We implemented a self-consistent, real-space x-ray absorption calculation within the FDMNES code. We performed the self-consistency within several schemes and identified which one is the most ...appropriate. We show a method that allows a rigorous setting of the Fermi level and thus an estimation of the energy cutoff for the identification and elimination of the occupied states. We investigated what are the structures where one can afford performing the self-consistent calculation at a lesser cluster radius than the absorption one. We exemplify the effects of the self-consistency at the K-edge and for several reference cases, including the copper Cu and the rutile TiO(2). We verified the robustness of our procedure on the transitional 3d and 4d elements. Although amelioration can be noticed, the self-consistency performed at the K-edge does not bring a major improvement of the calculated spectra. Taking into consideration a non-self-consistent, non-spherical potential gives better results than a self-consistent muffin-tin approximation calculation.
For an isolated quantum particle, such as an electron, the orbital (L) and spin (S) magnetic moments can change provided that the total angular momentum of the particle is conserved. In condensed ...matter, an efficient transfer between L and S can occur owing to the spin-orbit interaction, which originates in the relativistic motion of electrons. Disentangling the absolute contributions of the orbital and spin angular momenta is challenging, however, as any transfer between the two occurs on femtosecond timescales. Here we investigate such phenomena by using ultrashort optical laser pulses to change the magnetization of a ferromagnetic film and then probe its dynamics with circularly polarized femtosecond X-ray pulses. Our measurements enable us to disentangle the spin and orbital components of the magnetic moment, revealing different dynamics for L and S. We highlight the important role played by the spin-orbit interaction in the ultrafast laser-induced demagnetization of ferromagnetic films, and show also that the magneto-crystalline anisotropy energy is an important quantity to consider in such processes. Our study provides insights into the dynamics in magnetic systems as well as perspectives for the ultrafast control of information in magnetic recording media.
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DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The present manuscript reports vibrational spectra and optical studies of polycrystalline Fe1−xCrxVO4 solid solutions through FT–IR spectroscopy augmented with a group theory (G.T.) analysis and ...UV–Visible DRS spectroscopy. Full set of IR and Raman modes are determined by G. T. for various crystal symmetries in FeVO4–CrVO4 solid solutions where Triclinic, Monoclinic and Orthorhombic structures evolve with increasing Cr concentration. Experimentally obtained vibrational modes support the structural phase transitions and confirm formation of continuous solid solutions in Fe1−xCrxVO4. The Diffuse Reflectance Spectra (DRS) of Fe1−xCrxVO4 depicts the electronic structure and different optical transitions due to absorption of photon energy. The d–d transitions are manifested for all compounds in terms of crystal field stabilization energy (CFSE) caused by distorted lattice sites. The band gap energy of Fe1−xCrxVO4 is calculated using Tauc formula. It shows a red shift initially within triclinic structure then blue shift with the increase of Cr concentration. Urbach energy (Eu) tails in the spectra show the electronic structural disorder in Fe1−xCrxVO4 due to impurity energy levels of Cr ions within band gap region. It is observed that Eu decreases with the doping concentration due to the increase in crystal symmetry corresponding to the structural phase transitions in Fe1−xCrxVO4.
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•The solid solutions of FeVO4 – CrVO4 were studied through FT – IR, UV VIS DRS spectroscopy and Group theory analysis.•The evolution of optical and vibrational properties through the phase diagram is given in detail.•A detailed vibration mode analysis is given for Triclinic, Monoclinic and Orthorhombic phases in the phase diagram.•The optical band gap for these technologically important catalytic materials is also being evaluated through diffuse reflectance spectra of optical absorption using Tauc plot analysis.•The band gap shows a red shift in triclinic structure then shows blue shift corresponding to monoclinic and orthorhombic structure.•The obtained Urbach tails indicate the disorder energy levels into interband region in the present system.•Disorder energy decreases with the increasing of doping concentration associated with structural phase transition from Triclinic-Monoclinic-Orthorhombic.•Detailed account of d-d transitions in all the compounds is manifested on the basis of distorted crystal sites and CFSE of the systems.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract
Various thickness of Rhodamine B (RhB) laser dye was deposited on epoxy polymeric as a new dielectric organic substrate by spin coating method for the first time. This study focused on the ...newly considered RhB dye on an epoxy substrate for wide-scale applications. The thickness effect on structural, optical, and dielectric properties of the hybrid coating films was performed. The XRD patterns of the films indicated a large hump amorphous design and lack of Bragg peak intensity associated with the RhB laser dye, due to amorphous film concentration. From UV-Visible spectroscopy, the optical absorption edge shifts to the higher wavelengths direction (redshift) with the variation in RhB dye thicknesses. It was found that the energy band gap decreased when the RhB dye film thickness changed. The refractive index is an important parameter influencing the optical component design. Their values vary according to each relationship that extremely useful the films in optical devices. Laser power attenuation sensitivity of pure epoxy polymeric substrate and its coating films shows that under reducing the thicknesses of RhB dye, the laser power intensity effect increases. Several dielectric parameters are extracted from the series and parallel capacitance measurements. The present results offer new material films for luminescent energy solar concentrator applications.
Small‐angle X‐ray scattering is widely utilized to study biological macromolecules in solution. For samples containing specific (e.g. metal) atoms, additional information can be obtained using ...anomalous scattering. Here, measuring samples at different energies close to the absorption edges of relevant elements provides specific structural details. However, anomalous small‐angle X‐ray scattering (ASAXS) applications to dilute macromolecular solutions are challenging owing to the overall low anomalous scattering effect. Here, pilot ASAXS experiments from dilute solutions of ferritin and cobalt‐loaded apoferritin are reported. These samples were investigated near the resonance X‐ray K edges of Fe and Co, respectively, at the EMBL P12 bioSAXS beamline at PETRA III, DESY. Thanks to the high brilliance of the P12 beamline, ASAXS experiments are feasible on dilute protein solutions, allowing one to extract the Fe‐ or Co‐specific anomalous dispersion terms from the ASAXS data. The data were subsequently used to determine the spatial distribution of either iron or cobalt atoms incorporated into the ferritin/apoferritin protein cages.
Anomalous small‐angle X‐ray scattering (ASAXS) allows one to obtain information about the spatial distribution of specific atoms in a sample, but its application to dilute biological samples is challenging because of weak anomalous effects. ASAXS experiments from dilute solutions of ferritin and cobalt‐loaded apoferritin near the resonance X‐ray K edges of Fe and Co, respectively, have been performed at the P12 bioSAXS beamline of the EMBL at PETRA III synchrotron, DESY.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Progress in science often follows or parallels the development of new techniques. The optical microscope helped convert medicine and biology from a speculative activity in old times to today's ...sophisticated scientific disciplines. The telescope changed the study and interpretation of heavens from mythology to science. X-ray diffraction enabled the flourishing of solid state physics and materials science. The technique object of this review, Ambient Pressure Photoelectron Spectroscopy or APPES for short, has also the potential of producing dramatic changes in the study of liquid and solid surfaces, particularly in areas such as atmospheric, environment and catalysis sciences. APPES adds an important missing element to the host of techniques that give fundamental information, i.e., spectroscopy and microscopy, about surfaces in the presence of gases and vapors, as encountered in industrial catalysis and atmospheric environments. APPES brings electron spectroscopy into the realm of techniques that can be used in practical environments. Decades of surface science in ultra high vacuum (UHV) has shown the power of electron spectroscopy in its various manifestations. Their unique property is the extremely short elastic mean free path of electrons as they travel through condensed matter, of the order of a few atomic distances in the energy range from a few eV to a few thousand eV. As a consequence of this the information obtained by analyzing electrons emitted or scattered from a surface refers to the top first few atomic layers, which is what surface science is all about. Low energy electron diffraction (LEED), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), Ultraviolet photoelectron spectroscopy (UPS), and other such techniques have been used for decades and provided some of the most fundamental knowledge about surface crystallography, composition and electronic structure available today. Unfortunately the high interaction cross section of electrons with matter also prevents them from traveling long distances unscattered in gas environments. Above the millibar pressure range this distance is reduced to less that a millimeter, effectively preventing its use in the most relevant environments, usually between millibars and atmospheric pressures. There is therefore a large gap of several orders of magnitude where information about surfaces is scarce because these powerful electron spectroscopies cannot operate. One characteristic of surfaces in ambient pressure environments is that they are covered by dense layers of molecules, even when their binding energy is weak. Water for example is known to form layers several molecules thick at room temperature in humid environments. Metals readily form oxide films several layers thick in oxygen atmospheres. Dense layers of adsorbed molecules can also be produced in ultra high vacuum, often by the simple and expedient method of cooling the sample to cryogenic temperatures. A large amount of data has been obtained in the past in UHV by surface scientists using this method. While this has provided valuable information it begs the question of whether the structures formed in this manner represent equilibrium structures or metastable ones, kinetically trapped due to high activation energies that cannot be overcome at low temperature. From a thermodynamic point of view is interesting to consider the entropic contribution to the Gibbs free energy, which we can call 'the pressure factor', equal to kT.logP. This factor amounts to a sizeable 0.3 eV difference at room temperature between UHV (<10{sup -8} Pascal) and atmospheric pressures. Such change if free energy can definitely result in changes in surface structure and stability. Entire areas of the phase diagram are out of reach due to the pressure gap. Even when cooling is not necessary, many surface treatments and most chemical reactions necessitate the presence of gases at pressures ranging from millibar to bars. What is the structure and chemical nature of the species formed on the surface in equilibrium with such gases? As we shall illustrate in this review, APPES provides a much needed electron spectroscopy to analyze surface electronic structure and composition in equilibrium with gases.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
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•Cd-Zn sulphide films synthesized via chemical bath deposition technique.•Nanocrystalline phase of Cd-Zn sulphide films were seen in XRD studies.•Nanocrystalline structures of the ...films were also confirmed by the SEM.•The band gap of these films is a combination of composition and size.•EU and σ studies ascribed the shrinkage of absorption edges around the optical band-gaps.
In this article Cd-Zn sulphide thin films deposited onto soda lime glass substrates via chemical bath deposition (CBD) technique were investigated for photovoltaic applications. The synthesized films were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and ultraviolet visible (UV–vis) spectroscopic methodologies. A higher degree of crystallinity of the films was attained with the increase of film thicknesses. SEM micrographs exhibited a partial crystalline structure with a particulate appearance surrounded by the amorphous grain boundaries. The optical absorbance and absorption coefficient of the films were also enhanced significantly with the increase in film thicknesses. Optical band-gap analysis indicated a monotonic decrease in direct and indirect band-gaps with the increase of thicknesses of the films. The presence of direct and indirect transitional energies due to the exponential falling edges of the absorption curves may either be due to the lack of long-range order or to the existence of defects in the films. The declination of the optical absorption edges was also confirmed via Urbach energy and steepness parameters studies.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
The purpose of this work is to compare the two different procedures to calculate the L2,3 x-ray absorption spectra of transition-metal compounds: (1) the semi-empirical charge transfer multiplet ...(CTM) approach and (2) the ab initio configuration-interaction (CI) method based on molecular orbitals. We mainly focused on the difference in the treatment of ligand field effects and the charge transfer effects in the two methods. The reduction of multiplet interactions due to the solid state effects has been found by the ab initio CI approach. We have also found that the mixing between the original and the charge transferred configurations obtained by the ab initio CI approach is smaller than that obtained by the CTM approach, since charge transfer through the covalent bonding between metal and ligand atoms has been included by taking the molecular orbitals as the basis functions.
We report on the first demonstration of femtosecond x-ray absorption spectroscopy, made uniquely possible by the use of broadly tunable bending-magnet radiation from "laser-sliced" electron bunches ...within a synchrotron storage ring. We measure the femtosecond electronic rearrangements that occur during the photoinduced insulator-metal phase transition in VO2. Symmetry- and element-specific x-ray absorption from V2p and O1s core levels (near 500 eV) separately measures the filling dynamics of differently hybridized V3d-O2p electronic bands near the Fermi level.
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CMK, CTK, FMFMET, IJS, NUK, PNG, UM
We have studied the electronic structure of nanocrystalline NiO thin films, grown by radio-frequency magnetron sputtering under different experimental conditions, using x-ray absorption spectroscopy. ...The O 1s and Ni 2p spectra showed distinct changes as a function of O2 content in the plasma, which were reproduced with cluster model calculations. These changes are attributed to the incrementing of the surface contribution due to a decrease of the crystallite size as the O2 content in the plasma increases, and to the presence of induced nickel vacancies. Thus, the changes in the electronic structure can be related to the modification of structural and transport properties of these nanocrystalline films.
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