Repetitive Rolling\nof Triptycene-Based Molecules on\nCu Surfaces

The metal surface-supported rotation of artificial molecular\nstructures\nis technologically important for developing molecular-level devices.\nThe key factors leading to the practical applications of these molecular\nmachines on metal surfaces are the atomic-scale control of the rotation\nand the counterbalance of the temperature-driven instability of the\nmolecules. In this work, we present a means by which triptycene-based\nmolecular wheels can roll repetitively on a metal surface. Our results\nshow that regularly stepped surfaces are the perfect candidate not\nonly for stabilizing the molecule on the metal surface but also for\nproviding the pivot points needed for repetitive vertical rotation\nof the molecule at higher temperatures. In addition to the geometrical\ncompatibility of the substrate and the molecule, intermittent application\nof the external electric field is needed for rolling the molecule\non a metal-stepped surface in a controllable manner.