Reflectometry

From DANSE

Neutron reflectometry uses neutrons scattered at grazing angles from a flat specimen to probe its chemical layer composition and/or magnetic profile. Analogous to classical optics, neutrons striking the surface undergo refraction and reflection if the neutron refractive indices on opposite sides of an interface are different. By modeling a material as a stack of layers so that the expected reflection matches measured reflection, reflectometry can very precisely measure near surface density profiles.

Measurements of diffusely scattered neutrons with or without polarization analysis provide insight into the in-plane structures of magnetic and non-magnetic thin film systems. For biological materials, off-specular scattering will provide information about the secondary and tertiary structures of small proteins vectorially oriented in single-membrane systems. For magnetic materials, off-specular measurements will probe magnetic domains in patterned structures with potential applications as high-density storage media. Theoretical treatments for the quantitative analysis of diffuse (non-specular) neutron scattering have been developed in recent years and it is possible, in principle, to determine length scales associated with chemical inter-diffusion, structural roughness, magnetic roughness and magnetic domains across the plane of the film. However, only a few software packages have been developed for the analysis of off-specular data and their scope is limited. This area of development remains active, especially with the improvements in capabilities of neutron reflectometers for efficient measurements of diffuse scattering.