EM Mechanism of SERS

The overall SERS intensity depends on both the incoming ( inc) and the outgoing (cOs = roinc - vib) field  

Optimal SERS enhancement therefore requires that both the incident radiation at COinc and the Stokes Raman shifted radiation at cOs = cOinc vib are in resonance with the LSPR peak of the metallic nanostructure. Generally, the nanostructures with typical dimensions 30-100 nm are necessary to fulfil the conditions of LSPR resonance with visible light. LSPR strongly depends on the size and shape of nanostructures (Schatz et al. 2006) and is also strongly modified for closely spaced 

In the simple cases, the /sers can be reduced to (o)inc)r factor (Le Ru and Etchegoin 2009). Moderate increase of Eioc/Bmc leads to huge RS enhancements which is termed the SERS enhancement factor (EF). EM enhancement depends also on the properties of the metal and the distance of the molecule from the surface. The EM Fem(o)s) can be described explicitly for a small metallic sphere (its radius r is smaller than one twentieth of the incident light s wavelength) as  

3 Basics of Surface-Enhanced Raman Scattering (SERS) 

Nonhomogenous electric field around metallic nanostmcmre is responsible for the surface selection mles of SERS (Moskovits 1985). According to them, three types of vibrational modes may be found in SERS spectrum (i) those excited by the normal component of the field and resulting in an induced dipole with a strong component perpendicular to the surface, (ii) those excited by the tangential component of the field with a strongly induced dipole tangential to the surface and (iii) mixed cases. The intensity of particular Raman bands then depends on the orientation of the molecule with respect to the surface. 

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