Suchergebnisse

With first principles calculations, we predict a novel stable 2D layered structure for group VI elements Se and Te that we call square selenene and square tellurene, respectively. They have chair-like buckled structures similar to other layered materials such as silicene and germanene but with a square unit cell rather than a hexagonal one. This special structure gives rise to anisotropic band dispersions near the Fermi level that can be described by a generalized semi-Dirac Hamiltonian. We show that the considerably large band gap (∼0.1 eV) opened by spin-orbit coupling makes square selenene and tellurene topological insulators, hosting non-trivial edge states. Therefore, square selenene and tellurene are promising materials for novel electronic and spintronic applications. Finally, we show that this new type of 2D elemental materials can potentially be grown on proper substrates, such as a Au(1 0 0) surface. ; We acknowledge financial support from the European Research Council (ERC-2015-AdG-694097), Grupos Consolidados (IT578-13), and COST Action MP1306 (EUSpec). LX acknowledges support from the European Union's Horizon 2020 research and innovation programme under the Marie SkłodowskaCurie grant agreement No. 709382 (MODHET). APP acknowledges postdoctoral fellowship from the Spanish 'Juan de la Cierva-incorporación' program (IJCI-2014-20147). EB acknowledge the support by the National Science Foundation Graduate Research Fellowship under Grant No. (DGE-1450681). ; Peer Reviewed

PACS number(s): 71.30.+h, 72.80.Vp, 73.22.Pr.-- et al. ; The study of two-dimensional (2D) electronic systems is of great fundamental significance in physics. Atomic layers containing hybridized domains of graphene and hexagonal boron nitride (h-BNC) constitute a new kind of disordered 2D electronic system. Magnetoelectric transport measurements performed at low temperature in vapor phase synthesized h-BNC atomic layers show a clear and anomalous transition from an insulating to a metallic behavior upon cooling. The observed insulator to metal transition can be modulated by electron and hole doping and by the application of an external magnetic field. These results supported by ab initio calculations suggest that this transition in h-BNC has distinctly different characteristics when compared to other 2D electron systems and is the result of the coexistence between two distinct mechanisms, namely, percolation through metallic graphene networks and hopping conduction between edge states on randomly distributed insulating h-BN domains. © 2012 American Physical Society. ; P.M.A. acknowledges support from the Office of Naval Research (ONR) through MURI program, the Basic Energy Sciences division of the Department of Energy (DOE) and Rice University startup funds. L.S. is supported by DOE-BES program DE-SC0001479 for device fabrication and measurement. L.B. is supported by DOE-BES through award DE-SC0002613 and by the NHMFL-UCGP program for measurement. The NHMFL is supported by NSF through NSF-DMR-0084173 and the State of Florida. D.J.M., S.K., and A.R. acknowledge financial support from the Spanish "Juan de la Cierva" program (JCI-2010-08156), Spanish MICINN (FIS2010-21282- C02-01 and PIB2010US-00652), ACI-Promociona (ACI2009-1036), "Grupos Consolidados UPV/EHU del Gobierno Vasco" (IT-319-07), the European Union through the FP7 e-I3 ETSF (Contract No. 211956), European Research Council Advanced Grant DYNamo (ERC-2010-AdG -Proposal No. 267374), and THEMA (Contract No. 228539) projects and the Ikerbasque Foundation. R.B.C. acknowledges financial support from Brazilian agencies CNPq, CAPES, FAPERJ, and INCT—Nanomateriais de Carbono and the ONR MURI program. S.G.L. acknowledges supported from National Science Foundation Grant No. DMR10-1006184 and the ONR MURI program. L.C. is supported by ONR MURI program (Award No. N00014-09-1066) for sample growth. K.S. acknowledges support from the National Science Foundation Major Research Instrumentation program (NSF-MRI) DMR-0619801 and the Department of Energy National Nuclear Security Administration (DOE-NNSA) DE-FG52-05NA27036 and the PVAMU Title III program US department of Education. ; Peer Reviewed

In press ; Owing to their great interest for energy storage and sensing applications, multi-layer papers consisting of graphene oxide – carbon nanotube (GO-CNT) hybrid sheets were prepared by in-situ exfoliation of graphite oxide in the presence of oxidized CNTs (oCNTs). For the first time we elucidate the influence of oCNTs on chemisorbed water (CW), i.e. water molecules inherently bound to oxygen functional groups (OFGs) of graphene oxide (GO) and responsible for irreversible structural damage upon thermal reduction processes. We show that oCNTs self-assemble onto GO sheets during the liquid phase processing steps by forming cooperatively strengthened OH···O=C hydrogen bonds between the carboxylic groups of oCNTs and OFGs of GO. At oCNT contents of about 10 to 15 wt. % this leads to the displacement of considerable amounts of CW without altering the original chemical composition of GO. Thermally reduced GO-CNT (rGO-CNT) papers reveal improved sp2 character and an enhancement of the specific capacitance by 75% with respect to thermally reduced GO (rGO), largely due to the effective removal of CW by oxidized CNTs. These findings disclose the relevance of cooperative hydrogen bonding phenomena in graphene oxide paper/film electrodes for the development of improved electrochemical energy storage and sensing devices. ; JDN is thankful for his CSIC PhD grant JAEPre09-01155 covering also his research stay at Rice University. WKM and AMB acknowledge financial support from Spanish MINECO and the European Regional Development Fund through project grants ENE2013-48816-C5-5-R, ENE2016-79282-C5-1-R and the Government of Aragon and the European Social Fund under project DGA-FSE-T66 CNN. RA gratefully acknowledges the support from MINECO through project grants FIS2013-46159- C3-3-P and MAT2016-79776-P. Some of the research has received funding from the European Union FP7 program under Grant Agreement 312483 ESTEEM2 (Integrated Infrastructure Initiative – I3) and from the European Union H2020 program under the grant 696656 Graphene Flagship, and H2020 Marie Skłodowska-Curie grant 642742. ; Peer reviewed