Published: | By: Ute Schönfelder (translation: Christian Helgert)
A research team from the Friedrich Schiller University and the Physikalisch-Technische Bundesanstalt is developing new types of nano switches that can be operated using a light signal. In the journal "Chemistry A European Journal", the researchers present their concept of a photo-switchable field effect transistor. It uses ultra-thin intelligent materials: a conductive layer of graphene combined with a single molecular layer with functional azobenzene units.
The team around ACP scientist Prof. Dr. Andrey Turchanin develops intelligent materials. "In this context, intelligent means that materials adapt to changing environmental conditions and thereby change their properties," explains Prof. Turchanin. In his work, the materials scientist primarily focuses on graphene. Only one atomic layer thick, this form of the element carbon is particularly conductive, extremely tear-resistant and flexible, harder than steel and yet extremely light. "These properties make graphene interesting for use in electronic nano components, such as transistors," says Turchanin.
However, graphene only becomes "intelligent" if its electronic properties can be controlled and varied in a controlled manner. And that is exactly why Turchanin and his Jena colleagues have developed a promising method. In a recently published study, they combined graphene with an approximately one nanometer thin molecular nanosheet that is functionalized with azobenzene units (DOI: 10.1002/chem.202001491). "The special thing about this organic material is that it changes its molecular structure due to the influence of light," says Turchanin. Irradiation with ultraviolet light causes a configuration change in the azobenzene molecules, which leads to changed properties of the molecular layer – in this case to a changed dipole moment. The irradiation of visible light causes a configuration change in the opposite direction.
Light switches the current flow on or off
The tiny transistor made of a layer of graphene and an ultra-thin azobenzene-functionalized nanosheet coated works like this: When a voltage is applied, a current flows through the graphene layer. If UV light is switched on, the changed dipole properties of the azobenzene units induce an electric field in the graph below, which interrupts the current flow. If, however, the transistor is irradiated with blue light, the configuration changes again, which means that current flows again. "Thus, we can regulate the flow of electricity through targeted radiation," explains Andrey Turchanin.
According to the authors of the study, this sandwich principle can be used as the basis for a whole range of applications. Such two-dimensional switchable materials can be used, for example, in energy stores, such as capacitors and batteries, which change their capacity due to the incidence of light. Other possible uses are sensors, for example for the detection of pathogens. “Instead of the photosensitive azobenzene, molecules could be applied to the graphene layer, to which virus particles or bacteria specifically bind. As soon as this happens, the current flow in such a sensor would be interrupted and the detector would display a signal, ”says Turchanin.
Original publication: Z. Tang, A. George, A. Winter, D. Kaiser, C. Neuman, T. Weimann, and A. Turchanin, "Optically Triggered Control of the Charge Carrier Density in Chemically Functionalized Graphene Field Effect Transistors, "Chemistry A European Journal, https://doi.org/10.1002/chem.202001491 (2020).