Neutron reflectometry from solid-solid and solid-liquid interfaces at the TAS8 spectrometer at risø

In the last decade, neutron reflectometry has been established as a well-suited technique for probing the surface structure of stratified media along the surface normal. The large penetration depth for most materials and the large difference in scattering length of hydrogen and deuterium make neutrons ideally suited for investigations of soft condensed matter. The low absorption of neutrons in, e.g., single crystal quartz and silicon makes it possible to have liquid samples in thermostated enclosures and to study solid-liquid interfaces. The neutrons are able to transverse quartz and silicon crystals and can be reflected from the surface between the crystal and the liquid. One of the limitations in neutron reflectivity measurements is the relative low neutron flux, which has the consequence that a reasonable flux can only be obtained by relaxing the resolution of the reflectometer. For most samples this is not a serious limitation as the reflectivity curve of, e.g., polymers at a solid-liquid interface show only broad features. It is usually more important that the maximum scattering vectors for which the reflectivity can be measured are limited by the incoherent (and diffuse) scattering from the sample. This leads to a limitation of the real-space resolution which can be obtained.