Applications of Specular Neutron Reflectometry in Materials Science

Abstract

By counting the number of neutrons elastically and specularly reflected from a flat surface, as a function of glancing incidence angle, the in-plane average of the scattering density can be deduced at any specified distance along the normal from the surface. From this scattering length density profile, the concentration of atoms of a given type at a particular depth can, subsequently, be inferred. If, in addition, the incident beam is polarized and the resultant polarization of the reflected beam is analyzed, it also becomes possible to distinguish, in microscopic detail, possible magnetic contributions to the scattering density. In this paper the fundamentals of specular neutron reflectometry are described, including both experimental technique and analysis of the measured reflectivity data. Applications of neutron reflectometry to materials science problems are also illustrated by a number of specific examples involving the determination of the structure of polymer and superconducting thin films, magnetic multi-layers, and surfaces undergoing electrochemical reactions in contact with aqueous solutions.