The development of neutron reflectometry as a probe of the nanoscale structure of polymer thin film systems - founded on the pioneering work of Professor Thomas P. Russell.

Among Professor Russell's numerous, original, and significant contributions to polymer science are those in which he helped pioneer the application of neutron reflectometry to the study of thin film systems. For this groundbreaking work, along with his support of neutron scattering methods in general, he was awarded the 2020 Clifford G. Shull Prize by the Neutron Scattering Society of America, named after and in honor of the Nobel Prize laureate. This article highlights some of the first applications of neutron reflectometry to probe the nanoscale structure of polymer thin film systems that Professor Russell and his colleagues pioneered. A concise account of the subsequent evolution of even more powerful phase-sensitive reflectometry techniques, following the success of their early work, is then presented. In addition to a general description of this current methodology, several particularly relevant and illustrative examples are given.