Fig. 4: Plasmonic switch based on tunable control of GP transmission at air-dielectric substrate interfaces.
From: Active control of micrometer plasmon propagation in suspended graphene
a Schematic of the plasmonic switch. Black, red, and blue arrows represent incident, reflected, and transmitted plasmons, respectively. The green arrow stands for plasmon scattering (out-coupling) into radiation. The black-dashed line indicates the air-dielectric interface. b AFM topography images of suspended graphene with different heights of the graphene bubble d2, obtained by controlling the gas pressure for fixed hole depth d1 = 300 nm (see definitions in the inset of Fig. 3b). A negative value of d2 indicates that the graphene bubble is sunken inside the substrate dimple. We use a sample with a large value of d1 to avoid any complications in the interpretation. θ is the contact angle of suspended graphene and the substrate. c Near-field IR images of suspended graphene, taken simultaneously with the AFM topography for the corresponding suspension heights shown in (b). The incident light wavelength is λ0 = 10.87 μm (920 cm−1), and the graphene Fermi energy is 0.40 ± 0.03 eV. Since the entire sample is treated with the same gas concentration and doping time, we assume that the graphene has the same Fermi energy in the substrate and suspended regions. The bright fringes at the air-dielectric interface and natural graphene edge are indicated by white and green arrows, respectively. The scale bar indicates 2 µm. d Simulated spatial distribution of the electric field along the x direction as GPs propagate from the suspended region to the region supported by the SiO2 substrate, with d2 > 0 (upper part) and d2 < 0 (bottom part). Inset: expanded view of the boundary area. e Plasmon reflectance (red), transmittance (blue), and scattering (green) as a function of d2 and θ. Colored curves are numerical simulations with EF = 0.4 eV, whereas symbols represent experimental results extracted from (c). The vertical dashed line and two shaded areas are used to indicate the two cases where the suspension height is positive or negative. Error bars are extracted from different line profiles in each scanned image.
