X-ray photoelectron spectroscopy of CrCOOCH3 interfaces on self-assembled monolayers of 16-mercaptohexadecanoate

X-ray photoelectron spectroscopy (XPS) is used to identify the interactions at a metal/organic interface formed by evaporation of Cr overlayers on the methyl ester groups at the surface of a self-assembled monolayer (SAM) of 16-mercaptohexadecanoate [HS(CH2)15COOCH3] on gold. The high reactivity of Cr with COOCH3 groups promotes the growth of a relatively smooth Cr layer on top of the SAM. The CrCOOCH3 interaction forms a dominant species for Cr/end group ratios less than 1, which is similar to that formed in the CrCOOH interaction on a SAM, but an additional species corresponding to a O 1s component at a higher binding energy is also formed that is not understood. For higher Cr coverages, a Cr(III) oxide is formed by dissociation of oxygen primarily from the SAM end groups. Adsorption of oxygen-containing species from the UHV ambient was found to have little effect on the results for less than 0.6 nm Cr coverage.