Small clusters of nanoparticles are ideal substrates for SERS measurements, but the SERS signal enhancement by a particular cluster is strongly dependent on its structural characteristics and the measurement conditions. Two methods for high-throughput assembly of silver nanocubes into small clusters at predetermined locations on a substrate are presented. These fabrication techniques make it possible to study both the structure and the plasmonic properties of hundreds of nanoparticle clusters. The variations in SERS enhancement factors from cluster to cluster were analyzed and correlated with cluster size and configuration, and laser frequency and polarization. Using Raman instruments with 633？nm and 785？nm lasers and linear clusters of nanocubes, an increase in the reproducibility of the enhancement and an increase in the average enhancement values were achieved by increasing the number of nanocubes in the cluster, up to 4 nanocubes per cluster. By examining the effect of cluster configuration, it is shown that linear clusters with nanocubes attached in a face-to-face configuration are not as effective SERS substrates as linear clusters in which nanocubes are attached along an edge. 1. Introduction The assembly of plasmonic nanoparticles is a simple and inexpensive method for the production of nanoscale gaps between metallic surfaces that generate hot-spots (small volumes with intense electric field strength) when illuminated [1, 2]. The oscillating electric field in the gap can couple to electronic and vibrational modes of molecules present in the hot-spot. A possible outcome of these interactions is a change in the vibrational state of the molecule and the inelastic scattering of a photon—an event that is detected with a Raman spectrometer. Since the inelastic (Raman) scattering rate is approximately proportional to the 4th power of the amplitude of the electric field at the site of the molecule and the hot-spots typically enhance the field by a factor of 101-102, the Raman spectrum (or Raman map) may be dominated by photons scattered by the few molecules located in the hot-spots, in what is referred to as Surface-Enhanced Raman Scattering or Surface-Enhanced Raman Spectroscopy (SERS) [3, 4]. Knowing the geometry of the assembly and the optical properties of the nanoparticle material and the surrounding medium, the enhancement of the electric field on and near the surface of the nanoparticles can be calculated by solving Maxwell’s equations [5, 6]. Such calculations, as well as methodic experiments, show that there are many factors that determine
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