Electrochemically controlled winding and unwinding of substrate-supported carbon nanoscrolls
Carbon nanoscrolls (CNSs) formed spontaneously on the basal plane of highly ordered pyrolytic graphite (HOPG) show winding and unwinding movements when potential steps from 0 V to −0.5 V, −0.6 V and −0.9 V are applied on HOPG immersed in an aqueous electrolyte solution (0.1 M H2SO4). Reversible changes in CNS radial dimensions exceeding 10 nm in the axial direction and 50 nm in the lateral direction are ascribed to variations in the surface tension and electric double-layer structure under applied potentials. Radial motion is observed exclusively on scrolled tube-shaped nanostructures, while other parts of the HOPG surface including planar areas, simple bended and lifted step edges, and kinks remain intact. The mechanism explaining the observed phenomenon is proposed and its significance for prospective applications in electrochemically controlled nanomechanical actuators is outlined.