DEPOSITION EFFECTS ON THE STRUCTURE OF LANGMUIR-BLODGETT MONOLAYERS OF DOCOSANOIC ACID

When the native oxide layer of a silicon wafer was cleaned with an ammonium-peroxide mixture, the resulting surface was found to be not only sufficiently hydrophilic to give tilted packings of Langmuir-Blodgett monolayers deposited on it but also sufficiently uniform to allow meaningful measurements of the angle of molecular tilt. Docosanoic acid monolayers were deposited on such substrates over a range of surface pressures, and the tilt angles were determined using reflection high-energy electron diffraction(RHEED). For all but the highest pressures, the tilt angle in the deposited monolayer was found to differ from that of a monolayer on the water surface, but there were similarities of behavior conforming to predictions based on the principle of equivalent states. It was possible to determine a parameter of this theory characterizing the interactions between the monolayer and the substrate.