Fabrication and transport properties of suspended graphene

Graphene, a two-dimensional material consisting of single-layer carbon atoms, is found to exhibit remarkably high carrier mobility. However, conventional graphene devices deposited on SiO2/Si substrates suffer from charge impurity and electron-phonon scattering. Therefore, the extrinsic transport properties of graphene are degraded. In order to minimize the effects of carrier scattering due to SiO2/Si substrates, removing the substrate beneath graphene could improve its transport properties significantly. In 2008, Philip Kim’s group at the Columbia University reported the first suspended graphene devices. They observed more intrinsic transport properties in suspended graphene devices. Different from conventional graphene devices, we carried out resist-free method to fabricate suspended graphene devices. Experiment data shows that conductance is sub-linearly dependent on density of states at low temperature. Also, temperature dependence of resistivity exhibits approximately linear relation instead of activated behavior at high temperature (>100 K). This indicates that the remote interfacial phonon scattering due to surface phonon on SiO2 substrate is excluded by removing the substrates. Furthermore, owing to the reduced charged impurities from SiO2 substrates, the fluctuation energy of suspended graphene samples, E_F^sat≈15 meV, is much smaller than the value of non-suspended graphene samples. Our resist-free fabrication technique provides a feasible route to access the intrinsic transport properties of graphene