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TU Dresden » Faculty of Mechanical Science and Engineering » Institute for Materials Science » Chair of Materials Science and Nanotechnology



Tuesday, 09 December 2003
(at 10:15 in room Phy 4.1.13)
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Thermal fluctuations and phonon scattering on the electronic current through molecular wires

Alessandro Pecchia

Dipartimento di Ingegneria Elettronica
Universita di Roma Tor Vergata
  Italy  






Technological advances in fabrication, characterization and control at the nanoscale level have enabled the manufacturing of a variety of new organic-inorganic etero-structures with a good degree of reproducibility. This technology potentially enables to reach a miniaturisation level where the active component of the electronic devices can reach the scale of just a single molecule.[1] Understanding transport in such molecular-scale devices is, however, a challenging problem. In these systems transport is usually dominated by coherent tunneling. First-principles quantum-mechanical computations are usually necessary in order to compute accurate energy spectra and the exact nature of the molecule-contact interaction, both crucial for quantitative transport predictions.
Recently we have extended our density-functional tight-binding (DFTB) simulator for transport computations [2-3] to the non-equilibrium Green's function approach (NEGF). This scheme allows to treat contacts and molecules on an equal footing and the computation of the current flowing between the contacts in a fully self-consistent manner with the open boundary and non-equilibrium conditions that naturally arise in such transport problems. The method allows treatment of systems comprising a large number of atoms, retaining the basic quantum information.
The role of thermal fluctuations of the molecular geometry on the electronic transport is investigated. We show that a time-resolved current calculation along the steps of a classical Molecular Dynamics (MD) simulation can provide a good description of elastic scattering, because it takes fully into account for non-linearity and anharmonicity involved in the regime of large oscillation amplitudes, which in such systems intervene already at moderate temperatures.
The inelastic contribution is also considered. The Green's function technique has the great advantage that it can treat on one foot coherent and incoherent scattering, via appropriate self-energy renormalisations, that can be computed from many-body perturbation theory.[4] We implement the computation of the self-energy renormalisation into the Green's function formalism and study the various phonon scattering regimes.
work done in collaboration with: Marieta Gheorghe, Luca Latessa, Aldo Di Carlo, and Paolo Lugli

  1. R. S. Williams et al., Appl. Phys. Lett. 82, 1610 (2003)
  2. M. Elstner et al., Phys. Rev. B. 58, 7260 (1998)
  3. L. V. Keldysh, Sov. Phys. JEPT 20, 1018 (1965)
  4. H. Haug, A.-P. Jauho, `Quantum Kinetics in Transport and Optics of Semiconductors', Springer.



slides (pdf)

Invited by G. Cuniberti (MC seminar)

last modified: 2018.10.24 Mi
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