Inelastic neutron scattering analysis with time-dependent Gaussian-field models

• Published in: The Journal of chemical physics Vol. 155; no. 2; pp. 024121 - 24136
• Main Authors: Gommes, Cedric J., Zorn, Reiner, Jaksch, Sebastian, Frielinghaus, Henrich, Holderer, Olaf
• Format: Journal Article Web Resource
• Language: English
• Published: Melville American Institute of Physics 14.07.2021
• Subjects: Coherent scattering; Dynamic models; Engineering, computing & technology; Inelastic scattering; Ingénierie, informatique & technologie; Materials science & engineering; Neutron scattering; neutron spin echo; Neutrons; Physical, chemical, mathematical & earth Sciences; Physics; Physique; Physique, chimie, mathématiques & sciences de la terre; Science des matériaux & ingénierie; small-angle scattering; Time correlation functions; Time dependence
• ISSN: 0021-9606; 1089-7690; 1089-7690
• DOI: 10.1063/5.0053446

Converting neutron scattering data to real-space time-dependent structures can only be achieved through suitable models, which is particularly challenging for geometrically disordered structures. We address this problem by introducing time-dependent clipped Gaussian field models. General expressions are derived for all space- and time-correlation functions relevant to coherent inelastic neutron scattering for multiphase systems and arbitrary scattering contrasts. Various dynamic models are introduced that enable one to add time-dependence to any given spatial statistics, as captured, e.g., by small-angle scattering. In a first approach, the Gaussian field is decomposed into localized waves that are allowed to fluctuate in time or to move either ballistically or diffusively. In a second approach, a dispersion relation is used to make the spectral components of the field time-dependent. The various models lead to qualitatively different dynamics, which can be discriminated by neutron scattering. The methods of this paper are illustrated with oil/water microemulsion studied by small-angle scattering and neutron spin-echo. All available data—in both film and bulk contrasts, over the entire range of q and τ—are analyzed jointly with a single model. The analysis points to the static large-scale structure of the oil and water domains while the interfaces are subject to thermal fluctuations. The fluctuations have an amplitude of around 60 Å and contribute to 30% of the total interface area.