Home About us Contact
|
Home About us Contact | ||
|
|
||
Elastic Scattering (elastic + scattering)
Selected AbstractsElastic scattering of high-energy electrons by dopant atoms within a crystal in transmission electron microscopyACTA CRYSTALLOGRAPHICA SECTION A, Issue 6 2008B. G. Mendis A Bloch-wave model of dopant-atom scattering is developed using perturbation theory for parallel illumination in a transmission electron microscope. Dopant-atom scattering causes a change in the Bloch-wave excitations, with transitions from one Bloch state to another being governed by the amplitudes of the Bloch states at the dopant-atom position. The scattering mechanisms therefore depend on whether the dopant atom is substitutional or interstitial as well as the orientation of the crystal. The model is used to calculate the electron wavefunction for substitutional and interstitial Mo atoms in [111]- and [001]-oriented body-centred cubic Fe and the results overall are consistent with multislice simulations. However, subtle differences are also observed. For example, in the Bloch-wave model the phase change of the incident electrons (with respect to the perfect crystal) due to dopant-atom scattering varies with the crystallographic orientation while in multislice theory the phase change is constant. This is likely to be due to the assumptions made in the Bloch-wave model, such as neglect of elastic diffuse scattering. Apart from providing a fundamental understanding of dopant-atom scattering, the model can also potentially be extended to analyse dopant-atom imaging in a scanning transmission electron microscope. [source] Quantitative high-pressure pair distribution function analysisJOURNAL OF SYNCHROTRON RADIATION, Issue 5 2005John B. Parise The collection of scattering data at high pressure and temperature is now relatively straightforward thanks to developments at high-brightness synchrotron radiation facilities. Reliable data from powders, that are suitable for structure determination and Rietveld refinement, are routinely collected up to about 30,GPa in either a large-volume high-pressure apparatus or diamond anvil cell. In those cases where the total elastic scattering is of interest, as it is in the case of nano-crystalline and glassy materials, technical developments, including the use of focused high-energy X-rays (>80,keV), are advantageous. Recently completed experiments on nano-crystalline materials at the 1-ID beamline at the Advanced Photon Source suggest that quantitative data, suitable for pair distribution function analysis, can be obtained. [source] Quantum criticality of Ce1,xLaxRu2Si2: The magnetically ordered phasePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2010Stéphane Raymond Abstract We report specific heat and neutron scattering experiments performed on the system Ce1,xLaxRu2Si2 on the magnetic side of its quantum critical phase diagram. The Kondo temperature does not vanish at the quantum phase transition and elastic scattering indicates a gradual localization of the magnetism when x increases in the ordered phase. [source] Exciton states and tunneling in semimagnetic asymmetric double quantum wellsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2010S. V. Zaitsev Abstract Exciton level structure and interwell relaxation are studied in Cd(Mn,Mg)Te-based asymmetric double quantum wells (ADQWs) by a steady-state optical spectroscopy in magnetic fields up to B,=,10,T. The as grown heterostructures with CdTe QWs and nonmagnetic interwell CdMgTe barrier were subjected to a rapid temperature annealing to introduce Mn and Mg atoms from opposite barriers inside the QWs which results in a formation of the ADQW with completely different magnetic field behavior of the intrawell excitons. The giant Zeeman effect in the QW with magnetic Mn ions gives rise to a crossing of the ground exciton levels in two QWs at BC,,,3,6,T which is accompanied by a reverse of the interwell tunneling direction. In a single-particle picture the exciton tunneling is forbidden at B,<,1,T as supported by calculations. Experimentally, nevertheless, a very efficient interwell relaxation of excitons is found at resonant excitation in the whole magnetic field range, regardless of the tunneling direction, emphasizing importance of excitonic correlations in the interwell tunneling. At nonresonant excitation an unexpectedly slow relaxation of the ,, -polarized excitons from the nonmagnetic QW to the ,+ -polarized ground state in the semimagnetic QW is observed at B,>,BC, giving rise to a nonequilibrium distribution of excitons in ADQW. A strong dependence of the total circular polarization degree on the hh,lh splitting ,hh,lh in the nonmagnetic QW is found and attributed to the spin dependent interwell tunneling controlled by an exciton spin relaxation. Different charge-transfer mechanisms are analyzed in details and an elastic scattering due to a strong disorder is suggested as the main tunneling mechanism with the underlying influence of the valence band-mixing. [source] The role of phonons in establishing a non-equilibrium quasiparticle state in small gap multiple tunnelling superconducting tunnel junctionsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 11 2004A. G. Kozorezov Abstract We derive expressions for phonon escape times from a thin superconducting film. The escape time is determined by the rate of scattering conversion for phonons propagating beyond the critical cone for total internal reflection. The conversion is due to different scattering processes for the groups of Cooper pair breaking and sub-gap phonons. For pair breaking phonons the most efficient conversion mechanism is through the interaction with the condensate. For sub-gap phonons the conversion rate is much slower and for plane parallel films is due to elastic scattering at surface or interface roughness resulting in significantly slower escape times. We discuss implications of slow escape time for sub-gap phonons for the properties of the recently observed new non-equilibrium state in small gap multiple tunnelling superconducting tunnel junctions. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Two-wavelength inversion of multiply scattered soft X-ray intensities to charge densityACTA CRYSTALLOGRAPHICA SECTION A, Issue 1 2009J. C. H. Spence A method is described for reconstructing the two-dimensional real-space charge density of an isolated object from measurement of the soft X-ray transmission diffraction pattern when it is affected by strong multiple scattering. The Bloch-wave scattering-matrix approach is used to show that the diffracted amplitude depends only on a simple product of X-ray wavelength and sample thickness (unlike the case of relativistic electron diffraction) under reasonable approximations. The multislice formulation then gives the effect of a small change in wavelength, which involves only single scattering. Dynamical diffraction patterns are recorded at two adjacent wavelengths, phased by iterative methods, transformed to real space and divided to give a single-scattering wavefunction. This can then be used to produce a charge-density map. The extension of the method to tomography is discussed. Consideration is first also given to the possibility that absorption due to the photoelectric effect may be so severe for soft X-rays that multiple elastic scattering becomes so much less probable than photoelectric absorption that it may be neglected entirely. A discussion of signs in soft X-ray, positron and electron multiple-scattering theory is given. [source] | |||||||||||||