P. James Viccaro

A synchrotron x-ray liquid surface spectrometer

The design of a synchrotron x-ray liquid surface spectrometer at beamline X19C at the National Synchrotron Light Source is described. This spectrometer is capable of performing the full range of x-ray surface scattering techniques. A few examples of measurements made using this spectrometer are presented, including studies of organic monolayers on the surface of water and of the structure of strongly fluctuating oil–microemulsion interfaces. The measurements discussed illustrate the accuracy, resolution, and capabilities of the spectrometer.

The liquid surface/interface spectrometer at ChemMatCARS synchrotron facility at the Advanced Photon Source

We discuss results from the first experiments on a new liquid surface/interface X-ray spectrometer recently commissioned by ChemMatCARS at Sector 15 of the Advanced Photon Source. These experiments include studies of liquid/liquid interfaces, monolayers supported on the water surface, and liquid metal surfaces.

X-ray studies of polymer/gold nanocomposites

We demonstrate that x-ray reflection standing wave fluorescence spectroscopy is a highly sensitive technique for the determination of the distribution of metal nanoparticles inside polymer thin films. We investigate both the depth profile and the in-plane spatial correlation of gold nanoparticles in an asymmetric polystyrene-b-poly(2-vinylpyridine) block copolymer film. These copolymer films self-assemble into alternating, nanometer-sized domains that are, upon annealing, selectively decorated by thermally evaporated metal nanoparticles to form metal/polymer composites.

Determination of cations distribution in Mn3O4 by anomalous x-ray powder diffraction

The oxidation states of Mn at two different crystallographic sites in the distorted spinel structure of Mn3O4 were determined by the approach of anomalous synchrotron x-ray powder diffraction. The real parts of anomalous scattering factors for the two Mn sites were refined from a series of powder diffraction patterns collected at the vicinity of K absorption edge of Mn. The results of Rietveld refinements showed that the two distinct cation sites can obviously be distinguished from each other and that Mn2+ ions occupy the tetrahedral site and Mn3+ ions are located at the octahedral site.

Optical Performance of the GM/CA‐CAT Canted Undulator Beam lines for Protein Crystallography

A new macromolecular crystallographic facility developed by GM/CA‐CAT is operational at the Advanced Photon Source (APS). The facility consists of three beamlines: two lines based on the first “hard” dual canted undulators and one bending magnet beamline. The ID lines are operational, and the BM line is being commissioned. Both insertion device (ID) beamlines are independently tunable over a wide energy range. The inboard ID lines have been upgraded with a new insertion device to provide enhanced performance for MAD phasing experiments near the selenium and bromine K‐edges. The ID line monochromators’ crystals are indirectly, cryogenically cooled for improved performance and reliability. Focusing is achieved by long bimorph mirrors in a Kirkpatrick‐Baez geometry. This paper describes the design of the beam lines and the optical characterization of the mirrors and monochromators.

Performance analysis of a side-cooled vertical-focusing mirror for the undulator beamline at APS

A detailed thermal deformation and slope-error analysis is performed on an indirectly-cooled design of a high-heat-load vertical-focusing mirror.THe cooling of the mirror is through copper plates inserted into two grooves along the sides of the mirror. The contact between the mirror and the copper plate is through a gallium-indium eutectic bath in the groove. This configuration provides efficient thermal contact between the mirror substrate and the cooling block without applying stress to the mirror from the cooling block. This mirror will be used at the Advanced Photon Source Sector-15 ChemMatCARS undulator beamline for vertical focusing. It will be exposed to white beam with a heat load of about 1.1 kw.

Update in a Rietveld analysis program for x-ray powder spectro-diffractometry

A computer program for refining anomalous scattering factors using x-ray powder diffraction data was revised on the basis of the latest version of a versatile pattern-fitting system, RIETAN-2000 . The effectiveness of the resulting program was confirmed by applying it to simulated and measured powder-diffraction patterns of Mn 3 O 4 taken at a synchrotron light source.

Preliminary experiment for residual stress analysis at the advanced photon source

In order to evaluate and find the proper conditions for residual stress (RS) measurements, two kinds of preliminary x-ray diffraction experiments were conducted at the Advanced Photon Source: angle-dispersive x-ray diffraction and energy-dispersive x-ray diffraction. These two experimental methods and their precision were investigated for RS measurement. The results obtained and various factors that may influence the accuracy of these experiments are discussed.

General-purpose high-resolution double-channel-cut monochromator for use on the ChemMatCARS insertion-device beamline at the Advanced Photon Source

The high-brilliance radiation provided by third-generation synchrotron x-ray facilities such as the Advanced Photon Source has greatly enhanced the power of such chemical and materials research techniques as x-ray-absorption spectroscopy, surface scattering, small-angle x-ray scattering, and chemical crystallography. In order to take full advantage of these source properties, we propose the development of a general-purpose high-energy-resolution double-channel-cut monochromator based on a similar device developed for nuclear-resonant-scattering techniques by the Experimental Facilities Division at the APS. The instrumentation will be installed at the APS on the ChemMatCARS insertion-device beamline at sector 15. It will be used primarily for valence-specific static and time-resolved chemical-crystallography experiments as well as anomalous- scattering experiments planned for surface diffraction and small-angle/wide-angle x-ray scattering. Two channel-cut crystals placed in a dispersive (-n, +n, +n, -n) geometry provide a fixed-offset beam with an energy resolution (Delta) E/E approximately 10-5. Several sets of channel-cut-crystal pairs, designed to cover an energy range from 6 to 35 keV with a matching angular acceptance to the source, are used in conjunction with the beamline high- heat-load double-crystal monochromator.

COHERENT X-RAY SCATTERING FROM AN OPTICAL GRATING

X-ray speckles due to scattering of partially (transverse) coherent x rays from an optical reflection grating are observed. The speckles indicate the presence of surface inhomogeneities of the grating that are otherwise undetectable with either visible laser light or transversely incoherent x-ray scattering. Qualitative analysis of the speckle patterns provide information on the surface morphology of the grating. The underlying order due to the periodicity of the grating enhances the detection of the speckles.