Kinetic Control of Interparticle Spacing in Au Colloid-Based Surfaces:  Rational Nanometer-Scale Architecture

This paper details the kinetic aspects of covalent self-assembly of colloidal Au particles from solution onto immobilized organosilane polymers. On glass substrates, surface formation can be monitored using UV−vis spectroscopy and field emission scanning electron microscopy (FE-SEM). Correlation of these data allows the effect of nanostructure on bulk optical properties to be evaluated. At short derivatization times, particle coverage is proportional to (time)1/2. The particle sticking probability p, defined as the ratio of bound particles to the number of particles reaching the surface in a given time period, can be determined from a knowledge of the particle radius, solution concentration, temperature, and solution viscosity; for surfaces derivatized with (3-mercaptopropyl)trimethoxysilane (MPTMS), p ≈ 1. At longer derivatization times, interparticle repulsions result in a “saturation” coverage at ≈30% of a close-packed monolayer. Two approaches for modulating the rate of surface formation are described: electrochemical potential control on organosilane-modified SnO2 electrodes and charge screening by organic adsorbates. Self-assembly of colloidal Au particles onto functionalized substrate surfaces is a reproducible phenomenon, as evidenced by UV−vis and surface enhanced Raman scattering (SERS) measurements on identically prepared substrates.