A reflection high-energy electron diffraction study of ultra-thin Langmuir-Blodgett films of ?-tricosenoic acid

Abstract

Although there have been several previous reflection high-energy electron diffraction (RHEED) studies of ω-tricosenoic acid Langmuir-Blodgett films, very little attention has been given to the structure of the first few monolayers deposited. In this paper we show that, for films dipped onto hydrophilic silicon and comprising fewer than seven monolayers, the molecular chains are all tilted at ∼20° to the substrate normal, but the direction of this tilt vanes from grain to grain. In thicker films, the molecules in all of the grains are tilted in the same direction which is upwards from the substrate normal for vertical dipping: however, the isotropic structure of the underlying layers is retained. The effects of the chemical nature of the substrate surface, substrate orientation and dipping configuration are also described.