Principles of Design for Substrate-Supported Molecular Switches Based on Physisorbed and Chemisorbed States.

The physisorbed (precursor) and chemisorbed states of a molecule on metal surfaces can be utilized to build a logic switch at the single-molecule level, enabling further microminiaturization of electronic devices beyond the silicon limits. However, a serious drawback of this design is easy lateral diffusion of the molecule in the physisorbed state, which may destroy the normal switch operation. Here, we demonstrate that anchoring engineering can be an effective way to enhance the stability of molecular switches without degrading switching functionality. As exemplified by trans-ADT on Cu(111), we show that the lateral diffusion of such molecular switch can be obstructed by the anchoring of the ending thiophene groups, along with a rotation of the adsorbate during the switching process. More general, our results also suggest that when searching for molecular switches with reversible physisorbed and chemisorbed states with excellent bistability and lateral stability, the focus should be on finding molecules with a moderate HOMO-LUMO energy gap and anchoring atoms with positive charge that can then be deposited on substrates with which they interact moderately. This allows further improvement of the lateral and vertical stability of such a molecular switch by substituting the thiophene groups with selenophene, thus establishing trans-ADS on Cu(111) as a promising switch.