Rolling a single molecular wheel at the atomic scale

The design of a single-molecule machine consisting of functional components requires a detailed understanding of its mechanical motion(1,2). The scanning tunnelling microscope (STM) is the only available tool for driving and imaging such a nanoscale machine on a surface. Both lateral hopping motions and conformational changes of single molecules can be induced using the STM tip(3,4). However, no rolling of a wheel has been demonstrated so far at the nanoscale, even though this is a very useful motion at the macroscopic scale. Here we show how the rolling of a single molecule equipped with two wheels (0.8 nm in diameter) can be induced by the STM tip. The characteristics of the rolling are recorded in the STM feedback loop manipulation signal and in real time. We capture unambiguous signatures of the conformational change happening during the rolling. Our approach of controlling the intramolecular mechanics provides a path towards the bottom-up assembly of more complex molecular machines.