Influence of the scattering particle shape on the SiO2 silicate feature

Silicate dust particles are part of many astronomical objects such as comets and circumstellar disks. In a spectrum, silicates exhibit a number of characteristic silicate emission features. To study these features, Mie’s theory is usually used. This theory assumes that the scattering object is an ideal sphere. In this work, we investigated the contribution of non-spherical quartz particles (SiO2) to these features. We studied the influence of the deviation from sphericity on the 10-micron silicate feature of quartz. It is shown that the deviation from sphericity has a significant effect on both the scattered light intensity and the scattering factor Qsca, and this effect increases with increasing scattering particle size. The main peculiarities of the 10-micron silicate feature have been studied for both prolate and oblate spheroids.

Observation of ordered organic capping ligands on semiconducting quantum dots via powder X-ray diffraction

Powder X-ray diffraction is one of the key techniques used to characterize the inorganic structure of colloidal nanocrystals. The comparatively low scattering factor of nuclei of the organic capping ligands and their propensity to be disordered has led investigators to typically consider them effectively invisible to this technique. In this report, we demonstrate that a commonly observed powder X-ray diffraction peak around $$q=1.4{\AA}^{-1}$$ q = 1.4 Å − 1 observed in many small, colloidal quantum dots can be assigned to well-ordered aliphatic ligands bound to and capping the nanocrystals. This conclusion differs from a variety of explanations ascribed by previous sources, the majority of which propose an excess of organic material. Additionally, we demonstrate that the observed ligand peak is a sensitive probe of ligand shell ordering. Changes as a function of ligand length, geometry, and temperature can all be readily observed by X-ray diffraction and manipulated to achieve desired outcomes for the final colloidal system.

An Overview of the Compton Scattering Calculation

The Compton scattering process plays significant roles in atomic and molecular physics, condensed matter physics, nuclear physics and material science. It could provide useful information on the electromagnetic interaction between light and matter. Several aspects of many-body physics, such us electronic structures, electron momentum distributions, many-body interactions of bound electrons, etc., can be revealed by Compton scattering experiments. In this work, we give a review of ab initio calculation of Compton scattering process. Several approaches, including the free electron approximation (FEA), impulse approximation (IA), incoherent scattering function/incoherent scattering factor (ISF) and scattering matrix (SM) are focused on in this work. The main features and available ranges for these approaches are discussed. Furthermore, we also briefly introduce the databases and applications for Compton scattering.

X-Ray Diffraction

X-rays diffraction is fundamental to understanding the structure and crystallography of biological, geological, or technological materials. X-rays scatter predominantly by the electrons in solids, and have an elastic (coherent, Thompson) and an inelastic (incoherent, Compton) component. The atomic scattering factor is largest (= Z) for forward scattering, and decreases with increasing scattering angle and decreasing wavelength. The amplitude of the diffracted wave is the structure factor, F hkl, and its square gives the intensity. In practice, intensities are modified by temperature (Debye-Waller), absorption, Lorentz-polarization, and the multiplicity of the lattice planes involved in diffraction. Diffraction patterns reflect the symmetry (point group) of the crystal; however, they are centrosymmetric (Friedel law) even if the crystal is not. Systematic absences of reflections in diffraction result from glide planes and screw axes. In polycrystalline materials, the diffracted beam is affected by the lattice strain or grain size (Scherrer equation). Diffraction conditions (Bragg Law) for a given lattice spacing can be satisfied by varying θ or λ — for study of single crystals θ is fixed and λ is varied (Laue), or λ is fixed and θ varied to study powders (Debye-Scherrer), polycrystalline materials (diffractometry), and thin films (reflectivity). X-ray diffraction is widely applied.

Extinction Effect of Gold Nanocatalysts on Photocatalytic Activities under Plasmonic Excitation

Plasmonic nanoparticles (NPs), particularly Au NPs, are potential candidates for photocatalysts because of their unique optical properties. The size of Au NPs plays a crucial role in effective light absorption, which is an important factor in photocatalytic reactions. Although Au NP-based photocatalysts have garnered significant researched interest, the size effect of Au NPs on a photocatalytic reaction has not been sufficiently studied. We characterized the effect of size on the photocatalytic activity of Au NPs of different sizes. We found that the absorption cross-section of the Au NPs gradually increased as the size of the Au NPs increased. However, the reaction rate for each size of NP was inversely proportional to the absorption cross-section. Based on the simulation results, we found that larger Au NPs have a higher scattering factor than that of smaller Au NPs. Consequently, the scattering effect of Au NPs hinders effective light absorption, resulting in slower reaction kinetics. These findings can contribute to the rational design of high-efficiency plasmonic photocatalysts.

Direct recovery of interfacial topography from coherent X-ray reflectivity: model calculations for a 1D interface

The use of coherent X-ray reflectivity to recover interfacial topography is described using model calculations for a 1D interface. The results reveal that the illuminated topography can be recovered directly from the measured reflected intensities. This is achieved through an analysis of the Patterson function, the Fourier transform of the scattering intensity (as a function of lateral momentum transfer, Q //, at fixed vertical momentum transfer, Q z ). Specifically, a second-order Patterson function is defined that reveals the discrete set of separations and contrast factors (i.e. the product of changes in the effective scattering factor) associated with discontinuities in the effective interfacial topography. It is shown that the topography is significantly overdetermined by the measurements, and an algorithm is described that recovers the actual topography through a deterministic sorting of this information.

Exposing the inadequacy of redox formalisms by resolving redox inequivalence within isovalent clusters

In this report we examine a family of trinuclear iron complexes by multiple-wavelength, anomalous diffraction (MAD) to explore the redox load distribution within cluster materials by the free refinement of atomic scattering factors. Several effects were explored that can impact atomic scattering factors within clusters, including 1) metal atom primary coordination sphere, 2) M−M bonding, and 3) redox delocalization in formally mixed-valent species. Complexes were investigated which vary from highly symmetric to fully asymmetric by 57Fe Mössbauer and X-ray diffraction to explore the relationship between MAD-derived data and the data available from these widely used characterization techniques. The compounds examined include the all-ferrous clusters [nBu4N][(tbsL)Fe3(μ3–Cl)] (1) ([tbsL]6– = [1,3,5-C6H9(NC6H4-o-NSitBuMe2)3]6–]), (tbsL)Fe3(py) (2), [K(C222)]2[(tbsL)Fe3(μ3–NPh)] (4) (C222 = 2,2,2-cryptand), and the mixed-valent (tbsL)Fe3(μ3–NPh) (3). Redox delocalization in mixed-valent 3 was explored with cyclic voltammetry (CV), zero-field 57Fe Mössbauer, near-infrared (NIR) spectroscopy, and X-ray crystallography techniques. We find that the MAD results show an excellent correspondence to 57Fe Mössbauer data; yet also can distinguish between subtle changes in local coordination geometries where Mössbauer cannot. Differences within aggregate oxidation levels are evident by systematic shifts of scattering factor envelopes to increasingly higher energies. However, distinguishing local oxidation levels in iso- or mixed-valent materials can be dramatically obscured by the degree of covalent intracore bonding. MAD-derived atomic scattering factor data emphasize in-edge features that are often difficult to analyze by X-ray absorption near edge spectroscopy (XANES). Thus, relative oxidation levels within the cluster were most reliably ascertained from comparing the entire envelope of the atomic scattering factor data.

On the Origin of Charge Compensation in Aluminum-Implanted n-Type 4H-SiC by Analysis of Hall Effect Measurements

Aluminum implanted 4H-SiC often shows an unexpected increase of the free hole density at elevated temperatures in Hall Effect measurements. Here we show that this phenomenon cannot solely be traced down to the Hall scattering factor and the presence of excited acceptor states. It is necessary to assume an additional defect center in the lower half of the band gap with ionization energies higher than that of aluminum to explain this behavior. Therefore, we investigated ion-implanted square van-der-Pauw samples with Hall Effect and complementary SIMS measurements. An analysis of the data using the neutrality equation reveals compensation ratios of 20 % to 90 %, depending on the aluminum concentration and the concentration of the deep defect center of up to 50 % of the doping.