Adsorbate-driven cooling of carbene-based molecular junctions.

Giuseppe Foti,Héctor Vázquez

doi:10.3762/bjnano.8.206

Abstract

We study the role of an NH2 adsorbate on the current-induced heating and cooling of a neighboring carbene-based molecular circuit. We use first-principles methods of inelastic tunneling transport based on density functional theory and non-equilibrium Green’s functions to calculate the rates of emission and absorbtion of vibrations by tunneling electrons, the population of vibrational modes and the energy stored in them. We find that the charge rearrangement resulting from the adsorbate gates the carbene electronic structure and reduces the density of carbene states near the Fermi level as a function of bias. These effects result in the cooling of carbene modes at all voltages compared to the “clean” carbene-based junction. We also find that the direct influence of adsorbate states is significantly smaller and tends to heat adsorbate vibrations. Our results highlight the important role of molecular adsorbates not only on the electronic and elastic transport properties but also on the current-induced energy exchange and stability under bias of single-molecule circuits.

Highlights

Molecular electronics has experienced a remarkable progress since its first proposal [1]
As we show in this paper, the presence of adsorbates not bonded directly to the molecule gives rise to pronounced deviations from its behavior as an isolated molecule, resulting in marked changes in the heating and cooling dynamics (HCD) of the junction
We show how the change in the electronic structure of the junction induced by the presence of the adsorbate promotes the cooling of NHC vibrational modes through i) electrostatic gating of molecular levels and ii) quenching of carbene density of states (DOS) as a function of the applied bias

Summary

Introduction

Molecular electronics has experienced a remarkable progress since its first proposal [1]. We show how the change in the electronic structure of the junction induced by the presence of the adsorbate promotes the cooling of NHC vibrational modes through i) electrostatic gating of molecular levels and ii) quenching of carbene density of states (DOS) as a function of the applied bias.

Results

Conclusion