National Physical Laboratory

Tuning epitaxial graphene sensitivity to water by hydrogen intercalation

We investigate the effects of humidity on the electronic properties of as-grown and quasi-free standing (QFS) single layer graphene (1LG) on 4H-SiC(0001) (obtained by hydrogen intercalation of the interfacial layer), via simultaneous magneto-transport in the van der Pauw geometry and local work function measurements in a controlled environment.

Using magneto-transport measurements in a highly controlled environment, as compared to the as-grown epitaxial graphene, we demonstrate a two-fold increase in sensitivity to changes in relative humidity (R H) for QFS 1LG. This enhanced sensitivity to water is attributed to the lowering of the hydrophobicity of QFS 1LG, which results from the spontaneous polarization of 4H-SiC(0001) strongly influencing the graphene (inducing hole conduction compared to electron in as-grown). Moreover, the superior carrier mobility of the QFS 1LG system (more than three times higher than as-grown) is retained even at the highest humidity (80% R  H). Furthermore, local work function measurements using Kelvin probe force microscopy revealed higher sensitivity to water for 1LG compared to 2LG in both QFS 1LG and as-grown systems, a result which is in agreement with our previous works on epitaxial graphene.

This work demonstrates the importance of following a standardised procedure for accurate characterisation of magneto-transport properties. The environmental condition and carrier concentration value should be accompanied by the corresponding mobility value, as environmental conditions such as humidity can greatly influence the conduction. This is particularly important for future graphene-based electronics, which will operate under different environmental conditions (i.e. from vacuum to variable humidity). These results point to a new field of applications for QFS 1LG, i.e. as humidity sensors, and the need for proper encapsulation of future graphene-based devices. Most importantly, this work was the result of the development of a custom made environmental transport properties measurements system for characterisation of graphene and 2D materials in controlled environmental.

Tuning epitaxial graphene sensitivity to water by hydrogen intercalation

(a) Carrier concentration (black) and mobility (red) at various humidity levels for as-grown
(squares, bottom panel) and QFS 1LG (circles, top panel);
(b–c) Carrier mobility as a function of carrier concentration for (b) as-grown; and
(c) QFS for various humidity levels.

Read the full paper online at RSC Nanoscale

More on NPL's work on Graphene

For further details, please contact Christos Melios and Olga Kazakova

Last Updated: 13 Mar 2017
Created: 13 Mar 2017

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