Search

We report on a spatial mapping of the electronic and vibrational structure of three-dimensional (3D) nanoporous graphene architectures, which have a hierarchical pore structure. We demonstrate that the topology, curvature, and pores lead to local changes in the electronic and vibrational structure and in the hybridization states of the carbon atoms (sp 2 vs. sp 3 -like). Nitrogen substitutions in pyrrolic bonding configurations also contribute to local distortions of the planar geometry of graphene. The distortions influence the electronic density of states at the Fermi level by shifting the Dirac cone apex, opening potential avenues for applications of two-dimensional graphene in 3D devices. [ABSTRACT FROM AUTHOR]

Modifications of graphene's electronic band structure can be achieved through periodic bending strain and related potential in samples grown on stepped substrates, opening a viable route to implement the periodicity effects in this ultimate two-dimensional (2D) material. We studied graphene grown on stepped Ir(332), which can be benchmarked to a well-known graphene on flat Ir(111) recognized for a weak van der Waals (vdW) interaction. The structural characterization indicated that graphene growth induces reversible, well defined faceting of iridium surface into alternating terraces and step bunches, while spectroscopy techniques revealed substantial changes of graphene's electronic structure. Crucially, highly concentrated Ir step edges, resulting in locally strong chemical bonding of graphene, introduce a dominant energy parameter which overwhelms the induced strain and presents a driving force for the surface faceting. This sets a general framework for the understanding of graphene mediated faceting of stepped substrates whenever the corresponding low index surface exhibits dominantly vdW interaction with graphene, which can be also supplemented to other 2D materials. Interestingly, the graphene π band becomes pronouncedly anisotropic due to the presence of a periodic potential originating from steps, and lateral variation of the charge carrier concentration enabling a straightforward electronic band engineering in graphene. [ABSTRACT FROM AUTHOR]

Abstract: Among the many anticipated applications of graphene, some – such as transistors for Si microelectronics – would greatly benefit from the possibility to deposit graphene directly on a semiconductor grown on a Si wafer. We report that Ge(001) layers on Si(001) wafers can be uniformly covered with graphene at temperatures between 800°C and the melting temperature of Ge. The graphene is closed, with sheet resistivity strongly decreasing with growth temperature, weakly decreasing with the amount of deposited C, and reaching down to 2k . Density functional theory calculations indicate that the major physical processes affecting the growth are (1) substitution of surface Ge by C, (2) interaction between C clusters and Ge monomers, and (3) formation of bonds between graphene edge and Ge(001), and that the processes 1 and 2 are surpassed by CH2 surface diffusion when carbon is delivered from CH4. The results of this study indicate that graphene can be produced directly at the active region of the transistor in a process compatible with the Si technology. [Copyright &y& Elsevier]