Atomic Manipulation and Spectroscopy

Group Leader: Aitor Mugarza



  • Tuning the Magnetic Anisotropy of Lanthanides on a Metal Substrate by Metal–Organic Coordination

    Parreiras S.O., Moreno D., Cirera B., Valbuena M.A., Urgel J.I., Paradinas M., Panighel M., Ajejas F., Niño M.A., Gallego J.M., Valvidares M., Gargiani P., Kuch W., Martínez J.I., Mugarza A., Camarero J., Miranda R., Perna P., Écija D. Small; 17 (35, 2102753) 2021. 10.1002/smll.202102753. IF: 13.281

    Taming the magnetic anisotropy of lanthanides through coordination environments is crucial to take advantage of the lanthanides properties in thermally robust nanomaterials. In this work, the electronic and magnetic properties of Dy-carboxylate metal–organic networks on Cu(111) based on an eightfold coordination between Dy and ditopic linkers are inspected. This surface science study based on scanning probe microscopy and X-ray magnetic circular dichroism, complemented with density functional theory and multiplet calculations, reveals that the magnetic anisotropy landscape of the system is complex. Surface-supported metal–organic coordination is able to induce a change in the orientation of the easy magnetization axis of the Dy coordinative centers as compared to isolated Dy atoms and Dy clusters, and significantly increases the magnetic anisotropy. Surprisingly, Dy atoms coordinated in the metallosupramolecular networks display a nearly in-plane easy magnetization axis despite the out-of-plane symmetry axis of the coordinative molecular lattice. Multiplet calculations highlight the decisive role of the metal–organic coordination, revealing that the tilted orientation is the result of a very delicate balance between the interaction of Dy with O atoms and the precise geometry of the crystal field. This study opens new avenues to tailor the magnetic anisotropy and magnetic moments of lanthanide elements on surfaces. © 2021 The Authors. Small published by Wiley-VCH GmbH


  • Absence of Magnetic Proximity Effect at the Interface of Bi2Se3 and (Bi,Sb)2Te3 with EuS

    Figueroa A.I., Bonell F., Cuxart M.G., Valvidares M., Gargiani P., Van Der Laan G., Mugarza A., Valenzuela S.O. Physical Review Letters; 125 (22, 226801) 2020. 10.1103/PhysRevLett.125.226801. IF: 8.385

    We performed X-ray magnetic circular dichroism (XMCD) measurements on heterostructures comprising topological insulators (TIs) of the (Bi,Sb)2(Se,Te)3 family and the magnetic insulator EuS. XMCD measurements allow us to investigate element-selective magnetic proximity effects at the very TI/EuS interface. A systematic analysis reveals that there is neither significant induced magnetism within the TI nor an enhancement of the Eu magnetic moment at such interface. The induced magnetic moments in Bi, Sb, Te, and Se sites are lower than the estimated detection limit of the XMCD measurements of ∼10-3 μB/at. © 2020 American Physical Society.

  • Band Depopulation of Graphene Nanoribbons Induced by Chemical Gating with Amino Groups

    Li J., Brandimarte P., Vilas-Varela M., Merino-Díez N., Moreno C., Mugarza A., Mollejo J.S., Sánchez-Portal D., Garcia De Oteyza D., Corso M., Garcia-Lekue A., Peña D., Pascual J.I. ACS Nano; 14 (2): 1895 - 1901. 2020. 10.1021/acsnano.9b08162. IF: 14.588

    The electronic properties of graphene nanoribbons (GNRs) can be precisely tuned by chemical doping. Here we demonstrate that amino (NH2) functional groups attached at the edges of chiral GNRs (chGNRs) can efficiently gate the chGNRs and lead to the valence band (VB) depopulation on a metallic surface. The NH2-doped chGNRs are grown by on-surface synthesis on Au(111) using functionalized bianthracene precursors. Scanning tunneling spectroscopy resolves that the NH2 groups significantly upshift the bands of chGNRs, causing the Fermi level crossing of the VB onset of chGNRs. Through density functional theory simulations we confirm that the hole-doping behavior is due to an upward shift of the bands induced by the edge NH2 groups. © 2020 American Chemical Society.

  • Enhanced Magnetism through Oxygenation of FePc/Ag(110) Monolayer Phases

    Bartolomé E., Bartolomé J., Sedona F., Lobo-Checa J., Forrer D., Herrero-Albillos J., Piantek M., Herrero-Martín J., Betto D., Velez-Fort E., García L.M., Panighel M., Mugarza A., Sambi M., Bartolomé F. Journal of Physical Chemistry C; 124 (25): 13993 - 14006. 2020. 10.1021/acs.jpcc.0c01988. IF: 4.189

    Iron phthalocyanines (FePc) adsorbed onto a Ag(110) substrate self-assemble into different monolayer phases going from rectangular to different oblique phases, with increasing molecular density. We have investigated the oxygen uptake capability of the different phases and their associated magneto-structural changes. Our study combines scanning tunneling microscopy and spectroscopy (STM/STS), X-ray magnetic circular dichroism (XMCD), and density functional theory (DFT) calculations. STM measurements reveal that the oxygenation reaction of the FePc/Ag(110) generally involves a displacement and a rotation of the molecules, which affects the electronic state of the Fe centers. The oxygen intercalation between FePc and the substrate is greatly obstructed by the steric hindrance in the high-density phases, to the point that a fraction of oblique phase molecules cannot change their position after oxidizing. Depending on the oxidation state and adsoption geometry, the STS spectra show clear differences in the Fe local density of states, which are mirrored in the XAS and XMCD experiments. Particularly, XMCD spectra of the oxidized phases reflect the distribution of FePc species (nonoxygenated, oxygenated-rotated, and oxygenated-unrotated) in the different cases. Sum rule analysis yields the effective spin (mseff) and orbital (mL) magnetic moments of Fe in the different FePc species. Upon oxygenation, the magnetic moment of FePc molecules increases about an order of magnitude, reaching mTOT ∼2.2 μB per Fe atom. © 2020 American Chemical Society.

  • Influence of 4f filling on electronic and magnetic properties of rare earth-Au surface compounds

    Fernandez L., Blanco-Rey M., Castrillo-Bodero R., Ilyn M., Ali K., Turco E., Corso M., Ormaza M., Gargiani P., Valbuena M.A., Mugarza A., Moras P., Sheverdyaeva P.M., Kundu A.K., Jugovac M., Laubschat C., Ortega J.E., Schiller F. Nanoscale; 12 (43): 22258 - 22267. 2020. 10.1039/d0nr04964f. IF: 6.895

    One-atom-thick rare-earth/noble metal (RE-NM) compounds are attractive materials to investigate two-dimensional magnetism, since they are easy to synthesize into a common RE-NM2 structure with high crystal perfection. Here we perform a comparative study of the GdAu2, HoAu2, and YbAu2 monolayer compounds grown on Au(111). We find the same atomic lattice quality and moiré superlattice periodicity in the three cases, but different electronic properties and magnetism. The YbAu2 monolayer reveals the characteristic electronic signatures of a mixed-valence configuration in the Yb atom. In contrast, GdAu2 and HoAu2 show the trivalent character of the rare-earth and ferromagnetic transitions below 22 K. Yet, the GdAu2 monolayer has an in-plane magnetic easy-axis, versus the out-of-plane one in HoAu2. The electronic bands of the two trivalent compounds are very similar, while the divalent YbAu2 monolayer exhibits different band features. In the latter, a strong 4f-5d hybridization is manifested in neatly resolved avoided crossings near the Fermi level. First principles theory points to a residual presence of empty 4f states, explaining the fluctuating valence of Yb in the YbAu2 monolayer. © The Royal Society of Chemistry.

  • Molecular Approach for Engineering Interfacial Interactions in Magnetic/Topological Insulator Heterostructures

    Cuxart M.G., Valbuena M.A., Robles R., Moreno C., Bonell F., Sauthier G., Imaz I., Xu H., Nistor C., Barla A., Gargiani P., Valvidares M., Maspoch D., Gambardella P., Valenzuela S.O., Mugarza A. ACS Nano; 14 (5): 6285 - 6294. 2020. 10.1021/acsnano.0c02498. IF: 14.588

    Controlling interfacial interactions in magnetic/topological insulator heterostructures is a major challenge for the emergence of novel spin-dependent electronic phenomena. As for any rational design of heterostructures that rely on proximity effects, one should ideally retain the overall properties of each component while tuning interactions at the interface. However, in most inorganic interfaces, interactions are too strong, consequently perturbing, and even quenching, both the magnetic moment and the topological surface states at each side of the interface. Here, we show that these properties can be preserved using ligand chemistry to tune the interaction of magnetic ions with the surface states. By depositing Co-based porphyrin and phthalocyanine monolayers on the surface of Bi2Te3 thin films, robust interfaces are formed that preserve undoped topological surface states as well as the pristine magnetic moment of the divalent Co ions. The selected ligands allow us to tune the interfacial hybridization within this weak interaction regime. These results, which are in stark contrast with the observed suppression of the surface state at the first quintuple layer of Bi2Se3 induced by the interaction with Co phthalocyanines, demonstrate the capability of planar metal-organic molecules to span interactions from the strong to the weak limit. © 2020 American Chemical Society.

  • Neutral Organic Radical Formation by Chemisorption on Metal Surfaces

    Ajayakumar M.R., Moreno C., Alcón I., Illas F., Rovira C., Veciana J., Bromley S.T., Mugarza A., Mas-Torrent M. Journal of Physical Chemistry Letters; 11 (10): 3897 - 3904. 2020. 10.1021/acs.jpclett.0c00269. IF: 6.710

    Organic radical monolayers (r-MLs) bonded to metal surfaces are potential materials for the development of molecular (spin)electronics. Typically, stable radicals bearing surface anchoring groups are used to generate r-MLs. Following a recent theoretical proposal based on a model system, we report the first experimental realization of a metal surface-induced r-ML, where a rationally chosen closed-shell precursor 3,5-dichloro-4-[bis(2,4,6-trichlorophenyl)methylen]cyclohexa-2,5-dien-1-one (1) transforms into a stable neutral open-shell species (1) via chemisorption on the Ag(111) surface. X-ray photoelectron spectroscopy reveals that the >C=O group of 1 reacts with the surface, forming a C-O-Ag linkage that induces an electronic rearrangement that transforms 1 to 1. We further show that surface reactivity is an important factor in this process whereby Au(111) is inert towards 1, whereas the Cu(111) surface leads to dehalogenation reactions. The radical nature of the Ag(111)-bound monolayer was further confirmed by angle-resolved photoelectron spectroscopy and electronic structure calculations, which provide evidence of the emergence of the singly occupied molecular orbital (SOMO) of 1. © 2020 American Chemical Society.

  • Stabilizing Edge Fluorination in Graphene Nanoribbons

    Panighel M., Quiroga S., Brandimarte P., Moreno C., Garcia-Lekue A., Vilas-Varela M., Rey D., Sauthier G., Ceballos G., Peña D., Mugarza A. ACS Nano; 14 (9): 11120 - 11129. 2020. 10.1021/acsnano.0c01837. IF: 14.588

    The on-surface synthesis of edge-functionalized graphene nanoribbons (GNRs) is challenged by the stability of the functional groups throughout the thermal reaction steps of the synthetic pathway. Edge fluorination is a particularly critical case in which the interaction with the catalytic substrate and intermediate products can induce the complete cleavage of the otherwise strong C-F bonds before the formation of the GNR. Here, we demonstrate how a rational design of the precursor can stabilize the functional group, enabling the synthesis of edge-fluorinated GNRs. The survival of the functionalization is demonstrated by tracking the structural and chemical transformations occurring at each reaction step with complementary X-ray photoelectron spectroscopy and scanning tunneling microscopy measurements. In contrast to previous attempts, we find that the C-F bond survives the cyclodehydrogenation of the intermediate polymers, leaving a thermal window where GNRs withhold more than 80% of the fluorine atoms. We attribute this enhanced stability of the C-F bond to the particular structure of our precursor, which prevents the cleavage of the C-F bond by avoiding interaction with the residual hydrogen originated in the cyclodehydrogenation. This structural protection of the linking bond could be implemented in the synthesis of other sp2-functionalized GNRs. © 2020 American Chemical Society.

  • Supergiant Barocaloric Effects in Acetoxy Silicone Rubber over a Wide Temperature Range: Great Potential for Solid-state Cooling

    Imamura W., Usuda É.O., Paixão L.S., Bom N.M., Gomes A.M., Carvalho A.M.G. Chinese Journal of Polymer Science (English Edition); 38 (9): 999 - 1005. 2020. 10.1007/s10118-020-2423-9. IF: 3.154

    Solid-state cooling based on caloric effects is considered a viable alternative to replace the conventional vapor-compression refrigeration systems. Regarding barocaloric materials, recent results show that elastomers are promising candidates for cooling applications around room-temperature. In the present paper, we report supergiant barocaloric effects observed in acetoxy silicone rubber—a very popular, low-cost and environmentally friendly elastomer. Huge values of adiabatic temperature change and reversible isothermal entropy change were obtained upon moderate applied pressures and relatively low strains. These huge barocaloric changes are associated both to the polymer chain rearrangements induced by confined compression and to the first-order structural transition. The results are comparable to the best barocaloric materials reported so far, opening encouraging prospects for the application of elastomers in near future solid-state cooling devices. © 2020, Chinese Chemical Society Institute of Chemistry, Chinese Academy of Sciences Springer-Verlag GmbH Germany, part of Springer Nature.

  • Waste Tire Rubber-based Refrigerants for Solid-state Cooling Devices

    Bom N.M., Usuda É.O., da Silva Gigliotti M., de Aguiar D.J.M., Imamura W., Paixão L.S., Carvalho A.M.G. Chinese Journal of Polymer Science (English Edition); 38 (7): 769 - 775. 2020. 10.1007/s10118-020-2385-y. IF: 3.154

    Management of discarded tires is a compelling environmental issue worldwide. Although there are several approaches developed to recycle waste tire rubbers, their application in solid-state cooling is still unexplored. Considering the high barocaloric potential verified for elastomers, the use of waste tire rubber (WTR) as a refrigerant in solid-state cooling devices is very promising. Herein, we investigated the barocaloric effects in WTR and polymer blends made of vulcanized natural rubber (VNR) and WTR, to evaluate its feasibility for solid-state cooling technologies. The adiabatic temperature changes and the isothermal entropy changes reach giant values, as well as the performance parameters, being comparable or even better than most barocaloric materials in literature. Moreover, pure WTR and WTR-based samples also present a faster thermal exchange than VNR, consisting of an additional advantage of using these discarded materials. Thus, the present findings evidence the encouraging perspectives of employing waste rubbers in solid-state cooling based on barocaloric effects, contributing to both the recycling of polymers and the sustainable energy technology field. © 2020, Chinese Chemical Society Institute of Chemistry, Chinese Academy of Sciences Springer-Verlag GmbH Germany, part of Springer Nature.


  • Critical Role of Phenyl Substitution and Catalytic Substrate in the Surface-Assisted Polymerization of Dibromobianthracene Derivatives

    Moreno C., Panighel M., Vilas-Varela M., Sauthier G., Tenorio M., Ceballos G., Peña D., Mugarza A. Chemistry of Materials; 31 (2): 331 - 341. 2019. 10.1021/acs.chemmater.8b03094. IF: 10.159

    Understanding the nature and hierarchy of on-surface reactions is a major challenge for designing coordination and covalent nanostructures by means of multistep synthetic routes. In particular, intermediates and final products are hard to predict since the reaction paths and their activation windows depend on the choice of both the molecular precursor design and the substrate. Here, we report a systematic study of the effect of the catalytic metal surface to reveal how a single precursor can give rise to very distinct polymers that range from coordination and covalent nonplanar polymer chains of distinct chirality to atomically precise graphene nanoribbons and nanoporous graphene. Our precursor consists on adding two phenyl substituents to 10,10′-dibromo-9,9′-bianthracene, a well-studied precursor in the on-surface synthesis of graphene nanoribbons. The critical role of the monomer design in the reaction paths is inferred from the fact that the phenyl substitution leads to very distinct products in each one of the studied metallic substrates. © 2018 American Chemical Society.

  • Nanoarquitecturas de grafeno con precisión atómica

    C. Moreno, A. Garcia-Lekue, A. Mugarza Revista Española de Física; 33 (4) 2019. noDOI-Moreno.

    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.

  • Polarization dependence of angle-resolved photoemission with submicron spatial resolution reveals emerging one-dimensionality of electrons in NbSe3

    Valbuena M.A., Chudzinski P., Pons S., Conejeros S., Alemany P., Canadell E., Berger H., Frantzeskakis E., Avila J., Asensio M.C., Giamarchi T., Grioni M. Physical Review B; 99 (7, 075118) 2019. 10.1103/PhysRevB.99.075118. IF: 3.736

    In materials with nearly commensurate band filling the electron liquid may spontaneously separate into components with distinct properties, yielding complex intra-and interunit cell ordering patterns and a reduced dimensionality. Polarization-dependent angle-resolved photoemission data with submicron spatial resolution demonstrate such an electronic self-organization in NbSe3, a compound considered to be a paradigm of charge order. The new data indicate the emergence of a novel order, and reveal the one-dimensional (1D) physics hidden in a material which naively could be considered the most three dimensional of all columnar chalcogenides. The 1D physics is evidenced by a new selection rule-in two polarizations we observe two strikingly different dispersions each closely resembling apparently contradicting results of previous studies of this material. © 2019 American Physical Society.

  • Unraveling the Impact of Halide Mixing on Perovskite Stability

    Hieulle J., Wang X., Stecker C., Son D.-Y., Qiu L., Ohmann R., Ono L.K., Mugarza A., Yan Y., Qi Y. Journal of the American Chemical Society; 141 (8): 3515 - 3523. 2019. 10.1021/jacs.8b11210. IF: 14.695

    Increasing the stability of perovskites is essential for their integration in commercial photovoltaic devices. Halide mixing is suggested as a powerful strategy toward stable perovskite materials. However, the stabilizing effect of the halides critically depends on their distribution in the mixed compound, a topic that is currently under intense debate. Here we successfully determine the exact location of the I and Cl anions in the CH 3 NH 3 PbBr 3-y I y and CH 3 NH 3 PbBr 3-z Cl z mixed halide perovskite lattices and correlate it with the enhanced stability we find for the latter. By combining scanning tunneling microscopy and density functional theory, we predict that, for low ratios, iodine and chlorine incorporation have different effects on the electronic properties and stability of the CH 3 NH 3 PbBr 3 perovskite material. In addition, we determine the optimal Cl incorporation ratio for stability increase without detrimental band gap modification, providing an important direction for the fabrication of stable perovskite devices. The increased material stability induced by chlorine incorporation is verified by performing photoelectron spectroscopy on a half-cell device architecture. Our findings provide an answer to the current debate on halide incorporation and demonstrate their direct influence on device stability. © Copyright 2019 American Chemical Society.


  • Bottom-up synthesis of multifunctional nanoporous graphene

    Moreno C., Vilas-Varela M., Kretz B., Garcia-Lekue A., Costache M.V., Paradinas M., Panighel M., Ceballos G., Valenzuela S.O., Peña D., Mugarza A. Science; 360 (6385): 199 - 203. 2018. 10.1126/science.aar2009. IF: 41.058

    Nanosize pores can turn semimetallic graphene into a semiconductor and, from being impermeable, into the most efficient molecular-sieve membrane. However, scaling the pores down to the nanometer, while fulfilling the tight structural constraints imposed by applications, represents an enormous challenge for present top-down strategies. Here we report a bottom-up method to synthesize nanoporous graphene comprising an ordered array of pores separated by ribbons, which can be tuned down to the 1-nanometer range. The size, density, morphology, and chemical composition of the pores are defined with atomic precision by the design of the molecular precursors. Our electronic characterization further reveals a highly anisotropic electronic structure, where orthogonal one-dimensional electronic bands with an energy gap of ∼1 electron volt coexist with confined pore states, making the nanoporous graphene a highly versatile semiconductor for simultaneous sieving and electrical sensing of molecular species. 2017 © The Authors

  • In-Situ Scrutiny of the Relationship between Polymorphic Phases and Properties of Self-Assembled Monolayers of a Biphenyl Based Thiol

    Paradinas M., Munuera C., Buck M., Ocal C. Journal of Physical Chemistry B; 122 (2): 657 - 665. 2018. 10.1021/acs.jpcb.7b05958. IF: 3.146

    Two polymorphic phases of ω-(4′-methylbiphenyl-4-yl) butane-1-thiol (BP4) molecules formed on Au(111) were investigated by multidimensional atomic force microscopy, combining conductivity measurements, electrostatic characterization, friction force mapping, and normal force spectroscopy. Based on the same molecular structure but differing in molecular order, packing density, and molecular tilt, the two phases serve as a test bench to establish the structure-property relationships in self-assembled monolayers (SAMs). From a detailed analysis of the charge transport and electrostatics, the contributions of geometrical and electronic effects to the tunneling are discussed. © 2017 American Chemical Society.

  • On-surface synthesis of superlattice arrays of ultra-long graphene nanoribbons

    Moreno C., Paradinas M., Vilas-Varela M., Panighel M., Ceballos G., Peña D., Mugarza A. Chemical Communications; 54 (68): 9402 - 9405. 2018. 10.1039/c8cc04830d. IF: 6.290

    We report the on-surface synthesis of graphene nanoribbon superlattice arrays directed by the herringbone reconstruction of the Au(111) surface. The uniaxial anisotropy of the zigzag pattern of the reconstruction defines a one dimensional grid for directing the Ullmann polymerization and inducing periodic arrays of parallel ultra-long nanoribbons (>100 nm), where the periodicity is varied with coverage at discrete values following a hierarchical templating behavior. © 2018 The Royal Society of Chemistry.

  • Pentacene/TiO2 Anatase Hybrid Interface Study by Scanning Probe Microscopy and First Principles Calculations

    Todorović M., Stetsovych O., Moreno C., Shimizu T.K., Custance O., Pérez R. ACS Applied Materials and Interfaces; 10 (40): 34718 - 34726. 2018. 10.1021/acsami.8b09203. IF: 8.097

    The understanding and control of the buried interface between functional materials in optoelectronic devices is key to improving device performance. We combined atomic resolution scanning probe microscopy with first-principles calculations to characterize the technologically relevant organic/inorganic interface structure between pentacene molecules and the TiO2 anatase (101) surface. A multipass atomic force microscopy imaging technique overcomes the technical challenge of imaging simultaneously the corrugated anatase substrate, molecular adsorbates, monolayers, and bilayers at the same level of detail. Submolecular resolution images revealed the orientation of the adsorbates with respect to the substrate and allowed direct insights into interface formation. Pentacene molecules were found to physisorb parallel to the anatase substrate in the first contact layer, passivating the surface and promoting bulk-like growth in further organic layers. While molecular electronic states were not significantly hybridized by the substrate, simulations predicted localized pathways for molecule-surface charge injection. The localized states were associated with the molecular lowest unoccupied molecular orbital inside the oxide conduction band, pointing to efficient transfer of photo-induced electron charge carriers across this interface in prospective photovoltaic devices. In uncovering the atomic arrangement and favorable electronic properties of the pentacene/anatase interface, our findings testify to the maturity and analytic power of our methodology in further studies of organic/inorganic interfaces. © 2018 American Chemical Society.

  • Real Space Demonstration of Induced Crystalline 3D Nanostructuration of Organic Layers

    Paradinas M., Pérez-Rodríguez A., Barrena E., Ocal C. Journal of Physical Chemistry B; 122 (2): 633 - 639. 2018. 10.1021/acs.jpcb.7b05342. IF: 3.146

    The controlled 3D nanostructuration of molecular layers of the semiconducting molecules C22H14 (pentacene) and N,N′-dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C8) is addressed. A tip-assisted method using atomic force microscopy (AFM) is developed for removing part of the organic material and relocating it in up to six layer thick nanostructures. Moreover, unconventional molecular scale imaging combining diverse friction force microscopy modes reveals the stacking sequence of the piled layers. In particular, we unambiguously achieve epitaxial growth, an issue of fundamental importance in thin film strategies for the nanostructuration of more efficient organic nanodevices. © 2017 American Chemical Society.

  • Structure and electronic states of vicinal Ag(111) surfaces with densely kinked steps

    Ortega J.E., Vasseur G., Piquero-Zulaica I., Matencio S., Valbuena M.A., Rault J.E., Schiller F., Corso M., Mugarza A., Lobo-Checa J. New Journal of Physics; 20 (7, 073010) 2018. 10.1088/1367-2630/aacbb7. IF: 3.579

    Vicinal surfaces exhibiting arrays of atomic steps are frequently investigated due to their diverse physical-chemical properties and their use as growth templates. However, surfaces featuring steps with a large number of low-coordinated kink-atoms have been widely ignored, despite their higher potential for chemistry and catalysis. Here, the equilibrium structure and the electronic states of vicinal Ag(111) surfaces with densely kinked steps are investigated in a systematic way using a curved crystal. With scanning tunneling microscopy we observe an exceptional structural homogeneity of this class of vicinals, reflected in the smooth probability distribution of terrace sizes at all vicinal angles. This allows us to observe, first, a subtle evolution of the terrace-size distribution as a function of the terrace-width that challenges statistical models of step lattices, and second, lattice fluctuations around resonant modes of surface states. As shown in angle resolved photoemission experiments, surface states undergo stronger scattering by fully-kinked step-edges, which triggers the full depletion of the two-dimensional band at surfaces with relatively small vicinal angles. © 2018 The Author(s). Published by IOP Publishing Ltd on behalf of Deutsche Physikalische Gesellschaft.

  • Towards microscopic control of the magnetic exchange coupling at the surface of a topological insulator

    Philipp Rüßmann, Sanjoy K Mahatha, Paolo Sessi, Miguel A Valbuena, Thomas Bathon, Kai Fauth, Sylvie Godey, Aitor Mugarza, Konstantin A Kokh, Oleg E Tereshchenko, Pierluigi Gargiani, Manuel Valvidares, Erika Jiménez, Nicholas B Brookes, Matthias Bode, Gustav Bihlmayer, Stefan Blügel, Phivos Mavropoulos, Carlo Carbone, Alessandro Barla Journal of Physics: Materials; 1 (1): 15002. 2018. 10.1088/2515-7639/aad02a.

    Magnetically doped topological insulators may produce novel states of electronic matter, where for instance the quantum anomalous Hall effect state can be realized. Pivotal to this goal is a microscopic control over the magnetic state, defined by the local electronic structure of the dopants and their interactions.Wereport on the magnetic coupling amongMnor Co atoms adsorbed on the surface of the topological insulator Bi2Te3. Our findings uncover the mechanisms of the exchange coupling between magnetic atoms coupled to the topological surface state in strong topological insulators. The combination of x-ray magnetic circular dichroism and ab initio calculations reveals that the sign of the magnetic coupling at short adatom–adatom distances is opposite forMnwith respect to Co. For both elements, the magnetic exchange reverses its sign at a critical distance between magnetic adatoms, as a result of the interplay between superexchange, double exchange and Ruderman–Kittel–Kasuya– Yoshida interactions.


  • Electronic Structure of Titanylphthalocyanine Layers on Ag(111)

    Lerch A., Fernandez L., Ilyn M., Gastaldo M., Paradinas M., Valbuena M.A., Mugarza A., Ibrahim A.B.M., Sundermeyer J., Höfer U., Schiller F. Journal of Physical Chemistry C; 121 (45): 25353 - 25363. 2017. 10.1021/acs.jpcc.7b09147. IF: 4.536

    We have investigated the electronic structures of axially oxo functionalized titanylphthalocyanine (TiOPc) on Ag(111) by X-ray and ultraviolet photoelectron spectroscopies, two-photon photoemission, X-ray absorption spectroscopy, and X-ray magnetic circular dichroism. Furthermore, we use complementary data of TiOPc on graphite and planar copper phthalocyanine (CuPc) on Ag(111) for a comparative analysis. Both molecules adsorb on Ag(111) in a parallel orientation to the surface, for TiOPc with an oxygen-up configuration. The interaction of nitrogen and carbon atoms with the substrate is similar for both molecules, while the bonding of the titanium atom to Ag(111) in the monolayer is found to be slightly more pronounced than in the CuPc case. Ultraviolet photoemission spectroscopy reveals an occupation of the lowest unoccupied molecular orbital (LUMO) level in monolayer thick TiOPc on Ag(111) related to the interaction of the molecules and the silver substrate. This molecule-metal interaction also causes an upward shift of the Ag(111) Shockley state that is transformed into an unoccupied interface state with energies of 0.23 and 0.33 eV for the TiOPc monolayer and bilayer, respectively, at the Brillouin zone center. © 2017 American Chemical Society.

  • Growth of Twin-Free and Low-Doped Topological Insulators on BaF2(111)

    Bonell F., Cuxart M.G., Song K., Robles R., Ordejón P., Roche S., Mugarza A., Valenzuela S.O. Crystal Growth and Design; 17 (9): 4655 - 4660. 2017. 10.1021/acs.cgd.7b00525. IF: 4.055

    We demonstrate the growth of twin-free Bi2Te3 and Sb2Te3 topological insulators by molecular beam epitaxy and a sizable reduction of the twin density in Bi2Se3 on lattice-matched BaF2(111) substrates. Using X-ray diffraction, electron diffraction and atomic force microscopy, we systematically investigate the parameters influencing the formation of twin domains and the morphology of the films, and show that Se- and Te-based alloys differ by their growth mechanism. Optimum growth parameters are shown to result in intrinsically low-doped films, as probed by angle-resolved photoelectron spectroscopy. In contrast to previous approaches in which twin-free Bi2Se3 films are achieved by increasing the substrate roughness, the quality of our Bi2Te3 is superior on the flattest BaF2 substrates. This finding indicates that, during nucleation, the films not only interact with the topmost atomic substrate layer but also with buried layers that provide the necessary stacking information to promote a single twin, an observation that is supported by ab initio calculations. © 2017 American Chemical Society.

  • Inductively coupled remote plasma-enhanced chemical vapor deposition (rPE-CVD) as a versatile route for the deposition of graphene micro- and nanostructures

    Cuxart M.G., Šics I., Goñi A.R., Pach E., Sauthier G., Paradinas M., Foerster M., Aballe L., Fernandez H.M., Carlino V., Pellegrin E. Carbon; 117: 331 - 342. 2017. 10.1016/j.carbon.2017.02.067. IF: 6.337

    Multiple layers of graphene thin films with micro-crystalline orientation and vertical graphene nano-sheets were grown on different substrates (i.e., polycrystalline nickel foil, Ni(111), highly oriented pyrolytic graphite) using a single-step process based on low-pressure remote Plasma-Enhanced Chemical Vapor Deposition (rPE-CVD). In contrast to previous studies, a novel basic approach to this technique including a new remote inductively coupled RF plasma source has been used to (i) minimize the orientational effect of the plasma electrical fields during the catalyst-free growth of graphene nano-sheets, (ii) warrant for a low graphene defect density via low plasma kinetics, (iii) decouple the dissociation process of the gas from the growth process of graphene on the substrate, (iv) tune the feedstock gas chemistry in view of improving the graphene growth, and (v) reduce the growth temperature as compared to conventional chemical vapor deposition (CVD). In order to study the various aspects of the rPE-CVD graphene growth modes and to assess the characteristics of the resulting graphene layers, Raman spectroscopy, XPS, SEM, and STM were used. The results give evidence for the successful performance of this new rPE-CVD plasma deposition source, that can be combined with in situ UHV-based processess for the production of, e. g., hybrid metal ferromagnet/graphene systems. © 2017 Elsevier Ltd

  • Kondo screening of the spin and orbital magnetic moments of Fe impurities in Cu

    Joly L., Kappler J.-P., Ohresser P., Sainctavit P., Henry Y., Gautier F., Schmerber G., Kim D.J., Goyhenex C., Bulou H., Bengone O., Kavich J., Gambardella P., Scheurer F. Physical Review B; 95 (4, 041108) 2017. 10.1103/PhysRevB.95.041108. IF: 3.836

    We use x-ray magnetic circular dichroism to evidence the effect of correlations on the local impurity magnetic moment in an archetypal Kondo system, namely, a dilute Cu:Fe alloy. Applying the sum rules on the Fe L2,3 absorption edges, the evolution of the spin and orbital moments across the Kondo temperature are determined separately. The spin moment presents a crossover from a nearly temperature-independent regime below the Kondo temperature to a paramagneticlike regime above. Conversely, the weak orbital moment shows a temperature-independent behavior in the whole temperature range, suggesting different Kondo screening temperature scales for the spin and orbital moments. © 2017 American Physical Society.

  • Partial oxidation in a dense phase sub-monolayer of Fe-phthalocyanine on Ag(110)

    Bartolomé E., Bartolomé J., Sedona F., Herrero-Albillos J., Lobo J., Piantek M., García L.M., Panighel M., Mugarza A., Sambi M., Bartolomé F. Solid State Phenomena; 257: 219 - 222. 2017. 10.4028/ IF: 0.493

    In this contribution we report on the structural and magnetic changes along a catalytic cycle of a new dense, “quasi-squared” FePc submonolayer phase (R3) evaporated on Ag(110). X-ray magnetic circular dichroism (XMCD) experiments at the Fe L2,3 edge were performed on four samples: the as-evaporated phase (R3), two differently oxygenated samples (OX1 and OX2) and the annealed phase (ANN). It is concluded that all characterized phases display planar anisotropy, and the values of ms eff/nh are one order of magnitude larger than mL/nh. By oxidation, the isotropic moment increases from 7.2 x 10-2 μB/hole to 1.8 x 10-1 μB/hole, which is about a factor of 2 smaller than the increase achieved for the low-density phase. © 2017 Trans Tech Publications, Switzerland.

  • Symmetry forbidden morphologies and domain boundaries in nanoscale graphene islands

    Parreiras S.O., Gastaldo M., Moreno C., Martins M.D., Garcia-Lekue A., Ceballos G., Paniago R., Mugarza A. 2D Materials; 4 (2, 025104) 2017. 10.1088/2053-1583/aa70fa. IF: 6.937

    The synthesis of graphene nanoislands with tailored quantum properties requires an atomic control of the morphology and crystal structure. As one reduces their size down to the nanometer scale, domain boundary and edge energetics, as well as nucleation and growth mechanisms impose different stability and kinetic landscape from that at the microscale. This offers the possibility to synthesize structures that are exclusive to the nanoscale, but also calls for fundamental growth studies in order to control them. By employing high-resolution scanning tunneling microscopy we elucidate the atomic stacking configurations, domain boundaries, and edge structure of graphene nanoislands grown on Ni(1 1 1) by CVD and post-annealed at different temperatures. We find a non-conventional multistep mechanism that separates the thermal regimes for growth, edge reconstruction, and final stacking configuration, leading to nanoisland morphologies that are incompatible with their stacking symmetry. Whole islands shift their stacking configuration during cooling down, and others present continuous transitions at the edges. A statistical analysis of the domain structures obtained at different annealing temperatures reveals how polycrystalline, ill-defined structures heal into shape-selected islands of a single predominant stacking. The high crystallinity and the control on morphology and edge structure makes these graphene nanoislands ideal for their application in optoelectronics and spintronics. © 2017 IOP Publishing Ltd.


  • Film Quality and Electronic Properties of a Surface-Anchored Metal-Organic Framework Revealed by using a Multi-technique Approach

    Liu J., Paradinas M., Heinke L., Buck M., Ocal C., Mugnaini V., Wöll C. ChemElectroChem; 3 (5): 713 - 718. 2016. 10.1002/celc.201500486. IF: 3.506

    The virtually unlimited versatility and unparalleled level of control in the design of metal-organic frameworks (MOFs) has recently been shown to also entail a potential for applications based on the electrical and electronic properties of this rich class of materials. At present, methods to provide reliable and reproducible contacts to MOF materials are scarce; therefore, we have carried out a detailed, multi-technique investigation of an empty and loaded prototype MOF, HKUST-1. Epitaxial thin films of this material grown on a substrate by using liquid-phase epitaxy have been studied by cyclic voltammetry, atomic force microscopy, and quartz crystal microbalance and their quality assessed. By using an ionic liquid as the electrolyte, it is shown that redox-active molecules like ferrocene can be embedded in the pores, enabling a change in the overall conductivity of the framework and the study of the redox chemistry of guest molecules inside the MOF. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  • High Temperature Ferromagnetism in a GdAg2 Monolayer

    Ormaza M., Fernández L., Ilyn M., Magana A., Xu B., Verstraete M.J., Gastaldo M., Valbuena M.A., Gargiani P., Mugarza A., Ayuela A., Vitali L., Blanco-Rey M., Schiller F., Ortega J.E. Nano Letters; 16 (7): 4230 - 4235. 2016. 10.1021/acs.nanolett.6b01197. IF: 13.779

    Materials that exhibit ferromagnetism, interfacial stability, and tunability are highly desired for the realization of emerging magnetoelectronic phenomena in heterostructures. Here we present the GdAg2 monolayer alloy, which possesses all such qualities. By combining X-ray absorption, Kerr effect, and angle-resolved photoemission with ab initio calculations, we have investigated the ferromagnetic nature of this class of Gd-based alloys. The Curie temperature can increase from 19 K in GdAu2 to a remarkably high 85 K in GdAg2. We find that the exchange coupling between Gd atoms is barely affected by their full coordination with noble metal atoms, and instead, magnetic coupling is effectively mediated by noble metal-Gd hybrid s,p-d bands. The direct comparison between isostructural GdAu2 and GdAg2 monolayers explains how the higher degree of surface confinement and electron occupation of such hybrid s,p-d bands promote the high Curie temperature in the latter. Finally, the chemical composition and structural robustness of the GdAg2 alloy has been demonstrated by interfacing them with organic semiconductors or magnetic nanodots. These results encourage systematic investigations of rare-earth/noble metal surface alloys and interfaces, in order to exploit them in magnetoelectronic applications. © 2016 American Chemical Society.

  • Manipulating the Topological Interface by Molecular Adsorbates: Adsorption of Co-Phthalocyanine on Bi2Se3

    Caputo M., Panighel M., Lisi S., Khalil L., Santo G.D., Papalazarou E., Hruban A., Konczykowski M., Krusin-Elbaum L., Aliev Z.S., Babanly M.B., Otrokov M.M., Politano A., Chulkov E.V., Arnau A., Marinova V., Das P.K., Fujii J., Vobornik I., Perfetti L., Mugarza A., Goldoni A., Marsi M. Nano Letters; 16 (6): 3409 - 3414. 2016. 10.1021/acs.nanolett.5b02635. IF: 13.779

    Topological insulators are a promising class of materials for applications in the field of spintronics. New perspectives in this field can arise from interfacing metal-organic molecules with the topological insulator spin-momentum locked surface states, which can be perturbed enhancing or suppressing spintronics-relevant properties such as spin coherence. Here we show results from an angle-resolved photemission spectroscopy (ARPES) and scanning tunnelling microscopy (STM) study of the prototypical cobalt phthalocyanine (CoPc)/Bi2Se3 interface. We demonstrate that that the hybrid interface can act on the topological protection of the surface and bury the Dirac cone below the first quintuple layer. © 2016 American Chemical Society.

  • Microfluidic pneumatic cages: A novel approach for in-chip crystal trapping, manipulation and controlled chemical treatment

    Abrishamkar A., Paradinas M., Bailo E., Rodriguez-Trujillo R., Pfattner R., Rossi R.M., Ocal C., Demello A.J., Amabilino D.B., Puigmartí-Luis J. Journal of Visualized Experiments; 2016 (113, e54193) 2016. 10.3791/54193. IF: 1.113

    The precise localization and controlled chemical treatment of structures on a surface are significant challenges for common laboratory technologies. Herein, we introduce a microfluidic-based technology, employing a double-layer microfluidic device, which can trap and localize in situ and ex situ synthesized structures on microfluidic channel surfaces. Crucially, we show how such a device can be used to conduct controlled chemical reactions onto on-chip trapped structures and we demonstrate how the synthetic pathway of a crystalline molecular material and its positioning inside a microfluidic channel can be precisely modified with this technology. This approach provides new opportunities for the controlled assembly of structures on surface and for their subsequent treatment. © 2016 Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

  • Misfit Dislocation Guided Topographic and Conduction Patterning in Complex Oxide Epitaxial Thin Films

    Sandiumenge F., Bagués N., Santiso J., Paradinas M., Pomar A., Konstantinovic Z., Ocal C., Balcells L., Casanove M.-J., Martínez B. Advanced Materials Interfaces; 3 (14, 1600106) 2016. 10.1002/admi.201600106. IF: 3.365

    Interfacial dissimilarity has emerged in recent years as the cornerstone of emergent interfacial phenomena, while enabling the control of electrical transport and magnetic behavior of complex oxide epitaxial films. As a step further toward the lateral miniaturization of functional nanostructures, this work uncovers the role of misfit dislocations in creating periodic surface strain patterns that can be efficiently used to control the spatial modulation of mass transport phenomena and bandwidth-dependent properties on a ≈20 nm length scale. The spontaneous formation of surface strain-relief patterns in La0.7Sr0.3MnO3/LaAlO3 films results in lateral periodic modulations of the surface chemical potential and tetragonal distortion, controlling the spatial distribution of preferential nucleation sites and the bandwidth of the epilayer, respectively. These results provide insights into the spontaneous formation of strain-driven ordered surface patterns, topographic and functional, during the growth of complex oxide heterostructures on lengths scales far below the limits achievable through top-down approaches. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

  • Superparamagnetism-induced mesoscopic electron focusing in topological insulators

    Sessi P., Rüßmann P., Bathon T., Barla A., Kokh K.A., Tereshchenko O.E., Fauth K., Mahatha S.K., Valbuena M.A., Godey S., Glott F., Mugarza A., Gargiani P., Valvidares M., Long N.H., Carbone C., Mavropoulos P., Blügel S., Bode M. Physical Review B; 94 (7, 075137) 2016. 10.1103/PhysRevB.94.075137. IF: 0.000

    Recently it has been shown that surface magnetic doping of topological insulators induces backscattering of Dirac states which are usually protected by time-reversal symmetry [Sessi, Nat. Commun. 5, 5349 (2014)10.1038/ncomms6349]. Here we report on quasiparticle interference measurements where, by improved Fermi level tuning, strongly focused interference patterns on surface Mn-doped Bi2Te3 could be directly observed by means of scanning tunneling microscopy at 4 K. Ab initio and model calculations reveal that their mesoscopic coherence relies on two prerequisites: (i) a hexagonal Fermi surface with large parallel segments (nesting) and (ii) magnetic dopants which couple to a high-spin state. Indeed, x-ray magnetic circular dichroism shows superparamagnetism even at very dilute Mn concentrations. Our findings provide evidence of strongly anisotropic Dirac-fermion-mediated interactions and demonstrate how spin information can be transmitted over long distances, allowing the design of experiments and devices based on coherent quantum effects in topological insulators. © 2016 American Physical Society.


  • Atomic species identification at the (101) anatase surface by simultaneous scanning tunnelling and atomic force microscopy

    Stetsovych O., Todorovi A.M., Shimizu T.K., Moreno C., Ryan J.W., León C.P., Sagisaka K., Palomares E., Matolín V., Fujita D., Perez R., Custance O. Nature Communications; 6 ( 7265) 2015. 10.1038/ncomms8265. IF: 11.470

    Anatase is a pivotal material in devices for energy-harvesting applications and catalysis. Methods for the accurate characterization of this reducible oxide at the atomic scale are critical in the exploration of outstanding properties for technological developments. Here we combine atomic force microscopy (AFM) and scanning tunnelling microscopy (STM), supported by first-principles calculations, for the simultaneous imaging and unambiguous identification of atomic species at the (101) anatase surface. We demonstrate that dynamic AFM-STM operation allows atomic resolution imaging within the materiala € s band gap. Based on key distinguishing features extracted from calculations and experiments, we identify candidates for the most common surface defects. Our results pave the way for the understanding of surface processes, like adsorption of metal dopants and photoactive molecules, that are fundamental for the catalytic and photovoltaic applications of anatase, and demonstrate the potential of dynamic AFM-STM for the characterization of wide band gap materials. © 2015 Macmillan Publishers Limited. All rights reserved.

  • Exchange bias of TbPc2 molecular magnets on antiferromagnetic FeMn and ferromagnetic Fe films

    Nistor C., Krull C., Mugarza A., Stepanow S., Stamm C., Soares M., Klyatskaya S., Ruben M., Gambardella P. Physical Review B - Condensed Matter and Materials Physics; 92 (18, 184402) 2015. 10.1103/PhysRevB.92.184402. IF: 3.736

    Improving the magnetic stability of single-molecule magnets is a key challenge facing molecular spintronics. We use x-ray magnetic circular dichroism to explore the possibility of magnetically stabilizing TbPc2 molecules by attaching them to ultrathin Fe and FeMn films. We show that TbPc2 deposited on antiferromagnetic FeMn films exhibits magnetic hysteresis and exchange bias as a consequence of coupling to the uncompensated interfacial Fe spins. The FeMn-thickness dependence of the coercive field and exchange bias of TbPc2 is similar to that of inorganic ferromagnetic/antiferromagnetic systems. The magnetic remanence is comparable with the fraction of molecules attached to pinned interfacial Fe spins. The Tb magnetic moments are antiferromagnetically coupled to the Fe thin films as well as to the uncompensated Fe spins at the FeMn interface. The sign of the coupling changes from antiferromagnetic to ferromagnetic after doping the interface with electron-donor Li atoms. ©2015 American Physical Society.

  • Giant reversible nanoscale piezoresistance at room temperature in Sr2IrO4 thin films

    Domingo N., López-Mir L., Paradinas M., Holy V., Železný J., Yi D., Suresha S.J., Liu J., Rayan Serrao C., Ramesh R., Ocal C., Martí X., Catalan G. Nanoscale; 7 (8): 3453 - 3459. 2015. 10.1039/c4nr06954d. IF: 7.394

    Layered iridates have been the subject of intense scrutiny on account of their unusually strong spin-orbit coupling, which opens up a narrow bandgap in a material that would otherwise be a metal. This insulating state is very sensitive to external perturbations. Here, we show that vertical compression at the nanoscale, delivered using the tip of a standard scanning probe microscope, is capable of inducing a five orders of magnitude change in the room temperature resistivity of Sr2IrO4. The extreme sensitivity of the electronic structure to anisotropic deformations opens up a new angle of interest on this material, with the giant and fully reversible perpendicular piezoresistance rendering iridates as promising materials for room temperature piezotronic devices. This journal is © The Royal Society of Chemistry.

  • Spin-flip and element-sensitive electron scattering in the BiAg2 surface alloy

    Schirone S., Krasovskii E.E., Bihlmayer G., Piquerel R., Gambardella P., Mugarza A. Physical Review Letters; 114 (16, 166801) 2015. 10.1103/PhysRevLett.114.166801. IF: 7.512

    Heavy metal surface alloys represent model systems to study the correlation between electron scattering, spin-orbit interaction, and atomic structure. Here, we investigate the electron scattering from the atomic steps of monolayer BiAg2 on Ag(111) using quasiparticle interference measurements and density functional theory. We find that intraband transitions between states of opposite spin projection can occur via a spin-flip backward scattering mechanism driven by the spin-orbit interaction. The spin-flip scattering amplitude depends on the chemical composition of the steps, leading to total confinement for pure Bi step edges, and considerable leakage for mixed Bi-Ag step edges. Additionally, the different localization of the occupied and unoccupied surface bands at Ag and Bi sites leads to a spatial shift of the scattering potential barrier at pure Bi step edges. © 2015 American Physical Society.

  • Substrate-induced stabilization and reconstruction of zigzag edges in graphene nanoislands on Ni(111)

    Garcia-Lekue A., Olle M., Sanchez-Portal D., Palacios J.J., Mugarza A., Ceballos G., Gambardella P. Journal of Physical Chemistry C; 119 (8): 4072 - 4078. 2015. 10.1021/jp511069y. IF: 4.772

    We combine experimental observations by scanning tunneling microscopy (STM) and density functional theory (DFT) to reveal the most stable edge structures of graphene on Ni(111) as well as the role of stacking-driven activation and suppression of edge reconstruction. Depending on the position of the outermost carbon atoms relative to hollow and on-top Ni sites, zigzag edges have very different energies. Triangular graphene nanoislands are exclusively bound by the more stable zigzag hollow edges. In hexagonal nanoislands, which are constrained by geometry to alternate zigzag hollow and zigzag top edges along their perimeter, only the hollow edge is stable, whereas the top edges spontaneously reconstruct into the (57) pentagon-heptagon structure. Atomically resolved STM images are consistent with either top-fcc or top-hcp epitaxial stacking of graphene and Ni sites, with the former being favored by DFT. Finally, we find that there is a one-to-one relationship between the edge type, graphene stacking, and orientation of the graphene islands. © 2015 American Chemical Society.


  • Coupling of single, double, and triple-decker metal-phthalocyanine complexes to ferromagnetic and antiferromagnetic substrates

    Lodi Rizzini, A.; Krull, C.; Mugarza, A.; Balashov, T.; Nistor, C.; Piquerel, R.; Klyatskaya, S.; Ruben, M.; Sheverdyaeva, P.M.; Moras, P.; Carbone, C.; Stamm, C.; Miedema, P.S.; Thakur, P.K.; Sessi, V.; Soares, M.; Yakhou-Harris, F.; Cezar, J.C.; Stepanow, S.; Gambardella, P. Surface Science; 630: 361 - 374. 2014. 10.1016/j.susc.2014.07.008. IF: 1.870

  • Fieldlike and antidamping spin-orbit torques in as-grown and annealed Ta/CoFeB/MgO layers

    Avci, C.O.; Garello, K.; Nistor, C.; Godey, S.; Ballesteros, B.; Mugarza, A.; Barla, A.; Valvidares, M.; Pellegrin, E.; Ghosh, A.; Miron, I.M.; Boulle, O.; Auffret, S.; Gaudin, G.; Gambardella, P. Physical Review B - Condensed Matter and Materials Physics; 89: 21 - 214419. 2014. 10.1103/PhysRevB.89.214419. IF: 3.664

  • Metallic thin films on stepped surfaces: lateral scattering of quantum well states

    Schiller, F. ; Abd El-Fattah, Z. M.; Schirone, S. ; Lobo-Checa, J. ; Urdanpilleta, M. ; Ruiz-Osés, M.; Cordón, J.; Corso, M.; Sanchez-Portal, D.; Mugarza, A. ; Ortega, J. E. New Journal of Physics; 16: 123025. 2014. 10.1088/1367-2630/16/12/12302. IF: 3.671

  • Spin tuning of electron-doped metal-phthalocyanine layers

    Stepanow, S.; Lodi Rizzini, A.; Krull, C.; Kavich, J.; Cezar, J.C.; Yakhou-Harris, F.; Sheverdyaeva, P.M.; Moras, P.; Carbone, C.; Ceballos, G.; Mugarza, A.; Gambardella, P. Journal of the American Chemical Society; 136 (14): 5451 - 5459. 2014. 10.1021/ja501204q. IF: 11.444

  • Spin-dependent electron scattering at graphene edges on Ni(111)

    Garcia-Lekue, A.; Balashov, T.; Olle, M.; Ceballos, G.; Arnau, A.; Gambardella, P.; Sanchez-Portal, D.; Mugarza, A. Physical Review Letters; 2014. 10.1103/PhysRevLett.112.066802. IF: 7.728

  • Structure and magnetism of Tm atoms and monolayers on W(110)

    Nistor, C.; Mugarza, A.; Stepanow, S.; Gambardella, P.; Kummer, K.; Diez-Ferrer, J.L.; Coffey, D.; de la Fuente, C.; Ciria, M.; Arnaudas, J.I. Physical Review B - Condensed Matter and Materials Physics; 2014. 10.1103/PhysRevB.90.064423. IF: 3.664


  • Scattering of surface electrons by isolated steps versus periodic step arrays

    Ortega, J.E.; Lobo-Checa, J.; Peschel, G.; Schirone, S.; Abd El-Fattah, Z.M.; Matena, M.; Schiller, F.; Borghetti, P.; Gambardella, P.; Mugarza, A. Physical Review B - Condensed Matter and Materials Physics; 87 2013. 10.1103/PhysRevB.87.115425. IF: 3.767

  • Site- and orbital-dependent charge donation and spin manipulation in electron-doped metal phthalocyanines

    Krull, C.; Robles, R.; Mugarza, A.; Gambardella, P. Nature Materials; 12: 337 - 343. 2013. 10.1038/nmat3547. IF: 35.749

  • Symmetry and magnitude of spin-orbit torques in ferromagnetic heterostructures

    Garello, K.; Miron, I.M.; Avci, C.O.; Freimuth, F.; Mokrousov, Y.; Blügel, S.; Auffret, S.; Boulle, O.; Gaudin, G.; Gambardella, P. Nature Nanotechnology; 8 (8): 587 - 593-593. 2013. 10.1038/nnano.2013.145. IF: 31.170


  • Effect of surface reconstruction on the photoemission cross-section of the Au(111) surface state

    Borghetti, P.; Lobo-Checa, J.; Goiri, E.; Mugarza, A.; Schiller, F.; Enrique Ortega, J.; Krasovskii, E.E. Journal of Physics Condensed Matter; 24 2012. 10.1088/0953-8984/24/39/395006.

  • Electronic and magnetic properties of molecule-metal interfaces: Transition-metal phthalocyanines adsorbed on Ag(100)

    Mugarza, A.; Robles, R.; Krull, C.; Korytár, R.; Lorente, N.; Gambardella, P. Physical Review B - Condensed Matter and Materials Physics; 85 2012. 10.1103/PhysRevB.85.155437.

  • Exchange biasing single molecule magnets: coupling of TbPc2 to antiferromagnetic layers

    A. Lodi Rizzini; C. Krull; T. Balashov; A. Mugarza; C. Nistor; F. Yakhou; V. Sessi; S. Klyatskaya; M. Ruben; S. Stepanow; P. Gambardella Nano Letters; 12: 5703. 2012.

  • Magnetization switching of an MgO/Co/Pt layer by in-plane current injection

    C. Onur Avci; K. Garello; I.M. Miron; G. Gaudin; S. Auffret; O. Boulle; P. Gambardella Applied Physics Letters; 100: 212404. 2012. .


  • Coupling Single Molecule Magnets to Ferromagnetic Substrates

    Lodi Rizzini, A. ; Krull, C. ; Balashov, T.; Kavich, J. J.; Mugarza, A.; Miedema, P. S.; Thakur, P. K.; Sessi, V.; Klyatskaya, S.; Ruben, M. ; Stepanow, S. ; Gambardella, P. Physical Review Letters; 2011. .

  • Determination of the photoelectron reference plane in nanostructured surfaces

    Lobo-Checa, J.; Mugarza, A.; Ortega, J.E.; Michel, E.G. New Journal of Physics; 13 2011. 10.1088/1367-2630/13/10/103013.

  • Localization, splitting, and mixing of field emission resonances induced by alkali metal clusters on Cu(100)

    Stepanow, S.; Mugarza, A.; Ceballos, G.; Gambardella, P.; Aldazabal, I.; Borisov, A.G.; Arnau, A. Physical Review B - Condensed Matter and Materials Physics; 83 2011. 10.1103/PhysRevB.83.115101.

  • Mixed-valence behavior and strong correlation effects of metal phthalocyanines adsorbed on metals

    Stepanow, S.; Miedema, P. S.; Mugarza, A.; Ceballos, G. ; Moras, P. ; Cezar, J. C.; Carbone, C. ; de Groot, F. M. F.; Gambardella, P. Physical Review B; 2011. .

  • Self-Assembled Nanometer-Scale Magnetic Networks on Surfaces: Fundamental Interactions and Functional Properties

    Carbone, C.; Gardonio, S.; Moras, P.; Lounis, S.; Heide, M.; Bihlmayer, G.; Atodiresei, N.; Heinz Dederichs, P.; Blügel, S.; Vlaic, S.; Lehnert, A.; Ouazi, S.; Rusponi, S.; Brune, H.; Honolka, J.; Enders, A.; Kern, K.; Stepanow, S.; Krull, C.; Balashov, T.; Mugarza, A.; Gambardella, P. Advanced Functional Materials; 2011. .

  • Spin coupling and relaxation inside molecule-metal contacts.

    Mugarza, A.; Krull, C.; Robles, R.; Stepanow, S.; Ceballos, G.; Gambardella, P. Nature Communications; 2 2011. 10.1038/ncomms1497.


  • Correlated electrons step by step: Itinerant-to-localized transition of fe impurities in free-electron metal hosts

    Carbone, C.; Veronese, M.; Moras, P.; Gardonio, S.; Grazioli, C.; Zhou, P.H.; Rader, O.; Varykhalov, A.; Krull, C.; Balashov, T.; Mugarza, A.; Gambardella, P.; Lebèque, S.; Eriksson, O.; Katsnelson, M.I.; Lichtenstein, A.I. Physical Review Letters; 104 2010. 10.1103/PhysRevLett.104.117601.

  • Effect of crystalline disorder on quantum tunneling in the single-molecule magnet Mn12 benzoate

    Carbonera, C.; Luis, F.; Campo, J.; Sánchez-Marcos, J.; Camón, A.; Chaboy, J.; Ruiz-Molina, D.; Imaz, I.; Van Slageren, J.; Dengler, S.; González, M. Physical Review B - Condensed Matter and Materials Physics; 81: 014427-1 - 014427-10. 2010. 10.1103/PhysRevB.81.014427.

  • Giant spin and orbital moment anisotropies of a Cu-phthalocyanine monolayer

    Stepanow, S.; Mugarza, A.; Ceballos, G.; Moras, P.; Cezar, J.C.; Carbone, C.; Gambardella, P. Physical Review B - Condensed Matter and Materials Physics; 82 2010. 10.1103/PhysRevB.82.014405.

  • Orbital specific chirality and homochiral self-assembly of achiral molecules induced by charge transfer and spontaneous symmetry breaking

    Mugarza A., Lorente N., Ordejón P., Krull C., Stepanow S., Bocquet M.-L., Fraxedas J., Ceballos G., Gambardella P. Physical Review Letters; 105 (11, 115702) 2010. 10.1103/PhysRevLett.105.115702.

    We study the electronic mechanisms underlying the induction and propagation of chirality in achiral molecules deposited on surfaces. Combined scanning tunneling microscopy and ab initio electronic structure calculations of Cu-phthalocyanines adsorbed on Ag(100) reveal the formation of chiral molecular orbitals in structurally undistorted molecules. This effect shows that chirality can be manifest exclusively at the electronic level due to asymmetric charge transfer between molecules and substrate. Single molecule chirality correlates with attractive van der Waals interactions, leading to the propagation of chirality at the supramolecular level. Ostwald ripening provides an efficient pathway for complete symmetry breaking and self-assembly of homochiral supramolecular layers. © 2010 The American Physical Society.


  • Direct evidence of imprinted vortex states in the antiferromagnet of exchange biased microdisks

    Salazar-Alvarez, G.; Kavich, J.J.; Sort, J.; Mugarza, A.; Stepanow, S.; Potenza, A.; Marchetto, H.; Dhesi, S.S.; Baltz, V.; Dieny, B.; Weber, A.; Heyderman, L.J.; Nogués, J.; Gambardella, P. Applied Physics Letters; 95 2009. 10.1063/1.3168515.

  • La ciencia de superficies: aplicación al estudio de la adsorción del agua

    Mugarza, A.; Herranz, T.; Salmeron, M. Revista Española de Física; 23: 17. 2009. .

  • Water growth on metal and oxids: binding, dissociation and the role of hydroxyl groups

    Salmeron, M.; Bluhm, H.; Tatarkhanov, M.; Kettler, G.; Shimizu, T.K.; Mugarza, A.; Deng, X.; Herranz, T. Faraday Discussions; 141: 221 - 229. 2009. 10.1039/B806516K.


  • Adsorption of water on O(2×2)/Ru(0001): Thermal stability and inhibition of dissociation

    Mugarza, A.; Shimizu, T.K.; Cabrera-Sanfelix, P.; Sánchez-Portal, D.; Arnau, A.; Salmeron, M. Journal of Physical Chemistry C; 112: 14052 - 14057. 2008. 10.1021/jp8026622.

  • Structure and reactions of carbon and hydrogen on Ru(0001): A scanning tunneling microscopy study

    Shimizu, T.K.; Mugarza, A.; Cerdá, J.I.; Salmeron, M. Journal of Chemical Physics; 129 2008. 10.1063/1.2991434.

  • Surface species formed by the adsorption and dissociation of water molecules on a Ru(0001) surface containing a small coverage of carbon atoms studied by scanning tunneling microscopy

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