Mechanical conformation switching of a single pentacene molecule on Si(100)-(2 × 1)

cited By 2International audienceThe mechanical switching of a single pentacene molecule chemisorbed in a planar configuration along a dimer row of the Si(100)-(2 × 1) surface was performed experimentally using the tip apex of a scanning tunneling microscope. The mechanical switching reaction path was identified theoretically on the ground state potential energy surface of the pentacene/Si(100)-(2 × 1) system. A low-temperature scanning tunneling microscope as well as semiempirical ASED+ molecular mechanical and elastic scattering quantum chemistry (ESQC) calculations were employed to perform the studies. Pushing with the STM tip apex and at zero bias voltage exactly at the center of the chemisorbed pentacene molecule induces a mechanical conformation change of the pentacene from its metastable to its surface stable conformation on the Si(100)-(2 × 1) surface

Voltage-dependent conductance of a single graphene nanoribbon

Graphene nanoribbons could potentially be used to create molecular wires with tailored conductance properties. However, understanding charge transport through a single molecule requires length-dependent conductance measurements and a systematic variation of the electrode potentials relative to the electronic states of the molecule1, 2. Here, we show that the conductance properties of a single molecule can be correlated with its electronic states. Using a scanning tunnelling microscope, the electronic structure of a long and narrow graphene nanoribbon, which is adsorbed on a Au(111) surface, is spatially mapped and its conductance then measured by lifting the molecule off the surface with the tip of the microscope. The tunnelling decay length is measured over a wide range of bias voltages, from the localized Tamm states over the gap up to the delocalized occupied and unoccupied electronic states of the nanoribbon. We also show how the conductance depends on the precise atomic structure and bending of the molecule in the junction, illustrating the importance of the edge states and a planar geometry

On the vibrational behaviour of cyanide adsorbed at Pt(111) and Pt(100) surfaces in alkaline solutions

This communication deals with the vibrational behaviour of cyanide adlayers formed on Pt(111) and Pt(100) surfaces in the electrochemical environment. In situ FTIR spectroscopy can be employed to follow the potential dependence of the C–N stretching frequency in acidic electrolytes with quite a low uncertainty. Owing to the stability of the cyanide adlayer in alkaline solutions, experiments performed in NaOH medium are usually perturbed by the significant overlapping of the reference and the sample FTIR spectra. Deconvolution of the spectra was carried out assuming a Lorentz oscillator. The procedure allowed to confirm that two potential regions with different band centre frequency tuning coexist for Pt(111)–CN in perchloric acid medium. Conversely, in the alkaline electrolyte a single tuning rate for the band position was found for both surfaces studied. The lack of reorientation of the C–N molecular axis together with the occurrence of a certain screening effect of negatively charged hydroxyl anions on the electric field at the interface could be at the origin of the different behaviour displayed in both electrolytic media.Ministerio de Ciencia y Tecnología (MAT2004-1479); Generalitat Valenciana (GRUPOS04/75 y GV5/136) Programa Juan de la Cierva

Conductance of a single conjugated polymer as a continuous function of its length

The development of electronic devices at the single-molecule scale requires detailed understanding of charge transport through individual molecular wires. To characterize the electrical conductance, it is necessary to vary the length of a single molecular wire, contacted to two electrodes, in a controlled way. Such studies usually determine the conductance of a certain molecular species with one specific length. We measure the conductance and mechanical characteristics of a single polyfluorene wire by pulling it up from a Au(111) surface with the tip of a scanning tunneling microscope, thus continuously changing its length up to more than 20 nanometers. The conductance curves show not only an exponential decay but also characteristic oscillations as one molecular unit after another is detached from the surface during stretching

Competitive CN and N2 formation on Rh(111) : a case of entropic stabilization

Cyanide formation and nitrogen recombination on Rh(1 1 1) have been studied using density functional theory. CN can interact with the surface via several adsorption modes, all of them within a very narrow range of adsorption energies. CN can be regarded as a highly mobile species on the surface, and dissociation is associated with a considerable loss of entropy, which is by no means compensated from an energetic point of view. Consequently, CN dissociation is largely unfavored, which agrees with the experimentally observation that CN is stable for a wide range of temperatures on Rh(1 1 1) (450-850 K

Dangling-bond logic gates on a Si(100)-(2×1)-H surface

10.1088/0953-8984/24/9/095011Journal of Physics Condensed Matter249-JCOM

Single Molecular Wires Connecting Metallic and Insulating Surface Areas

Totally wired: A particular molecular adsorption geometry can be prepared by adsorbing single conjugated polyfluorene chains partially on a clean Au(111) surface and partially on a thin crystalline NaCl film, thus connecting metallic and insulating surface areas. This configuration allows the electronic characterization of one and the same molecular wire as a function of its atomic-scale environment in a planar configuration

Acetylene decomposition on Rh(100) : theory and experiment

The decomposition of acetylene on a Rh(100) single crystal was studied by a combination of experimental techniques [static secondary ion mass spectrometry (SSIMS), temperature-programmed desorption (TPD), and low-energy electron diffraction (LEED)] to gain insight into the reaction pathway and the nature of the reaction intermediates. The experimental techniques were combined with a computational approach using density functional theory (DFT). Acetylene adsorbs irreversibly on the Rh(100) surface and eventually decomposes to atomic carbon and gas-phase hydrogen. The combination of experimental and computational results enabled us to determine the most likely reaction pathway for the decomposition process

Einzelne molekulare Drähte verbinden metallische und isolierende Oberflächenbereiche

Verdrahtet: Eine spezielle molekulare Adsorptionskonfiguration lässt sich präparieren, indem einzelne konjugierte Polyfluorenketten teils auf einer Au(111)-Oberfläche und teils auf einem dünnen kristallinen NaCl-Film adsorbieren und so die metallischen und isolierenden Oberflächenbereiche verbinden. Diese Konfiguration ermöglicht die elektronische Charakterisierung eines Drahtes als Funktion seiner atomaren Umgebung in planarer Konfiguration

Mechanical behavior of nanocrystalline NaCl islands on Cu(111)

The mechanical response of ultrathin NaCl crystallites of nanometer dimensions upon manipulation with the tip of a scanning tunneling microscope (STM) is investigated, expanding STM manipulation to various nanostructuring modes of inorganic materials as cutting, moving, and cracking. In the light of theoretical calculations, our results reveal that atomic-scale NaCl islands can behave elastically and follow a classical Hooke’s law. When the elastic limit of the nanocrystallites is reached, the STM tip induces atomic dislocations and consequently the regime of plastic deformation is entered. Our methodology is paving the way to understand the mechanical behavior and properties of other nanoscale materials