bluuebunny/crossref_metadata_2025_split huggingface dataset:
Portuguese-Spanish Collaboration on LiNbO3
Authors: Soares J.C. , Agulló-Lopez F. 
Published: August 2016

Since 1987, an intensive Portuguese-Spanish collaboration program has been developed on microstructural characterization of LiNbO3 by nuclear (ion-beam and hyperfine interaction) techniques. The collaboration involves the Department of Applied Physics of the Universidad Autónoma de Madrid, on the Spanish side, and the Center of Nuclear Physics and the Department of Physics of LNETI, on the Portuguese side. The combined effort of the two latter institutions is now channeled through the recently created Center for Materials Characterization and Processing.LiNbO3 is an important material for optoelectronic applications, including light modulation, microwave filters, frequency doublers, and those applications based on the photorefractive effect. Photorefractive applications, still at the laboratory level, include holographic information storage, coherent beam amplification, beam deflectors, and applications relying on the production of phase-conjugated beams by four-wave mixing. LiNb03 is particularly useful for optical information processing, optical interconnects, associative memories, and neural net implementations. These applications involve bulk LiNbO3, but mostly waveguide structures fabricated in LiNbO3 substrates. Recently the development of efficient waveguide lasers on ion-implanted and proton-exchanged waveguides has opened a new field whose final objective is the fabrication of integrated laser modulators and frequency doublers on the same “chip.” The mastering and optimization of all these applications rely on an adequate microstructural characterization of the material with particular reference to both intrinsic and extrinsic point defects. The knowledge and control of this microstructure should permit the fabrication of well-characterized and reproducible devices.
Research on Cement-Based Materials: Expanding Our Horizons
Authors: Young J. Francis 
Published: August 2016

Concrete is the most widely used man-made product; in the United States we use about two tons per year per person. It has been estimated that the replacement value of concrete structures is over six trillion dollars, and that over one trillion dollars needs to be spent in the repair and rehabilitation of these structures over a 20-year period. By contrast, the resources devoted to the materials issues of the industry have been meager. This neglect may in part explain why the development of the science of cementitious materials had lagged behind that of other materials. The situation has been changing rapidly in recent years, however, and the articles in this issue have been selected to illustrate some of the advances that are being made.One key to the resurgence in research in cement-based materials is the realization of the pressing need to upgrade our deteriorating infrastructure. Another is the realization that a materials science and engineering approach is needed to provide a solid knowledge base to underpin new technologies. Chemistry took us a long way in the 1950s and 1960s, but an appreciation of how chemistry and processing could combine to create desirable micro-structures that would achieve desirable bulk properties came much later. It is significant that, with the noticeable exception of the Pennsylvania State University, cement research in universities in the United States previously was funded through civil engineering departments. Similarly, in Europe and Japan, research was conducted primarily in engineering faculties, although there were programs in a few chemistry departments. Now, however, on both sides of the Atlantic Ocean, research groups are well established in materials science departments. It is noteworthy that on an NSF Science and Technology Center devoted to advanced cement-based materials is funded through the Division of Materials Research.
Material Considerations in Musical Strings
Authors: Pickering Norman C. 
Published: August 2016

Strings for musical instruments seem to be among the simplest of devices. Textbooks on acoustics commonly use them as the most elementary example of a vibrating system. However, the assumptions often made to simplify mathematics are far from the conditions that exist in real strings made of even the most suitable materials available.Consider what a musician wants in any instrument: as wide a frequency range as practical; considerable acoustic power with a significant difference between loud and soft notes; and, if possible, the ability to play several notes at once. The last requirement dictates the presence of multiple oscillators. Long, thin strings in closely-spaced groups fit the bill, but they are inherently deficient in meeting the other criteria without help from additional devices.Direct acoustic output from a vibrating string is negligible because it alone cannot move enough air. This deficiency has been corrected in hundreds of ingenious ways over thousands of years by mechanical coupling to a light, stiff structure large enough to radiate the lowest pitch being produced, often incorporating air-cavity resonators tuned to enhance low-frequency output. In this electronic era, unlimited power can be obtained using transducers to detect string motion as electrical voltages that can be amplified and directed to loud-speakers.
Graphite-Epoxy Acoustic Guitar Technology
Authors: Decker John A. 
Published: August 2016

We have successfully developed an acoustic guitar (Figure 1) composed of graphite. Trademarked the RainSong® graphite guitar, this instrument uses no endangered tropical tonewoods. The instrument's sound quality is equal to that of a fine wooden guitar. At high frequencies, the clarity, sustain, and play-ability surpasses that of wooden guitars. Because of its construction, the instrument is sturdy and is impervious to humidity, heat, and water.The development of this guitar required analysis of the theory of anisotropic sound propagation in the guitar soundboard and body, and resulted in two patents. We designed prototype guitars in collaboration with Pimentel & Sons, Guitar Makers, and used combinations of unidirectional and woven graphite and aramid fibers in an epoxy-resin matrix.The goal of our project was to accurately duplicate—panel by panel—the acoustic properties of a fine wooden guitar. We had the resulting acoustic modes and frequencies verified in the laboratory. We then developed and constructed open-mold and resin-transfer molding tooling for a family of classical, steel-string acoustic and hollow-body electric guitars, which are now in commercial production.Possibly the first all-composite acoustic guitar, the RainSong® represents a fundamental change in stringed-instrument construction, perhaps the first since the 17th Century Italian masters.The RainSong® technology allows musicians to skirt the effects of climate and transport damage on their instruments. The instrument contains essentially no wood, and hence negates environmental concerns about rapid depletion of the virgin-forest woods, from which stringed instruments have traditionally been made.
Why In Situ, Real-Time Characterization of Thin-Film Growth Processes?
Authors: Auciello Orlando , Krauss Alan R. 
Published: August 2016

It is anticipated that a new generation of advanced electronic and optical devices will involve the synthesis of diverse materials in single or multielement thin-film form, or in layered heterostructures. These devices will most likely involve diverse materials such as high-temperature superconductors, ferroelectric, electrooptic, and optical materials; diamond; nitrides; semiconductors; insulators; and metals in the form of ultra-thin layers with sharp interfaces in which the layer thickness may reach atomic dimensions. Therefore, it becomes increasingly important to be able to monitor the deposition process in situ and in real time, particularly for complex multicomponent oxides or nitrides, in which the production of the desired phase is a highly sensitive function of the growth conditions, often requiring relatively high-pressure oxygen or nitrogen environments up to several hundred mTorr, and in some cases, several Torr. Consequently, the growth environment for many of these materials is incompatible with conventional surface-analytic methods, which are typically restricted to high-or ultrahigh-vacuum conditions. New deposition and analytical methods, or adaptation of those already established, will be required.Since thin-film growth occurs at the surface, the analytical methods should be highly surface-specific, although sub-surface diffusion and chemical processes also affect film properties. Sampling depth and ambient-gas compatibility are key factors which must be considered when choosing in situ probes of thin-film growth phenomena. In most cases, the sampling depth depends on the mean range of the exit species (ion, photon, or electron) in the sample.
Time-of-Flight, Ion-Beam Surface Analysis for In Situ Characterization of Thin-Film Growth Processes
Authors: Krauss Alan R. , Auciello Orlando , Schultz J. Albert 
Published: August 2016

Low-energy (5–15 keV) ion scattering spectroscopy (ISS) and direct recoil spectroscopy (DRS) are well-established analysis techniques that have been used for several years to characterize surfaces of materials. ISS utilizes a beam of ions in the 1–15 keV range which are scattered by a surface atom at an angle θ1 relative to the direction of incidence. In this energy range, the collisions are elastic and are described by classical two-body collision kinematics. The kinetic energy E1 of the scattered primary ion is given bywhere E0 is the primary ion kinetic energy and α = M2/M1. Note that Equation 1 has real values only if M2 > M1, and ISS is not able to detect surface atoms which are lighter than the primary ion beam.The kinetic energy of the backscattered primary particle may be measured either by using an electrostatic energy analyzer (ESA) or by pulsing the beam and using a time-of-flight (TOF) detection scheme. The ESA only detects the ion fraction (typically 10 2−10−4) of the scattered primary beam and transmits only a narrow portion of the energy distribution of these ions, whereas the TOF detection scheme simultaneously detects the full energy range of both ions and neutrals. Consequently, the required beam dose for TOF detection is 3–4 orders of magnitude smaller than that required by the ESA. A typical analysis beam dose for TOF detection is ∼1011−1012 ions/cm2, removing or displacing one part in 103−104 of the near-surface atoms and making the TOF scheme essentially nondestructive.
Laser-Reflectance Interferometry Measurements of Diamond-Film Growth
Authors: Zuiker Christopher D. , Gruen Dieter M. , Krauss Alan R. 
Published: August 2016

The remarkable properties of diamond, including its hardness, chemical inertness, high thermal conductivity, low coefficient of friction, optical transparency, and semiconducting properties, have led to considerable research in the area of diamond thin-film deposition. Diamond films have been characterized ex situ by a large number of diagnostic techniques including Raman spectroscopy, x-ray diffraction, SEM, and TEM. In situ diagnostics, which can provide information in real time as the film is growing, are less common.Laser-reflectance interferometry (LRI) has been used to monitor the growth of diamond films in situ. The technique involves measuring the intensity of a laser beam reflected from the substrate surface on which the film is growing. The reflected beam is the sum of beams reflected by the gas-diamond interface and the diamond-silicon interface. Oscillations in the reflectivity are observed as the film grows because of interference between the reflected beams. Each oscillation indicates an increase in film thickness of λ/2n, where λ is the laser wavelength and n is the index of refraction of the film. If the index of refraction of the film is known, the thickness and growth rate can be determined in situ. For LRI measurements with 632.8-nm-wavelength HeNe lasers, the index of refraction of diamond films has been found to be within 10% of the bulk diamond value of 2.4. Each oscillation therefore indicates an increase in film thickness of 0.13 μm.The reflectivity measured by LRI is also affected by scattering because of surface roughness.
Total-Reflection X-Ray Fluorescence Spectroscopy for In Situ, Real-Time Analysis of Growing Films
Authors: Roberts T.A. , Gray K.E. 
Published: August 2016

For many thin-film applications it is useful or necessary to accurately monitor and control the film's physical properties. Particularly important are composition and structure, which determine most of the material's properties. Examples include the semiconducting properties of SixGe1−x, the ferroelectric properties of BaTiO, and the superconducting properties of Bi2Sr2CaCu2Oy, all of which depend strongly on composition. The development of in situ analyses not only provides the possibility of feedback control during deposition, but also assists in a more efficient evaluation of the best processing conditions to achieve particular properties. Control of the film structure and composition during film growth has not been easy, and in situ analyses during film nucleation and growth has been a goal of many investigators.Our interest in in situ monitoring of film deposition was motivated by sputter growth of Bi2Sr2CaCu2Oy from a composite target. These studies found that the film composition was a strong function of deposition parameters, particularly the substrate temperature. Investigating these complex relationships required the growth and ex situ analysis of many films. It was clear that a technique to determine the composition of films during growth could efficiently unravel the complex relationships between composition and processing parameters.An important consideration for an in situ analysis technique is that it not interfere with the growth process either by altering the film surface or by changing the deposition dynamics. During deposition, the substrate temperature, gas flow, and deposition rate all must be maintained; any interruptions for the analysis may alter the growth irreversibly.
Real-Time Monitoring of Epitaxial Processes by Parallel-Polarized Reflectance Spectroscopy
Authors: Dietz Nikolaus , Bachmann Klaus J. 
Published: August 2016

The engineering of advanced micro-electronic circuits, optoelectronic devices, and integrated optical circuits requires precise control of the lateral dimensions and thicknesses of device features and of the stoichiometry and doping of epitaxial semiconductor regions. This is preferably achieved by real-time monitoring and control of the individual deposition and etching processes that constitute the processing sequence. The use of optical probe techniques for the real-time monitoring of etching and/or growth processes is favored because of their nondestructive character and their potential use in real-time feedback control. Some of these methods are ideal in monitoring the overall growth process and/or substrate temperature in industrial applications, requiring low cost and maintenance. For example, in situ reflectance-spectroscopy methods, such as dynamic optical reflectivity (DOS), spectral-resolved normal incidence reflectance spectroscopy (MRS), or pyrometric interferometry (PI), are successfully applied to various deposition processes and provide information on both the growth rate and the composition of the deposits. However, small changes in the reflectance (because of chemical interactions at the surface of the films with the reactants supplied from the vapor phase) are of the order of 10−3 to 10−4 and are hardly observable with normal-incidence reflectance techniques because of the high reflectivity of substrate/film interface, which is typically of the order of 40%–60% for many semiconductors.In order to increase the sensitivity to surface- and interface-related growth properties, alternative optical-observation methods such as reflectance difference spectroscopy (RDS), surface photoabsorption (SPA), and spectral ellipsometry (SE) have been developed.
The Coolidge Process for Making Tungsten Ductile: The Foundation of Incandescent Lighting
Authors: Briant C.L. , Bewlay Bernard P. 
Published: August 2016

Try to imagine a world without incandescent lamps. We light our homes with 20-200-watt lamps, which are routinely purchased in local stores. These lamps are made at the rate of millions per week and their manufacture represents a large global industry. The consumer expects them to last approximately 1,000 hours and to be energy efficient and inexpensive.Many types of incandescent lamps exist. Figure 1 shows several examples. The most common types are A-line (the general household lamp), automotive lamps, and reflector lamps for floodlight or projector applications. We also have many thousands of specialty lamps, which have a broad range of applications, such as audio-visual projectors, fiberoptic systems, video-camera lights, airport-runway markers, photoprinters, medical/scientific instruments, and stage/studio systems. They can have power ratings from a few watts to several thousand watts, but they all have at least one feature in common. They contain a filament made of tungsten wire. The diameter of the wire will vary, depending on the power rating and application of the lamp, but for most common household lamps it is less than 100 μm.
Magnetism on a Microscopic Scale
Authors: Krishnan Kannan M. 
Published: August 2016

Tremendous progress has been made in the field of magnetic-materials research and technology over the past few years. Superior properties and novel scientific questions arise from our ability to either synthesize artificial structures or tailor microstructures at the appropriate length scale. The development of enhanced macroscopic properties in such materials requires, in addition to synthesis, that the magnetic microstructure be quantitatively determined and its dependence on the physical/chemical microstructure at the appropriate length scale be understood. Such studies are also motivated by the technologies of information storage, magnetic and magnetooptic recording, sensors, and magnetic devices. While these applications have been the focus of earlier issues of the MRS Bulletin, here we emphasize the physics, materials science, novel magnetic measurements, and micromagnetics, as well as the implications of this work on emerging technologies.Magnetism, subtle in its manifestations, is electronically driven but weak compared to electrostatic interactions. It is quantum-mechanical in nature with its origins in the Pauli exclusion principle and the existence of electron spin. However, it is known for a variety of both classical and quantum-mechanical effects stemming from both short- and long-range forces. It has a wide association with what is traditionally known as “microstructure” or the morphological arrangement of phases, grains, or individual atoms themselves. These factors are in part the reason for the richness of structures and properties encountered in magnetic systems from which many useful engineering and technical applications arise. They are also in part the reason why magnetism remains poorly understood and why many fundamental questions remain unanswered.
Magnetic Microstructures of Perpendicular Magnetic-Recording Media
Authors: Lodder J. Cock 
Published: August 2016

Magnetic recording has been the dominant recording technology for information storage since the invention of the computer. Currently, 1-Gbit/in. longitudinal magnetic recording (LMR) systems have been realized and densities of 10 Gbit/in., having bit areas less than 0.1 μm, are being developed. To reach this goal, a drastic scaling down of the track pitch, bit-cell length, head gap, medium thickness, and head-medium spacing is required. If this trend of increasing densities continues, an areal density of more than 300 Gbit/in. is predicted in the 21st century, based on computer simulation using the perpendicular magnetic recording (PMR) mode instead of the current LMR scheme. Magnetic-recording technologies and related materials have already been discussed in another issue of the MRS Bulletin, and hence in this paper, we concentrate on Co-Cr-X material used as a medium for PMR.The PMR mode has been studied since 1975 and at present, Co-Cr-X (e.g., X = Ta) films with perpendicular anisotropy are the most promising media material. In general, such media should have the following properties: easy axis of magnetization perpendicular to the film plane, suitable coercivity (Hc) and remanent magnetization (Mr) for storing the information and reading it at a high signal-to-noise (S/N) level, uniform columnar size with a small diameter, magnetically uncoupled columns having a magnetization reversal based on rotation instead of a domain-wall motion, chemical stability under various environmental conditions, and a small surface roughness. In order to achieve the desired magnetic anisotropy and coercivity, a columnar morphology (small diameter) with an hep [0001] texture and exchange-decoupled, columnar boundaries—to create a magnetic microstructure for single domain switching columns with high coercivity—should be obtained. An overview of the preparation, microstructure, and magnetic properties of Co-Cr thin films is given in Reference 8. Depending on the deposition parameters, a so-called initial layer (with an in-plane magnetization) can be present.
Collimated Sputtering of Titanium and Titanium Nitride Films
Authors: Ryan James G. , Brodsky Stephen B. , Katata Tomio , Honda Makoto , Shoda Naohiro , Aochi Hideaki 
Published: August 2016

Collimated sputtering is a physical vapor deposition (PVD) method where a collimator is inserted between a conventional “full-face-erosion” sputtering target and a substrate (Figure 1). The collimator is a plate of hexagonal cells that acts as a filter to remove obliquely incident atoms before they arrive at the substrate. Only material with a nearly normal incidence trajectory may pass through the collimator and deposit on the substrate. Collimated sputtering was initially evaluated for conductor-level depositions in order to improve the filling of recessed features. Although the method has been successfully used to fill damascene structures, depositing thick conductor films is inefficient because most of the sputtered material is captured by the collimator, causing the collimator to clog quickly, necessitating frequent replacement.A more common use of collimated sputtering is associated with the deposition of thin “liner” films. For example, thin, collimated aluminum alloy films have been used as underlayers for aluminum reflow processes. Also, collimated Ti/TiN films are used as contact/adhesion layers for chemically vapor-deposited (CVD) W metallization. Collimation provides better bottom and sidewall coverage for small, high aspect-ratio features than conventionally sputtered films do.Coliimated sputtered films often exhibit unique properties because the angle of incidence of depositing atoms is controlled. Collimated AlMg alloys have superior electromigration resistance compared to noncollimated AlMg films. Collimated TiN films appear to exhibit denser grain structures when compared to films deposited with higher amounts of obliquely incident flux (Figure 2).