bluuebunny/crossref_metadata_2025 huggingface dataset:
Adhesion of Fine Particles at Solid/Solution Interfaces
Authors: Kallay Nikola
Published: August 2016

The adhesion of particles at solid surfaces in liquid media has attracted the attention of scientists because of its various applications as well as the theoretical significance of the processes involved. Early studies were characterized either by poorly defined systems or limited by the properties of a few morphologically well-defined model colloids, such as latex dispersions. Consequently, results were either of semiquantitative nature or were related to some specific cases, which eluded general conclusions. New methods for preparing uniform particles of different compositions, shapes, and sizes make it possible to approach the problem in a more comprehensive manner. For example, to demonstrate difficulties caused by polydispersity, it is sufficient to mention that the electrostatic interaction energy between a plane surface and a particle is approximately proportional to the particle radius, yet the rate of deposition depends exponentially on the height of the energy barrier.

In principle, static and dynamic approaches may be employed in the study of particle adhesion. The static method yields the force required to detach an adhered particle, while kinetic investigations of attachment and detachment give the rates of the respective processes. Both methods offer information on the stability of the system in terms of the bond strength of adhered solids. For small colloid particles, which are the subject of thermal random Brownian motion, the dynamic approach is more appropriate. This article emphasizes the kinetics of deposition and detachment of small colloid particles in liquid media.
Preparation and Characterization of Monodispersed Colloidal Particles
Authors: Sugimoto Tadao
Published: August 2016

Recently the science and technology of fine particles have been greatly advanced to meet the urgent demands of modern industries for specific and sophisticated functions for various materials, including catalysts, sensors, electromagnetic devices, and photosensitive materials. Monodispersed colloidal Systems are invaluable for this purpose because the entire system's uniform physicochemical properties directly reflect the properties of each constituent particle. Procedures for modifying monodispersed particles have progressed remarkably in recent years so that specific characteristics can be achieved. This article focuses on the backgrounds of science and technology for controlling the properties of inorganic monodispersed particles and on new developments in this field.

Colloidal particles are normally formed through a sequential process of nucleation and growth of the nuclei. To obtain a monodisperse System, the two stages must be strictly separated and nucleation avoided during the growth period. Since the steady concentration of monomers in the growth stage is determined by the balance between the rates of generation of monomers and their consumption by particle growth, the generation or introduction rate of monomers must be controlled so that it is low enough to keep the balanced monomer concentration below the critical supersaturation after the nucleation period. Typically, the initial concentrations of metal sait, pH, and temperature are adjusted to meet this requirement for the formation of monodispersed metal hydrous oxide particles by forced hydrolysis of metal ions.

An artificial separation between nucleation and growth processes may be achieved by “seeding,” in which foreign particles are introduced into the solution of monomers below the critical supersaturation. One may also lower the pH in hydrolysis of metal ions, dilute with solvent, add chelating agents, or suddenly change the temperature just after limited nucleation. All these procedures could cause the monomer concentration above the critical supersaturation to plunge to a level below it.
Preparation and Properties of Well-Defined Magnetic Particles
Authors: Ozaki Masataka
Published: August 2016

Magnetic particles are important not only in the technology, but also in the function of some biosystems. In addition, they are of great scientific interest in developing a better understanding of magnetic phenomena. Ever since magnetic recording media were first prepared, extensive efforts have been made to produce improved magnetic dispersions. The particle s for magnetic media must be of single domain, high saturation magnetization, and proper coercive force. However, the magnetic interactions between such particles are very strong, and stable dispersions are difficult to obtain. Originally, their use was limited to audio tapes, but presently they are employed in a variety of applications. Thus, small particles of different magnetic properties are constituents of magnetic fluids.

In 1975, magnetic particles were identified in the bodies of some bacteria, which can navigate along geomagnetic fields. It is also believed that certain animais have the ability to detect a magnetic field due to the presence of magnetic particles in their cells.

Techniques are being developed to introduce new functions to materials by incorporating magnetic particles. For example, magnetic particles that are encapsulated by nonmagnetic compounds (e.g. polymers) or particles are used for binding and separating enzymes from reactant mixtures. Efforts are under way to use magnetic particles in drug delivery Systems and for diagnosis.
Selected Refractory Advances in Steel-Handling Systems
Authors: Brezny B. , Vezza T.F. , Leitzel T.A.
Published: August 2016

The iron and steel industry is constantly undergoing technological changes in improving its processes to produce the highest quality world-class steels. As a consequence, the refractories industry has been challenged to keep in lock-step with the iron and steel industry to enhance, not detract from these processes.

Certain internal combinations have enabled these refractories changes. Three expositions can display the sophistication to which refractories have advanced, so this article will explore refractories for primary steelmaking, ladles, and slide-gate devices for continuous casting.

The start-up of the first top-blown oxygen vessel at the Linz Works in Austria 37 years ago was a historical milestone in the evolution of steelmaking. At that time the open-hearth process was the dominant steelmaking technology in the world. Ten to 12 hours were required to produce one batch of steel in the open-hearth furnace, but only one hour is needed to refine the same amount of steel in a basic oxygen furnace (BOF). In a top-blown BOF all oxygen required for refining is introduced into the vessel through the oxygen lance inserted through the top of the vessel.

Toward the end of the 1960s, bottom-blown processes, such as OBM and Q-BOP, became very important in oxygen steelmaking. In the bottom-blown process, oxygen and lime are blown into the steel batch through bottom tuyeres.
Refractories for Glass Making
Authors: Busby T.S.
Published: August 2016

Glass melting has changed very little in general principles since the earliest times, still being produced in fireclay pots or crucibles—even up to the present day. In Europe, experiments to melt glasses in tank furnaces began about 1700 A.D., but this became an important form of glass manufacture after Siemens introduced the regenerative furnace in 1870. This design was the basis for the development of modern furnaces and there is still a considerable similarity to the original.

Until the late 1920s the glass contact refractories used in tank furnaces were based on fireclay or sandstone blocks. About this time important changes began when sillimanite and fusion-cast mullite refractories became available. However, because of the higher cost of fusion-cast refractories the introduction of these materials was delayed and they did not come into general use for lining the glass melting tank until the late 1940s.

The high performance of tank furnaces today is related to a number of factors such as improved furnace design and regeneration, but the most significant has been an improved melting rate brought about by the use of higher temperatures. This has only been achievable as a result of the improved quality of fusion-cast and other refractory materials, such as those used in the furnace superstructure and regenerators. Garstang showed that there has been a steady increase in melting temperatures in the container glass industry. In data going back to 1920, there has been an increase from about 1300°C to some 1590°C. Bondarev showed that the increase in production achieved by using higher temperatures reduces the specific consumption of fuel.
Cathodoluminescence Microscopy: A Valuable Technique for Studying Ceramic Materials
Authors: Hagni Richard D. , Karakus Musa
Published: August 2016

Over the past 10 to 20 years, cathodo-luminescence microscopy (CLM) has become an important, standard technique for studying many geological materials, but its application to ceramic material has not been fully realized. CLM has been found to be especially valuable in determining original porosity in carbonate rocks, a feature that was extremely important in determining the ability of petroleum and related fluids to migrate through the rocks and concentrate in the favorable structures where petroleum is found today. CLM constitutes one of the most significant techniques employed in the exploration for petroleum, but the results of those investigations remain largely unpublished in company files. A number of investigations have discussed the application of cathodoluminescence (CL) to studies of porosity in carbonates.

Other applications of CLM to geology involve metals exploration. Halos of red CL feldspar in the rocks around carbon-atite deposits, which may contain rare earths, copper, and other metals, contrast with feldspar crystals with blue or blue-green CL that are distal from the ore deposits. Dolomite associated with lead-zinc ores may exhibit growth zoning by CL that can be used to trace the path of the ore fluids for distances of 100 miles or more. The detection of host rock limestone alteration in the Tri-State zinc-lead district, potassic and argillic alteration at the Henderson molybdenite mine, and ore guides in other metallic deposits by CL was discussed by Hagni.
Diamond Growth at Low Pressures
Authors: Angus J.C. , Buck F.A. , Sunkara M. , Groth T.F. , Hayman C.C. , Gat R.
Published: August 2016

Diamond synthesis has attracted attention ever since it was established in 1797 that diamond is a crystalline form of carbon. Initially, synthesis was attempted at high pressures because diamond is the densest carbon phase. As understanding of chemical thermodynamics developed through the 19th and 20th centuries, the pressure-temperature range of diamond stability was explored. These efforts culminated in the announcement in 1955 of a process for diamond synthesis with a molten transition metal solvent-catalyst at pressures where diamond is thermo-dynamically stable. Worldwide sales of synthetic diamond now approach 330 million carats (73 tons) with a market price of between $500 million to $1 billion.

Over the past 40 years a parallel effort has been directed toward the growth of diamond at low pressures, where it is metastable. Although diamond was successfully produced, low-pressure synthesis was plagued by extremely low growth rates. Recent developments have led to much higher growth rates, creating great interest in the field. Polycrystalline diamond films can now be produced on a variety of substrates at linear growth rates of tens to hundreds of micrometers per hour. In addition, the recognition of an entirely new class of solids, the so-called “diamondlike” carbons and hydrocarbons has arisen from this work. This article will discuss both crystalline diamond grown at low pressure and the diamondlike phases.

The interest in diamond is driven by its extreme properties, summarized in Table I. Diamond stands alone as the densest (number density), strongest (elastic modulus), and hardest known material.
Innovations in Testing Methodology for Fusion Reactor Materials Development
Authors: Lucas G.E. , Odette G.R. , Rowcliffe A. F.
Published: August 2016

The successful development of fusion power critically depends on structural materials which can maintain their integrity and dimensional stability in an extremely hostile service environment involving high temperatures and heat fluxes, corrosive media, high stresses, and intense fluxes of neutrons. Neutron irradiation results in a variety of mechanical, physical, and chemical property changes that are collectively referred to as radiation effects. The primary sources of damage are neutron-induced atomic displacements and transmutation products.

High-energy neutrons produce primary recoil atoms (PKAs) with energies ranging from less than 1 keV to more than 100 keV. The energetic PKAs create a cascade of additional displacements. About 10% of the displaced atoms survive cascade recombination as isolated vacancies and self-interstitials or small clusters of these defects. The mobile defects migrate to pre-existing sinks such as grain boundaries and dislocations, or cluster to form a variety of extended defects such as voids (vacancies) or faulted dislocation loops (interstitials).
A Historical Perspective on the Occurrence of Piezoelectricity in Materials
Authors: Dunn P.E. , Carr S.H.
Published: August 2016

This article provides an overview of the piezoelectric effect in all the classes of materials in which it is found to occur. This includes select materials from the categories of naturally occurring single crystals, polycrystalline ceramics, and semicrystalline polymers. Throughout this development, an attempt is made to point out the common factor for the piezoelectric effect in all these materials, namely, the presence of dipolar moieties, whose orientation brings about a net polarization in the material as a whole.

The applications of each of these classes of materials are covered briefly. Each such application has a specific value based on the aggregate properties of the material as a whole, making each material complementary rather than competitive in device applications.

Brief mention is made of the mathematics and geometry of the piezoelectric effect in order to define the piezoelectric constants by which the properties of these materials are described. The article then focuses on the basis of the piezoelectric response in synthetic polymers.

Piezoelectricity or “pressure electricity” was coined from the Greek verb “piezen,” to press, by Pierre and Jacques Curie in the 1880s during an investigation of the symmetry in crystals. In this work it was found that certain crystals, lacking a center of symmetry, produced an electrical charge when mechanically deformed. The converse effect was also found to occur, whereby applying an electric field caused the crystal to change its shape. This phenomenon was attributed to a deformation of the net internal polarization in the crystal. When no external forces are present, the centers of positive and negative charges will coincide, and there is no net polarization. The application of a stress, be it mechanical (pressure) or electrical (applied field), causes a displacement of the centers of gravity of the positive and negative charges. In the absence of a center of symmetry, the charge displacement will be nonsymmetrical and thereby produce an induced dipole moment. This dipole moment, if produced by a mechanical stress, will cause the surfaces to develop an effective charge. If an external field displaces the charges, by electrostatic attraction or repulsion, it produces a mechanical strain which causes the material to deform. The mathematical relations describing this effect were developed in the few years following their discovery, making use of tensor notation to describe the directionality of the applied stress and the resultant strain.
Ion Beam Deposition, Film Modification and Synthesis
Authors: Rossnagel S.M. , Cuomo J.J.
Published: August 2016

Ion beam processing for thin film deposition is rapidly overtaking some of the more conventional plasma-based thin film processing techniques. This is due to strong improvements in the types and reliabilities of the sources available as well as a growing understanding of the advantages and capabilities of using ion beams.

An ion beam process can be differentiated from a plasma-based process in that the plasma in an ion beam is generated away from the sample and a beam of ions is directed at the sample. In a plasma-based process, the sample is usually immersed in the plasma. This highlights the fundamental advantage of ion beam processing—control of the flux and energy of the ions incident on either a sample or a target (for sputter deposition). It is this control which is missing in plasma-based processing, where the ion flux (current), ion energy, chamber pressure, and gas species are all hopelessly intertwined. In addition, certain aspects of the ion bombardment—angle of incidence, complications of gas scattering, etc. —are essentially fixed in plasma-based processing, leaving no room to vary parameters, and in conjunction, film properties.

A wealth of different types of ion sources cover a broad range of beam currents and energies. At the high energy end (0.1 – 20 MeV) are the implantation sources, typically used for doping semiconductors and treating surfaces (hardening, for example) and for various types of nuclear chemical analysis. These sources, however, tend to be very low current (μA). At slightly lower energies (tens of kilo-electron volts), but significantly higher currents (50 A), are the ion sources used for heating fusion plasmas.
Sputter Deposition Processes
Authors: Westwood W.D.
Published: August 2016

Deposition of films by sputtering was observed first in 1852 by Grove. The technique was in general use through the 1920s for preparing reflective coatings and other thin film samples. Western Electric deposited gold on wax masters for phonograph recordings. The improvement in diffusion pump technology at that time caused thermal evaporation deposition to replace sputtering.

Not till the 1950s did sputter deposition reappear… Bell Laboratories developed tantalum hybrid circuit technology using sputter deposition. Besides depositing Ta, they created a new material, Ta2N, by reactively sputtering tantalum in gas mixtures of argon and N2. Since then, these two methods, sputtering of metals and alloys and reactive sputtering of compounds, have been investigated for many applications of thin film materials.

Although the general aspects of the methods have changed little in the past 30 years, the implementations have changed significantly, particularly since the introduction of magnetron systems in the 1970s. This review will concentrate mainly on these flexible, high rate magnetron deposition systems.

The term sputtering actually applies to the physical processes by which atoms are removed from a material. Momentum is transferred from an incident, energetic particle, usually in the form of an ion, to atoms of the target material. A large number of these atoms are displaced from their normal sites in the crystal lattice, producing a disordered structure that also contains some of the incident particles, which are implanted. Some of the target atoms are displaced from the surface; if they have enough energy, they escape from the target as sputtered atoms.
Plasma-Assisted Chemical Vapor Deposition Processes
Authors: Bachmann P.K. , Gärtner G. , Lydtin H.
Published: August 2016

Over the past two decades a vast number of publications have emerged from laboratories all over the world, describing the application of plasmas for preparing and processing materials. MRS symposia, scientific journals and books, and complete conference series are solely devoted to this specific topic.

Modern VLSI integrated circuits, for instance, would simply not exist without sophisticated plasma etching techniques. But highly reactive, partly ionized and dissociated, quasi-neutral gases—plasmas—are not only useful for etching purposes, i.e., the removal of materials. They are also very valuable tools for the deposition of materials with unique structures and compositions at lower temperatures than for conventional thermally induced chemical vapor deposition processes. Backed by intensive research activities and more than a decade of practical experiences, plasma deposition technologies are now penetrating a number of industrial manufacturing processes.

Plasmas can be classified into two basic categories — non-isothermal, and isothermal or thermal plasmas.

Within the high electric fields applied for non-isothermal plasma generation at reduced pressure, free electrons are accelerated to energies that correspond to several thousand degrees in the case of thermal activation. The neutral species in the gas phase and the heavy ions are either not influenced by the fields or cannot follow changing fields fast enough. Their temperature stays low, resulting in a difference between electron and gas temperature. In these nonequilibrium plasmas, the collisions of high energy electrons and gas molecules result in dissociation processes that would only occur at very high temperatures of more than 5,000 K in the case of thermal equilibrium. Therefore, non-isothermal plasmas allow the preparation of materials and compositions that are difficult to obtain using thermally activated, conventional CVD. Due to the initiation of chemical reaction by collisions with “hot” electrons rather than hot gas molecules, the processing temperature can, in many cases, be kept lower than in conventional deposition processes.
Thin Film Deposition Processes
Authors: Messier Russell
Published: August 2016

Thin film materials pervade our everyday life as transparent conductors in LCD watches and computer displays and in defrosters for automobiles... antireflection coatings for camera lenses… optical fibers for communication … architectural glass coatings for both color and energy efficiency… solar cells… decorative coatings on plastics such as for toys and automobiles parts… a whole host of electronic and optoelectronic devices… hard coatings for cutting tools, drill bits, and bearings … even metallic coatings inside potato chip bags to keep the chips crisp!

Without thin films our lifestyles would be drastically different. And this trend toward increased use of thin film technology will only continue.

The varied reasons for using thin films and the specific deposition processes for preparing them are often complex; but usually relate to function, cost, beauty, materials and energy efficiency, and performance. In addition to technological applications, scientists are finding thin films to be an invaluable tool for investigating new physical phenomena, even at the quantum level. For instance, two of the most important new materials—high temperature ceramic superconductors and diamond coatings — are currently being made by several thin film deposition processes in order to explore both their scientific and technological potential.

Just 25 years ago the variety of deposition processes for preparing thin films was quite limited. Thin film scientists and technologists had at their disposal electrodeposition, elementary chemical vapor deposition, evaporation, and dc sputtering. Commercial equipment for electron-beam evaporation, a mainstay in the optical coatings industry, was just being developed. Most of the deposition processes reviewed in this and next month's MRS BULLETIN were either not commercially available or were not even conceived of then.
Molecular Dynamics Simulation of Epitaxial Growth
Authors: Schuller Ivan K.
Published: August 2016

The growth of thin films has been instrumental in the study of many areas of material science, physics, metallurgy, and chemistry and is an important ingredient in the development of many devices. Although experimental studies have been extensively pursued for many years, theoretical studies have only been performed using model calculations which rely on a number of unknown parameters a priori. Only recently have attempts been made to understand thin film growth using realtime numerical simulation. The main reason for the recent increase of such studies is the development of computers capable of tackling a problem of the magnitude required to understand thin film growth. The phenomena present in thin film growth occur for systems containing many particles (e.g., columnar growth) and long relaxation times, which strain the capabilities presently available in modern supercomputers. Further increases in computational power might bring a number of important problems within reach and improve our understanding of thin film growth at the microscopic level.

I will present a number of epitaxial growth studies we have performed using molecular dynamics (MD) techniques. I will show that a number of properties predicted by these calculations are in good agreement with experimental observations. These include the microcrystalline and epitaxial growth of metal films, the growth of amorphous films in mixtures of metals, and the vapor phase growth of silicon. Finally, I will outline several important studies yet to be implemented.
Molecular Beam Epitaxy: Thin Film Growth and Surface Studies
Authors: Moustakas Theodore D.
Published: August 2016

Molecular Beam Epitaxy (MBE) is a thin film deposition process in which thermal beams of atoms or molecules react on the clean surface of a single-crystalline substrate, held at high temperatures under ultrahigh vacuum conditions, to form an epitaxial film. Thus, contrary to the CVD processes described in the other articles, the MBE process is a physical method of thin film deposition.

The vacuum requirements for the MBE process are typically better than 10−10torr. This makes it possible to grow epitaxial films with high purity and excellent crystal quality at relatively low substrate temperatures. Additionally, the ultrahigh vacuum environment allows the study of surface, interface, and bulk properties of the growing film in real time, by employing a variety of structural and analytical probes.

Although the MBE deposition process was first proposed by Günther in 1958, its implementation had to wait for the development of the ultrahigh vacuum technology. In 1968 Davey and Pankey successfully grew epitaxial GaAs films by the MBE process. At the same time Arthur's work on the kinetics of GaAs growth laid the groundwork for the growth of high quality MBE films of GaAs and other III-V compounds by Arthur and LePore and Cho.
Growth and Characterization of GaAs Single Crystals
Authors: Jordan A.S. , Parsey J.M
Published: August 2016

From a commercial viewpoint, gallium arsenide (GaAs) is currently the leading member of the III-V compound family. Oriented substrates, cut and polished from single-crystal boules, form the materials foundation for a rapidly maturing technology of high speed and high frequency electronic devices and circuits. The initial thrust of GaAs applications was in high powered lasers and light-emitting diodes (LEDs) fabricated on n-type (Si-doped) GaAs wafers grown by the horizontal Bridgman technique. One of the important benefits of using GaAs is the high electron mobility compared to Si. This property has driven the development of low noise and power field-effect transistors (FETs) for microwave applications. The semi-insulating substrate requirement (>107 Ω-cm) was initially met by chromium doping. Currently, the interest is focused on MMIC (microwave monolithic integrated circuits), MIMIC (millimeter microwave ICs), analog ICs for lightwave transmitters and receivers, and digital ICs. The digital circuits have been realized with ion-implanted FETs, selectively doped heterostructure transistors (SDHTs), and heterostructure bipolar transistors (HBTs). Presently, most of the semi-insulating (SI) material processed by the industry is nominally undoped, and grown by the liquid encapsulated Czochralski (LEC) technique. The SI behavior is attained via a delicate balance of deep EL2 donors and carbon acceptors, avoiding chromium in order to eliminate the anomalous out-diffusion and type-conversion associated with this dopant.

GaAs wafers up to 4 inches in diameter, with electrical properties homogenized by whole ingot annealing, are currently available from U.S. domestic and overseas suppliers. However, the overall quality is compromised by the large dislocation densities, varying 104 – 105/cm2.
Materials for Photonic Switching and Information Processing
Authors: Glass A.M.
Published: August 2016

In electronic processors, heat dissipation and interconnection delay are serious design and performance limiting factors. Why then consider photonic components where both the energy and size of the photon are large (˜1 eV and ˜1 μm, respectively) and the required nonlinear interactions between electric or magnetic fields and photons for switching or modulation are small? There are several answers to this question. First, the wide bandwidth of optical communications systems is taxing the current capabilities of electronic switching technologies. Even a slow optical switch can switch a very wide bandwidth optical signal from one fiber to another. External optical modulators will likely be required in ultrawide bandwidth communications because of basic limitations on direct modulation of lasers. Because of the weak electromagnetic interaction and low dispersion, optical interconnection of electronic circuits offers considerable advantages in high speed computer architectures. Some of these applications would appear to be relatively near term since they build on current capabilities of optical communication.

Longer term and more speculative are applications of photonics to computation and image processing — areas where electronics technology is already mature. Current research can be divided into two groups — ultrafast processing and parallel processing. The first group concentrates on processing with ultra-fast optical pulses. Optical pulses as short as 6 fs — orders of magnitude shorter than any electronic pulses — have been generated in the research laboratory. High processing rates are achievable by serial processing of high repetition rate ultrashort pulses. This approach requires ultrafast switches, which in turn requires materials with ultrafast nonlinear optical response time. Indeed, the shortest electrical signals are now measured by optical sampling techniques.
Organic Materials for Nonlinear Optics
Authors: Meredith Gerald R.
Published: August 2016

were very exciting but speculative, being technologically feasible only if new classes of materials could be developed The subject of materials in nonlinear optics (NLO) encompasses a wide range of important topics. Today the line between materials and NLO processes has become fuzzy, particularly for newer NLO processes (e.g. photorefrac-tion, and optical bistability, logic and computing). For more established NLO processes (e.g., harmonic generation, parametric processes, linear electro-optic effect, etc.) the subjects are well studied and the importance of various materials properties on the NLO process are known, though these properties are not necessarily predictable, controllable, or optimized in current materials.

A decade ago, having been introduced to NLO phenomena through postdoctoral research, I had an opportunity to define and pursue an NLO research program at Xerox's Webster Research Center. The question was posed: “Are new materials needed for NLO applications?” The answer must start with another question: “Which NLO process … with light of what wavelength, pulse duration, and power… and for what purpose?”

It was clear that important limitations to many of the novel things one might do with optics were: insufficient nonlin-earity magnitude, inability to fabricate reliable device structures, occurrence of deleterious optical properties, and restrictions due to other material properties. The newer NLO phenomena. Use of older NLO processes in new technological applications seemed a more down-to-earth quest.
Interface Studies with Nonlinear Optics
Authors: Rasing Th. , Shen Y.R.
Published: August 2016

The importance of interfaces for material science and electronic devices has stimulated great interest in the development of surface analytical tools. Among them, modern optical techniques using lasers have attracted the most attention in recent years. They have the advantage of being applicable to all interfaces accessible by light, and the high temporal, spatial, and spectral resolutions offer unique opportunities for studying ultrafast molecular dynamics and other transient phenomena at interfaces. Optical second harmonic generation (SHG) and sum-frequency generation (SFG) are particularly being noticed because of the many recent successful demonstrations of their versatility. This article briefly introduces these newly developed surface probes, first outlining the basic principles behind surface SHG and SFG, and then illustrating the power of the techniques with selected examples. A more complete treatment of the theory can be found in References 4–6. An overview of the earlier applications can be found in Reference 3.

SHG arises from the nonlinear polarization P(2)(2ω) induced in a medium by an incident laser field E(ω). In the electric dipole approximation, P is given by:

where is a second-order nonlinear susceptibility. For a medium with inversion symmetry, it follows directly from Eq. 1 that = 0. However, at an interface the surface nonlinear susceptibility is nonvanishing because there the inversion symmetry is necessarily broken.
Up Close: National Nanofabrication Facility at Cornell University
Authors: Galvin Gregory
Published: August 2016

The National Nanofabrication Facility began in 1977 out of the scientific community's recognition of a national need for an openly accessible resource in microfabrication. The NNF was then known as the National Research and Resource Facility for Submicron Structures (NRRFSS). In establishing the NRRFSS, Cornell University and the National Science Foundation launched an ambitious experiment both in an advanced technology and in a new research methodology. The current charter of the facility, which differs little from NRRFSS' original charter, is to:

∎ Develop state-of-the-art instrumentation and processes for fabrication and characterization of structures at dimensions below 100 nm.

∎ Provide for both nanofabrication and microfabrication a national facility that is available to any qualified researcher from U.S. universities, industry, and federal laboratories.

∎ Aggressively pursue applications of nanofabrication techniques in a broad spectrum of engineering and scientific disciplines.

∎ Train students, scientists, and engineers in nanofabrication and microfabrication and their applications.

∎ Transfer nanofabrication technology and information to the research and development communities.

To meet these goals, faculty involved with the NRRFSS committed themselves to establishing a world-class research center. They hired staff, purchased equipment, built a new building, attracted new students and faculty, and began innovative research that either utilized microfabrication techniques or advanced those techniques.
Advanced Processing of Composites
Authors: Tittmann B.
Published: August 2016

The preservation of U.S. aeronautical leadership is an economic and military necessity, but it is by no means assured. The rise of Airbus, Ariane, and Embraer has been lightning fast; tomorrow could see the development of Japan's FSC or Israel's Lavi. Our competitors are well organized and often enjoy the support of their governments. Our capabilities are no longer unique; thus our future work is clearly defined for us.

The key to continued U.S. preeminence in aerospace is to be found in the further research, development, and application of a group of revolutionary technologies in the areas of propulsion, numerical and symbolic computation, laminar flow modeling, and advanced materials and structures. Exploitation of the emerging technologies in these areas by industry, government, and universities will significantly impact the performance and cost of future aerospace vehicles and systems. Materials science and engineering, particularly the discipline of nondestructive evaluation, will play a major role in making such continued aerospace leadership a reality.

From the use of plastic and glass radomes in the first jet engine demonstrators to the composite parts of today's most advanced aircraft, the need to ensure reliable materials has always been critical. Advanced materials and structural concepts offer the opportunity for significant airframe improvements on all types of aircraft. Indeed tomorrow's aerospace structures, such as the National Aerospace Plane, the Space Station, as well as the ATF and SDI-related items will employ a myriad of exotic materials that must be extremely reliable and highly producible.
Ultrafine Metal Particles in Porous and Dense Silica Gels
Authors: Pope Edward J.A. , Mackenzie J.D.
Published: August 2016

The present trend of developing electronic devices with increasingly fine dimensions borders on a number of fundamental scientific questions about the very nature of how materials at ultrafine dimensions behave. This article addresses some of these questions. The fabrication of discrete metallic phases in porous and nonporous glassy matrices presents a number of exciting device possibilities. Methods of fabricating ultrafine metallic phases in silica via the sol-gel route are presented.

In attempting to fabricate materials with ultrafine physical dimensions for a wide variety of applications, several fundamental questions arise about the nature of materials behavior. For example, how many metal atoms are necessary to form a cluster exhibiting “metallic“ properties? Moreover, does the number of atoms necessary depend upon which metallic property is examined? This question has been partly addressed by D.C. Johnson and co-workers with regard to magnetism in osmium clusters. Their results show a threefold increase in magnetic susceptibility between clusters containing 3–10 osmium atoms.

Another important question, especially when considering device applications, is how the relative contributions of surface and bulk thermodynamics affect such properties as phase transformations. In addition, ultrafine phase dimensions interact with the fundamental unit lengths of a wide range of processes, including the wavelength of visible light, the mean free path lengths of conduction processes, the wavelengths of phonon vibrations, etc. How do these interactions affect optical, thermal, and electronic properties?

Fabrication of ultrafine metallic particles in porous and nonporous matrices may lead to many possible device applications including heterogeneous catalysts, nonlinear optic devices, highvoltage switching devices based on interparticle tunneling, and perhaps even new types of charge storage devices (capacitors).
Continuum Modeling
Authors: Davison Lee
Published: August 2016

Common experience with the thermomechanical properties and behavior of matter is usually at the continuum level, i.e., observations concern such phenomena as elastic and inelastic deformation of solids, flow of fluids, and conduction of heat. Continuum descriptions of these phenomena are expressed in terms of partial differential equations representing the principles of balance of mass, momentum, and energy. Since the basic principles apply to all materials, it is apparent that they alone will not suffice for solving specific problems. The peculiarities of individual materials are expressed in terms of constitutive equations, of which Hooke's law of elasticity and Newton's law of viscosity are examples. For the most part, “continuum modeling” refers to the process of devising constitutive equations. This work requires exercise of physical insight at both the macroscopic and microscopic levels, consideration of experimental observations, and application of formal mathematical principles.

Much of materials science is devoted to development and application of materials that have been selected for, or designed to have, useful properties different from those of existing materials. Many materials are of interest precisely because they have unusual properties. For example, paints and other coatings are often designed to flow easily when spread, but resist running afterward. Much work is devoted to analyzing manufacturing processes, whether they be processing of foodstuffs, forging metals, drawing films and fibers, or curing polymers. Properties and physical states of materials that are important during manufacture are often very different from those desired under service conditions.
Up Close: Johns Hopkins Center for Nondestructive Evaluation
Authors: Millberg L.S.
Published: August 2016

Nondestructive evaluation has historically been used almost exclusively for detecting macroscopic defects after materials have been made or put into service. However, the role of NDE is now changing to include in-process control in an effort to increase yields and performance of materials. This includes materials stability during transport, storage, and fabrication, as well as degradation behavior during in-service life. The NDE community has implied that applying NDE in these ways is crucial to solving the economic problems of U.S. manufacturing industries. So called “intelligent manufacturing” is impossible without integrating modern NDE techniques into the production of today's advanced materials.

The Johns Hopkins University Center for Nondestructive Evaluation (CNDE) was established in 1984 as an interdisciplinary center for research and instruction, drawing on the resources and talent of the School of Engineering, Applied Physics Laboratory, School of Medicine, and School of Arts and Sciences. Currently 31 faculty or senior staff work with the Center. The techniques being developed are aimed at reliable in-process control of materials and processes. Another important purpose is the education of talented students who will enter the NDE field; 150 students are associated with the Center, a third of whom are graduate students. The CNDE also provides both research collaborators and industrial sponsors with access to all NDE research and instruction at Johns Hopkins University. Twenty-six research institutions have formal cooperative research programs and 19 organizations are corporate sponsors (see Figure 1).
Ceramics
Authors: Eagan Robert J.
Published: August 2016

Until the 1980s, most people thought of ceramics as artware and artifacts. The recent development of advanced ceramics for high performance thermal insulation (space shuttle tiles), high temperature structures (heat engines), and electronics (superconductors) has dramatically changed perceptions about the utility of ceramics.

High technology ceramics are related to “traditional” ceramics only to the extent that they are inorganic, nonmetallic materials. Traditional ceramics are derived from minerals. For example, dinnerware and bricks consist mostly of clay, while sand is the major ingredient in flat glass and containers. Abundant raw materials, simple processing, adequate performance at low cost, and technological evolution have kept these industries viable for several thousand years.

But, for demanding electronic or structural applications, synthesizing ceramics from minerals is often unacceptable. The chemical variability of mineral deposits, the difficulty of obtaining a homogeneous mixture of powders, and the problems of consolidating the powders into a uniform ceramic with desirable grain morphology, chemistry and grain boundary phases have stimulated the development of chemically derived ceramic precursors.
The Use of Exothermic Reactions in the Synthesis and Densification of Ceramic Materials
Authors: Holt J.B.
Published: August 2016

This article will provide information about chemical processes which rely on the heat evolved during reaction to synthesize and, in some cases, to simultaneously density single-phase or composite ceramic materials. Although the basic concept underlying these processes is simple, the high temperature reactions are complex and require careful study with individual systems before their potential as fabrication processes can be fully realized.

Many reactions between solids involving elements and/or compounds, or between solids and gases are highly exothermic. Listed in Table I is a selected group of typical chemical reactions accompanied by their calculated adiabatic temperatures. As a general rule any reaction with an adiabatic temperature ~2000°C or over can be reacted under combustion conditions. For example, suppose that a cold-pressed cylindrical compact of titanium and boron powder (Eq. 1) is ignited at the top surface with a convenient source of heat such as a laser. From the igniting surface a combustion wave rapidly self-propagates down the compact, transforming the reactants into the TiB2 product. Figure 1 shows a Ti and C powder compact where the combustion wave has progressed about halfway down the compact.
Pattern Formation in Materials Science
Authors: Gollub J.P. , Sander L.M.
Published: August 2016

The growth of materials at interfaces frequently leads to patterns with length scales that can be much larger than atomic sizes. Patterns resulting from morphological instabilities occur during crystal growth and are responsible for the intricate shapes of snowflakes, dendritic crystals, and the like. They also occur during the electrochemical deposition of metals on surfaces, and during the growth of thin films by vapor deposition. Our purpose is to point out some particularly interesting connections that have come to be appreciated during the past five years between different types of pattern-forming phenomena, and to summarize some recent theoretical approaches to understanding them.

The phenomenon of dendritic crystal growth, though studied for many years, is still a great challenge. As an example, we show the development of a needle crystal of ammonium bromide (NH4Br) from supersaturated aqueous solution in Figure 1. The contours are cross sections of the interface at 20-second intervals, obtained by digital image analysis. One can see that an approximately parabolic tip translates at constant speed, and that the needle crystal is apparently unstable to the development of a train of sidebranches that propagate outward from the main stem but do not move forward with the tip.
Phosphate Glasses
Authors: Sales Brian C.
Published: August 2016

Until recently, phosphate glasses were regarded as somewhat of a scientific curiosity—materials limited in technological application but nevertheless exhibiting interesting fundamental properties. Although the basic properties of many phosphate glasses have been studied on a laboratory scale during the past 50 years, very few of these materials proved to be of commercial interest. This lack of extensive practical application was primarily related to their poor chemical durability and a tendency to crystallize during processing.

The pace of modern technological development continues to result in an increased demand for new materials with specific characteristics, and this demand has led to renewed interest in a number of previously neglected materials—including phosphate glasses. The combined physical and chemical characteristics of phosphate glasses make them relatively unique among the families of inorganic glasses. These characteristics include: large thermal expansion coefficients, low preparation and softening temperatures, low melt viscosities, chemical compatibility with living bone, and a polymeric structure similar to that in organic polymers. Most recent research on phosphate glasses has emphasized one or more of these characteristics.

The major scientific questions pertinent to technological applications of phosphate glasses are related to utilizing the desirable characteristics of these materials while maximizing their corrosion resistance and thermal stability. In order to tailor a phosphate glass for a particular application, the corrosion mechanism of the glass must often be understood in detail, along with the relationship between the microscopic structure of the glass and its macroscopic properties.