Underpotentially Deposited Copper Promotes Self-Assembly of Alkanephosphonate Monolayers on Gold Substrates

Gold surfaces that had been previously modified electrochemically by the underpotential deposition (upd) of a monolayer of copper adsorb alkanephosphonic acids from solution to form oriented monolayers. While bare gold surfaces do not adsorb alkanephosphonic acids, a layer of copper at less than a monolayer is sufficient to alter the chemisorptive properties of the gold substrate. Octadecanephosphonic acid forms oriented oleophobic monolayers on the Au/Cu(upd) surface that are stable in both polar and nonpolar solvents. The alkanephosphonate films on Au/Cu(upd) are less densely packed than those that form on copper, but the Au/Cu(upd) substrate offers greater tolerance against oxidation and greater convenience of use. Electroactive monolayers can be formed on Au/Cu(upd) using 11-ferrocenylundecanephosphonic acid, where the assembled films exhibit the reversible electrochemical signature of the ferrocenyl group and a surface coverage of ∼4.0 × 10 - 10 mol/cm 2 .