BUSCADOR RECOLECTA

Graphene holds great potential for superconductivity due to its pure 2D
nature, the ability to tune its carrier density through electrostatic gating, and
its unique, relativistic-like electronic properties. At present, still far from
controlling and understanding graphene superconductivity, mainly because
the selective introduction of superconducting properties to graphene is
experimentally very challenging. Here, a method is developed that enables
shaping at will graphene superconductivity through a precise control of
graphene-superconductor junctions. The method combines the proximity
effect with scanning tunnelling microscope (STM) manipulation capabilities.
Pb nano-islands are first grown that locally induce superconductivity in
graphene. Using a STM, Pb nano-islands can be selectively displaced, over
different types of graphene surfaces, with nanometre scale precision, in any
direction, over distances of hundreds of nanometres. This opens an exciting
playground where a large number of predefined graphene-superconductor
hybrid structures can be investigated with atomic scale precision. To illustrate
the potential, a series of experiments are performed, rationalized by the
quasi-classical theory of superconductivity, going from the fundamental
understanding of superconductor-graphene-superconductor heterostructures
to the construction of superconductor nanocorrals, further used as “portable”
experimental probes of local magnetic moments in graphene, The authors acknowledge funding from the Spanish Ministry of Science
and Innovation MCIN/AEI/10.13039/297 501100011033 though grants #
PID2020-115171GB-I00, PID2020-114880GB-I00, PID2019-107338RB-C61
and the “María de Maeztu” Programme for Units of Excellence in R&D
(CEX2018-000805-M, CEX2020-001038-M), the Comunidad de Madrid
NMAT2D-CM program under grant S2018/NMT-4511, the Comunidad de
Madrid, the Spanish State and the European Union by the Recovery, Transformation and Resilience Plan “Materiales Disruptivos Bidimensionales
(2D)” (MAD2D-CM)-UAM3 and the European Union through the Next
Generation EU funds and the Horizon 2020 FET-Open project SPRING
(No. 863098). J. C. C. thanks the German Science Foundation DFG and
SFB 1432 for sponsoring his stay at the University of Konstanz as a Mercator Fellow

Triangulene nanographenes are open-shell molecules with predicted high spin state due to the frustration of their conjugated network. Their long-sought synthesis became recently possible over a metal surface. Here, we present a macrocycle formed by six [3]triangulenes, which was obtained by combining the solution synthesis of a dimethylphenyl-anthracene cyclic hexamer and the on-surface cyclodehydrogenation of this precursor over a gold substrate. The resulting triangulene nanostar exhibits a collective spin state generated by the interaction of its 12 unpaired π-electrons along the conjugated lattice, corresponding to the antiferromagnetic ordering of six S=1 sites (one per triangulene unit). Inelastic electron tunneling spectroscopy resolved three spin excitations connecting the singlet ground state with triplet states. The nanostar behaves close to predictions from the Heisenberg model of an S=1 spin ring, representing a unique system to test collective spin modes in cyclic systems, We acknowledge funding from Agencia Estatal de Investigación (PID2019-107338RB, FIS2017-83780-P, MDM-2016-0618), from the Xunta de Galicia (Centro singular de investigación de Galicia, accreditation 2019–2022, ED431G 2019/03), the Basque Government (Grant IT1255-19), the European Union H2020 program (FET Open project SPRING #863098), the European Regional Development Fund and the Basque Departamento de Educación for the PhD scholarship no. PRE_2020_2_0049 (S.S.) The authors thank D. Pérez and E. Guitián for fruitful discussions, SI

The Diels–Alder reaction is one of the most popular reactions in organic chemistry. However, its use in the field of on-surface synthesis is hampered by the spatial restrictions of this cycloaddition reaction. Herein we selected a cyclic strained triyne to demonstrate an on-surface hexadehydro-Diels–Alder reaction in a single molecule. The reaction was studied in detail by means of atomic force microscopy (AFM) with CO-functionalized tips. Our results pave the way to use this iconic pericyclic reaction for on-surface synthesis, introducing the concept of atom economy in the field, We thank Rolf Allenspach and Enrique Guitián for discussions. We thank the European Union (Project SPRING, contract no. 863098), the ERC grant AMSEL (682144), the Spanish Agencia Estatal de Investigación (PID2019-107338RB-C62, PID2019-110037GB-I00 and PCI2019-111933-2), Xunta de Galicia (Centro de Investigación de Galicia accreditation 2019–2022, ED431G 2019/03) and the European Regional Development Fund-ERDF for financial support, SI

Glaser‐like coupling of terminal alkynes by thermal activation is extensively used in on‐surface chemistry. Here we demonstrate an intramolecular version of this reaction performed by atom manipulation. We used voltage pulses from the tip to trigger a Glaser‐like coupling between terminal alkyne carbons within a custom‐synthesized precursor molecule adsorbed on bilayer NaCl on Cu(111). Different conformations of the precursor molecule and the product were characterized by molecular structure elucidation with atomic force microscopy and orbital density mapping with scanning tunneling microscopy, accompanied by density functional theory calculations. We revealed partially dehydrogenated intermediates, providing insight into the reaction pathway, We thank the European Union (Project SPRING, contract no. 863098), the ERC grant AMSEL (682144), the Spanish Agencia Estatal de Investigación (MAT2016-78293-C6-3-R and CTQ2016-78157-R), Xunta de Galicia (Centro de Investigación de Galicia accreditation 2019–2022, ED431G 2019/03) and the EuropeanRegional Development Fund-ERDF for financial support, SI

Triangulenes are a class of open-shell triangular graphene flakes with total spin increasing with their size. In the last years, on-surface-synthesis strategies have permitted fabricating and engineering triangulenes of various sizes and structures with atomic precision. However, direct proof of the increasing total spin with their size remains elusive. In this work, we report the combined in-solution and on-surface synthesis of a large nitrogen-doped triangulene (aza-[5]-triangulene) on a Au(111) surface, and the detection of its high-spin ground state. Bond-resolved scanning tunneling microscopy images uncovered radical states distributed along the zigzag edges, which were detected as weak zero-bias resonances in scanning tunneling spectra. These spectral features reveal the partial Kondo screening of a high-spin state. Through a combination of several simulation tools, we find that the observed distribution of radical states is explained by a quintet ground state (S=2), instead of the quartet state (S=3/2) expected for the neutral species. This confirms that electron transfer to the metal substrate raises the spin of the ground state. We further provide a qualitative description of the change of (anti)aromaticity introduced by N-substitution, and its role in the charge stabilization on a surface, resulting in an S=2 aza-triangulene on Au(111), The authors gratefully acknowledge financial support from MCIN/AEI/10.13039/501100011033 through grants No. PID2019-107338RB, PID2019-109555GB-I00, PCI2019-111933-2 and TED2021-132388B-C42, FIS2017-83780-P, and CEX2020-001038-M, from the ELKARTEK project BRTA QUANTUM (no. KK-2022/00041), from the European Regional Development Fund, from the European Union (EU) H2020 program through the FET Open project SPRING (grant agreement No. 863098) and ERC Synergy Grant MolDAM (951519), Xunta de Galicia (Centro de Investigación de Galicia accreditation 2019–2022, ED431G 2019/03) and Xunta de Galicia-Gain Oportunius Program. F.R.-L. thanks the Spanish Ministerio de Educación y Formación Profesional through the PhD scholarship No. FPU20/03305. F.S. acknowledges funding by the Spanish Ministerio de Ciencia e Innovación through Ramón y Cajal Fellowship RYC2021-034304-I. M.E.S.-S. acknowledges the funding by the UK Research and Innovation under the UK government's Horizon Europe funding guarantee (grant number EP/X020908/1). We thank Thomas Frederiksen, Sofía Sanz, and Ricardo Ortiz for fruitful discussions, SI

Recently, the edges of single-layer graphene have been experimentally doped with silicon atoms by means of scanning transmission electron microscopy. In this work, density functional theory is applied to model and characterize a wide range of experimentally inspired silicon doped zigzag-type graphene edges. The thermodynamic stability is assessed and the electronic and magnetic properties of the most relevant edge configurations are unveiled. Importantly, we show that silicon doping of graphene edges can induce a reversion of the spin orientation on the adjacent carbon atoms, leading to novel magnetic properties with possible applications in the field of spintronics., A.U. gratefully acknowledges Eusko Jaurlaritza for his predoctoral grant. We thank the Provincial Council of Gipuzkoa (RED Gipuzkoa Next 2021-CIEN-000070-01), the Basque Department of Education (IT1254-19, PIBA2020-1-0014), the Spanish Ministry of Science and Innovation (PID2019-107338RB-C66, PID2020-114754GA-I00) and the European Union (EU) through Horizon 2020 (FET-Open project SPRING Grant No. 863098) for financial support. The authors thankfully acknowledge the computer resources at MareNostrum and the technical support provided by Barcelona Supercomputing Center (QHS-2021-3-0004). We also thank DIPC and SGI-IZOSGIker (UPV/EHU) for the generous allocation of computational resources.

Recently, planar and neutral tricoordinated oxygen embedded in graphene has been imaged experimentally (Nat. Commun., 2019, 10, 4570–4577). In this work, this unusual chemical species is studied utilizing a variety of state-of-the-art methods and combining periodic calculations with a fragmental approach. Several factors influencing the stability of trivalent oxygen are identified. A σ-donation and a π-backdonation mechanism between graphite and oxygen is established. π-Local aromaticity, with a delocalized 4c–2e bond involving the oxygen atom and the three nearest carbon atoms aids in the stabilization of this system. In addition, the framework in which the oxygen is embedded is crucial too to the stabilization, helping to delocalize the “extra” electron pair in the virtual orbitals. Based on the understanding gathered in this work, a set of organic molecules containing planar and neutral trivalent oxygen is theoretically proposed for the first time., This work was supported by funding provided by Gobierno Vasco-Eusko Jaurlaritza (IT1584-22). This work was also supported by grant PID2019-107338RB-C66 and PID2020-114754GA-I00, funded by MCIN/AEI/10.13039/501100011033, and PID2022-140845OB-C66, funded by MCIN/AEI/10.13039/501100011033 and FEDER. In addition, the work was supported by the Spanish Research Agency and the European Union NextGenerationEU/PRTR under Contract No. TED2021-132388B-C44, and the European Union (EU) H2020 program through the FET Open project SPRING (Grant Agreement No. 863098). A. G.-L. also acknowledges the financial support received from the IKUR Strategy under the collaboration agreement between Ikerbasque Foundation and DIPC on behalf of the Department of Education of the Basque Government. A. U. gratefully thanks Eusko Jaurlaritza for his predoctoral grant. I. C. R. acknowledges co-funding from the European Union's Horizon 2020 Research and Innovation Maria Skłodowska-Curie Actions, under grant agreement number 945380. We also thank DIPC and SGI-IZO-SGIker (UPV/EHU) for the generous allocation of computational resources. The authors thankfully acknowledge also the computer resources at MareNostrum and the technical support provided by Barcelona Supercomputing Center (QHS-2022-2-002 and QHS-2022-3-0015).

Chiral graphene nanoribbons are extremely interesting structures due to their narrow band gaps and potential development of spin-polarized edge states. Here, we study their band structure on low work function silver surfaces. The use of a curved Ag single crystal provides, within the same sample, regions of disparate step structure and step density. Whereas the former leads to distinct azimuthal growth orientations of the graphene nanoribbons atop, the latter modulates the substrate’s work function and thereby the interface energy level alignment. In turn, we disclose the associated charge transfer from the substrate to the ribbon and assess its effect on the nanoribbon’s properties and the edge state magnetization., We acknowledge financial support from MCIN/AEI/10.13039/501100011033 (grant nos. PID2019-107338RB-C62, PID2019-107338RB-C63, PID2019-107338RB-C66, and PCI2019-111933-2 and MAT-2017-88374-P), the European Union’s Horizon 2020 research and innovation program (FET Open project SPRING, grant no. 863098), the Xunta de Galicia (Centro Singular de Investigación de Galicia, 2019–2022, grant no. ED431G2019/03), the European Regional Development Fund, the Basque Government (Grant IT-1255-19), Gobierno Vasco-UPV/EHU (Project No. IT1246-19) and the Dpto. Educación Gobierno Vasco (Grant No. PIBA-2020-1-0014).

[EN] Nitrogen heteroatom doping into a triangulene molecule allows tuning its magnetic state. However, the synthesis of the nitrogen-doped triangulene (aza-triangulene) has been challenging. Herein, we report the successful synthesis of aza-triangulene on the Au(111) and Ag(111) surfaces, along with their characterizations by scanning tunneling microscopy and spectroscopy in combination with density functional theory (DFT) calculations. Aza-triangulenes were obtained by reducing ketone-substituted precursors. Exposure to atomic hydrogen followed by thermal annealing and, when necessary, manipulations with the scanning probe afforded the target product. We demonstrate that on Au(111), aza-triangulene donates an electron to the substrate and exhibits an open-shell triplet ground state. This is derived from the different Kondo resonances of the final aza-triangulene product and a series of intermediates on Au(111). Experimentally mapped molecular orbitals match with DFT-calculated counterparts for a positively charged aza-triangulene. In contrast, aza-triangulene on Ag(111) receives an extra electron from the substrate and displays a closed-shell character. Our study reveals the electronic properties of aza-triangulene on different metal surfaces and offers an approach for the fabrication of new hydrocarbon structures, including reactive open-shell molecules., We acknowledge financial support from MCIN/AEI/10.13039/501100011033 (grant nos. PID2019-107338RB-C61, PID2019-107338RB-C62, PID2019-107338RB-C63, PID2019-109555GB-I00, and FJC2019-041202-I); the Basque Government (IT-1255-19 and PIBA19-0004); the Spanish Research Council (ILINKC20002), the European Union’s Horizon 2020 research and innovation program (grant no. 863098 and Marie Skłodowska-Curie Actions Individual Fellowship no. 101022150); and the Xunta de Galicia (Centro Singular de Investigación de Galicia, 2019-2022, grant no. ED431G2019/03).

For the past three decades nanoscience has widely affected many areas in physics, chemistry and engineering, and has led to numerous fundamental discoveries, as well as applications and products. Concurrently, quantum science and technology has developed into a cross-disciplinary research endeavour connecting these same areas and holds burgeoning commercial promise. Although quantum physics dictates the behaviour of nanoscale objects, quantum coherence, which is central to quantum information, communication and sensing, has not played an explicit role in much of nanoscience. This Review describes fundamental principles and practical applications of quantum coherence in nanoscale systems, a research area we call quantum-coherent nanoscience. We structure this Review according to specific degrees of freedom that can be quantum-coherently controlled in a given nanoscale system, such as charge, spin, mechanical motion and photons. We review the current state of the art and focus on outstanding challenges and opportunities unlocked by the merging of nanoscience and coherent quantum operations., A.J.H. acknowledges financial support from the Institute for Basic Science under grant number IBS-R027-D1. W.D.O. received funding from the US Army Research Office under grant number W911WF-18-1-0116 and the National Science Foundation under grant number PHY-1720311. L.M.K.V. received funding from the European Research Council (grant number 882848) and A.A. from the UK Engineering and Physical Sciences Research Council (grant number EP/P000479/1) and the European Union’s Horizon 2020 research and innovation programme under grant agreement numbers 863098 and 862893. R.S. was funded by EU-H2020 research project number 862893. A.B.J. received funding from NSF award number QIS-1820938 and the NSF QLCI through grant number OMA-2016245. J.F.-R. was funded by Generalitat Valenciana funding Prometeo 2017/139 and MINECO-Spain (grant number PID2019-109539GB); A.L. by the UNSW Scientia Program; and A.M. by the Australian Research Council (grant numbers CE170100012 and DP180100969), the US Army Research Office (grant number W911NF-17-1-0200) and the Australian Department of Industry, Innovation and Science (grant number AUSMURI00002).

A review of the present status, recent enhancements, and applicability of the SIESTA program is presented. Since its debut in the mid-1990s,
SIESTA’s flexibility, efficiency, and free distribution have given advanced materials simulation capabilities to many groups worldwide. The core
methodological scheme of SIESTA combines finite-support pseudo-atomic orbitals as basis sets, norm-conserving pseudopotentials, and a realspace grid for the representation of charge density and potentials and the computation of their associated matrix elements. Here, we describe
the more recent implementations on top of that core scheme, which include full spin–orbit interaction, non-repeated and multiple-contact
ballistic electron transport, density functional theory (DFT)+U and hybrid functionals, time-dependent DFT, novel reduced-scaling solvers,
density-functional perturbation theory, efficient van der Waals non-local density functionals, and enhanced molecular-dynamics options. In
addition, a substantial effort has been made in enhancing interoperability and interfacing with other codes and utilities, such as WANNIER90 and
the second-principles modeling it can be used for, an AiiDA plugin for workflow automatization, interface to Lua for steering SIESTA runs, and
various post-processing utilities. SIESTA has also been engaged in the Electronic Structure Library effort from its inception, which has allowed
the sharing of various low-level libraries, as well as data standards and support for them, particularly the PSeudopotential Markup Language
definition and library for transferable pseudopotentials, and the interface to the ELectronic Structure Infrastructure library of solvers. Code
sharing is made easier by the new open-source licensing model of the program. This review also presents examples of application of the
capabilities of the code, as well as a view of on-going and future developments.
Published under license by AIP Publishing., Siesta development was historically supported by different Spanish National Plan projects (Project Nos. MEC-DGES-PB95-0202, MCyT-BFM2000-1312, MEC-BFM2003-03372, FIS2006-12117, FIS2009-12721, FIS2012-37549, FIS2015-64886-P, and RTC-2016-5681-7), the latter one together with Simune Atomistics Ltd. We are thankful for financial support from the Spanish Ministry of Science, Innovation and Universities through Grant No. PGC2018-096955-B.
We acknowledge the Severo Ochoa Center of Excellence Program [Grant Nos. SEV-2015-0496 (ICMAB) and SEV-2017-0706 (ICN2)], the GenCat (Grant No. 2017SGR1506), and the European Union MaX Center of Excellence (EU-H2020 Grant No. 824143).
P.G.-F. acknowledges support from Ramón y Cajal (Grant No. RyC-2013-12515). J.I.C. acknowledges Grant No. RTI2018-097895-B-C41.
R.C. acknowledges the European Union’s Horizon 2020 Research and Innovation Program under Marie Skłodoswka-Curie Grant Agreement No. 665919.
D.S.P, P.K., and P.B. acknowledge Grant No. MAT2016-78293-C6, FET-Open No. 863098, and UPV-EHU Grant No. IT1246-19.
V. W. Yu was supported by a MolSSI Fellowship (U.S. NSF Award No. 1547580), and V.B. and V.W.Y. were supported by the ELSI Development by the NSF (Award No. 1450280). We also acknowledge Honghui Shang and Xinming Qin for giving us access to the honpas code, where a preliminary version of the hybrid functional support described here was implemented.
We are indebted to other contributors to the Siesta project whose names can be seen in the Docs/Contributors.txt file of the Siesta distribution, and we thank those, too many to list, contributing fixes, comments, clarifications, and documentation for the code., Peer reviewed

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., We acknowledge financial support from (i) AEI/FEDER-EU through grant nos. MAT2016-78293-C6, FIS2017-83780-P AEI/FEDER, EU, the Maria de Maeztu unit of excellence MDM-2016-0618, and the Severo Ochoa program (ICN2) SEV-2017-0706; (ii) the European Research Council (grant agreement no. 635919); (iii) the Xunta de Galicia (Centro Singular De Investigacion de Galicia, accreditation 2016-2019, ED431G/09); (iv) the European FET-OPEN project SPRING (#863098); (v) the European Regional Development Fund (ERDF) under the program Interreg V-A España-Francia-Andorra (contract no. EFA 194/16 TNI); (vi) the CERCA Program/Generalitat de Catalunya; (vii) the Gobierno Vasco UPV/EHU (project IT1246-19); (viii) Basque Government Project (IT-1255-19); and (ix) Diputacion Foral De Gipuzkoa RED 2019-096., Peer reviewed

We extensively characterize the electronic structure of ultranarrow graphene nanoribbons (GNRs) with armchair edges and zigzag termini that have five carbon atoms across their width (5-AGNRs), as synthesized on Au(111). Scanning tunneling spectroscopy measurements on the ribbons, recorded on both the metallic substrate and a decoupling NaCl layer, show well-defined dispersive bands and in-gap states. In combination with theoretical calculations, we show how these in-gap states are topological in nature and localized at the zigzag termini of the nanoribbons. In addition to rationalizing the driving force behind the topological class selection of 5-AGNRs, we also uncover the length-dependent behavior of these end states which transition from singly occupied spin-split states to a closed-shell form as the ribbons become shorter. Finally, we demonstrate the magnetic character of the end states via transport experiments in a model two-terminal device structure in which the ribbons are suspended between the scanning probe and the substrate that both act as leads., We acknowledge funding from the European Union’s Horizon 2020 programme (Grant Agreement Nos. 635919 and 863098 from ERC and FET Open projects, respectively), from the Spanish MINECO (Grant Nos. FIS2017-83780-P and MAT2016-78293-C6), and from the University of the Basque Country (Grant IT1246-19). D.G.O. thanks the Alexander von Humboldt Foundation for supporting his research stay at the MPI, and Klaus Kern for hosting him., Peer reviewed

This article is part of the JCP Special Topic on Electronic Structure Software., A review of the present status, recent enhancements, and applicability of the SIESTA program is presented. Since its debut in the mid-1990s, SIESTA’s flexibility, efficiency, and free distribution have given advanced materials simulation capabilities to many groups worldwide. The core methodological scheme of SIESTA combines finite-support pseudo-atomic orbitals as basis sets, norm-conserving pseudopotentials, and a realspace grid for the representation of charge density and potentials and the computation of their associated matrix elements. Here, we describe the more recent implementations on top of that core scheme, which include full spin–orbit interaction, non-repeated and multiple-contact ballistic electron transport, density functional theory (DFT)+U and hybrid functionals, time-dependent DFT, novel reduced-scaling solvers, density-functional perturbation theory, efficient van der Waals non-local density functionals, and enhanced molecular-dynamics options. In addition, a substantial effort has been made in enhancing interoperability and interfacing with other codes and utilities, such as WANNIER90 and the second-principles modeling it can be used for, an AiiDA plugin for workflow automatization, interface to Lua for steering SIESTA runs, and various post-processing utilities. SIESTA has also been engaged in the Electronic Structure Library effort from its inception, which has allowed the sharing of various low-level libraries, as well as data standards and support for them, particularly the PSeudopotential Markup Language definition and library for transferable pseudopotentials, and the interface to the ELectronic Structure Infrastructure library of solvers. Code sharing is made easier by the new open-source licensing model of the program. This review also presents examples of application of the
capabilities of the code, as well as a view of on-going and future developments., Siesta development was historically supported by different Spanish National Plan projects (Project Nos. MEC-DGES-PB95-0202, MCyT-BFM2000-1312, MEC-BFM2003-03372, FIS2006-12117, FIS2009-12721, FIS2012-37549, FIS2015-64886-P, and RTC-2016-5681-7), the latter one together with Simune Atomistics Ltd. We are thankful for financial support from the Spanish Ministry of Science, Innovation and Universities through Grant No. PGC2018-096955-B. We acknowledge the Severo Ochoa Center of Excellence Program [Grant Nos. SEV-2015-0496 (ICMAB) and SEV-2017-0706 (ICN2)], the GenCat (Grant No. 2017SGR1506), and the European Union MaX Center of Excellence (EU-H2020 Grant No. 824143). P.G.-F. acknowledges support from Ramón y Cajal (Grant No. RyC-2013-12515). J.I.C. acknowledges Grant No. RTI2018-097895-B-C41. R.C. acknowledges the European Union’s Horizon 2020 Research and Innovation Program under Marie Skłodoswka-Curie Grant Agreement No. 665919. D.S.P, P.K., and P.B. acknowledge Grant No. MAT2016-78293-C6, FET-Open No. 863098, and UPV-EHU Grant No. IT1246-19. V. W. Yu was supported by a MolSSI Fellowship (U.S. NSF Award No. 1547580), and V.B. and V.W.Y. were supported by the ELSI Development by the NSF (Award No. 1450280)., Peer reviewed

This article is part of the themed collection: 2020 Chemical Science HOT Article Collection., Fine management of chiral processes on solid surfaces has progressed over the years, yet still faces the need for the controlled and selective production of advanced chiral materials. Here, we report on the use of enantiomerically enriched molecular building blocks to demonstrate the transmission of their intrinsic chirality along a sequence of on-surface reactions. Triggered by thermal annealing, the on-surface reactions induced in this experiment involve firstly the coupling of the chiral reactants into chiral polymers and subsequently their transformation into planar prochiral graphene nanoribbons. Our study reveals that the axial chirality of the reactant is not only transferred to the polymers, but also to the planar chirality of the graphene nanoribbon end products. Such chirality transfer consequently allows, starting from adequate enantioenriched reactants, for the controlled production of chiral and prochiral organic nanoarchitectures with pre-defined handedness., We acknowledge funding from the European Union's Horizon 2020 Programme (Grant Agreement No. 635919 (“SURFINK”) and 863098 (“SPRING”)), from the Spanish MINECO (Grant No. MAT2016-78293-C6), Xunta de Galicia (Centro singular de investigación de Galicia, accreditation 2016–2019, ED431G/09), and the Fondo Europeo de Desarrollo Regional (FEDER)., Peer reviewed

We analyze theoretically four-terminal electronic devices composed of two crossed graphene nanoribbons (GNRs) and show that they can function as beam splitters or mirrors. These features are identified for electrons in the low-energy region where a single valence or conduction band is present. Our modeling is based on
p
z
orbital tight binding with Slater-Koster-type matrix elements fitted to accurately reproduce the low-energy bands from density functional theory calculations. We analyze systematically all devices that can be constructed with either zigzag or armchair GNRs in AA and AB stackings. From Green's function theory the elastic electron transport properties are quantified as a function of the ribbon width. We find that devices composed of relatively narrow zigzag GNRs and AA-stacked armchair GNRs are the most interesting candidates to realize electron beam splitters with a close to 50:50 ratio in the two outgoing terminals. Structures with wider ribbons instead provide electron mirrors, where the electron wave is mostly transferred into the outgoing terminal of the other ribbon, or electron filters where the scattering depends sensitively on the wavelength of the propagating electron. We also test the robustness of these transport properties against variations in the intersection angle, stacking pattern, lattice deformation (uniaxial strain), inter-GNR separation, and electrostatic potential differences between the layers. These generic features show that GNRs are interesting basic components to construct electronic quantum optical setups., This work was supported by the project Spanish Ministerio de Economía y Competitividad (MINECO) through the Grants no. FIS2017-83780-P (Graphene Nanostructures “GRANAS”) and no.MAT2016-78293-C6-4R, the Basque Departamento de Educación through the PhD fellowship no. PRE_2019_2_0218 (S.S.), the University of the Basque Country through the Grant no. IT1246-19, and the European Union (EU) through Horizon 2020 (FET-Open project SPRING Grant no. 863098)., Peer reviewed

Graphene nanoribbons (GNRs), low-dimensional platforms for carbon-based electronics, show the promising perspective to also incorporate spin polarization in their conjugated electron system. However, magnetism in GNRs is generally associated with localized states around zigzag edges, difficult to fabricate and with high reactivity. Here we demonstrate that magnetism can also be induced away from physical GNR zigzag edges through atomically precise engineering topological defects in its interior. A pair of substitutional boron atoms inserted in the carbon backbone breaks the conjugation of their topological bands and builds two spin-polarized boundary states around them. The spin state was detected in electrical transport measurements through boron-substituted GNRs suspended between the tip and the sample of a scanning tunneling microscope. First-principle simulations find that boron pairs induce a spin 1, which is modified by tuning the spacing between pairs. Our results demonstrate a route to embed spin chains in GNRs, turning them into basic elements of spintronic devices., We gratefully acknowledge financial support from Spanish Agencia Estatal de Investigación (AEI) (MAT2016-78293, PID2019-107338RB, FIS2017-83780-P, and the Maria de Maeztu Units of Excellence Programme MDM-2016-0618), from the European Union (EU) through Horizon 2020 (FET-Open project SPRING Grant. No. 863098), the Basque Departamento de Educación through the PhD fellowship No. PRE_2019_2_0218 (S.S.), the Xunta de Galicia (Centro de Investigación de Galicia accreditation 2019–2022, ED431G 2019/03), the University of the Basque Country (Grant IT1246-19), and the European Regional Development Fund (ERDF). I. P. also thanks Xunta de Galicia and European Union (European Social Fund, ESF) for the award of a predoctoral fellowship-, Peer reviewed

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., C.M. was supported by the Agency for Management of University and Research grants (AGAUR) of the Catalan government through the FP7 framework program of the European Commission under Marie Curie COFUND action 600385 funded by the CERCA Program/Generalitat de Catalunya. We acknowledge support from the Spanish Ministry of Economy and Competitiveness, MINECO (under Contracts Nos. MAT2016-78293-C6 and FIS2017-83780-P and SEV-2017-0706), the Spanish Research Agency (AEI /10.13039/501100011033, under Contracts Nos. PID2019-107338RB, PCI2019-111890-2), the European Regional Development Fund (ERDF), the Interreg V-A España-Francia-Andorra program (Contract No. EFA 194/16 TNSI), the EU project SPRING (863098), the Xunta de Galicia (Centro singular de investigación de Galicia accreditation 2019-2022, ED431G 2019/03)., Peer reviewed

OPEN DATA related to the research publication:
Niklas Friedrich, Pedro Brandimarte, Jingcheng Li, Shohei Saito, Shigehiro Yamaguchi, Iago Pozo, Diego Peña, Thomas Frederiksen, Aran Garcia-Lekue, Daniel Sánchez-Portal, and José Ignacio Pascual, Magnetism of Topological Boundary States Induced by Boron Substitution in Graphene Nanoribbons, Phys. Rev. Lett. 125, 146801 (2020) [arXiv:2004.10280], Graphene nanoribbons (GNRs), low-dimensional platforms for carbon-based electronics, show the promising perspective to also incorporate spin polarization in their conjugated electron system. However, magnetism in GNRs is generally associated with localized states around zigzag edges, difficult to fabricate and with high reactivity. Here we demonstrate that magnetism can also be induced away from physical GNR zigzag edges through atomically precise engineering topological defects in its interior. A pair of substitutional boron atoms inserted in the carbon backbone breaks the conjugation of their topological bands and builds two spin-polarized boundary states around them. The spin state was detected in electrical transport measurements through boron-substituted GNRs suspended between the tip and the sample of a scanning tunneling microscope. First-principle simulations find that boron pairs induce a spin 1, which is modified by tuning the spacing between pairs. Our results demonstrate a route to embed spin chains in GNRs, turning them into basic elements of spintronic devices., We acknowledge funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 863098 (FET-Open project "SPRING")., Peer reviewed

Graphene nanoribbons (GNRs) and their derivatives attract growing attention due to their excellent electronic and magnetic properties as well as the fine-tuning of such properties that can be obtained by heteroatom substitution and/or edge morphology modification. Here, we introduce graphene nanoribbon derivatives—organometallic hybrids with gold atoms incorporated between the carbon skeleton and side Cl atoms. We show that narrow chlorinated 5-AGNROHs (armchair graphene nanoribbon organometallic hybrids) can be fabricated by on-surface polymerization with omission of the cyclodehydrogenation reaction by a proper choice of tailored molecular precursors. Finally, we describe a route to exchange chlorine atoms connected through gold atoms to the carbon skeleton by hydrogen atom treatment. This is achieved directly on the surface, resulting in perfect unsubstituted hydrogen-terminated GNRs. This will be beneficial in the molecule on-surface processing when the preparation of final unsubstituted hydrocarbon structure is desired., This work was supported by the National Science Center, Poland (2019/35/B/ST5/02666), and the EU Project PAMS (610446). A.G.L., D.S.P., and P.B. acknowledge the Spanish Agencia Estatal de Investigación (Grants MAT2016-78293-C6-4-R, PID2019-107338RB-C66, and FIS2017-83780-P), Dep. Educación of the Basque Government and UPV/EHU (Grant IT-756-13), and the European Union (EU) through Horizon 2020 (FET-Open project SPRING Grant 863098) for support., Peer reviewed

Trabajo presentado al Symposium on Surface Science (3S), celebrado en Austria del 1 al 7 de marzo de 2020., Support by the European Union FET Open project SPRING (grant 863098) and by the Spanish Ministry of Economy and Competitiveness, MINECO (grants FIS2017-83780-P and MAT2016-78293-C6)., Peer reviewed

Trabajo presentado al Symposium on Surface Science (3S), celebrado en Austria del 1 al 7 de marzo de 2020., We acknowledge funding from the European Union’s Horizon 2020 programme (Grant Agreement Nos. 635919 and 863098 from ERC and FET Open projects, respectively), from the Spanish MINECO (Grant Nos. FIS2017-83780-P and MAT2016-78293-C6) and from the University of the Basque Country (Grant IT1246-19). D. G. O. thanks the Alexander von Humboldt Foundation for supporting his research stay at the MPI, and Klaus Kern for hosting him., Peer reviewed

The on-surface synthesis of non-planar nanographenes is a challenging task. Herein, with the aid of bond-resolving scanning tunneling microscopy (BRSTM) and density functional theory (DFT) calculations, we present a systematic study aiming at the fabrication of corannulene-based nanographenes via intramolecular cyclodehydrogenation on a Au(111) surface. The formation of non-planar targeted products is confirmed to be energetically unfavorable compared to the formation of planar/quasi-planar undesired competing monomer products. In addition, the activation of intermolecular coupling further inhibits the formation of the final targeted product. Although it was not possible to access the corannulene moiety by means of on-surface synthesis, partial cyclodehydrogenation of the molecular precursors was demonstrated., This work was financially supported by the Spanish Agencia Estatal de Investigacion (PID2019-107338RB-C62, PID2019-107338RB-C63, PID2019-110037GB-I00 and MAT2016-78293-C6; AEI/FEDER, UE), the Basque Government (IT-1255-19), the
European Union’s Horizon 2020 Program (Grant No. 863098), the Xunta de Galicia (Centro singular de investigacion de Galicia accreditation 2019–2022, ED431G 2019/03), the European Union (European Regional Development Fund-ERDF), and European Union’s Horizon 2020 Research and Innovation Programme under the project MEMO (Grant No. 766864)., Peer reviewed

Combining on-surface synthetic methods with the power of scanning tunneling microscopy to characterize novel materials at the single molecule level, we show how to steer the reactivity of one anthracene-based precursor towards different product nanostructures. Whereas using a Au(111) surface with three-fold symmetry results in the dominant formation of a starphene derivative, the two-fold symmetry of a reconstructed Au(110) surface allows the selective growth of non-benzenoid linear conjugated polymers. We further assess the electronic properties of each of the observed product structures via tunneling spectroscopy and DFT calculations, altogether advancing the synthesis and characterization of molecular structures of notable scientific interest that have been only scarcely investigated to date, as applies both to starphenes and to non-benzenoid conjugated polymers., We acknowledge funding from the European Union's Horizon 2020 programme (Grant Agreement No. 635919 and 863098), from the Spanish Agencia Estatal de Investigación (Grant No. MAT2016-78293-C6, PID2019-107338RB-C63, PID2019-107338RB-C66 and FIS2017-83780-P), Xunta de Galicia (Centro singular de investigación de Galicia, accreditation 2019–2022, ED431G 2009/03), Dep. Educación of the Basque Government and UPV/EHU (Grant No. IT-756-13), and the European Regional Development Fund (ERDF)., Peer reviewed

A prerequisite to characterize magnetic materials is the capability to describe systems containing unpaired electrons. In this study, we benchmark the one-shot GW (G0W0) on top of different unrestricted mean-field solutions for open-shell molecules using Dunning's correlation-consistent basis sets expanded in terms of Gaussian functions. We find that the G0W0 correction to hybrid functionals provides reasonably accurate results for the ionization energies of open-shell systems when compared to those obtained from high-level ab initio methods. Moreover, the quality of the G0W0 exchange–correlation approximation is evaluated by the discrepancy between the ionization energy of the neutral molecules and the electron affinity of the corresponding cations. Furthermore, we assess the capability of the GW to reproduce the correct energy ordering of molecular spin–orbitals. To such an aim, we thoroughly discuss three open-shell molecules CN, NH2, and O2, for which approximate functionals fail to correctly capture the single-electron spectrum. Particularly, we demonstrate that the overestimation of the exchange energy in the studied spin–orbitals is reduced by the GW dynamic correlation term, restoring the molecular orbital ordering. Interestingly, we find that deviations of the exchange and correlation energies, in comparison with our ab initio reference, can be very different for molecular orbitals with different symmetry, e.g. σ and π-type orbitals., Authors acknowledge support from Spanish Agencia Estatal de Investigación (Grant Nos. PID2019-107338RB-C66, PID2019-109555GB-I00 and RTC-2016-5681-7), and the Eusko Jaurlaritza and UPV/EHU (Grant Nos. PIBA19-0004 and IT1246-19). DSP also acknowledges support from the European Union (EU) through Horizon 2020 (FET-Open project SPRING Grant No. 863098)., Peer reviewed

This article belongs to the Special Issue On-Surface Synthesis of Low-Dimensional Organic Nanostructures., Chiral graphene nanoribbons are extremely interesting structures due to their narrow band gaps and potential development of spin-polarized edge states. Here, we study their band structure on low work function silver surfaces. The use of a curved Ag single crystal provides, within the same sample, regions of disparate step structure and step density. Whereas the former leads to distinct azimuthal growth orientations of the graphene nanoribbons atop, the latter modulates the substrate’s work function and thereby the interface energy level alignment. In turn, we disclose the associated charge transfer from the substrate to the ribbon and assess its effect on the nanoribbon’s properties and the edge state magnetization., We acknowledge financial support from MCIN/AEI/10.13039/501100011033 (grant nos. PID2019-107338RB-C62, PID2019-107338RB-C63, PID2019-107338RB-C66, and PCI2019-111933-2 and MAT-2017-88374-P), the European Union’s Horizon 2020 research and innovation program (FET Open project SPRING, grant no. 863098), the Xunta de Galicia (Centro Singular de Investigación de Galicia, 2019–2022, grant no. ED431G2019/03), the European Regional Development Fund, the Basque Government (Grant IT-1255-19), Gobierno Vasco-UPV/EHU (Project No. IT1246-19) and the Dpto. Educación Gobierno Vasco (Grant No. PIBA-2020-1-0014)., Peer reviewed

Master's in Nanoscience., The study of magnetism in organic materials have been classically a controversial
eld up to now. Currently, there is no doubt that pi-electronic systemscan host localized magnetic moments. Especially, the study of graphene nanostructures is hot topic. The ability of tailoring the shape of these nanostructures and probing their electronic properties in the atomic level, allowed the fabrication and characterization of magnetic open-shell nanographene (OSNG). In this sense, on-surface synthesis (OSS) strategies and state-of-the-art scanning tunneling microscope (STM) techniques and inelastic electron tunneling spectroscopy (IETS) were crucial to the development of the eld.
The theoretical study of spin chains has been going on for decades. Nevertheless,
the experimental research on pi-magnetic chains is still an unexplored route. The weak magnetic anistropy and spin-orbit coupling of light carbon materials is key for the long range magnetic ordering of spin chains. The OSNG triangulene showing a S = 1 magnetic ground state makes the perfect building block for magnetic chains. In this work, the results of a closed chain of 6 triangulene units and of short open chains of 3, 4 and 6 units are presented. By means of theoretical calculations, based on model Hamiltonians with empirical parameters, the magnetic ordering is simulated. Then, the nanostructure is fabricated via OSS under ultra-high vacuum (UHV) conditions. Lastly, the chemical structure of the chains is resolved thanks to ultra-low temperature (ULT) UHV STM and
the spin excitations are measured as the inelastic signal in scanning tunneling
spectroscopy (STS). We found that such chains show antiferromagnetic (AFM) ordering and that the open or close topology strongly determines the spin excitation spectrum.
This spectrum arises from the collective spin states de ning the chain, as a manifestation of many-body effect in these highly correlated systems., Research in the frame of the SPRING European project., Peer reviewed

Nitrogen heteroatom doping into a triangulene molecule allows tuning its magnetic state. However, the synthesis of the nitrogen-doped triangulene (aza-triangulene) has been challenging. Herein, we report the successful synthesis of aza-triangulene on the Au(111) and Ag(111) surfaces, along with their characterizations by scanning tunneling microscopy and spectroscopy in combination with density functional theory (DFT) calculations. Aza-triangulenes were obtained by reducing ketone-substituted precursors. Exposure to atomic hydrogen followed by thermal annealing and, when necessary, manipulations with the scanning probe afforded the target product. We demonstrate that on Au(111), aza-triangulene donates an electron to the substrate and exhibits an open-shell triplet ground state. This is derived from the different Kondo resonances of the final aza-triangulene product and a series of intermediates on Au(111). Experimentally mapped molecular orbitals match with DFT-calculated counterparts for a positively charged aza-triangulene. In contrast, aza-triangulene on Ag(111) receives an extra electron from the substrate and displays a closed-shell character. Our study reveals the electronic properties of aza-triangulene on different metal surfaces and offers an approach for the fabrication of new hydrocarbon structures, including reactive open-shell molecules., We acknowledge financial support from MCIN/AEI/10.13039/501100011033 (grant nos. PID2019-107338RB-C61, PID2019-107338RB-C62, PID2019-107338RB-C63, PID2019-109555GB-I00, and FJC2019-041202-I); the Basque Government (IT-1255-19 and PIBA19-0004); the Spanish Research Council (ILINKC20002), the European Union’s Horizon 2020 research and innovation program (grant no. 863098 and Marie Skłodowska-Curie Actions Individual Fellowship no. 101022150); and the Xunta de Galicia (Centro Singular de Investigación de Galicia, 2019-2022, grant no. ED431G2019/03)., Peer reviewed

Open-shell graphene nanoribbons have become promising candidates for future applications, including quantum technologies. Here, we characterize magnetic states hosted by chiral graphene nanoribbons (chGNRs). The substitution of a hydrogen atom at the chGNR edge by a ketone effectively adds one pz electron to the π-electron network, producing an unpaired π-radical. A similar scenario occurs for regular ketone-functionalized chGNRs in which one ketone is missing. Two such radical states can interact via exchange coupling, and we study those interactions as a function of their relative position, which includes a remarkable dependence on the chirality, as well as on the nature of the surrounding ribbon, that is, with or without ketone functionalization. Besides, we determine the parameters whereby this type of system with oxygen heteroatoms can be adequately described within the widely used mean-field Hubbard model. Altogether, we provide insight to both theoretically model and devise GNR-based nanostructures with tunable magnetic properties., We acknowledge financial support from the MCIN/AEI/10.13039/501100011033 (Grants PID2019-107338RB-C62, PID2019-107338RB-C63, PID2020-115406GB-I00, PCI2019-111933-2 (FLAG-ERA grant LEGOCHIP), and Juan de la Cierva Grant FJC2019-041202-I), the European Union’s Horizon 2020 research and innovation program (FET-OPEN project SPRING, Grant No. 863098 and Marie Skłodowska-Curie Actions Individual Fellowship No. 101022150), the Xunta de Galicia (Centro Singular de Investigación de Galicia, 2019-2022, Grant ED431G2019/03), the European Regional Development Fund, the Basque Government (IT-1255-19), the Basque Government (PIBA Grant PI_2020_1_0014), the Basque Departamento de Educación through the Ph.D. scholarship No. PRE_2020_2_0049 (S.S.), the Spanish Research Council (LINKC20002)., Peer reviewed

The synthesis of novel organic prototypes combining different functionalities is key to achieve operational elements for applications in organic electronics. Here we set the stage towards individually addressable magneto-optical transducers by the on-surface synthesis of optically active manganese-phthalocyanine derivatives (MnPc) obtained directly on a metallic substrate. We created these 2D nanostructures under ultra-high vacuum conditions with atomic precision starting from a simple phthalonitrile precursor with reversible photo-induced reactivity in solution. These precursors maintain their integrity after powder sublimation and coordinate with the Mn ions into tetrameric complexes and then transform into MnPcs on Ag(111) after a cyclotetramerization reaction. Using scanning tunnelling microscopy and spectroscopy together with DFT calculations, we identify the isomeric configuration of two bi-stable structures and show that it is possible to switch them reversibly by mechanical manipulation. Moreover, the robust magnetic moment brought by the central Mn ion provides a feasible pathway towards magneto-optical transducer fabrication. This work should trigger further research confirming such magneto-optical effects in MnPcs both on surfaces and in liquid environments., We gratefully acknowledge financial support from the Spanish Ministries of Economy, Industry and Competitiveness (MINECO, grants MAT2016-78293-C6-4-R and MAT2016-78293-C6-6) and of Science and Innovation (MICINN, grant no. PID2019-107338RB-C62, PID2019-107338RB-C64, PID2019-107338RB-C66/AEI/10.13039/501100011033 and RED2018-102833-T), the regional Governments of Aragon (E13-20R and E12-20R), the Xunta de Galicia (Centro de Investigación de Galicia acreditation 2019–2022, ED431G 2019/03), the Dept. of Education of the Basque Government and UPV/EHU (grant no. IT1246-19), the Spanish Research Agency (AEI), the European Regional Development Fund (ERDF) under the program Interreg V-A España-Francia-Andorra (contract no. EFA194/16 TNSI) and the European Union through Horizon 2020 (FET-Open project SPRING grant. no. 863098)., We acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI)., Peer reviewed

Spin-hosting graphene nanostructures are promising metal-free systems for elementary quantum spintronic devices. Conventionally, spins are protected from quenching by electronic band gaps, which also hinder electronic access to their quantum state. Here, we present a narrow graphene nanoribbon substitutionally doped with boron heteroatoms that combines a metallic character with the presence of localized spin 1/2 states in its interior. The ribbon was fabricated by on-surface synthesis on a Au(111) substrate. Transport measurements through ribbons suspended between the tip and the sample of a scanning tunneling microscope revealed their ballistic behavior, characteristic of metallic nanowires. Conductance spectra show fingerprints of localized spin states in the form of Kondo resonances and inelastic tunneling excitations. Density functional theory rationalizes the metallic character of the graphene nanoribbon due to the partial depopulation of the valence band induced by the boron atoms. The transferred charge builds localized magnetic moments around the boron atoms. The orthogonal symmetry of the spin-hosting state’s and the valence band’s wave functions protects them from mixing, maintaining the spin states localized. The combination of ballistic transport and spin localization into a single graphene nanoribbon offers the perspective of electronically addressing and controlling carbon spins in real device architectures., We gratefully acknowledge financial support from Grants PID2019-107338RB-C61, PID2019-107338RB-C62, PID2019-107338RB-C66, PID2019-110037GB-I00, and PCI2019-111933-2 and the Maria de Maeztu Units of Excellence Program CEX2020-001038-M funded by MCIN/AEI/10.13039/501100011033, the European Regional Development Fund, the European Union (EU) H2020 program through the FET Open project SPRING (Grant Agreement No. 863098), the Xunta de Galicia (Centro de Investigación de Galicia accreditation 2019–2022, ED431G 2019/03), the Dpto. Educación Gobierno Vasco (Grant Nos. PIBA-2020-1-0014, IT1246-19, and IT-1569-22) and the Programa Red Guipuzcoana de Ciencia, Tecnología e Innovación 2021 (Grant No. 2021-CIEN-000070-01. Gipuzkoa Next). The authors acknowledge the financial support received from the IKUR Strategy under the collaboration agreement between Ikerbasque Foundation and DIPC on behalf of the Department of Education of the Basque Government., Peer reviewed

Carbon nanostructures with zigzag edges exhibit unique properties—such as localized electronic states and spins—with exciting potential applications. Such nanostructures however are generally synthesized under vacuum because their zigzag edges are unstable under ambient conditions: a barrier that must be surmounted to achieve their scalable integration into devices for practical purposes. Here we show two chemical protection/deprotection strategies, demonstrated on labile, air-sensitive chiral graphene nanoribbons. Upon hydrogenation, the chiral graphene nanoribbons survive exposure to air, after which they are easily converted back to their original structure by annealing. We also approach the problem from another angle by synthesizing a form of the chiral graphene nanoribbons that is functionalized with ketone side groups. This oxidized form is chemically stable and can be converted to the pristine hydrocarbon form by hydrogenation and annealing. In both cases, the deprotected chiral graphene nanoribbons regain electronic properties similar to those of the pristine nanoribbons. We believe both approaches may be extended to other graphene nanoribbons and carbon-based nanostructures., Research was supported by MCIN/AEI/10.13039/501100011033 (grant nos PID2019-107338RB-C62 (D.P.), PID2019-107338RB-C63 (M.C. and D.G.d.O.) and FJC2019-041202-I (F.S.)); the European Union’s Horizon 2020 programme (grant nos 863098 (D.P.) and 635919 (D.G.d.O.), and Marie Skłodowska-Curie Actions Individual Fellowship no. 101022150 (T.W.)); the Gobierno Vasco (grant no. PIBA_2020_1_0036 (D.G.d.O.)); the Xunta de Galicia (Centro Singular de Investigación de Galicia, 2019–2022, grant no. ED431G2019/03 (D.P.)); the European Regional Development Fund; the Praemium Academie of the Academy of Science of the Czech Republic (GACR project no. 20-13692X (P.J.)); the Czech Nanolab Research Infrastructure supported by MEYS CR (project no. LM2018110 (P.J.)); and the Operational Programme for Research, Development and Education of the European Regional Development Fund (project no. CZ.02.1.01/0.0/0.0/16_019/0000754 (P.J.))., Peer reviewed

Emergence of π-magnetism in open-shell nanographenes has been theoretically predicted decades ago but their experimental characterization was elusive due to the strong chemical reactivity that makes their synthesis and stabilization difficult. In recent years, on-surface synthesis under vacuum conditions has provided unprecedented opportunities for atomically precise engineering of nanographenes, which in combination with scanning probe techniques have led to a substantial progress in our capabilities to realize localized electron spin states and to control electron spin interactions at the atomic scale. Here we review the essential concepts and the remarkable advances in the last few years, and outline the versatility of carbon-based π-magnetic materials as an interesting platform for applications in spintronics and quantum technologies., This work was funded by the Spanish MCIN/AEI/ 10.13039/501100011033 (PID2020-115406GB-I00 and PID2019-107338RB-C63), the Basque Department of Education (PIBA-2020-1-0014), and the European Union's Horizon 2020 (FET-Open Project SPRING Grant No. 863098)., Peer reviewed

Activating the strong C–C σ-bond is a central problem in organic synthesis. Directly generating activated C centers by metalation of structures containing strained four-membered rings is one maneuver often employed in multistep syntheses. This usually requires high temperatures and/or precious transition metals. In this paper, we report an unprecedented C–C σ-bond activation at room temperature on Cu(111). By using bond-resolving scanning probe microscopy, we show the breaking of one of the C–C σ-bonds of a biphenylene derivative, followed by insertion of Cu from the substrate. Chemical characterization of the generated species was complemented by X-ray photoemission spectroscopy, and their reactivity was explained by density functional theory calculations. To gain further insight into this unique reactivity on other coinage metals, the reaction pathway on Ag(111) was also investigated and the results were compared with those on Cu(111). This study offers new synthetic routes that may be employed in the in situ generation of activated species for the on-surface synthesis of novel C-based nanostructures., The authors acknowledge financial support from MCIN/AEI/10.13039/501100011033 (Grants PID2019-107338RB-C62, PID2019-107338RB-C63, PID2019-109555GB-I00, and TED2021-132388B-C43), the Basque Government (IT1591-22 and PIBA19-0004), the Spanish Research Council (ILINKC20002), the European Union’s Horizon 2020 research and innovation program (Grant 863098 and Marie Skłodowska-Curie Actions Individual Fellowship 101022150), and the Xunta de Galicia (Centro Singular de Investigación de Galicia, 2019-2022, Grant ED431G2019/03). A.P.P. thanks the UAEU for an internal start-up grant (31S410)., Peer reviewed

Breaking a correlated pair in a superconductor requires an even number of fermions providing at least twice the pairing energy Δ. Here, we show that a single tunneling electron can also excite a pair breaking excitation in a proximitized gold film in the presence of magnetic impurities. Combining scanning tunneling spectroscopy with theoretical modeling, we map the excitation spectrum of an Fe-porphyrin molecule on the Au/V(100) proximitized surface into a manifold of entangled Yu-Shiba-Rusinov and spin excitations. Pair excitations emerge in the tunneling spectra as peaks outside the spectral gap only in the strong coupling regime, where the presence of a bound quasiparticle in the ground state ensures the even fermion parity of the excitation. Our results unravel the quantum nature of magnetic impurities on superconductors and demonstrate that pair excitations unequivocally reveal the parity of the ground state., We acknowledge financial support from Grants No. TED2021-130292B-C42, No. PID2019-107338RBC61, No. CEX2020-001038-M, No. PID2020–112811 GB-I00, and Grant No. PID2020–114252 GB-I00, funded by MCIN/AEI/10.13039/501100011033, from the Diputación Foral de Guipuzcoa, and from the European Union (EU) through the Horizon 2020 FET-Open projects SPRING (No. 863098) and SUPERTED (No. 800923), and the European Regional Development Fund (ERDF). M. A. C. has been supported by Ikerbasque, Basque Foundation for Science, and MCIN Grant No. PID2020–120614 GB-I00 (ENACT). F. S. B. thanks Prof. Björn Trauzettel for his hospitality at Würzburg University, and the A. v. Humboldt Foundation for financial support. J. O. acknowledges the scholarship PRE_2021_1_0350 from the Basque Government., Peer reviewed

Spin-flip excitations of iron porphyrin molecules on Au(111) are investigated with a low-temperature scanning tunneling microscope. The molecules adopt two distinct adsorption configurations on the surface that exhibit different magnetic anisotropy energies. Density functional theory calculations show that the different structures and excitation energies reflect unlike occupations of the Fe 3d levels. We demonstrate that the magnetic anisotropy energy can be controlled by changing the adsorption site, the orientation, or the tip–molecule distance., X.M., A.W., C.L., and R.B. acknowledge support by Kiel Nano, Surface and Interface Science (KiNSIS). J.M. and R.H. thank the German Research Foundation for support via Project DFG HE 1530/20-1. M.M., D.S.-P., and A.G.-L. acknowledge financial support from Grant PID2019-107338RB-C66 funded by Grant MCIN/AEI/10.13039/501100011033, the European Union H2020 program through the FET Open Project SPRING (Grant Agreement 863098), the Programa Red Guipuzcoana de Ciencia, Tecnología e Innovación 2021 (Grant 2021-CIEN-000070-01, Gipuzkoa Next) and from Eusko Jaurlaritza and UPV/EHU through Grants IT1246-19 and IT-1569-22, and financial support received from the IKUR Strategy under the collaboration agreement between Ikerbasque Foundation and DIPC on behalf of the Department of Education of the Basque Government. C.L. also thanks the Alexander von Humboldt-Foundation for a research fellowship., Peer reviewed

We study theoretically electron interference in a Mach–Zehnder-like geometry formed by four zigzag graphene nanoribbons arranged in parallel pairs, one on top of the other, such that they form intersection angles of 60∘. Depending on the interribbon separation, each intersection can be tuned to act either as an electron beam splitter or as a mirror, enabling tuneable circuitry with interfering pathways. Based on the mean-field Hubbard model and Green's function techniques, we evaluate the electron transport properties of such eight-terminal devices and identify pairs of terminals that are subject to self-interference. We further show that the scattering matrix formalism in the approximation of independent scattering at the four individual junctions provides accurate results as compared with the Green's function description, allowing for a simple interpretation of the interference process between two dominant pathways. This enables us to characterize the device sensitivity to phase shifts from an external magnetic flux according to the Aharonov–Bohm effect as well as from small geometric variations in the two path lengths. The proposed devices could find applications as magnetic field sensors and as detectors of phase shifts induced by local scatterers on the different segments, such as adsorbates, impurities or defects. The setup could also be used to create and study quantum entanglement., This work was funded by the Spanish MCIN/AEI/ 10.13039/501100011033 (PID2020-115406GBI00 and PID2019-107338RB-C66), the Basque Department of Education (PIBA-2020-1-0014), the University of the Basque Country (UPV/EHU) through Grant IT-1569-22, and the European Union’s Horizon 2020 (FET-Open Project SPRING Grant No. 863098)., Peer reviewed

We study theoretically electron interference in a Mach–Zehnder-like geometry formed by four zigzag graphene nanoribbons (ZGNRs) arranged in parallel pairs, one on top of the other, such that they form intersection angles of 60˚ Depending on the interribbon separation, each intersection can be tuned to act either as an electron beam splitter or as a mirror, enabling tuneable circuitry with interfering pathways. Based on the mean-field Hubbard model and Green's function techniques, we evaluate the electron transport properties of such 8-terminal devices and identify pairs of terminals that are subject to self-interference. We further show that the scattering matrix formalism in the approximation of independent scattering at the four individual junctions provides accurate results as compared with the Green's function description, allowing for a simple interpretation of the interference process between two dominant pathways. This enables us to characterize the device sensitivity to phase shifts from an external magnetic flux according to the Aharonov–Bohm effect as well as from small geometric variations in the two path lengths. The proposed devices could find applications as magnetic field sensors and as detectors of phase shifts induced by local scatterers on the different segments, such as adsorbates, impurities or defects. The setup could also be used to create and study quantum entanglement., We acknowledge funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 863098 (FET-Open project "SPRING"), Peer reviewed

Triangulenes are a class of open-shell triangular graphene flakes with total spin increasing with their size. In the last years, on-surface-synthesis strategies have permitted fabricating and engineering triangulenes of various sizes and structures with atomic precision. However, direct proof of the increasing total spin with their size remains elusive. In this work, we report the combined in-solution and on-surface synthesis of a large nitrogen-doped triangulene (aza-[5]-triangulene) on a Au(111) surface, and the detection of its high-spin ground state. Bond-resolved scanning tunneling microscopy images uncovered radical states distributed along the zigzag edges, which were detected as weak zero-bias resonances in scanning tunneling spectra. These spectral features reveal the partial Kondo screening of a high-spin state. Through a combination of several simulation tools, we find that the observed distribution of radical states is explained by a quintet ground state (S=2), instead of the quartet state (S=3/2) expected for the neutral species. This confirms that electron transfer to the metal substrate raises the spin of the ground state. We further provide a qualitative description of the change of (anti)aromaticity introduced by N-substitution, and its role in the charge stabilization on a surface, resulting in an S=2 aza-triangulene on Au(111)., The authors gratefully acknowledge financial support from MCIN/AEI/10.13039/501100011033 through grants No. PID2019-107338RB, PID2019-109555GB-I00, PCI2019-111933-2 and TED2021-132388B-C42, FIS2017-83780-P, and CEX2020-001038-M, from the ELKARTEK project BRTA QUANTUM (no. KK-2022/00041), from the European Regional Development Fund, from the European Union (EU) H2020 program through the FET Open project SPRING (grant agreement No. 863098) and ERC Synergy Grant MolDAM (951519), Xunta de Galicia (Centro de Investigación de Galicia accreditation 2019–2022, ED431G 2019/03) and Xunta de Galicia-Gain Oportunius Program. F.R.-L. thanks the Spanish Ministerio de Educación y Formación Profesional through the PhD scholarship No. FPU20/03305. F.S. acknowledges funding by the Spanish Ministerio de Ciencia e Innovación through Ramón y Cajal Fellowship RYC2021-034304-I. M.E.S.-S. acknowledges the funding by the UK Research and Innovation under the UK government's Horizon Europe funding guarantee (grant number EP/X020908/1)., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2020-001038-M)., Peer reviewed

We argue that the formation of Yu-Shiba-Rusinov excitations in proximitized thin films is largely mediated by a type of Andreev-bound state named after de Gennes and Saint-James. This is shown by studying an experimentally motivated model and computing the overlap of the wave functions of these two subgap states. We find the overlap stays close to unity even as the system moves away from weak coupling across the parity-changing quantum phase transition. Based on this observation, we introduce a single-site model of the bound state coupled to a quantum spin. The adequacy of this description is assessed by reintroducing the coupling to the continuum as a weak perturbation and studying its scaling flow using Anderson's poor man's scaling., We acknowledge financial support from MCIN Grants No. PID2020-120614GB-I00 (ENACT), No. PID2019-107338RB-C61, No. CEX2020-001038-M, No. PID2020-112811GB-I00, No. TED2021-130292B-C42, and No. PID2020-114252GB-I00, funded by MCIN/AEI/10.13039/501100011033, from the Diputación Foral de Guipuzcoa, the ELKARTEK project BRTA QUANTUM (No. KK-2022/00041), and from the European Union (EU) through the Horizon 2020 FET-Open projects SPRING (No. 863098), and the European Regional Development Fund (ERDF). M.A.C. has been supported by Ikerbasque, Basque Foundation for Science. F.S.B. thanks financial support from the Basque Government through Grant No. IT-1591-22. J.O. acknowledges the scholarship PRE_2022_2_0095 from the Basque Government., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2020-001038-M)., Peer reviewed

Low dimensional carbon-based materials can show intrinsic magnetism associated to p-electrons in open-shell π-conjugated systems. Chemical design provides atomically precise control of the π-electron cloud, which makes them promising for nanoscale magnetic devices. However, direct verification of their spatially resolved spin-moment remains elusive. Here, we report the spin-polarization of chiral graphene nanoribbons (one-dimensional strips of graphene with alternating zig-zag and arm-chair boundaries), obtained by means of spin-polarized scanning tunnelling microscopy. We extract the energy-dependent spin-moment distribution of spatially extended edge states with π-orbital character, thus beyond localized magnetic moments at radical or defective carbon sites. Guided by mean-field Hubbard calculations, we demonstrate that electron correlations are responsible for the spin-splitting of the electronic structure. Our versatile platform utilizes a ferromagnetic substrate that stabilizes the organic magnetic moments against thermal and quantum fluctuations, while being fully compatible with on-surface synthesis of the rapidly growing class of nanographenes., We acknowledge financial support from the Spanish Ministry of Science and Innovation MICIN through grant nos. PID2019-107338RB-C64 (D.S. and J.L.C.), PID2019-107338RB-C61 (J.I.P.), PID2019-107338RB-C62 (D.P.), PID2019-107338RB-C63 (D.G.O.), PID2020-115406GB-I00 (T.F.) funded by AEI/10.13039/501100011033; grant no. PCI2019-111933-2; and red temática RED2018-102833-T. This work was also supported by European Regional Development Fund (ERDF) under the program Interreg V-A España-Francia-Andorra (grant no. EFA194/16 TNSI), the European Union (EU) H2020 program through the FET-Open project SPRING (Grant Agreement No. 863098, J.I.P. and T.F.) and the NextGeneration/PRTR grant no. TED2021-132388B-C43 (D.G.O.), the Maria de Maeztu Units of Excellence Program CEX2020-001038-M (J.L.P.), the Aragon Government (E13-20R (D.S.) and E12-20R (J.L.C.)), the Programa Red Guipuzcoana de Ciencia, Tecnología e Innovación 2021 (Grant No. 2021-CIEN-000069-01, Gipuzkoa Next, J.I.P.), the Basque Department of Education (PRE-2021-2-0190 and PIBA-2020-1-0014, T.F.), and the Xunta de Galicia (Centro de Investigación accreditation 2019-2022, ED431G2019/03, D.P.), With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2020-001038-M)., Peer reviewed

On-surface synthesis of graphene nanoribbons enables engineering their electronic and magnetic properties, which sensitively depend on their precise bonding structure, morphology and chemical composition. Here, we investigate nitrogen and boron co-doping in order to better understand the effects of simultaneous chemical substitution in sites along the backbone of 7AGNRs. In a comparative analysis with the pristine system, the origin of the impurity bands that nitro-borylated systems exhibit was addressed. In addition to this, we studied the appearance of an electric dipolar moment, the charge transfer mechanism behind it and its dependence on the distance between BN centres. The high defect concentration limit and the dilute limit were investigated, along with various doping schemes with four substitutional doping sites and the possible emergence of magnetism in these systems., This work was supported by grant PID2019-107338RB-C66 funded by MCIN/AEI/10.13039/501100011033, grant TED2021-132388B-C44 funded by MCIN/AEI/10.13039/501100011033 and Unión Europea Next Generation EU/PRTR, grant PID2022-140845OB-C66 funded by MCIN/AEI/10.13039/501100011033 and FEDER Una manera de hacer Europa, the European Union H2020 program through the FET Open project SPRING (Grant Agreement No. 863098) and the Basque Department of Education (IT1569-22). The authors also acknowledge the financial support received from the IKUR Strategy under the collaboration agreement between Ikerbasque Foundation and DIPC on behalf of the Department of Education of the Basque Government., Peer reviewed

Organic diradicals are envisioned as elementary building blocks for designing a new generation of spintronic devices and have been used in constructing prototypical field effect transistors and nonlinear optical devices. Open-shell systems, however, are also reactive, thus requiring design strategies to "protect" their radical character from the environment, especially when they are embedded in solid-state devices. Here, we report the persistence on a metallic surface of the diradical character of a diindeno[b,i]anthracene (DIAn) core protected by bulky end-groups. Our scanning tunneling spectroscopy measurements on single-molecules detected singlet-triplet excitations that were absent for DIAn species packed in assembled structures. Density functional theory simulations unravel that the molecular geometry on the metal substrate can crucially modify the value of the singlet-triplet gap via the delocalization of the radical sites. The persistence of the diradical character over metallic substrates is a promising finding for integrating radical-based materials into functional devices., We gratefully acknowledge financial support from Spanish MCIN/AEI/10.13039/501100011033 and the European Regional Development Fund (ERDF) through Grants PID2019-107338RBC61, PID2020-115406GB-I00, PID2021-127127NB-I00, and CEX2020-001038-M and from the European Union (EU) through Horizon 2020 (FET-Open project SPRING Grant 863098). J.C. also acknowledges the Junta de Andalucía, Spain (PROYEXCEL-0328), and M.M.H. acknowledges the NSF (CHE-1954389) for financial support., With funding from the Spanish government through the "Severo Ochoa Centre of Excellence" accreditation (CEX2020-001038-M)., Peer reviewed

We investigated the Kondo effect of cobalt(II)-5-15-bis(4′-bromophenyl)-10,20-bis(4′-iodophenyl)porphyrin (CoTPPBr2I2) molecules on Au(111) with low-temperature scanning tunneling microscopy under ultrahigh vacuum conditions. The molecules exhibit four adsorption configurations at the top and bridge sites of the surface with different molecular orientations. The Kondo resonance shows extraordinary sensitivity to the adsorption configuration. By switching the molecule between different configurations, the Kondo temperature is varied over a wide range from ≈8 up to ≈250 K. Density functional theory calculations reveal that changes of the adsorption configuration lead to distinct variations of the hybridization between the molecule and the surface. Furthermore, we show that surface reconstruction plays a significant role for the molecular Kondo effect., This work was supported by grant PID2019-107338RB-C66 funded by MCIN/AEI/10.13039/501100011033, grant TED2021-132388B-C44 funded by MCIN/AEI/10.13039/501100011033 and Unión Europea Next Generation EU/PRTR, grant PID2022-140845OB-C66 funded by MCIN/AEI/10.13039/501100011033 and FEDER Una manera de hacer Europa, the European Union H2020 program through the FET Open project SPRING (Grant Agreement No. 863098) and the Basque Department of Education (IT1569-22). The authors also acknowledge the financial support received from the IKUR Strategy under the collaboration agreement between Ikerbasque Foundation and DIPC on behalf of the Department of Education of the Basque Government., Peer reviewed

Low dimensional carbon-based materials can show intrinsic magnetism associated to p-electrons in open-shell π-conjugated systems. Chemical design provides atomically precise control of the π-electron cloud, which makes them promising for nanoscale magnetic devices. However, direct verification of their spatially resolved spin-moment remains elusive. Here, we report the spin-polarization of chiral graphene nanoribbons (one-dimensional strips of graphene with alternating zig-zag and arm-chair boundaries), obtained by means of spin-polarized scanning tunnelling microscopy. We extract the energy-dependent spin-moment distribution of spatially extended edge states with π-orbital character, thus beyond localized magnetic moments at radical or defective carbon sites. Guided by mean-field Hubbard calculations, we demonstrate that electron correlations are responsible for the spin-splitting of the electronic structure. Our versatile platform utilizes a ferromagnetic substrate that stabilizes the organic magnetic moments against thermal and quantum fluctuations, while being fully compatible with on-surface synthesis of the rapidly growing class of nanographenes.