We have studied the Surface-Enhanced Raman Scattering (SERS) of shape controlled metallic nanowires which can act as nano-antenna, designed through electron beam lithography and lift off techniques. We have notably studied the influence of localized surface plasmon resonance (LSPR) on the efficiency of SERS [1,2].

The deposited molecular probe used is the trans-1,2-Bis(4-pyridyl)ethylen (BPE) with two different excitation wavelengths of 632.8 nm and 676 nm. The nanowire lengths vary from 50 nm up to 1 µm (the width and the height of the nanowires is fixed). The observation of the dependence of the Raman enhancement versus the nanowire length is clearly demonstrated and remarkably the enhancement is observed to be maximum for a specific length. Moreover, we have compared our SERS results to the particle LSPR and we have determined that the best enhancement is obtained for a LSPR position close to the Raman wavelength. For such arrays, we also observe the existence of multipolar surface plasmon modes (up to 7th order) and we show clearly that multipolar LSP modes exhibits a stronger efficiency than the first dipolar order in SERS process [2].

Our results support the fact that the optimization of SERS efficiency, relative to the LSPR, strongly depends on the shape of the metallic nanoparticles. The enhancement strongly depends on the nanowire parameters which is a crucial point to determine the optical efficiencies of such structure and to optimise the SERS processes.

[1] J. Grand, M. Lamy de la Chapelle, J.-L. Bijeon, P.-M. Adam, A. Vial, and P. Royer, Phys. Rev. B 72, 033407 (2005)

[2] L. Billot, M. Lamy de la Chapelle, A.-S. Grimault, A. Vial, D. Barchiesi, J.-L. Bijeon, P.-M. Adam and P. Royer, Chem. Phys. Lett. 422, 303 (2006)

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1. Study of the light depolarization induced by sharp dielectric and metallic tips and of its effects on the selection rules of polarized Tip-Enhanced Raman Scattering on crystals