Small-scale contacts between platinum and gold have applications in advanced technologies, including conductive atomic force microscopy, probe-based lithography, and molecular electronics. The performance in these applications depends on the electrical and thermal transport across the contact, which is determined by the mechanical properties, such as adhesion, contact size, and elastic and inelastic deformation. It is common to use contact mechanics to predict these mechanical properties, and several investigations support continuum-like behavior – even at the nanoscale. However, prior work on gold and silver nanocontacts has shown that these materials exhibit surface-diffusion-mediated cold welding of the two bodies upon contact, such that their separation is not described by traditional contact mechanics models at all.
In the present investigation, the distinction between contact-like separation and liquid-like separation is studied using in situ transmission electron microscopy (TEM). The force of decohesion is measured between nanoscale contacts composed of gold and platinum. High-resolution TEM images are used to characterize the bodies before and after contact, while lower resolution real-time videos are used to determine the instantaneous shape and applied stress during the contact. Results are analyzed in terms of material properties (including shape and crystallographic orientation) as well as contact properties (including applied load and time in contact).