Qualitative and quantitative studies of the oxidation of molecularly modified polycrystalline copper (Cu) thin films upon exposure to ambient air conditions for long periods (on the order of several months) are reported in this work. Thin films of Cu, prepared by thermal evaporation, were analyzed by means of x-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) to gain an understanding on the growth mechanism of oxide on bare and molecularly modified Cu surfaces. The results from all techniques points for an unstable behavior of bare Cu surfaces characterized in very fast and continuous growth of Cu oxide layers during first 60 days of exposure to overall 6 nm oxide thickness. However, Cu films prepared under the same conditions, but covered with a self-assembled organic thin film layer of 1,4-phenylene diisocyanide (PDI) molecules adsorbed from solution, showed a decrease in the thickness of the copper oxide layer on the Cu surface. Our findings imply that chemisorbed PDI monolayers can serve as protective coatings for Cu.
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