33 research outputs found
Magnetic properties of self-organized lateral arrays of (Fe,Ag)/Mo(110) nanostripes
We report the fabrication of self-organized arrays of Fe nanostripes with a
period of 3.5 nm, by sequential deposition of Fe and Ag on Mo(110). The wires
display a strong in-plane uniaxial anisotropy along their length, and are
superparamagnetic above Tb=185+/-15K. The large value of nucleation volumes,
inferred from the analysis of the thermal dependence of coercivity below TB,
suggests the existence of interactions between the wires.Comment: 3 pages journal-style Proceedings of MMM0
Kinetic self-organization of trenched templates for the fabrication of versatile ferromagnetic nanowires
We have self-organized versatile magnetic nanowires, ie with variable period
and adjustable magnetic anisotropy energy (MAE). First, using the kinetic
roughening of W(110) uniaxial templates of trenches were grown on commercial
Sapphire wafers. Unlike most templates used for self-organization, those have a
variable period, 4-12nm are demonstrated here. Fe deposition then results in
the formation of wires in the trenches. The magnitude of MAE could be
engineered up or down by changing the capping- or underlayer, in turn affecting
the mean superparamagnetic temperature, raised to 175K so far.Comment: 3 page
Electronic and Geometric Corrugation of Periodically Rippled, Self-nanostructured Graphene Epitaxially Grown on Ru(0001)
Graphene epitaxially grown on Ru(0001) displays a remarkably ordered pattern
of hills and valleys in Scanning Tunneling Microscopy (STM) images. To which
extent the observed "ripples" are structural or electronic in origin have been
much disputed recently. A combination of ultrahigh resolution STM images and
Helium Atom diffraction data shows that i) the graphene lattice is rotated with
respect to the lattice of Ru and ii) the structural corrugation as determined
from He diffraction is substantially smaller (0.015 nm) than predicted (0.15
nm) or reported from X-Ray Diffraction or Low Energy Electron Diffraction. The
electronic corrugation, on the contrary, is strong enough to invert the
contrast between hills and valleys above +2.6 V as new, spatially localized
electronic states enter the energy window of the STM. The large electronic
corrugation results in a nanostructured periodic landscape of electron and
holes pockets.Comment: 16 pages, 6 figure
Remotely controlled isomer selective molecular switching
Nonlocal addressing—the “remote control”—of molecular switches promises more efficient processing for information technology, where fast speed of switching is essential. The surface state of the (111) facets of noble metals, a confined two-dimensional electron gas, provides a medium that enables transport of signals over large distances and hence can be used to address an entire ensemble of molecules simultaneously with a single stimulus. In this study we employ this characteristic to trigger a conformational switch in anthradithiophene (ADT) molecules by injection of hot carriers from a scanning tunneling microscope (STM) tip into the surface state of Cu(111). The carriers propagate laterally and trigger the switch in molecules at distances as far as 100 nm from the tip location. The switching process is shown to be long-ranged, fully reversible, and isomer selective, discriminating between cis and trans diastereomers, enabling maximum control.PostprintPeer reviewe
Bipolar conductance switching of single anthradithiophene molecules
The authors acknowledge funding by the Emmy-Noether-Program of the Deutsche Forschungsgemeinschaft, the SFB 767, and the Baden-Württemberg Stiftung. R.P. and A.A. thank the Basque Departamento de Universidades e Investigacion (grant no. IT-756-13) and the Spanish Ministerio de Economia y Competitividad (grant no. FIS2013-48286-C2-8752-P) for financial support.Single molecular switches are basic device elements in organic electronics. The pentacene analogue anthradithiophene (ADT) shows a fully reversible binary switching between different adsorption conformations on a metallic surface accompanied by a charge transfer. These transitions are activated locally in single molecules in a low-temperature scanning tunneling microscope . The switching induces changes between bistable orbital structures and energy level alignment at the interface. The most stable geometry, the “off” state, which all molecules adopt upon evaporation, corresponds to a short adsorption distance at which the electronic interactions of the acene rings bend the central part of the molecule toward the surface accompanied by a significant charge transfer from the metallic surface to the ADT molecules. This leads to a shift of the lowest unoccupied molecular orbital down to the Fermi level (EF). In the “on” state the molecule has a flat geometry at a larger distance from the surface; consequently the interaction is weaker, resulting in a negligible charge transfer with an orbital structure resembling the highest occupied molecular orbital when imaged close to EF. The potential barrier between these two states can be overcome reversibly by injecting charge carriers locally into individual molecules. Voltage-controlled current traces show a hysteresis characteristic of a bipolar switching behavior. The interpretation is supported by first-principles calculations.PostprintPeer reviewe
Understanding the self-assembly of TCNQ on Cu(111): a combined study based on scanning tunnelling microscopy experiments and density functional theory simulations
Two polymorphic structures of TCNQ on Cu(111) can be formed by varying the deposition conditions.</p
Chiral and catalytic effects of site-specific molecular adsorption
Open access funded by Max Planck Society. The authors acknowledge the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy-EXC-2123 Quantum Frontiers - 390837967; Core program PC2-PN23080202 and the PN-III-P2-2.1-PED-2021-0378 (contract no. 575PED/2022) granted projects, financed by the Romanian Ministry of Research, Innovation and Digitalization/UEFISCDI; and the generous allocation of computer time at the computing center of Donostia International Physics Center and at the Red Española de Supercomputación (project QHS-2021-2-0019). A.A. acknowledges support from Project No. PID2019-103910GB-I00, funded by MCIN/AEI/10.13039/501100011033/ and FEDER Una manera de hacer Europa, and Project No. IT-1527-22 funded by the Basque Government.The changes of properties and preferential interactions based on subtle energetic differences are important characteristics of organic molecules, particularly for their functionalities in biological systems. Only slightly energetically favored interactions are important for the molecular adsorption and bonding to surfaces, which define their properties for further technological applications. Here, prochiral tetracenothiophene molecules are adsorbed on the Cu(111) surface. The chiral adsorption configurations are determined by Scanning Tunneling Microscopy studies and confirmed by first-principles calculations. Remarkably, the selection of the adsorption sites by chemically different moieties of the molecules is dictated by the arrangement of the atoms in the first and second surface layers. Furthermore, we have investigated the thermal effects on the direct desulfurization reaction that occurs under the catalytic activity of the Cu substrate. This reaction leads to a product that is covalently bound to the surface in chiral configurations.Publisher PDFPeer reviewe
Electric-field-driven direct desulfurization
The ability to elucidate the elementary steps of a chemical reaction at the atomic scale is important for the detailed understanding of the processes involved, which is key to uncover avenues for improved reaction paths. Here, we track the chemical pathway of an irreversible direct desulfurization reaction of tetracenothiophene adsorbed on the Cu(111) closed-packed surface at the submolecular level. Using the precise control of the tip position in a scanning tunneling microscope and the electric field applied across the tunnel junction, the two carbon–sulfur bonds of a thiophene unit are successively cleaved. Comparison of spatially mapped molecular states close to the Fermi level of the metallic substrate acquired at each reaction step with density functional theory calculations reveals the two elementary steps of this reaction mechanism. The first reaction step is activated by an electric field larger than 2 V nm–1, practically in absence of tunneling electrons, opening the thiophene ring and leading to a transient intermediate. Subsequently, at the same threshold electric field and with simultaneous injection of electrons into the molecule, the exergonic detachment of the sulfur atom is triggered. Thus, a stable molecule with a bifurcated end is obtained, which is covalently bound to the metallic surface. The sulfur atom is expelled from the vicinity of the molecule.PostprintPeer reviewe
Controlling single molecule conductance by a locally induced chemical reaction on individual thiophene units
The authors acknowledge the Emmy-Noether-Program of the Deutsche Forschungsgemeinschaft, the SFB 767, Core Program PN19-03 (contract number 21 N/08.02.2019) founded by the Romanian Ministry of Research and Innovation, Basque Departamento de Universidades e Investigación (grant no. IT-756-13), the Spanish Ministerio de Economía y Competitividad (grant no. FIS2013-48286-C2-8752-P and FIS2016-75862-P) andthe Operational Programme Research, Development and Education financed by European Structural and Investment Funds and the Czech Ministry of Education, Youth and Sports (Project No. SOLID21 CZ.02.1.01/0.0/0.0/16_019/0000760).Among the prerequisites for the progress of single‐molecule‐based electronic devices are a better understanding of the electronic properties at the individual molecular level and the development of methods to tune the charge transport through molecular junctions. Scanning tunneling microscopy (STM) is an ideal tool not only for the characterization, but also for the manipulation of single atoms and molecules on surfaces. The conductance through a single molecule can be measured by contacting the molecule with atomic precision and forming a molecular bridge between the metallic STM tip electrode and the metallic surface electrode. The parameters affecting the conductance are mainly related to their electronic structure and to the coupling to the metallic electrodes. Here, the experimental and theoretical analyses are focused on single tetracenothiophene molecules and demonstrate that an in situ‐induced direct desulfurization reaction of the thiophene moiety strongly improves the molecular anchoring by forming covalent bonds between molecular carbon and copper surface atoms. This bond formation leads to an increase of the conductance by about 50 % compared to the initial state.Publisher PDFPeer reviewe
Molecular sensitised probe for amino acid recognition within peptide sequences
The combination of low-temperature scanning tunnelling microscopy with a mass-selective electro-spray ion-beam deposition established the investigation of large biomolecules at nanometer and sub-nanometer scale. Due to complex architecture and conformational freedom, however, the chemical identification of building blocks of these biopolymers often relies on the presence of markers, extensive simulations, or is not possible at all. Here, we present a molecular probe-sensitisation approach addressing the identification of a specific amino acid within different peptides. A selective intermolecular interaction between the sensitiser attached at the tip-apex and the target amino acid on the surface induces an enhanced tunnelling conductance of one specific spectral feature, which can be mapped in spectroscopic imaging. Density functional theory calculations suggest a mechanism that relies on conformational changes of the sensitiser that are accompanied by local charge redistributions in the tunnelling junction, which, in turn, lower the tunnelling barrier at that specific part of the peptide