Description: This article discusses charge transfer equilibria in ambient-exposed epitaxial graphene on (0001) 6 H-SiC. Abstract: The transport properties of electronic materials have been long interpreted independently from both the underlying bulk-like behavior of the substrate or the influence of ambient gases. This is no longer the case for ultra-thin graphene whose properties are dominated by the interfaces between the active material and its surroundings. Here, the authors show that the graphene interactions with its environments are critical for the electrostatic and electrochemical equilibrium of the active device layers and their transport properties. Based on the prototypical case of epitaxial graphene on (0001) 6 H-SiC and using a combination of 'in-situ' thermoelectric power and resistance measurements and simulations from first principles, the authors demonstrate that the cooperative occurrence of an electrochemically mediated charge transfer from the graphene to air, combined with the peculiar electronic structure of the graphene/SiC interface, explains the wide variation of measured conductivity and charge carrier type found in prior reports.

Description: This article discusses electric field induced phase transitions in polymers. Abstract: Using first-principles simulations, the authors identify the microscopic origin of the nonlinear dielectric response and high energy density of polyvinylidene-fluoride-based polymers as a cooperative transition path that connects nonpolar and polar phases of the system. This path explores a complex torsional and rotational manifold and is thermodynamically and kinetically accessible at relatively low temperatures. Furthermore, the introduction of suitable copolymers significantly alters the energy barriers between phases providing tunability of both the energy density and the critical fields.

Description: This article discusses electronic properties of the graphene/6H-SiC(0001̅) interface. Abstract: Using calculations from first principles, we show how the structural and electronic properties of epitaxial graphene on 6H-SiC(0001̅) are determined by the geometry and the chemical functionalization of the interface region. We also demonstrate that these properties can be correctly captured only if a proper treatment of the van der Waals interactions is included in the theoretical description based on density functional theory. Our results reproduce the experimentally observed n-type doping of monolayer epitaxial graphene and prove the possibility of opening a sizable (150 meV) energy gap in the bilayer case under special growth conditions. Depending on the details of the bonding at the interface, the authors are able to interpret recent experimental observations and provide a clear insight into the mechanisms of charge transfer and interface stability.

Description: In this article, the authors report that hydrogenation of mono-, bi-, and trilayer graphene samples via exposure to H2 plasma occurs as a result of electron irradiation of H2O adsorbates on the samples, rather than H species in the plasma as reported by [Elias et al., Science 323, 610 (2009)]. The authors propose that the hydrogenation mechanism is electron-impact fragmentation of H2O adsorbates into H+ ions. At incident electron energies >60 eV, the authors observe hydrogenation that is significantly more stable at temperatures >200 ºC than previously reported.

Description: In this paper, the authors show using scanning tunneling microscopy, spectroscopy, and ab initio calculations that several intercalation structures exist for Na in epitaxial graphene on SiC(0001). Intercalation takes place at room temperature and Na electron-dopes the graphene. It intercalates in-between single-layer graphene and the carbon-rich interfacial layer. It also penetrates beneath the interfacial layer and decouples it to form a second graphene layer. This decoupling is accelerated by annealing and is verified by direct Na deposition onto the interface layer. The authors' observations show that intercalation in graphene is fundamentally different than in graphite and is a versatile means of electronic control.