Experimental Evidence of Negative Thermal Expansion in a Composite Nanocable of Single-Walled Carbon Nanotubes and Amorphous Carbon along the Axial Direction

When a composite nanocable of single-walled carbon nanotubes (SWNTs) and amorphous carbon is fixed at one end and the other end is free, the free end is observed to be bent with a scanning electron microscope and a transmission electron microscope. The bending of the free end of the nanocable is found to be toward the reverse direction of incident electrons. Also, the bending of the composite nanocable depends on the energy and exposure time of the incident electron beam. The mechanism of these observations is attributed to inhomogeneous temperature rise by absorption of incident electrons and a negative thermal expansion (NTE) of the composite nanocable along the axial direction. The NTE property demonstrates the potential for using electron beam irradiation to investigate and manipulate SWNTs in nanodevices and making a zero-expansion composite material.