Surface enhanced Raman scattering on long-range ordered noble-metal nanocrescent arrays.

Long-range ordered noble-metal nanocrescent arrays of different sizes and shapes have been successfully fabricated by using both nanoimprint lithography and e-beam lithography techniques. Large surface enhanced Raman scattering (SERS) enhancements in the detection of rhodamine 6G (R6G) molecules on these arrays have been observed and attributed to the enhancement of the local electromagnetic (EM) fields near individual nanocrescents. Electromagnetic enhancement factors for crescents of different shapes are computed using the discrete dipole approximation and compared with experimental measurements of the R6G Raman intensities. It is found that the maximum values of SERS intensity appear at an intermediate value of the crescent eccentricity and the observed behaviour is related to the spatial distributions of the enhancement of the local EM field (hot spots).