Electrostatically Controlled Organization of Carboxylic Acid Derivatized Colloidal Silver Particles on Amine-Terminated Self-Assembled Monolayers

The formation of self-assembled monolayers (SAMs) of an aromatic bifunctional molecule, 4-aminothiophenol (4-ATP) on gold and the subsequent organization of carboxylic acid derivatized silver colloidal particles is described. Quartz crystal microgravimetry (QCM) measurements have been used to follow the formation of 4-ATP SAMs as well as electrostatic assembly of the colloidal silver particles on the SAM surface. It is shown that the electrostatic interaction between the negatively charged colloidal particle surface-bound carboxylic acid groups and the terminal amine groups in the SAM can be modulated by variation of the colloidal solution pH. This enables control over the surface coverage of the colloidal particles on the SAM surface with a maximum surface coverage of 18% being attained. The SAMs as well as the colloidal particle covered SAM films were further characterized with X-ray photoemission spectroscopy (XPS) and energy-dispersive analysis of X-rays (EDAX) measurements.