Co-refinement of multiple-contrast neutron/X-ray reflectivity data using<i>MOTOFIT</i>

TLDR

Contrast‑variation neutron/X‑ray reflectometry highlights scattering from distinct structural components and requires a single structural model to describe all measured contrasts. MOTOFIT applies a slab‑model with the Abeles matrix and surface‑roughness extensions, performing nonlinear least‑squares regression while supporting inter‑parameter constraints, multilayer analysis, and simulated annealing. The resulting MOTOFIT package, running in IGOR Pro, provides an intuitive GUI for simultaneous fitting of multiple contrasts, making it a powerful tool for reflectometry analysis.

Abstract

The contrast-variation technique is employed in multiple-contrast neutron/X-ray reflectometry experiments to highlight scattering from different structural components that are present at a surface or interface. The advantage of this technique is that the structural model used to describe the interfacial scattering length density profile must apply to all the contrasts measured. A new reflectivity analysis package, MOTOFIT , which runs in the IGOR Pro environment (http://www.wavemetrics.com), has been created to aid the simultaneous fitting (with the same structural model) of these multiple-contrast data, using an intuitive graphical user interface, which most co-refinement packages do not possess. MOTOFIT uses a slab-model approach with the Abeles matrix method, and extensions for surface roughness to perform non-linear least-squares regression on the experimental reflectivity curves. Other features, such as the ability to create complicated interparameter constraints or analyse reflectivity from multilayers, simulated annealing, etc. , make MOTOFIT a powerful reflectometry analysis package