Azimuthal vector beam illuminating plasmonic tips circular cluster for surface-enhanced Raman spectroscopy

Noble metallic nanostructures with strong electric near-field enhancement can significantly improve nanoscale light–matter interactions and are critical for high-sensitivity surface-enhanced Raman spectroscopy (SERS). Here, we use an azimuthal vector beam (AVB) to illuminate the plasmonic tips circular cluster (PTCC) array to enhance the electric near-field intensity of the PTCC array, and then use it to improve SERS sensitivity. The PTCC array was prepared based on the self-assembled and inductive coupled plasmon (ICP) etching methods. The calculation results show that, compared with the linearly polarized beam (LPB) and radial vector beam excitations, the AVB excitation can obtain stronger electric near-field enhancement due to the strong resonant responses formed in the nanogap between adjacent plasmonic tips. Subsequently, our experimental results proved that AVB excitation increased SERS sensitivity to 10⁻¹³ mol/L, which is two orders of magnitude higher than that of LPB excitation. Meanwhile, the PTCC array had excellent uniformity with the Raman enhancement factor calculated to be ∼2.4 × 10⁸. This kind of vector light field enhancing Raman spectroscopy may be applied in the field of sensing technologies, such as the trace amount detection.