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.

Feasibility of one-shot-per-crystal structure determination using Laue diffraction.

Crystal size is an important factor in determining the number of diffraction patterns which may be obtained from a protein crystal before severe radiation damage sets in. As crystal dimensions decrease this number is reduced, eventually falling to one, at which point a complete data set must be assembled using data from multiple crystals. When only a single exposure is to be collected from each crystal, the polychromatic Laue technique may be preferable to monochromatic methods owing to its simultaneous recording of a large number of fully recorded reflections per image. To assess the feasibility of solving structures using single Laue images from multiple crystals, data were collected using a 'pink' beam at the CHESS D1 station from groups of lysozyme crystals with dimensions of the order of 20-30 microm mounted on MicroMesh grids. Single-shot Laue data were used for structure determination by molecular replacement and correct solutions were obtained even when as few as five crystals were used.

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

A pre-focused X-ray beam at 12 keV and 9 keV has been used to illuminate a single-bounce capillary in order to generate a high-flux X-ray microbeam. The BioCAT undulator X-ray beamline 18ID at the Advanced Photon Source was used to generate the pre-focused beam containing 1.2 x 10(13) photons s(-1) using a sagittal-focusing double-crystal monochromator and a bimorph mirror. The capillary entrance was aligned with the focal point of the pre-focused beam in order to accept the full flux of the undulator beam. Two alignment configurations were tested: (i) where the center of the capillary was aligned with the pre-focused beam (;in-line') and (ii) where one side of the capillary was aligned with the beam (;off-line'). The latter arrangement delivered more flux (3.3 x 10(12) photons s(-1)) and smaller spot sizes (< or =10 microm FWHM in both directions) for a photon flux density of 4.2 x 10(10) photons s(-1) microm(-2). The combination of the beamline main optics with a large-working-distance (approximately 24 mm) capillary used in this experiment makes it suitable for many microprobe fluorescence applications that require a micrometer-size X-ray beam and high flux density. These features are advantageous for biological samples, where typical metal concentrations are in the range of a few ng cm(-2). Micro-XANES experiments are also feasible using this combined optical arrangement.

Silicon nitride transmission X-ray mirrors.

Transmission X-ray mirrors have been fabricated from 300-400 nm-thick low-stress silicon nitride windows of size 0.6 mm x 85 mm. The windows act as a high-pass energy filter at grazing incidence in an X-ray beam for the beam transmitted through the window. The energy cut-off can be selected by adjusting the incidence angle of the transmission mirror, because the energy cut-off is a function of the angle of the window with respect to the beam. With the transmission mirror at the target angle of 0.22 degrees , a 0.3 mm x 0.3 mm X-ray beam was allowed to pass through the mirror with a cut-off energy of 10 keV at the Cornell High Energy Synchrotron Source. The energy cut-off can be adjusted from 8 to 12 keV at an angle of 0.26 degrees to 0.18 degrees , respectively. The observed mirror transmittance was above 80% for a 300 nm-thick film.