Viable Method to Enhance the Electrical Conductivity of CNT Bundles: Direct In Situ TEM Evaluation
Carbon nanotubes (CNTs) exhibit outstanding electrical and mechanical properties, but these superior properties are often compromised as nanotubes are assembled into bulk structures, which limits the use of CNT assemblies. Despite much work in the field, few studies have made in situ observations of the relationship between electrical conductivity and the amount of nanowelding within pristine CNT assemblies at microscopic scale. Here, we report in situ transmission electron microscope observations of electrical conductivity shoot-up of CNT bundles. High-temperature Joule heating was applied to a CNT bundle to fuse adjacent carbon nanofibers with graphitic carbon bonds, as this induces the electrical conductivity of the CNT bundle to increase three orders of magnitude. Except for the welded process of the cross-over CNT bundles, we further observed a new case of welded process for parallel CNT bundles. Here, we not only obtain the relationship between electrical conductivity of CNT bundles and their merged processes, but also give the relationship between electrical conductivity and Joule-heating induced temperature on CNT bundles, which follows natural logarithm law. Improving effective inter-bonds between neighboring nanotubes would help facilitate large-scale development of high-performing, bulk-carbon-based materials from nanostructures in applications such as flexible devices, energy storage, and electrocatalysis.