High performance micro/nanofabricated AFM-TERS probes based on a metallic nanocone/nanodisk integrated on silicon cantilever

We present modelling, fabrication and characterization of atomic force microscopy-tip enhancement Raman spectroscopy (AFM–TERS) probes which demonstrate a very high electromagnetic (EM) enhancement due to a novel metallic... [ view full abstract ]

We present modelling, fabrication and characterization of atomic force microscopy-tip enhancement Raman spectroscopy (AFM–TERS) probes which demonstrate a very high electromagnetic (EM) enhancement due to a novel metallic nanocone/nanodisk combination at the tip apex. Calculations of the EM enhancement are obtained by finite element methods to improve the understanding of underlying physical phenomena and processes in the near-field and far-field optics. In addition, to the known ‘lightning rod effect’ and plasmonic resonance properties of a bulk metal tip, we study the cavity resonance modes of surface plasmons related to the dimensions and nature of the metal part of the tip. We demonstrate advantages an isolate metallic nanoparticule at the apex rather than a full metallic system, with an original shape as a nano-antenna . We also highlight the importance of the radiative losses at the metal-dielectric interface that has motivated us to propose a particular shape of the apex which greatly improves the EM enhancement with a precise control of the spectral position of the optical response as a function of the nano-antenna dimensions, shape and material composition. The cantilever-based probes were fabricated using top-down micro/nanotechnology to enable many probes to be fabricated on single silicon wafers. Dark-field microscopy combined with a total internal reflexion excitation is used to characterize the optical properties of the localized EM enhancement in order to compare with the predictions of the numerical calculations. Compatible with a standard AFM cantilever mounting, the microfabricated AFM-TERS probes are novel high-performance optical near-field elements that will enable a powerful optical analysis and imaging technique for high resolution Raman microscopy.