Kinetic roughening of the interfaces of Langmuir-Blodgett films

We report x-ray scattering and atomic force microscopy measurements on the interfacial roughening of cadmium stearate Langmuir-Blodgett (LB) films of different total thickness. It is shown that the growth front becomes rougher as the film grows thicker. The initial sublayers in the films follow the fluctuations of the substrate. However, intrinsic roughening induced by pinholes shows up very soon so that the interfaces eventually exhibit logarithmic correlation. All experiments are explained quantitatively using the correlation function derived from a recently proposed growth equation for imperfect LB films. This supports the idea that the interfacial morphology in LB films is determined by the competition between the roughening arising from pinholes and the smoothening due to the surface tension of the membranes.