Abstract
We give a theoretical study on the near field enhancement and far field spectrum of an adjacent graphene-wrapped sphere dimer with different radii. The Fano profile is found in the near field enhancement spectrum of such a symmetry-broken dimer system, which is, however, hidden in the far field spectrum. We demonstrate that this kind of Fano profile is rising from the coupling of dimer’s plasmon hybridization modes by analyzing the dipole moments of each sphere. Moreover, different orientation of incident wave polarization will lead to the different plasmon hybridization coupling, thus giving rise to a different Fano profile. By changing the Fermi energy level, we could achieve tunable Fano profile in near field enhancement.
Highlights
As a promising plasmonic materials, graphene has unique optical and electronic properties due to its high electron mobility, unique field enhancement by the plasmons in THz [1,2,3,4,5] as well as nonlinearity [6,7,8,9], so that it has potential applications in modulators [10,11], optical sensing, polarizers, mid-infrared photodetectors [5,12]
Based on the dipole–dipole approximation, we demonstrate that the different coupling modes of the dimer will lead to different Fano profiles in their near field enhancement spectrum, and this kind of Fano profile will be generally hidden in the far-field spectrum
As the small particle (NP1) grows, the internal field enhancement spectra for each particle show additional peaks indicating strong interaction between the graphene-wrapped dimer particles, and these additional resonant peaks dominate with stronger particle–particle interaction
Summary
As a promising plasmonic materials, graphene has unique optical and electronic properties due to its high electron mobility, unique field enhancement by the plasmons in THz [1,2,3,4,5] as well as nonlinearity [6,7,8,9], so that it has potential applications in modulators [10,11], optical sensing, polarizers, mid-infrared photodetectors [5,12]. The plasmonic property of the graphene layer is comparable to that of thin metal sheets with the thickness of tens of nanometers [13]. The high-sensitivity tunable plasmonic biosensor has been demonstrated, and the spatial light confinement in graphene is up to two orders of magnitude higher than that in metals [15]. On the other hand, coupled plasmonic nano-elements (nanoparticle or nanocrystal) attract more and more attention due to the new freedom of operation of localized surface plasmon resonances [17,18]
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