Presenter

Ms. Hameda Alkorre - ETRO, Vrije Universiteit Brussel [Email]

Abstract

The 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 which comprise of 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 that utilize 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. In This PhD thesis, an analytical model was constructed for the dispersion relation of several waveguiding structures that utilize graphene. Numerical solution provided insights in the dependence of the dispersion characteristics of all modes on geometrical and material parameters. The study revealed for the first time that this 4-layer structure is much richer in surface wave solutions, which can interact under the appropriate combinations of frequency, structure geometry and material parameters. For instance for frequencies smaller than 0.75 THz (for the structures under consideration), 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 behavior was noted for TM waveguide SPs, where they were not splitting effect for TE waveguide SPs. Moreover devices have been designed and fabricated and experiments were carried out in the laboratory to validate the models, where an interesting experimental results were obtained. The findings of this work will pave the way towards more intriguing structures which will target to ultrasensitive sensors or modulators.

Short CV

Master in Nanophysics, Antwerp University, 2007