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Abstract: Atom-resolving x-ray holography is a recently developed method for direct imaging of local three-dimensional structures at the atomic level. We investigate analytically and numerically additional effects arising from the long-range order in an object. It is shown that they are not correctly taken into account by existing image reconstruction procedures used commonly in the analysis of experimental data. It is proven that low-pass filtering cannot be used for extracting information about the short-range order in crystalline samples.
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Aug 2002
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Abstract: The adsorption and growth of Ti on Si(111)-7×7 surface at room temperature was studied with x-ray standing waves and high energy x-ray photoelectron spectroscopy. The surface morphology of the specimens was analyzed using atomic force microscopy. We observed that at the submonolayer (0.08–0.24 ML) coverage a significant fraction of the metal atoms are coherently located in the near-surface interstitial positions of the Si lattice. For a higher Ti coverage (1.8 ML), the coherently ordered fraction almost vanishes and the surface is covered with three-dimensional islands. The Ti-coverage results are interpreted in terms of an interfacial transition layer containing Ti interstitials below the Si surface at low coverage, and a disordered mixed Ti–Si phase at higher Ti concentration.
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Nov 2002
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Abstract: DIAMOND is a new synchrotron light source currently being designed in the UK. The control system for DIAMOND will be a site wide monitoring and control system for the accelerators, beamlines and conventional facilities. Initial work on the control system has selected EPICS as the basis for the control system design. The requirements of the control system are presented. The technical solutions being considered to interface EPICS to the equipment being controlled are discussed together with the requirements for configuration and management of a large EPICS installation. Options being considered for the procurement, installation and commissioning of the control system are also presented.
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Nov 2002
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Abstract: A holographic approach to the analysis of a Bragg scattering pattern has been described by Szoke [Acta Cryst. (1993), A49, 853-866]. The combination of crystallographic procedures and holographic interpretation allows reconstruction of an unknown part of the crystalline structure model-free if the other part of the structure is known. By introducing the concept of an average crystal, this approach is extended to point defect structures in inorganic crystals. In this case, the host lattice is well known while the defect structure is regarded as the unknown part. To demonstrate the feasibility of this approach, an Sc2O3 sample doped with Er at low concentration has been studied. An additional electron density has been observed, which can be interpreted as an interstitial Er position.
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Jan 2003
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Controls
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Abstract: Diamond is a new synchrotron light source currently being designed and constructed in the UK. The Diamond personnel safety system will protect people from the hazards associated with the accelerators and photon beamlines. The choice of technology and conceptual design of the Diamond Personnel Safety System (PSS) are presented, together with planned analysis methods that will provide a quantitative measure of the overall reliability of the PSS.
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Jan 2003
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Abstract: Gerhard Materlik, Chief Executive Officer of Diamond Light Source Ltd., describes Diamond, the new generation synchrotron light source set to open at the Rutherford Appleton Laboratory in 2007, and discusses how it will push back the boundaries of what chemists can achieve in many research areas.
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Apr 2003
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Abstract: GaAs(100) single crystal substrates have been implanted with 1.00 MeV C + and 2.00 MeV C + 2 at various ion doses. The surfacetopography and roughness of the implantedsurfaces are studied by atomic force microscopy and x-ray reflectometry. Above a threshold dose, production of surface defects is observed, which results in an overall increase of the rms roughness parameter. The enhanced rms roughnesses induced by monomer and by dimer ions at a given dose are comparable. The influence of C + and C + 2 irradiations on the change of lattice parameter in GaAs, and the effect of thermal annealing, are examined by high-resolution x-ray diffraction. For the as-implanted specimens, an increase of the lattice constant, caused by the accumulation of implantation-induced point defects, has been observed and quantified. Thermal treatment of the implantation damage stimulates an almost complete recovery of the primary defects, leaving the crystal practically free from any lattice strain. The electrical characteristics of the C + and C + 2 implantations are also briefly presented and discussed
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May 2003
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Accelerator Physics
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Abstract: The current status of the detailed design and construction of the UK's new third generation light source, Diamond, is described.
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May 2003
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Abstract: The current status of the detailed design and construction of the UK's new 3rd generation light source, Diamond.
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May 2003
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Abstract: H2S induces rapid sulfidation of the Rh nanoparticles at room temperature and completely poisons NO reduction by H-2; SO2 elicits an equally rapid but subtle modification of nanoparticle structure but has little effect upon NO reduction at 523 K.
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Jun 2003
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