Red-Shift Effects in Surface Enhanced Raman Spectroscopy: Spectral or Intensity Dependence of the Near-Field?

Abstract

International audienceOptimum amplification in surface enhanced Raman scattering (SERS) from individual nanoantennas is expected when the excitation is slightly blue-shifted with respect to the localized surface plasmon resonance (LSPR), so that the LSPR peak falls in the middle between the laser and the Stokes Raman emission. Recent experiments have shown when moving the excitation from the visible to the near-infrared that this rule of thumb is no more valid. The excitation has to be red-shifted with respect to the LSPR peak, up to 80 nm, to obtain highest SERS. Such discrepancy is usually attributed to a near-field (NF) to far-field (FF) spectral shift. Here we critically discuss this hypothesis for the case of gold nanocylinders. By combining multiwavelength-excitation SERS experiments with numerical calculations, we show that the red-shift of the excitation energy does not originate from a spectral shift between the extinction (FF) and the near-field distribution (NF), which is found to be not larger than 10 nm. Rather, it can be accounted for by looking at the peculiar spectral dependence of the near-field intensity on the cylinders diameter, characterized by an initial increase, up to 180 nm diameter, followed by a decrease and a pronounced skewness

Plasmonic Properties of Aluminum Nanocylinders in the Visible Range

“…This is similar to a previous study considering gold and aluminium nanocylinders 18,34 in this spectral range. Indeed, the red-shift increases with the damping of the electron cloud oscillation inside the nanocylinder.…”

“…17 However, the widths are still comparable or even thinner than the ones measured for gold nanocylinders. [18][19][20] This is actually remarkable since the imaginary part of Al is largely higher than the one of Au (between 10 and 50 times higher on the 600-900 nm range). This property could be exploited in sensors based on the observation of the LSPR shift due to the adsorption of molecules at the nanostructure surface and could confer to such systems a very high sensitivity Moreover, the bandwidth has a direct influence on the Q-factor of the resonance.…”

Substrate Oxide Layer Thickness Optimization for a Dual-Width Plasmonic Grating for Surface-Enhanced Raman Spectroscopy (SERS) Biosensor Applications

“…Therefore, the proposed dual-width grating device is desirable for SERS due to its high tunability, the presence of many plasmonic hot spots, and the degree of enhancement capable of being produced by a fully optimized structure. Previous works report comparisons of plasmonic structures for different surrounding dielectric media [ 72 , 73 , 74 ]. The present work additionally shows that for a given substrate with a top oxide, it can be valuable to optimize this layer in addition to tailoring the plasmonic structures themselves, to maximize the enhancement factor.…”

SERS Active Hierarchical Nanopillar-huddle Array Fabricated via the Combination of Nanoimprint Lithography and Anodization

“…16,41,44 Further enhancement can be expected by altering excitation laser wavelength (Eq. (3) 45 ), varying anodization voltage and duration or varying metal deposition thickness. 46…”