Polarized-SERS of non-isotropic molecules on thermally-induced corrugated plasmonic surface supporting a NIR-SPP mode

[Display omitted] •Fabrication of large-area robust and transparent corrugated templates with different periods for ultra-thin metal deposition.(utilization of thermally induced surface reconstruction of M plane sapphire).•Excitation of surface plasmon polaritons (SPP) in the near-infrared range (NIR) exhibiting reduced photo-induced disadvantages.in the SERS of chemisorbed thiophenol molecules.•High reproducibility of SERS substrate fabrication and large are sensing uniformity.•A dichroic SERS behaviour with a cos2(σ) dependency (σ = azimuthal angle) observed in polarized SERS measurement.•Investigating molecular vibrations -polariton interaction on corrugated metal surface.by analysing the SERS dichroism of PT Raman modes of different polarizability tensor.•SERS dichroism were determined mostly by the excitation of SPP along the corrugation vector rather than the orientation of PT on the surface. Thermally-induced surface reconstruction of α-Al2O3 was used to fabricate corrugated templates of different periods to support percolated ultrathin metal film. Reflectance analysis and simulations revealed the coupling of a hybrid NIR-SPP mode along its corrugation vector (kcorrugation). The fabricated samples enhanced Raman signals of phenyl thiolates (PT) with reduced photo-induced disadvantages at λexc = 785 nm. Polarized SERS were performed to study adsorbed molecule – polariton interaction on these corrugated thin film surface. A twofold SERS anisotropy with a cos2(σ) dependency (σ = azimuthal angle) was observed. SERS dichroism of PT Raman modes of different polarizability tensors were analysed. A more pronounced dependence on corrugation period was observed for totally symmetric a1 modes than the non-totally symmetric b1 and b2 modes. Apart from the relative SERS intensity, their SERS dichroism was determined mostly by the excitation of SPP along the kcorrugation rather than the orientation of PT on sample surface. Edge-on orientation of adsorbed PT was predicted due to the absence of a2 modes with both tensor components parallel to the surface. Shorter corrugation periods fabricated were reproducible and ample for uniform, large-area sensing due to effective SPP coupling at σ = 0° resulting in a spatially extended SERS excitation volume.