(Invited) Graphene and 2D-Materials for Gas, Pressure and Mass Sensing
Authors: Lemme Max Christian 
Published: July 2021

Introduction
Graphene and related materials are by their very definition as “two-dimensional” (2D) suitable for sensing applications that exploit their high surface to volume ratio and / or their low mass [1]. In this talk, I will summarize ongoing research on graphene and platinum diselenide-based (PtSe2) sensors, both integrated on conventional semiconductor substrates and suspended to form micro- and nanoelectromechanical systems (MEMS/NEMS).
Gas Sensors
We demonstrated humidity sensing using resistance changes in single- layer chemical vapor deposited (CVD) graphene on top of oxidized silicon wafers [2]. The selectivity of the sensors towards the most common constituents in air was investigated individually for water vapor (H2O), nitrogen (N2), oxygen (O2), and argon (Ar). Humidity sensing works efficiently from 1% relative humidity (RH) to 96% RH. We further analyzed the cross sensitivity with carbon dioxide [3], and humidity sensing when bilayer graphene is used as the active sensor material [4]. Finally, the noble metal dichalcogenide PtSe2 has been investigated with respect to its gas sensing properties, in particular its selectivity regarding nitrogen dioxide (NO2) [5].
Suspended Membrane-based Sensors
Membrane-based sensors benefit mainly form the ultimate thinness of 2D materials. We have investigated a number of potential sensor applications for such 2D membranes. First, we have proposed pressure sensors from single and bilayer graphene membranes with very high sensitivity, despite a low, single-digit gauge factor of graphene [6]–[8]. This work has been expanded to PtS2 membranes, which show even higher sensitivity and miniaturability due to a much larger piezoresistive gauge factor [9]. Recently, we have been successful in attaching silicon proof masses to graphene membranes that result in highly sensitive accelerometers [10], [11]. Without proof masses, nanoscale graphene membranes may even have the potential to resonantly detect single molecule weights [12]. Finally, graphene membranes can be utilized as highly sensitive Hall sensors and microphones that are resonance-free in the acoustic wave region for frequencies up to 700 kHz, which is an advantage over conventional MEMS microphones [13].

Results and Conclusions

Graphene and 2D materials have tremendous potential for sensing applications due to their intrinsic material properties. Whether these can be utilized in future products for applications such as the Internet of Things, autonomous mobility or smart cities now depends largely on the availability of process technologies for large scale manufacturing, reliability and, ultimately, on the cost / functionality ratio [14].

Acknowledgements

The authors acknowledge funding through the European Union’s Horizon 2020 research and innovation programme under grant agreements 881603 (Graphene Flagship) and 825272 (ULISSES), the German BMBF grants NobleNEMS and GIMMIK (16ES1121, 03XP0210) and the German Research Foundation, DFG (2DNEMS, LE 2440/11-1).

References

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