Underpotentially deposited copper promotes self-assembly of alkanephosphonate monolayers on gold substrates

Gold surfaces that had been previously modified electrochemically by the un derpotential deposition (upd) of a monolayer of copper adsorb alkanephospho nic acids from solution to form oriented monolayers. While bare gold surfac es do not adsorb alkanephosphonic acids, a layer of copper at less than a m onolayer is sufficient to alter the chemisorptive properties of the gold su bstrate. 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 tho se that form on copper, but the Au/Cu(upd) substrate offers greater toleran ce against oxidation and greater convenience of use. Electroactive monolaye rs 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 similar to 4.0 x 10(-10) mol/cm(2).