Sequential electrostatic assembly of amine-derivatized gold and carboxylic acid-derivatized silver colloidal particles on glass substrates

The formation of alternating layers of positively charged gold and negatively charged silver colloidal particles on glass substrates via electrostatic interaction is described. The charging of the gold and silver colloidal particles is accomplished by self-assembly of 4-aminothiophenol (4-ATP) and 4-carboxythiophenol (4-CTP) monolayers on the colloidal particles respectively and subsequent ionization of the functional groups at appropriate pH values of the colloidal solution. Glass substrates, which are negatively charged at pH > 3, are immersed first in the positively charged amine-derivatized gold solution leading to the formation of a monolayer of the gold particles and charge reversal of the glass surface. Thereafter, the gold particle covered glass surface is immersed in the negatively charged carboxylic acid-derivatized colloidal silver solution and the silver particles electrostatically self-assembled on the glass surface. This process map be continued to yield multilayer structures of the colloidal particles. The kinetics of electrostatic self-assembly of the colloidal particles on glass, the formation of the multilayer films, and their thermal stability have been followed with UV-vis spectroscopy, X-ray diffraction, ellipsometry, and X-ray photoemission spectroscopy measurements.