Tailoring magnetism in silicon-doped zigzag graphene edges

Recently, the edges of single-layer graphene have been experimentally doped with silicon atoms by means of scanning transmission electron microscopy. In this work, density functional theory is applied to model and characterize a wide range of experimentally inspired silicon doped zigzag-type graphene edges. The thermodynamic stability is assessed and the electronic and magnetic properties of the most relevant edge configurations are unveiled. Importantly, we show that silicon doping of graphene edges can induce a reversion of the spin orientation on the adjacent carbon atoms, leading to novel magnetic properties with possible applications in the field of spintronics.A.U. gratefully acknowledges Eusko Jaurlaritza for his predoctoral grant. We thank the Provincial Council of Gipuzkoa (RED Gipuzkoa Next 2021-CIEN-000070-01), the Basque Department of Education (IT1254-19, PIBA2020-1-0014), the Spanish Ministry of Science and Innovation (PID2019-107338RB-C66, PID2020-114754GA-I00) and the European Union (EU) through Horizon 2020 (FET-Open project SPRING Grant No. 863098) for financial support. The authors thankfully acknowledge the computer resources at MareNostrum and the technical support provided by Barcelona Supercomputing Center (QHS-2021-3-0004). We also thank DIPC and SGI-IZOSGIker (UPV/EHU) for the generous allocation of computational resources

Tunneling spectroscopy of close-spaced dangling-bond pairs in Si(001):H

We present a combined experimental and theoretical study of the electronic properties of close-spaced dangling-bond (DB) pairs in a hydrogen-passivated Si(001):H p-doped surface. Two types of DB pairs are considered, called “cross” and “line” structures. Our scanning tunneling spectroscopy (STS) data show that, although the spectra taken over different DBs in each pair exhibit a remarkable resemblance, they appear shifted by a constant energy that depends on the DB-pair type. This spontaneous asymmetry persists after repeated STS measurements. By comparison with density functional theory (DFT) calculations, we demonstrate that the magnitude of this shift and the relative position of the STS peaks can be explained by distinct charge states for each DB in the pair. We also explain how the charge state is modified by the presence of the scanning tunneling microscopy (STM) tip and the applied bias. Our results indicate that, using the STM tip, it is possible to control the charge state of individual DBs in complex structures, even if they are in close proximity. This observation might have important consequences for the design of electronic circuits and logic gates based on DBs in passivated silicon surfaces

Magnetism of topological boundary states induced by boron substitution in graphene nanoribbons

Graphene nanoribbons (GNRs), low-dimensional platforms for carbon-based electronics, show the promising perspective to also incorporate spin polarization in their conjugated electron system. However, magnetism in GNRs is generally associated with localized states around zigzag edges, difficult to fabricate and with high reactivity. Here we demonstrate that magnetism can also be induced away from physical GNR zigzag edges through atomically precise engineering topological defects in its interior. A pair of substitutional boron atoms inserted in the carbon backbone breaks the conjugation of their topological bands and builds two spin-polarized boundary states around them. The spin state was detected in electrical transport measurements through boron-substituted GNRs suspended between the tip and the sample of a scanning tunneling microscope. First-principle simulations find that boron pairs induce a spin 1, which is modified by tuning the spacing between pairs. Our results demonstrate a route to embed spin chains in GNRs, turning them into basic elements of spintronic devices.We gratefully acknowledge financial support from Spanish Agencia Estatal de Investigación (AEI) (MAT2016-78293, PID2019-107338RB, FIS2017-83780-P, and the Maria de Maeztu Units of Excellence Programme MDM-2016-0618), from the European Union (EU) through Horizon 2020 (FET-Open project SPRING Grant. No. 863098), the Basque Departamento de Educación through the PhD fellowship No. PRE_2019_2_0218 (S.S.), the Xunta de Galicia (Centro de Investigación de Galicia accreditation 2019–2022, ED431G 2019/03), the University of the Basque Country (Grant IT1246-19), and the European Regional Development Fund (ERDF). I. P. also thanks Xunta de Galicia and European Union (European Social Fund, ESF) for the award of a predoctoral fellowship-Peer reviewe

Electronic consequences of chemical doping of 7-Armchair Graphene Nanoribbons

Resumen del trabajo presentado a la International Conference on Nanoscience + Technology (ICN+T), celebrada en Brno (Czech Republic) del 22 al 27 de julio de 2018.The tunable electronic structure of Graphene Nanoribbons (GNRs) with different edge types has provoked great interest due to potential applications in electronic devices as molecular diodes or transistors. Thanks to the on-surface synthesis of chemically customized molecular precursors, nanoribbons with atomically defined structure can be grown. This high precision in their bottom-up growth allows to tune their electronic structure via width control or chemical doping. Here we use two different strategies to chemically modify 7-armchair GNRs (7-AGNRs) to clarify how the chemical modifications on the nanoribbons’ structure affect their electronic properties. By means of Scanning Tunneling Spectroscopy we tackle with atomic precision this issue on 7-AGNRs with substitutional nitrile functional groups at the ribbons’ edges and on 7-AGNRs with substitutional boron atoms within the ribbons’ backbone. We find that in the first case the CN groups lead to an efficient n-like doping of the ribbon, while in the second case B atoms induce the formation of a new acceptor band and bandgap renormalization.Peer Reviewe

Magnetism found in zigzag graphene nanoribbons

News & views.The inclusion of nitrogen atoms stabilizes the zigzag edges of carbon-based nanoribbons, enabling the ribbons to be decoupled from a substrate and providing a probe for their unconventional magnetism.Peer reviewe

Plane-wave based electron tunneling through Au nanojunctions

Resumen del trabajo presentado al Symposium on Surface Science (3S), celebrado en Baqueira Beret, Lleida, Spain del 6 al 12 de marzo de 2011.Support from the Basque Departamento de Educacion, UPV/EHU (Grant No. IT-366-07), the Spanish Ministerio de Ciencia e Innovacion (Grant No. FIS2007-6671-C02-00), the ETORTEK program funded by the Basque Departamento de Industria and the Diputacion Foral de Guipuzcoa, and the DMS/BES/SC of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231 are gratefully acknowledged. It used the resources of the National Energy Research Scientific Computing Center (NERSC).Peer reviewe

Exploring large O 1s and N 1s core level shifts due to intermolecular hydrogen bond formation in organic molecules

Core level shifts (CLSs) induced by intermolecular hydrogen bond (H-bond) formation are studied with a recent implementation based on density functional theory using pseudopotentials and localized atomic orbitals, as applied to the SIESTA code. By calculating different CLSs for a set of representative simple systems containing O and/or N atoms as proton donors and/or acceptors, we are able to determine the role of the core hole screening, from the difference of CLS values calculated in the final and initial state approximations. Our calculations show that CLSs are dominated by electrostatic effects, and that the final magnitude of the CLSs, which are positive (higher binding energy) for the proton acceptor and negative for the proton donor, can be larger than 1 eV for strong H-bonds. We also find that core hole screening contribution to final CLS absolute values is always negative, thus being responsible for the difference in the magnitude of the CLS of the proton donor and proton acceptor. © 2013 Elsevier B.V.We acknowledge funding support from the Basque Departamento de Educatión, UPV/EHU (Grant No. IT-756-13), the Spanish Ministerio de Ciencia e Innovación (Grant No. FIS2010-19609-C02-01) and the ETORTEK program funded by the Basque Departamento de Industria.Peer Reviewe

Simulation of inelastic electron tunneling spectroscopy of single molecules with functionalized tips

10 páginas, 6 figuras, 1 tabla.-- PACS number(s): 72.10.−dThe role of the tip in inelastic electron tunneling spectroscopy (IETS) performed with scanning tunneling microscopes (STM) is theoretically addressed via first-principles simulations of vibrational spectra of single carbon monoxide (CO) molecules adsorbed on Cu(111). We show how chemically functionalized STM tips modify the IETS intensity corresponding to adsorbate modes on the sample side. The underlying propensity rules are explained using symmetry considerations for both the vibrational modes and the molecular orbitals of the tip and sample. This suggests that single-molecule IETS can be optimized by selecting the appropriate tip orbital symmetry.Support from the Basque Departamento de Educación, UPV/EHU (Grant No. IT-366-07), the Spanish Ministerio de Ciencia e Innovación (Grant No. FIS2010-19609-C02-00), the ETORTEK program funded by the Basque Departamento de Industria and the Diputacion Foral de Guipuzcoa are gratefully acknowledged.Peer reviewe

Nanoarquitecturas de grafeno con precisión atómica

La síntesis de arquitecturas covalentes en superficie y con precisión atómica se ha erigido como uno de los métodos más prometedores para dotar de nuevas funcionalidades al grafeno, un material ya de por si superlativo en múltiples aspectos. La fortaleza de este método estriba en su flexibilidad para crear una vasta gama de arquitecturas grafénicas. Para llegar a la estructura final buscada se diseñan moléculas precursoras prácticamente a la carta. El diseño de estas moléculas contiene dos aspectos comunes, la parte que dará conformación a la estructura final y la parte que servirá para enlazar dichas moléculas de forma ordenada como si se tratase de piezas de Lego. El resultado final son tiras de grafeno semiconductoras con un alto potencial en aplicaciones en nanoelectrónica o fotónica. También ha sido posible materializar el hito de sintetizar grafeno nanoporoso con precisión atómica. Esto podría suponer un gran avance en el desarrollo de nuevas membranas más ligeras, con velocidades de filtrado mayores, con un menor coste energético de filtrado y con un mayor grado de selectividad.Peer reviewe

Plane-wave based electron tunneling through field emission resonance states

Field emission resonances (FERs) on Cu(100) surface are investigated by means of tunneling regime simulations performed with a plane-wave based transport calculation method. FERs are located near the surface and decay into the vacuum, and their accurate simulation requires a faithful description of vacuum states. This type of simulations is thus not possible using the popular transport methods based on atom-centered localized basis sets and the use of plane waves becomes important. We introduce a procedure to treat self-consistently (SC) the finite bias nonequilibrium problem in tunneling regime. Image potential effects are included in a semiempirical way within the SC calculation. Tunneling through FERs is studied following a practical strategy to approximate the inelastic transmission for states lying in the band gap of the surface. As our approach permits the use of any tip geometry, tip effects on the energy and wave functions of FERs are explored. The method reported here provides an ideal tool for the simulation of FERs aimed at the understanding of experimental STS (scanning tunneling spectroscopy) observations. © 2013 American Physical Society.We acknowledge support from the Basque Departamento de Educación and the UPV/EHU (Grant No. IT-756-13), the Spanish Ministerio de Ciencia e Innovación (Grant No. FIS2010-19609-C02-00), and the ETORTEK program funded by the Basque Departamento de Industria and the Diputación Foral de Gipuzkoa. L.W. Wang is supported by the US DOE/SC/BES under contract No. DE-AC02-05CH11231.Peer Reviewe