Approximating the Fermi Level PositionIn order to determine the Fermi level position of our devices, we first measured the resistance vs.applied gate voltage dependence of the graphene sheet that contained the nanoresonators, as shown in Fig. S1. From these measurements we were able to determine the charge neutral point (CNP) for each device, which corresponds to applied gate voltage that aligns the Fermi level of the graphene with the Dirac point, leading to a peak in the resistance curve. Once the CNP was known, we used a simple capacitor model in order to approximate the position of E F for a given gate voltage. For a 285nm SiO 2 layer, this relationship is given by ‫ܧ|‬ ி | ൌ 0.0319ඥ|ܸ ே െ ܸ ீ |.For most devices, V G could be varied from -100V to +200V without causing electric breakdown of the SiO 2 layer.We found that our as-prepared samples were hole doped, and that the degree of hole doping was dependent on the etchant we used to remove the copper foil that the graphene was grown on. As shown in Fig. S1, when an Ammonium Persulfate (APS) solution (2% by wt.) was used as the etchant, the CNP typically occurred near V G =50V. In contrast, when an Iron(III) Chloride (FeCl) solution (40% by wt.) was used as the etchant, the CNP occurred at much higher gate biases, typically with V G near +180V. This intrinsic hole doping allowed us to electrostatically shift the E F from 0 to -0.52 eV.The above analysis applies to the bare graphene surface. However, it has been recently observed by Thongrattanasiri, et al 1 that the simple capacitance model typically used to estimate the Fermi level position of graphene devices may change when the graphene is patterned in a nanoribbon geometry. In particular, it was predicted by those authors that the Fermi level position can deviate strongly near the nanoribbon edges, and that this deviation can affect the plasmonic

Infrared transmission measurements reveal the hybridization of graphene plasmons and the phonons in a monolayer hexagonal boron nitride (h-BN) sheet. Frequencywavevector dispersion relations of the electromagnetically coupled graphene plasmon/h-BN phonon modes are derived from measurement of nanoresonators with widths varying from 30 to 300 nm. It is shown that the graphene plasmon mode is split into two distinct optical modes that display an anticrossing behavior near the energy of the h-BN optical phonon at 1370 cm −1 . We explain this behavior as a classical electromagnetic strong-coupling with the highly confined near fields of the graphene plasmons allowing for hybridization with the phonons of the atomically thin h-BN layer to create two clearly separated new surface-phonon-plasmon-polariton (SPPP) modes.

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A fundamental building block for nanophotonics is the ability to achieve negative refraction of polaritons, because this could enable the demonstration of many unique nanoscale applications such as deep-subwavelength imaging, superlens, and novel guiding. However, to achieve negative refraction of highly squeezed polaritons, such as plasmon polaritons in graphene and phonon polaritons in boron nitride (BN) with their wavelengths squeezed by a factor over 100, requires the ability to flip the sign of their group velocity at will, which is challenging. Here we reveal that the strong coupling between plasmon and phonon polaritons in graphene-BN heterostructures can be used to flip the sign of the group velocity of the resulting hybrid (plasmon-phonon-polariton) modes. We predict allangle negative refraction between plasmon and phonon polaritons and, even more surprisingly, between hybrid graphene plasmons and between hybrid phonon polaritons. Graphene-BN heterostructures thus provide a versatile platform for the design of nanometasurfaces and nanoimaging elements.negative refraction | plasmon polariton | phonon polariton | graphene-boron nitride heterostructure P olaritons with high spatial confinement, such as plasmon polaritons in graphene (1-5) and phonon polaritons in a thin hexagonal boron nitride (BN) slab (6-15), enable control over the propagation of light at the extreme nanoscale, due to their in-plane polaritonic wavelength that can be squeezed by a factor over 100. Henceforth we use the term squeezing factor (or confinement factor) to define the ratio between the wavelength in free space and the in-plane polaritonic wavelength. The combination of tunability, low losses, and ultraconfinement (1,2,8,10,11,15) makes them superior alternatives to conventional metal plasmons and highly appealing for nanophotonic applications (3-5, 10-13, 15). Their extreme spatial confinement, however, also limits our ability to tailor their dispersion relations.Unlike the case of 2D plasmons, the coupling between metal plasmons in a metal-dielectric-metal structure dramatically changes their dispersion relation and can even flip the sign of their group velocities (16,17). This has led to exciting applications by tailoring the in-plane plasmonic refraction, giving flexibility in controlling the energy flow of light. Specifically, by flipping the sign of the group velocity of metal plasmons, plasmonic negative refraction has been predicted (16) and demonstrated (17). The negative refraction has also been extensively explored in metamaterials, metasurfaces, and photonic crystals (18-26), but they become experimentally very challenging to realize when dealing with polaritons with high squeezing factors. In contrast to metal plasmons, the group velocity of graphene plasmons (2,11,27) and all other 2D plasmons (28-32) is always positive, including that in graphene-based multilayer structures (33). This has made the in-plane negative refraction for highly squeezed 2D plasmon polaritons seem impossible to achieve.Contrary to 2D plas...

By varying the evaporation conditions and the nanotube and surfactant concentrations, large-area, aligned single-walled carbon nanotube (SWCNT) thin films are fabricated from electronically monodisperse SWCNT solutions by evaporation-driven self-assembly with precise control over the thin film growth geometry. Tunability is possible from 0.5 μm stripes to continuous thin films. The resulting SWCNT thin films possess highly anisotropic electrical and optical properties that are well suited for transparent conductor applications.