Electrical characterization of quasi fullerene junctions formed with different metallic electrodes
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We calculate, compare, and discuss the charge transport properties through quasi fullerene C40 obtained in three different electrode–C40–electrode testbeds by employing density functional theory combined with nonequilibrium Green’s function, to predict the electronic structure of molecular junctions formed from copper, silver, and gold electrodes. We investigate various metrics such as chemical potential of electrodes, density of states, transmission spectra, Mulliken population, and molecular projected self-consistent Hamiltonian eigen states to develop a novel insight about the varying transport phenomenon as the metallic part of the scattering region is modified. We conclude that all the junctions exhibit strong metallic character displaying ballistic conductance of order of more than G0 accompanied by pronounced ripples in their conductance spectrum and small rectifying behavior in their current spectrum. This rectifying behavior is found to stem from the asymmetric shifting of orbital energies with changing bias voltage due to change in relative charge transfer through central molecule C40.
I. INTRODUCTION
Molecular electronics promises to deliver ultra highdensity memory and logic circuits that can be realized with dimensions well below the scaling limits of conventional top-down fabrication methods associated with silicon technology.1 Acquiring control over electronic transport at the atomic scale requires the ability to fabricate electronic devices in atomic resolution. The high level of control over the atomic structure of organic molecules promoted the use of molecular junctions (MJs) as a testbed for electronic transport at the atomic scale.2–7 However, the structure of these junctions is limited to a molecule sandwiched between two macro-scale electrodes with typical conductance restricted to off-resonance tunneling (several orders of magnitude lower than G0). Ideally, one would like to have the freedom to wire individual organic molecules to other atomic scale conductors8–10 with minimal conductance attenuation to form efficient MJs based on more than a single atomic scale component junction. The wiring process while making MJs is done in a mechanically controllable break junction set up by pulling atom after atom from metallic electrodes. When atomic chains are pulled between metallic electrodes in the presence of diatomic molecules, the chains can be decorated by the small molecules or their decomposed atoms.11–16 In the case of organic molecules connected by thiol groups between two gold Contributing Editor: Mauricio Terrones a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.292
electrodes, stretching the junction can lead to its elongation.17–20 Direct binding of alkanes to gold electrodes showed similar behavior.21 A variety of MJs have been synthesized and experimentally studied22–36 by numerous researchers in an attempt to better understand their important conduction mechanisms. The intensity of this experimental activity has been equally matche
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