Smart molecules could enable computers with bigger memories

An international team of researchers have discovered a single-molecule ‘switch’, measuring around 5 nm² in size, that can act like a transistor and offers the potential to store binary information — such as the 1s and 0s used in classical computing. Writing in the journal Angewandte Chemie, the scientists claim that molecules like this one could offer information density of around 250 terabits per square inch — around 100 times the storage density of current hard drives.

In the team’s study, molecules of an organic salt were switched using a small electrical input to appear either bright or dark, providing binary information. Crucially, this information can be written, read and erased at room temperature and in normal air pressures. These are important characteristics for practical application of the molecules in computing storage devices. Most previous research into molecular electronics for similar applications has been conducted in vacuum and at very low temperatures.

“There is an entire list of properties that a molecule has to possess to be useful as a molecular memory,” said lead researcher Dr Stijn Mertens, from Lancaster University. “Apart from being switchable in both directions under ambient conditions, it has to be stable for a long time in the bright and dark state, and also spontaneously form highly ordered layers that are only one molecule thick, in a process called self-assembly. Ours is the first example that combines all these features in the same molecule.”

In laboratory experiments, the research team used small electric pulses in a scanning tunnelling microscope to switch individual molecules from bright to dark. They were also able to read and erase the information afterwards, 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, also 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.

Although the researchers do not expect that the particular molecules they discovered will be used in real hard drives, the study is an important proof of concept that brings us closer to the brave new world of true molecular electronics.

“Because chemistry allows us to make molecules with sophisticated functions in enormous numbers and with atomic precision, molecular electronics may have a very bright future,” Dr Mertens said.

Pictured: An image of the smart molecular switches as seen with a scanning tunnelling microscope. Every bright square is a single switch.

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