Hexagonal boron nitride (h-BN) is a natural hyperbolic material, in which the dielectric constants are the same in the basal plane (ε(t) ≡ ε(x) = ε(y)) but have opposite signs (ε(t)ε(z) < 0) in the normal plane (ε(z)). Owing to this property, finite-thickness slabs of h-BN act as multimode waveguides for the propagation of hyperbolic phonon polaritons--collective modes that originate from the coupling between photons and electric dipoles in phonons. However, control of these hyperbolic phonon polaritons modes has remained challenging, mostly because their electrodynamic properties are dictated by the crystal lattice of h-BN. Here we show, by direct nano-infrared imaging, that these hyperbolic polaritons can be effectively modulated in a van der Waals heterostructure composed of monolayer graphene on h-BN. Tunability originates from the hybridization of surface plasmon polaritons in graphene with hyperbolic phonon polaritons in h-BN, so that the eigenmodes of the graphene/h-BN heterostructure are hyperbolic plasmon-phonon polaritons. The hyperbolic plasmon-phonon polaritons in graphene/h-BN suffer little from ohmic losses, making their propagation length 1.5-2.0 times greater than that of hyperbolic phonon polaritons in h-BN. The hyperbolic plasmon-phonon polaritons possess the combined virtues of surface plasmon polaritons in graphene and hyperbolic phonon polaritons in h-BN. Therefore, graphene/h-BN can be classified as an electromagnetic metamaterial as the resulting properties of these devices are not present in its constituent elements alone.

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We present a pressure sensor based on the piezoresistive effect of graphene. The sensor is a 100 nm thick, 280 lm wide square silicon nitride membrane with graphene meander patterns located on the maximum strain area. The multilayer, polycrystalline graphene was obtained by chemical vapor deposition. Strain in graphene was generated by applying differential pressure across the membrane. Finite element simulation was used to analyze the strain distribution. By performing electromechanical measurements, we obtained a gauge factor of $1.6 for graphene and a dynamic range from 0 mbar to 700 mbar for the pressure sensor. V C 2013 AIP Publishing LLC [http://dx

We report on nano-infrared (IR) imaging studies of confined plasmon modes inside patterned graphene nanoribbons (GNRs) fabricated with high-quality chemical-vapordeposited (CVD) graphene on Al2O3 substrates. The confined geometry of these ribbons leads to distinct mode patterns and strong field enhancement, both of which evolve systematically with the ribbon width. In addition, spectroscopic nano-imaging in midinfrared 850-1450 cm -1 allowed us to evaluate the effect of the substrate phonons on the plasmon damping. Furthermore, we observed edge plasmons: peculiar one-dimensional modes propagating strictly along the edges of our patterned graphene nanostructures. KeywordsGraphene nanoribbons, CVD graphene, nano-infrared imaging, plasmon-phonon coupling, edge plasmons Main textSurface plasmon polaritons, collective oscillation of charges on the surface of metals or semiconductors, have been harnessed to confine and manipulate electromagnetic energy at the nanometer length scale. 1 In particular, surface plasmons in graphene are collective oscillations of Dirac quasiparticles that reveal high confinement, electrostatic tunability and long lifetimes. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Plasmons in graphene are promising for optoelectronic and nanophotonic applications in a wide frequency range from the terahertz to the infrared (IR) regime. 16,17 One common approach to investigate plasmons is based on nano-structuring of plasmonic media. 12,18 Large area structures comprised of graphene nanoribbons (GNRs) and graphene nano-disks have been extensively investigated by means of various spectroscopies. [12][13][14][15][16][17] These types of structures are of interest in light of practical applications including: surface enhanced IR vibrational spectroscopy 19,20 , modulators 21 , photodetectors 22 and tunable metamaterials 23,24 . Whereas the collective, area-averaged responses of graphene nanotructures are well characterized, the real-space characteristics of confined plasmon modes within these nanostructures remain completely unexplored.In this work, we performed nano-IR imaging on patterned GNRs utilizing an antennabased nanoscope that is connected to both continuous-wave and broadband lasers 25 (Supporting Information). As shown in Figure 1a, the metalized tip of an atomic force microscope (AFM) is illuminated by IR light thus generating strong near fields underneath the tip apex. These fields have a wide range of in-plane momenta q thus facilitating energy transfer and momentum bridging from photons to plasmons. [3][4][5][6][7][8][9][10][11][12] Our GNR samples were fabricated by lithography patterning of high quality CVD-grown graphene single crystals 26 on aluminum oxide (Al2O3) substrates (Supporting Information). As discussed in detail below, the optical phonon of Al2O3 is below  = 1000 cm -1 ( Figure S2), allowing for a wide mid-IR frequency region free from phonons.In Figure 1b, we show the AFM phase image displaying arrays of GNRs with various widths (darker parts correspond to gr...

The use of a coherent field-emission electron source in transmission electron microscopy is combined with phase retrieval by digital processing of a focal image series. For the first time, a dramatic improvement of the high-resolution performance of the electron microscope beyond the usual "point-to-point" resolution has been realized: Experiments on a 200-kV microscope with a point resolution of 0.24 nm reveal reconstructed information down to 0.14 nm. Examples are shown in the field of high-Tc superconductors and ferroelectric oxides. The oxygen sublattice in these structures is revealed.