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FEFF8
FEFF is a software program used in x-ray absorption spectroscopy. It contains self-consistent real space multiple-scattering code for simultaneous calculations of x-ray-absorption spectra and electronic structure. Output includes extended x-ray-absorption fine structure ( EXAFS), full multiple scattering calculations of various x-ray absorption spectra ( XAS) and projected local densities of states ( LDOS). The spectra include x-ray absorption near edge structure ( XANES), x-ray natural circular dichroism (XNCD), and non-resonant x-ray emission spectra. Calculations of the x-ray scattering amplitude (Thomson and anomalous parts) and spin dependent calculations of x-ray magnetic circular dichroism ( XMCD) and spin polarized x-ray absorption spectra (SPXAS and SPEXAFS) are also possible, but less automated. The most recent version of FEFF is FEFF10, released in 2020. Uses FEFF is used as external program to calculate basic spectra for XANES fitting using FitIt. Atomic scattering a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
XANES
X-ray absorption near edge structure (XANES), also known as near edge X-ray absorption fine structure (NEXAFS), is a type of absorption spectroscopy that indicates the features in the X-ray absorption spectra ( XAS) of condensed matter due to the photoabsorption cross section for electronic transitions from an atomic core level to final states in the energy region of 50–100 eV above the selected atomic core level ionization energy, where the wavelength of the photoelectron is larger than the interatomic distance between the absorbing atom and its first neighbour atoms. Terminology Both XANES and NEXAFS are acceptable terms for the same technique. XANES name was invented in 1980 by Antonio Bianconi to indicate strong absorption peaks in X-ray absorption spectra in condensed matter due to multiple scattering resonances above the ionization energy. The name NEXAFS was introduced in 1983 by Jo Stohr and is synonymous with XANES, but is generally used when applied to surface and mole ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
FitIt
FitIt is graphical software to fit X-ray absorption near edge structure (XANES). It can be used to determine the values of local atomic structure parameters on the basis of minimization between theoretical and experimental spectra. It is the program for the fitting and therefore it always uses external programs, for example FEFF8 or FDMNES, for fixed geometry calculations of XANES. In order to minimize the number of such calculations, which can be very time-consuming, multidimensional interpolation algorithm is implemented into the FitIt. Such approach has allowed also to develop visual control of the fitting procedure and it is possible to vary structural parameters by sliders and immediately see the theoretical spectrum corresponding to these structural parameters.C. Battocchio, F. D’Acapito, G. Smolentsev, A.V. Soldatov, I. Fratoddi, G. Contini, I. Davoli, G. Polzonetti and S. Mobilio, ''XAS study of a Pt-containing rod-like organometallic polymer''Chem. Phys. 325, 422 (2006)/re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
X-ray Absorption Spectroscopy
X-ray absorption spectroscopy (XAS) is a set of advanced techniques used for probing the local environment of matter at atomic level and its electronic structure. The experiments require access to synchrotron radiation facilities for their intense and tunable X-ray beams. Samples can be in the gas phase, solutions, or solids. Background XAS data are obtained by tuning the photon energy, using a crystalline monochromator, to a range where core electrons can be excited (0.1-100 keV). The edges are, in part, named by which core electron is excited: the principal quantum numbers n = 1, 2, and 3, correspond to the K-, L-, and M-edges, respectively. For instance, excitation of a 1s electron occurs at the metal K-edge, K-edge, while excitation of a 2s or 2p electron occurs at an metal L-edge, L-edge (Figure 1). There are three main regions found on a spectrum generated by XAS data, which are then thought of as separate spectroscopic techniques (Figure 2): # The ''absorption thresho ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Space
Space is a three-dimensional continuum containing positions and directions. In classical physics, physical space is often conceived in three linear dimensions. Modern physicists usually consider it, with time, to be part of a boundless four-dimensional continuum known as '' spacetime''. The concept of space is considered to be of fundamental importance to an understanding of the physical universe. However, disagreement continues between philosophers over whether it is itself an entity, a relationship between entities, or part of a conceptual framework. In the 19th and 20th centuries mathematicians began to examine geometries that are non-Euclidean, in which space is conceived as '' curved'', rather than '' flat'', as in the Euclidean space. According to Albert Einstein's theory of general relativity, space around gravitational fields deviates from Euclidean space. Experimental tests of general relativity have confirmed that non-Euclidean geometries provide a bet ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
X-ray
An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ranging from 10 Nanometre, nanometers to 10 Picometre, picometers, corresponding to frequency, frequencies in the range of 30 Hertz, petahertz to 30 Hertz, exahertz ( to ) and photon energies in the range of 100 electronvolt, eV to 100 keV, respectively. X-rays were discovered in 1895 in science, 1895 by the German scientist Wilhelm Röntgen, Wilhelm Conrad Röntgen, who named it ''X-radiation'' to signify an unknown type of radiation.Novelline, Robert (1997). ''Squire's Fundamentals of Radiology''. Harvard University Press. 5th edition. . X-rays can penetrate many solid substances such as construction materials and living tissue, so X-ray radiography is widely used in medical diagnostics (e.g., checking for Bo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Absorption Spectrum
Absorption spectroscopy is spectroscopy that involves techniques that measure the absorption of electromagnetic radiation, as a function of frequency or wavelength, due to its interaction with a sample. The sample absorbs energy, i.e., photons, from the radiating field. The intensity of the absorption varies as a function of frequency, and this variation is the absorption spectrum. Absorption spectroscopy is performed across the electromagnetic spectrum. Absorption spectroscopy is employed as an analytical chemistry tool to determine the presence of a particular substance in a sample and, in many cases, to quantify the amount of the substance present. Infrared and ultraviolet–visible spectroscopy are particularly common in analytical applications. Absorption spectroscopy is also employed in studies of molecular and atomic physics, astronomical spectroscopy and remote sensing. There is a wide range of experimental approaches for measuring absorption spectra. The most common ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
X-ray Absorption Spectroscopy
X-ray absorption spectroscopy (XAS) is a set of advanced techniques used for probing the local environment of matter at atomic level and its electronic structure. The experiments require access to synchrotron radiation facilities for their intense and tunable X-ray beams. Samples can be in the gas phase, solutions, or solids. Background XAS data are obtained by tuning the photon energy, using a crystalline monochromator, to a range where core electrons can be excited (0.1-100 keV). The edges are, in part, named by which core electron is excited: the principal quantum numbers n = 1, 2, and 3, correspond to the K-, L-, and M-edges, respectively. For instance, excitation of a 1s electron occurs at the metal K-edge, K-edge, while excitation of a 2s or 2p electron occurs at an metal L-edge, L-edge (Figure 1). There are three main regions found on a spectrum generated by XAS data, which are then thought of as separate spectroscopic techniques (Figure 2): # The ''absorption thresho ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Local Density Of States
In condensed matter physics, the density of states (DOS) of a system describes the number of allowed modes or states per unit energy range. The density of states is defined as where N(E)\delta E is the number of states in the system of volume V whose energies lie in the range from E to E+\delta E. It is mathematically represented as a distribution by a probability density function, and it is generally an average over the space and time domains of the various states occupied by the system. The density of states is directly related to the dispersion relations of the properties of the system. High DOS at a specific energy level means that many states are available for occupation. Generally, the density of states of matter is continuous. In isolated systems however, such as atoms or molecules in the gas phase, the density distribution is discrete, like a spectral density. Local variations, most often due to distortions of the original system, are often referred to as local densities o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Circular Dichroism
Circular dichroism (CD) is dichroism involving circular polarization, circularly polarized light, i.e., the differential Absorption (electromagnetic radiation), absorption of left- and right-handed light. Left-hand circular (LHC) and right-hand circular (RHC) polarized light represent two possible spin angular momentum of light, spin angular momentum states for a photon, and so circular dichroism is also referred to as dichroism for spin angular momentum. This phenomenon was discovered by Jean-Baptiste Biot, Augustin Fresnel, and Aimé Cotton in the first half of the 19th century. Circular dichroism and optical rotation, circular birefringence are manifestations of optical activity. It is exhibited in the absorption (electromagnetic radiation), absorption bands of optical activity, optically active chirality (chemistry), chiral molecules. CD spectroscopy has a wide range of applications in many different fields. Most notably, Ultraviolet, far-UV CD is used to investigate the second ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Scattering Amplitude
In quantum physics, the scattering amplitude is the probability amplitude of the outgoing spherical wave relative to the incoming plane wave in a stationary-state scattering process. Formulation Scattering in quantum mechanics begins with a physical model based on the Schrodinger wave equation for probability amplitude \psi: -\frac\nabla^2\psi + V\psi = E\psi where \mu is the reduced mass of two scattering particles and is the energy of relative motion. For scattering problems, a stationary (time-independent) wavefunction is sought with behavior at large distances (asymptotic form) in two parts. First a plane wave represents the incoming source and, second, a spherical wave emanating from the scattering center placed at the coordinate origin represents the scattered wave: \psi(r\rightarrow \infty) \sim e^ + f(\mathbf_f,\mathbf_i)\frac The scattering amplitude, f(\mathbf_f,\mathbf_i), represents the amplitude that the target will scatter into the direction \mathbf_f. In gener ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thomson Scattering
Thomson scattering is the elastic scattering of electromagnetic radiation by a free charged particle, as described by classical electromagnetism. It is the low-energy limit of Compton scattering: the particle's kinetic energy and photon frequency do not change as a result of the scattering. This limit is valid as long as the photon energy is much smaller than the mass energy of the particle: , or equivalently, if the wavelength of the light is much greater than the Compton wavelength of the particle (e.g., for electrons, longer wavelengths than hard x-rays). Description of the phenomenon Thomson scattering describes the classical limit of electromagnetic radiation scattering from a free particle. An incident plane wave accelerates a charged particle which consequently emits radiation of the same frequency. The net effect is to scatter the incident radiation. Thomson scattering is an important phenomenon in plasma physics and was first explained by the physicist J. J. Thomson ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
