Dendrimer-modified silicon oxide surfaces as platforms for the deposition of gold and silver colloid monolayers: Preparation method, characterization, and correlation between microstructure and optical properties

We describe a novel approach for Au and Ag colloid monolayer formation on different silicon oxide surfaces such as glass, silicon, and ITO. The preparation method is simple and yields monolayers with easily controlled spacing within the monolayer without aggregation of metal particles. The colloid monolayers are prepared in two steps: (1) modification of the substrates with starburst dendrimers and (2) noble metal colloid deposition onto the dendrimer layer. Different Au and Ag colloids, ranging from 15 to 80 nm in particle diameter, have been deposited onto the dendrimer-modified surfaces. The structure and properties of the resulting particle arrays have been studied by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, and surface-enhanced Raman scattering(SERS). XPS data show that the dendrimers spontaneously adsorb to various silicon oxide surfaces. The thickness of the dendrimer overlayer has been calculated and lies in the d = 14-25 Angstrom range. SEM and AFM data show that the colloids spontaneously form continuous films on the dendrimer-modified surfaces. The noble metal particles are well isolated and confined to a single layer, and aggregation does not occur on the surface. The interparticle spacing (74-829 nm) and surface coverage can be controlled over a wide range by colloid size, colloid concentration, and immersion time. UV-vis spectroscopic data show that the microstructure directly controls the optical properties of the layer. Finally, we demonstrate that the prepared substrates provide a useful platform for SERS studies of materials adsorbed on the metal particles.