Transition from tunneling to direct contact in tungsten nanojunctions

TL;DR

This study investigates the unique transition from tunneling to direct contact in tungsten nanojunctions using mechanically controllable break junctions, revealing complex conductance behaviors influenced by tungsten's surface states.

Contribution

It provides new insights into tungsten's tunneling-to-contact transition, highlighting the influence of surface states and electrode relief on conductance patterns.

Findings

Rich variety of conductance transition patterns observed.

Conductance histograms show either featureless or two-peak distributions.

Surface states significantly contribute to junction conductance at very small separations.

Abstract

We apply the mechanically controllable break junctions technique to investigate the transition from tunneling to direct contact in tungsten. This transition is quite different from that of other metals and is determined by the local electronic properties of the tungsten surface and the relief of the electrodes at the point of their closest proximity. The conductance traces show a rich variety of patterns from the avalanche-like jump to a mesoscopic contact to the completely smooth transition between direct contact and tunneling. Due to the occasional absence of an adhesive jump the conductance of the contact can be continuously monitored at ultra-small electrode separations. The conductance histograms of tungsten are either featureless or show two distinct peaks related to the sequential opening of spatially separated groups of conductance channels. The role of surface states of tungsten and their contribution to the junction conductance at sub-Angstrom electrode separations are discussed.