Supplementary Information for “ Highly Confined Tunable Mid - Infrared Plasmonics in Graphene Nanoresonators ”

In 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 EF for a given gate voltage. For a 285nm SiO2 layer, this relationship is given by | | 0.0319 | |. For most devices, VG could be varied from -100V to +200V without causing electric breakdown of the SiO2 layer.