Reflectivity and Grazing Incidence Diffraction

 Neutron and X-ray scattering techniques are probably the most effective tools to be employed in order to determine the structure of liquid interfaces on molecular length scales. Two modes of scattering, reflectivity and grazing incidence diffraction (GID) are used in the investigation of interfaces.


In the reflectivity mode, the incident beam is specularily reflected as shown:

From the reflectivity, the neutron scattering length density or electron density (X-rays) can be determined and correlated with the structure at the interface. The reflectivity from a film, with scattering length density (SLD) r(z) is given by 

where Rf is the reflectivity from an ideally flat substrate with SLD rho_subphase.


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