The ability of thiol groups (X = -SH) to graft on pure zinc surfaces through self assembled monolayers (SAMs) formed by chernisorption of (3-mercaptopropyl)trimethoxysilane, (MeO)(3)Si-(CH2)(3)-SH, was investigate and compared to the grafting of n-dodecanethiol, CH3-(CH2)(11)-SH,-alkanethiol of different chain length (n = 11 instead of 3) terminated with a non-reactive functional group (Y = -CH3 instead of-Si(OMe)(3)). Monolayers are obtained by immersion of mechanically polished zinc substrates in ethanolic solutions, nevertheless this solvent is not the finest choice. The effects of the alkanethiols concentration (10(-1), 10(-2) and 10(-3) M) and of the surface immersion times (t = 30 min, 1, 5, 24 h) upon the monolayers' formation have been evidenced by X-ray photoelectron spectroscopy (XPS). This study highlighted an interesting competition effect between the two reactive tails of the (3-mercaptopropyl)trimethoxysilane molecule. (C) 2003 Elsevier Science B.V. All rights reserved.