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Review
. 2024 Aug 27;57(Pt 5):1282-1287.
doi: 10.1107/S1600576724007246. eCollection 2024 Oct 1.

The promise of GaAs 200 in small-angle neutron scattering for higher resolution

A Magerl  1   2 , H Lemmel  3   4 , M Appel  4 , M Weisser  5 , U Kretzer  6 , M Zobel  2   7
Affiliations
Review

The promise of GaAs 200 in small-angle neutron scattering for higher resolution

A Magerl et al. J Appl Crystallogr. .

Abstract

The Q resolution in Bonse-Hart double-crystal diffractometers is determined for a given Bragg angle by the value of the crystallographic structure factor. To date, the reflections Si 220 or Si 111 have been used exclusively in neutron scattering, which provide resolutions for triple-bounce crystals of about 2 × 10-5 Å-1 (FWHM). The Darwin width of the GaAs 200 reflection is about a factor of 10 smaller, offering the possibility of a Q resolution of 2 × 10-6 Å-1 provided crystals of sufficient quality are available. This article reports a feasibility study with single-bounce GaAs 200, yielding a Q resolution of 4.6 × 10-6 Å-1, six times superior in comparison with a Si 220 setup.

Keywords: Bonse–Hart diffractometer; GaAs 200; USANS; ultra-small-angle neutron diffraction.

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Figures

Figure 1
Figure 1
Layout of the in-plane geometry for energy-dispersive X-ray topography in HexBay.
Figure 2
Figure 2
Top: energy-dispersive X-ray topography of a 3 mm-thick GaAs crystal. The MAR area detector is positioned 6 m from the sample (see Fig. 1 ▸). Exposure time 60 min. Bottom: intensity pattern between the two horizontal lines of Fig. 2 ▸ (top) projected downwards to create a line profile. It shows on the left the onset of the characteristic Kβ1 line and the characteristic Kβ2 line of the tungsten anode followed at higher energies by the intensity pattern of the crystal with Pendellösung oscillations.
Figure 3
Figure 3
Layout of a BH diffractometer with a nested Si (e.g. Si 220) and a GaAs 200 monochromator providing an identical beam path to the sample and with two separate analyzer crystals and detectors.
Figure 4
Figure 4
Resolutions of DCD setups measured with single-bounce perfect Si 220 crystal slabs (green) and single-bounce GaAs 200 discs (blue). In addition, the resolution with a triple-bounce Si 220 (standard USANS setup of S18) is shown in gray.
Figure 5
Figure 5
Small-angle pattern of an etched grid with a nominal periodicity of 28 µm (Trinker, 2006 ▸) measured with two triple-bounce Si 220 crystals (green dots and brown fitting line) and with two single-bounce GaAs 200 crystal slabs (red dots with blue fitting line).
Figure 6
Figure 6
The xUSANS pattern between 0.3 × 10−4 and 1.2 × 10−4 Å−1, i.e. in the range from the second to the fifth order of diffraction, taken with Si 220 (top) and GaAs 200 (bottom). See text for details.
Figure 7
Figure 7
Q values and order of diffraction for GaAs 200. Error bars are smaller than the symbols.
See this image and copyright information in PMC

References

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