Coherence phenomena in x-ray diffuse scattering on organic multilayers

X-ray diffuse scattering (XDS) is used to detect the lateral structure of organic multilayers of Cd-stearte. XDS from the 30-layer sample reveals a coherence phenomenon dependent on theta, the half angle between the incident beam and the reflected beam direction: for small theta, distortions within metallic layers are interpreted as height fluctuations. For increasing theta, these distortions are seen as mosaicity due to the decrease of the lateral coherence length of x-rays. Usually, the only effect of the finite instrumental resolution is considered to be line broadening of XDS signals. Additionally, we show that the decreasing lateral coherence length of x-rays leads to incoherent scattering from samples. As a striking consequence in scattering experiments, the interpretation of real structure features of samples can change. The inhomogenities of the multilayer structure are described as height fluctuations of Cd layers and mosaicity of molecular clusters.