bluuebunny/crossref_metadata_2025 huggingface dataset:
Colloidal Quantum Dots of III-V Semiconductors
Authors: Nozik Arthur J. , Mićić Olga I.
Published: August 2016

Quantization effects in semiconductor structures were first demonstrated in the early 1970s in III-V quantum wells; these structures consisted of a thin epitaxial film of a smaller bandgap (Eg) semiconductor (e.g., GaAs, Eg = 1.42 eV) sandwiched between two epitaxial films of a larger bandgap semiconductor (e.g., Al0.3Ga0.7As, Eg = 2.0 eV). The conduction- and valence-band offsets of the two semiconductor materials produce potential barriers for electrons and holes, respectively. The smaller bandgap semiconductor constitutes the quantum-well region and the larger bandgap material the potential barrier region. If the film of the smaller bandgap material is sufficiently thin (thickness less than the de-Broglie wavelength of the charge carriers, which typically requires thicknesses less than about 300 Å for III-V semiconductors), then the charge carriers are confined in one dimension by the potential barriers, and quantization of the energy levels for both electrons and holes can occur (Figure 1).
Electronic-Structure Theory of Semiconductor Quantum Dots
Authors: Zunger Alex
Published: August 2016

Progress made in the growth of “free-standing” (e.g., colloidal) quantum dots (see also articles in this issue by Nozik and Mićić, and by Alivisatos) and in the growth of semiconductor-embedded (“self-assembled”) dots (see also the article by Bimberg, Grundmann, and Ledentsov in this issue) has opened the door to new and exciting spectroscopic studies of quantum structures. These have revealed rich and sometimes unexpected features such as quantum-dot shape-dependent transitions, size-dependent (red) shifts between absorption and emission, emission from high excited levels, surface-mediated transitions, exchange splitting, strain-induced splitting, and Coulomb-blockade transitions. These new observations have created the need for developing appropriate theoretical tools capable of analyzing the electronic structure of 103–106-atom objects. The main challenge is to understand (a) the way the one-electron levels of the dot reflect quantum size, quantum shape, interfacial strain, and surface effects and (b) the nature of “many-particle” interactions such as electron-hole exchange (underlying the “red shift”), electron-hole Coulomb effects (underlying excitonic transitions), and electron-electron Coulomb (underlying Coulomb-blockade effects).

Interestingly, while the electronic structure theory of periodic solids has been characterized since its inception by a diversity of approaches (all-electron versus pseudopotentials; Hartree Fock versus density-functional; computational schemes creating a rich “alphabetic soup,” such as APW, LAPW, LMTO, KKR, OPW, LCAO, LCGO, plane waves, ASW, etc.), the theory of quantum nano-structures has been dominated mainly by a single approach so widely used that I refer to it as the “Standard Model”: the effective-mass approximation (EMA) and its extension to the “k · p” (where k is the wave vector and p is the momemtum). In fact, speakers at nanostructure conferences often refer to it as “theory” without having to specify what is being done. The audience knows.
Lateral Manipulation of Single Adsorbates and Substrate Atoms With the Scanning Tunneling Microscope
Authors: Meyer G. , Rieder K.H.
Published: August 2016

The stability and precision of modern scanning-tunneling-microscope (STM) systems allow positioning of the tip on a subnanometer scale. This advancement has stimulated diverse efforts on surface modifications in the nanometer and even atomic range, as recently reviewed by Avouris. The lateral movement of individual adatoms and molecules in a controlled manner on solid surfaces and the construction of structures on a nanoscale were first demonstrated by Eigler and collaborators at 4 K. The reason for operating the STM at low temperatures (apart from increased stability and sensitivity of the STM setup itself) is the necessity to freeze the motion of single adsorbates, which are very often mobile at ambient temperatures. By selecting strongly bonded adsorbate/substrate combinations and large molecules, it was possible to extend the lateral manipulation technique even to room temperature. In the case of large molecules, not only their translational motion but also internal flexure of the molecule during the positioning process must be considered. In general, different physical and chemical interaction mechanisms between tip and sample can be exploited for atomic-scale manipulation. We will concentrate in the following on lateral manipulation where solely the forces that act on the adsorbate because of the proximity of the tip are used. This means that long-range van der Waals and short-range chemical forces can be used to move atoms or molecules along the surface. No bias voltage or tunneling current is necessary. Apart from this technique, additional advances using the effects caused by the electric field generated by the bias voltage between tip and sample and by the current flowing through the gap region can be used for atomic or molecular modification.
Ultrasonic Nondestructive Techniques for Materials Characterization
Authors: Matikas Theodore E. , Crane Robert L.
Published: August 2016

Characterization of materials properties is critical for the understanding of materials behavior and performance under operating conditions. Tailoring materials properties, which are functions of the materials states, is essential for advanced product design. The need to characterize materials for a myriad of applications has spurred the development of many new methods and instruments. Unfortunately many of these characterization tools require destructive sectioning. Also many characterization techniques do not provide key information about material parameters in their operating environments. An ideal characterization tool would provide data about the material properties that are related to micro-and macrostructure without destructive sectioning. Such data can only be obtained using nondestructive-evaluation (NDE) methodologies. Therefore NDE is essential for almost any industrial product. Nondestructive evaluation has become an integral part of materials research because it enables the determination of material parameters (such as micro- and macrostructure, stress, physical properties, and defects) at nearly any point, line, surface, or volume element of interest and at nearly any state during the life of the material. Nondestructive evaluation is based on many different methods that rely on elastic waves, penetrating radiation, light, electric and magnetic fields, chemical sensing, etc. The large number of potential methods makes NDE not a single field but a synergism of many scientific and engineering disciplines. Since it would be impractical here to present all the new NDE methodologies with application to materials research, this issue of MRS Bulletin focuses exclusively on those ultrasonic techniques that are increasingly important in materials characterization.
Ultrasonic Force Microscopy
Authors: Yamanaka Kazushi
Published: August 2016

As an imaging method of elastic properties and subsurface features on the microscopic scale, the scanning acoustic microscope (SAM) provides spatial resolution comparable or superior to that of optical microscopes. Nondestructive evaluation methods of defects and elastic properties on the microscopic scale were developed by using the SAM, and they have been widely applied to various fields in science and technology. One major problem in acoustic microscopy is resolution. The best resolution of SAM with water as the coupling fluid has been 240 nm at a frequency of 4.4 GHz. At a more conventional frequency of 1 GHz, the resolution is about 1 μm. Therefore the resolution of SAM is not always sufficient for examining nanoscale defects and advanced micro/nanodevices.

For materials characterization on the nanometer scale, atomic force microscopy (AFM) was developed and extended in order to observe elastic properties in force-modulation mode. In the force-modulation mode, the sample is vibrated, and the resultant cantilever-deflection vibration is measured and used to produce elasticity images of objects. The lateral force-modulation AFM can evaluate the friction force or the shear elasticity in real time. However in the force-modulation mode, it is difficult to analyze stiff objects such as metals and ceramics.

When the sample is vertically vibrated at ultrasonic frequencies much higher than the cantilever resonance frequency, the tip cannot vibrate due to the inertia of the cantilever. However by modulating the amplitude of the ultrasonic vibration, deflection vibration of the cantilever at the modulation frequency is excited due to the rectifier effect of the nonlinear force curves. Based on the tip-sample indentation during ultrasonic vibration, we developed ultrasonic force microscopy (UFM) for contact elasticity and subsurface imaging of rigid objects using a soft cantilever with a stiffness of the order of 0.1 N/m.
Tissue Engineering: An Overview
Authors: Kohn Joachim
Published: August 2016

When trying to identify the beginnings of “tissue engineering” as a defined scientific field, the first major scientific meeting devoted to “tissue engineering” comes to mind. This meeting took place in 1988 at Granlibakken, Lake Tahoe, California. When looking through the proceedings of this meeting, one can see that many of the fundamental challenges of tissue engineering, still unresolved today, were articulated back at that time. As practiced today, the field of tissue engineering is based on a blending of engineering principles in the materials sciences with the principles of cell and tissue biology to create functional replacements for aged, traumadamaged, or diseased human tissues and organs.

The driving force behind the field of “tissue engineering” is the desire to replace defective human tissue with artificial substitutes to improve the quality of human life. This desire is not unique to our times but can be traced back several thousand years. The earliest reports of the use of artificial materials in wound healing are contained in the Edgar Smith papyrus. This historic document mentions the use of sutures and woundclosure devices around 4000 B.C. and the use of metals in bone repair around 2000 B.C. In ancient times, Native Americans apparently used silk and hair as suture materials.

In 1900 natural tissues like amnion and placenta were suggested as skin replacements, an approach that was obviously doomed to fail due to immunological reactions. The general lack of understanding of the immune response at the beginning of this century forced researchers and clinicians to abandon attempts to use natural tissues as medical implants and contributed to a focus on synthetic materials. Advances in metallurgy facilitated the introduction of metals for bone reconstruction and dental prosthesis, and the large number of casualties during World War I resulted in the establishment of stainless steel and other metals as the preferred orthopedic implant materials.
In SituMaterial Transformations in Tissue Engineering
Authors: Hubbell Jeffrey A.
Published: August 2016

Novel applications exist for biomedical materials that can undergo transitions in material propertiesin situ—that is, at the site of implantation in the body. Such transitions in polymeric biomaterials can be accomplished by crosslinking a materialin situ, by heating or cooling to induce thermal transitions, and by precipitating polymer from solutionin situ. This article will point out the need for materials that can be induced to undergo such transitions in situ and will describe selected tissue-engineering approaches that have been employed for this purpose.

Delivering materials to the body in one form and utilizing them in another form after a transition at the site of implantation has, generally speaking, two potential advantages: (1) the ability to match the morphology of a material implant to a complex tissue shape and (2) the ability to deliver a large device through a small hole in the body. With respect to the former motivation, tissue shapes in the body have an enormous range of complexity: a region of a blood vessel—for example with a curved central axis, a diameter that varies along the length, an eccentric diseased plaque, and numerous side branches. One could develop a variety of implant shapes—arterial stents in this example (for use in structurally supporting arteries after balloon angioplasty, thereby creating a larger cross section for blood flow above the diseased plaque)—and then select the most appropriate implant shape after detailed imaging of the tissue site. One can alternatively attempt to employ some material transformation to deliver a precursor to the final shape of the implant, utilizing the tissue shape to obtain the proper final implant morphology. With regard to the second motivation, it may be desirable to deliver a large object through a small hole, utilizing material transformations. Advances in surgery have focused on manipulating (cutting, coagulating, suturing, stapling) large tissue sites through small holes in the body via minimally invasive surgery. Using such approaches, it has become possible to perform many complex surgical procedures in the joints, abdominopelvic cavity, thoracic cavity, and nasal sinuses, for example, using surgical instruments that are manipulated through surgical access holes less than 1 cm in diameter. Even procedures as complex as coronary-artery bypass surgery have been performed in this way. It still remains generally impossible however to implant devices in the body through such holes unless these implants are very small. If such devices were for example able to be delivered as liquids and then shaped into devices at the implant site, such minimally invasive surgical-device placement could be envisioned.
Binders in Paintings
Authors: Newman Richard
Published: August 2016

Many naturally occurring adhesive materials have been used throughout history to bind pigments in paintings. A number of synthetic materials have been added to these during the twentieth century.

Availability and tradition can influence the choice of binders made by artists. Probably the most widely used medium throughout history, animal glue, is also the most easily obtained. Glues made from the connective tissues or skins of local animals were major media in ancient Egyptian painting and in Chinese and Japanese painting, as well as in many other cultures throughout world history. In many cases, a variety of natural binders were available, and additional factors influenced the choice of binder by a culture. Different media have highly variable properties that affect how they are used in painting. Among these properties are solubility, the transparency or depth of color that is obtainable with a given pigment, and handling properties–how the paint flows, how quickly it dries, whether it can be applied in very thick and very thin layers, etc. Knowledge of the media utilized in paintings can help us understand the intentions of artists. Medieval European painting can be used as an example.
Revelations Beneath the Surface: Paper and Fiber Microscopy
Authors: Mayer Debora D.
Published: August 2016

Paper is one of the most common supports for printed, painted, written, and drawn images. It is composed of fibers and other ingredients intertwined into a compact web, usually in the form of a thin sheet. Making paper involves combining fibers and fillers into a pulp slurry, depositing the suspension on a screen or roll, draining the water, and drying the pulp. Since the invention of paper about 2,000 years ago, the basic papermaking processes have gone unchanged, though hand papermaking has given way to a series of mechanical operations capable of manufacturing a continuous sheet of paper at phenomenal speeds. The selection of the fiber material and the method of treating the pulp during manufacture influence the qualities of the formed sheet of paper.
Polymer Chains Under Strong Flow: Stems and Flowers
Authors: Brochard-Wyart F. , Buguin A.
Published: August 2016

A long deoxyribose-nucleic-acid (DNA) molecule can be seen directly under an optical microscope if it is suitably decorated by fluorescent dyes. This makes it possible to see how a long chain responds to external forces f. The conformation of a uniformly stretched chain has been discussed by Pincus. Under a force f, acting on the two free ends, the chain configuration is modified only above a scale length ξ = kT/f where T is temperature and k is Boltzmann's constant. The chain (Figure 1a), containing N monomers, can be pictured as a string of blobs of size ξ containing g monomers with ξ = gva, where a is the monomer size (v = 1/2 in a θ solvent: the chain is ideal, v = 3/5 in a good solvent). The end-to-end distance is L = (N/g)ξ, that is,

For DNA, which is a semirigid chain, ideal behavior has been observed for chain lengths up to 20 μm when f is small. At higher f ( ≅ 100 pN), Cluzel et al. found a structural phase transition, corresponding to a plateau in the curve f versus elongation. Going even further, one reaches the break point.

Another method to stretch DNA is based on optical tweezers. Here one end of the DNA is attached to a bead of glass of high polarizability, which is attracted by a region of large (optical) electric field. This was used by the Stanford group: In one series of experiments, they observed the conformations of the chain, pulled at one end by a constant force f. The friction on monomers are cumulative, and the tension along the chain is not uniform—it increases from the free end to the tethered end.
Material Matters
Authors: Oversby Virginia M.
Published: August 2016

The use of nuclear fission to generate power results in waste materials that can be hazardous to people and to other life forms, particularly in the first few hundred years after the wastes are created. There is a worldwide consensus that the management of these wastes must not place undue burdens on future generations. In some countries, the opinion is openly stated that those who enjoyed the benefits of the power that produced the wastes must be responsible for taking care of the wastes. Opinions diverge when discussion turns to the question of whether the wastes will always be a liability or eventually become an asset.

Another point of consensus is that at least some of the radioactive wastes should be disposed of by a method that securely isolates them from the accessible environment of plant, animal, and human life until the radioactivity levels have decayed to levels similar to those found in natural environments. Different countries take different positions on the details of what the activity level might be that constitutes the end of moral responsibility for the wastes, but the general position is basically the same worldwide. I explore some concerns about how disposal containers and waste repositories might be marked with suitable identification. In particular, I examine whether the message to be conveyed by the markings needs to change with time and with the entity examining the objects, and whether we can design markers that will convey this potentially variable message.
Reactive Molecular-Beam Epitaxy for Wurtzite GaN
Authors: Mohammad S.N. , Kim W. , Salvador A. , Morkoç H.
Published: August 2016

A1N, GaN, and InN are very promising materials for use in optoelectronic and high-temperature electronic devices. These materials and their ternary and quaternary alloys cover an energy bandgap range of 1.9–6.2 eV, suitable for band-to-band light generation with colors ranging from red to ultraviolet (uv), with wavelengths ranging from 650 to 200 nm. On the device front, they are suitable for example for negative electron-affinity cold cathodes, electronic devices, surface acoustic wave devices, uv detectors, Bragg reflectors and waveguides, uv and visible light-emitting diodes (LEDs), and laser diodes (LDs) for digital data read-write applications. Stifled by the absence of native substrates, growth and doping of high-quality III-V-nitride thin films, particularly p-type, have been major obstacles for developing GaN-based devices. Development of electronic devices such as modulation-doped field-effect transistors (MODFETs) and opto-electronic devices such as LEDs and LDs has also proven challenging.
Blue-Green Light-Emitting Diodes and Violet Laser Diodes
Authors: Nakamura Shuji
Published: August 2016

Short-wavelength-emitting devices, such as blue laser diodes (LDs) and light-emitting diodes (LEDs), are currently sought for a number of applications, including full-color electroluminescent displays, laser printers, read-write laser sources for high-density information storage on magnetic and optical media, and sources for undersea optical communications. For these purposes, II–VI materials such as ZnSe and SiC, and III–V-nitride semiconductors such as GaN have been investigated intensively for a long time. However it was impossible to obtain high-brightness (over 1 cd) blue LEDs and reliable LDs. Much progress has been achieved recently on green LEDs and LDs using II–VI-based materials. The short lifetimes prevent II–VI-based devices from commercialization at present. The short lifetime of these II-VI-based devices may be caused by the crystal defects at a density of 103/cm2 because one crystal defect would cause the propagation of other defects leading to failure of the devices. Another wide-bandgap material for blue LEDs is SiC. The brightness of SiC blue LEDs is only between 10 mcd and 20 mcd because of the indirect bandgap of this material.

On green LEDs, the external quantum efficiency of conventional, green GaP LEDs is only 0.1% due to the indirect bandgap of this material. The peak wavelength is 555 nm (yellowish green). As another material for green emission devices, AlInGaP has been used. The present performance of green AlInGaP LEDs is an emission wavelength of 570 nm (yellowish green) and maximum external quantum efficiency of 1%.
SiC-Seeded Crystal Growth
Authors: Glass R.C. , Henshall D. , Tsvetkov V.F. , Carter C.H.
Published: August 2016

To take advantage of the superior properties of SiC-based devices, the industry must be able to produce high-quality SiC homoepitaxial films on single-crystal SiC wafers. Silicon- and GaAs-based semiconductor devices have taken advantage of the industry's ability to produce largediameter, high-quality substrates to develop large-volume, low-cost devices. For the same reasons, the development of low-cost, high-quality single-crystal SiC substrates has been pursued since the first Lely (nonseeded growth process) platelets were used to make devices. Currently several groups (ATMI, USA; Northrop Grumman Research Center, USA; Okmetic Ltd., Finland; Nippon Steel Corporation, Japan; and our company, Cree Research, Inc., USA) are working toward SiC substrate fabrication. University researchers also play an important role in the search for solutions to fundamental outstanding issues. These efforts are important because the future success of the SiC industry is closely related to the successful development of the SiC bulk growth process.
Radiation Effects in Ceramics
Authors: Pells G.P.
Published: August 2016

Ceramics are inorganic, nonmetallic materials, a class that includes solids with both crystalline and glassy (i.e., aperiodic) atomic structures. This article will emphasize radiation effects in conventional refractory oxide ceramics and glasses that display high-temperature strength, chemical inertness, and high electrical resistivity. The introduction to this issue cites various radiation environments to which materials may be exposed; a number of these environments receive mention in this article. However emphasis here is on giving the reader an overview of damage mechanisms and of the changes in key physical properties (optical, thermal, electrical, and mechanical) that can affect the behavior of these materials. The broad subject of radiation-damage phenomena in ceramics has recently been reviewed by Hobbs et al.

Even at low doses of energetic radiation, whether particulate or electromagnetic, isolated atomic-level defects may be generated and can offer the potential to induce changes in physical properties. However for some applications such as fission reactors, fusion reactors (now in the conceptual design stages), and high-energy accelerators, one must deal with high fluences capable of generating relatively large damage aggregates such as dislocation loops and voids. Thus one must understand the evolution of damage microstructures from point defects to aggregates in both model materials and engineering ceramics. Even when induced changes are only electronic in nature, the effects on some properties (e.g., electrical conductivity) can be dramatic. In the following sections, evolution of the damage state and consequent changes in key properties are described, with some attention to the often critical role of impurities.
The Art of Simplification in Materials Science 1996 MRS Fall Meeting Von Hippel Address
Authors: Cottrell Alan
Published: August 2016

The following is an edited version of the Von Hippel Award address, given by recipient Sir Alan Cottrell at the 1996 MRS Fall Meeting. Cottrell received the Materials Research Society's highest honor for “converting crystal dislocations from a hand-waving hypothesis to a rigorous discipline, transforming the understanding of brittle fracture, making varied and crucial advances in the theory of radiation damage, and for transforming the teaching of materials science throughout the academic world through his pioneering textbooks.” Cottrell is an honorable distinguished research Fellow in the Department of Materials Science and Metallurgy, University of Cambridge.
The Microstructure of Metalorganic-Chemical-Vapor-Deposition GaN on Sapphire
Authors: Hersee S.D. , Ramer J.C. , Malloy K.J.
Published: August 2016

The group-III-N materials (GaN and its related alloys, InGaN and AlGaN) are a rapidly emerging family of compound semiconductors that have great potential for a wide range of optoelectronics and electronics applications.

GaN-based blue light-emitting diodes (LEDs) are commercially available and can already be found in full-color, billboard-size displays in major cities in Japan. Achievement of continuous-wave (cw) laser operation at blue wavelengths will lead to the commercialization of these coherent sources probably within the next few years. Like other semiconductor lasers, these devices can be manufactured relatively cheaply (eventually for a few dollars), and they are expected to replace current ($1,000 and up) ultraviolet and blue-laser sources in medical spectroscopy, high-density information storage, and in projection displays.

This article reviews the key role of the crystal structure of GaN grown on sapphire, which is currently the most widely used substrate. We trace the origin of this crystal structure from nucleation and show how it evolves as growth proceeds. We show that the final GaN film is an ordered polycrystal (rather than a single crystal), in which the individual grains are of high crystalline quality but are “tilted” and “twisted” with respect to one another. We conclude by speculating on how this microstructure may explain the unusual optical and electrical properties of GaN.
Polymerization and Properties of Polymer-Stabilized Ferroelectric Liquid Crystals
Authors: Bowman Christopher N. , Guymon C. Allan
Published: August 2016

The following is based on the presentation made by Christopher N. Bowman, recipient of the MRS Outstanding Investigator Award, at the 1997 MRS Spring Meeting.

I would like to focus on our recent work involving photopolymerizations of monomers in a liquid-crystalline environment. This work is one of the many aspects of photopolymerizations that we are focusing on at the University of Colorado. In particular this effort concentrates on understanding the influence of a liquid-crystalline medium and monomer segregation on polymerization behavior and polymer structure. These studies are of considerable importance for polymer-stabilized ferroelectric liquid crystals (FLCs) because of the enormous potential impact on the area.

I will briefly introduce liquid crystals (LCs), FLCs, and photopolymerizations. I will then discuss the observed electrooptic properties and how these properties change as the LC phase during polymerization is varied. Finally I will address how polymerization kinetics are affected by the LC phase and monomer segregation. This discussion will include results from x-ray diffraction, polarized infrared spectroscopy, and differential scanning calorimetry experiments.
Surface and Interface Modification of Polymers
Authors: Koberstein Jeffrey T.
Published: August 2016

The properties of polymeric surfaces and interfaces are ubiquitous in their myriad commercial applications: paints and coatings, adhesives, lubrication, biocompatible materials, flocculation and steric stabilization of colloids, membranes and separation media, immiscible polymer blends, and filled composites. Some of these applications require low-energy surfaces that are chemically inert and are not easily wet with other materials. Other applications require high adhesion and strong interactions between the polymer and substrate. This article discusses fundamental principles governing the behavior of polymer surfaces and interfaces, then illustrates various means available for polymer-interface modification.
Spectroscopic Characterization of Polymer Surfaces
Authors: Zhuang Hengzhong , Gardella Joseph A.
Published: August 2016

The surface science of polymer materials has recently grown to a dynamic field, largely because of application in such areas as composite materials, wetting, coatings, adhesion, friction, and biocompatibility. The synthesis of new polymer materials, resulting in desired polymer-surface structures and composition, has become more sophisticated and is driving the development of new spectroscopic probes and continuing evolution of more established methods.

A good example of how instrumentation development has led to better applications in polymer-surface science is to follow the growth of studies using x-ray photoelectron spectroscopy (XPS)—also called electron spectroscopy for chemical analysis (ESCA). ESCA is now routinely used to obtain surface composition of polymers, and to follow processing steps and degradation chemistry. Advances in instrumentation have driven many of these more sophisticated applications.

Nevertheless, to improve the understanding of polymer-surface chemistry, more information is needed about surface structure with further sophistication, at a higher level of precision. For example, the knowledge of orientation and subsequent reactive availability of functional groups and of monomer ar rangement along a chain in copolymers and intrachain interactions is important. Macromolecular chain arrangement, termination, branching, and micromorphological information (i.e., domain size and distribution), molecular-weight distributions at or near the surface (in comparison with the average, bulk distribution), and higher degrees of spatial resolution in all three dimensions are all important in determining sophisticated surface structure-property relationships. To approach this level of structural and reactivity information at surfaces and interfaces, evolution of established methods and development of new methods must both be accomplished.
Electromagnetic Applications of Intermetallic Compounds
Authors: Masumoto Katashi , McGahan William A.
Published: August 2016

Intermetallic compounds constitute a very important class of materials for electromagnetic applications. In this article, some important materials and applications are discussed in the following areas: (1) magnetic, magnetoresistive, and magnetostrictive applications; (2) superconductor applications; (3) semiconductor and optical applications; (4) magneto-optical applications; and (5) thermoelectric applications. Emphasis is placed on materials that are important in existing devices and applications or show promise for future applications. The interested reader should consult the reviews in Westbrook and Fleischer's book, and the many references contained therein, for further information.
Miscellaneous Applications of Intermetallic Compounds
Authors: Schetky L.McD.
Published: August 2016

So ubiquitous are intermetallic compounds (IMCs) in all areas of materials application that examples of their use in industrial, medical, consumer, and military products are almost limitless. We will in this brief discussion attempt to identify some of the more important of these applications, which we categorize as miscellaneous. These include shape-memory alloys (SMAs), gold alloys used in jewelry, dental amalgams, tribology applications, diffusion barriers in electronic devices, elevated-heat storage systems, nuclear applications, metal-matrix composites, and high damping alloys. In some cases, the IMC is present as a precipitate or dispersed particle that provides strengthening or other property modification while in other examples, the IMC is employed in bulk form.
Plasma Surface Engineering of Metals
Authors: Rie Kyon-Tschong , Menthe Erich , Matthews Allan , Legg Keith , Chin Jack
Published: August 2016

The marketplace is continually demanding better functionality in the surface and near-surface properties of metal components and tools. In the last 20 years, plasma and ion-assisted techniques have enabled new methods to substantially improve wear, corrosion, and fatigue resistance. In most cases, plasmas are used to enhance well-established processes such as thermochemical diffusion treatment and physical and chemical vapor deposition (PVD and CVD), but their operation in a plasma atmosphere has led to major improvements in their reliability and efficacy, as well as extending the range of materials and components that can be treated.
Film as a Composite Material
Authors: Fleischer Cathy A. , Bauer Charles L. , Massa Dennis J. , Taylor Jeffrey F.
Published: August 2016

Since its development over 150 years ago, silver-halide imaging has retained a central role in the imaging world, despite advances in electronic imaging over the last five to 10 years. At present the high cost of electronic cameras and printing systems prohibits their widespread general use. Nevertheless digital electronic features are now being incorporated into silver-halide-based imaging systems. Development of new films that incorporate magnetic-storage capability into conventional silver-halide film, as well as smaller cameras and tighter winding radii, put more stringent requirements on the physical performance of the final silver-halide-based product.

For many years, advances in silver-halide imaging focused on improved photographic emulsions, providing improvements in resolution, color balance, and latitude. Advances in the photographic emulsions resulted from particle shape and morphology control of the silver-halide crystal, as well as new sensitizing dyes, couplers, and other image-modifying addenda that provided increases in speed and quality. Literature on the “science of photography” and “photographic materials and processes” emphasizes silver-halide chemistry and the function of sensitizing dyes and couplers in color photography as they impact film latitude, resolution, color balance, etc., with minor mention of the support materials and properties. Literature on support characteristics and physical properties is limited.
Application of Electroceramic Thin Films to Optical Waveguide Devices
Authors: Fork David K. , Armani-Leplingard Florence , Kingston John J.
Published: August 2016

Electro-optic devices such as fast (>20 GHz) modulators are one application of ferroelectric-oxide thin-film waveguides. A compact, blue laser source of a few milliwatts power capable of lasting thousands of hours is of great interest as applied to optical data storage and xerography. Ferroelectric-oxide thin films offer several potential advantages over bulk materials for optical waveguides, though no electroceramic thin-film devices have replaced bulk devices yet. Bulk waveguides are defined by ion exchange, which produces only a small index difference. Thin films therefore permit higher intensity per unit power in the guide, and hence larger nonlinear effects and shorter interaction lengths.
Ferroelectric Thin Films in Micro-electromechanical Systems Applications
Authors: Polla D.L. , Francis L.F.
Published: August 2016

Ferroelectric ceramic thin films fit naturally into the burgeoning field of microelectromechanical systems (MEMS). Microelectromechanical systems combine traditional Si integrated-circuit (IC) electronics with micromechanical sensing and actuating components. The term MEMS has become synonymous with many types of microfabricated devices such as accelerometers, infrared detectors, flow meters, pumps, motors, and mechanical components. These devices have lateral dimensions in the range of 10 μm–10 mm. The ultimate goal of MEMS is a self-contained system of interrelated sensing and actuating devices together with signal processing and control electronics on a common substrate, most often Si. Since fabrication involves methods common to the IC industry, MEMS can be mass-produced. Commercial applications for MEMS already span biomedical (e.g., blood-pressure sensors), manufacturing (e.g., microflow controllers), information processing (e.g., displays), and automotive (e.g., accelerometers) industries. More applications are projected in consumer electronics, manufacturing control, communications, and aerospace. Materials for MEMS include traditional microelectronic materials (e.g., Si, SiO2, Si3N4, polyimide, Pt, Al) as well as nontraditional ones (e.g., ferroelectric ceramics, shapememory alloys, chemical-sensing materials). The superior piezoelectric and pyroelectric properties of ferroelectric ceramics make them ideal materials for microactuators and microsensors.
Materials for Flat-Panel Displays
Authors: Im James S. , Chiang Anne
Published: August 2016

Flat-panel displays (FPDs) will soon become ubiquitous products in our homes, workplaces, and a number of places in between. Familiar display applications pioneered by the venerable cathode-ray tube (CRT) will progressively utilize a number of different FPDs. Flat-panel displays will also initiate and pioneer new applications, as was the case with notebook computers and personal digital assistants.

The future proliferation of FPDs can no longer be doubted for two simple reasons. First, such devices help us cope with this already information-saturated society. Second, the technological momentum and financial commitment needed for FPDs to take hold are already irreversibly set in place. It is the insatiable current and near-future demand that are pulling the field, and that are fueling a flurry of research and development activities. The display market has grown in size from tens of millions of dollars only a decade ago to a nearly ten-billion-dollar industry. This market growth is expected to continue at a brisk pace during the next decade.

This of course is in no way bad news for materials scientists and engineers. We nearly always benefit from development of new and complex products. It is in regard to these rather incipient but advanced manufacturing technologies where we often encounter challenging, relevant, and interesting materials problems. The better we address these obstacles during these early and therefore critical times, the more successful the FPD technology will be in fulfilling the potential opportunities that lie ahead.
Materials Issues in Magnetic-Disk Performance
Authors: Doerner Mary F. , White Richard L.
Published: August 2016

The continued exponential growth in areal density for longitudinal magnetic-recording devices places ever more stringent demands on disk performance. The design of materials and processes must provide the required advances in technology. The magnetic properties are controlled through the choice of underlayers, magnetic alloys, and the deposition processes that control crystallographic orientation and magnetic isolation between grains. The requirement of lower head-disk spacing places increasing stress on the tribological performance of the disks, controlled by a very thin overcoat and lubricant layer. This article reviews the various materials issues relevant to magnetic-disk technology.

The major obstacle for achieving high areal density in thin-film media is transition noise. This noise arises from the zig-zag transition boundaries that occur due to cooperative switching of the magnetic grains. Both exchange coupling between grains and magnetostatic interactions cause magnetic-cluster sizes larger than the grain size. The goal is to magnetically isolate the grains and keep the grain size small. As the dimensions of the bit cell shrink, smaller grain size is required to obtain enough grains per bit cell to maintain the required signal-to-noise ratio (SNR). In the 10–40-Gbits/in.2 areal-density range, the issue of thermal stability of small (<10 nm), isolated grains needs to be addressed.

In addition to good SNR, a narrow transition width is needed in order to pack the transitions closer together. The objective is to minimize interactions between transitions to reduce nonlinear amplitude loss and superlinear noise.
Recent Developments in Aggregation Kinetics
Authors: Asnaghi D. , Carpineti M. , Giglio M.
Published: August 2016

Colloidal aggregation is a very old field of research. The basic mechanism that controls the stability of colloidal solutions has been described in the celebrated papers of Derjaguin, Landau, Verwey, and Overbeek (DLVO), and indeed the prevention of undesired aggregation is one of the primary concerns in many industrial processes involving colloids. In the last 10 years a resurgence of interest in aggregation rather than in stability has been spurred by a number of fortuitous coincidences. Both through simulations and experiments, it was realized that colloidal aggregates exhibit a fractal nature. More importantly, it was found that there are two universal modes of aggregation, irrespective of the type of colloidal system. The aggregates grown according to these modes have different fractal dimensions, different reaction kinetics, and different mass distributions. The two modes are called diffusion-limited cluster aggregation (DLCA) and reaction-limited cluster aggregation (RLCA), according to whether the probability that a bond formed as a consequence of an encounter is equal to, or much smaller than one, respectively. The study of these limiting cases has been the object of extensive studies in the late 1980s, and many of the features of these modes are by now well understood.

This article describes some recent results in the area of colloidal aggregation. Although we present mostly static light-scattering data from our laboratory, connections to similar work from other groups are also discussed. For the convenience of the reader, we start by recalling some of the relevant features of both DLCA and RLCA.
Critical Fluids in Porous Media
Authors: Frisken B.J. , Liu Andrea J. , Cannell David S.
Published: August 2016

The behavior of fluids confined in porous materials has been of interest to engineers and scientists for many decades. Among the applications driving this research are the use of porous membranes to achieve liquid-liquid separations and to deionize water, the use of porous materials as beds for catalysis, and the need to extract liquids (especially oil and water) from such media. Many of these applications depend on transport, which is governed by flow or diffusion in the imbibed fluids. Both the flow and diffusion of multiphase fluids in porous media, however, strongly depend on the morphology of phase-separated domains, and on the kinetics of domain growth. Thus, it is worthwhile to study the behavior of multiphase fluids in porous media in the absence of flow. Recently, much attention has focused on even simpler systems that still capture these essential features, namely, near-critical binary liquid mixtures and vapor-liquid systems in model porous media, such as Vycor and dilute silica gels. Although near-critical fluids may seem rather artificial as models for multiphase liquids, there are several advantages associated with them. In general, domain morphology and growth kinetics are governed primarily by competition between interfacial tension and the preferential attraction of one phase to the surface of the medium. In near-critical fluids, the relative strength of these two energy scales is sensitive to temperature, and can therefore be altered in a controlled fashion. In addition, the kinetics of domain growth are sensitive to the temperature quench depth, and can be controlled.
Studies of Material Reactions by In Situ High-Resolution Electron Microscopy
Authors: Sinclair Robert
Published: August 2016

Processing has always been a key component in the development of new materials. Basic scientific understanding of the reactions and transformations that occur has obvious importance in guiding progress. Invaluable insight can be provided by observing the changes during processing, especially at high magnification by in situ microscopy. Now that this can be achieved at the atomic level by using high-resolution electron microscopy (HREM), atomic behavior can be seen directly. Accordingly, many deductions concerning reactions in materials at the atomic scale are possible.

The purpose of this article is to illustrate the level reached by in situ HREM. The essential procedure is to form a high-resolution image of a standard transmission electron microscope (TEM) sample and then to alter the structure by some means in a controlled manner, such as by heating. Continual recording on videotape allows subsequent detailed analysis of the behavior, even on a frame-by-frame (1/30 second) basis. The most obvious advantage is to follow the atomic rearrangements directly in real time. However, in addition, by continuous recording no stages in a reaction are missed, which can often occur in a series of conventional ex situ annealed samples because of the limited number of samples that can realistically be examined by HREM. One can be sure that the same reaction, in the same area, is being studied. Furthermore, by changing the temperature systematically, extremely precise kinetic measurements can be made (e.g., for activation energies and kinetic laws) and the whole extent of a material transformation can be investigated in one sample, something that would take months of work if studied conventionally. The information provided by in situ HREM is often unique and so it can become an important technique for fundamental materials investigations.
Novel Concepts of the Aggregation Structure of Organic Monolayers on the Surface of Water
Authors: Kajiyama Tisato
Published: August 2016

Langmuir-Blodgett (LB) films have been applied to molecular electronics, nonlinear optics, and biosensors. Their useful properties can be accessed by using a defect-free monolayer—the precursor of LB films. In order to prepare a defect-free or defect-diminished monolayer, it is necessary to estimate the molecular arrangements and structural defects in the monolayer. The actual structure of monolayers on the surface of water have been proposed on the basis of recent morphological and structural studies. Molecular-aggregation processes or monolayer-formation processes do not always match the general concept concluded from surface pressure-area (π-A) isotherms. Therefore, a universal understanding has not been reached. Here we present a novel and systematic classification for the aggregation structure of monolayers on the water surface and also demonstrate how to prepare defect-diminished monolayers.