Steven R. Parnell

A quasi-binary two-dimensional Ising critical system with the main components D2O and butyric acid confined by surfactant layers has been studied. The surfactant forms large planar layers and is the basis of the charge density waves with wave fronts aligned with the layers. To orient the domains in an external magnetic field, thulium ions were added to the system (replacing sodium in the surfactant with thulium and adding more TmCl3). The critical behavior of the forward scattering and the correlation length were observed to be more mean-field-like. This can be explained by the presence of the trivalent thulium ions mediating between water and butyric acid. The high-Q scattering could be distinguished in the different directions and the ideal two-dimensional critical composition fluctuation exponent ηxy = 1/4 was observed, while the other exponent ηz = −0.08 ± 0.06 was slightly negative due to a finite acceptance angle and the finite magnetic field. The orientationally averaged high-Q exponent x of this study is well-explained by ηxy = 1/4 of the two-dimensional Ising behavior and ηz = 0.

Spin-echo small-angle neutron scattering (SESANS) revealed structure in polymer–carbon nanocomposites over multiple length scales with unprecedented range (10 nm–16 μm). Data from two SESANS instruments and other methods were analysed with SasView.

We show the implementation of superconducting magnetic Wollaston prisms for spin echo small-angle neutron scattering. Two calibration methods for the spin echo length are presented: one utilizing spin echo modulated small-angle neutron scattering and the other based on the neutron refraction by quartz wedge crystals. Our experimental results with polystyrene nano-particle colloids showcase the system’s efficacy in measuring both dilute and concentrated colloidal systems. Additionally, investigations into the pore diameter and pitch of a nano-porous alumina membrane demonstrate its capability in analyzing nano-porous materials. Furthermore, we discuss potential optimizations to further extend the accessible spin echo length.

The structure of cellulose films prepared by nonsolvent-induced phase separation in coagulation baths of different mixtures and temperatures. High water volume fractions in the coagulation bath result in a highly reproducible gel-like structure with inhomogeneities.

We conduct simulations of Spin Echo Small Angle Neutron Scattering (SESANS) by employing Monte Carlo methods to a setup using four magnetic Wollaston prisms. Our primary focus involves the validation of these models, encompassing monochromatic scenarios across various neutron wavelengths to ascertain the reliability of the simulations. Subsequently, we extend this validation to encompass simulations in time-of-flight mode. Our model consistently and precisely predicts the scattering patterns emanating from dilute spheres in both monochromatic and time-of-flight modes. Notably, it also accurately reproduces the intricate encoding associated with scattering occurring between the third and fourth magnetic Wollaston prism, which provides us with another approach to increase the solid angle coverage of a SESANS instrument. This validation process conclusively demonstrates the efficacy of our simulation methods. Importantly, it paves the way for simulating more intricate and realistic instrumental configurations, broadening the horizons for future research endeavours.

The spin-echo small-angle neutron scattering (SESANS) technique utilises a series of inclined magnetic fields before and after the sample to encode the scattering angle into the polarisation to obtain a much higher resolution than in conventional SANS. The analogous technique (spin echo modulated SANS (SEMSANS)) implements spin manipulations before the sample only to encode the scattering into an intensity modulation. The technique can be combined with SANS to expand the length scale range probed from 1 nm to microns. Using McStas we show that using a series of four magnetic Wollaston prisms in two orthogonal pairs with a 90° rotation can be utilised to create SEMSANS modulations in 2-D. These modulations can also be of different periods in each encoding direction. This method can be applied to anisotropic scattering samples. Also this allows for the simultaneous measurement at two orthogonal independent spin-echo lengths. This technique yields directly information about the structure of oriented structures.

Tailoring the solution chemistry of metal halide perovskites requires a detailed understanding of precursor aggregation and coordination. In this work, we use various scattering techniques, including dynamic light scattering (DLS), small angle neutron scattering (SANS), and spin-echo SANS (SESANS) to probe the nanostructures from 1 nm to 10 μm within two different lead-halide perovskite solution inks (MAPbI₃ and a triple-cation mixed-halide perovskite). We find that DLS can misrepresent the size distribution of the colloidal dispersion and use SANS/SESANS to confirm that these perovskite solutions are mostly comprised of 1-2 nm-sized particles. We further conclude that if there are larger colloids present, their concentration must be 3 solutions age more drastically than triple cation solutions.