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 g old. Gold films were deposited on glass microscope slides, high-index glass, and polycarbonate ''track-etch'' (PCTE) membranes using an elec troless 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 s ubstrates. Although the largest peaks in X-ray diffraction patterns co rresponded to Au(111), electroless gold has significant (200), (220), and (311) reflections and is, therefore, different from Au(111) textur ed gold films prepared by evaporation. Self-assembled monolayers forme d from alkanethiols on electroless gold were characterized by contact angles of hexadecane, cyclic voltammetry, and grazing-angle FTIR spect roscopy. To form close-packed SAMs, it was necessary to apply postplat ing treatments to the electroless gold such as immersion in 25% HNO3 f or membrane-supported gold and thermal annealing in combination with e lectrochemical cleaning for glass-supported gold. The coverage of SAMs on electroless gold, as estimated from cyclic voltammograms, was grea ter than 99.8%. Peak positions of C-H stretching modes in IR spectra w ere consistent with past measurements obtained using SAMs supported on evaporated films of gold. The IR spectra suggested, however, a smalle r tilt angle (from the surface normal) of the alkyl chains on electrol ess gold than on evaporated gold, a conclusion that is consistent with the presence of Au(200) on the surface of electroless gold.