Fabrication and characterization of sub-3 nm gaps for single-cluster and single-molecule experiments

We describe a simple process for preparing sub-3 nm gaps by means of controllable breaking of gold wires lithographed on a SiO2/Si substrate at low temperature (4.2 K). We show that the mechanism involved is thermally assisted electromigration. We investigate the effect of the high electric field developed at the final stage of the breaking of the nanowire and observe that the current-voltage characteristics (I-V) of the resulting electrodes are stable up to similar to5 V. This high-electric-field stability gives access to the well-known Fowler-Nordheim regime (eV > Phi(0)) in the I-V characteristic, thus allowing an accurate characterization of the gap size. The size of the gap is found to be between 1 and 2 nm. We validate this characterization by fabricating single-electron tunnelling devices based on alkylthiol capped gold nanoparticles.