the steel pan during the last half century represents the emergence of a truly new musical instrument. Originating in the folk culture of the Caribbean, it has become popular throughout North and South America, as well as in Europe. The haunting sounds of steel drums, generally called “steel pans” by players and tuners, are now enjoyed worldwide. Pans are usually crafted from commercial 55-gallon steel oil drums. The top with its various openings is discarded, and only the bottom, along with the side, is used for the pan. The length of the side skirt varies depending on the pitch range of the completed instrument. Thus, a bass pan will utilize almost the entire length of the original drum, whereas a lead pan, or a single tenor, will be cut to retain only a very short skirt. The pitch of each note section is primarily determined by the size and geometric shape of the section as bounded by a grooved seam. Figure 1 shows representative layouts of several pans. The note arrangement in some pans is such that several pans are required to play a melody. For example, a double-second instrument consists of two pans, while a bass includes as many as six. In addition to the section size, the mass density, stiffness, and curvature contribute significantly to the pitch of each note. The overall timbre of the tone produced depends to a great extent on the spectral content of the note. This, in turn, depends strongly on the normal modes of the excited note section, and to some lesser extent, on the normal modes of all other sections. This latter dependence is caused by the fact that all note sections are imbedded in the same solid matrix of the drumhead. Therefore, vibrations in one note section cause all note sections to vibrate. The nature of the coupling between sections has been the subject of considerable interest to researchers in the field. Inasmuch as the entire pan represents a highly nonlinear system, the tone quality also varies significantly with excitation amplitude.
Molecular Beam Epitaxy From Research to Manufacturing
Authors: Cho A.Y.
Published: August 2016

Tonight I will talk about molecular beam epitaxy (MBE) from research to manufacturing. First I will discuss the introduction of MBE in the early 1970s and the exciting achievements made with it. I will conclude with some new directions for MBE.

First let us review this technology. Through MBE, materials like semiconducting materials, metals, and insulating materials are grown, atom layer by atom layer. Figure 1 shows a stainless steel MBE chamber, pumped to a pressure of approximately 10−10 torr, with liquid-nitrogen-cooled shrouds to further condense the water vapor in the vacuum system. To grow gallium arsenide (GaAs), we mount a substrate in the center where it continuously rotates to give us the uniformity we need, and it is heated to about 580° or 600°C. The effusion cells are filled with pure Ga, pure As, and doping elements such as silicon for n-type doping, and then germanium or beryllium for p-type doping. Important in this MBE system are the in situ monitoring techniques. The system contains a reflection high energy electron diffraction (RHEED) apparatus, producing an electron beam with a grazing angle to the substrate of about one degree. The diffracted electrons are projected on a fluorescent screen. Through the diffraction pattern, we can look at the surface as it is cleaned by desorption of the oxide before we deposit and grow semiconducting materials.
Substrate Selection for Thin-Film Growth
Authors: Phillips Julia M.
Published: August 2016

Although it is an integral part of any structure involving a film, the substrate is often taken for granted. The choice of substrate is, however, one of the most important materials issues in thin-film growth. This article focuses on substrates for thin films and will provide criteria for selecting the proper material needed to fill specific application requirements. As will become obvious, the ideal substrate for a given film often does not exist. Specific applications require different substrate materials that offer an acceptable compromise for the purpose at hand. Ideally, the substrate should give mechanical support but not interact with the film except to provide sufficient adhesion, and in many cases, the provision of a template for atomic ordering. In practice, however, the substrate exerts considerable influence on film characteristics. The search for viable substrate materials is an active area of research.
Modeling Diffusion in Gallium Arsenide: Recent Work
Authors: Haddara Yaser M. , Lee Cynthia C. , Hu Jerry C. , Deal Michael D. , Bravman John C.
Published: August 2016

Second to silicon (Si), the most highly developed technology for semiconductor processing exists for gallium arsenide (GaAs). Unfortunately, GaAs processing is more complex than that of Si, mainly because GaAs is a compound semiconductor. Additionally, the lack of a stable native GaAS oxide and other disadvantages relative to Si have prevented this material from expanding beyond the small niche of applications where its high intrinsic electron mobility, superior radiation hardness, and direct bandgap are essential. Adequate understanding and modeling of the process physics are important for extending the “process window” available to GaAs manufacturers and for increasing the appeal of this material. This article deals with one of the most important process events: dopant diffusion.

In the next section we briefly describe device-fabrication technology and show the importance of diffusion modeling in the prediction of device characteristics. We then review some elementary diffusion mechanisms and outline the dopants that are important in GaAs-processing technology as well as the methods by which these dopants are introduced into the substrate. In subsequent sections we review the research community's current understanding of diffusion mechanisms as well as model parameters for specific dopants. Much work has been done in this field, at Stanford and by other groups, since the publication of a major review of the subject by Tan et al. in 1991. In this article, we focus on these recent contributions.
Semiconductor Nanocrystals
Authors: Alivisatos A. Paul
Published: August 2016

The following is an edited transcript of the presentation given by A. Paul Alivisatos, recipient of the Outstanding Young Investigator Award, at the 1995 MRS Spring Meeting in San Francisco.

The work I will describe on semiconductor nanocrystals started with the realization that it is possible to precipitate a semiconductor out of an organic liquid. We can precipitate out a semiconductor as a colloid—a very small-sized semiconductor with reduced dimensionality—that will show large, quantum size effects. A dream at that time was to make an electronic material by such a process in a liquid beaker, by starting with an organic fluid and somehow injecting something into the fluid to make very small particles, which we could use in electronics. The materials we use in electronics today have perfect crystalline order. We are able to put in dopants very specifically, or control precisely their arrangements in space in enormously complicated ways. The level of purity of electronic materials is so high that making an electronic material in a wet chemistry approach seems almost impossible. If, in addition, we specify that the size must be controlled precisely, we recognize the project is a problem for basic research, yet not one ready for applications. Many fundamental problems arise if we try to make semiconductor particles, in a liquid, of such high quality that they can be used as electronic materials.
Electronic Access to Factual Materials Information: The State of the Art
Authors: Westbrook J.H. , Kaufman J.G. , Cverna F.
Published: August 2016

Over the past 30 years we have seen a strong but uncoordinated effort to both increase the availability of numeric materials-property data in electronic media and to make the resultant mass of data more readily accessible and searchable for the end-user engineer. The end user is best able to formulate the question and to judge the utility of the answer for numeric property data inquiries, in contrast to textual or bibliographic data for which information specialists can expeditiously carry out searches.

Despite the best efforts of several major programs, there remains a shortfall with respect to comprehensiveness and a gap between the goal of easy access to all the world's numeric databases and what can presently be achieved. The task has proven thornier and therefore much more costly than anyone envisioned, and computer access to data for materials scientists and engineers is still inadequate compared, for example, to the situation for molecular biologists or astronomers. However, progress has been made. More than 100 materials databases are listed and categorized by Wawrousek et al. that address several types of applications including: fundamental research, materials selection, component design, process control, materials identification and equivalency, expert systems, and education. Standardization is improving and access has been made more easy.

In the discussion that follows, we will examine several characteristics of available information and delivery systems to assess their impact on the successes and limitations of the available products. The discussion will include the types and uses of the data, issues around data reliability and quality, the various formats in which data need to be accessed, and the various media available for delivery. Then we will focus on the state of the art by giving examples of the three major media through which broad electronic access to numeric properties has emerged: on-line systems, workstations, and disks, both floppy and CD-ROM. We will also cite some resources of where to look for numeric property data.
New Rapid Failure Analysis Techniques for Multilevel Metallization
Authors: Cole Edward I. , Anderson Richard E.
Published: August 2016

Open interconnections on integrated circuits (ICs) are a serious and ubiquitous problem throughout the micro-electronics industry. The efforts to understand the mechanisms responsible for producing open interconnections and to develop analytical methods to localize them demonstrate the concern manufacturers have for this problem. Multiple layers of metallization not only increase the probability that an open conductor or via will occur because of the increased number of interconnections and vias but also increase the difficulty in localizing the site of the failure because upper layers may mask the failure site.

Rapid failure analysis of open-conductor defects is critical in new product development and reliability assessment of ICs where manufacturing and product development delays can cost millions of dollars a day. In this article, we briefly review some standard failure analysis approaches and then concentrate on new techniques to rapidly locate open-conductor defects that would have been difficult or impossible to identify using earlier methods. Each method is described in terms of the physics of signal generation, application, and advantages and disadvantages when compared to existing methods.
The Reliability of Aluminum/Tungsten Technology for VLSI Applications
Authors: Shacham-Diamand Yosi
Published: August 2016

Interconnects technology and back-end processing moved to the center stage of very large-scale integration (VLSI) technology in the mid-1980s. At that time, the critical dimensions dropped below 1 μm while the chip size and complexity increased to a level where interconnects were recognized to be a limiting factor. As dimensions decreased, the step coverage of sputtered aluminum inside contacts and via-contact holes decreased and alternative technologies were studied. The increasing cost of ownership (COO) of single-wafer Al sputtering processes also supported the search for alternative technologies, such as tungsten chemical vapor deposition (CVD) for via contacts and plugs (Figure 1). Only recently have all the W CVD process steps been optimized to lower cost without loss of reliability and/or performance. The development of cluster tool technology and multiwafer process modules also allowed reliable and cost-effective utilization of the W/Al technology.

Tungsten technology for VLSI circuits became complementary to that of aluminum. Tungsten thin-film resistivity ρw = 7–8 μΩ cm is much higher than that of aluminum ρAl = 3–4 μΩ cm, introducing large W interconnect resistance-capacitance (RC) delays compared to Al. Therefore, tungsten is not favorable for high-speed global-interconnect schemes. However, tungsten is suitable for local interconnects where the impedance of the driving transistors is dominant and the RC interconnect delay is less significant. Tungsten is also suitable for contact filling, in which the via resistance is negligible. For these applications, tungsten became a dominant technology and was integrated with the aluminumalloy-based technology used for global interconnects.
Sputter Synthesis of Ferroelectric Films and Heterostructures
Authors: Auciello O. , Kingon A.I. , Krupanidhi S.B.
Published: August 2016

Ferroelectric films can display a wide range of dielectric, ferroelectric, piezoelectric, electrostrictive, and pyroelectric properties. The potential utilization of these properties in a new generation of devices has driven the intensive studies on the synthesis, characterization, and determination of processing-microstructure-property relationships of ferroelectric thin films during the last five years. In addition there has been an increased drive for integrating ferroelectric film-based heterostructures with different substrate materials to demonstrate numerous devices that exploit the dielectric, ferroelectric, piezoelectric, electrostrictive, and pyroelectric properties of these materials. For example the high dielectric permittivities of perovskite-type materials can be advantageously used in dynamic random-access memories (DRAMs), while the large values of switchable remanent polarization of ferroelectric materials are suitable for nonvolatile ferroelectric random-access memories (NVFRAMs).

Various vapor-phase deposition techniques such as plasma and ion-beam sputter deposition (PSD and IBSD, respectively), pulsed laser-ablation deposition (PLAD), electron-beam or oven-induced evaporation for molecular-beam epitaxy (MBE), and chemical vapor deposition (CVD) have been applied to produce ferroelectric films and layered heterostructures. See References 4–7 for recent reviews. However, work is still necessary to optimize the techniques to produce device-quality films on large semiconductor substrates in a way that is fully compatible with existing semiconductor process technology. Therefore research efforts should be focused on the optimization of suitable process methods and on the investigation of processing-composition-microstructure property relationships. These efforts are the focus of this article with emphasis on PSD and IBSD techniques.
Chemical Vapor Deposition of Electroceramic Thin Films
Authors: de Keijser M. , Dormans G.J.M.
Published: August 2016

A nonconventional way of producing nonvolatile memories is to use ferroelectrics, a class of electroceramic materials. These materials have a remanent polarization. The direction of this polarization can be changed by an electric field. Ferroelectric materials possess a “natural memory,” so to speak. Ferroelectrics have been known for a long time, and the idea to use them for binary data storage originates in the 1950s. The basic element of this type of memory is formed by a ferroelectric capacitor—a ferroelectric layer sandwiched between electrodes. Early prototypes were unsuccessful because rather high voltages were needed to switch the ferroelectric capacitor (200–300 V) and the memories suffered from crosstalk. (Programming one particular cell influenced neighboring cells.) The revival of ferroelectric memories was driven by the development of thin-film deposition techniques that allowed the formation of capacitors with ferroelectric thin films of submicron thicknesses. These capacitors can be switched with normal intergrated-circuit (IC) voltages. The crosstalk problem is circumvented by isolating each memory cell by a transistor (similar to a dynamic random-access memory [DRAM]). Compared to “standard” nonvolatile memories, ferroelectric memories offer the advantage of very fast access times (both for reading and writing), low-voltage operation, and good write/read endurance. A ferroelectric material that is already being used in commercially available memories is lead zirconate titanate, PbZrxTi 1−xO3. To combine a ferroelectric material with IC technology is a challenge, and many problems have been (and will be) encountered.
Embedded-Atom and Related Methods for Modeling Metallic Systems
Authors: Foiles Stephen M.
Published: August 2016

This article discusses simple but realistic models of the bonding in metallic systems. As is discussed in the introduction, such methods are valuable both to study complex systems that are intractable with more rigorous methods and to study generic properties that do not depend on the fine details of the energetics. In addition, simple models are useful for gaining a physical understanding of a system.

As discussed in the article by Vitek, a great deal of progress in the understanding of defect structures has been gained by the use of constant-volume pair potentials, that is, pair-potential models that include a volume-dependent term. In this picture, the energy is assumed to have two parts, a large density-dependent but structure-independent part and a structure-dependent part that is represented by pair interactions. This view follows from a physical picture where the metal is viewed as a uniform electron gas and the interactions between the atoms are obtained by performing perturbation theory on this reference system. This approach has a serious limitation, though, in that it is restricted to situations where the system is essentially uniform such as when the bulk or defects do not introduce significant changes in the local density. This is true for two reasons. First, there is not a clear prescription for how the structure-independent part of the energy should be treated in an inhomogeneous region. This is a serious problem since a large part of the binding energy is included in this term. Second, the pair-potential term in this picture depends on the overall density. In the vicinity of a inhomogeneity such as a surface, there is no prescription for how the pair-potential term should vary.
Biosynthesis and Processing of Silk Proteins
Authors: Kaplan David L. , Fossey Stephen , Mello Charlene M. , Arcidiacono Steven , Senecal Kris , Muller Wayne , Stockwell Scott , Beckwitt Richard , Viney Christopher , Kerkam Keven
Published: August 2016

Silks produced by silkworms (e.g.,Bombyx mori) and orb-web weaving spiders (e.g.,Nephila clavipes) are essentially pure protein, that is, complexes of amino acid polymers. They are the most common fibers spun by biological systems. There has been a long-standing interest in the use of these and similar fibers in textiles, cables, fiber reinforcement in composites, in addition, for example, to cross hairs in optical instruments, and fishing nets. Both nylon, a homo-polymer of the amino acid glycine, and Kevlar, a polymer of a nonnatural aromatic amino acid, can be considered modified, synthetic versions of silk and are used for some of the applications mentioned above. The potential for genetic manipulation, through recombinant DNA technology, of the natural biosynthetic process for these natural proteins (see the article by Cappello in this issue) has renewed interest in the production of new silklike proteins.

The natural silks are characterized by aβ-sheet secondary structure which is stabilized by interchain hydrogen bonds and intersheet hydrophobic interactions (Figure 1). Silks can be considered block copolymers, with crystalline domains consisting of short side chain monomers (the amino acids glycine, alanine, and serine) interspersed in amorphous domains consisting of bulkier side chain amino acids.

This family of fibers is naturally tailored to perform functions such as catching prey (orb web) or serving as a barrier against environmental challenges (cocoon). The domestic silkworm (B. mori) produces only one type of silk, cocoon silk, at only one stage in its lifecyle, during the fifth larval instar just before molt to the pupa. The silk is produced in modified salivary glands and spun from the mouth.
Microbial Synthesis and Properties of Polyhydroxy-alkanoates
Authors: Doi Yoshiharu
Published: August 2016

A wide variety of microorganisms accumulate an optically active polymer of D(−)-3-hydroxybutyric acid, P(3HB), as an intracellular storage material of carbon and energy. The P(3HB) was first isolated fromBacillus megateriumin 1925 by Lemoigne. Many prokaryotic organisms, such as bacteria and cyanobacteria, have been found to accumulate P(3HB) up to 80% of their cellular dry weight when growth is limited by the depletion of an essential nutrient such as nitrogen, oxygen, phosphorus, or magnesium. Recently, many bacteria have been found to accumulate copolymers of D(−)3-hydroxy-alkanoic acids with a chain length ranging from three to 14 carbon atoms. In addition, 4-hydroxybutyric acid was found as a constituent of bacterial polyhy-droxyalkanoates (PHA).

Bacterial PHA polymers have attracted much attention as environmentally degradable thermoplastics for a wide range of agricultural, marine, and medical applications. PHA is degraded in soil, sludge, or sea water. Some microorganisms such as bacteria and fungi secrete extracellular PHA depolymerases to degrade environmental PHA and utilize the decomposed compounds as nutrients. In this article, I report the metabolism, production, and properties of bacterial PHA.
Structure-Properties Relations in Cheese
Authors: Sharkasi Tawfik , Kilara Arun
Published: August 2016

Cheese is a popular food among people of all ages and its popularity stems from its nutritional value and convenience. Cheese comes in many varieties, shapes, and sizes. It makes an ideal snack food. The recent expansion of ethnic foods that include cheese as an ingredient is somewhat responsible for the increased use of cheese. Per capita consumption of cheese has roughly doubled over the past 20 years. The annual U.S. per capita consumption increased from 12.4 to 24.7 lbs. Rapidly expanding restaurant pizza sales and changes in lifestyles that emphasize convenience food are also major factors affecting cheese trends. The increasing popularity of pizza has caused consumption of mozzarella cheese to more than double in the past decade alone. Cheese sales in 1993 reached about $17.2 billion. Concerns over fat intake and its affect on health has resulted in a growing production of the “light” varieties, which represent about 38% of all new cheese products introduced in the past two years.

The origin of cheese as a staple in the human diet is lost in history. By some accounts, cheese has been around for 6,000 to 7,000 years. It was standard fare for the Egyptians of about 2000 B.C. and many types were made by the Romans. Cheese making skills were brought by settlers who migrated due to famine, conflicts, and invasions. The Roman invasion of Britain brought a new art of cheesemaking to that country, although cheese may have been made there previously.
Copper Metallization Technology for Deep Submicron ULSIs
Authors: Arita Y. , Awaya N. , Ohno K. , Sato M.
Published: August 2016

Investment in high-performance and large-scale integration (LSI) has been increasing and low-cost fabrication equipment, simple processing, and short turnaround are big concerns. The propagation delay time in a device is reduced with a reduction in device size, and wiring delay becomes longer than device delays. Wiring then has become as important as the device itself. Future multilevel wiring will require five to seven levels. The multilayer wiring itself will not be easy to achieve, because of increased wiring cost, process complexity, and longer turnaround. We must overcome these problems.

The materials required for wiring so that ULSI performance and reliability in RISC (reduced instruction set computer), and CISC (complex instruction set computer) type processors and DSPs (digital signal processors) can be increased must have a lower resistivity and higher resistance to electromigration (EM) and stress migration (SM) than do aluminum alloys. Gold, copper, and silver are candidate wiring materials. Copper is especially attractive, but we must overcome several obstacles to take advantage of its potential.

This article will discuss wring and via resistance delay, Cu CVD technology, the surface reaction mechanism, copper patterning technology, copper oxidation and diffusion prevention, and copper wiring reliability.
European Copper Interconnection Project
Authors: Torres J.
Published: August 2016

Multilevel metallization is becoming an increasingly interesting area of research as circuit fabrication technologies are scaled down to deep submicron dimensions. The mainstream of today's interconnection technology is AlSiCu metallization. Al-based solutions, however, seem to be limited in resistivity as well as in electromigration performance. Because of its low electrical resistivity and its resistance to electromigration, copper is considered to be a promising new solution for on-chip interconnections. The performance of copper would allow its use in wiring with very small linewidths, as required for ULSI circuits. Before considering copper metallization in ULSI processing, however, major problems still have to be overcome.

Taking into account these considerations, a European project is now devoted to the evaluation of copper-based metallization for ULSI applications. The project, Copper Interconnection (COIN), associates the efforts of seven European partners.

The objectives of COIN are to evaluate and develop a set of optimized solutions which demonstrate to our industrial partners the interest of using on-chip copper metallization. High deposition rates, low temperature processing, thermal stability, reliability, and low cost are the main goals.

The COIN project is devoted to an exploratory study concerning the major issues to be addressed in order to reach the above targets. The choice is to limit, for as long as possible, the modifications of existing multilevel metallization (MLM) structures to a simple replacement of the aluminum by copper interconnection levels. The refractory metal layers in MLM structures (TiSi2, Ti, TiN, W) will be maintained in the copper metallization scheme as will the use of SiO2 as the dielectric material. Another consideration in our approach is the possibility of achieving this substitution with minimum modification to existing fabrication lines. Thus, processes for copper deposition and copper patterning will be developed using existing machines and machine concepts for as long as possible.
Crystal Growth and Atomic-Level Characterization of YBa2Cu3O7–δ Epitaxial Films
Authors: Kawasaki Masashi , Nantoh Masashi
Published: August 2016

Epitaxial thin-film growth of high-critical-temperature (Tc) superconductors has been intensively studied not only because it is one of the key technologies for electronic application but also because it provides suitable specimens for elucidating the superconducting mechanism. For simply making thick (>100 nm) epitaxial films, various deposition techniques such as sputtering, pulsed laser deposition (PLD), evaporation, including molecular beam epitaxy (MBE), and chemical vapor deposition (CVD) have been verified as applicable. For instance, high-quality YBa2Cu3O7–δ (YBCO) films, in terms of superconducting properties (Tc and critical current Jc), can be made by adjusting the cationic composition and choosing the right deposition conditions, e.g., oxygen pressure and temperature close to the decomposition line in the phase diagram. The knowledge and techniques accumulated in the high Tc field have been successfully transferred for the film growth of such oxides as dielectric, ferroelectric, magnetic, and optically functional materials. Pulsed laser deposition, especially, is now widely used for those materials and was addressed in a previous issue of the MRS Bulletin. However, as the demand for film quality increases, allowing films to be used in complex heterostructures like Josephson tunnel junctions and in well-designed physics studies, the meaning of the term “highquality film” has been changing.
Water Effects on Corrosion Behavior of Structural Ceramics
Authors: Gogotsi Yury G. , Yoshimura Masahiro
Published: August 2016

Environmental degradation poses a serious limitation on the utility of engineering materials such as metals, plastics, glasses, and structural ceramics. However, at least water would seem to be a harmless environment for ceramics, which are considered to be the most corrosion-resistant of all materials. When we drink water from a glass or a ceramic cup, we never think about an aqueous alteration of these materials. We cannot imagine that our ceramic mug may be dissolved in water or fail due to stress corrosion during breakfast. Even hot water which we use to make coffee or tea does not seem to be a hazardous environment for our china and earthenware. Why then are we going to discuss the effect of water on structural ceramics? The answer is simple: Under conditions of normal use of structural ceramics, which include high temperatures, high pressures, and mechanical stresses (Figure 1), even the most stable and corrosion-resistant materials may interact with water and water may become a hostile environment. It can be adsorbed on the surface of ceramics and act as a solvent for oxide ceramics or as an oxidant for non-oxide ceramics (Figure 2). However, water can cause a degradation of glasses and oxide ceramics even at room temperature if mechanical stresses are simultaneously applied (so-called stress corrosion). Water or humid air can decrease significantly the mechanical properties of certain zirconia ceramics at only slightly elevated temperatures (~200°C).
Materials Science of Radioactive Waste Forms
Authors: Ewing R.C. , Lutze W.
Published: August 2016

The materials science of radioactive waste forms and containment materials has long been a subject of interest to the Materials Research Society. One of the earliest (and continuing) MRS symposia, the Scientific Basis for Nuclear Waste Management, has been held 18 times since 1978. This symposium rotates abroad every third year: Berlin in 1982, Stockholm in 1985, Berlin in 1988, Strasbourg in 1991, and Kyoto this past October. Nearly 170 papers were presented at the Kyoto meeting.

Materials science issues for nuclear waste disposal are unique in their scale and consequences. The wastes include an extremely wide variety of materials: spent nuclear fuel from commercial and research reactors; high-level liquid waste produced at West Valley, New York, during the reprocessing of commercial spent nuclear fuel; high-level waste (HLW) generated by the nuclear weapons program; nearly pure plutonium from the dismantling of nuclear weapons; highly enriched uranium from weapons; low-level, medium-level, and mixed waste from laboratories and medical facilities; and, finally, mill tailings from uranium mines and the residues from chemical processing, such as the radium-bearing filtrate presently in storage at Fernald, Ohio, and Niagara Falls, New York. Some material can be simply stabilized and monitored in situ, as is done for most uranium mill tailings and residues, but other materials require retrieval, processing, immobilization, and permanent disposal. The volumes of material that will require handling, immobilization, and disposal are enormous. In the United States, much of the weapons program waste is stored in tanks at Hanford, Washington and Savannah River, South Carolina.
Fundamentals of Residual Stresses in Joints Between Dissimilar Materials
Authors: Rabin B.H. , Williamson R.L. , Suresh S.
Published: August 2016

When a discontinuity in material properties exists across a bonded interface, stresses are generated as a result of any thermal or mechanical loading. These stresses significantly affect strength and failure characteristics and may be large enough to prevent successful fabrication of a reliable joint. The use of an interlayer material to successfully reduce mismatch stresses, thereby preventing joint failure or improving joint strength and reliability, requires knowledge of failure mechanisms and of the effects of interlayer properties on the critical stress components.

The origin of residual stresses developed during cooling of a ceramic-metal joint from an elevated fabrication temperature is illustrated qualitatively in Figure 1. Away from edges, the in-plane (parallel to interface) stresses are typically compressive in the ceramic and tensile in the metal. These stresses can cause cracking perpendicular to the interface, leading to spalling or delamination failures. Such failures are frequently observed in thin-film and coating geometries. Where the interface intersects a free edge, large shear and axial (perpendicular to the interface) stresses are generated. The edge stresses are typically tensile within the ceramic and tend to promote crack propagation within the ceramic parallel and adjacent to the interface. This is the most commonly observed failure mode in bonded structural components.
Functional Gradient Structure and Properties of a Bivalve Hinge Ligament
Authors: Ono Katsumichi
Published: August 2016

A characteristic feature of soft biological tissue is a low compression modulus at small strains. On the other hand, the compression modulus of artificial elastomers, such as vulcanized rubber, generally increases with decreasing strain, according to the theory of rubber elasticity. In this paper, I will consider that the low compression modulus of biological tissue is possibly brought about by the organic and inorganic FGM structure of the tissue. An example of a bivalve hinge ligament is given here.

The tissue of the hinge ligament of a bivalve (Spisula sachalinensis) is a hybrid material, composed of a soft cross-linked protein matrix and inorganic calcium carbonate crystals (aragonite). In this example, small rectangular strips were cut from the ligament. The aragonite can then be easily removed from the tissue by treating it with dilute acetic acid (to decalcify the sample). At this point, mechanical anisotropy and swelling were measured and discussed, based on the anisotropic, fine structure of the aragonite.

Figure 1 shows the coordinates for a bivalve hinge ligament. The x axis and y axis are the growth direction and the tangential direction against the growth line, respectively. The z axis is approximately normal in direction to the shell surface. X-ray diffraction of a long strip cut along the x axis showed a typical fiber pattern characteristic of the aragonite structure. The crystallographic c axis of the aragonite coincided with the x direction.
Unique Microstructural Development in SiC Materials with High Fracture Toughness
Authors: Shinozaki S.S.
Published: August 2016

Application of silicon carbide (SiC) as a structural material has been limited thus far by its low fracture toughness, even though, in comparison to other ceramic materials, SiC has superior high-temperature strength and creep, wear, corrosion, and oxidation resistance. For automotive applications, a higher fracture toughness is required. For example, the brittleness and catastrophic fracture behavior of SiC materials have resulted in limited use in automobile exhaust-valve systems and turbocharger rotors. High-density SiC bodies can be produced by a pressureless sintering process. However, the sintered bodies often include flaws which are related to processing, primarily, the presence of agglomerates and crystallographic defects in the starting powders. The importance of grain size and shape refinement in the improvement of mechanical properties has been recognized, and thus, processing procedures and sintering aid compositions have been examined extensively. However, one of the key factors is the “as-received” powder characterization (distribution of grain sizes, polytypes, and impurities) for producing sintered bodies of SiC with consistent physical properties.

A complexity in SiC materials is that SiC can form various crystal structures having essentially the same chemical composition but a differing number of stacking layers in the unit cell. This is commonly called a polytype. There is only one crystal structure with cubic symmetry, which is identified as 3C or the β-phase. At high temperature, the β-phase transforms to α-phases with hexagonal or rhombohedral symmetry, with 4H, 15R, and 6H (Ramsdell notation) being the major polytypes observed in SiC materials. Preference of the polytype selection during the β- to α-phase transformation is dependent on the chemistry of the sintering aids and metallic impurities in the grain boundaries.
Stresses in Multilayered Thin Films
Authors: Cammarata Robert C. , Bilello John C. , Greer A. Lindsay , Sieradzki Karl , Yalisove Steven M.
Published: August 2016

Almost all thin films deposited on a substrate are in a state of stress. Fifty years ago pioneering work concerning the measurement of thin-film stresses was conducted by Brenner and Senderoff. They electroplated a metal film onto a thin metal substrate strip fixed at one end and measured the deflection of the free end of the substrate with a micrometer. Using a beam-bending analysis, they were able to calculate a residual stress from the measured deflection of the bimetallic film-substrate system. A variety of other, more sensitive methods of measuring the curvature of the surface of a film-substrate system have since been developed using, for example, capacitance measurements and interferometry techniques.

When a monochromatic x-ray beam is incident onto a curved single crystal, the diffraction condition is satisfied only for regions of the crystal where the inclination angle with respect to the incident beam exactly matches the Bragg angle. When a parallel beam plane-wave source is used, the diffracted beam from a particular set of (hkl) planes gives rise to a single narrow-contour band. If the crystal is rocked by an angle ω, the contour band will move by a certain distance D. The radius of curvature R of the crystal lattice planes is given by

where θ is the Bragg angle. Equal rocking angles produce equivalent D values for uniform curvature, or varied D values for nonuniform curvature. Using this procedure, detailed contour maps of the angular displacement field of the crystal can be mapped in two dimensions.
John Bardeen and the BCS Theory of Superconductivity
Authors: Hoddeson Lillian
Published: August 2016

Every theory of superconductivity can be disproved! This tongue-in-cheek theorem struck a chord when Felix Bloch announced it in the early 1930s. Virtually every major physicist then working on theory—including Bloch, Niels Bohr, Wolfgang Pauli, Werner Heisenberg, Lev Landau, Leon Brillouin, W. Elsasser, Yakov Frenkel, and Ralph Kronig—had tried and failed to explain the mysterious phenomenon in which below a few degrees kelvin certain metals and alloys lose all their electrical resistance. The frequency with which Bloch's theorem was quoted suggests the frustration of the many physicists who were struggling to explain superconductivity.

Neither the tools nor the evidence were yet adequate for solving the problem. These would gradually be created during the 1940s and 1950s, but bringing them to bear on superconductivity and solving the long-standing riddle required a special set of talents and abilities: a deep understanding of quantum mechanics and solid-state physics, confidence in the solubility of the problem, intuition about the phenomenon, a practical approach to problem-solving, patience, teamwork, and above all refusal to give up in the face of repeated failures. When John Bardeen took on the problem of superconductivity in the late 1930s, he held it like a bulldog holds a piece of meat, until he, his student J. Robert Schrieffer, and postdoctoral candidate Leon Cooper solved it in 1957.
Membranes and Membrane Processes
Authors: Burganos Vasilis N.
Published: August 2016

Membrane separation science has enjoyed tremendous progress since the first synthesis of membranes almost 40 years ago, which was driven by strong technological needs and commercial expectations. As a result, the range of successful applications of membranes and membrane processes is continuously broadening. An additional change lies in the nature of membranes, which is now extended to include liquid and gaseous materials, biological or synthetic. Membranes are understood to be thin barriers between two phases through which transport can take place under the action of a driving force, typically a pressure difference and generally a chemical or electrical potential difference.

An attempt at functional classification of membranes would have to include diverse categories such as gas separation, pervaporation, reverse osmosis, micro- and ultrafiltration, and biomedical separations. The dominant application of membranes is certainly the separation of mixed phases or fluids, homogeneous or heterogeneous. Separation of a mixture can be achieved if the difference in the transport coefficients of the components of interest is sufficiently large. Membranes can also be used in applications other than separation targeting: They can be employed in catalytic reactors, energy storage and conversion systems, as key components of artificial organs, as supports for electrodes, or even to control the rate of release of both useful and dangerous species.

In order to meet the requirements posed by the aforementioned applications, membranes must combine several structural and functional properties.
Alloy Corrosion
Authors: Newman R.C. , Corcoran S.G. , Erlebacher J. , Aziz M.J. , Sieradzki K.
Published: August 2016

The corrosion properties of alloys are of enormous practical importance: modern life would be very different without stainless steels. Alloy corrosion is also an intriguing field of scientific study that combines electrochemical kinetics with fashionable aspects of the morphological evolution of surfaces and even a dash of ancient history, via the studies of Forty and Lechtman on “depletion gilding” practiced by Early Andeans during pre-Columbian times in South America.

The basic alloy corrosion process, as used by the metalsmiths to gold-coat artifacts, is de-alloying. This is defined as the selective electrolytic dissolution of one or more components from a metallic solid solution. For this to happen, there must be a significant difference in the equilibrium metal/metal-ion electrode potentials for the two metals, taking into account any complex ions that might be formed in the electrolyte. For example, we can expect de-alloying in Au-Cu alloys, but not in Au-Pt alloys.

De-alloying shows sharp parting limits, expressed as critical atom percentages of the more reactive component above which that component can be removed from the alloy by electrochemical dissolution in an oxidizing environment such as nitric acid. Parting limits range from about 20 at.% to 60 at.%. This concept is still used in noble metal technology to separate noble metals from base metals. For example, an alloy of 55 at.% gold and 45 at.% silver does not de-alloy, but if it is re-melted with additional silver so that the atom fraction of Ag is greater than 60%, the gold can be separated almost completely by nitric acid immersion.