National Physical Laboratory

Atmospheric doping effects in epitaxial graphene: correlation of local and global electrical studies

We directly correlate the local (20 nm scale) and global electronic properties of a device containing mono-, bi- and tri-layer epitaxial graphene (EG) domains on 6H-SiC(0001) by simultaneously performing local surface potential measurements using Kelvin probe force microscopy and global transport measurements.

Using well-controlled environmental conditions, we investigate the doping effects of N2, O2, water vapour and NO2 at concentrations representative of the ambient air. We show that presence of O2, water vapour and NO2 leads to p-doping of all EG domains. However, the thicker layers of EG are significantly less affected. Furthermore, we demonstrate that the general consensus of O2 and water vapour present in ambient air providing majority of the p-doping to graphene is a common misconception. We experimentally show that even the combined effect of O2, water vapour, and NO2 at concentrations higher than typically present in the atmosphere does not fully replicate p-doping from ambient air. Thus, for EG gas sensors it is essential to consider naturally occurring environmental effects and properly separate them from those coming from targeted species.

Measurements of surface potential and global transport in vacuum, N2, synthetic air, 40%-60%-20% relative humidity and ambient air

Measurements of surface potential and global transport in vacuum, N2, synthetic air, 40%-60%-20% relative humidity and ambient air:
(a) Individual surface potential maps (400 mV colour scale) for ambient air, vacuum, N2, synthetic air, 40% relative humidity and ambient air. The scan size is 6×3 μm2. Dashed lines mark 1-2-3LG domains.
(b) Surface potential difference (ΔVSP) between 1-2LG, 1-3LG and 2-3LG as derived from local surface potential maps.
(c) Carrier density for 1LG and 2LG and carrier mobility for FLG channel in the controlled environments as derived from transport measurements.

Read the full paper online at 2D Materials

More on NPL's work on Graphene

For further details, please contact Olga Kazakova

Last Updated: 17 Mar 2016
Created: 12 Feb 2016

Registration

Please note that the information will not be divulged to third parties, or used without your permission

Login