Search results for "scatter"
showing 10 items of 8475 documents
Atomic diffraction from nanostructured optical potentials
2002
We develop a versatile theoretical approach to the study of cold-atom diffractive scattering from light-field gratings by combining calculations of the optical near-field, generated by evanescent waves close to the surface of periodic nanostructured arrays, together with advanced atom wavepacket propagation on this optical potential.
Diffractive vector meson production in ultraperipheral heavy ion collisions from the Color Glass Condensate
2014
We compute cross sections for incoherent and coherent diffractive J/$\Psi$ and $\Psi(2S)$ production in ultraperipheral heavy ion collisions. The dipole models used in these calculations are obtained by fitting the HERA deep inelastic scattering data and compared with available electron-proton diffraction measurements. We obtain a reasonably good description of the available ALICE data. We find that the normalization of the ultraperipheral cross section has large model dependence, but the rapidity dependence is more tightly constrained.
Optical control of vibrational coherence triggered by an ultrafast phase transition
2019
Femtosecond time-resolved x-ray diffraction is employed to study the dynamics of the periodic lattice distortion (PLD) associated with the charge-density-wave (CDW) in K0.3MoO3. Using a multi-pulse scheme we show the ability to extend the lifetime of coherent oscillations of the PLD about the undistorted structure through re-excitation of the electronic states. This suggests that it is possible to enter a regime where the symmetry of the potential energy landscape corresponds to the high symmetry phase but the scattering pathways that lead to the damping of coherent dynamics are still controllable by altering the electronic state population. The demonstrated control over the coherence time …
Imaging spin filter for electrons based on specular reflection from iridium (001)
2013
Abstract As Stern–Gerlach type spin filters do not work with electrons, spin analysis of electron beams is accomplished by spin-dependent scattering processes based on spin–orbit or exchange interaction. Existing polarimeters are single-channel devices characterized by an inherently low figure of merit (FoM) of typically 10 −4 –10 −3 . This single-channel approach is not compatible with parallel imaging microscopes and also not with modern electron spectrometers that acquire a certain energy and angular interval simultaneously. We present a novel type of polarimeter that can transport a full image by making use of k -parallel conservation in low-energy electron diffraction. We studied specul…
Electromagnetic Singularities and Resonances in Near-Field Optical Probes
2007
Over the last two decades scanning near-field optical microscopy (SNOM) has demonstrated its ability to provide optical resolution significantly better than the diffraction limit (<20 nm). The general principle of SNOM relies on the approach of a nanometer-sized object in the optical near-field of a sample to be studied. This nano-object (NO) is usually the extremity of a probe. Regardless of the nature of the observed SNOM signal (inelastic scattering, fluorescence, etc.), the detection of the light is achieved in the far-field regime where the NO acts as a mediator between the optical near-field and the detector. Figure 1 is a schematic illustration of the SNOM principle.
IMAGING OF DICHROISM IN PHOTOEMISSION ELECTRON MICROSCOPY AT NONMAGNETIC MATERIALS USING CIRCULARLY POLARIZED SOFT X-RAYS
2002
A new approach for investigations of circular dichroism in the angular distribution of photoelectrons (CDAD) is presented. The image contrast using a photoemission line of a certain material is combined with imaging of the angular distribution pattern using a photoemission electron microscope (PEEM). CDAD can be used to investigate pure scattering information by means of the same instrument in microscopically selected regions on a surface. The experiment combines angle-resolved XPS imaging with the indirect mapping of the local environment of atoms by means of CDAD holography. In a conventional photoelectron diffraction or photoelectron holography experiment, it is necessary to move the sa…
Photoemission from Pt(111)-(hex)-Rb and Pt(111)-(4×1)-RbO using polarised synchrotron radiation
2001
Abstract In various experiments it has been demonstrated that the circular dichroism in the angular distribution of photoelectrons (CDAD) is not only observed from oriented initial states (aligned adsorbed molecules or magnetised samples), but also arises as a consequence of the scattering of photoelectrons from the surrounding atoms in a solid or an adsorbate. In this work we will show first measurements performed at the SGM beamline of the Brazilian Synchrotron Light Source (LNLS) on a (4×1) superstructure of 1 ML RbO adsorbed on Pt(111). Measurements from the 4s core levels of Rb adsorbed at Pt(111) were also performed at the PM-III beamline at BESSY. The measured variations of the inten…
High-pressure theoretical and experimental study of HgWO4
2011
HgWO 4 at ambient pressure is characterized using a combination of ab initio calculations, X-ray diffraction and Raman scattering measurements. The effect of low pressure and temperature on the structural stability is analysed. Extending our ab initio study to the range of higher pressures, a sequence of stable phases up to 30GPa is proposed. © 2011 Taylor & Francis.
Automated electron diffraction tomography - a new tool for nano crystal structure analysis
2011
Automated electron Diffraction Tomography (ADT) comprises an upcoming method for “ab intio” structure analysis of nano crystals. ADT allows fine sampling of the reciprocal space by sequential collection of electron diffraction patterns while tilting a nano crystal in fixed tilt steps around an arbitrary axis. Electron diffraction is collected in nano diffraction mode (NED) with a semi-parallel beam with a diameter down to 50 nm. For crystal tracking micro-probe STEM imaging is used. Full automation of the acquisition procedure allowed optimisation of the electron dose distribution and therefore analysis of highly beam sensitive samples. Cell parameters, space group and reflection intensitie…
Elucidating structural order and disorder phenomena in mullite-type Al4B2O9 by automated electron diffraction tomography
2017
The crystal structure and disorder phenomena of Al4B2O9, an aluminum borate from the mullite-type family, were studied using automated diffraction tomography (ADT), a recently established method for collection and analysis of electron diffraction data. Al4B2O9, prepared by sol-gel approach, crystallizes in the monoclinic space group C2/m. The ab initio structure determination based on three-dimensional electron diffraction data from single ordered crystals reveals that edge-connected AlO6 octahedra expanding along the b axis constitute the backbone. The ordered structure (A) was confirmed by TEM and HAADF-STEM images. Furthermore, disordered crystals with diffuse scattering along the b axis…