Silver Filled Carbon Nanotubes used as Spectroscopic Enhancers
  We analyse from a theoretical point of view the optical properties of arrays of carbon nanotubes filled with silver. Dependence of these properties on the different parameters involved is studied using a Transfer Matrix formalism able to work with tensor-like dielectric functions and including the full electromagnetic coupling between the nanotubes. We find these structures exhibit very strong linear optical response and hence could be used as spectroscopic enhancers or chemical sensors in the visible range. Very localised surface plasmons, created by the electromagnetic interaction between the capped silver cylinders, are responsible of this enhancing ability. Enhancements of up to $10^6$ in the Raman signal of molecules absorbed on these arrays could be obtained. 
F.J. Garcia-Vidal (Universidad Autonoma de Madrid), J.M. Pitarke   (Euskal Herriko Unibersitatea) and J.B. Pendry (Imperial ...