Surface-enhanced Raman scattering (SERS) has been a powerful analytical tool in chemical and biosensing applications. Silver nanorod array fabricated by oblique angle deposition can give a very strong SERS enhancement (>10⁸). For the Ag nanrod SERS substrates, we have performed detailed SERS characterizations and found that the SERS enhancement strongly depends on the length of nanorods, the incident angle of excitation light, the polarization states of excitation light, and the reflectance from the substrate. A modified Greenler's model based on the reflection from a single Ag nanorod and the substrate as well as dipole radiation has been proposed and can quantitatively explain these SERS characteristics. We have also designed experiments to selectively put Raman probe molecules on different locations of the Ag nanorods, and found that most SERS signals come from the gap between the Ag nanorods, which is consistent with our numerical calculations of the local electromagnetic field enhancement around Ag nanorod array. All those results show that the SERS mechanism of Ag nanorod arrays is very complicated, and more works need to be done to understand the essential mechanism.

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