Fundamental Studies of Microscopic Wetting on Organic Surfaces. 1. Formation and Structural Characterization of a Self-Consistent Series of Polyfunctional Organic Monolayers.

Monolayers of a series of terminally substituted alkyl thiols, X(CH sub 2) Sub 15 SH (where X = CH sub 3, CH sub 2 OH, CO sub 2 H, CO sub 2 CH sub 3, and CONH sub 2), have been prepared by adsorption from solution onto evaporated gold substrates. The structures have been characterized by infrared spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), ellipsometry, and temperature programmed desorption spectroscopy (TPD). The monolayer films are densely packed, crystalline-like structures with all trans conformation alkyl chains exhibiting average tilt angles of the chain axis in a range of 28-40 degrees from the surface normal and an approximate 55 degrees twist of the chain axis away from a configuration with the CCC plane perpendicular to the surface face plane. Thermal desorption results set a lower limit of interaction between the CH sub 2 groups in the films of ~0.8 kcal/mole. We find that the terminal groups are exposed at the ambient interface and, based on an analysis of the IR data, an assessment of the conformations and molecular environments of these groups is made.