Micro x-ray small-angle scattering with synchrotron radiation

Abstract

Three small-angle scattering cameras based on mirror/monochromator optics, a circular Bragg-Fresnel (BF) lens, and a microcollimation system combined with a double-focusing mirror have been tested for microfocusing applications. In order to reach a focal spot less than or equal to 10 μm. a microcollimation system provides a flexible solution for medium-resolution applications. When using a glass capillary as a collimation system, a minimum s-value of 5·10^?2 nm^?1 was attained. Scanning small-angle x-ray scattering (SAXS) patterns from a poly(tetramethyl-p-silphenylene)-siloxane spherulite and a 40-μm polyethyl-eneterephthalate fiber were obtained in a few seconds per pattern with a 4 μm diameter beam at a wavelength of λ = 0.095 nm.     

High-pressure studies with nuclear scattering of synchrotron radiation

Hyperfine Interactions - The nuclear forward scattering (NFS) of synchrotron radiation is especially suited for probing magnetism at high pressure (h.p.), here in the Mbar range, by the nuclear...     

Nuclear resonant scattering using synchrotron radiation

A one-dimensional quantum model for nuclear resonant scattering using synchrotron radiation has been developed. This model gives a clear physical interpretation of the most prominent features of the coherent forward scattering process namely, the “speed-up” and “dynamical beat” effects. The form of the solution, for the time-dependent forward scattered intensity of the resonant radiation from the resonant medium after synchrotron radiation excitation, is a finite series. This unique solution can be interpreted in terms of a summation over all multiple forward scattering paths the radiation takes in reaching the detector. The resonant medium is represented by a linear chain of N effective resonant nuclei. The analysis starts from a coupled set of quantum mechanical equations for the relevant amplitudes in frequency space. Transformation to the time domain gives an analytical expression for the forward scattered intensity. The contribution of every order of the multiple scattering processes from the N effective nuclei appears naturally. The expression gives a clear physical understanding of all relevant aspects of resonant forward nuclear scattering. Furthermore, the present formalism allows the consideration of incoherent processes. This permits the study of processes in which there is gamma emission with recoil or emission of internal-conversion electrons. This revised version was published online in August 2006 with corrections to the Cover Date.     

Small angle x-ray and neutron scattering studies of plasma-deposited amorphous silicon-hydrogen films

Small-angle scattering measurements using both neutrons and X-rays have been made on a series of plasma-deposited a-Si : H films. One class of sample exhibits strong anisotropic scattering indicating rod-like microstructure normal to the film surface with a dominant rod diameter of ~ 60 Å. Other samples show isotropic scattering with a similar dimension or no scattering at all within the resolution of the experiment.     

Modelling x-ray scattering from quantum dots using Keating energy-minimised structures

In a traditional analysis of surface x-ray diffraction data, the surface unit cell can be defined by a small set of parameters, and fitting of experimental data is accomplished using well-established procedures. A quantum dot (QD), however, may contain as many as 20,000 atoms, so a different approach to data analysis is required. A method for modelling a quantum dot and relaxing the structure by minimising the Keating energy is presented, and the simulation of x-ray scattering from such models is described. A method is then developed for simulating the alloying of InAs and GaAs inside the QDs using intermediate Keating parameters. This removes the need to relax and average multiple models with randomly distributed atoms, which would increase the computation time significantly.     

Non-resonant and resonant x-ray scattering studies on multiferroic TbMn2O5

Comprehensive x-ray scattering studies, including resonant scattering at Mn L, Tb L, and M edges, were performed on single crystals of TbMn2O5 for crystallographic data to elucidate the nature of its commensurate and incommensurate phases. The scattering results provide direct evidence of symmetry lowering to the ferroelectric phase driven by magnetically induced lattice modulations and show the presence of multiple magnetic orders. The competing orders under spin-frustrated geometry are believed to cause discommensuration and result in the commensurate-to-incommensurate phase transition around 24 K. It is proposed that the low temperature incommensurate phase consists of commensurate domains separated by antiphase domain walls which change both signs of spontaneous polarizations and x-ray scattering amplitudes for forbidden reflections.     

Parametric x-ray radiation along the velocity of relativistic electron in a Bragg scattering geometry

Based on the dynamic scattering theory, forward parametric x-ray radiation (FPXR) of a relativistic electron is investigated in a single crystal plate in a Bragg scattering geometry. Analytical expressions for the spectral-angular distribution of FPXR and transition radiation (TR) including the crystal surface orientation with respect to a system of diffracting atomic planes are derived, which allow one to identify the conditions under which a contribution from FPXR is considerable even in the case of a thick absorbing crystal. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 48–56, June, 2007.     

Magnetic domain fluctuations in an antiferromagnetic film observed with coherent resonant soft x-ray scattering

We report the direct observation of slow fluctuations of helical antiferromagnetic domains in an ultrathin holmium film using coherent resonant magnetic x-ray scattering. We observe a gradual increase of the fluctuations in the speckle pattern with increasing temperature, while at the same time a static contribution to the speckle pattern remains. This finding indicates that domain-wall fluctuations occur over a large range of time scales. We ascribe this nonergodic behavior to the strong dependence of the fluctuation rate on the local thickness of the film.     

Magnetic structure determination using polarised resonant X-ray scattering

Full polarisation analysis of resonant X-ray magnetic scattering (RXMS) is shown to advance the determination of magnetic moment directions of complex magnetic structures within single crystals. Key features of this novel method are the variation of the incident beam polarisation through the use of an X-ray phase plate, and the measurement of the scattered beam polarisation in terms of Poincaré-Stokes parameters. Contrary to the established method, no azimuthal rotation is required. Thus, the major sources of systematic error are eliminated, and the method is compatible with exotic and complex sample environments. The technique is demonstrated with the example of TbMn₂O₅. The RXMS theory briefly outlined in this paper was fitted to the data, and the local and delocalized, band-specific moment directions associated with the magnetic order of the resonating species was refined with a high degree of accuracy.     

In-situ study of precipitates in Al–Zn–Mg–Cu alloys using anomalous small-angle x-ray scattering

In the present work,the precipitate compositions and precipitate amounts of these elements(including the size distribution,volume fraction,and inter-precipitate distance) on the Cu-containing 7000 series aluminum alloys(7150 and 7085 Al alloys),are investigated by anomalous small-angle x-ray scattering(ASAXS) at various energies.The scattering intensity of 7150 alloy with T6 aging treatment decreases as the incident x-ray energy approaches the Zn absorption edge from the lower energy side,while scattering intensity does not show a noticeable energy dependence near the Cu absorption edge.Similar results are observed in the 7085 alloy in an aging process(120℃) by employing in-situ ASAXS measurements,indicating that the precipitate compositions should include Zn element and should not be strongly related to Cu element at the early stage after 10 min.In the aging process,the precipitate particles with an initial average size of ~ 8 ?A increase with aging time at an energy of 9.60 ke V,while the increase with a slower rate is observed at an energy of 9.65 ke V as near the Zn absorption edge.     

Measurement of two solvation regimes in water-ethanol mixtures using x-ray compton scattering

Water-ethanol mixtures exhibit interesting anomalies in their macroscopic properties. Despite a lot of research, the origin of the anomalies and the microscopic structure itself is still far from completely known. We have utilized the synchrotron x-ray Compton scattering technique to elucidate the structure of aqueous ethanol from a new experimental perspective. The technique is uniquely sensitive to the local molecular geometries at the angstrom and subangstrom scales. The experiments reveal two distinct mixing regimes in terms of geometry: the dilute 5 mol % and the concentrated >15 mol % regimes. By comparing with pure liquids, the former regime is characterized by an intramolecular and the latter by an intermolecular change. The findings bring new light to evaluating the hypothesis of formation of clathratelike structures at the dilute concentrations.