Abstract
Crystal collimation offers a viable alternative to the commonly used pinhole collimation in small-angle X-ray scattering (SAXS) for specific applications requiring highest angular resolution. This scheme is not affected by the parasitic scattering and diffraction-limited beam broadening. The Darwin width of the rocking curve of the crystals mainly defines the ultimate beam divergence. For this purpose, a dispersive Si-111 crystal collimation set-up based on two well conditioned pseudo channel-cut crystals (pairs of well polished, independent parallel crystals) using a higher-order reflection (Si-333) has been developed. The gain in resolution is obtained at the expense of flux. The system has been installed at the TRUSAXS beamline ID02 (ESRF) for reducing the horizontal beam divergence in high-resolution mesurements. The precise mechanics of the system allows reproducible alignment of the Bragg condition. The high resolution achieved at a sample-detector distance of 31 m is demonstrated by ultra-small-angle X-ray scattering measurements on a model system consisting of micrometre-sized polystyrene latex particles with low polydispersity.
Highlights
Ultra-small-angle X-ray scattering (USAXS) is a powerful technique for the structural elucidation of bulk materials over a size range from about a hundred nanometres to several micrometres (Bonse & Hart, 1965; Ilavsky et al, 2009; Narayanan, 2014)
To reach the lowest possible q values (USAXS), the parasitic halo around the direct beam has to be reduced to the minimum possible
We report a dispersive Si-111 crystal collimation scheme based on two well conditioned pseudo channel-cut crystals using higher-order reflections
Summary
Ultra-small-angle X-ray scattering (USAXS) is a powerful technique for the structural elucidation of bulk materials over a size range from about a hundred nanometres to several micrometres (Bonse & Hart, 1965; Ilavsky et al, 2009; Narayanan, 2014). A USAXS instrument employing an area detector has multiple advantages when investigating oriented samples and time-dependent processes (Kishimoto et al, 2014; Narayanan et al, 2018) Such a set-up imposes more stringent constraints on the beam collimation compared with traditional pinhole collimation widely used on small-angle scattering instruments (Narayanan, 2014). In this case, it is the width of the rocking curve of the crystals which limits the divergence (Bonse & Hart, 1965; Agamalian et al, 2010). In order to maintain the beam position, a system of two Si-111 channel-cut crystals [C1 and C2, with each two
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