Controlling the absorption of graphene
Graphene, a flat sheet of graphite just one carbon atom thick, displays unique optical and electronic properties for use in future devices. In particular, graphene is nearly transparent to light and other EM waves, making it useful for LCDs and LEDs. However, some researchers want to make graphene absorb more EM radiation so that other proposed applications, such as photodetectors and solar cells, can be realised.
Riichiro Saito and his team at Tohoku University are taking a new approach to this problem by exploiting the fact that the absorption of a surface depends strongly on the angle of the incident light. They propose sandwiching a single layer of graphene between two different dielectric (insulating) materials. With this setup, the proportions of radiation reflected, absorbed or transmitted by the graphene can be changed by adjusting the angle of incidence of the radiation, the properties of the dielectrics or the energy of electrons in the graphene.
Figure 1 - In this proposed device, the dielectrics are silicon (ε1) and a vacuum (ε2) and the energy of electrons in the graphene can be controlled using voltage gates.
One of Saito’s students, Muhamad Shoufie Ukhtary, performed theoretical calculations to show that, by carefully choosing the right materials and design, the absorption of microwave radiation (at 10-100GHz) in their setup could be tuned from values near 0 to almost 100%. The researchers used this principle to describe a practical EM wave-switching device in which the two dielectrics surrounding the graphene would be silicon and a vacuum. The electron energy could then be tuned using voltage gates (see Figure 1, above). They are hopeful that an experimental model of this relatively simple design could be built in the near future.
This research was reported in Applied Physics Express (APEX).
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