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

Perovskite solar cells have shown unprecedent performance increase up to 22% efficiency. However, their photovoltaic performance has shown fast deterioration under light illumination in the presence of humid air even with encapulation. The stability of perovskite materials has been unsolved and its mechanism has been elusive. Here we uncover a mechanism for irreversible degradation of perovskite materials in which trapped charges, regardless of the polarity, play a decisive role. An experimental setup using different polarity ions revealed that the moisture-induced irreversible dissociation of perovskite materials is triggered by charges trapped along grain boundaries. We also identified the synergetic effect of oxygen on the process of moisture-induced degradation. The deprotonation of organic cations by trapped charge-induced local electric field would be attributed to the initiation of irreversible decomposition.

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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