Cu surfaces and polished aluminum alloy 2024 T3 substrates were derivatized at open-circuit potential with aryl diazonium salts in both aprotic and aqueous media. Raman spectroscopy confirmed the presence of a derivatized film on the substrates before and after exposure to boiling water and sonication in acetone. Two different Cu substrate surfaces were prepared and used for X-ray photoelectron spectroscopy (XPS) analysis of the derivatization results. One surface was native oxide Cu, predominantly in the form of Cu2O, and one surface was predominantly Cu-0. Results of the XPS analysis indicate the presence of both a Cu-O-C linkage and a Cu-C covalent bond between the aryl ring and the Cu substrate, and a high coverage of the organic layer. XPS results also indicate the formation multilayers on both types of Cu surfaces with different percentages of azo coupling within the multilayers on the two surfaces. Applications of a covalently bonded organic film on copper and alloy surfaces include adhesion promotion, corrosion protection, and possibly inhibition of oxygen reduction. (C) 2004 The Electrochemical Society.