Quantitative determination of the contact size for a platinum nanocontact

 

Sai Bharadwaj Vishnubhotla1, Rimei Chen 2, Subarna R. Khanal1, Jing Li3, Eric A. Stach3, Ashlie Martini2, Tevis Jacobs1

 

1 Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA

2 Mechanical Engineering, University of California-Merced, Merced, CA

3 Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY

The electrical properties of metallic contacts between nanoscale bodies are relevant in advanced technologies including conductive atomic force microscopy, probe-based lithography, electromechanical switches, and molecular electronics. In all cases, the current flow through the nanoscale interface depends on the contact size. Contact mechanics models are commonly used in predicting nanoscale contact area; however, it has been shown that these models may break down at the nanoscale.

The present investigation used in situ experiments and matched simulations to compare and evaluate three independent measurements of contact size during loading and unloading: (i) direct measurements from in situ transmission electron microscopy video of the contact; (ii) direct measurements from molecular dynamics simulations that were performed for nanocontacts with precisely-matched materials, crystal orientations, geometry, and loading conditions; and (iii) measurements of conductance extracted from real-time current-voltage sweeps. The combined experimental and simulation investigations yielded two primary findings. First, the measured contact area deviated from the predictions of contact mechanics, primarily due to dislocation activity in the near-surface material. Second, the contact area was significantly larger than predicted by classical electrical constriction theories. The physical mechanism for this deviation is shown to be either electron scattering off of crystal defects or the presence of insulating surface species.