Molecules on a surface can assume switchable configurations that can be toggled by applying a voltage pulse using a scanning tunnelling microscope (STM) tip. This motion might be exploited for computation if the switching could be coupled among adjacent molecules. Now, Wasio et al. show that a self-assembled array of molecular rotors exhibits correlated switching in response to a voltage pulse.
The researchers prepare a two-dimensional crystal in which two brominated ethylbenzene molecules are linked through a Cu adatom on the surface. This interaction forces the ethyl rotor groups to assume either an up or down configuration. A high-voltage pulse supplied by an STM tip localized on top of one rotor causes its configuration to switch. By imaging the surface, Wasio et al. observe that adjacent rotors, namely the next closest rotor and the third rotor over, also change their configuration as a result of the high-voltage pulse. According to Monte Carlo simulations, this correlated switching is due to the intermolecular interaction among the molecules and the crystal packing on the surface. Using molecules with different packing arrangements, the researchers show that correlated switching occurs at different places with respect to the location of the triggering pulse.