Investigating load-dependent conduction through platinum nanocontacts using in situ electromechanical testing inside a transmission electron microscope

Fundamental understanding of the mechanics of contact for metallic nanocontacts is crucial for scanning probe microscopy (SPM) techniques that enable precise measurements of electrical properties of surfaces. The conventional approach for quantitative analysis of electrical SPM measurements relies on combining continuum mechanics models of contact with classical or ballistic electronic transport theories to understand the current flow through the nanocontact. To investigate the robustness of this conventional analysis approach, in situ electrical testing was conducted on a platinum/platinum nanocontact inside of a transmission electron microscope (TEM). The results demonstrate that the conventional approach accurately describes trends of conductance with force; however, the measured resistivity at the contact was an order of magnitude larger than the commonly-assumed bulk value. Using the Sharvin theory of ballistic transport, with the DMT and JKR theories of mechanical contact, the measured resistivity is 81 cm and 210 cm, respectively. This is significantly larger than the bulk value for platinum (10 cm). This high value of resistivity does not appear to be caused by surface contamination or oxides, both because the electrical contact was ohmic, and because chemical analysis did not demonstrate a significant presence of carbon or oxygen at the surface. Therefore, the high surface resistivity is assumed to be caused by defects at or near the interface.