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We report phonon renormalisation in bilayer graphene as a function of doping. The Raman G peak stiffens and sharpens for both electron and hole doping, as a result of the non-adiabatic Kohn anomaly at the Γ point. The bilayer has two conduction and valence subbands, with splitting dependent on the interlayer coupling. This results in a change of slope in the variation of G peak position with doping, which allows a direct measurement of the interlayer coupling strength.Graphene is the latest carbon allotrope to be discovered [1,2,3,4,5]. Near-ballistic transport at room temperature and high carrier mobilities [2,3,4,5,6,7,8], make it a potential material for nanoelectronics [9,10,11], especially for high frequency applications. It is now possible to produce areas exceeding thousands of square microns by means of micro-mechanical cleavage of graphite. An ongoing effort is being devoted to large scale deposition and growth on different substrates of choice.Unlike single layer graphene (SLG), where electrons disperse linearly as massless Dirac fermions [1,2,3,4,5], bilayer graphene (BLG) has two conduction and valence bands, separated by γ 1 , the interlayer coupling [12,13]. This was measured to be∼0.39eV by angle resolved photoelectron spectroscopy [14]. A gap between valence and conduction bands could be opened and tuned by an external electric field (∼100meV for∼10 13 cm −2 doping) [15,16], making BLG a tunable-gap semiconductor.Graphene can be identified in terms of number and orientation of layers by means of elastic and inelastic light scattering, such as Raman [17] and Rayleigh spectroscopies [18,19]. Raman spectroscopy also allows V TG Laser Spectrometer 50 X Objective SLG BLG Si Si SiO SiO 2 2 Pt A u A u FIG. 1: (color online). Experimental setup. The black dotted box on SiO2 indicates the polymer electrolyte (PEO + LiClO4). The left inset shows an SEM image of the SLG and BLG. Scale bar: 4µm. The right inset, the 2D Raman band monitoring of doping and defects [4,20,21,22,23,24,25]. Indeed, Raman spectroscopy is a fast and non-destructive characterization method for carbons [26]. They show common features in the 800-2000 cm −1 region: the G and D peaks, around 1580 and 1350 cm −1 , respectively. The G peak corresponds to the E 2g phonon at the Brillouin zone center (Γ). The D peak is due to the breathing modes of sp 2 atoms and requires a defect for its activation [27,28,29]. The most prominent feature in SLG is the second order of the D peak: the 2D peak [17]. This lies at ∼ 2700 cm −1 and involves phonons at K+∆q [17,23]. ∆q depends on the excitation energy, due to double-resonance, and the linear dispersion of the phonons around K [17,29,30]. 2D is a single peak in SLG, whereas it splits in four in BLG, reflecting the evolution of the band structure [17]. The 2D peak is always seen, even when no D peak is present, since no defects are required for overtone activation.In SLG, the effects of back and top gating on Gpeak position (Pos(G)) and Full Width at Half Maximum (FWHM(G)) were reported in Refs[20,21,...

Interaction of two different samples of graphene with DNA nucleobases and nucleosides is investigated by isothermal titration calorimetry. The relative interaction energies of the nucleobases decrease in the order guanine (G)>adenine (A)>cytosine (C)>thymine (T) in aqueous solutions, although the positions of C and T seem to be interchangeable. The same trend is found with the nucleosides. Interaction energies of the A-T and G-C pairs are somewhere between those of the constituent bases. Theoretical calculations including van der Waals interaction and solvation energies give the trend G>A approximately T>C. The magnitudes of the interaction energies of the nucleobases with graphene are similar to those found with single-walled carbon nanotubes.

We show the evolution of Raman spectra with a number of graphene layers on different substrates, SiO 2 /Si and conducting indium tin oxide (ITO) plate. The G mode peak position and the intensity ratio of G and 2D bands depend on the preparation of sample for the same number of graphene layers. The 2D Raman band has characteristic line shapes in single and bilayer graphene, capturing the differences in their electronic structure. The defects have a significant influence on the G band peak position for the single layer graphene: the frequency shows a blue shift up to 12 cm -1 depending on the intensity of the D Raman band, which is a marker of the defect density. Most surprisingly, Raman spectra of graphene on the conducting ITO plates show a lowering of the G mode frequency by ~ 6 cm -1 and the 2D band frequency by ~ 20 cm -1 . This red-shift of the G and 2D bands is observed for the first time in single layer graphene.

Entanglement is at the heart of the Einstein-Podolsky-Rosen paradox, where the non-locality is a necessary ingredient. Cooper pairs in superconductors can be split adiabatically, thus forming entangled electrons. Here, we fabricate such an electron splitter by contacting an aluminium superconductor strip at the centre of a suspended InAs nanowire. The nanowire is terminated at both ends with two normal metallic drains. Dividing each half of the nanowire by a gate-induced Coulomb blockaded quantum dot strongly impeds the flow of Cooper pairs due to the large charging energy, while still permitting passage of single electrons. We provide conclusive evidence of extremely high efficiency Cooper pair splitting via observing positive two-particle correlations of the conductance and the shot noise of the split electrons in the two opposite drains of the nanowire. Moreover, the actual charge of the injected quasiparticles is verified by shot noise measurements.

In situ Raman experiments together with transport measurements have been carried out on carbon nanotubes as a function of gate voltage. In metallic tubes, a large increase in the Raman frequency of the G(-) band, accompanied by a substantial decrease of its linewidth, is observed with electron or hole doping. In addition, we see an increase in the Raman frequency of the G(+) band in semiconducting tubes. These results are quantitatively explained using ab initio calculations that take into account effects beyond the adiabatic approximation. Our results imply that Raman spectroscopy can be used as an accurate measure of the doping of both metallic and semiconducting nanotubes.

We report a nuclear magnetic resonance (NMR) study of confined water inside approximately 1.4 nm diameter single-walled carbon nanotubes (SWNTs). We show that the confined water does not freeze even up to 223 K. A pulse field gradient (PFG) NMR method is used to determine the mean squared displacement (MSD) of the water molecules inside the nanotubes at temperatures below 273 K, where the bulk water outside the nanotubes freezes and hence does not contribute to the proton NMR signal. We show that the mean squared displacement varies as the square root of time, predicted for single-file diffusion in a one-dimensional channel. We propose a qualitative understanding of our results based on available molecular dynamics simulations.