Sequential tunneling and inelastic cotunneling in nanoparticle arrays

TL;DR

This paper studies charge transport mechanisms in nanoparticle arrays, demonstrating how inelastic cotunneling dominates at low bias and temperature, while sequential tunneling prevails at higher bias and temperature, through systematic experiments on gold nanocrystal arrays.

Contribution

It provides experimental evidence distinguishing inelastic cotunneling from sequential tunneling in nanoparticle arrays, highlighting their roles under different bias and temperature conditions.

Findings

Transport is dominated by inelastic cotunneling within Coulomb blockade.

Sequential tunneling takes over at high bias and temperature.

Experimental data supports the transition between tunneling regimes.

Abstract

We investigate transport in weakly-coupled metal nanoparticle arrays, focusing on the regime where tunneling is competing with strong single electron charging effects. This competition gives rise to an interplay between two types of charge transport. In sequential tunneling, transport is dominated by independent electron hops from a particle to its nearest neighbor along the current path. In inelastic cotunneling, transport is dominated by cooperative, multi-electron hops that each go to the nearest neighbor but are synchronized to move charge over distances of several particles. In order to test how the temperature-dependent cotunnel distance affects the current-voltage ($I-V$) characteristics we perform a series of systematic experiments on highly-ordered, close-packed nanoparticle arrays. The arrays consist of $\sim 5.5$nm diameter gold nanocrystals with tight size dispersion, spaced $\sim 1.7$nm apart by interdigitating shells of dodecanethiol ligands. We present $I-V$ data for mono-, bi-, tri- and tetralayer arrays. For stacks 2-4 layers thick we compare in-plane measurements with data for vertical transport, perpendicular to the array plane. Our results support a picture whereby transport inside the Coulomb blockade regime occurs by inelastic cotunneling, while sequential tunneling takes over at large bias above the global Coulomb blockade threshold $V_t(T)$, and at high temperatures.