Sum-Frequency Generation Vibrational Spectroscopy Investigations of Phosphonic Acids on Anodic Aluminum Oxide Films

Abstract

Self-assembled monolayers of alkyl phosphonic acids on anodic aluminum oxide (AlOx) surfaces are important as dielectric layers in thin film electronic devices. Assessing the properties and quality of these monolayers on amorphous AlOx is limited to a few surface-sensitive methods. In this work, we study using nonlinear optical measurements the molecular ordering in n-alkyl phosphonic acids with various alkyl chain lengths (6 to 18 carbons) deposited on AlOx and show the influence of temperature on stability and conformational order. The results demonstrate that the octadecylphosphonic acid has fewest defects in the chain orientation. A detailed comparison of the longest and the shortest alkyl chain revealed different behavior in conformational ordering upon annealing.

Applications of sum-frequency generation vibrational spectroscopy in friction interface

“…Such a significant structural change would result in the appearance of a large number of molecules with gauche defects at the interface. For a hydrocarbon chain with a methyl group, the ratio of the peak intensities of methylene and methyl can be used to describe the accumulation of gauche defects in the films, considering the correlation between methylene stretching and the conformation of the hydrocarbyl chain [67,68]. However, the mechanism of recovery of the SFG signal after the force is released remains unclear.…”