Interface states, negative differential resistance, and rectification in molecular junctions with transition-metal contacts

Abstract

We present a theory of nonlinear transport phenomena in molecular junctions where single thiolated organic molecules bridge transition metal nanocontacts whose densities of states have strong d orbital components near the Fermi level. At moderate bias, we find electron transmission between the contacts to be mediated by interface states within the molecular highest-occupied-molecular-orbital-lowest-unoccupied-molecular-orbital gap that arise from hybridization between the thiol-terminated ends of the molecules and the d orbitals of the transition metals. Because these interface states are localized mainly within the metal electrodes, we find their energies to accurately track the electrochemical potentials of the contacts when a variable bias is applied across the junction. We predict resonant enhancement and reduction of the interface state transmission as the applied bias is varied, resulting in negative differential resistance ͑NDR͒ in molecular junctions with Pd nanocontacts. We show that these nonlinear phenomena can be tailored by suitably choosing the nanocontact materials: If a Rh electrode is substituted for one Pd contact, we predict enhancement of these NDR effects. The same mechanism is also predicted to give rise to rectification in Pd/molecule/Au junctions. The dependences of the interface state resonances on the orientation of the metal interface, the adsorption site of the molecule, and the separation between the thiolated ends of the molecule and the metal contacts are also discussed.

Visualizing the Role of Molecular Orbitals in Charge Transport through Individual Diarylethene Isomers

“…Each state is coupled to the nearby electrode by the broadening parameter Γ. t H is associated with the energy splitting of the two states Δ E , such as Δ E = 2 t H . Thereby, the transmission function for the open-form LUMO states is given by 32,33 where ϵ L is the energy of the LUMO without splitting, i . e ., ≈ 1.7 eV.…”

Impact of edge shape on the functionalities of graphene-based single-molecule electronics devices

“…Another possible mechanism is a voltage-driven energy mismatch of molecular levels which leads to the destruction of resonances. [37][38][39][40] The specific NDR effect demonstrated in this paper is originated by the presence of pairs of electronic states placed close to the Fermi level, and localized close to the molecule-graphene contacts. Each of these two states moves in opposite energy directions under the application of a bias voltage.…”

Transport Through Self-Assembled Monolayer Molecular Junctions: Role of In-Plane Dephasing

“…This effect has been observed in a large variety of molecular junctions, and it can be chemical in origin (i.e. due to chemical changes in the junction at some voltage) or electronic in origin [74][75][76][77][78][79][80][81][82][83][84][85][86][87][88][89].…”