Low-temperature cotunneling electron transport in photo-switchable molecule-nanoparticle networks

TL;DR

This study investigates how photo-switchable azobenzene molecules in nanoparticle networks influence low-temperature electron cotunneling, revealing that isomerization slightly increases cotunneling events without significantly altering Coulomb charging energy.

Contribution

It provides new insights into temperature-dependent electron transport mechanisms in photo-switchable nanoparticle arrays, highlighting the role of azobenzene isomerization on cotunneling behavior.

Findings

Electron cotunneling dominates transport below 77 K and 1 V.

Azobenzene isomerization slightly increases cotunneling events from 1.4 to 1.7.

Coulomb charging energy remains around 15 meV regardless of isomerization.

Abstract

We report the temperature-dependent (4.2 - 300 K) electron transport properties (current-voltage) of photo-switchable two-dimensional arrays of gold nanoparticles (10 nm in diameter) functionalized by azobenzene derivatives. Under UV-light irradiation at 4.2 K, the azobenzene moieties are switched from the trans to cis isomers, leading to an increase of the current. In both conformations, at low temperature (< 77 K) and low voltage (< 1 V) the voltage- and temperature-dependent current behaviors show that electron cotunneling is the dominant transport mechanism. The number of cotunneling events Ncot slightly increases from ca. 1. 4 to 1.7 upon trans-to-cis isomerization of the azobenzenes. The nanoparticle Coulomb charging energy is not significantly modified (ca. 15 meV) by the azobenzene isomerization. This weak increase of Ncot is explained by the modest cis/trans current ratio (< 10) and the limited numbers of nanoparticle-molecule-nanoparticle junctions inserted between the two nanoscale electrodes (< 50 nm apart) connecting the network.