Due to its single-molecule sensitivity, high carrier density and low noise levels, graphene — an atomic-thick sheet of carbon — has found enormous uses in gas sensors. The much-heralded sensitivity of graphene, however, also implies that it is inherently non-selective to any gas.
Figure 1 Device schematic of the activated-carbon functionalized graphene sensor with the inset showing the porous activated carbon-graphene interface. Image Credit: Manoharan Muruganathan from Japan Advanced Institute of Science and Technology.
As a result, when exposed to atmospheric air, it readily undergoes massive p-doping (a drop in graphene electron density), limiting demonstrations of its selectivity to inert settings such as dry air or nitrogen. However, atmospheric exposure is essential for the commercialization of graphene in applications like environmental monitoring or breath/skin gas clinical sensors.
The goal to develop simultaneous atmospheric passivation and high-speed selective gas detection in graphene has become necessary. Polymer coatings on graphene are a common approach for producing selectivity. This method, however, alters graphene’s fundamental properties while still exposing large parts of the graphene channel to air doping.
In collaboration with industrial partners Mr. Hisashi Maki, Mr. Masashi Hattori, and Mr. Kenichi Shimomai, a research team led by Dr. Manoharan Muruganathan (Senior Lecturer) and Professor Hiroshi Mizuta at the Japan Advanced Institute of Science and Technology (JAIST) created a nanoporous activated-carbon functionalized graphene channel to accomplish simultaneous atmospheric passivation and selective gas sensors in graphene.
According to the researchers, Dr. A. Osazuwa Gabriel and Dr. R. Sankar Ganesh, the activated-carbon functionalized chemical vapor deposition (CVD)-graphene channel (Figure 1) was obtained by pyrolysis of a post-lithographic Novolac resin polymer.
The electrical features of the CVD-graphene are preserved in the sensor due to the comparable work-function of activated carbon and graphene, with little air doping, however, after 40 minutes of atmospheric exposure.
Furthermore, the oxidized activated-carbon-graphene interface specifies ammonia selective adsorption sites, leading in single-digit parts per billion (ppb) ammonia sensitivity in atmospheric air with a few seconds response time at room temperature. As a result, molecular sieve functioning was discovered in atmospheric air.
Using the same sensor, they developed the charge neutrality point disparity approach, a new molecule identification methodology, which makes use of the electric-field-dependent charge transmission properties of adsorbed gases on the graphene channel.
This sensor is suited for clinical and environmental sensor applications because of its extreme ammonia selectivity, atmospheric passivation and simple and scalable lithographic production.
These results take graphene gas sensors from demonstrations in controlled environments to actual atmospheric applications, opening a new vista in graphene-based gas sensing.
Mr. Masashi Hattori, Research Collaborator, Manager, TAIYO YUDEN CO., LTD.
Journal Reference:
Agbonlahor, O. G., et al. (2021) Interfacial Ammonia Selectivity, Atmospheric Passivation, and Molecular Identification in Graphene-Nanopored Activated Carbon Molecular-Sieve Gas Sensors. ACS Applied Materials & Interfaces. doi.org/10.1021/acsami.1c19138.