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Resumen del trabajo presentado a la Grenoble-Barcelona twin conference: From quantum systems to new materials and smart electrical energy (GreBa-QME), celebrada en Grenoble (Francia) del 23 al 25 de octubre de 2019.

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, Fundamental research on new states of the matter and technological applications in fields like spintronics (1) relays on the interfaces between magnetic materials and other states of the matter like superconductors, semiconductors or topological insulators. In the case of twodimensional (2D) ferromagnetic materials, it is necessary to keep the long-range magnetic order. To maintain this 2D magnetism the chemical and structural stability is mandatory. A molecular overlayer could influence these properties due to charge transfer. 2D rareearth/Noble-metal monolayer alloys show great potential as nanostructured magnetic patterns. Many of the lanthanides have shown already its potential by forming highly ordered corrugated structures when deposited on Au(111) and Ag(111) (2) nevertheless their magnetic and electronic structure after molecular deposition remains unknown. Here, we show evidence of the interaction between a GdAu2 monolayer alloy and magnetic molecules (metal centered porphyrin and phthalocyanines) that mutually influence their magnetic behavior. For example in the case of a one monolayer (ML) Co-tetraphenylporphyrin we observe a ferromagnetic interaction of the Co atom to the substrate, while the underlying material keeps basically its electronic and magnetic properties (Fig. 1). On the other hand a ML thick Co-phthalocyanine molecules film does not reveal any magnetic interaction. Only the second layer show a small magnetic signal.

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., 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 one 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 DFT-STS study further reveal a highly anisotropic electronic structure, where orthogonal one-dimensional electronic bands with an energy gap of ~1 eV coexist with confined pore states that can be regarded as 2D analogues of the superatom states found in fullerene. The combined structural and electrical properties makes this nanoporous 2D material a highly versatile semiconductor for simultaneous sieving and electrical sensing of molecular species.

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., The on-surface synthesis of graphene nanoribbons (GNRs) has been subject of intense research in recent years. Focused mainly on the realization of GNRs with different shape, edge structure and chemical composition, few studies have paid attention to the control of their distribution throughout the surface, which is critical for integration in devices. The most representative advance in this direction has been the use of stepped surfaces as templates to align the GNRs along one direction at the cm scale, a distribution that can be then replicated after transfer to insulating substrates. Here we show how the herringbone reconstruction can be used as template for inducing different GNR superlattice patterns. Hydrogenated and fluorinated triphenylene derivatives lead to GNRs that interact strongly with the surface reconstruction, which constrains their growth along the fcc domains. This results in a 2D superlattice that replicates the herringbone pattern, and limits the GNR size to the straight domains of the zig-zag. In contrast, GNRs obtained with diphenyl–DBBA undergo a more subtle interaction, where the interaction with the reconstruction is only exploited for the parallel alignment of GNRs without limiting their size. As a consequence we obtain parallel arrays of ultra-long GNRs (>100nm) of different periodicity depending on the coverage (Fig .1). The parallel distribution is optimum for the realization of multichannel electronic devices and optical superlattices, and additionally provides an ideal configuration for the subsequent lateral coupling of GNRs that give rise to nanoporous graphene.

Resumen del póster presentado a la 13th European Conference on Surface Crystallography and Dynamics, celebrada en Donostia-San Sebastián (España) del 19 al 21 de junio de 2017., From the physical point of view, the tribological response, in particular frictional properties, of organic surfaces is an obvious subject of interest by itself. As a powerful tool to understand different dissipation mechanisms at surfaces, we commonly employ the scanning force microscope by measuring the lateral force perpendicular to the scan direction (also known as friction force microscopy, FFM). As for inorganic materials, FFM helps visualizing regions of different chemical nature. However, more subtle surface characteristics influence the frictional properties of molecular systems and well-designed and sensitive FFM measurements permit obtaining detailed structural details as molecular order (stick-slip) as well as molecular tilt angles and/or tilt angle azimuths. This is the case of observing friction anisotropy or friction asymmetry. The term anisotropy refers to the variation of friction with the relative orientation angle between sliding surfaces and is commonly correlated with surface crystallographic orientations, while asymmetry refers to a change in friction when the sliding direction is changed by 180°. FFM has been successfully employed in organic self-assembled monolayers (SAMs) not only to discriminate between ordered configurations presenting different friction coefficients or different packing, but also to decipher between equivalent structural domains as well as to identify highly dissipative transient molecular configurations during phase transitions. Outstandingly, crystallographic aspects including "stick-slip" can also be extracted from the torsion of the cantilever during scanning along its axis in the so-called transverse shear microscopy (TSM).

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., Authors would like to thank the financial support from Swiss National Science Foundation (SNF) through the project no. 200021_160174.

International audience

Under the terms of the Creative Commons Attribution License 3.0 (CC-BY)., There is increasing evidence supporting the strong potential of twin walls in ferroic materials as distinct, spatially tunable, functional elements in future electronic devices. Here, we report an increase of about one order of magnitude in conductivity and more robust magnetic interactions at (100)-type twin walls in La0.7Sr0.3MnO3 thin films. The nature and microscopic origin of such distinctive behavior is investigated by combining conductive, magnetic, and force modulation scanning force microscopies with transmission electron microscopy techniques. Our analyses indicate that the observed behavior is due to a severe compressive strained state within an ∼1nm slab of material centered at the twin walls, promoting stronger Mn 3d-O2p orbital overlapping leading to a broader bandwidth and enhanced magnetic interactions., This research was sponsored by the Spanish MINECO (Grants No. MAT2011- 29081-C02, No. MAT2012-33207, and No. MAT2013-47869-C4-1-P) projects. We also acknowledge financial aid from the Generalitat de Catalunya (2014 SGR 501). N.B. and F.S. also acknowledge funding from the European Union Seventh Framework Programme under Grant Agreement No. 312483-ESTEEM2 (Integrated Infrastructure Initiative I3) for providing access to aberration corrected electron microscopes at CEMES (Toulouse) and LPS (Orsay). R.G. and N.B. thank the Spanish MINECO for financial support through the FPI program. F.S. acknowledges support from the Labex (Excellence Laboratory) NEXT through a visiting scientist fellowship at CEMES (Toulouse, France).

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., C. M. was supported by AGAUR through the FP7-EU under Marie Curie COFUND action 600385. M. P. acknowledges the Spanish Government for financial support through PTA2014-09788-I. Funded by the CERCA Programme/Generalitat de Catalunya. We acknowledge support from the Ministerio de Ciencia e Innovación (MAT2013-46593-C6-2-P, MAT2013-46593-C6-5-P, MAT2016-78293-C6-2-R, MAT2016-78293-C6-4-R and Severo Ochoa No. SEV-2013-0295), the EU project PAMS (610446) the Xunta de Galicia (Centro singular de investigacion de Galicia accreditation 2016–2019, ED431G/09), and the European Regional Development Fund.