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Trabajo presentado al International Workshop on Spintronics, celebrado en San Carlos de Bariloche, Río Negro (Argentina) del 6 al 11 de noviembre de 2022., Topological insulators are a recently discovered class of materials exhibiting interesting properties for applications such as quantum computation devices. Recently, metal-organic frameworks (MOF) have been theoretically proposed as the organic counterpart of topological insulators. Despite the experimental achievement of several of the proposed MOFs, their edge state visualization, which is the fingerprint of 2D topological insulator, remains elusive. We have formed these proposed MOFs with expected topological insulator character using 9,10-dicyanoanthracene molecules and Cu, Fe and Co adatoms on a the three (111) noble metal substrates. The lattices generally extend throughout the surface as single-domain and exhibit an almost perfect order. By means of scanning tunneling spectroscopy and angle-resolved photoemission spectroscopy we studied their electronic structure, and commonly find total absence of an edge state despite the excellent network order. Functionalized tip measurements and tight-binding calculations suggest that structural asymmetries drive the networks into a topologically trivial case that destroys its edge state. However, we observe an edge state emerging when the SOC of the coordination atom is significantly increased. Thus, we present the first experimental evidence compatible with the Organic Topological Insulator prediction., PID2019-107338RB-C64, RED2018-102833-T, financiado porMCIN/AEI /10.13039/501100011033 Regional Government of Aragon (E12-20R). European Research Council under European Union’s Horizon 2020 research and innovation programme of Marie Skłodowska-Curie grant agreementULTIMATE-I Nº 101007825 Access to STM instruments: LMA-University of Zaragoza

Resumen del trabajo presentado al Joint European Magnetic Symposia (JEMS), celebrado en Warsaw (Poland) del 24 al 29 de julio de 2022.

Trabajo presentado en 20th Trends in Nanotechnology International Conference (2019), celebrada en San Sebastián (España), del 30 de septiembre al 4 de octubre de 2019, In the early 1900’s Fritz Ullmann first reported the synthesis of biaryls from aryl halides mediated by a fine copper powder1 , demonstrating with this the aromatic nucleophilic substitution mediated by copper, now known as Ullmann condensation reaction. More than hundred years after, this reaction is routinely used in numerous industrial applications and, nowadays it becomes widely used for the synthesis on metal surfaces of atomically precise graphene nanoribbons2 The next step to move toward device applications requires performing the synthesis directly on suitable substrates such as semiconducting, insulating or magnetic substrates. Whit in this context, in the present work we explore the Ullmann based synthesis of polymers on magnetic and insulating substrates. In particular we demonstrate the aryl homocoupling synthesis of 4,4-Dibromo (or diiodo)-p-terphenyl precursor into molecular poly-p-phenylene wires on the semiconductor TiO2 surface3 and on the bimetallic (and ferromagnetic) GdAu2 surface alloy4 . Moreover, we propose a reaction pathway during the polymerization. To monitor the chemical reaction complementary microscopic and spectroscopic surface science techniques (, scanning tunneling microscopy, X-ray photoemission spectroscopy, angle-resolved Photoemission spectroscopy) are used.

Trabajo presentado en el X Iberian Conference on Tribology y XI Iberian Vacuum Conference (IBERTRIVA) celebrada en Sevilla (España), del 26 al 28 de junio de 2019, In the early 1900’s Fritz Ullmann first reported the synthesis of biaryls from aryl halides mediated by a fine copper powder , demonstrating with this the aromatic nucleophilic substitution mediated by copper, now known as Ullmann condensation reaction. More than hundred years after, this reaction is routinely used in numerous industrial applications and, nowadays it becomes widely used for the synthesis on metal surfaces of atomically precise graphene nanoribbons The next step to move toward device applications requires performing the synthesis directly on suitable substrates such as semiconducting, insulating or magnetic substrates. Whit in this context, in the present work we explore the Ullmann based synthesis of polymers on magnetic and insulating substrates. In particular we demonstrate the aryl homocoupling synthesis of 4,4- Dibromo (or diiodo)-p-terphenyl precursor into molecular poly-p-phenylene wires on the semiconductor TiO2 surface3 and on the bimetallic (and ferromagnetic) GdAu2 surface alloy4 . Moreover, we propose a reaction pathway during the polymerization. To monitor the chemical reaction complementary microscopic and spectroscopic surface science techniques (, scanning tunneling microscopy, X-ray photoemission spectroscopy, angle-resolved Photoemission spectroscopy) are used.

Trabajo presentado al IX AUSE Congress and IV ALBA User's Meeting, celebrados en Barcelona (España) del 8 al 11 de octubre de 2019., MINECO MAT2016-78293-C6; EFA 194/16 (TNSI, (FEDER, EU).

Resumen del trabajo presentado a la XXXVII Reunión Bienal de la Real Sociedad Española de Física celebrada en Zaragoza del 15 al 19 de julio de 2019., The achievement of single atom arrays is key to new fundamental properties that lead to exciting physical properties, like for instance single-atom magnets. However, the resulting position of these atoms has a strong dependence on the supporting substrate and the system temperature. Liquid helium temperatures are required to freeze the atoms, which are often found random sites. A way to generate precise arrays of single atoms stable up to room temperature is the growth of self-assembled metalorganic coordination networks (MOCN) using organic molecules as spacers. Here, by means of STM/STS we probe the electronic properties of different single coordinating atoms embedded in an array di-cyano anthracene (DCA) molecules formed upon the three (111) noble metal surfaces. We have achieved these spontaneously formed MOCN using Fe, Co or Cu (see Fig. 1). We observe distinct spectroscopic fingerprints in the LDOS that leads to shifts of the molecular LUMO levels and relevant surface state pore confinements. We will discuss the effect that the different chemical species and the substrate have on the overall electronic properties of the system.

Resumen del trabajo presentado a la 8th International Conference on Scanning Probe Spectroscopy (SPS), celebrada en Hamburgo (Alemania) del 17 al 20 de junio de 2019., On-surface synthesized Graphene nanoribbons (GNRs) and oligophenylene chains provide a vast playground for developing organic semiconductors with distinct electronic properties. Studies on aligned poly-(paraphenylene) and armchair-GNRs resulted in highly dispersive electronic bands with large HOMO-LUMO gap. However, generating non-straight atomically precise and per fectly aligned chains allows us to go beyond the use of local techniques (STS) and complement it with averaging techniques (ARPES). Combining on-surface synthesis processes and the use of vicinal Ag(111) surfaces we achieved the formation of a monolayer of poly-(metaphenylene) (PMP) zigzag chains for the first time. We use STS and ARPES techniques to unraveled the band structure and HOMO-LUMO gap of zigzag chains. We find that the electronic structure presents weakly dispersive bands with an increase of its gap that is compatible with 1D electron confinement within straight sections. Both magnitudes are observed to vary with the straight section length following a 1/N tendency. These results, supported with DFT calculations, suggest a strong tunability of the polymer’s electronic properties that can be correlated to its topology.

Resumen del trabajo presentado a la XXXVII Reunión Bienal de la Real Sociedad Española de Física celebrada en Zaragoza del 15 al 19 de julio de 2019., Nanostructured Fe clusters whose atoms have a low average coordination number are expected to present enhanced orbital magnetic moment and anisotropy. Metal-organic interactions exhibit custom reversibility in bond formation that may result in large and extended self-assembled structures. Under ultra-high vacuum conditions, we use a Cu(111) monocrystal as substrate and generate an extended metalorganic network that fully covers its surface, which is stable at room temperature. When Fe is evaporated onto this molecular array, instead of the usual triangular bi-layer islands, single atomic height nanoclusters are formed (Fig. 1). The obtained structures are characterized as a function of coverage and temperature by means of Scanning Tunneling Microscopy. We find that both parameters affect the resulting nanodot sizes implying that a certain control can be exerted on its fabrication. Moreover, X-ray Magnetic Circular Dichroism experiments onto these samples show that the Fe nanostructures, which are stable at room temperature, significantly change the magnetic anisotropy compared to the case when the molecular layer is missing.

Trabajo presentado al 32nd Symposium on Surface Science (3S'19), celebrado en Baqueira Beret, Lleida (España) del 10 al 16 de marzo de 2019., Support by the Spanish Ministry of Economy, Industry and Competitiveness (MINECO, Grant No. MAT2016-78293-C6-6-R) from the regional Government of Aragón (RASMIA project) and from the European Regional Development Fund (ERDF) under the program Interreg V-A España-Francia-Andorra (Contract No. EFA 194/16 TNSI) is thankfully acknowledged.

Trabajo presentado a la X Iberian Conference on Tribology y a la XI Iberian Vacuum Conference (IBERTRIVA), celebradas en Sevilla (España) del 26 al 28 de junio de 2019.

Trabajo presentado a la XXXVII Reunión Bienal de la Real Sociedad Española de Física celebrada en Zaragoza del 15 al 19 de julio de 2019., Organic nanoporous networks grown on (111) noble metal surfaces, also referred to as quantum dot arrays since they can confine surface state electrons, are highly successful model systems to study scattering phenomena. On such surfaces, the 2D molecular scaffolds, commonly exhibit an upward energy shift of the Shockley state and the formation of shallow bands, which results from the repulsive scattering at the molecular walls and partial quantum confinement within each nanodot. In this work, we present experimental evidence of a tunable downward energy shift through scalable metalorganic nanoporous networks grown on Au(111). The electronic structure is determined by two state-ofthe- art, highly complementary techniques (STM and ARPES), and supported by first principles and model calculation. Notably, the counterintuitive downshift is gradual with decreasing pore size and increasing adatom density, something that cannot be explained through standard quantum confinement in the molecular cavity. Therefore we assign the origin of this effect to metal-organic overlayer-substrate interactions in the form of adatom-surface state hybridizations. This local coupling keeps the Shockley state nature, but renormalizes it, thereby changing its fundamental energy and effective mass. The absence to date of the experimental band structure resulting from single adatom metal-coordinated nanoporous networks has precluded the observation of the significant surface state renormalization we have observed.

Resumen del trabajo presentado al Joint Meeting of the DPG and EPS Condensed Matter Divisions (CMD27), celebrado en Berlin (Alemania) del 11 al 16 de marzo de 2018., Quantum dot (QD) arrays on surfaces, in the form of nanoporous networks, are candidates for studying fundamental physical phenomena such as 2DEG confinement. Tunability has been accomplished by varying the pore size, geometrical shape and molecule substrate interactions. Moreover, inter-dot coupling is validated by photoemission through the generation of new dispersive bands and modulated through thermodynamics and the condensation of guest elements. Here, we validate the 2DEGs’ modification through inter-dot barrier width by STM/STS/AFM, ARPES and extended model calculations. We engineer the inter-dot barrier width by substitution of a single atom in a haloaromatic compound and tune the confinement properties at each nanopore, affecting the degree of QD intercoupling both on bulk and thin Ag films alike.

Póster presentado a la Conferencia bienal Fuerzas y Túnel, celebrada en Jaca (España) del 27 al 29 de junio de 2018., Quantum dot (QD) arrays on surfaces, generated through molecular self-assembly processes, have so far provided researchers with a vast playground to study the electronic properties of new and exotic 2D materials in ultra-high-vacuum (UHV) conditions. By selecting the proper molecular constituents (tectons) and substrate, long-range ordered, periodic and robust nanoporous networks have been achieved, ranging from hydrogen-bonded to metal-organic structures. These are candidates for studying fundamental physical phenomena such as confinement through the scattering of two-dimensional electron gases (2DEGs). Indeed, confinement tunability has already been accomplished by varying the pore (i.e. quantum dot) dimensions, geometrical shape and molecule substrate interactions. In addition, inter-dot coupling has been shown by photoemission that can be modulated through thermodynamics and the condensation of guest elements (Xe atoms). To date, 2DEGs' modification through inter-dot barrier width variations has not been experimentally demonstrated. Herein, sustained upon a combination of local scanning probes (STM/STS/AFM), angle resolved photoemission spectroscopy (ARPES) and extended model calculations, we show that we can precisely engineer the inter-dot barrier width by substitution of a single atom in a haloaromatic compound. As a result, we tune the confinement properties at each nanopore affecting the degree of QD intercoupling both on bulk and thin Ag films alike. Our findings complete the toolbox for tuning surface electronic properties, which started in the 90's with the quantum corrals.

Resumen del trabajo presentado a la Conferencia bienal Fuerzas y Túnel, celebrada en Jaca (España) del 27 al 29 de junio de 2018., Carbon based low-dimensional nanostructures such as on-surface synthesized Graphene nanoribbons (GNRs) and oligophenylene chains provide a vast playground for developing organic semiconductors with specific electronic properties. For instance, recent ARPES and STM/STS band structure studies on macroscopically aligned poly (para-phenylene) (PPP) and armchair-GNRs resulted in highly dispersive electronic bands with a large HOMO-LUMO gap. Analogously, we generate atomically precise, wellaligned and covalently bonded zigzag polymers on a curved vicinal Ag(111) surface. With the use of ARPES, we unravel its band structure for the first time and find weakly dispersive bands with considerably increased HOMO LUMO gap. These results, supported with DFT calculations, suggest a strong tunability of the polymer’s electronic properties, which can be correlated to its topology.

Trabajo presentado al X Meeting de GEFES (División de Física de la Materia Condensada de la Real Sociedad Española de Física), celebrado en Valencia del 24 al 26 de enero de 2018., This work focuses on the growth and characterization of three different transition metals (Mn, Fe and Co) upon selected molecular networks under ultra-high vacuum conditions. The resulting self-assembled structures are characterized by means of Scanning Tunneling Microscopy (STM) and Low Energy Electron Diffraction (LEED). We use a Cu(111) monocrystal as substrate and generate two well-characterized and extended molecular networks that are partially covered or disrupted by the addition of the transition metals. From the highly resolved STM study we can study their mutual interaction and we detect structures that vary from regular nanodots to one dimensional chains.

Resumen del trabajo presentado al 2nd ELECMI International Workshop celebrado en Zaragoza (España) del 11 al 13 de junio de 2018., In the early 1900's Fritz Ullmann first reported the synthesis of biaryls from aryl halides mediated by a fine copper powder, demonstrating with this the aromatic nucleophilic substitution mediated by copper, now known as Ullmann condensation reaction. More than hundred years after, this reaction is routinely used in numerous industrial applications and, nowadays it becomes widely used for the synthesis on metal surfaces of atomically precise graphene nanoribbons. The next step to move toward device applications requires performing the synthesis directly on suitable substrates such as semiconducting, insulating or magnetic substrates. Whit in this context, in the present work we explore the Ullmann based synthesis of polymers on magnetic and insulating substrates. In particular we demonstrate the aryl homocoupling synthesis of 4,4-Dibromo (or diiodo)-p-terphenyl precursor into molecular poly-p-phenylene wires on the semiconductor TiO2 surface and on the bimetallic (and ferromagnetic) GdAu2 surface alloy. Moreover, we propose a reaction pathway during the polymerization. To monitor the chemical reaction complementary microscopic and spectroscopic surface science techniques (scanning tunneling microscopy, X-ray photoemission spectroscopy, angle-resolved Photoemission spectroscopy) are used.

Resumen del trabajo presentado a la 21st International Conference on Magnetism (ICM), celebrada en San Francisco (US) del 15 al 20 de julio de 2018., Metal-organic interactions are weaker than the covalent ones, allowing the bond formation and breaking necessary to self-assemble, but are stronger than the purely intermolecular interactions. This is why metalorganic networks own so interesting properties. In this work, we grow and characterize Fe upon a selected molecular network under ultra-high vacuum conditions. The resulting self-assembled structures are characterized by means of Scanning Tunnelling Microscopy and Low Energy Electron Diffraction. We use a Cu(111) monocrystal as substrate and generate a self-assembled, extended metalorganic network which is stable at room temperature. It will be shown that depending on the molecular coverage the porous network evolves into a compact structure detectable by LEED. Once the porous network is formed, Fe atoms are evaporated on the surface. Instead of he usual bi-layer islands, the Fe forms single atomic height nanoclusters. We have performed a STM study of the Fe nanostructures as a function of coverage and deposition temperature. In addition, X-ray Magnetic Circular Dichroism experiments at the European Synchrotron Radiation Facility show that the Fe nanostructures (stable also at room temperature) significantly change their magnetic anisotropy compared to the case when the molecular layer is missing.

Resumen del trabajo presentado al International workshop On-Surface Synthesis (OSS), celebrado en Sant Feliu de Guíxol (España) del 23 al 28 de septiembre de 2018., Carbon based low-dimensional nanostructures such as on-surface synthesized Graphene nanoribbons (GNRs) and oligophenylene chains provide a vast playground for developing organic semiconductors with distinct electronic properties.

Resumen del trabajo presentado a la Conferencia bienal Fuerzas y Túnel, celebrada en Jaca (España) del 27 al 29 de junio de 2018., Metal-organic interactions are weaker than covalent ones, allowing the bond breaking and formation necessary to generate large and extended self-assembled structures. Under ultra-high vacuum conditions, we grow and characterize Fe clusters using a selected metalorganic network as a buffer layer. The resulting self-assembled structures are characterized by means of Scanning Tunnelling Microscopy and Low Energy Electron Diffraction. We use a Cu(111) monocrystal as substrate and generate an extended metalorganic network, which is stable at room temperature. It will be shown that depending on the molecular coverage the porous network evolves into a compact structure detectable by LEED. Once the porous network is formed, Fe atoms are evaporated on the surface. Instead of the usual bi-layer islands, the Fe forms single atomic height nanoclusters. We have performed a STM study of such Fe nanostructures as a function of coverage and deposition temperature. In addition, X-ray Magnetic Circular Dichroism (XMCD) experiments at the ESRF show that the Fe nanostructures (stable at room temperature) significantly change the magnetic anisotropy compared to the case when the molecular layer is missing.