Optimizing experimental design in neutron reflectometry

Abstract

Using the Fisher information (FI), the design of neutron reflectometry experiments can be optimized, leading to greater confidence in parameters of interest and better use of experimental time [Durant, Wilkins, Butler & Cooper (2021). J. Appl. Cryst. 54, 1100–1110]. In this work, the FI is utilized in optimizing the design of a wide range of reflectometry experiments. Two lipid bilayer systems are investigated to determine the optimal choice of measurement angles and liquid contrasts, in addition to the ratio of the total counting time that should be spent measuring each condition. The reduction in parameter uncertainties with the addition of underlayers to these systems is then quantified, using the FI, and validated through the use of experiment simulation and Bayesian sampling methods. For a `one-shot' measurement of a degrading lipid monolayer, it is shown that the common practice of measuring null-reflecting water is indeed optimal, but that the optimal measurement angle is dependent on the deuteration state of the monolayer. Finally, the framework is used to demonstrate the feasibility of measuring magnetic signals as small as 0.01 μB per atom in layers only 20 Å thick, given the appropriate experimental design, and that the time to reach a given level of confidence in the small magnetic moment is quantifiable.

AutoRefl: active learning in neutron reflectometry for fast data acquisition

“…7(b)]. Such an approach can complement established techniques for a priori experiment optimization (Treece et al, 2019;Durant et al, 2022). For example, the 2:1 ratio of the time spent by a simulated AutoRefl experiment in D 2 O-or H 2 O-based buffers, shown in Fig.…”

Neutron Reflectometry Studies of the Hydrated Structure of Polymer Thin Films

“…By measuring the same sample with different ratios of deuterated and hydrogenated solvent, most commonly with H2O and D2O, and simultaneously fitting the datasets, constraining the SLD of the polymer layer according to the equation above, and can be determined. Although, measuring with two solvents would provide enough information to solve the equation, measuring a third contrast increases the precision of the modelling 110 . In Paper II and Paper IV this method was used to determine the volume fraction depth profiles of the polymer in the hydrated layers.…”

“…It has to be noted though, that NR data is usually measured with a better statistic in the high Q region than the data presented in Figure 14. However, as available neutron time is a limiting factor for the experiments 110 , reference samples with less added contrast are sought after. Current research in developing magnetic reference layer structures is focusing on SiO2 cover layers instead of Au.…”

Structure of Self-Initiated Photopolymerized Films: A Comparison of Models

“…Measuring multiple contrasts increases the precision in the determination of the volume fraction profiles. Further details about optimizing reflectometry measurements can be found in the work of Durant et al 51 The reflectometer was set to time-of-flight mode, and the beam height (with a vertically mounted sample) was set to 38 mm. Slits S1 (at the guide exit) and S4 (in front of the detector) were fixed to 4 mm widths.…”