Suchergebnisse

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.). ; 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

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

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

Metal halides are a class of layered materials with promising electronic and magnetic properties persisting down to the two-dimensional limit. While most recent studies focused on the trihalide components of this family, the rather unexplored metal dihalides are also van der Waals layered systems with distinctive magnetic properties. Here we show that the dihalide NiBr2 grows epitaxially on a Au(111) substrate and exhibits semiconducting and magnetic behavior starting from a single layer. Through a combination of a low-temperature scanning-tunneling microscopy, low-energy electron diffraction, X-ray photoelectron spectroscopy, and photoemission electron microscopy, we identify two competing layer structures of NiBr2 coexisting at the interface and a stoichiometrically pure layer-by-layer growth beyond. Interestingly, X-ray absorption spectroscopy measurements revealed a magnetically ordered state below 27 K with in-plane magnetic anisotropy and zero-remanence in the single layer of NiBr2/Au(111), which we attribute to a noncollinear magnetic structure. The combination of such two-dimensional magnetic order with the semiconducting behavior down to the 2D limit offers the attractive perspective of using these films as ultrathin crystalline barriers in tunneling junctions and low-dimensional devices. ; D.B. acknowledges funding from the Austrian Science Fund (FWF) under the Erwin Schrödinger fellowship agreement (project number: J4395-N). C.G.-O. and M.P.-D. acknowledge funding of the Ph.D. fellowship from the MPC Foundation. We gratefully acknowledge financial support from Spanish AEI (Grant Nos. PID2019-107338RB-C6, RTI-2018-095303-C53, and the Maria de Maeztu Units of Excellence Programme MDM-2016-0618) and from the European Union (EU) through Horizon 2020 (SUPERTED Grant No. 800923), from Interred POCTEFA V-A Spain/France/Andorra Program (EFA 194/16/TNSI), the Basque Government (GV/EJ) under grants IT-1255-19, and the European Regional Development Fund. P.G. acknowledges funding from MINECO Grant No. FIS2016-78591-C3-2-R and FLAG-ERA Grant No. PCI2019-111908-2. ; Peer reviewed