5 Conclusion
The present studies show that array structures can be used to produce local field enhancements that are considerably larger than is found for isolated particles or dimers. These enhancements are large enough, in fact, that singlemolecule SERS measurements may be possible. The largest enhancements were obtained using a structure of two one-dimensional arrays, one parallel to the wavevector direction and one perpendicular to it. The particle at the crossing point of the two arrays is replaced by a dimer of particles, so that the local field between the particles is enhanced both by short-range near-field behavior of the dimer and also by long-range photonic interactions associated with resonances in the two arrays. This structure produced a field enhancement of 3.9 × 105 for a dimer of spheres, which is twice what we have been able to generate for a dimer in a single chain. Computational limitations make it impossible for us to study a dimer of nonspherical particles for this array structure, but similar studies for an isolated dimer of truncated tetrahedrons produced an extra factor of over 102 in the enhancement over the equivalent sphere result, suggesting that ∥E∥2 values of over 107 are possible for the “+” structure with a truncated tetrahedron dimer at the center. Furthermore, the resonance structures in this case are broad enough that significant enhancements at both the incoming and outgoing wavelengths is possible. Thus we conclude that this structure holds promise for single-molecule SERS measurements.