What Effect Does Humidity have on Graphene Sensors?

Graphene created using chemical vapor deposition (CVD) will become an essential part of future graphene-based biological, chemical and other types of sensors. However, graphene is highly sensitive to air, especially to humidity.

It is very important to explore the mechanisms where water, as environmental humidity, affects graphene sheets. This knowledge helps to prevent unnecessary background effect caused by humidity and to calibrate future sensors.

Effect of Humidity on CVD Graphene

Researchers from Graphenea, the National Physical Laboratory (NPL, UK), and the University of Surrey collaborated to study the effects of humidity on the local surface potential and electrical transport of CVD graphene.

They studied single-layer graphene and double-layer graphene created by placing one graphene layer on top of the other, and successfully decoupled the substrate effects from interlayer coupling and atmospheric effects, especially the effects of humidity.

The single-layer graphene on the standard SiO₂ substrate is found to be extremely sensitive to water vapor. Here, water molecules acted as physisorbed loosely bound p-dopants. It is possible to remove the adsorbed water when the sample is placed in vacuum.

Random orientation and decoupling of graphene layers is performed for bi-layered stacks that are formed by double transfer of two graphene layers. As a result, the top graphene layer of the bi-layer stack is externally doped by the water vapor, while the bottom layer is largely affected by the substrate charges (Figure 1).

The results validate previous research findings that bilayer and monolayer graphene behave differently upon exposure to humidity. They also explain the reason for the presence of fewer amounts of p-dopants in bilayer graphene, which is due to the effect of substrate on the bottom graphene layer.

Figure 1. Humidity effect on graphene doping

Conclusion

The study results demonstrate that it is necessary to appropriately encapsulate the electronic systems employing CVD graphene on SiO₂ in order to achieve stable operation. The effects of ambient humidity on sensors can be minimized through appropriate calibration. The findings of the study were reported in the July issue of Carbon.

This information has been sourced, reviewed and adapted from materials provided by Graphenea.

For more information on this source, please visit Graphenea.