Functionality in single-molecule devices: Model calculations and applications of the inelastic electron tunneling signal in molecular junctions

TL;DR

This paper demonstrates how inelastic electron tunneling spectroscopy (IETS) can be used to create functional single-molecule devices by analyzing vibrational signals and controlling vibronic properties with external electric fields.

Contribution

It combines non-equilibrium Green's functions and ab-initio calculations to show the robustness of IETS signals and how external fields can enable device functionalities like switching.

Findings

IETS features are independent of molecule-lead contact nature.

Vibronic properties can be controlled by gate voltage.

Functional device behavior achieved through IETS signal manipulation.

Abstract

We analyze how functionality could be obtained within single-molecule devices by using a combination of non-equilibrium Green's functions and ab-initio calculations to study the inelastic transport properties of single-molecule junctions. First we apply a full non-equilibrium Green's function technique to a model system with electron-vibration coupling. We show that the features in the inelastic electron tunneling spectra (IETS) of the molecular junctions are virtually independent of the nature of the molecule-lead contacts. Since the contacts are not easily reproducible from one device to another, this is a very useful property. The IETS signal is much more robust versus modifications at the contacts and hence can be used to build functional nanodevices. Second, we consider a realistic model of a organic conjugated molecule. We use ab-initio calculations to study how the vibronic properties of the molecule can be controlled by an external electric field which acts as a gate voltage. The control, through the gate voltage, of the vibron frequencies and (more importantly) of the electron-vibron coupling enables the construction of functionality: non-linear amplification and/or switching is obtained from the IETS signal within a single-molecule device.