Plasmons get tuned up

showing instead non-directional rotation at a much higher speed of rotation. The directional rotation is provoked by the chirality of the STM tip (Fig. 1c)5. In particular, the differences observed for enantiomers on electrical excitation with the same STM tip are attributed to non-identical tip–molecule interactions. The intramolecular vibrational energy redistribution from the high-energy C–H stretch modes to the lowerenergy rotational states is a complex process, and depends both on the symmetry of the tip and molecule. Efficient coupling leads to many rotational events of larger hop angles. Inefficient coupling however results in slower, but directional, hopping. By using different STM tips, both enantiomers are also found to sometimes exhibit no directionality, which would be expected for the interaction of enantiomers with an achiral probe. The molecular motor created by Sykes and colleagues is far from a practical machine — its maximum directionality is 5% at a rotation hop rate of ~50 Hz. However, the creation of functional molecular motors is stimulating to both scientists and the wider public. Moreover, the work illustrates how these motors can be addressed individually, and highlights the importance of the symmetry of nanoscale contacts. ❐