Self-Assembled Monolayer Films of C₆₀ on Cysteamine-Modified Gold

Self-assembled monolayer films (SAMs) of C₆₀ on cysteamine-modified and cysteamine/ethanethiol-modified Au are reported. The monolayers were characterized via contact angle measurements, X-ray photoelectron spectroscopy, electrochemistry, and quartz crystal microbalance (QCM) measurements. C₆₀ surface coverage (2.0 × 10⁻¹⁰ mol/cm²) for a film formed on pure cysteamine was determined by QCM measurements and compares remarkably well with monolayer coverage (1.9 × 10⁻¹⁰ mol/cm²) predicted by a model based on crystallographic data for C₆₀- These experiments demonstrate the utility of the QCM in characterizing and monitoring the growth of fullerene SAMs. Ceo SAMs formed on pure cysteamine yield strikingly different electrochemical responses than those formed on prelayers consisting of varying ratios of ethanethiol and cysteamine and previously reported monolayers of C₆₀ on (aminopropyl)silanized oxide surfaces. Although the C₆₀ SAMs are stable under ambient conditions, the fullerenes may be desorbed from the surface through electrochemical reduction of the films for extended periods of time (>10 min).