Dynamical Tuning of Graphene Plasmonic Resonances by Ultraviolet Illuminations

Abstract

has some disadvantages. To realize a dynamical tuning, graphene structures should have electrical connections. As a result, electrodes, ion gels, or conducting substrates have to be introduced to attain an electrical connection. The method has been successfully applied to graphene sheets and ribbons. However, it is especially difficult and challenging for isolated graphene structures such as graphene disks. [35,36] Moreover, intrinsic absorptions from either conducting substrates or ion gels are inevitable, which may degrade considerably graphene plasmonic resonances. Thus, to find a way to tune plasmonic resonances in all kinds of graphene structures without the introduction of electrical connections is of great significance.In this paper, we develop a simple and efficient method to tune graphene plasmonic resonances by UV illuminations. We show that UV illuminations can induce a dynamical tuning of plasmonic resonances in all kinds of graphene structures both with and without electrical connections. Factors that influence this tuning process including the operating wavelength, power density, and illumination time of UV light sources are discussed.Plasmonic resonances in both graphene and graphene structures depend strongly on their Fermi levels, [4] E F . Consequently, a variation of the Fermi level can lead to a change in plasmonic resonances. To show UV illuminations can induce a change in the Fermi level, we measure the response of resistance and transmission spectra of graphene samples on an insulating BaF 2 substrate. The UV source used is a 355 nm solid-state laser. Figure 1a shows the resistance οf graphene changing with time upon UV illuminations at different power densities. Once the UV laser is switched on, the resistance undergoes an increase with time and reaches saturated values a few minutes later. If switching off the UV laser, the resistance decreases with time and resumes the original values without UV illuminations eventually. Obviously, the larger the power density of the UV laser is, the higher the resistance is. Correspondingly, the resuming time needed after switching off the UV laser is more. Physically, a change in resistance means a variation of the carrier concentration in graphene samples induced by UV illuminations. A higher resistance corresponds to a lower carrier concentration, implying a lower Fermi level. Thus, the time-dependent resistance measurements show unambiguously that the Fermi level of graphene can be modified by UV illuminations in a dynamical and reversible way. One of the unique features of plasmonic resonances in graphene structuresis the enabled tunability through external means. Up to now, electrical gating is extensively adopted to tune graphene plasmonic resonances. This method is, however, limited unfortunately only to graphene structures with electrical connections. Here, a simple and efficient method to tune graphene plasmonic resonances by ultraviolet illuminations in a dynamical and reversible way is demonstrated. It is purely an optical means and can be a...

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