Tuning epitaxial graphene sensitivity to water by hydrogen intercalation

Abstract

The effects of humidity on the electronic properties of quasi-free standing one layer graphene (QFS 1LG) are investigated via simultaneous magneto-transport in the van der Pauw geometry and local work function measurements in a controlled environment. QFS 1LG on 4H-SiC(0001) is obtained by hydrogen intercalation of the interfacial layer. In this system, the carrier concentration experiences a two-fold increase in sensitivity to changes in relative humidity as compared to the as-grown epitaxial graphene. This enhanced sensitivity to water is attributed to the lowering of the hydrophobicity of QFS 1LG, which results from spontaneous polarization of 4H-SiC(0001) strongly influencing the graphene. Moreover, the superior carrier mobility of the QFS 1LG system is retained even at the highest humidity. The work function maps constructed from Kelvin probe force microscopy also revealed higher sensitivity to water for 1LG compared to 2LG in both QFS 1LG and as-grown systems. These results point to a new field of applications for QFS 1LG, i.e., as humidity sensors, and the corresponding need for metrology in calibration of graphene-based sensors and devices.

Water on graphene: review of recent progress

“…Δne Epitaxial [83] Δnh QFS 1LG grown [83] Δnh CVD grown [ Water not only affects graphene through changing the carrier concentration. As it was recently demonstrated by our group [83], water is also responsible for changes in the carrier mobility.…”

“…Δne Epitaxial [83] Δnh QFS 1LG grown [83] Δnh CVD grown [ Water not only affects graphene through changing the carrier concentration. As it was recently demonstrated by our group [83], water is also responsible for changes in the carrier mobility. This is particularly important for standardisation procedures were simply quoting the carrier mobility and carrier concentration is not sufficient; one must also specify the environmental conditions in which the measurement are conducted.…”

“…However, in the case of the p-doped QFS 1LG (Figure 10b), the presence of water further increases the hole concentration and the two mechanisms of carrier scattering and Coulomb and impurity scattering (due to water) act together to decrease the mobility by ~76 cm 2 /Vs (~3 times larger effect as compared to the epitaxial graphene). [83]. Red stars indicate the average value for carrier concentration and mobility at each R.H. step.…”

“…Carrier type p-type [29], [103] n-type [83], [90] p-type [83], [91], [92] Total carrier concentration change 0-60% R.H. 2LG stacking Weakly coupled [101], [102] AB-stacked [104] AB-stacked [104] Hydrophilicity of 1LG and 2LG…”

Detection of Ultralow Concentration NO2 in Complex Environment Using Epitaxial Graphene Sensors

“…23 Approximately half of the reduction in the electron carrier density was previously attributed to p-doping, e.g. from water vapour and NO2 present in the atmosphere, with different sensitivities among 1 and 2LG 25,[34][35][36][37] .…”