Researchers from Manchester University have demonstrated that graphene can be used to investigate how light interacts (via plasmon resonance) with gold nanostructures of different shape, size and geometry. This could lead to more efficient solar cells and photo detectors.
The researchers explain that when light shines on a metal particle smaller than the wavelength of the light, the electrons in the particle start to move back and forth along with the light wave. This causes an increase in the electric field at the surface of the particle. When two such metal particles are close to each other, the oscillating electrons in the two particles interact with each other, forming an even higher electric field which results in a coupling between the two particles. Up until now it was difficult to experimentally observe and measure the magnitude of this coupling and electric field.
Now the researchers used graphene for this investigation. They placed a graphene sheet on top of two gold nanoparticles (they call these nano-antennas) of different shapes, and performed Raman spectroscopy on the graphene. The spectroscopy allowed them to observe and measure the coupled plasmonic system. The graphene bends around the particles and gets stretched in the gap between the particles. When light falls on the graphene, it is scattered to different extents from the strained and unstrained parts of the graphene.
The strained part of the graphene also lies in the same region as the plasmonic electric field – in the cavity in between the two dots. This means you can compare the amount of light scattered by the plasmonic cavity and the surrounding region, and derive a quantity for the enhancement from the plasmonic antenna cavity.