A reflection high energy electron diffraction analysis of the orientation of the monoclinic subcell of 22-tricosenoic acid langmuir-blodgett bilayers as a function of the deposition pressure

Abstract

Reflection high energy electron diffraction (RHEED) patterns from bilayers of 22-tricosenoic acid Langmuir-Blodgett (LB) films have been interpreted as arising from a mixture of orthorhombic and monoclinic subcells. Translational correlation between subcells extends only over very short distances. All the observed orthorhombic grains are oriented such that their c 0 axes are perpendicular to the substrate and their a 0 axes are perpendicular to the dipping direction. The monoclinic subcells have a much wider distribution of orientation, with the c 0 axis making an angel to the substrate normal which varies continuously with deposition pressure from a maximum value of 18° for a pressure of 25 mN m -1 to a minimum of 11° for a pressure of 42 mN m -1. The direction of the tilt of the monoclinic grains displays an azimuthal spread of about ± 70° about the dipping direction.