Processors, such as those found in computers or mobile phones, contain billions of tiny switches known as transistors. Could they be any smaller? Yes, they could – and more than a thousand times faster too, according to Oldenburg-based physicist Martin Silies. He impressed the judges with his idea for an optical transistor in a competition organised by the Federal Ministry of Education and Research and now heads his own early-career research group.
His experiments are invisible to the naked eye and even to some conventional microscopes: Dr Martin Silies is planning a transistor on the smallest conceivable scale, in which a single molecule, as it were, determines whether a single particle of light crosses the gap between two miniature gold antennas – thereby closing the switch – or whether the switch reopens. And all of this happens at an unimaginably fast pace, within trillionths of a second – smaller, more precise, faster: that is the goal.
To advance his research, the postdoctoral researcher in Prof. Dr Christoph Lienau’s ‘Ultrasريع Nano-Optics’ (UNO) research group at the Institute of Physics is now being granted his own junior research group with two PhD positions. The funding period under the ‘NanoMatFutur’ programme of the Federal Ministry of Education and Research (BMBF) is four years and may be extended to six years if necessary. Initially, Silies has around 1.3 million euros at his disposal for the next four years.
We encounter transistors in everyday life in every electronic device. Although these electronic switches are now so small that billions of them can be fitted onto a single processor, However, it is not possible to make them any smaller – nor, as a result of smaller components, to increase their speed any further. Consequently, the speed of these transistors has so far been limited to a clock frequency of a few gigahertz – that is, a few billion switching operations per second.
Silies’ research could increase clock frequencies by more than a thousandfold, thereby potentially speeding up the operation of mainframe computers considerably. His aim is to control individual particles of light – known as photons – in such a precise manner that they can be used to operate an optical transistor. The distance between the tips of two wafer-thin gold wires converging on one another is merely a few millionths of a millimetre. Whether a photon traverses these few nanometres – and thus closes the switch – is to be controlled by molecules which, depending on their own light saturation, either allow the photon to pass or block it. The light saturation of the molecules can also be controlled by light at an unimaginable speed.
Over the next four years, 35-year-old Silies and his doctoral candidates intend, firstly, to investigate the interaction of various dye molecules and other molecules on this smallest possible spatial scale. Before that, the team will work on the most delicate gold contacts imaginable, produced using a novel technique – helium-ion lithography. In this process, a beam of helium ions first cuts the fine wires from a wafer-thin gold film and then etches extremely fine lines into them. These lines act, so to speak, as guides for the photons, directing them in the desired direction.
Previously, physicists produced gold antennas for such photonic switches using gallium-ion lithography. As helium ions are significantly smaller, they can now be used to fabricate much more delicate structures. Silies: “By comparison, the gallium ions act like a cannon – the helium ions cut more slowly, but are comparable to a scalpel.” For his research, he collaborates with Carl Zeiss Microscopy GmbH, currently the world’s only manufacturer of helium-ion microscopes.
Such co-operations are welcomed within the BMBF programme: after all, its aim is to foster new interdisciplinary approaches in nano- and materials technologies that also hold potential for industrial application. The ‘NanoMatFutur’ competition provides annual funding for a maximum of seven early-career research groups nationwide, particularly in the research fields of climate/energy, mobility, health, or information and communication.
Silies, the new head of the early-career research group in Oldenburg, studied physics at Steinfurt University of Applied Sciences. He completed his PhD at the University of Münster in 2009 on so-called time-resolved X-ray diffraction – a topic which also involved ultra-fast interaction processes between light and other matter. Silies has been a member of the UNO research group in Oldenburg since 2009, where he is one of a total of five postdoctoral researchers.
