Innovative gas sensor is based on graphene FET
Whether in vehicles or smartphones, in research laboratories or industrial plants – sensors are ubiquitous. They record certain physical or chemical properties, such as pressure, strain or gas molecules, and forward the data for processing. Sensors are characterised by their selectivity, i.e. the ability to detect a certain property even in the presence of other, potentially disturbing properties, as well as their sensitivity, i.e. the ability to detect even low values.
Researchers at KIT and the Technical University of Darmstadt have succeeded in developing a novel sensor for gas molecules in the gas phase. As the scientists report in the journal Advanced Materials, the functional principle of this new class of sensors is based on the combination of sensitive graphene transistors with customised metal-organic coatings. This combination enables the selective detection of molecules. As a prototypical example, the authors demonstrate a specific ethanol sensor that, unlike currently available commercial sensors, reacts neither to other alcohols nor to moisture.
Graphene is a manifestation of carbon with a two-dimensional structure. By nature, graphene is highly sensitive to foreign molecules that accumulate on its surface. “However, graphene as such does not show any molecule-specific interaction as required for an application as a sensor,” explains Ralph Krupke, professor at the Institute of Nanotechnology (INT) of KIT and at the Institute of Materials Science of TU Darmstadt, who was in charge of the study together with his colleagues Wolfgang Wenzel of INT and Christof Wöll, head of the Institute of Functional Interfaces (IFG) of KIT. The first author is Sandeep Kumar, who is doing his PhD in Molecular Nanostructures at the Institute of Materials Science at TU Darmstadt. “To achieve the required selectivity, we grew a metal-organic framework on the surface,” Krupke explains.
Metal-organic frameworks (MOFs) are made up of metallic nodes and organic molecules as connecting struts. Through various combinations, these highly porous crystalline materials can be tailored for specific applications, for example to achieve the desired selective absorption capacity for certain molecules in sensors. The researchers demonstrated a selective sensor platform by growing a surface-mounted metal-organic framework (SURMOF) directly onto a graphene field-effect transistor (GFET). Such a device benefits from both the high sensitivity and ease of readout of a GFET and the high selectivity of a SURMOF.
“Combining the unique electronic properties of graphene with the immense chemical variability of MOFs opens up huge potential,” comments Wöll. Since SURMOFs can be made in many variants and the interface between GFET and SURMOFs can be designed chemically differently, the research team’s work paves the way for a whole new class of sensors with precisely tuned selectivity and sensitivity. New sensors can be designed with relatively little effort – the experts can build and simulate MOFs on the computer without having to produce them synthetically, says Wenzel.
https://www.kit.edu/english/index.php, https://www.tu-darmstadt.de/index.en.jsp
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