Exploiting the potential of beam-compressing channel-cut monochromators for laboratory high-resolution small-angle X-ray scattering experiments

Abstract

A systematic study of beam‐compressing monolithic channel‐cut monochromators (CCMs) with a V‐shaped channel was performed. The CCMs were optimized in terms of a chosen output beam parameter for exploitation in laboratory high‐resolution small‐angle X‐ray scattering (SAXS) and grazing‐incidence SAXS (GISAXS) experiments. Ray‐tracing simulations provided maps of particular Ge(220) CCM output beam parameters over the complete set of asymmetry angles of the two CCM diffractions. This allowed the design and fabrication of two dedicated CCMs, one optimized for maximum photon flux per detector pixel and the other for Kα2 suppression. The output beam quality was tested in SAXS/GISAXS experiments on a commercial setup with a liquid‐metal‐jet Ga microfocus X‐ray source connected to 2D collimating Montel optics. The performance of the CCM optimized for maximum photon flux per detector pixel was limited by the quality of the inner channel walls owing to a strongly asymmetric design. However, the CCM optimized for Kα2 suppression exhibited an excellent resolution of 314 nm in real space. This was further enhanced up to 524 nm by a parallel Ge(220) CCM in the dispersive configuration at a still applicable output flux of 3 × 106 photon s−1. The 314 nm resolution outperforms by more than 2.5× the upper resolution limit of the same setup with a pinhole collimator instead of the CCM. Comparative SAXS measurements on the same setup with a Kratky block collimator as an alternative to the CCM showed that the CCM provided more than one order higher transmittance at a comparable resolution or twice higher resolution at a comparable transmittance. These results qualify CCMs for a new type of integrated reflective–diffractive optics consisting of Göbel mirrors and V‐shaped CCMs for the next generation of high‐performance microfocus laboratory X‐ray sources.

A high-throughput assembly of beam-shaping channel-cut monochromators for laboratory high-resolution X-ray diffraction and small-angle X-ray scattering experiments

“…The other two assemblies show significant differences which, despite the restriction 4 ! À17 introduced in the simulations, can be attributed to surface imperfections of the channel walls of the CCMs, according to our previous experience (Ná daždy et al, 2019). In particular, the angles of incidence and exit are large in PSCCMs.…”

“…Recently, we have presented a systematic theoretical study of the Ge(220) CCM, which enabled a tailored design in terms of the two asymmetry angles in order to maximize the photon flux density. Experimental testing of this CCM has revealed better SAXS resolution than the Kratky block camera at the same transmittance (Ná daždy et al, 2019). This demonstrates the excellent X-ray beam collimation achieved by V-shaped CCMs.…”

“…The restriction 4 ! À17 excluded extremely small exit angles from the second CCM, which in our previous experience would lead to strong diffuse scattering due to imperfect surface finishing of the hard-to-reach channel walls (Ná daždy et al, 2019). It follows from Table 1 that, on increasing the distance, the M factor grows and the beam divergence decreases as a consequence of Liouville's theorem.…”

“…These represent a current challenge for the polishing technology of confined surfaces in X-ray crystal optics, such as CCM channel walls, especially when combining multiple CCMs. Single CCMs have shown significantly better agreement between measurement and simulation (Ná daždy et al, 2019).…”

Multipurpose diffractometer for in situ X-ray crystallography of functional materials

“…The choice of the asymmetric diffraction angles was optimized by ray-tracing simulation for both transmittance and divergence. The spectral purity of the beam, the suppression of the K 2 line, the transmission and the spatial compression rates were calculated using a beam-tracing procedure described previously (Mikulík & Kubě na, 2005;Vé gsö et al, 2016;Ná daždy et al, 2019). According to these calculations, this configuration is expected to give $6 times higher transmittance rate (flux), compared with the standard Ge(220) four-bounce symmetric (Bartels) scheme.…”