Electroless gold as a substrate for self-assembled monolayers

We demonstrate that close-packed self-assembled monolayers (SAMs) can be formed from long chain alkanethiols on the surface of electroless gold. Gold films were deposited on glass microscope slides, high-index glass, and polycarbonate "track-etch" (PCTE) membranes using an electroless plating technique. The roughness of the surface of electroless gold was large but could be reduced to levels comparable to those for evaporated films by thermal annealing of samples supported on glass substrates. Although the largest peaks in X-ray diffraction patterns corresponded to Au(111), electroless gold has significant (200), (220), and (311) reflections and is, therefore, different from Au(111) textured gold films prepared by evaporation. Self-assembled monolayers formed from alkanethiols on electroless gold were characterized by contact angles of hexadecane, cyclic voltammetry, and grazing-angle FTIR spectroscopy. To form close-packed SAMs, it was necessary to apply postplating treatments to the electroless gold such as immersion in 25% HNO3 for membrane-supported gold and thermal annealing in combination with electrochemical cleaning for glass-supported gold. The coverage of SAMs on electroless gold, as estimated from cyclic voltammograms, was greater than 99.8%. Peak positions of C-H stretching modes in IR spectra were consistent with past measurements obtained using SAMs supported on evaporated films of gold. The IR spectra suggested, however, a smaller tilt angle (from the surface normal) of the alkyl chains on electroless gold than on evaporated gold, a conclusion that is consistent with the presence of Au(200) on the surface of electroless gold.