(Invited) Graphene and 2D-Materials for Gas, Pressure and Mass Sensing
Authors: Lemme Max Christian 
Published: May 2020

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 is 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 785219 (Graphene Flagship) and 825272 (ULISSES) and the German BMBF grant NobleNEMS (16ES1121).

References

[1] M. C. Lemme et al., “Suspended two-dimensional Materials for Sensor Applications,” under revision 2020.

[2] A. D. Smith et al., “Resistive graphene humidity sensors with rapid and direct electrical readout,” Nanoscale, vol. 7, no. 45, pp. 19099–19109, 2015.

[3] A. D. Smith et al., “Graphene-based CO2 sensing and its cross-sensitivity with humidity,” RSC Adv., vol. 7, no. 36, pp. 22329–22339, 2017.

[4] X. Fan et al., “Humidity and CO2 gas sensing properties of double-layer graphene,” Carbon, vol. 127, pp. 576–587, Feb. 2018.

[5] C. Yim et al., “High-Performance Hybrid Electronic Devices from Layered PtSe2 Films Grown at Low Temperature,” ACS Nano, vol. 10, no. 10, pp. 9550–9558, Oct. 2016.

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[7] A. D. Smith et al., “Piezoresistive Properties of Suspended Graphene Membranes under Uniaxial and Biaxial Strain in Nanoelectromechanical Pressure Sensors,” ACS Nano, vol. 10, no. 11, pp. 9879–9886, Nov. 2016.

[8] S. Wagner et al., “Graphene transfer methods for the fabrication of membrane-based NEMS devices,” Microelectron. Eng., vol. 159, pp. 108–113, Jun. 2016.

[9] S. Wagner et al., “Highly Sensitive Electromechanical Piezoresistive Pressure Sensors Based on Large-Area Layered PtSe2 Films,” Nano Lett., vol. 18, no. 6, pp. 3738–3745, Jun. 2018.

[10] X. Fan et al., “Graphene ribbons with suspended masses as transducers in ultra-small nanoelectromechanical accelerometers,” Nat. Electron., vol. 2, pp. 394–404, Sep. 2019.

[11] X. Fan et al., “Suspended Graphene Membranes with Attached Silicon Proof Masses as Piezoresistive Nanoelectromechanical Systems Accelerometers,” Nano Lett., Sep. 2019.

[12] T. Mashoff et al., “Bistability and Oscillatory Motion of Natural Nanomembranes Appearing within Monolayer Graphene on Silicon Dioxide,” Nano Lett., vol. 10, no. 2, pp. 461–465, Feb. 2010.

[13] S. Wittmann et al., “Graphene Membranes for Hall Sensors and Microphones Integrated with CMOS-Compatible Processes,” ACS Appl. Nano Mater., vol. 2, no. 8, pp. 5079–5085, Aug. 2019.

[14] D. Neumaier, S. Pindl, and M. C. Lemme, “Integrating graphene into semiconductor fabrication lines,” Nat. Mater., vol. 18, no. 6, p. 525, Jun. 2019.