Electrically tunable SERS active substrate exploiting electro-optic property of LiNbO3 on Au-grating

Abstract The authors demonstrate the feasibility of the electrically tunable Surface enhanced Raman spectroscopy (SERS) based sensor by utilizing the electro-optic properties of Lithium Niobate in conjunction with the plasmonic properties of gold. A design of the gold grating pattern has been proposed in this study that supports the gap plasmon mode. This ensures high sensitivity (amplification of Raman signal ∼ 106) and high efficiency (hot spot cross-sectional area ∼10% of the total pattern area). The stokes wavelength of the pattern is electrically tunable (from ∼838 nm to 853 nm) by varying potential bias, making it possible to detect different analytes using the proposed SERS substrate. The design parameters of the substrate are so chosen that it can be fabricated using the existing nanolithography tools such as e-beam lithography. Fabrication of nanostructures being a multi-step process, deviations in device parameters are inevitable. Tolerance analysis with respect to design dimensions presented in this study reveals that the proposed pattern is robust. It has been ensured that the enhancement of the Raman signals does not get affected severely even if there is departure in fabricated pattern from the proposed dimensions (∼20%). The proposed SERS-active substrate will find extensive applications in narco-analysis, bio-diagnostics, explosive detection etc.