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Abstract: Calcium phosphate cluster formation leads to the
nucleation of apatite. Apatite controls phosphorus availability
in the geosphere and is also an important biomineral (e.g.
bone, tooth). Formation of apatite at the atomic scale is
believed to take place via the formation of a Ca3
(PO4
)2
precursor. Very little is currently known about the nature and
evolution (in saturated aqueous solutions) of this precursor,
and how this may be affected/controlled by the presence of
organic species. Using the materials processing beamline, 6.2,
at Daresbury Synchrotron Radiation Source for in-situ
simultaneous small- and wide- angle X-ray scattering
(SAXS/WAXS) experiments, we were able to to monitor
apatite nucleation from supersaturated solutions at times
scales of up to 30 minutes and at 10 second resolution. Our
aim was to test the influence of a range of organic ligands
(citrate, oxalate, osteocalcin) on nucleation and growth. Our
preliminary observations suggest that organic ligands affect
both the onset and the rate of crystal formation and growth, as
well as the settling properties of apatite nucleating from a
supersaturated solution (Figure 1). We discuss our results in
the context of the precipitating apatite, as a proxy for
bioapatites
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Jan 2004
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Abstract: A new high-pressure single-crystal diffraction facility has been constructed on station 9.8 at the Synchrotron Radiation Source, Daresbury Laboratory, for a range of studies on a variety of systems of relevance to physics, chemistry and materials science that would otherwise prove intractable with conventional laboratory-based methods. The station has been equipped with a modified Enraf-Nonius CAD4 four-circle diffractometer for high-pressure studies which can be conveniently, and rapidly, interchanged with the Bruker SMART CCD area-detector system when more routine ambient-pressure diffraction work is to be undertaken. This rapid change-over has been achieved by permanently mounting the CAD4 on its own jacking table, formerly used for the station's white-beam diffraction mode, which allows the alignment of the SMART diffractometer to remain undisturbed when the CAD4 is in use. Early results on the test low-melting-point compound ethanol (CH3CH2OH) reveal that excellent refined structures can be obtained, including the location and refinement of the H atoms, demonstrating that one of the original, and major, objectives of the station has been accomplished.
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Jan 2004
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Abstract: We recorded X-ray resonant magnetic scattering (XRMS) patterns from a 40 nm thin FePd film that exhibits magnetic stripes with ?100 nm period. Measurements were performed using a CCD camera in reflection geometry for different light polarizations at the Fe L3 resonance. We observed dichroic effects using circular polarization. By combining the scattering patterns obtained with both helicities we obtain the symmetric and antisymmetric part of the pattern. The experimental results are in agreement with a simple theoretical model.
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Dec 2003
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Abstract: The growth of platinum on a nickel ~111! single crystal under ultrahigh vacuum conditions was studied using surface x-ray diffraction on the ID03 beamline of the ESRF. Film thickness ranged from one to eight monoatomic layers ~ML!. Specular reflectivity was used to determine the growth mode and vertical lattice parameter of the Pt film. A two-dimensional ~2D! growth up to 1 ML followed by more 3D growth was found. A small expansion of the Pt vertical lattice parameter was found. The Pt in-plane lattice parameter was measured. Its relaxation was found to be very slow, with a residual contraction of 2.3% in an 8-ML-thick film ~with respect to bulk Pt!. A Ni crystal truncation rod measured before and after growing 1 ML of Pt revealed the presence of a small amount of pseudomorphic Pt, adsorbed on both fcc and hcp sites. The stacking of the ~111! Pt planes was investigated by measuring stacking-sensitive Pt diffraction rods. A strong tendency to stacking reversal was found at room temperature, with an amount of ‘ ‘reversed’’ Pt about ten times higher than the amount of Pt with the same stacking as the Ni. An eight-layer Ni film on Pt~111! was also studied for comparison
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Dec 2003
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Abstract: A Michelson interferometer for X- rays of wavelength similar to 1 Angstrom has been proposed to test the temporal coherence of FEL radiation. Such a device has been made at HASYLAB from a silicon single crystal. It is based on the BBB interferometer of Bonse and Hart. One of its mirrors can be pushed by a piezo to introduce the desired beam path difference. For the preliminary tests described in this paper, the crystal was also equipped with an LLL interferometer to check the quality of the crystal and of its preparation. The rotation of a phase- shifting object ( a Plexiglas plate) in one of the LLL's beam paths has been found to produce a fringe pattern which can be shown to yield the phase- shifting material's index of refraction. The interferometer crystal's front section was held fixed with a compression spring. At the same time, the interferometer was bathed in viscous silicone oil to reduce vibrations.
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Nov 2003
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Controls
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Abstract: Whilst the Diamond control system is based on the EPICS control system toolkit, significant use is being made of industrial controllers and control system solutions procured from industry. The choice and implementation of the industrial controllers are presented, together with the approach to procuring control systems from industry that use both industrial controllers and EPICS.
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Oct 2003
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Controls
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Abstract: The Diamond timing system is the next generation development of the design, principles and technologies currently implemented on the Advanced Photon Source and Swiss Light Source. It provides the features to distribute events, RF clock and time stamps over the same medium. To support the required level of precision for distributing timing fiducials and clocks, the transmission will use higher bit rates (at least 2.5 Gbps). It is currently envisaged that OM3 multimode fibre optic cable will be used as a medium. A new 4 channel timer module will be designed, with a resolution better than 20 ps, for systems which require fine time tuning. The timing system will be controlled through the Diamond distributed control system which is based on EPICS.
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Oct 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 control system for Diamond will be a site-wide monitoring and control system for the accelerators, beamlines and conventional facilities. Progress on the detailed design of the control system is presented. This includes refinement in the choice of EPICS tools, the development of tools and applications, and design of the control system structure, including solutions for interface options, control system networking, machine protection, wide band signals and physical implementation.
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Oct 2003
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Abstract: We have measured the resonance spectrum of glide-plane forbidden x-ray diffraction in hexagonal ZnO as a function of temperature. This is the only method to observe deformations of the electronic states caused by thermal atomic motion. The results provide the first evidence for a complex line shape in the spectrum of thermal-motion-induced scattering and the first observation of a dramatic change in resonance spectrum with temperature. The measurements are in agreement with a phenomenological model, based on a combination of constant (most probably dipole-quadrupole) and temperature-dependent amplitudes. This model provides a means of separating the two components, including their relative phase.
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Aug 2003
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J. T.
Hoeft
,
M.
Polcik
,
D. I.
Sayago
,
M.
Kittel
,
R.
Terborg
,
R. L.
Toomes
,
J.
Robinson
,
D. P.
Woodruff
,
M.
Pascal
,
G.
Nisbet
,
C. L. A.
Lamont
Abstract: The local adsorption geometry of CO adsorbed in different states on Ni(1 0 0) and on Ni(1 0 0) precovered with atomic hydrogen has been determined by C 1s (and O 1s) scanned-energy mode photoelectron diffraction, using the photoelectron binding energy changes to characterise the different states. The results confirm previous spectroscopic assignments of local atop and bridge sites both with and without coadsorbed hydrogen. The measured Ni–C bondlengths for the Ni(1 0 0)/CO states show an increase of 0.16 ± 0.04 Å in going from atop to bridge sites, while comparison with similar results for Ni(1 1 1)/CO for threefold coordinated adsorption sites show a further lengthening of the bond by 0.05 ± 0.04 Å. These changes in the Ni–CO chemisorption bondlength with bond order (for approximately constant adsorption energy) are consistent with the standard Pauling rules. However, comparison of CO adsorbed in the atop geometry with and without coadsorbed hydrogen shows that the coadsorption increases the Ni–C bondlength by only 0.06 ± 0.04 Å, despite the decrease in adsorption energy of a factor of 2 or more. This result is also reproduced by density functional theory slab calculations. The results of both the experiments and the density functional theory calculations show that CO adsorption onto the Ni(1 0 0)/H surface is accompanied by significant structural modification; the low desorption energy may then be attributed to the energy cost of this restructuring rather than weak local bonding.
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Aug 2003
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