Suchergebnisse

The magnetic structure of a monolayer-thick GdAu2 surface alloy on Au(111) has been investigated down to the atomic level by spin-polarized scanning tunneling microscopy. Spin-resolved tunneling spectroscopy combined with density-functional theory calculations reveal the local spin polarization of both Gd and Au atomic sites within the surface alloy. Moreover, the impact of dislocation lines on the atomic-scale magnetic structure as well as on the local coercive field strength is demonstrated. ; We gratefully acknowledge financial support from the Office of Naval Research via Grant No. N00014-16-1-2900. Moreover, M.A. and J.B. acknowledge funding from the Spanish MINECO under Contracts No. MAT2013-46593-C6- 4-P and No. MAT2016-78293-C6-5-R as well as the Basque Government Grants No. IT621-13 and No. IT-756-13. T.H. acknowledges support by the DFG under Grant No. HA 6037/2-1. E.S. acknowledges financing from Polish budget funds for science in 2014–2017 as a research project in the program "Diamond Grant" No. 0084/DIA/2014/43. M.H. acknowledges the support from the Ministry of Science and Higher Education in Poland within Project realized at Faculty of Technical Physics, Poznan University of Technology, and Poznan Supercomputing and Networking Center (PSNC)

et al. ; A vicinal rutile TiO(110) crystal with a smooth variation of atomic steps parallel to the [1-10] direction was analyzed locally with STM and ARPES. The step edge morphology changes across the samples, from [1-11] zigzag faceting to straight [1-10] steps. A step-bunching phase is attributed to an optimal (110) terrace width, where all bridge-bonded O atom vacancies (O vacs) vanish. The [1-10] steps terminate with a pair of 2-fold coordinated O atoms, which give rise to bright, triangular protrusions (S) in STM. The intensity of the Ti 3d-derived gap state correlates with the sum of O vacs plus S protrusions at steps, suggesting that both O vacs and steps contribute a similar effective charge to sample doping. The binding energy of the gap state shifts when going from the flat (110) surface toward densely stepped planes, pointing to differences in the Ti polaron near steps and at terraces. ; We acknowledge financial support from the Spanish Ministry of Economy (Grants MAT2013-46593-C6-4-P and MAT2013-46593-C6-2-P) and the Basque Government (Grant IT621-13 and IT756-13). M.S. and U.D. acknowledge support from the ERC Advanced Grant "OxideSurfaces". D.S.P. and M.M. acknowledge support from the Marie Curie ITN "THINFACE" and financial support by the Deutsche Forschungsgemeinschaft. through SFB 1083 "Structure and Dynamics of Internal Interfaces". ; Peer Reviewed

A combined scanning tunneling microscopy, x-ray photoelectron spectroscopy, angle-resolved photoemission spectroscopy, and density functional theory study of graphene on a Fe-Ir(111) alloy with variable Ir concentration is presented. Starting from an intercalated Fe layer between the graphene and Ir(111) surface we find that graphene-substrate interaction can be fine-tuned by Fe-Ir alloying at the interface. When a critical Ir-concentration close to 0.25 is reached in the Fe layer, the Dirac cone of graphene is largely restored and can thereafter be tuned across the Fermi level by further increasing the Ir content. Indeed, our study reveals an abrupt transition between a chemisorbed phase at small Ir concentrations and a physisorbed phase above the critical concentration. The latter phase is highly reminiscent of the graphene on the clean Ir(111) surface. Furthermore, the transition is accompanied by an inversion of the graphene's induced magnetization due to the coupling with the Fe atoms from antiferromagnetic when chemisorbed to weakly ferromagnetic in the physisorption regime, with spin polarizations whose magnitude may be tuned with the amount of Fe content. ; This work has been funded by the Spanish MINECO under contract Nos. FIS2013-48286-C2-1-P, MAT2013-47878-C2-R, MAT2015-66888-C3-1R, and MAT2013-46593-C6-4-P as well as the Basque Government Grants IT621-13 and IT756-13. ; Peer Reviewed

Surface-confined dehalogenation reactions are versatile bottom-up approaches for the synthesis of carbonbased nanostructures with predefined chemical properties. However, for devices generally requiring low-conductivity substrates, potential applications are so far severely hampered by the necessity of a metallic surface to catalyze the reactions. In this work we report the synthesis of ordered arrays of poly(p-phenylene) chains on the surface of semiconducting TiO(110) via a dehalogenative homocoupling of 4,4″- dibromoterphenyl precursors. The supramolecular phase is clearly distinguished from the polymeric one using low-energy electron diffraction and scanning tunneling microscopy as the substrate temperature used for deposition is varied. X-ray photoelectron spectroscopy of C 1s and Br 3d core levels traces the temperature of the onset of dehalogenation to around 475 K. Moreover, angle-resolved photoemission spectroscopy and tightbinding calculations identify a highly dispersive band characteristic of a substantial overlap between the precursor's π states along the polymer, considered as the fingerprint of a successful polymerization. Thus, these results establish the first spectroscopic evidence that atomically precise carbon-based nanostructures can readily be synthesized on top of a transition-metal oxide surface, opening the prospect for the bottom-up production of novel molecule-semiconductor devices. ; This work was supported by the Spanish Ministry of Economy (Grant No. MAT2013-46593-C6-4-P), the Basque Government (Grant No. IT-621-13), and the European Research Council under the EU Horizon 2020 research and innovation program (Grant Agreement No. 635919). We also acknowledge support from the Basque Department of Education, UPV/EHU (Grant No. IT-756-13), the Spanish Ministry of Science and Innovation (Grant No. MAT2013-46593-C6-2-P), and the European Union FP7-ICT Integrated Project PAMS (Contract No. 610446). ; Peer Reviewed

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY). ; We report measurements of a new type of magnetoresistance in Pt and Ta thin films. The spin accumulation created at the surfaces of the film by the spin Hall effect decreases in a magnetic field because of the Hanle effect, resulting in an increase of the electrical resistance as predicted by Dyakonov [Phys. Rev. Lett. 99, 126601 (2007)]. The angular dependence of this magnetoresistance resembles the recently discovered spin Hall magnetoresistance in Pt/Y3Fe5O12 bilayers, although the presence of a ferromagnetic insulator is not required. We show that this Hanle magnetoresistance is an alternative simple way to quantitatively study the coupling between charge and spin currents in metals with strong spin-orbit coupling. ; This work was supported by the European Union 7th Framework Programme under NMP Project No. 263104-HINTS and the European Research Council (Project No. 257654-SPINTROS), by the Spanish Ministry of Economy and Competitiveness under Projects No. MAT2012-37638, No. FIS2011-28851-C02-02, No. FIS2014-55987-P, and No. MAT2013-46593-C6-4-P, and by the Basque Government under UPV/EHU Projects No. IT-756-13 and No. IT-621-13. M. I. and E. S. thank the Basque Government and the Spanish Ministry of Education, Culture and Sport, respectively, for a Ph.D. fellowship (Grants No. BFI-2011-106 and No. FPU14/03102). ; Peer Reviewed

We report the on-surface synthesis of 7-armchair graphene nanoribbons (7-AGNRs) substituted with nitrile (CN) functional groups. The CN groups are attached to the GNR backbone by modifying the 7-AGNR precursor. Whereas many of these groups survive the on-surface synthesis, the reaction process causes the cleavage of some CN from the ribbon backbone and the on-surface cycloisomerization of few nitriles onto pyridine rings. Scanning tunneling spectroscopy and density functional theory reveal that CN groups behave as very efficient n-dopants, significantly downshifting the bands of the ribbon and introducing deep impurity levels associated with the nitrogen electron lone pairs. ; This work was supported by FP7 FET-ICT "Planar Atomic and Molecular Scale devices" (PAMS) project (funded by the European Commission under Contract No. 610446), by the Agencia Estatal de Investigacion (Cooperative Grant No. MAT2016-78293 and Grant FIS2015-62538-ERC), the Basque Government (Dep. de Educacion and UPV/EHU, Grant No. IT-756-13, and Dep. Industry, Grant PI_2015_1_42), the Xunta de Galicia (Centro singular de investigacion de Galicia accreditation 2016−2019, ED431G/09), and the European Regional Development Fund (ERDF). ; Peer Reviewed

Trabajo presentado al Symposium on Surface Science (3S), celebrado en St. Christoph am Arlberg (Austria) del 21 al 27 de febrero de 2016. ; We acknowledge financial support from the Spanish Ministry of Economy (grant MAT2013-46593-C6-4-P and MAT2013-46593-C6-2-P) and the Basque Government (grant IT621-13 and IT756-13), the ERC Advanced Grant "OxideSurfaces"., and the Marie Curie ITN "THINFACE". ; Peer reviewed