Self-assembled monolayers (SAMs) of alkanethiols act as barrier films that retard the oxidation of Cu polycrystalline surfaces. However, oxygen molecules permeate through SAMs based on simple alkanethiols producing oxidation products at the Cu/SAMs interface. Therefore, the growth of multilayers seems to be a promising alternative to deal with this problem.
In this work we followed the strategy of forming salts based on mercaptoalkanoic acids and metal cations. We have therefore selected HS(CH2)15COOH and MSO4 (M=Cu2+, Mg2+, Zn2+) for surface multilayer synthesis.
The formation process proceeds via the following steps. The Cu substrate is exposed to 5 mM solution of 16-mercaptohexadecanoic acid dissolved in hexanes for one hour producing a monolayer. After rinsing with ethanol and water, the surface is exposed to a 1mM solution of MSO4 for ten minutes, washed in ethanol and exposed to thiol solution again. Repetition of both steps leads to the formation of the multilayer. The electronic properties were studied by conventional electrochemical techniques such as Cyclic Voltamerty (CV), Electrochemistry Impedance Spectroscopy (EIS) and Open Circuit Potential measurements (OCP). Structural, mechanical and optical properties were investigated through Atomic Force Microscopy (AFM) and Ellipsometry. Monolayers of SH(CH2)15COOH formed on polycrystalline copper surfaces present higher capacitance and lower resistance values than SH(CH2)15CH3 monolayers. EIS data indicate that the COOH terminated films are less compact than the CH3 terminated SAMs, probably due to the presence of pores. The interaction of the M2+ cation with COOH terminated monolayers produces a decrease in the capacitance, indicating a possible dehydration of the film. AFM, OCP and Ellipsometry indicate that the multilayer grows layer by layer. The influence of the M2+ nature was established as well.
The formation process proceeds via the following steps. The Cu substrate is exposed to 5 mM solution of 16-mercaptohexadecanoic acid dissolved in hexanes for one hour producing a monolayer. After rinsing with ethanol and water, the surface is exposed to a 1mM solution of MSO4 for ten minutes, washed in ethanol and exposed to thiol solution again. Repetition of both steps leads to the formation of the multilayer.
The electronic properties were studied by conventional electrochemical techniques such as Cyclic Voltamerty (CV), Electrochemistry Impedance Spectroscopy (EIS) and Open Circuit Potential measurements (OCP). Structural, mechanical and optical properties were investigated through Atomic Force Microscopy (AFM) and Ellipsometry. Monolayers of SH(CH2)15COOH formed on polycrystalline copper surfaces present higher capacitance and lower resistance values than SH(CH2)15CH3 monolayers. EIS data indicate that the COOH terminated films are less compact than the CH3 terminated SAMs, probably due to the presence of pores. The interaction of the M2+ cation with COOH terminated monolayers produces a decrease in the capacitance, indicating a possible dehydration of the film. AFM, OCP and Ellipsometry indicate that the multilayer grows layer by layer. The influence of the M2+ nature was established as well.
