Neutron and X-ray reflectometry studies of rough interfaces in a Langmuir-Blodgett film

Neutron and X-ray reflectometry are used to study interlayer roughness and islanding in a 20-bilayer barium stearate Langmuir-Blodgett film with alternating hydrogenated and deuterated bilayers. The interlayer roughness is highly conformal, and analysis of the diffuse X-ray peak widths suggests it is approximately self-affine with a roughness exponent of h ≈ 0.82. This roughness exponent describes the film in all directions, even though steps on the substrate interrupt the correlation of the film across the steps. The neutron and X-ray specular reflectivities contain modulated Kiessig fringes, indicating the presence of islands on the top of the film. Odd Bragg peaks in the neutron specular reflectivity are broadened, implying long-range disorder in the H-D bilayer structure. These data suggest that the islands arose from incomplete coverage during the film preparation.