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

Abstract

Copper surfaces have been modified by self-assembled techniques. The adsorption of 3-mercaptopropyltrimethoxysilane (MPS), 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 Å, 14±2 Å, and 12±2 Å 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 Na 2SO 4 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 2.7×10 −6 cm (27 nm) was obtained and the Pb 2+ diffusion coefficient in the pinhole was 2.9×10 −8 cm 2 s −1. The Cu/1-PT electrode showed the smallest R a (9.1×10 −6 cm, 91 nm) for a desorption potential of −0.70 V vs. saturated calomel reference electrode. The Pb 2+ diffusion coefficient was 3.5×10 −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.