Suchergebnisse

Two polymorphic phases of ω-(4′-methylbiphenyl-4-yl) butane-1-thiol (BP4) molecules formed on Au(111) were investigated by multidimensional atomic force microscopy, combining conductivity measurements, electrostatic characterization, friction force mapping, and normal force spectroscopy. Based on the same molecular structure but differing in molecular order, packing density, and molecular tilt, the two phases serve as a test bench to establish the structure–property relationships in self-assembled monolayers (SAMs). From a detailed analysis of the charge transport and electrostatics, the contributions of geometrical and electronic effects to the tunneling are discussed. ; This work has been supported by the Spanish Government under projects MAT2013-47869-C4-1-P and MAT2016-77852- C2-1-R (AEI/FEDER, UE) and the Generalitat de Catalunya 2014 SGR501. We acknowledge the MINECO project MAT2015-68994-REDC and the "'Severo Ochoa"' Program for Centers of Excellence in R&D (SEV-2015-0496). M. Paradinas thanks the Spanish Government for financial support through BES-2008-003588 FPI and PTA2014-09788-I fellowships. C. Munuera acknowledges financial support from the "Ramon y Cajal ́ " program RYC-2014-16626. ; Peer reviewed

The controlled 3D nanostructuration of molecular layers of the semiconducting molecules C22H14 (pentacene) and N,N′-dioctyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C8) is addressed. A tip-assisted method using atomic force microscopy (AFM) is developed for removing part of the organic material and relocating it in up to six layer thick nanostructures. Moreover, unconventional molecular scale imaging combining diverse friction force microscopy modes reveals the stacking sequence of the piled layers. In particular, we unambiguously achieve epitaxial growth, an issue of fundamental importance in thin film strategies for the nanostructuration of more efficient organic nanodevices. ; We thank M. Aghamohammadi for her help with the film growth. This work has been supported by the Spanish Government under projects MAT2013-47869-C4-1-P and MAT2016-77852-C2-1-R (AEI/FEDER, UE) and the Generalitat de Catalunya 2014 SGR501. We acknowledge the MINEICO project MAT2015-68994-REDC and the "Severo Ochoa" Program for Centers of Excellence in R&D (SEV-2015- 0496). M.P. thanks the Spanish Government for financial support through BES-2008-003588 FPI and PTA2014-09788-I fellowships. ; Peer reviewed

The virtually unlimited versatility and unparalleled level of control in the design of metal-organic frameworks (MOFs) has recently been shown to also entail a potential for applications based on the electrical and electronic properties of this rich class of materials. At present, methods to provide reliable and reproducible contacts to MOF materials are scarce; therefore, we have carried out a detailed, multi-technique investigation of an empty and loaded prototype MOF, HKUST-1. Epitaxial thin films of this material grown on a substrate by using liquid-phase epitaxy have been studied by cyclic voltammetry, atomic force microscopy, and quartz crystal microbalance and their quality assessed. By using an ionic liquid as the electrolyte, it is shown that redox-active molecules like ferrocene can be embedded in the pores, enabling a change in the overall conductivity of the framework and the study of the redox chemistry of guest molecules inside the MOF. ; VM acknowledges the EU for the funding through the granting of a Marie Curie Intra-European Fellowship (FP7-PEOPLE-2011; MOLSURMOF-301110). JL acknowledges the program of China Scholarship Council (CSC) for financial support. VM, JL and CW acknowledge A. Terfort for supplying the thiol derivatives. MP and CO acknowledge financial support from the Spanish Government through grants projects MAT2013-47869-C4-1-P and SEV-2015–0496, and Generalitat de Catalunya through grant project 2014 SGR 501. ; Peer reviewed

The chemical modification of an immobilized single crystal in a fluid cell is reported, whereby a material with switching functions is generated in situ by generating a chemical reagent in the flow. Crystals of the insulating organic crystal of TCNQ (tetracyanoquinodimethane) were grown in a microfluidic channel and were trapped using a pneumatic valve, a nascent technique for materials manipulation. They were subsequently reduced using solution-deposited silver to provide a conducting material in situ by a heterogeneous reaction. Removal of the new material from the chip proved it to be the silver salt of reduced TCNQ. Uniquely, conducting atomic force microscope (CAFM) studies show three regions in the solid. The localized original neutral organic material crystal is shown to be an insulator but to produce areas with Ohmic conducting characteristics after reduction. This inhomogeneous doping provides an opportunity for probing electrical materials properties side by side. Measurements with the CAFM witness this conducting material where the TCNQ is fully transformed to the silver salt. Additionally, an intermediate phase is observed that exhibits bipolar resistive switching typical of programmable resistive memories. Raman microscopy proves the conversion of the material in specific regions and clearly defines the intermediate phase region that could be responsible for the switching effect in related materials. This kind of >on crystal chemistry> exploiting immobilization and masking by a pneumatic clamp in a microfluidic channel shows how material can be selectively converted to give different functionalities in the same material piece, even though it is not a single crystal to single crystal conversion, and beckons exploitation for the preparation of systems relevant for molecular electronics as well as other areas where chemical manipulation of single crystals could be beneficial. © The Royal Society of Chemistry 2015. ; This research was supported by the Spanish MINECO project MAT2013-47869-C4 and the Ramon y Cajal program (RYC-2011- 08071). We also acknowledge nancial aid from the Generalitat de Catalunya (2014 SGR 501). RR was funded by the Generalitat de Catalunya and the COFUND programme of the Marie Curie Actions of the 7th R&D Framework Programme of the European Union (BP-B 00256). We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI) ; Peer Reviewed

We have investigated the electronic structures of axially oxo functionalized titanylphthalocyanine (TiOPc) on Ag(111) by X-ray and ultraviolet photoelectron spectroscopies, two-photon photoemission, X-ray absorption spectroscopy, and X-ray magnetic circular dichroism. Furthermore, we use complementary data of TiOPc on graphite and planar copper phthalocyanine (CuPc) on Ag(111) for a comparative analysis. Both molecules adsorb on Ag(111) in a parallel orientation to the surface, for TiOPc with an oxygen-up configuration. The interaction of nitrogen and carbon atoms with the substrate is similar for both molecules, while the bonding of the titanium atom to Ag(111) in the monolayer is found to be slightly more pronounced than in the CuPc case. Ultraviolet photoemission spectroscopy reveals an occupation of the lowest unoccupied molecular orbital (LUMO) level in monolayer thick TiOPc on Ag(111) related to the interaction of the molecules and the silver substrate. This molecule-metal interaction also causes an upward shift of the Ag(111) Shockley state that is transformed into an unoccupied interface state with energies of 0.23 and 0.33 eV for the TiOPc monolayer and bilayer, respectively, at the Brillouin zone center. ; The authors acknowledge financial support from the Deutsche Forschungsgemeinschaft through SFB 1083 "Structure and Dynamics of Internal Interfaces", the Spanish CSIC I-Link programm, the Spanish Ministry of Economy and Competitiveness, MINECO (under Contract No. MAT2016-78293-C6-2-R, and Severo Ochoa No. SEV-2013-0295.), and by the Secretariat for Universities and Research, Knowledge Department of the Generalitat de Catalunya (2014 SGR 715). M. Paradinas thanks the Spanish Government for financial support through PTA2014-09788-I fellowships. ICN2 is funded by the CERCA Programme/Generalitat de Catalunya. ; Peer Reviewed

Interfacial dissimilarity has emerged in recent years as the cornerstone of emergent interfacial phenomena, while enabling the control of electrical transport and magnetic behavior of complex oxide epitaxial films. As a step further toward the lateral miniaturization of functional nanostructures, this work uncovers the role of misfit dislocations in creating periodic surface strain patterns that can be efficiently used to control the spatial modulation of mass transport phenomena and bandwidth-dependent properties on a ≈20 nm length scale. The spontaneous formation of surface strain-relief patterns in La0.7Sr0.3MnO3/LaAlO3 films results in lateral periodic modulations of the surface chemical potential and tetragonal distortion, controlling the spatial distribution of preferential nucleation sites and the bandwidth of the epilayer, respectively. These results provide insights into the spontaneous formation of strain-driven ordered surface patterns, topographic and functional, during the growth of complex oxide heterostructures on lengths scales far below the limits achievable through top-down approaches. ; The authors thank Dr. Belén Ballesteros for her assistance with electron microscopy experiments. This research was sponsored by the Spanish MINECO ("Severo Ochoa" Programme for Centres of Excellence in R&D: SEV- 2015-0496, MAT2015-71664-R, FEDER program, MAT2012-33207, and MAT2013-47869-C4-1-P), and the European Union Horizon 2020 research and innovation program under the Marie Sklodowska–Curie grant agreement No. 645658. The authors also acknowledge fi nancial 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 312483-ESTEEM2 (Integrated Infrastructure Initiative I3) for providing access to aberration corrected electron microscope at CEMES (Toulouse). N.B. thanks the Spanish MINECO for fi nancial support through the FPI program. F.S. acknowledges support from the Labex (Excellence Laboratory) NEXT for a visiting scientist fellowship at CEMES (Toulouse, France). Z.K. is grateful for the support from the Ministry of Education, Science, and Technological Development of the Republic of Serbia through Project III45018. ; Peer reviewed

We address the impact of the relative orientation between donor (D) and acceptor (A) molecules at the D/A heterojunction on the exciton dissociation. For this purpose, two-dimensional heterojunctions of diindenoperylene (DIP) and N,N'-dioctyl-3,4,9,10-perylene tetracarboxylicdiimide (PTCDI-C8) deposited onto SiO2/Si are grown, which exemplify two model interfaces with the π-staking direction either perpendicular or parallel to the interface. Aspects related to the morphology of the heterojunctions and charge photogeneration are studied by scanning probe force methods and photoluminescence (PL) spectroscopy. Results from PL spectroscopy indicate that the exciton dissociation is influenced by the different relative molecular orientations of A and D. For the configuration with stronger orbital overlap between A and D at the interface, the exciton dissociation is dominated by recombination from an interfacial charge-transfer state. ; Financial support by the Spanish Government (projects MAT2010-20020 and NANOSELECT CSD2007-00041) and by the German Research Foundation (DFG) within the priority program SPP1355 is acknowledged. ; Peer Reviewed

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 1-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 electronic characterization further reveals a highly anisotropic electronic structure, where orthogonal one-dimensional electronic bands with an energy gap of ∼1 electron volt coexist with confined pore states, making the nanoporous graphene a highly versatile semiconductor for simultaneous sieving and electrical sensing of molecular species. ; This research was funded by the Centres de Recerca de Catalunya Programme–Generalitat de Catalunya, the Xunta de Galicia (Centro singular de investigacion de Galicia accreditation 2016–2019, ED431G/09), and the European Regional Development Fund. This research was supported by the Spanish Ministry of Economy and Competitiveness (under contract no. MAT2016-78293-C6-2-R, MAT2016-78293-C6-3-R, MAT2016-78293-C6-4-R, and MAT2016-75952-R and Severo Ochoa no. SEV-2013-0295); the Secretariat for Universities and Research, Knowledge Department of the Generalitat de Catalunya 2014 SGR 715, 2014 SGR 56, and 2017 SGR 827; the Basque Department of Education (contract no. PI-2016-1-0027); and the European Union's Horizon 2020 research and innovation program under grant agreement 696656. 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. ; Peer reviewed

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). ; Peer Reviewed

Taming the magnetic anisotropy of lanthanides through coordination environments is crucial to take advantage of the lanthanides properties in thermally robust nanomaterials. In this work, the electronic and magnetic properties of Dy-carboxylate metal–organic networks on Cu(111) based on an eightfold coordination between Dy and ditopic linkers are inspected. This surface science study based on scanning probe microscopy and X-ray magnetic circular dichroism, complemented with density functional theory and multiplet calculations, reveals that the magnetic anisotropy landscape of the system is complex. Surface-supported metal–organic coordination is able to induce a change in the orientation of the easy magnetization axis of the Dy coordinative centers as compared to isolated Dy atoms and Dy clusters, and significantly increases the magnetic anisotropy. Surprisingly, Dy atoms coordinated in the metallosupramolecular networks display a nearly in-plane easy magnetization axis despite the out-of-plane symmetry axis of the coordinative molecular lattice. Multiplet calculations highlight the decisive role of the metal–organic coordination, revealing that the tilted orientation is the result of a very delicate balance between the interaction of Dy with O atoms and the precise geometry of the crystal field. This study opens new avenues to tailor the magnetic anisotropy and magnetic moments of lanthanide elements on surfaces. ; The ALBA synchrotron is acknowledged for providing beam time at BOREAS beamline (proposal number 2015091454). This project has received funding from the European Research Council (ERC, grant 766555) and Marie Sklodowska-Curie Actions (MSCA, project 894924) under the European Union's Horizon 2020 research and innovation programme. This work has been financed by the Spanish Ministerio de Economía, Industria y Competitividad (projects FIS2016-78591-C3-1-R, RTI2018-097895-B-C42, MAT2016-78293-C6-2-R, MAT2017-85089-C2-1-R, and PID2019-107338RB-C65); the Comunidad de Madrid (Projects S2013/MIT-2850, P2018/NMT4321, and S2018/NMT-4367); the European Regional Development Fund (ERDF) under the program Interreg V-A España-Francia-Andorra (Contract No. EFA 194/16 TNSI); and "Severo Ochoa" Programme for Centres of Excellence in R&D (grants SEV-2016-0686, and SEV-2017-0706).