Correlations in the interface structure of Langmuir-Blodgett films observed by x-ray scattering

X-ray scattering experiments within the region of total external reflection as well as grazing-incidence-diffraction measurements from Langmuir-Blodgett films are shown. All measurements are explained quantitatively using the distorted-wave Born approximation (small ${\mathit{q}}_{\mathit{z}}$ regions) or a simple kinematic scattering theory (large ${\mathit{q}}_{\mathit{z}}$ regions) for layered systems. Since rather imperfect systems are investigated, strong vertical correlations between the roughnesses of the organic layer interfaces were found for two samples consisting of 9 and 11 layers, respectively, of cadmium-arachidate on silicon (100) surfaces. This conformal roughness does not stem from the substrate but from defects and holes of the first transferred layer. The model of self-affine rough interfaces yields consistent parameters compared with grazing incidence diffraction experiments and no hints towards a cadmium-arachidate island formation are observed. © 1996 The American Physical Society.