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In angle-resolved photoemission (ARPES) from crystalline solids, wave-vector conservation applies to the two-dimensional (2D) surface, which may thus be defined as the reference plane in ARPES. We investigate whether such reference varies for photoemitted electrons in nanometer-sized systems that expose different crystal planes. To this aim, we exploit the structural tunability of the Ag/Cu(223) system which is capable of offering surfaces with periodic arrays of nanofacets of varying size and orientation. A thorough, photonenergy- dependent analysis of the surface states confined to such nanostructures is performed comparing different reference planes for photoemitted electrons. Assuming the premise that k|| must be a good quantum number for 2D states, we conclude that the (final state) photoelectron reference direction is not the average optical direction but the local facet that confines the (initial state) surface electrons. Moreover, in the general case of nanostructured systems with uneven surfaces, we show how the photoelectron reference plane can be empirically determined through such a photon-energy-dependent ARPES analysis ; JLC and AM acknowledge the Spanish Ministerio de Ciencia e Innovación (MICINN) for financial support through the research program Ramón y Cajal. JEO acknowledges support from the Spanish MICINN (MAT2010-21156-C03-01), the Basque Government (IT-257-07) and the DIPC (sabbatical program). EGM acknowledges support from the Spanish MICINN (FIS2008-00399)

In angle-resolved photoemission (ARPES) from crystalline solids, wave-vector conservation applies to the two-dimensional (2D) surface, which may thus be defined as the reference plane in ARPES. We investigate whether such reference varies for photoemitted electrons in nanometer-sized systems that expose different crystal planes. To this aim, we exploit the structural tunability of the Ag/Cu(223) system which is capable of offering surfaces with periodic arrays of nanofacets of varying size and orientation. A thorough, photonenergy- dependent analysis of the surface states confined to such nanostructures is performed comparing different reference planes for photoemitted electrons. Assuming the premise that k|| must be a good quantum number for 2D states, we conclude that the (final state) photoelectron reference direction is not the average optical direction but the local facet that confines the (initial state) surface electrons. Moreover, in the general case of nanostructured systems with uneven surfaces, we show how the photoelectron reference plane can be empirically determined through such a photon-energy-dependent ARPES analysis ; JLC and AM acknowledge the Spanish Ministerio de Ciencia e Innovación (MICINN) for financial support through the research program Ramón y Cajal. JEO acknowledges support from the Spanish MICINN (MAT2010-21156-C03-01), the Basque Government (IT-257-07) and the DIPC (sabbatical program). EGM acknowledges support from the Spanish MICINN (FIS2008-00399)

In angle-resolved photoemission (ARPES) from crystalline solids, wave-vector conservation applies to the two-dimensional (2D) surface, which may thus be defined as the reference plane in ARPES. We investigate whether such reference varies for photoemitted electrons in nanometer-sized systems that expose different crystal planes. To this aim, we exploit the structural tunability of the Ag/Cu(223) system which is capable of offering surfaces with periodic arrays of nanofacets of varying size and orientation. A thorough, photonenergy- dependent analysis of the surface states confined to such nanostructures is performed comparing different reference planes for photoemitted electrons. Assuming the premise that k|| must be a good quantum number for 2D states, we conclude that the (final state) photoelectron reference direction is not the average optical direction but the local facet that confines the (initial state) surface electrons. Moreover, in the general case of nanostructured systems with uneven surfaces, we show how the photoelectron reference plane can be empirically determined through such a photon-energy-dependent ARPES analysis. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. ; JLC and AM acknowledge the Spanish Ministerio de Ciencia e Innovación (MICINN) for financial support through the research program Ramón y Cajal. JEO acknowledges support from the Spanish MICINN (MAT2010-21156-C03-01), the Basque Government (IT-257-07) and the DIPC (sabbatical program). EGM acknowledges support from the Spanish MICINN (FIS2008-00399). ; Peer Reviewed

The photoemission cross-section of Shockley states of Cu(111) and Ag(111) surfaces is studied over a wide range of photon energies. The constant initial-state spectra are very different for the two surfaces and show rich structure that does not follow the generally accepted nearly free electron model for the final state. Angle resolved photoemission data are interpreted within a one-step ab initio theory, revealing a multiple Bloch wave structure of photoemission final states. The inelastic scattering parameter—optical potential—is determined, and the energy dependence of the mean free path of the outgoing electron is calculated, which turns out to be the key for the understanding of the photoemission cross-section curve. These are essential steps for future exploration of wave function perturbations in the presence of surface nanostructures ; This work was supported by the Spanish Ministerio de Ciencia e Innovación (Grants No. FIS2010-19609-C02-02, FIS2008- 00399, MAT2010-21156-C03-01, and MAT2010-21156-C03-02 and through the Research Program Ramón y Cajal) and the Basque Government (IT-257-07). The SRC is funded by the National Science Foundation (Award No. DMR-0084402)

The photoemission cross-section of Shockley states of Cu(111) and Ag(111) surfaces is studied over a wide range of photon energies. The constant initial-state spectra are very different for the two surfaces and show rich structure that does not follow the generally accepted nearly free electron model for the final state. Angle resolved photoemission data are interpreted within a one-step ab initio theory, revealing a multiple Bloch wave structure of photoemission final states. The inelastic scattering parameter-optical potential-is determined, and the energy dependence of the mean free path of the outgoing electron is calculated, which turns out to be the key for the understanding of the photoemission cross-section curve. These are essential steps for future exploration of wave function perturbations in the presence of surface nanostructures. 2011 American Physical Society. ; This work was supported by the Spanish Ministerio de Ciencia e Innovación (Grants No. FIS2010-19609-C02-02, FIS2008-00399, MAT2010-21156-C03-01, and MAT2010-21156-C03-02 and through the Research Program Ramón y Cajal) and the Basque Government (IT-257-07). The SRC is funded by the National Science Foundation (Award No. DMR-0084402). ; Peer Reviewed

Communication.-- et al. ; A 2D array of electronically coupled quantum boxes is fabricated by means of on-surface self-assembly assuring ultimate precision of each box. The quantum states embedded in the boxes are configured by adsorbates, whose occupancy is controlled with atomic precision. The electronic interbox coupling can be maintained or significantly reduced by proper arrangement of empty and filled boxes. ; The authors would like to acknowledge financial support from the Swiss Nanoscience Institute (SNI), Swiss National Science Foundation (Grants Nos. 200020-149713 and 206021-121461), the Spanish Ministry of Economy (Grant No. MAT2013-46593-C6-4-P), the Basque Government (Grant No. IT621-13), the São Paulo Research Foundation (Grant No. 2013/04855-0), Swiss Government Excellence Scholarship Program, Netherlands Organization for Scientific Research NWO (Chemical Sciences, VIDI-Grant No. 700.10.424), the European Research Council (ERC-2012-StG 307760-SURFPRO), University of Basel, University of Heidelberg, Linköping University, University of Groningen, Paul Scherrer Institute, and the Japan Science and Technology Agency (JST) "Precursory Research for Embryonic Science and Technology (PRESTO)" for a project of "Molecular technology and creation of new function." ; Peer Reviewed

This is an open access article published under an ACS AuthorChoice License.-- et al. ; The tunable properties of molecular materials place them among the favorites for a variety of future generation devices. In addition, to maintain the current trend of miniaturization of those devices, a departure from the present top-down production methods may soon be required and self-assembly appears among the most promising alternatives. On-surface synthesis unites the promises of molecular materials and of self-assembly, with the sturdiness of covalently bonded structures: An ideal scenario for future applications. Following this idea, we report the synthesis of functional extended nanowires by self-assembly. In particular, the products correspond to one-dimensional organic semiconductors. The uniaxial alignment provided by our substrate templates allows us to access with exquisite detail their electronic properties, including the full valence band dispersion, by combining local probes with spatial averaging techniques. We show how, by selectively doping the molecular precursors, the product's energy level alignment can be tuned without compromising the charge carrier's mobility. ; This work was partially funded by MIUR (PRIN 2010/11, Project 2010BNZ3F2: "DESCARTES"), by EU project PAMS (Agreement No. 610446), by the European Research Council (ERC) under the EU Horizon 2020 research and innovation programme (Grant Agreement No. 635919), by the European Community's Seventh Framework Programme (FP7/2007-2013) CALIPSO under Grant Agreement No. 312284, by the Spanish Ministry of Science and Competitiveness (MINECO, MAT2013-46593-C6-6-P and MAT2013-46593-C6-4-P) and FEDER, by the Basque Government (Grant Nos. IT-621-13 and IT-627-13)) and by the University of Padova (Grant CPDA154322, Project AMNES). ; Peer Reviewed

Two-dimensional organic and metal-organic nanoporous networks can scatter surface electrons, leading to their partial localization. Such quantum states are related to intrinsic surface states of the substrate material. We further corroborate this relation by studying the thermally induced energy shifts of the electronic band stemming from coupled quantum states hosted in a metal-organic array formed by a perylene derivative on Cu(111). We observe by angle-resolved photoemission spectroscopy (ARPES), that both, the Shockley and the partially localized states, shift by the same amount to higher binding energies upon decreasing the sample temperature, providing evidence of their common origin. Our experimental approach and results further support the use of surface states for modelling these systems, which are expected to provide new insight into the physics concerning partially confined electronic states: scattering processes, potential barrier strengths, excited state lifetimes or the influence of guest molecules. ; We acknowledge financial support from the Spanish Ministry of Economy (grant MAT2013-46593-C6-4-P), the Basque Government (grant IT621-13), the Spanish Research Council (CSIC-201560I022), the Swiss Nanoscience Institute (SNI), Swiss National Science Foundation (grants Nos. 200020-149713, 206021-121461), the Netherlands Organization for Scientific Research (NWO Vidi grant No. 700.10.424), the European Research Council (ERC-2012-StG 307760-SURFPRO) and the Paul Scherrer Institute. ; Peer Reviewed

Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. ; The fields of organic electronics and spintronics have the potential to revolutionize the electronics industry. Finding the right materials that can retain their electrical and spin properties when combined is a technological and fundamental challenge. We carry out the study of three archetypal organic molecules in intimate contact with the BiAg2 surface alloy. We show that the BiAg2 alloy is an especially suited substrate due to its inertness as support for molecular films, exhibiting an almost complete absence of substrate-molecular interactions. This is inferred from the persistence of a completely unaltered giant spin-orbit split surface state of the BiAg 2 substrate, and from the absence of significant metallic screening of charged molecular levels in the organic layer. Spin-orbit split states in BiAg2 turn out to be far more robust to organic overlayers than previously thought. © 2014 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. ; This work is supported by the Spanish Ministerio de Economia y Competitividad (MAT2010-21156-C03-01, PIB2010US-00652), by the Basque Government (IT-257-07), and the Deutsche Forschungsgemeinschaft through the SFB 616 'Energy Dissipation at Surfaces'. MCC additionally thanks the Studienstiftung des deutschen Volkes for support. MCC, JS, CAB and RM would like to thank the DFG for support within the program 'open access publizieren'. ; Peer Reviewed

Vicinal surfaces may undergo structural transformations as a function of temperature or in the presence of adsorbates. Step-doubling in which monatomic steps pair up forming double-atom high staircases is the simplest example. Here we investigate the case of Ni(111) using a curved crystal surface, which allows us to explore the occurrence of step-doubling as a function of temperature and vicinal plane (miscut α and step type). We find a striking A-type ({100}-like microfacets) versus B-type ({111}-like) asymmetry toward step-doubling. The terrace-width distribution analysis performed from scanning tunneling microscopy data points to elastic step interactions overcoming entropic effects at very small miscut α in A-type vicinals, as compared to B-type steps. For A-type vicinals, we elaborate the temperature/miscut phase diagram, on which we establish a critical miscut αc = 9.3° for step-doubling to take place. ; We acknowledge financial support from the Spanish Ministry of Economy (Grant MAT2013-46593-C6-4-P) and Basque Government (Grant IT621-13). ; Peer Reviewed

This work is licensed under a Creative Commons Attribution 4.0 International License.-- et al. ; Surface chemistry and catalysis studies could significantly gain from the systematic variation of surface active sites, tested under the very same conditions. Curved crystals are excellent platforms to perform such systematics, which may in turn allow to better resolve fundamental properties and reveal new phenomena. This is demonstrated here for the carbon monoxide/platinum system. We curve a platinum crystal around the high-symmetry (111) direction and carry out photoemission scans on top. This renders the spatial core-level imaging of carbon monoxide adsorbed on a 'tunable' vicinal surface, allowing a straightforward visualization of the rich chemisorption phenomenology at steps and terraces. Through such photoemission images we probe a characteristic elastic strain variation at stepped surfaces, and unveil subtle stress-release effects on clean and covered vicinal surfaces. These results offer the prospect of applying the curved surface approach to rationally investigate the chemical activity of surfaces under real pressure conditions. ; We acknowledge financial support from the Spanish Ministry of Economy (Grants MAT2013-46593-C6-4-P and MAT2013-46593-C6-2-P ), Basque Government (Grants IT621-13 and IT756-13). A.L.W. acknowledges support from the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-SC0012704. AXBR acknowledges support from the Basque Departamento de Educación and the UPV/EHU through the Zabalduz program. AXBR, PCS and DSP acknowledge the Deutsche Forschungsgemeinschaft through the Sonderforschungsbereich 1083. ; Peer Reviewed

7 páginas, 5 figuras, 3 tablas.-- El pdf del artículo es la versión pre-print. ; A novel approach of identifying metal atoms within a metal–organic surface coordination network using scanning tunnelling microscopy (STM) is presented. The Cu adatoms coordinated in the porous surface network of 1,3,8,10-tetraazaperopyrene (TAPP) molecules on a Cu(111) surface give rise to a characteristic electronic resonance in STM experiments. Using density functional theory calculations, we provide strong evidence that this resonance is a fingerprint of the interaction between the molecules and the Cu adatoms. We also show that the bonding of the Cu adatoms to the organic exodentate ligands is characterised by both the mixing of the nitrogen lone-pair orbitals of TAPP with states on the Cu adatoms and the partial filling of the lowest unoccupied molecular orbital (LUMO) of the TAPP molecule. Furthermore, the key interactions determining the surface unit cell of the network are discussed. ; This work was financially supported by the European Union through the Marie Curie Research Training Network PRAIRIES (MRTN-CT-2006-035810). Support from the Swiss National Science Foundation, the National Center of Competence in Research (NCCR) ''Nanoscale Science'' and the Wolfermann Naegeli Stiftung is also acknowledged. MP is also grateful for support from the Swedish Research Council (VR). ; Peer reviewed

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

The electronic character of a π-conjugated molecular overlayer on a metal surface can change from semiconducting to metallic, depending on how molecular orbitals arrange with respect to the electrodes Fermi level. Molecular level alignment is thus a key property that strongly influences the performance of organic-based devices. In this work, we report how the electronic level alignment of copper phthalocyanines on metal surfaces can be tailored by controlling the substrate work function. We even show the way to finely tune it for one fixed phthalocyanine-metal combination without the need to intercalate substrate-functionalizing buffer layers. Instead, the work function is trimmed by appropriate design of the phthalocyanines supramolecular environment, such that charge transfer into empty molecular levels can be triggered across the metal-organic interface. These intriguing observations are the outcome of a powerful combination of surface-sensitive electron spectroscopies, which further reveal a number of characteristic spectroscopic fingerprints of a lifted LUMO degeneracy associated with the partial phthalocyanine charging. ; This work was supported by the Spanish Grant Nos. MAT2010-21156-C03-01, PIB2010US-00652, and the Basque Government Grant No. IT-621-13. We acknowledge funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under Grant No. 226716. ; Peer Reviewed

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY).-- et al. ; Codeposition of two molecular species [copper phtalocyanine (CuPc, donor) and perfluoropentacene (PFP, acceptor)] on noble metal (111) surfaces leads to the self-assembly of an ordered mixed layer with a maximized donor-acceptor contact area. The main driving force behind this arrangement is assumed to be the intermolecular C-Hâ̄F hydrogen-bond interactions. Such interactions would be maximized for a coplanar molecular arrangement. However, precise measurement of molecule-substrate distances in the molecular mixture reveals significantly larger adsorption heights for PFP than for CuPc. Most surprisingly, instead of leveling to increase hydrogen-bond interactions, the height difference is enhanced in the blends as compared to the heights found in single-component CuPc and PFP layers. The increased height of PFP in mixed layers points to an overall reduced interaction with the underlying substrate, and its influence on electronic properties like the interface dipole is investigated through work function measurements. © 2014 American Physical Society. ; This work was supported by the Spanish Grants No. MAT2010-21156-C03-01 and-C03-03, as well as No. PIB2010US-00652, and by the Basque Government (Grant No. IT-621-13). D. G. O. acknowledges support from the European Union under Grant No. FP7-PEOPLE-2010-IOF-271909. We acknowledge funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under Grant No. 226716. ; Peer Reviewed