Electron cotunneling transport in gold nanocrystal arrays

TL;DR

This paper investigates how electron transport in gold nanocrystal arrays transitions from sequential tunneling to cotunneling regimes by varying ligand length, revealing different temperature and electric field dependencies.

Contribution

It demonstrates the tunability of electron transport mechanisms in nanocrystal arrays through ligand length modification, highlighting the crossover from sequential tunneling to cotunneling regimes.

Findings

Long ligands lead to activated tunneling behavior.

Short ligands exhibit Efros-Shklovskii cotunneling laws.

Transport can be controlled by adjusting tunnel barrier transparency.

Abstract

We describe current-voltage characteristics I(V) of alkyl-ligated gold nanocrystals $\sim 5 nm$ arrays in long screening length limit. Arrays with different alkyl ligand lengths have been prepared to tune the electronic tunnel coupling between the nanocrystals. For long ligands, electronic diffusion occurs through sequential tunneling and follows activated laws, as function of temperature $\sigma \propto e^{-T_0/T}$ and as function of electric field $I \propto e^{-\mathcal{E}_0/\mathcal{E}}$. For better conducting arrays, i.e. with small ligands, the transport properties crossover to the cotunneling regime and follows Efros-Shklovskii laws as function of temperature $\sigma \propto e^{-(T_{ES}/T)^{1/2}}$ and as function of electric field $I \propto e^{-(\mathcal{E}_{ES}/\mathcal{E})^{1/2}}$. The data shows that electronic transport in nanocrystal arrays can be tuned from the sequential tunneling to the cotunneling regime by increasing the tunnel barrier transparency.