Current rectification by simple molecular quantum dots: an ab-initio study

TL;DR

This study uses ab-initio non-equilibrium Green's function calculations to analyze current rectification in molecular quantum dots with conjugated groups, revealing a rectification ratio of about 35 due to resonant tunneling.

Contribution

It demonstrates how molecular structure influences rectification in quantum dots and suggests methods to enhance rectification by chemical modifications.

Findings

Rectification ratio ~35 observed at specific molecular lengths.

Resonant tunneling through the molecular orbital causes rectification.

Interference of conducting orbitals limits rectification, but can be mitigated.

Abstract

We calculate a current rectification by molecules containing a conjugated molecular group sandwiched between two saturated (insulating) molecular groups of different length (molecular quantum dot) using an ab-initio non-equilibrium Green's function method. In particular, we study S-(CH2)m-C10H6-(CH2)n-S dithiol with Naphthalene as a conjugated central group. The rectification current ratio ~35 has been observed at m = 2 and n = 10, due to resonant tunneling through the molecular orbital (MO) closest to the electrode Fermi level (lowest unoccupied MO in the present case). The rectification is limited by interference of other conducting orbitals, but can be improved by e.g. adding an electron withdrawing group to the naphthalene.