Mechanics of CNT-palladium Interfaces for Sensor Applications Simulated with Molecular Dynamics

We present force-displacement data simulated with molecular dynamics of quasi-static displacement controlled pull-out tests of single-walled carbon nanotubes (CNT) embedded in palladium. With our simulations we focus on the mechanical interface behavior at the atomic scale which is of importance for thermo-mechanical reliability predictions and failure-mechanistic treatment of future CNT devices. In general, an incommensurate interface structure can be predicted, when a chiral CNT is in contact with a noble metal like palladium. This originates in lattices with different basis and periodicities as well as a strong metal interaction, a strong carbon interaction and a weak metal carbon interaction, which in this paper is assumed to be of van der Waals type. We report on an interface fracture with a complete detachment of CNT and palladium. The pull-out forces we calculated are in the nano Newton range for models with CNTs embedded 5 to 10 nm and increase when the CNT has intrinsic defects or functional groups are attached. Furthermore, for ideal cases the pull-out behavior is independent of the embedding length and although bond breaking and forming occurs, there is no associated energy dissipation. Due to the incommensurate interface some atoms assist while others resist the pull-out displacement. In effect the pull-out force is then a restoring force, which is fed by the surface potential energy that is lowered when the CNT shares maximum contact area with the palladium. In contrast, defects in the CNT like kinks or functional groups alter this behavior and then energy dissipation becomes a pronounced effect due to sudden changes of unstable atomic configurations.