Abstract
Specular neutron reflectivity is a technique enabling the measurement of coherent neutron scattering length density profile perpendicular to the plane of a surface or interface, and thereby the profile of chemical composition. The characteristic sizes that are probed range from around 5Å up 5000 Å. It is a scattering technique that averages information over the entire surface and it is therefore not possible to obtain information on correlations in the plane of the interface. The specific properties of neutrons (possibility of tuning the contrast by isotopic substitution, negligible absorption, low energy of the incident neutrons) makes it particularly interesting in the fields of soft matter and biophysics. This course is composed of three parts describing respectively its principle, the experimental aspects (diffractometers, samples), and some scientific examples of neutron reflectometry focusing on the use of contrast variation to probe polymeric systems.
Highlights
Neutron reflectivity (NR) is a technique enabling to measure the thickness and the chemical composition of one or several thin layers at a surface or at an interface
This is of the same order of magnitude of what can be measured by X-Ray reflectivity, whose principle is similar to NR, on laboratory instruments
Four types of interfaces are interesting to be studied: air/solid, air/liquid, solid/liquid and liquid/liquid interfaces
Summary
Neutron reflectivity (NR) is a technique enabling to measure the thickness and the chemical composition of one or several thin layers at a surface or at an interface. Some unique specific properties with respect to photons that enable some measurements impossible with X-rays, such as the characterization of buried interfaces, the study of materials containing hydrogen or for magnetic materials Such specificities have made NR experiments very popular since the early 90’s: -First, the neutron-matter interaction directly occurs between the neutron and the nuclei of atoms, and not with the electronic cloud, as for X-rays. The imaginary part of the neutron refractive indexes is usually negligible, and not considered in neutron reflectivity calculations, contrarily to calculations of X-Ray reflectivity This weak interaction opens the way to the study of buried interfaces or to achieve in situ experiments in various sample environments. The third part is devoted to the presentation of some examples dedicated to the use of neutron NR for polymeric systems, with a specific emphasis on the different strategies of contrast variation that can be envisaged for such studies
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