Controlled self-assembly of mercapto and silane terminated molecules at Cu surfaces

Copper surfaces have been modified by self-assembled techniques. The adsorption of 3-mercaptopropyltrimethoxysilane (NIPS), propyltrimethoxysilane (PTS), and 1-propanethiol (1-PT) at copper surfaces was carried out by controlling the adsorption time or desorption potential. The monolayer thicknesses were determined by angle resolved X-ray photoelectron spectroscopy. The thickness values were 17+/-2 Angstrom, 14+/-2 Angstrom, and 12+/-2 Angstrom for MPS, PTS, and 1-PT, respectively. The controlled surface modification was evaluated by using these modified Cu electrodes for the study of Pb electrodeposition. This study was followed by cyclic voltammetry, electrochemical impedance spectroscopy, and X-ray photoelectron spectroscopy analysis. The methods used for the surface modification were (a) the controlled exposure time of copper surfaces in the modifier +ethanol solution and (b) the use of different reductive desorption potentials in 0.50 mol l(-1) Na2SO4 Solutions to control the level of Cu surface modification with MPS, PTS, and 1-PT. From the impedance measurements, by using the Pb electrodeposition process in the pinholes, the Cu/1-PT electrode showed the smallest pinhole radius (R-a). For 180 min of exposure of the Cu surface in a 1-PT solution, a R-a of 2.7 x 10(-6) cm (27 nm) was obtained and the Pb2+ diffusion coefficient in the pinhole was 2.9 x 10(-8) cm(2) s(-1). The Cu/1-PT electrode showed the smallest R-a (9.1 X 10(-6) cm 91 nm) for a desorption potential of -0.70 V vs. saturated calomel reference electrode. The Pb2+ diffusion coefficient was 3.5 x 10(-8) cm(2) s(-1). The first modification method (i.e. exposure time) is most appropriate to control the pinholes formed with thiol molecules on Cu surfaces. (C) 2003 Elsevier B.V. All rights reserved.