F. Flores

Tuning the conductance of single-walled carbon nanotubes by ion irradiation in the Anderson localization regime.

Carbon nanotubes1,2 are a good realization of one-dimensional crystals where basic science and potential nanodevice applications merge3. Defects are known to modify the electrical resistance of carbon nanotubes4; they can be present in as-grown carbon nanotubes, but controlling their density externally opens a path towards the tuning of the electronic characteristics of the nanotube. In this work, consecutive Ar+ irradiation doses are applied to single-walled nanotubes (SWNTs) producing a uniform density of defects. After each dose, the room-temperature resistance versus SWNT length (R(L)) along the nanotube is measured. Our data show an exponential dependence of R(L) indicating that the system is within the strong Anderson localization regime. Theoretical simulations demonstrate that mainly di-vacancies contribute to the resistance increase induced by irradiation, and that just a 0.03% of di-vacancies produces an increase of three orders of magnitude in the resistance of a SWNT of 400 nm length.

Dipole formation at metal/PTCDA interfaces: Role of the Charge Neutrality Level

The formation of a metal/PTCDA (3, 4, 9, 10-perylenetetracarboxylic dianhydride) interface barrier is analyzed using weak-chemisorption theory. The electronic structure of the uncoupled PTCDA molecule and of the metal surface is calculated. Then, the induced density of interface states is obtained as a function of these two electronic structures and the interaction between both systems. This induced density of states is found to be large enough (even if the metal/PTCDA interaction is weak) for the definition of a Charge Neutrality Level for PTCDA, located 2.45 eV above the highest occupied molecular orbital. We conclude that the metal/PTCDA interface molecular level alignment is due to the electrostatic dipole created by the charge transfer between the two solids.

Barrier formation at metal-organic interfaces: dipole formation and the charge neutrality level

The barrier formation for metal–organic semiconductor interfaces is analyzed within the induced density of interface states (IDIS) model. Using weak chemisorption theory, we calculate the induced density of states in the organic energy gap and show that it is high enough to control the barrier formation. We calculate the charge neutrality levels of several organic molecules: 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA), 3,4,9,10-perylenetetracarboxylic bisbenzimidazole (PTCBI) and 4,4 0 ,N,N 0 -dicarbazolyl biphenyl (CBP) and the interface Fermi level for their contact with a Au (1 1 1) surface. We find an excellent agreement with the experimental evidence and conclude that the barrier formation is due to the charge transfer between the metal and the states induced in the organic energy gap. # 2004 Elsevier B.V. All rights reserved.

Electron correlation resonances in the transport through a single quantum level.

Correlation effects in the transport properties of a single quantum level coupled to electron reservoirs are discussed theoretically using a nonequilibrium Green function approach. Our method is based on the introduction of a second-order self-energy associated with the Coulomb interaction that consistently eliminates the pathologies of previous perturbative calculations. We present results for the current-voltage characteristic illustrating the different correlation effects that may be found in this system, including the Kondo anomaly and Coulomb blockade. We discuss the experimental conditions for the simultaneous observation of these effects in an ultrasmall quantum dot

Solvent‐Induced Delamination of a Multifunctional Two Dimensional Coordination Polymer

A coordination polymer is fully exfoliated by solvent-assisted interaction only. The soft-delamination process results from the structure of the starting material, which shows a layered structure with weak layer-to-layer interactions and cavities with the ability to locate several solvents in an unselective way. These results represent a significant step forward towards the production of structurally designed one-molecule thick 2D materials with tailored physico-chemical properties.

C6H6/Au(111): Interface dipoles, band alignment, charging energy, and van der Waals interaction

We analyze the benzene/Au(111) interface taking into account charging energy effects to properly describe the electronic structure of the interface and van der Waals interactions to obtain the adsorption energy and geometry. We also analyze the interface dipoles and discuss the barrier formation as a function of the metal work-function. We interpret our DFT calculations within the induced density of interface states (IDIS) model. Our results compare well with experimental and other theoretical results, showing that the dipole formation of these interfaces is due to the charge transfer between the metal and benzene, as described in the IDIS model.

Tunneling spectroscopy: surface geometry and interface potential effects

Abstract The dependence of the oscillations observed in scanning tunneling microscopy of the tunneling conductance with applied bias voltage on the tips curvature and the interface potential has been studied. A trial and error analysis of the distance-voltage and conductance-voltage characteristics is used to determine both the radius of the tip and the parameters fixing the interface potential. The effect of asperities in the tip and sample on the oscillations and the dependence of the oscillations on the sign of the applied bias are also discussed.

Anderson localization in carbon nanotubes: defect density and temperature effects.

The role of irradiation induced defects and temperature in the conducting properties of single-walled (10, 10) carbon nanotubes has been analyzed by means of a first-principles approach. We find that divacancies modify strongly the energy dependence of the differential conductance, reducing also the number of contributing channels from two (ideal) to one. A small number of divacancies (5-9) brings up strong Anderson localization effects and a seemly universal curve for the resistance as a function of the number of defects. It is also shown that low temperatures, about 15-65 K, are enough to smooth out the fluctuations of the conductance without destroying the exponential dependence of the resistivity as a function of the tube length.

Conductance quantization and electron resonances in sharp tips and atomic-size contacts

The electronic and transport properties of atomic-size contacts are analyzed theoretically using a self-consistent tight-binding model. Our results show that, for

Interaction between two hydrogen atoms approaching a metal surface

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