Computing with molecules

Faster computers that consume less electricity – spintronics would have many advantages over conventional microelectronics. Tiny, switchable molecules could make data storage even smaller, totally revolutionizing computers.

“Molecules are the smallest stable entities that we can create with atomic precision and exactly defined properties. Plus, it is possible to synthesize billions of exactly identical molecular components,” said Rainer Herges, Professor of Organic Chemistry. Together with Richard Berndt, Professor of Experimental Physics, he has been working for a long time on developing molecules that react to electrical or optical stimulus and thus fulfil chemical and physical functions. Experimental physicist Dr Manuel Gruber is especially interested in such molecules, which can serve as magnetic switches. “This makes them unique candidates for spintronics to create new classes of electronic components,” he is convinced.

Spintronics, also known as spinelectronics, is a relatively new research area in the field of nanoelectronics. It uses not only the electrical charge of the electrons to transport, save and process information, but also their magnetic properties – “spin”. Information processing takes place by virtue of the fact that molecules can be switched between two different spin states. Computers process information using the binary code 0 and 1 according to a similar principle. The research field of molecular spintronics attempts to further reduce the size of data storage by controlling the spin in individual molecules.

“We have now succeeded in building individual molecules with stable switchable spin states and mounting them on a surface. Conventional organic molecules normally lose their functionality on surfaces,” explained Dr Gruber, speaking of the results of an international cooperation project he is leading. Alongside the working groups from Kiel, partners at the French SOLEIL electron synchrotron and the Swiss Light Source synchrotron at the Paul Scherrer Institute in Switzerland were involved.  

Their molecular spin switches even exhibit spin states as single molecules that are stable for several days. “We used a trick here that resembles the basic and smallest switching units in a computer. In these “flip-flops”, the output signal is fed back to the input in order to realize two different switching states, 0 and 1,” explained Dr Gruber. The newly developed molecules possess three properties that are linked together in such circuits and can each switch between two states. Their spin state can be high or low, their shape flat or curved and their atoms can be arranged in a coordinated or uncoordinated manner. Only two combinations of the three properties are stable and strengthen one another. 

An electrical pulse can be used to switch between the states of the molecules. To enable this, the research team mounted the molecules to a metal surface through evaporation, where they arranged themselves independently in a regular, ordered layer. In this arrangement, every molecule can be given an extremely small electrical pulse with the atomically fine metal point of an ultra-high resolution scanning tunnelling microscope. The states can be switched by applying either a positive or negative charge. 

“With our new spin switches, we have taken a huge step towards further miniaturization,” said Herges. Next, the researchers want to link up these molecular spin switches to form complicated electronic circuits able to perform simple computing operations. 

Author: Julia Siekmann