Magneto-Raman-scattering experiments from the surface of graphite reveal novel features associated to purely electronic excitations which are observed in addition to phonon-mediated resonances. Graphene-like and graphite domains are identified through experiments with ∼1  μm spatial resolution performed in magnetic fields up to 32 T. Polarization resolved measurements emphasize the characteristic selection rules for electronic transitions in graphene. Graphene on graphite displays the unexpected hybridization between optical phonon and symmetric across the Dirac point inter Landau level transitions. The results open new experimental possibilities--to use light scattering methods in studies of graphene under quantum Hall effect conditions.

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Solid mixed conductors with significant ionic as well as electronic conduction play a pivotal role for mass transfer and storage as required in battery electrodes. Singlephase materials with simultaneously high electronic and ionic conductivity at room temperature are hard to come by and therefore multi-phase systems with separate ion and electron channels have been put forward instead. Here, we explore bilayer graphene as a true single phase mixed conductor and demonstrate ultrafast lithium diffusion exceeding diffusion in bulk graphite by an order of magnitude and even surpassing diffusion of sodium chloride in liquid water. To this end, an innovative electrochemical cell architecture has been developed where the redoxreaction forcing lithium intercalation is localized at a protrusion of the device only. Its remainder consists of pristine bilayer graphene unperturbed by an electrolyte. The geometry lends itself to the use of magnetotransport machinery known from mesoscopic low-dimensional physics. Time dependent Hall measurements across spatially displaced Hall probes deliver a direct view on the in-plane diffusion kinetics. The device layout with a perimeterial electrochemical cell is transferable to other 2D materials as well as thin films and may promote a paradigm shift on the use of electrolytes in on-chip experiments.The electrodes of state-of-the-art Li-ion batteries consist primarily of mixed conducting compounds, in which, by ambipolar motion, Li-ions diffuse coupled to electron transport. The higher both ionic and electronic conductivities of these electrodes are, the faster one may insert (and remove) Li-ions up to full storage capacity. However, room-temperature values for the chemical diffusion coefficient of Li, D δ , are typically rather low in common Li insertion compounds, with higher values potentially conceivable in artificially designed heterogeneous mixed conductors. 1 In practical electrodes, which are composites containing the insertion compound (typically as a powder) and additives such as binders, Li diffusion is a complex process with D δ being an effective parameter. For insertion compounds with a highly anisotropic ionic conductivity such as bulk graphitic carbons, 2,3 reported values spread over many orders of magnitude as D δ ≈ 10 −12 − 10 −5 cm 2 /s, 4-13 partially also reflecting difficulties to reliably extract this parameter from electrochemical measurements. 8,11,12 Nanoscale derivatives of bulk insertion compounds might therefore offer a better platform both to determine and to exploit their likely similar if not better mixed conducting properties. As such, graphene -a single sheet of carbon atoms -has been used in various electrodes as helpful current-collecting admixture, and a possibly increased capacity over graphite by Li adsorption on both sides is being discussed. 14,15 Here, we study bilayer graphene, which features a single van der Waals-gap between its two carbon sheets suitable for Li intercalation. With current nanofabrication methods and characterization tools, ...

We use polarized magneto-Raman scattering to study purely electronic excitations and the electron-phonon coupling in bulk graphite. At a temperature of 4.2 K and in magnetic fields up to 28 T we observe K-point electronic excitations involving Landau bands with ∆|n| = 0 and with ∆|n| = ±2 that can be selected by controlling the angular momentum of the excitation laser and of the scattered light. The magneto-phonon effect involving the E2g optical phonon and K-point inter Landau bands electronic excitations with ∆|n| = ±1 is revealed and analyzed within a model taking into account the full kz dispersion. These polarization resolved results are explained in the frame of the Slonczewski-Weiss-McClure (SWM) model which directly allows to quantify the electron-hole asymmetry.

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Confined fluids and electrolyte solutions in nanopores exhibit rich and surprising physics and chemistry that impact the mass transport and energy efficiency in many important natural systems and industrial applications. Existing theories often fail to predict the exotic effects observed in the narrowest of such pores, called single-digit nanopores (SDNs), which have diameters or conduit widths of less than 10 nm, and have only recently become accessible for experimental measurements. What SDNs reveal has been surprising, including a rapidly increasing number of examples such as extraordinarily fast water transport, distorted fluid-phase boundaries, strong ion-correlation and quantum effects, and dielectric anomalies that are not observed in larger pores. Exploiting these effects presents myriad opportunities in both basic and applied research that stand to impact a host of new technologies at the water−energy nexus, from new membranes for precise separations and water purification to new gas permeable materials for water electrolyzers and energy-storage devices. SDNs also present unique opportunities to achieve ultrasensitive and selective chemical sensing at the single-ion and single-molecule limit. In this review article, we summarize the progress on nanofluidics of SDNs, with a focus on the confinement effects that arise in these extremely narrow nanopores. The recent development of precision model systems, transformative experimental tools, and multiscale theories that have played enabling roles in advancing this frontier are reviewed. We also identify new knowledge gaps in our understanding of nanofluidic transport and provide an outlook for the future challenges and opportunities at this rapidly advancing frontier.

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