Our team has discovered a single-molecule switch that can act like a transistor and store binary information such as the 1s and 0s used in classical computing. The molecule is around five square nanometers in size — more than one billion of them would fit onto the cross-section of a human hair. Based on our experiments, molecules like the ones they have discovered could offer information densities of around 250 terabits per square inch, which is around 100 times the storage density of current hard drives.
In the study, molecules of an organic salt can be switched using a small electrical input to appear either bright or dark, providing binary information (see image). This information can be written, read, and erased at room temperature and under normal air pressures. These are important characteristics for practical application of the molecules in computer storage devices. Most previous research into molecular electronics for similar applications has been conducted in vacuum and at very low temperatures.
There are several properties that a molecule must possess to be useful as a molecular memory. Apart from being switchable in both directions under ambient conditions, it must be stable for a long time in the bright and dark state and spontaneously form highly ordered layers that are only one molecule thick in a process called self-assembly. To our knowledge, ours is the first example that combines all these features in the same molecule.
In laboratory experiments, our team used small electric pulses in a scanning tunneling microscope to switch individual molecules from bright to dark. We were also able to read and erase the information afterward at the press of a button. During the switching, the electric pulse changes the way the cation and the anion in the organic salt are stacked together and this stacking causes the molecule to appear either bright or dark. Apart from the switching itself, the spontaneous ordering of the molecules is crucial — through self-assembly, they find their way into a highly ordered structure (a two-dimensional crystal) without the need for expensive manufacturing tools, as is the case in currently used electronics. Also, the smart molecules themselves are prepared using standard synthetic chemistry protocols, which allows to make them in astronomic numbers and with atomic precision at low cost, something that is hard to imagine for any top-down nanoscale object.
Angewandte Chemie Int. Ed. 2020, 59, 14049–14053, doi.org/10.1002/anie.202004016