Direct observation of zipper-like wall-to-wall coalescence of double-wall carbon nanotubes

In situ transmission electron microscope (TEM) observation has become a fairly powerful characterization method to uniquely provide the real-time information on the dynamics and kinetics of physical and chemical transformations at the nanometer scale. Here, we report a development of a high-temperature-compatible specimen heating holder equipped with a micro-sized carbon nanotube (CNT) network heater. The CNT network heater can heat samples up to extremely high temperature, as high as >2000 °C, while minimizing the spatial drift of the samples induced by the heating. This has directly led to a real-time imaging of a purely thermally-driven nano-welding process between two parallel-aligned double-wall carbon nanotubes (DWCNTs) using low-voltage TEM (80 keV); a single larger-diameter DWCNT was formed after the reaction and the reaction rate was determined. This technique developed is basically applicable to the in situ TEM study of various thermal-driven solid-phase dynamical changes/reactions and should provide more significant insight on nanoscience and nanothermodynamics.