Memristive hysteresis and stacking-fault-induced semiconductor to metal transition in sulfur-modified multiwall carbon nanotubes

Abstract

The recent identification of superconductive phenomena in few-layer and multi-layer graphene systems has attracted significant attention. Superconductivity has also been reported to occur in pyrolytic graphite, where, together with the narrow-gap semiconducting Bernal (ABA) phase, a critical role is played by stacking-faults which behave either as metallic-like and/or granular superconducting regions. Here, we investigate the current vs. voltage properties of stacking-faults nucleated in multiwall carbon nanotubes (CNTs) by annealing with diluted amounts of sulfur. By employing a combination of atomic force microscopy (AFM) and high-resolution transmission electron microscopy (HRTEM), we identify an interplay of semiconducting and metallic components in coexistence with memristive responses, with a local semiconducting to metallic transition occurring in the stacking-fault regions. The observed transition in the CNT-structure (the stacking-fault) is ascribed to a localized sulfur-induced modification of the graphitic stacking-order and partial amorphization of the CNT-walls, leading to a local structural-collapse of the CNT. Comparative investigations performed on highly crystalline graphitic multiwall CNTs and multilayered carbon nano-onions (with a turbostratic structure) revealed an important interplay of contributions arising from Bernal and turbostratic graphite-phases. This translates into a competing semiconducting and metallic behaviour in coexistence with the observed memristive characteristics.