Abstract

Graphene is a two-dimensional material comprised of only carbon atoms closely packed in a honeycomb crystal structure. Devices fabricated out of epitaxial graphene grown on SiC have shown great promise for commercialization [1,2]. However, due to the complicated growth procedure, even the best epitaxial samples contain _{95% mono-layer (1LG) and} 5% bi-layer (2LG) graphene coverage [3]. Such samples have been shown to exhibit a work function difference of ~110±21 meV between 1LG and 2LG [4], which can affect the transport properties of graphene devices. We apply scanning gate microscopy with conductive (and magnetic) probes to studies of the local properties of graphene devices. We investigate the transverse voltage (Vxy) response of the sensor to a non-uniform magnetic field produced by a magnetic probe. Using this technique, we are able determine the stray field of a few types of commercial probes and optimize the magnetic response of the graphene Hall sensor [5]. We demonstrate that graphene Hall sensors can be successfully used to measure small magnetic fields and moments. We also study the electronic properties of 1LG and 2LG by measuring the longitudinal voltage (Vxx) and Vxy response to an electric field produced by a local scanning gate. The Vxx and Vxy mapping indicates that isolated 2LG islands provide an effect of screening the local electric field, and can affect transport measurements. The screening efficiency will depend on geometry of 2LG domains and their exact position with respect to the leads. These measurements allow investigating the possible effect of decoupling between individual layers of graphene.

[1] C. Dimitrakopoulos et al., 28 (5), 985 (2010). [2] Y.-M. Lin et al., Science 327, 662 (2010). [3] V. Panchal et al., 12th IEEE Conf. on Nanotechnology (2012). [4] O. Kazakova et al., Crystals 3 (1), 191-233 (2013). [5] V. Panchal et al., IEEE Trans. Magn. 49 (7), in press (2013).