bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cyclic Voltammetry
Authors: Bocarsly Andrew B. 
Published: October 2003

Abstract
A system is completely characterized from an electrochemical point of view if its behavior in the three‐dimensional (3D) space composed of current, potential, and time is fully specified. In theory, from such phenomenologic data one can determine all of the system's controlling thermodynamic and kinetic parameters, including the mechanism of charge transfer, rate constants, diffusion coefficients, standard redox potentials, electron stoichiometry, and reactant concentrations.

The enormous information content and complexity of electrochemical dynamics in the current‐potential‐time domain introduces two major experimental complications associated with electrochemical data. First is the pragmatic consideration of how much time is necessary to obtain a sufficiently complete data set to allow for a useful analysis. The second, far more serious complication is that different charge‐transfer mechanisms often translate into subtle changes in the
i
(
E
,
t
) response. Thus, even after one has access to a complete data set, visual inspection is typically an insufficient means to determine the mechanism of charge transfer. Furthermore, knowledge of this mechanism is critical to determining the correct approach to data analysis. Thus, given the requisite data set, one must rely on a series of large calculations to move from the data to chemically meaningful parameters.

The approach described so far is of limited value as a survey tool, or as a global mechanistic probe of electrochemical phenomena. It is, however, a powerful technique for obtaining precise thermodynamic and kinetic parameters once the reaction mechanism is known. The mathematical resolution to the problem posed here is to consider the projection of the
i
(
E
,
t
) surface onto a plane that is not parallel to the
i
‐
E
‐
t
axis system. This is the basis of cyclic voltammetry. A single projection is not sufficient to completely characterize a system; however, if judiciously chosen, a limited set of projections (on the order of a half dozen) will provide sufficient information to determine the reaction mechanism and obtain the key reaction parameters to relatively high precision. Perhaps more importantly, reduction of the data to two dimensions allows one to determine the mechanism based on pattern recognition, and thus no calculational effort is required.

The qualitative aspect of cyclic voltammetry has made it a general tool for the evaluation of electrochemical systems. With regard to materials specifically, the technique has found use as a method for investigating the electrosynthesis of materials (including conducting polymers and redox‐produced crystalline inorganics), the mechanism of corrosion processes, the electrocatalytic nature of various metallic systems, and the photoelectrochemical properties of semiconducting junctions. Here a general description of the cyclic voltammetric technique is provided along with some examples focusing on materials science applications.
Optical Imaging and Spectroscopies
Authors: Samuels Alan C. 
Published: October 2003

Abstract

All materials absorb and emit electromagnetic radiation. The characteristics of a material frequently manifest themselves in the way it interacts with radiation. The fundamental basis for the interaction varies with the wavelength of the radiation, and the information gleaned from the material under study will likewise vary. Materials interact with radiation in some fashion across the entire electromagnetic spectrum, which can be thought of as spanning the frequency realm from near DC oscillations found in circuits (<1 Hz) through the extremely high frequency oscillations typical of gamma radiation (>10
19
Hz).

The articles in this category present methods that are useful in the optical characterization of materials. The preceding discussion illustrates how spectroscopy permeates the entire encyclopedia—called upon where appropriate to specific materials studies. Spectroscopy, as a general category of techniques, will certainly remain central to the characterization of materials as materials science continues its advance.
Resonance Methods
Authors: Fultz Brent 
Published: October 2003

Abstract
This chapter shows how nuclear and electron resonance spectroscopies can help solve problems in materials science. The concept of a probe, located centrally within a material, is common to all resonance spectroscopy techniques. For example, the nucleus serves as the probe in nuclear magnetic resonance (NMR), nuclear quadrupole resonance (NQR), and Mössbauer spectrometry, while a paramagnetic atom (i.e., one containing unpaired electrons) often serves as a probe in electron spin resonance (ESR). Sometimes the interest is in measuring the total numbers of probes within a material, or the concentration profiles of probe nuclei as in the case for basic NMR imaging. More typically, details of the measured energy spectra are of interest. The spectra provide the energies of photons that are absorbed by the probe, and these are affected by the electronic and/or nuclear environment in the neighborhood of the probe. It is often a challenge to relate this local electronic information to larger features of the structure of materials.
The articles in this category describe how local electronic and magnetic structure can be studied with resonance techniques.
Electron Paramagnetic Resonance Spectroscopy
Authors: Eaton Sandra S. , Eaton Gareth R. 
Published: October 2003

AbstractElectron paramagnetic resonance (EPR) spectroscopy, also called electron spin resonance (ESR) or electron magnetic resonance (EMR), measures the absorption of electromagnetic energy by a paramagnetic center with one or more unpaired electrons. In the presence of a magnetic field, the degeneracy of the electron spin energy levels is removed and transitions between the energy levels can be caused to occur by supplying energy. When the energy of the microwave photons equals the separation between the energy levels of the unpaired electrons, there is absorption of energy by the sample and the system is said to be at “resonance”. Typically the experiment is performed with magnetic fields such that the energies are in the microwave region. Hyperfine splitting of the signal occurs due to interaction with nuclear spins and can therefore be used to identify the number and types of nuclear spins in proximity to the paramagnetic center.The information content of EPR arises from the ability to detect a signal and from characteristics of the signal, including integrated intensity, hyperfine splitting by nuclear spins,gvalue, line shape, and electron spin relaxation time. The characteristics of the signal may depend on environmental factors, including temperature, pressure, solvent, and other chemical species. Various types of EPR experiments can optimize information concerning these observables. Some commonly asked materials science questions that one might seek to answer based on these observables and some corresponding experimental design considerations are listed. Some general information and practical considerations are given in this article.Whenever unpaired electrons are involved, EPR is potentially the best physical technique for studying the system. Historically, the majority of applications of EPR have been to the study of organic free radicals and transition metal complexes. Today, these applications continue, but in the context of biological systems, where the organic radicals are naturally occurring radicals, spin labels, and spin‐trapped radicals, and the transition metals are in metalloproteins. Applications to the study of materials are extensive, but deserve more attention than they have had in the past. Recent studies include the use of EPR to monitor the age of archeological artifacts, characterize semiconductors and superconductors, measure the spatial distribution of radicals in processed polymers, monitor photochemical degradation of paints, and characterize the molecular structure of glasses. In this article enough information is provided so that a potential user can determine whether EPR is likely to be informative for a particular type of sample, and which type of EPR experiment would most likely be useful.
X‐Ray and Neutron Diffuse Scattering Measurements
Authors: Ice Gene E. , Robertson James L. , Sparks Cullie J. 
Published: October 2003

AbstractDiffuse scattering from crystalline solid solutions is used to measure local compositional order among the atoms, dynamic displacements (phonons), and mean species‐dependent static displacements. In locally ordered alloys, fluctuations of composition and interatomic distances break the long‐range symmetry of the crystal within local regions and contribute to the total energy of the alloy. Local ordering can be a precursor to a lower temperature equilibrium structure that may be unattainable because of slow atomic diffusion. In addition to local atomic correlations, neutron diffuse scattering methods can be used to study the local short‐range correlations of the magnetic moments. Interstitial defects, as opposed to the substitutional disorder defects described above, also disrupt the long‐range periodicity of a crystalline material and give rise to diffusely scattered x rays, neutrons, and electrons.This article will concentrate on the use of diffuse x‐ray and neutron scattering from single crystals to measure local chemical correlations and chemically specific static displacements. Particular emphasis is placed on the use of resonant (anomalous) x‐ray techniques to extract information on atomic size from binary solid solutions with short‐range order. Here the alloys have a well‐defined average lattice but have local fluctuations in composition and displacements from the average lattice. In stoichiometric crystals with long‐range periodicity, sharp superlattice Bragg reflections appear. If the compositional order is correlated only over short distances, the superlattice reflections are so broadened that measurements throughout a symmetry related volume in reciprocal space are required to determine its distribution. In addition, the displacement of the atom pairs (e.g., the A‐A, A‐B, and B‐B pairs in a binary alloy) from the sites of the average lattice because of different atom sizes also contributes to the distribution of this diffuse scattering. By separating this diffuse intensity into its component parts—that associated with the chemical preference for A‐A, A‐B, and B‐B pairs for the various near‐neighbor shells and that associated with the static and dynamic displacements of the atoms from the sites of the average lattice—we are able to recover pair correlation probabilities for the three kinds of pairs in a binary alloy. The interpretation of diffuse scattering associated with dynamic displacements of atoms from their average crystal sites are discussed only briefly in this article.
X‐Ray Diffraction Techniques for Liquid Surfaces and Monomolecular Layers
Authors: Vaknin David 
Published: October 2003

Abstract
X‐ray and neutron scattering techniques are probably the most effective tools employed to determine the structure of liquid interfaces on molecular‐length scales. These are not different in principle from conventional x‐ray diffraction techniques that are usually applied to three‐dimensional crystals, liquids, solid surfaces etc. However, special diffractometers that enable scattering from fixed horizontal surfaces are required to carry out the experiments. Indeed, systematic studies of liquid surfaces had not begun until the introduction of the first liquid surface reflectometer.
A basic property of a liquid‐gas interface is the length scale over which the molecular density changes from the bulk value to that of the homogeneous gaseous medium. Molecular size and capillary waves, which depend on surface tension and gravity, are among the most important factors that shape the density profile across the interface and the planar correlations. In some instances the topmost layers of liquids are packed differently than in the bulk, giving rise to layering phenomena at the interface. Monolayers of compounds different than the liquid can be spread at the gas‐liquid interface, and are termed Langmuir monolayers. The spread compound might “wet” the liquid surface to form a film of homogeneous thickness or cluster to form an inhomogeneous rough surface. The x‐ray reflectivity (XR) technique allows one to determine the electron density across such interfaces, from which the molecular density and the total thickness can be extracted. The grazing angle diffraction (GID) technique is commonly used to determine lateral arrangements and correlations of the topmost layers at interfaces. GID is especially efficient in cases where surface crystallization of the liquid or spread monolayers occurs. Both techniques (XR and GID) provide structural information that is averaged over macroscopic areas, in contrast to scanning probe microscopies (SPMs), where local arrangements are probed. For an inhomogeneous interface, the reflectivity is an incoherent sum of reflectivities, accompanied by strong diffuse scattering, which, in general, is difficult to interpret definitively and often requires complementary techniques to support the x‐ray analysis. Therefore, preparation of well‐defined homogeneous interfaces is a key to a more definitive and straightforward interpretation.
X‐Ray Magnetic Circular Dichroism
Authors: Lang J.C. 
Published: October 2003

AbstractX‐ray magnetic circular dichroism (XMCD) is a measure of the difference in the absorption coefficient, with the helicity of incident circularly polarized light parallel and antiparallel to the local magnetization direction of the absorbing material. These measurements are typically made at x‐ray energies spanning an absorption edge, where a deep atomic core electron is photoexited into the valence band. Because the binding energy of these core electrons is associated with specific elements, XMCD can be used to separately measure the magnetic contributions from individual constituents in a complex material, by tuning the incident beam energy to a specific edge. Furthermore, different absorption edges of the same element provide information on the magnetic contributions of different kinds of valence electrons within a single element.XMCD measurements yield two basic types of magnetic information, both of which are specific to the element and orbital determined by the choice of measured absorption edge. First, the strength of the dichroic signal is proportional to the projection of the magnetic moment along the incident x‐ray beam direction. Thus, the signal can be used to determine magnetization direction for a sample in remanence or changes in the sample magnetization upon varying the applied magnetic field or temperature. Secondly, XMCD can be used to separate the orbital and spin contributions to the magnetic moment. This is possible through sum rules.This article concentrate on the techniques employed in the hard x‐ray regime, but considerable mention will be made of soft x‐ray results and techniques because of the fundamental importance in magnetism of the final states probed by edges in this energy regime. Emphasis is given to the methods used for the collection of XMCD spectra rather than to detailed analysis of specific features in the XMCD spectra of a particular edge.
Surface X‐Ray Diffraction
Authors: Robinson I.K. 
Published: October 2003

AbstractSurface x‐ray diffraction allows the determination of atomic structures of ordered crystal surfaces in an analogous way to x‐ray crystallography for the determination of three‐dimensional crystal structures. In doing this, crystallographic parameters such as lattice constants and Debye‐Waller factors (thermal vibration amplitudes) are also accessed, so surface x‐ray diffraction should be considered as a valid method for measuring these quantities too. Surface x‐ray diffraction also probes surface morphological properties, such as roughness and facet formation, and allows the investigation of their thermodynamic and kinetic aspects, such as the study of phase transitions in surfaces.Because x rays probe deep inside matter, buried interfaces can be treated in exactly the same manner as surfaces, so throughout this unit the wordssurfaceandinterfaceare used synonymously. In fact, some of the best applications of the method are for buried interfaces, where complementary electron‐based probes such as low‐energy electron diffraction and reflection high‐energy electron diffraction cannot reach.Surface x‐ray diffraction is not a laboratory technique. While there are one or two exceptions of installations in individual laboratories, the majority are associated with national or international facilities. Even the very early experiments used synchrotron radiation. By now, facility‐based science is already rather common and will become more so in the future, as it has considerable economies of scale and advantages of centralized operational safety. The practice of surface x‐ray diffraction should necessarily be considered as a facility‐based operation, and it will be assumed that the reader will have access as a “user” to one of these facilities. This is usually handled by the submission of a proposal to be judged on the importance of the science to be carried out. Access is then usually free of charge.Because surface x‐ray diffraction is facility based, it is not a technique for which one can purchase the equipment piecemeal from a vendor. Every surface x‐ray diffraction installation is slightly different, but most were derived from and are based on the description that follows, which is the X16A facility of the National Synchrotron Light Source (NSLS).Others use basically the same control and analysis programs and procedures as those described here.
Electron Techniques
Authors: Fultz Brent 
Published: October 2003

Abstract
This section describes how electrons are used to probe the microstructures of materials. These methods are arguably the most powerful and flexible set of tools available for materials characterization. For the characterization of structures internal to materials, electron beam methods provide capabilities for determining crystal structure, crystal shapes and orientations, defects within the crystals, and the distribution of atoms within these individual crystals. For characterizing surfaces, electron methods can determine structure and chemistry at the level of the atomic monolayer.
The methods in this category use electrons with kinetic energies spanning the range from 1 to 1,000,000 eV.
Electron scattering from a material can be either elastic or inelastic. In general, elastic scattering is used for imaging measurements, whereas inelastic scattering provides for spectroscopy. (Electron beam techniques are enormously versatile, however, so there are many exceptions to this generality.).
The articles are this category enumerate some requirements for sample preparation, but it is remarkable that any one of these techniques permits studies on a large variety of samples. All classes of materials (metals, ceramics, polymers, and composites) have been studied by all of these electron techniques. Except for some problems with the lightest (or heaviest) elements in the periodic table, the electron beam techniques have few compositional limitations.
Transmission Electron Microscopy
Authors: Howe James M. , Fultz Brent 
Published: October 2003

Abstract
Transmission electron microscopy (TEM) is the premier tool for understanding the internal microstructure of materials at the nanometer level. Although x‐ray diffraction techniques generally provide better quantitative information than electron diffraction techniques, electrons have an important advantage over x rays in that they can be focused using electromagnetic lenses. This allows one to obtain real‐space images of materials with resolutions on the order of a few tenths to a few nanometers, depending on the imaging conditions, and simultaneously obtain diffraction information from specific regions in the images (e.g., small precipitates) as small as 1 nm. Variations in the intensity of electron scattering across a thin specimen can be used to image strain fields, defects such as dislocations and second‐phase particles, and even atomic columns in materials under certain imaging conditions. Transmission electron microscopy is such a powerful tool for the characterization of materials that some microstructural features are defined in terms of their visibility in TEM images.
In addition to diffraction and imaging, the high‐energy electrons (usually in the range of 100 to 400 keV of kinetic energy) in TEM cause electronic excitations of the atoms in the specimen. Two important spectroscopic techniques make use of these excitations by incorporating suitable detectors into the transmission electron microscope, energy‐dispersive x‐ray spectroscopy (EDS), and electron energy loss spectroscopy (EELS).

A fully equipped transmission electron microscope has the capability to record the variations in image intensity across the specimen using mass thickness or diffraction contrast techniques, to reveal the atomic structure of materials using high‐resolution (phase‐contrast) imaging or
Z
‐contrast (incoherent) imaging, to obtain electron diffraction patterns from small areas of the specimen using a selected‐area aperture or a focused electron probe, and to perform EELS and EDS measurements with a small probe. Additional lenses can be installed in conjunction with an EELS spectrometer to create an energy filter, enabling one to form energy‐filtered TEM images. These images enable mapping of the chemical composition of a specimen with nanometer spatial resolution.

In addition to the main techniques of (1) conventional imaging, (2) phase‐contrast imaging, (3)
Z
‐contrast imaging, (4) electron diffraction, (5) EDS, and (6) EELS, in TEM many other analyses are possible.
Scanning Tunneling Microscopy
Authors: Salmeron Miquel 
Published: October 2003

Abstract
Scanning tunneling microscopy (STM) is a technique for the determination of the structure of surfaces, with spatial resolution on the angstrom scale. In an oversimplified description, STM allows imaging of the surface of conductive materials down to the atomic level.
The technique is based on the measurement and control of the current of electrons tunneling between a sharp stylus (hereafter called the tip) and the sample surface. During imaging, the tip is separated a few angstroms (3 to 10 Å) from the surface, while it is being rastered with the help of piezoelectric transducers. The area scanned is tens to thousands of angstroms on a side. STM has the advantage over other microscopies that its operation does not require any special environmental conditions. Imaging can be performed in vacuum, at high pressures (including air), and in liquids. The choice of the environment is determined mostly by the requirements of the sample and its surface condition.
Acquisition of STM images is relatively simple with modern instruments. Most of the experimental time is spent on sample preparation and tip conditioning in the appropriate environment (ultrahigh vacuum, electrochemical cell, or controlled atmosphere). Tip conditioning and noise reduction can sometimes add considerable time, depending on factors such as the nature of the experiment and reactivity of the sample. This time depends also on the type of information being sought.
In considering the ultimate resolution obtainable with the STM, it is important to consider the role of tip geometry. On flat parts of the sample, where one tip atom is responsible for the tunneling, STM reaches its maximum performance. On rough surfaces, however, the tunneling point on the tip apex changes as it moves over sharp corners and changing slopes. The image is then a convolution of the tip and surface shapes, and the final resolution is determined by the tip radius and profile. STM is thus not the best technique to probe, for example, highly corrugated a patterned surfaces, and porous materials.