Suchergebnisse

Understanding the connection of graphene with metal surfaces is a necessary step for developing atomically precise graphene-based technology. Combining high-resolution STM experiments and DFT calculations, we have unambiguously unveiled the atomic structure of the boundary between a graphene zigzag edge and a Pt(111) step. The graphene edges minimize their strain by inducing a 3-fold edge-reconstruction on the metal side. We show the existence of an unoccupied electronic state that is mostly localized on the C-edge atoms of one particular graphene sublattice, which could have implications in the design of graphene based devices. © 2014 American Chemical Society. ; We acknowledge financial support from Spanish Grants MAT2010-17720, MAT2011-23627, MAT2011-26534, CSD2008-00041, CSD2010-00024, PLE2009-0061 (MINECO, Spain) and S2009/MAT-1467 (CAM, Spain). The research leading to these results has received funding from the European Union Seventh Framework Programme under Grant agreement No. 604391 Graphene Flagship. P.P. and P.M. were supported by the Ramón y Cajal and "Rafael Calvo Rodés" programs, respectively. ; Peer Reviewed

9 pages, 9 figures.-- Available online 21 February 2014 ; The effect of -irradiation on the structure and composition of chemically synthesized few-layered graphene materials was studied. Fully oxidized graphene oxide and graphene nanoribbons, as well as their respective chemically post-reduced forms, were treated under -irradiation in an air-sealed environment. Three different irradiation doses of 60, 90 and 150 kGy were applied. Structure and composition of the irradiated materials were analyzed by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), Raman spectroscopy and Xray photoelectron spectroscopy (XPS). The XRD patterns were not affected by - irradiation, and small changes were observed in the FTIR and TGA results. However, significant modifications were detected by Raman spectroscopy and XPS, particularly in the Raman G/D band intensity ratios and in the C 1s XPS profiles. Comparatively, the changes in Raman and XPS spectra after -irradiation were even greater than those occurring during the chemical reduction of graphene oxides. Our results indicate that the graphene carbon lattice was strongly affected by -irradiation, but the materials experienced small variations in their oxygen content. ; This work was funded by the Spanish MINECO under the projects TEC2010-15736, MAT2010-15026, MAT2010-16175 (CICYT) and PRI-PIBAR-2011-1, CSIC under Project 201080E124 and the Government of Aragon (DGA) and the European Social Fund (ESF) under Project DGA-ESF-T66 CNN. ; Peer reviewed

4 páginas, 4 figuras.-- PACS number(s): 61.46.Km, 73.63.−b, 62.25.−g.-- et al. ; The electrical response of graphene-based materials can be tailored under mechanical stress. We report different switching behaviors that take place in mechanically deformed graphene nanoribbons prior to the breakage of the junction. By performing tight-binding molecular dynamics, the study of structural changes of graphene nanoribbons with different widths is achieved, revealing that carbon chains are the ultimate bridges before the junction breaks. The electronic and transport calculations show that binary on/off states can be switched prior to and during breakage depending on the atomic details of the nanoribbon. This work supports the interpretation of recent experiments on nonvolatile memory element engineering based on graphene break junctions. ; This work is supported by the European Union and the Freistaat Sachsen (Project No. 13857/2379), the NANOSIM-GRAPHENE Project (ANR-09-NANO-016- 01) of ANR/P3N2009, and the Alexander von Humboldt Foundation. ; Peer reviewed

10 Figuras, 2 Tablas ; Graphene oxide nanoribbons (GONRs), obtained from the oxidative unzipping of carbon nanotubes, have been investigated as building blocks towards reaching active platforms in surface‐enhanced Raman scattering (SERS). The complete development of carbon nanomaterials is strongly related to the exploitation of their chemical versatility, so this work is focused on the positive effect that a specific chemical functionalization provides to the SERS effect when gold nanoparticles are used. The covalent derivatization of GONRs with terminal thiol groups boosts their interaction with different types of gold nanoparticles (namely, 'naked' or citrate‐stabilized), and the resulting two‐dimensional aggregates show an intense enhancement of the Raman scattering from the carbon nanostructures because of their two‐dimensional extended aggregation pattern. The SERS effect has been corroborated by theoretical calculations and a conceptual proof of SERS‐based sensing. ; AC, LL and MM would like to thank the University of Padova for funding (P‐DiSC #04BIRD2016‐UNIPD and the strategic program NAMECA). This project has received funding from the European Union's Horizon 2020 Research and Innovation Programme under the Marie Skłodowska‐Curie Grant Agreement n° 734834 (INFUSION) and from the PEOPLE Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme FP7 Grant Agreement n°290023 (RADDEL). ; Peer reviewed

Trabajo presentado al 42th "Jaszowiec" International School and Conference on the Physics of Semiconductors (Wisla-Polonia 2013). ; We study graphene nanoribbons and carbon nanotubes with divacancies, i.e., local defects composed of one octagon and a pair of pentagons. We show that the presence of divacancies leads to the appearance of gap states, which may act as acceptor or donor states. We explain the origin of those defect-localized states and prove that they are directly related to the zero-energy states of carbon ring forming the octagonal topological defect. ; This work was supported by the Polish National Science Center (grant DEC-2011/03/B/ST3/00091), the Spanish Ministry of Economy and Competitiveness (grant No. FIS2012-33521), the Basque Departamento de Educación and the University of the Basque Country (grant No. IT-366-07), the Basque Departamento de Industria and the Diputación Foral de Guipuzcoa under the ETORTEK program (NANO-IKER grant No. IE11-304). ; Peer Reviewed

Owing to its array of unique properties, graphene is a promising material for a wide variety of applications. Being two-dimensional, the properties of graphene are also easily tuned via proximity to other materials. In this work, we investigate the possibility of inducing electrical and optical anisotropy in graphene by interfacing it with other anisotropic carbon systems, including nanoporous graphene and arrays of graphene nanoribbons. We find that such materials do indeed induce such anisotropy in graphene while also preserving the unique properties offered by graphene's Dirac band structure, namely, its superior charge transport and long-wavelength optical absorption. The optical anisotropy makes such heterostructures interesting for their use in applications related to long-wavelength polarimetry, while the electrical anisotropy may be valuable for enhancing the performance of graphene photothermoelectric detectors. ; ICN2 is supported by the Severo Ochoa Centers of Excellence Program, funded by the Spanish State Research Agency (AEI, Grant No. SEV-2017-0706). ICN2 is also supported by the CERCA Program of the Generalitat de Catalunya. This work received funding from the European Union's Horizon 2020 Research and Innovation Program under Grant Agreement No. 825272 (ULISSES) and from the project "Waveguide-Integrated Mid-Infrared Graphene Detectors for Optical Gas Sensor Systems," Reference No. PCI2018-093128, funded by the Spanish Ministry of Science and Innovation—AEI.

Motivated by the recent synthesis of single layer TiSe2,we used state-of-the-art density functional theory calculations, to investigate the structural and electronic properties of zigzag and armchairedged nanoribbons (NRs) of this material. Our analysis reveals that, differing from ribbons of other ultra-thin materials such as graphene, TiSe2 NRs have some distinctive properties. The electronic band gap of the NRs decreases exponentially with the width and vanishes for ribbons wider than 20 Å. For ultranarrow zigzag-edged NRs we find odd-even oscillations in the band gap width, although their band structures show similar features. Moreover, our detailed magnetic-ground-state analysis reveals that zigzag and arm chair edged ribbons have non-magnetic ground states. Passivating the dangling bonds with hydrogen at the edges of the structures influences the band dispersion. Our results shed light on the characteristic properties of T phase NRs of similar crystal structures. ; Flemish Science Foundation (FWO-Vl); Methusalem foundation of the Flemish government; FWO Pegasus Long Marie Curie Fellowship; FWO Pegasus Short Marie Curie Fellowship; TUBITAK (114F397)

arXiv:1506.00869v1 ; We report the electronic properties of two-dimensional systems made of graphene nanoribbons, which are patterned with ad-atoms in two separated regions. Due to the extra electronic confinement induced by the presence of impurities, we find resonant levels, quasi-bound and impurity-induced localized states, which determine the transport properties of the system. Regardless of the ad-atom distribution in the system, we apply band-folding procedures to simple models and predict the energies and the spatial distribution of those impurity-induced states. We take into account two different scenarios: gapped graphene and the presence of randomly distributed ad-atoms in a low dilution regime. In both cases the defect-induced resonances are still detected. Our findings would encourage experimentalists to synthesize these systems and characterize their quasi-localized states by employing, for instance, scanning tunneling spectroscopy (STS). Additionally, the resonant transport features could be used in electronic applications and molecular sensing devices. ; This work has been partially supported by the Project FIS2013-48286-C2-1-P of the Spanish Ministry of Economy and Competitiveness MINECO (JWG, AA), the Basque Government through the NANOMATERIALS project (Grant IE14-393) under the ETORTEK Program Nanogune14 (JWG, AA) and the University of the Basque Country (Grant No. IT-366-07) (JWG, AA). Chilean FONDECYT grants: 1140388 (LR), and 1151316 (MP), and DGIP/USM internal grant 11.14.68 (MP), CONICYT ACT 1204 (LR, MP). ; Peer Reviewed

This article is part of the themed collection: 2020 Chemical Science HOT Article Collection. ; Fine management of chiral processes on solid surfaces has progressed over the years, yet still faces the need for the controlled and selective production of advanced chiral materials. Here, we report on the use of enantiomerically enriched molecular building blocks to demonstrate the transmission of their intrinsic chirality along a sequence of on-surface reactions. Triggered by thermal annealing, the on-surface reactions induced in this experiment involve firstly the coupling of the chiral reactants into chiral polymers and subsequently their transformation into planar prochiral graphene nanoribbons. Our study reveals that the axial chirality of the reactant is not only transferred to the polymers, but also to the planar chirality of the graphene nanoribbon end products. Such chirality transfer consequently allows, starting from adequate enantioenriched reactants, for the controlled production of chiral and prochiral organic nanoarchitectures with pre-defined handedness. ; We acknowledge funding from the European Union's Horizon 2020 Programme (Grant Agreement No. 635919 ("SURFINK") and 863098 ("SPRING")), from the Spanish MINECO (Grant No. MAT2016-78293-C6), Xunta de Galicia (Centro singular de investigación de Galicia, accreditation 2016–2019, ED431G/09), and the Fondo Europeo de Desarrollo Regional (FEDER). ; Peer reviewed

Theoretical progress in graphene physics has largely relied on the application of a simple nearest-neighbor tight-binding model capable of predicting many of the electronic properties of this material. However, important features that include electron-hole asymmetry and the detailed electronic bands of basic graphene nanostructures (e.g., nanoribbons with different edge terminations) are beyond the capability of such a simple model. Here we show that a similarly simple plane-wave solution for the one-electron states of an atom-based two-dimensional potential landscape, defined by a single fitting parameter (the scattering potential), performs better than the standard tight-binding model, and levels to density-functional theory in correctly reproducing the detailed π-band structure of a variety of graphene nanostructures. In particular, our approach identifies the three hierarchies of nonmetallic armchair nanoribbons, as well as the doubly-degenerate flat bands of free-standing zigzag nanoribbons with their energy splitting produced by symmetry breaking. The present simple plane-wave approach holds great potential for gaining insight into the electronic states and electro-optical properties of graphene nanostructures and other two-dimensional materials with intact or gapped Dirac-like dispersions. ; This work has been supported in part by the Spanish MINECO (Grants No. MAT2014-59096-P, No. MAT2016-78293-C6, No. MAT-2017-88374-P, No. MAT2017-88492-R, and No. SEV2015-0522), the Basque Government (Grant No. IT-1255-19), the European Research Council (Advanced Grant No. 789104-eNANO), the European Commission (Graphene Flagship 696656), the Catalan CERCA Program, Fundació Privada Cellex, and AGAUR (Grant No. 2017 SGR 1651).

[EN] On-surface synthesis, complementary to wet chemistry, has been demonstrated to be a valid approach for the synthesis of tailored graphenic nanostructures with atomic precision. Among the different existing strategies used to tune the optoelectronic and magnetic properties of these nanostructures, the introduction of non-hexagonal rings inducing out-of-plane distortions is a promising pathway that has been scarcely explored on surfaces. Here, we demonstrate that non-hexagonal rings, in the form of tropone (cycloheptatrienone) moieties, are thermally transformed into phenyl or cyclopentadienone moieties upon an unprecedented surface-mediated retro–Buchner-type reaction involving a decarbonylation or an intramolecular rearrangement of the CO unit, respectively. ; We acknowledge the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (ERC-2015-STG-677023 and ERC-2013-SYG-610256 NANOCOSMOS) and the innovation program under grant agreement No. 696656 (GrapheneCore1-Graphene-based disruptive technologies) and grant agreement No. 785219 (GrapheneCore2-Graphenebased disruptive technologies) for financial support. Grants PGC2018-101181-B-I00 and MAT2017- 85089-C2-1-R funded by MCIN/AEI/10.13039/501100011033 and "ERDF A way of making Europe" by the "European Union", and grant PID2020-113142RB-C21 funded by MCIN/AEI/ 10.13039/501100 011033 also provided financial support. We also acknowledge Comunidad de Madrid via Programade Investigación Tecnologías 2018 (FOTOART-CM S2018/NMT-4367), the Swiss National Science Foundation (grant number 200020-182015), the NCCR MARVEL funded by the Swiss National Science Foundation (grant number 51NF40-182892) and FEDER/Junta de Andalucía-Consejería de Economía y Conocimiento (B-FQM-428-UGR20). C. S. S. and N. R. A. acknowledge Grants RYC2018-024364-I and BES-2015-072642, respectively, funded by MCIN/AEI/ 10.13039/501100011033 and "ESF Investing in your future". I. R. M. acknowledges the University of Granada for her postdoctoral contract (Contrato Puente-Plan Propio UGR). F.V. thanks Ministerio de Universidades for the FPU grant (FPU18/05938). ; Peer reviewed

We present electronic structure calculations based on a single-parameter plane wave expansion method for basic graphene building blocks, namely n-oligophenylenes and n-oligoacenes, revealing excellent agreement with density-functional theory. When oligophenylene molecules are joined through meta (zigzag) or ortho (chevron) junctions, the resulting molecular dimers and polymers exhibit a semiconducting character. While zigzag dimers of oligoacenes also exhibit gapped electronic structures, their chevron-phase features a sharp metallic band at the Fermi energy. This zero-point-energy state, which transforms into Dirac-like band in chevron polymers, survives at the outer elbows of the dimer irrespective of the molecular length, and has the same origin as reported for the polyacetylene and topologically induced edge states at edge-decorated graphene nanoribbons. These findings assist the engineering of topological electronic states at the molecular level and complement the toolbox of quantum phases in carbon-based nanostructures. ; JEO acknowledges financial support from the Spanish Ministry of Science and Innovation (Grants PID2019-107338RB-C63) and the Basque Government (Grant IT-1255-19). ; Peer reviewed