Structural assembly of Cd-arachidate molecules in multilayers

Abstract

The three-dimensional (vertical and lateral) structure of Cd-arachidate multilayers prepared on two different substrates, glass and silicon, is studied simultaneously by grazing incidence x-ray reflection/diffraction. The grazing incidence reflectivity studies indicate the formation of a well-ordered layered structure on both the substrates. The reflectivity simulations show that the bilayer spacing in the case of a glass substrate is 5.54 nm while that on a silicon substrate is only 5.44 nm, indicating a vertical tilt of the Cd-arachidate molecules on a glass substrate by about 9.5 degrees. The interface roughness is found to be 0.3 nm for multilayers on a glass substrate and 0.4 nm on the silicon substrate. The interface topography, determined by studying the nonspecular scattering behavior, is found to be replicated between the various interfaces in the multilayers, independent of the type of substrate. The lateral topography of the interfaces in multilayers on a glass substrate shows a self-affine nature with no lateral length limit for the roughness fluctuations. The interfaces in multilayers on a silicon substrate, however, exhibit a saturation behavior for the roughness fluctuations. In the plane of the multilayers the Cd-arachidate molecules on a glass substrate have a centered rectangular lattice arrangement while they have a distorted hexagonal lattice arrangement on a silicon substrate. (C) 1999 [S0021-9606(99)70548-9].