Sterling Cornaby

High-flux hard X-ray microbeam using a single-bounce capillary with doubly focused undulator beam

A pre-focused X-ray beam has been used to illuminate a single-bounce capillary in order to generate a high-flux X-ray microbeam at the BioCAT undulator X-ray beamline at the Advanced Photon Source. The combined optical arrangement makes it suitable for many microprobe fluorescence applications and micro-XANES experiments for biological samples.

Microbeam high angular resolution x-ray diffraction in InGaN∕GaN selective-area-grown ridge structures

GaN-based 6-μm-wide ridge waveguides with InGaN∕GaN multiple-quantum-wells (MQWs) produced by metal organic vapor-phase epitaxy in the regime of selective-area growth have been studied with microbeam high angular resolution x-ray diffraction and reciprocal-space mapping. Variation of the strain from 0.9% to 1.05% and a factor of 3 for the thickness enhancement of the MQW period have been measured for different widths of the oxide mask surrounding the GaN-based ridges. Only when the trapezoidal shape of the ridge cross section is taken into account can the difference between the experimentally measured thickness enhancement and predictions of the long-range gas-phase diffusion model be reconciled.

Focusing capillary optics for use in solution small-angle X-ray scattering

Measurements of the global conformation of macromolecules can be carried out using small-angle X-ray scattering (SAXS). Glass focusing capillaries, manufactured at the Cornell High Energy Synchrotron Source (CHESS), have been successfully employed for SAXS measurements on the heme protein cytochrome c. These capillaries provide high X-ray flux into a spot size of tens of micrometres, permitting short exposures of small-volume samples. Such a capability is ideal for use in conjunction with microfluidic mixers, where time resolution may be determined by beam size and sample volumes are kept small to facilitate mixing and conserve material.

Microcrystallography using single-bounce monocapillary optics

X-ray microbeams have become increasingly valuable in protein crystallography. A number of synchrotron beamlines worldwide have adapted to handling smaller and more challenging samples by providing a combination of high-precision sample-positioning hardware, special visible-light optics for sample visualization, and small-diameter X-ray beams with low background scatter. Most commonly, X-ray microbeams with diameters ranging from 50 microm to 1 microm are produced by Kirkpatrick and Baez mirrors in combination with defining apertures and scatter guards. A simple alternative based on single-bounce glass monocapillary X-ray optics is presented. The basic capillary design considerations are discussed and a practical and robust implementation that capitalizes on existing beamline hardware is presented. A design for mounting the capillary is presented which eliminates parasitic scattering and reduces deformations of the optic to a degree suitable for use on next-generation X-ray sources. Comparison of diffraction data statistics for microcrystals using microbeam and conventional aperture-collimated beam shows that capillary-focused beam can deliver significant improvement. Statistics also confirm that the annular beam profile produced by the capillary optic does not impact data quality in an observable way. Examples are given of new structures recently solved using this technology. Single-bounce monocapillary optics can offer an attractive alternative for retrofitting existing beamlines for microcrystallography.

Optimizing Monocapillary Optics for Synchrotron X-ray Diffraction, Fluorescence Imaging, and Spectroscopy Applications

A number of synchrotron x‐ray applications such as powder diffraction in diamond anvil cells, microbeam protein crystallography, x‐ray fluorescence imaging, etc. can benefit from using hollow glass monocapillary optics to improve the flux per square micron on a sample. We currently draw glass tubing into the desired elliptical shape so that only one‐bounce under total reflection conditions is needed to bring the x‐ray beam to a focus at a 25 to 50 mm distance beyond the capillary tip. For modest focal spot sizes of 10 to 20 microns, we can increase the intensity per square micron by factors of 10 to 1000. We show some of the results obtained at CHESS and Hasylab with capillaries focusing 5 to 40 keV radiation, their properties, and how even better the experimental results could be if more ideal capillaries were fabricated in the future.

Nanocomposite characterization on multiple length scales using µSAXS.

Nanocomposites have great potential for the rational synthesis of tailored materials. However, the templating process that transfers the self-organized nanostructure of a block copolymer or other mesophase onto the functional material is by no means trivial, and often involves multiple steps, each of which presents its own chemical and physical challenges. As a result the nanocomposite may not be homogeneous, but can be phase-separated into various components which may feature their own specific microstructure. Here it is shown how scanning microbeam small-angle X-ray scattering (µSAXS) can be used to characterize a thermoset resol/poly(isoprene-block-ethylene oxide) nanocomposite on multiple length scales with respect to homogeneity and microphase separation.

C2 DESIGN OF SINGLE-BOUNCE MONOCAPILLARY X-RAY OPTICS

Ellip tically-shaped hollow glass capillaries are the custom ary optic for micro X-ray beam experiments at the Cornell High Energy Synchrotron Source (CHESS). We have been able to manufacture optics that have produced x-ray spot sizes from 5 to 50 μm, gains in intensity of 10 to 500, divergences from 2 to 9 milliradians, and working distances between the tip of the capillary to the focus ranging from 20 to 150 mm. We discuss the basics in capillary design and explore the question of how well a single-bounce monocapillary can best match synchrotron sources to particular microbeam experiments, such as confocal X-ray fluorescence, microbeam powder X-ray diffraction, microbeam protein crystallography, and microbeam small angle X-ray scattering.

Silicon nitride transmission X-ray mirrors

X-ray transmission mirrors, which function as high-pass energy filters, have been made out of silicon nitride and tested in synchrotron X-ray beams. The high-energy cut-off can be selected by adjusting the incidence angle of the transmission mirror.

BIFOCAL MINIATURE TOROIDAL SHAPED X-RAY MIRRORS

We have fabricated a bifocal miniature torodial mirror that horizontally and vertically focuses to two different locations to provide a smaller footprint of beam for grazing-incidence wide-angle scattering (GIWAXS), while at the same time focusing the beam in the horizontal direction on the detector to further enhance the angular resolution. At CHESS we traditionally use glass single-bounce monocapillary optics for a wide range of x-ray experiments to get a fine x-ray beam of 5t o 20 ture toroidal mirror was prepared by designing and fabricating an x-ray focusing capillary, in which the sagittal and meridional focusing is decoupled, and only a quadrant of the accepted annulus is used for focusing the beam. The mirror produced a 120 horizontal by 25 at 50 mm from the tip of the optic, and a 44 70at 150 mm from the tip of the optic.