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.