bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nuclear Quadrupole Resonance
Authors: Herreros Bruno , Harbison Gerard S. 
Published: October 2003

AbstractNuclear quadrupole resonance (NQR) was once written off as a “dead” field, but has recently had a modest rebirth, and has been applied with success to several areas of materials science, most notably the high‐Tcsuperconductors. The name itself is a misnomer—NQR is really (NMR) at zero field. For that reason, it has many of the same disadvantages as the more familiar NMR spectroscopy e.g., poor sensitivity and complications arising from molecular dynamics, but because it does not require a superconducting magnet, NQR is generally cheaper and can be applied to a far greater number of nuclei. It is inherently noninvasive and nondestructive, and can be applied both to pure substances and to materials in situ. It is currently, for example, being used as an antiterrorist technique to screen persons and baggage for the presence of explosives, using receiver coils that are of the order of 1 m in radius. The principal disadvantage of NQR, other than sensitivity, is that, as a radiofrequency (RF) technique, it is incompatible with conducting or ferromagnetic materials; however, for the somewhat narrow range of materials to which it can be applied, NQR gives information which is otherwise unavailable.The NQR properties of a material are primarily defined by a transition frequency or set of transition frequencies, which can be used to determine two parameters—the quadrupole coupling constant, and the asymmetry parameter. These quantities are often quite characteristic of particular materials—as when they are used to detect drugs or explosives—but are also sensitive to temperature and pressure, and can therefore be used as a noninvasive probe of these properties. Moreover, by applying external spatially varying magnetic or radiofrequency fields, the NQR signal can be made position‐dependent, allowing the distribution of the NQR‐active species in the material to be imaged. Finally, the relaxation times of NQR nuclei are highly sensitive to dynamics, and so can be used as a local probe of molecular mobility.The internal structure of materials can also be imaged by x‐ray tomography and ultrasonic methods, which depend on the existence of inhomogeneities in the distribution of x‐ray absorbers, or acoustic properties, respectively. The stress and pressure dependences of the NQR frequency are generally much stronger than those of NMR imaging, and therefore NQR is a superior method for mapping the temperature or stress distribution across a sample. Such stress distributions can be determined for optically transparent material by using polarized light; for opaque material, there may be no alternative methods.This article aims to be a general and somewhat cursory review of the theory and practice of modern one‐dimensional (1D) and two‐dimensional (2D) NQR and NQR imaging.
Cyclotron Resonance
Authors: Kono J. 
Published: October 2003

Abstract

Cyclotron resonance (CR) is a method for measuring the effective masses of charge carriers in solids. It is by far the most direct and accurate method for providing such information. In the simplest description, the principle of the method can be stated as follows. A particle of effective mass

and charge

in a DC magnetic field

executes a helical motion around

with the cyclotron frequency

. If, at the same time, an AC electric field of frequency

is applied to the system, perpendicular to

, the particle will resonantly absorb energy from the AC field. Since

and/or ω can be continuously swept through the resonance and known to a very high degree of accuracy,

can be directly determined with high accuracy by

.

As a secondary purpose, one can also use CR to study carrier scattering phenomena in solids by examining the scattering lifetime τ (the time between collisions, also known as the collision time or the transport/momentum relaxation time), which can be found from the linewidth of CR peaks.
Although this article is mainly concerned with the simplest case of free carrier CR in bulk semiconductors, one can also study a wide variety of FIR magneto‐optical phenomena with essentially the same techniques as CR. These phenomena (“derivatives” of CR) include: (a) spin‐flip resonances, (b) resonances of bound carriers, (c) polaronic coupling, and (d) 1‐D and 2‐D magneto‐plasmon excitations.
It is important to note that all the early CR studies were carried out on semiconductors, not on metals.
Many techniques can provide information on effective masses, but none can rival CR for directness and accuracy. Effective masses can be estimated from the temperature dependence of the amplitude of the galvanomagnetic effects.
The basic theory and experimental methods of cyclotron resonance are presented in this article. Basic theoretical background is presented. A detailed description is given of the actual experimentation procedures. Finally, typical data analysis procedures are presented.
Mössbauer Spectrometry
Authors: Fultz Brent 
Published: October 2003

AbstractMössbauer spectrometry is based on the quantum‐mechanical “Mössbauer effect,” which provides a nonintuitive link between nuclear and solid‐state physics. Mössbauer spectrometry measures the spectrum of energies at which specific nuclei absorb γ rays. Curiously, for one nucleus to emit a γ ray and a second nucleus to absorb it with efficiency, the atoms containing the two nuclei must be bonded chemically in solids.Most applications of Mössbauer spectrometry in materials science utilize “hyperfine interactions,” in which the electrons around a nucleus perturb the energies of nuclear states. Hyperfine interactions cause very small perturbations of 10−9to 10−7eV in the energies of Mössbauer γ rays.Interpretations of Mössbauer spectra have few parallels with other methods of materials characterization. A Mössbauer spectrum looks at a material from the “inside out,” where “inside” means the Mössbauer nucleus. Hyperfine interactions are sensitive to the electronic structure at the Mössbauer atom, or at its nearest neighbors. The important hyperfine interactions originate with the electron density at the nucleus, the gradient of the electric field at the nucleus, or the unpaired electron spins at the nucleus. These three hyperfine interactions are called the “isomer shift,” “electric quadrupole splitting,” and “hyperfine magnetic field,” respectively.The viewpoint from the nucleus is sometimes too small to address problems in the microstructure of materials. In general, it is found that Mössbauer spectrometry is best for identifying the electronic or magnetic structure at the Mössbauer atom itself, such as its valence, spin state, or magnetic moment. The Mössbauer effect is sensitive to the arrangements of surrounding atoms, however, because the local crystal structure will affect the electronic or magnetic structure at the nucleus. Different chemical and structural environments around the nucleus can often be assigned to specific hyperfine interactions.Other applications of the Mössbauer effect utilize its sensitivity to vibrations in solids, its timescale for scattering, or its coherence. To date these phenomena have seen little use outside the international community of a few hundred Mössbauer spectroscopists. Nevertheless, some new applications for them have recently become possible with the advent of synchrotron sources for Mössbauer spectrometry.This article is not a review of the field, but an instructional reference that gives the working materials scientist a basis for evaluating whether or not Mössbauer spectrometry may be useful for a research problem.A few representative applications to materials studies are presented.
X‐Ray Techniques
Authors: Goldman Alan I. 
Published: October 2003

Abstract
This article explores the wide variety of applications of x‐ray scattering and spectroscopy techniques to the study of materials. Materials, in this sense, include not only bulk condensed matter systems, but liquids and surfaces as well. The term “scattering,” is generally used to include x‐ray measurements on noncrystalline systems, such as glasses and liquids, or poorly crystallized materials, such as polymers, as well as x‐ray diffraction from crystalline solids. Information concerning long‐range, short‐range, and chemical ordering as well as the existence, distribution and characterization of various defects is accessible through these kinds of measurements. Spectroscopy techniques generally make use of the energy dependence of the scattering or absorption cross‐section to study chemical short‐range order, identify the presence and location of chemical species, and probe the electronic structure through inelastic excitations.
The energy dependence of the x‐ray absorption cross‐section is punctuated by absorption edges or resonances that are associated with interatomic processes of constituent elements. These resonances can be used to great advantage to investigate element‐specific properties of the material and are the basis of many of the spectroscopic techniques described in set of articles.
X‐Ray Powder Diffraction
Authors: Stephens Peter W. , Bendele Goetz M. 
Published: October 2003

AbstractX‐ray powder diffraction is used to determine the atomic structure of crystalline materials without the need for large (∼100‐μm) single crystals. “Powder” can be a misnomer; the technique is applicable to polycrystalline phases such as cast solids or films grown on a substrate. X‐ray powder diffraction can be useful in a wide variety of situations. A number of questions that can be effectively addressed by this technique are listed. This is an attempt to illustrate the versatility of x‐ray powder diffraction and not, by any means, a complete list. Six experiments are described as concrete examples and constitute an assortment of problems of varying difficulty.X‐ray powder diffraction is an old technique, in use for most of this century. The capabilities of the technique have recently grown for two main reasons: (1) development of x‐ray sources and optics (e.g., synchrotron radiation, Göbel mirrors) and (2) the increasing power of computers and software for analysis of powder data. This article discusses the fundamental principles of the technique, including the expression for the intensity of each diffraction peak, gives a brief overview of experimental techniques, describes several illustrative examples, gives a description of the procedures to interpret and analyze diffraction data, and discusses weaknesses and sources of possible errors.
XAFSSpectroscopy
Authors: Heald Steve 
Published: October 2003

AbstractX rays, like other forms of electromagnetic radiation, are both absorbed and scattered when they encounter matter. X‐ray scattering and diffraction are widely utilized structural methods employed in thousands of laboratories around the world. X‐ray diffraction techniques are undeniably among the most important analysis tools in nearly every physical and biological science. As this article shows, x‐ray absorption measurements are achieving a similar range of application and utility. Absorption methods are often complementary to diffraction methods in terms of the area of application and the information obtained.The basic utility of x‐ray absorption arises from the fact that each element has characteristic absorption energies, usually referred to as absorption edges.The widespread use of x‐ray absorption methods is intimately connected to the development of synchrotron radiation sources. The measurements require a degree of tunability and intensity that is difficult to obtain with conventional laboratory sources. Because of this need and of advances in the theoretical understanding that came at about the same time as the major synchrotron sources were first developed, the modern application of absorption methods for materials analysis is only ∼25 years old. However, it has a long history as a physical phenomenon to be understood, with extensive work beginning in the 1930s.This article concentrates on the modern application of XAS at synchrotron sources. Conducting experiments at remote facilities is a process with its own style that may not be familiar to new practitioners. Some issues related to working at synchrotrons are discussed.
Magnetic X‐Ray Scattering
Authors: Hill J.P. 
Published: October 2003

AbstractThere are two regimes of importance in magnetic x‐ray scattering, characterized by the incident photon energy relative to the positions of the absorption edges in the system under study. These are the nonresonant and resonant limits to the cross‐section.This article provides an overall background to the theoretical and experimental principles of nonresonant and resonant magnetic x‐ray scattering. The experimental techniques are very similar to standard synchrotron x‐ray diffraction experiments; therefore discussion of the beamlines and spectrometers are limited, with only those elements particular to magnetic scattering, such as polarization analyzers, discussed in any detail. At high incident photon energy, it is possible to perform inelastic experiments utilizing the nonresonant magnetic scattering terms in the cross‐section. This allows for the measurement of magnetic Compton profiles (projections of the momentum density of the magnetic electrons, along a given direction). Magnetic Compton scattering may only be applied to ferromagnets, because of the incoherent nature of the inelastic scattering, and the technique differs in many aspects of its practical implementation from the diffraction experiments discussed here.
Resonant Scattering Techniques
Authors: Finkelstein Kenneth D. 
Published: October 2003

Abstract

This article will describes resonant (anomalous) x‐ray diffraction as it is used to obtain information about the roles of symmetry and bonding on the electronic structure of selected atoms in a crystal. These effects manifest themselves as crystal orientation‐dependent changes in the diffracted signal when the x‐ray energy is tuned through the absorption edges for those atoms. Applications of the method have demonstrated it is useful in: (1) providing site‐specific electronic structure information in a solid containing the same atom in several different environments; (2) determining the positions of specific atoms in a crystal structure; (3) distinguishing electronic from magnetic contributions to diffraction; (4) isolating and characterizing multipole contributions to the x‐ray scattering that are sensitive to the local environment of atoms in the solid; and (5) studying the ordering of 3
d
electron orbitals in the transition metal oxides.

This article describes resonant x‐ray scattering by presenting its principles, illustrating them with several examples, providing background on experimental methods, and discussing the analysis of data. Principles of the method presented are the classical picture of x‐ray scattering, including anomalous dispersion, followed by a quantum‐mechanical description for the scattering amplitudes, and ends with a discussion on techniques of symmetry analysis useful in designing experiments. Two examples from the literature are used to illustrate the technique. This is followed by a discussion of experimental aspects of the method, including the principles of x‐ray polarization analysis. A list of criteria is given for selecting systems amenable to the technique, along with an outline for experimental design. A general background on data collection and analysis includes references to sources of computational tools and expertise in the field.
X‐Ray Microprobe for Fluorescence and Diffraction Analysis
Authors: Ice Gene E. 
Published: October 2003

AbstractX‐ray diffraction and x‐ray‐excited fluorescence analysis are powerful techniques for the nondestructive measurement of crystal structure and chemical composition. X‐ray fluorescence analysis is inherently nondestructive, with orders‐of‐magnitude lower power deposited for the same detectable limit as with fluorescence excited by charged particle probes. X‐ray diffraction analysis is sensitive to crystal structure with orders‐of‐magnitude greater sensitivity to crystallographic strain than electron probes. When a small‐area x‐ray microbeam is used as the probe, chemical composition, crystal structure, crystalline texture, and crystalline strain distributions can be determined. These distributions can be studied both at the surface of the sample and deep within the sample. Current state‐of‐the‐art can achieve an ∼1‐μm diameter x‐ray microprobe and an ∼0.1 μm diameter x‐ray microprobe has been demonstrated.Despite their great chemical and crystallographic sensitivities, x‐ray microprobe techniques have until recently been restricted by inefficient x‐ray focusing optics and weak x‐ray sources; x‐ray microbeam analysis was largely superseded by electron techniques in the 1950s. However, interest in x‐ray microprobe techniques has now been revived by the development of efficient x‐ray focusing optics and ultra‐high‐intensity synchrotron x‐ray sources. These advances have increased the achievable microbeam flux by more than 12 orders of magnitude; the flux in a tunable 1 μm‐diameter beam on a so‐called third‐generation synchrotron source such as the Advanced Photon Source (APS) can exceed the flux in a fixed‐energy mm2beam on a conventional source. These advances place x‐ray microfluorescence and x‐ray microdiffraction analysis techniques among the most powerful techniques available for the nondestructive measurement of chemical and crystallographic distributions in materials.This article reviews the physics, advantages, and scientific applications of hard x‐ray (E> 3 keV) microfluorescence and x‐ray microdiffraction analysis. Because practical x‐ray microbeam instruments are extremely rare, a special emphasis will be placed on instrumentation, accessibility, and experimental needs which justify the use of x‐ray microbeam analysis.
Scanning Electron Microscopy
Authors: Chandler Gary W. , Seraphin Supapan 
Published: October 2003

Abstract
The scanning electron microscope (SEM) is one of the most widely used instruments in materials research laboratories and is common in various forms in fabrication plants. Scanning electron microscopy is central to microstructural analysis and therefore important to any investigation relating to the processing, properties, and behavior of materials that involves their microstructure. The SEM provides information relating to topographical features, morphology, phase distribution, compositional differences, crystal structure, crystal orientation, and the presence and location of electrical defects. The SEM is also capable of determining elemental composition of micro‐volumes with the addition of an x‐ray or electron spectrometer and phase identification through analysis of electron diffraction patterns. The strength of the SEM lies in its inherent versatility due to the multiple signals generated, simple image formation process, wide magnification range, and excellent depth of field.
Lenses in the SEM are not a part of the image formation system but are used to demagnify and focus the electron beam onto the sample surface. This gives rise to two of the major benefits of the SEM: range of magnification and depth of field in the image. Depth of field is that property of SEM images where surfaces at different distances from the lens appear in focus, giving the image three‐dimensional information. The SEM has more than 300 times the depth of field of the light microscope. Another important advantage of the SEM over the optical microscope is its high resolution. Resolution of 1 nm is now achievable from an SEM with a field emission (FE) electron gun. Magnification is a function of the scanning system rather than the lenses, and therefore a surface in focus can be imaged at a wide range of magnifications from 3× up to 150,000×. The higher magnifications of the SEM are rivaled only by the transmission electron microscope (TEM), which requires the electrons to penetrate through the entire thickness of the sample. As a consequence, TEM sample preparation of bulk materials is tedious and time consuming, compared to the ease of SEM sample preparation, and may damage the microstructure. The information content of the SEM and TEM images is different, with the TEM image showing the internal structure of the material.
Due to these unique features, SEM images frequently appear not only in the scientific literature but also in the daily newspapers and popular magazines. The SEM is relatively easy to operate and affordable and allows for multiple operation modes, corresponding to the collection of different signals. This article reviews the SEM instrumentation and principles, its capabilities and applications, and recent trends and developments.
Low‐Energy Electron Diffraction
Authors: Gerken Craig A. , Somorjai Gabor A. 
Published: October 2003

AbstractLow‐energy electron diffraction (LEED) is a powerful method for determining the geometric structure of solid surfaces. It is similar to x‐ray diffraction (XRD) in the type of information that it provides, and XRD will be frequently referred to for analogy throughout this unit. The most obvious difference is that a beam of electrons, rather than x rays, is used. Since electrons have a mean free path (or attenuation length) measured in angstroms (Å) as opposed to microns (μ) for x rays, LEED is particularly sensitive to surface geometry.LEED is a structural technique that can provide essentially two levels of information. In both cases, it is most commonly used to determine the structure of a solid surface when the bulk structure of the material is already known by other means (e.g., XRD). It is possible, and indeed straightforwardly simple, to use LEED to determine both the absolute dimensions of the surface unit cell and the unit cell symmetry. One can easily deduce that, for example, a surface has a two‐dimensional (2D) unit cell twice as large as that of the bulk; this often allows a reasonable guess at the true structure. Sometimes it is sufficient to know that a particular phase is present without knowing the details of the structure. Determination of the exact atomic positions is more difficult, but quantitative experiments can elucidate this second level of information. Sophisticated calculations, generally run on a workstation, can provide atomic coordinates with a typical precision of ±0.05 Å, which is generally more than adequate to determine the adsorption site of a molecule or the atomic positions in a reconstructed surface.Many different surfaces can be examined by LEED, and their terminology must be understood.LEED is a mature area of surface science and it is useful to consider the state of the art in this field. A great deal of work has been done on clean metal and semiconductor surfaces, and much of this is considered “done”; current work in this area consists mostly of refinements.