Conduction Percolation in MoS2 Nanoink Humidity Sensors: Critical Exponents and Nanochannel Dimensionality

• Published in: Journal of physical chemistry. C 2024-05, Vol.128 (19), p.8042-8047
• Main Authors: Mendonça, Bruno H. S., Pereira, Neuma, Rezende, Natália P., Moraes, Elizane E. de, Lacerda, Rodrigo G., Chacham, Helio
• Format: Article
• Language: English
• Subjects: C: Physical Properties of Materials and Interfaces
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.4c00078

In this paper, we adopt a novel approach to investigate the ionic conduction near the percolation transition in a porous nanomaterial. We make use of a recently discovered humidity sensing property of aerosol-printed MoS2 ink films, where the conductance, originated from ionic transport through water nanochannels within the films, is dependent on the ambient humidity. The experiments, performed for a set of four devices inside a chamber with controlled humidity, allow the experimental fine-tuning of the ionic conduction percolation within each nanoporous device by changing the ambient relative humidity, without the need of different samples for different stoichiometries as in usual percolation experiments. Our results indicate the existence, in our devices, of a common phenomenology consisting of two sequential modifications of the conductance as a function of humidity near percolation. The first is the true percolation transition with a universal critical exponent very close to unity. This is followed by an apparent increase in the critical exponent above the true transition. We also perform molecular dynamics simulations that allow the identification of a possible mechanism for dimensionality changes in the water nanochannels inside the material as a function of either humidity or material geometry as a possible scenario for the observed conductance modification in the conductive phase.