Model-independent recovery of interfacial structure from multi-contrast neutron reflectivity data

Abstract

Neutron specular reflectivity at soft interfaces provides sub-nanometre information concerning the molecular distribution of thin films, while the application of contrast variation can highlight the scattering from different parts of the system and lead to an overall reduction in fitting ambiguity. Traditional modelling approaches involve the construction of a trial scattering length density profile based on initial speculation and the subsequent refinement of its parameters through minimization of the discrepancy between the calculated and measured reflectivity. In practice this might produce an artificial bias towards specific sets of solutions. On the other hand, direct inversion of reflectivity data, despite its ability to provide a unique solution, is subject to limitations and experimental complications. Presented here is an integrated indirect Fourier transform/simulated annealing method that, when applied to multiple solvent contrast reflectivity data and within the limits of finite spatial resolution, leads to reliable reconstructions of the interfacial structure without the need for any a priori assumptions. The generality of the method permits its straightforward application in common experimental contrast-variation investigations at the solid/liquid and air/liquid interface.

Understanding the Structure and Dynamics of Complex Biomembrane Interactions by Neutron Scattering Techniques

“…Briefly, prior knowledge of the system, such as the substrate, component, and solution nSLDs and the expected interfacial arrangement, is used to construct a model of the interfacial structure. However, if these are unknown, then new tools are available which will provide a starting point for the analysis . The model is used to generate a model reflectivity profile, and least-squares fitting is used to repeat interactions of the model parameters until a fit between the model and experimental data is achieved.…”

“…However, if these are unknown, then new tools are available which will provide a starting point for the analysis. 146 The model is used to generate a model reflectivity profile, and least-squares fitting is used to repeat interactions of the model parameters until a fit between the model and experimental data is achieved. The SLD/model parameters are then interrogated to produce an understanding of the interfacial assemblage.…”

Determining the Proximity Effect-Induced Magnetic Moment in Graphene by Polarized Neutron Reflectivity and X-ray Magnetic Circular Dichroism

“…Both the 10 and the 300 K data sets were fitted simultaneously to provide further constraint to the fits. This is analogous to the isotropic contrast matching , used in soft matter neutron reflectivity experiments. This is very important in this case due to the attempt to measure a thin layer of graphene within a limited total Q range for PNR.…”

anaklasis: a compact software package for model-based analysis of specular neutron and X-ray reflectometry data sets

“…Several different 'model-independent' approaches for the reconstruction of interfacial structure from reflectivity measurements have been reported, based either on experimental (Majkrzak & Berk, 1998;Majkrzak et al, 2003Majkrzak et al, , 2000 or on numerical/stochastic methods (Pedersen, 1992;Hohage et al, 2008;Kunz et al, 1993;Zhou & Chen, 1993;Koutsioubas, 2019). However, the vast majority of investigations in the literature rely traditionally on model-dependent refinements, where the interface is modelled as a stratified medium (succession of slabs) with prior knowledge about the system being embodied in the bounds and relations between the sld, thickness and roughness of each slab.…”