Nanoscience: Single-molecule instant replay.

Abstract

A nanoscale imaging method that uses ultrashort light pulses to initiate and follow the motion of a single molecule adsorbed on a solid surface opens a window onto the physical and chemical dynamics of molecules on surfaces. See Letter p.263 Direct observation of the movement of a single molecule calls for measurements that combine ultrafast temporal resolution with atomic spatial resolution. Jascha Repp and colleagues now show that this is possible when combining scanning tunnelling microscopy with lightwave electronics, a technique that uses laser pulses to directly manipulate electronic motion on the fastest timescales. In this approach, light pulses transiently open a tunnelling channel to remove a single electron from the highest occupied orbital of an individual molecule. The effect makes it possible to record sequences of femtosecond snapshot images of the orbital structure and directly track molecular vibrations with sub-angstrom spatial resolution, and to present the snapshots as single-molecule movies. This method is a step towards potentially controlling electronic motion inside individual molecules at optical clock rates.