| AVS 62nd International Symposium & Exhibition | |
| 2D Materials Focus Topic | Friday Sessions |
| Session 2D+EM+IS+NS+PS+SP+SS-FrM |
| Session: | Surface Chemistry of 2D Materials: Functionalization, Membranes, Sensors |
| Presenter: | Richard Rojas Delgado, University of Wisconsin-Madison |
| Authors: | R. Rojas Delgado, University of Wisconsin-Madison F. Cavallo, University of New Mexico R.M. Jacobberger, University of Wisconsin-Madison J.R. Sanchez Perez, University of Wisconsin-Madison D. Schroeder, University of Wisconsin-Madison M.A. Eriksson, University of Wisconsin-Madison M.S. Arnold, University of Wisconsin-Madison M.G. Lagally, University of Wisconsin-Madison |
| Correspondent: | Click to Email |
The properties of graphene (G) make it an outstanding candidate for electronic-device applications, especially those that require no band gap but a high conductance. The conductance, involving both carrier mobility and carrier concentration, will depend critically on the substrate to which G is transferred. We demonstrate an exceptionally high conductance for G transferred to Ge(001) and provide an understanding of the mechanism.[1] Essential in this understanding is an interfacial chemistry consisting of Ge oxide and suboxide layers that provide the necessary charges to dope the graphene sheet, and whose chemical behavior is such that one can obtain long-term stability in the conductance. In contrast, when high-quality G is grown directly on Ge (100), (111), or (110), the conductance is unexceptional, but oxidation of the surface is significantly delayed and slowed, relative to both clean Ge and Ge with G transferred to its surface . [2,3] We fabricate Hall bars in G transferred to Ge and G grown using atmospheric-pressure CVD with methane precursors . X-ray photoelectron spectroscopy (XPS) is used to investigate the oxide in all stages of the measurements. The sheet resistance and Hall effect are measured from 300K to 10K for transferred and grown samples. Values of mobility and carrier concentration are extracted. It appears we have reached the highest combination of mobility and carrier concentration in graphene (suspended or supported) for temperatures from 10 to 300K. The implication is that the primary mechanisms for scattering charge in the G, roughness and a non-uniform electrostatic potential due to fixed charges, have limited effect when the substrate is oxidized Ge. Finally the subsequent oxidation kinetics of Ge (001) are compared for graphene directly grown on Ge and for graphene transferred to Ge. XPS shows that for graphene grown on Ge(001) the interface is oxide-free and remains so over long periods of time. For graphene transferred to Ge(001) the interface contains stoichiometric and substoichiometric oxides. The thickness of these oxides increases with time, but quite slowly. Using spatially resolved XPS, we propose a model of diffusion limited oxidation initiated at edges of the graphene.
Research supported by DOE.
[1]Cavallo, Francesca, et al. "Exceptional Charge Transport Properties of Graphene on Germanium." ACS nano 8.10 (2014): 10237-10245.
[2] R. M. Jacobberger, et al. "Oriented Bottom-Up Growth of Armchair Graphene Nanoribbons on Germanium." Nature Comm., under review.
[3] R. Rojas, et. al "Passivation of Ge by Graphene.", in process.