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Intriguing properties of coupled metal-graphene surface plasmons Host Publication: 4th NSE PhD Vrije Universiteit Brussel Authors: H. Alkorre, J. Stiens and G. Shkerdin Publication Date: May. 2015 Number of Pages: 19
Abstract: IntroductionThe following fundamental intriguing question was raised: Can a one-atom thin graphene layer, whose carrier concentration can be easily modified, efficiently interact with a million times larger sub-THz electromagnetic wave? If this would be the case, this could trigger the development of a whole bunch of novel modulation and sensing devices in this part of the electromagnetic spectrum where a strong need exists for novel ground-breaking devices. When first considering structures comprising only graphene as the conductive material, it appeared that pure graphene based surface plasmons (SPs) in the sub-THz range generally are too lossy for further exploration.An interesting next step was to investigate structures comprising a metal substrate, a dielectric buffer, a monolayer of graphene and air as the superstrate, where graphene based SPs could interfere with more classic based metal SPs. This study explored the impact of the coupling between metal and graphene surface plasmons on the propagation characteristics of sub-THz waves.Methods and Material Analytical model was constructed, numerical model was employed by using various computer softwares, to estimate the analytical solutions, and the outcome of this simulation was published in the international conferences and journal. Moreover fabrication processes and experiments are carried out in the Lab to validate this model.Results and discussionThe study revealed for the first time that this 4L-structure is much richer in surface wave solutions, which can interact under the appropriate combinations of frequency, geometrical and material parameters. For instancefor frequencies smaller than 0.75 THz (for this structure), the metal-like SPs split up into two branches depending on the graphene charge concentration: one of the branches exists in the whole range of the buffer thickness and being a short-range mode for small thicknesses, another one undergoes cutoff and exists only within a limited range of buffer thicknesses turning into a Brewster-type mode at cutoff conditions, a similar behaviorwas noted for TM waveguide SPs, where they were not splitting effect for TE waveguide SPs.Conclusion and applicationsIn order to modulate coupled metal graphene plasmon and waveguide modes the electron concentration in the graphene layer, and the buffer layer thickness are preferable, in other words graphene is an efficient to control (sub)-THz waves.This findings will pave the way towards more intriguing structures which will target to ultrasensitive sensors or modulators.
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