X-ray diffuse scattering in Langmuir-Blodgett multilayers prepared from fatty acid salts

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Abstract
Multilayers from fatty acid salts, such as Pb or Cd stearate, exhibit a perfect lamellar stacking along the surface normal but a powder-like behaviour in the plane. The amphiphilic molecules are arranged into single-crystalline domains, which are randomly distributed around the surface normal. Using X-ray scattering methods, our films show strong resonant as well as non-resonant diffuse scattering in non-specular directions. The off-specular scattering of lamellar systems is usually described by Sinha's model, which considers the diffuse scattering from rough interfaces as the main process. We present an alternative model, which takes the two-dimensional small-angle scattering of randomly distributed domains into account.