bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.