Suppression of surface-enhanced raman scattering on gold nanostructures by metal adhesion layers

We report on the suppression of localized surface plasmon resonance (LSPR) and surface-enhanced Raman scattering (SERS) of 60 nm thick gold nanostructures by titanium adhesion layers. Significant plasmon damping is observed for titanium layer thicknesses up to t(Ti) = 5 nm, which cannot be fully explained by simulation models that account for the overlap of the electric field in the bimetal layer with the titanium layer. Furthermore, the relationship between the SERS enhancement factor and the LSPR quality-factor G proportional to Q(4) breaks down as t(T1), is increased beyond 1 nm. We attribute the LSPR and SERS suppression to plasmon damping and spectral broadening of interband absorption due to the field overlap with the titanium layer and titanium impurities that interdiffuse through the grain boundaries of the polycrystalline gold layer during the deposition of the Au-Ti bimetal. These observations and analyses serve as a guide for improving the reliability of gold nanoplasmonic sensors