A high‐throughput assembly of beam‐shaping channel‐cut monochromators for laboratory high‐resolution X‐ray diffraction and small‐angle X‐ray scattering experiments. Issue 3 (16th April 2021)

• Record Type: Journal Article
• Authors: Nadazdy, Peter; Hagara, Jakub; Mikulik, Petr; Zaprazny, Zdenko; Korytar, Dusan; Majkova, Eva; Jergel, Matej; Siffalovic, Peter
• Is Part Of: Journal of applied crystallography. Volume 54:Issue 3(2021)
• Page Start: 730
• Page End: 738
• Publication Date: 2021-04-16
• Subjects: X‐ray beam collimation -- channel‐cut monochromators -- ray‐tracing simulations; Crystallography -- Periodicals; 548.05
• DOI: 10.1107/S1600576721002338
• Languages: English
• ISSNs: 0021-8898

Abstract

Abstract : Comprehensive ray‐tracing simulations of the output beam parameters over all possible combinations of the asymmetry angles of a four‐bounce assembly composed of Ge(111) and Ge(220) monolithic channel‐cut X‐ray monochromators allowed the design and manufacture of a monochromator assembly optimized for the highest photon flux density at a particular detector distance behind the assembly. Comparative small‐angle X‐ray scattering and high‐resolution X‐ray diffraction measurements revealed up to one order of magnitude higher transmittance compared with traditional symmetric and asymmetric Ge(220) Bartels monochromators, while high beam collimation was still maintained. Abstract : A four‐bounce monochromator assembly composed of Ge(111) and Ge(220) monolithic channel‐cut monochromators with V‐shaped channels in a quasi‐dispersive configuration is presented. The assembly provides an optimal design in terms of the highest transmittance and photon flux density per detector pixel while maintaining high beam collimation. A monochromator assembly optimized for the highest recorded intensity per detector pixel of a linear detector placed 2.5 m behind the assembly was realized and tested by high‐resolution X‐ray diffraction and small‐angle X‐ray scattering measurements using a microfocus X‐ray source. Conventional symmetric and asymmetric Ge(220) Bartels monochromators were similarly tested and the results were compared. The new assembly provides a transmittance that is an order of magnitude higher and 2.5 times higher than those provided by the symmetric and asymmetric Bartels monochromators, respectively, while the output beam divergence is twice that of the asymmetric Bartels monochromator. These results demonstrate the advantage of the proposed monochromator assembly in cases where the resolution can be partially sacrificed in favour of higher transmittance while still maintaining high beam collimation. Weakly scattering samples such as nanostructures are an example. A general advantage of the new monochromator is a significant reduction in the exposure time required to collect usable experimental data. A comparison of the theoretical and experimental results also reveals the current limitations of the technology of polishing hard‐to‐reach surfaces in X‐ray crystal optics.