Tracking the ultrafast motion of a single molecule by femtosecond orbital imaging

• Published in: Nature (London) 2016-11, Vol.539 (7628), p.263-267
• Main Authors: Cocker, Tyler L., Peller, Dominik, Yu, Ping, Repp, Jascha, Huber, Rupert
• Format: Article
• Language: English
• Subjects: 140/125; 639/624/400/584; 639/638/542/968; 639/766/119/998; 639/766/36/1122; 639/766/400/561; Humanities and Social Sciences; letter; Microscopy; Molecules; multidisciplinary; Nanotechnology; Particle physics; Photochemistry; Science; Scientific imaging
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature19816

Watching a single molecule move calls for measurements that combine ultrafast temporal resolution with atomic spatial resolution; this is now shown to be possible by combining scanning tunnelling microscopy with lightwave electronics, through a technique that involves removing a single electron from the highest occupied orbital of a single pentacene molecule in a time window shorter than an oscillation cycle of light. Single-molecule movement, the movie 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-ångström 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. Watching a single molecule move on its intrinsic timescale has been one of the central goals of modern nanoscience, and calls for measurements that combine ultrafast temporal resolution 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 with atomic spatial resolution 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 . Steady-state experiments access the requisite spatial scales, as illustrated by direct imaging of individual molecular orbitals using scanning tunnelling microscopy 9 , 10 , 11 or the acquisition of tip-enhanced Raman and luminescence spectra with sub-molecular resolution 26 , 27 , 28 . But tracking the intrinsic dynamics of a single molecule directly in the time domain faces the challenge that interactions with the molecule must be confined to a femtosecond time window. For individual nanoparticles, such ultrafast temporal confinement has been demonstrated 18 by combining scanning tunnelling microscopy with so-called lightwave electronics 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , which uses the oscillating carrier wave of tailored light pulses to directly manipulate electron