Role of adhesion in shear strength of nanowire-substrate interfaces

The shear strength of nanowire-substrate contact critically influences the electrical and mechanical contact characteristics of nanowire-based sensors, actuators and nanoelectronic devices. Yet, very few studies are available in the literature because of the experimental challenges associated with these one-dimensional nanostructures and none of the existing contact mechanics models account for their ultra-high bending compliance. Using a novel experimental setup that effectively decouples adhesion and friction forces, we show that the friction coefficient for the zinc oxide nanowires and silicon system can be about two orders of magnitude higher than the bulk values, even under zero externally applied normal loads. We model nanowire bending compliance and capillary line tension as competing mechanisms to explain the observed anomalous adhesion-friction coupling and establish a criterion for contact area dependence in friction in one-dimensional interfaces.