SELF-ASSEMBLED LAYERS OF ALKANETHIOLS ON COPPER FOR PROTECTION AGAINST CORROSION

Self-assembled monolayers of alkanethiols CnH2n+1SH (n = 6 approximately 18) adsorbed on the surface of a polycrystalline bulk Cu were constructed and characterized by x-ray photoelectron (XPS) and surface-enhanced Raman scattering (SERS) spectroscopy and contact angle and impedance measurements. The protection ability of the alkanethiol monolayers against Cu corrosion in an aerated 0.5M Na2SO4 solution was examined by impedance and polarization techniques. Results of XPS, SERS, and contact angle measurements showed that alkanethiols were chemisorbed on the Cu surface by the formation of strong bonds between Cu and S atoms following cleavage of a S-H bond and formed densely packed, water-repellent monolayers on the surface. The advancing contact angle of these monolayer films was comparable to that of alkanethiolate monolayers adsorbed at a vapor-deposited Cu on a Si wafer. However, sufficiently high protection abilities of the films against Cu corrosion were not obtained in 0.5M Na2SO4. A preliminary experiment demonstrated the formation of a promising protective film which was prepared on the Cu surface by modification of self-assembled 11-mercapto-1-undecanol monolayer with octyltrichlorosilane to form cross-linkages between the thiol molecules with siloxane bonds.