Neutron (and X-ray) reflectometry constitute complementary interfacially sensitive techniques that open access to studying the structure within thin films of both soft and hard condensed matter. Film thickness starts oxide surfaces on bulk substrates, proceeding to (pauci-)molecular layers and up to hundreds of nanometers. Thickness resolution for flat surfaces is in the range of few Ǻngstrøm, and as a peculiar benefit, the presence and properties of buried interfaces are accessible. Focus here will be on neutron reflectometry, a technique that is unique in applications involving composite organic films or films with magnetic properties. The reason is the peculiar property of neutron light since the mass of a neutron is close to the one of a proton, and since it bears a magnetic moment. The optical properties of matter, when interacting with neutrons, are described by a refractive index that is tightly related to the scattering length density of the material. The corresponding quantity for the interaction with X-rays is the electron density. The course of the neutron scattering length density over the elements of the periodic table is not as continuous as the electron density is with big differences among isotopes. Especially, there is a huge between for hydrogen and deuterium, and as well for magnetic materials like iron and the different isotopes of nickel. Accordingly, optical contrast may be varied by distinct deuteration allowing for selective optical matching and contrast enhancement of desired information. In the course, an introduction into the method and an overview on selected instruments at large scale facilities will be presented. Examples will be given that illustrate the potential of the method, mostly based on organic films. Results from the investigation of layered films and the detection on nanoscopic roughnesses will be shown. The potential of neutron reflectometry is not only of academic origin. It may turn out to be useful in the design and development of new functional materials even though it will never develop into a standard method to be applied in the product control of new material. Understanding self-assembly of 2D-3D nanostructures at surfaces and the related interfaces in layered films is a precondition for the development of tailored tools with distributed functions, like new clothes (self-cleaning surfaces combined with mechanical resistance, low permeability of polar molecules like water and high permeability for gases), films to be applied as specific sensors or for packaging, surface coverage for implants with incorporated antibiotics, thin magnetic material with designed domain distributions, … . The structures of interest range from a few Ǻngstrøm up to several hundreds of nanometers in dimensions, and they are often difficult to characterize using optical techniques due to their small size, or because many interesting phenomena are located at buried interfaces.
|Status||Udgivet - 2014|