Investigation of the vertical molecular exchange in a complex organic multilayer system

A vertically stacked Langmuir-Blodgett (LB) multilayer system composed of undeuterated and deuterated Cd-stearate bilayers being separated by bilayers of the amphiphilic copolymer MSA22 has been investigated. Specular and off-specular scattering curves were collected at room temperature and under thermal annealing up to 85 degrees C. The neutron measurements have been performed on the new neutron reflectometer ADAM at the Institute Laue-Langevin at Grenoble for the first time. Already at room temperature the intermixing between deuterated and non-deuterated molecules amounts to 20% and increases during thermal annealing. In contrast to recent measurements of samples without copolymers the thermally induced interdiffusion is significantly reduced now, unfortunately at the cost of losing the lamellar order. The evaluated activation energy of molecular exchange confirms our recent results. X-ray and neutron specular reflectivity curves cannot be interpreted solely by the Parrat formalism. Under relaxed condition of experimental resolution the off-specular scattering dominates the reflectivity curves even for large q(z). On the other hand, the evaluated q(z)-dependence of the resonant-diffuse scattering reveals that the height-height correlation of interfaces roughness is the main origin of diffuse scattering in such multilayers. (C) 1998 Elsevier Science B.V. All rights reserved.