Molecular dynamic simulations of maximum pull-out forces of embedded CNTs for sensor applications and validating nano scale experiments

Abstract

We present investigations of pull-out tests on CNTs embedded in palladium by means of molecular dynamics (MD) and compare our results of maximum pull-out forces with values of nano scale in situ pull-out tests inside a scanning electron microscope (SEM). Our MD model allows the investigation of crucial influencing parameters on the interface behaviour, like CNT diameter, intrinsic CNT defects and functional groups. For the experiments we prepared simple specimens using silicon substrates and wafer level compliant technologies. We realised the nano scale experiment with a nanomanipulation system supporting an AFM cantilever with known stiffness as a force sensing element inside a SEM. Greyscale correlation has been used to evaluate the cantilever deflection. From simulations derived maximum pull-out forces are approximately 17 nN and depend on the existence of intrinsic defects or functional groups and weakly on temperature. Experimentally obtained maximum pull-out forces with values between 16-29 nN are in good agreement with the computational predictions. Our results are of significant interest for the design and a failure-mechanistic treatment of future mechanical sensors with integrated single-walled CNTs showing high piezoresistive gauge factor or other nano scale systems incorporating CNT-metal interfaces.