76 research outputs found
Dielectric properties of thin insulating layers measured by Electrostatic Force Microscopy
In order to measure the dielectric permittivity of thin insulting layers, we developed a method based on electrostatic force microscopy (EFM) experiments coupled with numerical simulations. This method allows to characterize the dielectric properties of materials without any restrictions of film thickness, tip radius and tip-sample distance. The EFM experiments consist in the detection of the electric force gradient by means of a double pass method. The numerical simulations, based on the equivalent charge method (ECM), model the electric force gradient between an EFM tip and a sample, and thus, determine from the EFM experiments the relative dielectric permittivity by an inverse approach. This method was validated on a thin SiO2 sample and was used to characterize the dielectric permittivity of ultrathin poly(vinyl acetate) and polystyrene films at two temperatures
Steering alkyne homocoupling with on-surface synthesized catalysts
We report a multi-step on-surface synthesis strategy. The first step consists
in the surface-supported synthesis of metal-organic complexes, which are
subsequently used as catalysts to steer on-surface alkyne coupling reactions.
In addition, we analyze and compare the electronic properties of the different
coupling motifs obtained
Transferring Axial Molecular Chirality Through a Sequence of On-Surface Reactions
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 reac-tions 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 ad-equate enantioenriched reactants, for the controlled production of
chiral and prochiral organic nanoarchi-tectures with pre-defined handedness
Electronic decoupling of polyacenes from the underlying metal substrate by sp <sup>3</sup> carbon atoms
We report on the effect of sp3 hybridized carbon atoms in acene derivatives
adsorbed on metal surfaces, namely decoupling the molecules from the supporting
substrates. In particular, we have used a Ag(100) substrate and hydrogenated
heptacene molecules, in which the longest conjugated segment determining its
frontier molecular orbitals amounts to five consecutive rings. The
non-planarity that the sp3 atoms impose on the carbon backbone results in
electronically decoupled molecules, as demonstrated by the presence of charging
resonances in dI/dV tunneling spectra and the associated double tunneling
barriers, or in the Kondo peak that is due to a net spin S=1/2 of the molecule
as its LUMO becomes singly charged. The spatially dependent appearance of the
charging resonances as peaks or dips in the differential conductance spectra is
further understood in terms of the tunneling barrier variation upon molecular
charging, as well as of the different orbitals involved in the tunneling
process
Survival of spin state in magnetic porphyrins contacted by graphene nanoribbons
We report on the construction and magnetic characterization of a fully functional hybrid molecular system composed of a single magnetic porphyrin molecule bonded to graphene nanoribbons with atomically precise contacts. We use on-surface synthesis to direct the hybrid creation by combining two molecular precursors on a gold surface. High-resolution imaging with a scanning tunneling microscope finds that the porphyrin core fuses into the graphene nanoribbons through the formation of new carbon rings at chemically predefined positions. These ensure the stability of the hybrid and the extension of the conjugated character of the ribbon into the molecule. By means of inelastic tunneling spectroscopy, we prove the survival of the magnetic functionality of the contacted porphyrin. The molecular spin appears unaffected by the graphenoid electrodes, and we simply observe that the magnetic anisotropy appears modified depending on the precise structure of the contacts.We acknowledge the financial support from Spanish Agencia Estatal de
Investigación (AEI) (project nos. MAT2016-78293-C6 and FIS2015-62538-ERC, and the Maria de
Maeztu Units of Excellence Programme MDM-2016-0618), the Basque Government (Department
Industry, grant no. PI-2015-1-42), the European project PAMS (610446), the Xunta de Galicia (Centro
singular de investigación de Galicia accreditation 2016 to 2019, ED431G/09), the European Research
Council (grant agreement no. 635919), and the European Regional Development FundS
On-surface synthesis of heptacene on Ag(001) from brominated and non-brominated tetrahydroheptacene precursors
Achieving the Ag(001)-supported synthesis of heptacene from two related reactants reveals the effect of the presence of Br atoms on the reaction process. The properties of reactants, intermediates and end-products are further characterized by scanning tunneling microscopy and spectroscopy.Fil: Colazzo, Luciano. Donostia International Physics Center; España. Consejo Superior de Investigaciones Científicas; EspañaFil: Mohammed, Mohammed S. G.. Donostia International Physics Center; España. Consejo Superior de Investigaciones Científicas; EspañaFil: Dorel, Ruth. Barcelona Institute of Science and Technology; EspañaFil: Nita, Pawel. Donostia International Physics Center; España. Consejo Superior de Investigaciones Científicas; EspañaFil: García Fernández, Carlos. Donostia International Physics Center; EspañaFil: Abufager, Paula Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Lorente Palacios, Nicolas. Donostia International Physics Center; España. Consejo Superior de Investigaciones Científicas; EspañaFil: Echavarren, Antonio M.. Barcelona Institute of Science and Technology; España. Universitat Rovira I Virgili; EspañaFil: De Oteyza, Dimas G.. Donostia International Physics Center; España. Consejo Superior de Investigaciones Científicas; España. Ikerbasque; Españ
Decacyclene Trianhydride at Functional Interfaces: An Ideal Electron Acceptor Material for Organic Electronics
We report the interface energetics of decacyclene trianhydride (DTA) monolayers on top of two distinct model surfaces, namely, Au(111) and Ag(111). On the latter, combined valence band photoemission and X-ray absorption measurements that access the occupied and unoccupied molecular orbitals, respectively, reveal that electron transfer from substrate to surface sets in. Density functional theory calculations confirm our experimental findings and provide an understanding not only of the photoemission and X-ray absorption spectral features of this promising organic semiconductor but also of the fingerprints associated with the interface charge transfer
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