Surface-enhanced Raman scattering intensity versus the separation of 100 nm diameter Au nanopost array on Si substrate was investigated. The relative Raman peak intensity per nanopost at different Raman modes rapidly decreases in a similar manner with the increase in the separation. This experimental result agrees well with the localized electric field enhancement calculation by three dimensional finite-difference time-domain method. The Raman peak intensity is mainly due to the edge enhancement of the nanopost through the coupling effect, and the nonenhancement contribution from the top of the nanopost also plays an important role.

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