Water on graphene: review of recent progress

Abstract

The sensitivity of graphene to the surrounding environment is given by its π electrons, which are directly exposed to molecules in the ambient. The high sensitivity of graphene to the local environment has shown to be both advantageous but also problematic for graphene-based devices, such as transistors and sensors, where the graphene carrier concentration and mobility change due to ambient humidity variations. In this review, recent progress in understanding the effects of water on different types of graphene, grown epitaxially and quasi-free standing on SiC, by chemical vapour deposition on SiO2, as well as exfoliated flakes, are presented. It is demonstrated that water withdraws electrons from graphene, but the graphene-water interaction highly depends on the thickness, layer stacking, underlying substrate and substrate-induced doping. Moreover, we highlight the importance of clear and unambiguous description of the environmental conditions (i.e. relative humidity) whenever a routine characterisation for carrier concentration and mobility is reported (often presented as a simple figure-of-merit), as these electrical characteristics are highly dependent on the adsorbed molecules and the surrounding environment.

Graphene Electromechanical Water Sensor: The Wetristor

“…Either there is a charge transfer process at the graphene/water interface, which promotes doping of graphene by increasing its charge density n, or there are morphological changes at graphene/water interface, such as wrinkle reduction, that somehow reduce charge scattering and enhance graphene mobility µ (in the conductivity equation above, e is the elementary charge). [20] Thus, our work provides a conclusive answer to the discussion presented above. The overall prediction, in the case of suspended graphene, is that the doping effects should be small and strongly dependent on molecule orientation.…”

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between water and graphene is crucial for building up novel and smart biointerfaces. [20,21] For instance, several experimental works demonstrate that the charge transfer process that happens between graphene and water molecules is highly dependent on the underlying substrate. [20,21] For instance, several experimental works demonstrate that the charge transfer process that happens between graphene and water molecules is highly dependent on the underlying substrate.

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“…[18,19] Additionally, the study of reactivity and structure of water at the graphene interface has also generated intriguing questions and controversial results. [20,22] Thus, it would be highly desirable to elucidate the above discussion by probing the electrical response of a suspended graphene membrane in contact with water without the presence of any substrate. [20,22] Thus, it would be highly desirable to elucidate the above discussion by probing the electrical response of a suspended graphene membrane in contact with water without the presence of any substrate.…”

Towards standardisation of contact and contactless electrical measurements of CVD graphene at the macro-, micro- and nano-scale

“…Scientific RepoRtS | (2020) 10:3223 | https://doi.org/10.1038/s41598-020-59851-1 www.nature.com/scientificreports www.nature.com/scientificreports/ measurements. Moreover, 2-3LG islands demonstrate lower work functions than 1LG, due to screening of the substrate charges 24,25 . The summarized results of work function measurements of the different samples are shown in Fig.…”

“…Spectroscopy (THz-TDS) 16,[19][20][21][22][23] measurements provided a non-contact method of measuring the conductivity of graphene films. Despite the attractiveness of these techniques, fluctuations in ambient conditions (such as humidity) affect the electrical properties of graphene 24,25 , resulting in discriminations between measurements at different laboratories.…”