Virtual probe stimulated tip-enhanced Raman spectroscopy: The extreme field enhancement in virtual-real probe dimer

Abstract

Tip-enhanced Raman spectroscopy (TERS) can be used for scanning imaging, molecular detection, and chemical analysis. The improvement of detection sensitivity, which is related to the electric field enhancement in the TERS substrate, has attracted much attention from researchers. In this work, we numerically studied the local electric field enhancement in the virtual-real probe dimer structure with a vertical gap. We mainly analyzed the influence of the structure parameters on the field enhancement using the finite-difference time-domain method. The Raman enhancement factor could reach up to 1.6×1015. The local field enhancement benefits from plasmon hybridization between the longitudinal component of the virtual probe and the local surface plasmon of the real probe. We also found that the full width at half maximum of the electric field was as narrow as 7.8 nm, and the volume of the hotspot for single-molecule detection can reach a maximum value of 155 nm3. The virtual-real probe dimer structure has ultrahigh field enhancement and spatial resolution, which is promising for high-sensitivity detection and high-resolution imaging.