Gating the charge state of a single molecule by local electric fields

TL;DR

This study demonstrates how local electric fields can reversibly control the charge state of a single molecule, TCNQ, by using scanning tunneling spectroscopy to observe changes in its electronic states on a gold surface.

Contribution

It introduces a method to gate the charge state of a molecule via local electric fields, revealing reversible oxidation and reduction in a single-molecule system.

Findings

Reversible switching between charge states of TCNQ observed.

Zero-bias Kondo resonance used to identify charge states.

Surface potential variations influence molecular charge states.

Abstract

The electron acceptor molecule TCNQ is found in either of two distinct integer charge states when embedded into a monolayer of a charge transfer-complex on a gold surface. Scanning tun- neling spectroscopy measurements identify these states through the presence/absence of a zero-bias Kondo resonance. Increasing the (tip-induced) electric field allows us to reversibly induce the ox- idation/reduction of TCNQ species from their anionic or neutral ground state, respectively. We show that the different ground states arise from slight variations in the underlying surface potential, pictured here as the gate of a three-terminal device.