SELF-ASSEMBLED MONOLAYERS OF N-ALKANETHIOLATES ON COPPER ARE BARRIER FILMS THAT PROTECT THE METAL AGAINST OXIDATION BY AIR

Self-assembled monolayers (SAMs) derived from adsorption of n-alkanethiols onto the surfaces of copper slow the oxidation of the copper surface by reaction with atmospheric dioxygen. Angstrom-level changes in the thickness of the monolayer result in readily observable differences (by X-ray photoelectron spectroscopy, XPS) in the rates of oxidation of the copper and adsorbed thiolates. The rates of oxidation of the copper and the thiolates can be decreased by approximately 50% by increasing the length of the adsorbate, and thus of the SAM, by four CH2 units. The species present on the oxidized interface-both alkanesulfonate and Cu(II)-are replaced when the assemblage is exposed to solutions of alkanethiols, and the resulting SAMs resembled those that were present before the oxidation, although the supporting surface is rougher.