ABSTRACT
Atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and near-field scanning optical microscopy (NSOM) have been used to characterize the nanostructure of Au colloid-based surfaces. Because these substrates are composed of particles whose dimensions are known prior to assembly, they are well-suited for a critical comparison of the capabilities and limitations of each nanoscale imaging technique. The three criteria for this comparison, which are relevant to the field of nanoparticle assemblies in general, are (i) accuracy in establishing particle size, particle coverage, and interparticle spacing; (ii) accuracy in delineating surface topography; and (iii) ease of sample preparation, data acquisition, and image analysis. For colloidal Au arrays, TEM gives the most reliable size and spacing information but exhibits the greatest constraints with regard to sample preparation; in contrast, AFM is widely applicable but yields data that are the least straightforward to interpret. For accurate information regarding nanometer-scale architecture of particle-based surfaces, a combination of at least one scanning probe method (AFM, NSOM) and one accelerated-electron method (TEM, FE-SEM) is required.
ABSTRACT
The self-assembly of monodisperse gold and silver colloid particles into monolayers on polymer-coated substrates yields macroscopic surfaces that are highly active for surface-enhanced Raman scattering (SERS). Particles are bound to the substrate through multiple bonds between the colloidal metal and functional groups on the polymer such as cyanide (CN), amine (NH(2)), and thiol (SH). Surface evolution, which can be followed in real time by ultraviolet-visible spectroscopy and SERS, can be controlled to yield high reproducibility on both the nanometer and the centimeter scales. On conducting substrates, colloid monolayers are electrochemically addressable and behave like a collection of closely spaced microelectrodes. These favorable properties and the ease of monolayer construction suggest a widespread use for metal colloid-based substrates.
