Anisotropic Ag nanoparticle arrays were created by metal evaporation on rippled silicon templates for sensing of molecules with surface-enhanced Raman spectroscopy. Our results show that these substrates can be used for analysis of complex molecular mixtures and discrimination of solvent molecules. These properties are due to their polarization and wavelength dependency that provide enhancement in a wide spectral range. The dielectric function parallel and perpendicular to the long axis of the nanostructures was determined via ellipsometry yielding two different plasmonic resonances. Polarized surface-enhanced raman scattering (SERS) was subsequently measured as a function of the polarization angle θ for a 4-mercaptobenzonitrile self-assembled monolayer covalently attached to the Ag surface. For 514 nm excitation a cos2 θ-dependence and for 647 nm excitation a sin2 θ-dependency were found, with the maxima expressing the resonances perpendicular and parallel to the ripples, respectively. Those results open the path for using such a substrate as a chemical sensor providing strong enhancement in a broad range of laser wavelengths on only one sensing surface and increasing the specificity by matching resonant Raman conditions.

A metal nanoisland layer with varying plasmonic responses offers surface enhanced Raman scattering and infrared absorption optimal sites on a single surface.

a Polyhedron Ag nanostructures were created on top of a polished Au electrode via step-wise electrodeposition and tested as substrates for SERS spectroscopy. Average Raman enhancement factors were derived by combining SERS measurements with electrochemical impedance spectroscopy (EIS), which is able to determine the electroactive surface area of a randomly nanostructured surface. Depending on the deposition step an alternating increase and decrease of surface area was observed while the SERS intensity showed a clear maximum for the first deposition cycle. SEM pictures reveal the formation of Ag polyhedrons that are randomly dispersed on the Au surface. Furthermore the presence of a sub nanostructure on top of the polyhedron after the first deposition cycle is observed which becomes smoother after subsequent deposition cycles. Correlating the SEM pictures with SERS and EIS measurements it is concluded that the coral-like sub nanostructure is dominating the enhancement factor while the polyhedron structure itself only plays a minor role for electromagnetic field enhancement.