Deformation Pathway and Electronic Transition of Individual Single-Walled Carbon Nanotubes under Pressure.

Structural deformation of single-walled carbon nanotubes (SWNTs) under harsh conditions can profoundly modify their physical and mechanical properties. However, the intrinsic transformation mechanism and consequent electronic transitions at the individual SWNT level with identified (n, m) remain challenging, despite much effort devoted to nanotube bundles and solutions with significant tube-tube interactions. Herein, we experimentally demonstrated that radial compression of individual SWNTs follows a universal and reversible deformation pathway: circular-elliptical-racetrack-peanut shaped-nanoribbon, through in situ electrical and Raman measurements under high pressure. The critical pressures exhibited a general diameter dependence based on the modified Lévy-Carrier model. Furthermore, we provided direct electrical evidence that this structural collapse can trigger the semiconducting to metallic transition of SWNTs, potentially driven by pressure-induced σ-π orbital hybridization and bandgap closure. This established transformation mechanism can shed light on structural transitions of various nanomaterials and further evoke their potential applications in nanoelectronics and nanomechanics.