Formation of monolayer films by the spontaneous assembly of organic thiols from solution onto gold.

Long-chain alkanethiols, HS(CH sub 2) sub n X, adsorb from solution onto gold surfaces and form oriented, and perhaps ordered, monolayer films. The properties of the interfaces between the films and liquids are independent of chain length when n>10; in particular, wetting is not directly influenced by the proximity of the underlying gold substrate. The specific interaction of gold with sulfur and other "soft" nucleophiles and its low reactivity toward most "hard" acids and bases make it possible to vary the structure of the terminal group X widely, and thus permits the introduction of a great range of functional groups into a surface. Studies of wettability of these monolayers and of their composition using X-ray photoelectron spectroscopy (XPS) indicate that the monolayers are oriented with the tail group, X, exposed at the monolayer-air or monolayer-liquid interface.