Enhanced Raman scattering from vertical silicon nanowires array

We fabricated ordered hexagonal-packed vertical silicon nanowire (SiNW) arrays with varying diameters of 450–900 nm and varying lengths of 0.54–7.3 μm, and studied their Raman enhancement properties. We found the Raman enhancement per unit volume (REV) increased with decreasing wire diameters and oscillated with wire length, and the REV of seven 450-nm-diameter, 3-μm-long SiNWs was about twice that of a single SiNW having the same size. The differences were attributed to the vertical finite-length cylinder structures of the SiNW array, as supported by finite-difference-time-domain simulation results based on the helical resonant surface wave model.