Ultrathin epitaxial graphite was grown on single-crystal silicon carbide by vacuum graphitization. The material can be patterned using standard nanolithography methods. The transport properties, which are closely related to those of carbon nanotubes, are dominated by the single epitaxial graphene layer at the silicon carbide interface and reveal the Dirac nature of the charge carriers. Patterned structures show quantum confinement of electrons and phase coherence lengths beyond 1 micrometer at 4 kelvin, with mobilities exceeding 2.5 square meters per volt-second. All-graphene electronically coherent devices and device architectures are envisaged.

We have produced ultrathin epitaxial graphite films which show remarkable 2D electron gas (2DEG) behavior. The films, composed of typically 3 graphene sheets, were grown by thermal decomposition on the (0001) surface of 6H-SiC, and characterized by surface-science techniques. The low-temperature conductance spans a range of localization regimes according to the structural state (square resistance 1.5 kΩ to 225 kΩ at 4 K, with positive magnetoconductance). Low resistance samples show characteristics of weak-localization in two dimensions, from which we estimate elastic and inelastic mean free paths. At low field, the Hall resistance is linear up to 4.5 T, which is well-explained by n-type carriers of density 10 12 cm −2 per graphene sheet. The most highlyordered sample exhibits Shubnikov -de Haas oscillations which correspond to nonlinearities observed in the Hall resistance, indicating a potential new quantum Hall system. We show that the high-mobility films can be patterned via conventional lithographic techniques, and we demonstrate modulation of the film conductance using a top-gate electrode. These key elements suggest electronic device applications based on nano-patterned epitaxial graphene (NPEG), with the potential for large-scale integration.

Transport in ultrathin graphite grown on silicon carbide is dominated by the electron-doped epitaxial layer at the interface. Weak antilocalization in 2D samples manifests itself as a broad cusplike depression in the longitudinal resistance for magnetic fields 10 mT

The electroreduction of nitrate (NO3−) pollutants to ammonia (NH3) offers an alternative approach for both wastewater treatment and NH3 synthesis. Numerous electrocatalysts have been reported for the electroreduction of NO3− to NH3, but most of them demonstrate poor performance at ultralow NO3− concentrations. In this study, a Cu‐based catalyst for electroreduction of NO3− at ultralow concentrations is developed by encapsulating Cu nanoparticles in a porous carbon framework (Cu@C). At −0.3 V vs reversible hydrogen electrode (RHE), Cu@C achieves Faradaic efficiency for NH3 of 72.0% with 1 × 10−3 m NO3−, which is 3.6 times higher than that of Cu nanoparticles. Notably, at −0.9 V vs RHE, the yield rate of NH3 for Cu@C is 469.5 µg h−1 cm−2, which is the highest value reported for electrocatalysts with 1 × 10−3 m NO3−. An investigation of the mechanism reveals that NO3− can be concentrated owing to the enrichment effect of the porous carbon framework in Cu@C, thereby facilitating the mass transfer of NO3− for efficient electroreduction into NH3 at ultralow concentrations.