| AVS 60th International Symposium and Exhibition | |
| Graphene and Other 2D Materials Focus Topic | Thursday Sessions |
| Session GR+AS+BI+PS+SS-ThA |
| Session: | Plasma Processing, Surface Chemistry, Functionalization, and Sensor Applications of 2D Materials |
| Presenter: | G. Mordi, The University of Texas at Dallas |
| Authors: | G. Mordi, The University of Texas at Dallas S. Jandhyala, The University of Texas at Dallas S. McDonnell, The University of Texas at Dallas R.M. Wallace, The University of Texas at Dallas J. Kim, The University of Texas at Dallas |
| Correspondent: | Click to Email |
As the performance of graphene based devices has continued to improve over the years (mobility, contact resistance, transconductance), the realization of novel logic devices as the BiSFET (Bi-layer Pseudospin Field-Effect Transistor) for ultra-fast switching speeds and ultra-low power consumptions may not be far off. One of the challenges in realizing BiSFET1 is the integration of a thin (1-2 nm), low-k (~2) dielectric material which can electrically isolate the two graphene layers in which a condensate is formed and at the same time act as a tunnel barrier.
One approach for obtaining a low-k dielectric is using two dimensional materials similar to graphene which can be manufactured independently and transferred on top of graphene. Covalent functionalization of graphene is a process of adding functional groups which covalently bind to the graphene network, changing its structure from sp2 to sp3 hybridization resulting in opening of a band gap. Fluorination among other processes (graphene oxide1, graphane2) can be used to covalently functionalize graphene. Fluorinated graphene (GrF) is an interesting material because of its atomically thin nature, thermodynamically more stable compared to graphene oxide and graphane, has a wide band gap (~3-7.5 eV) and a potentially low-k dielectric (expected to have dielectric constant of ~2)2.
In this study we utilized fluorine based plasma (CF4) to covalently functionalize graphene films. We established suitable CF4 plasma exposure parameters and then investigate the conduction mechanisms across GrF based devices. Raman spectroscopy studies showed the evolution of Raman active D (~1350 cm-1), G (~1595 cm-1), D' (1620 cm-1) and 2D (~2680 cm-1) peaks as function of plasma exposure (fluorination) time. XPS studies revealed the type of bonding that exists between fluorine and carbon atoms of the graphene lattice. Conductive atomic force microscopy (C-AFM) showed the out-of-plane conductivity on the GrF films were significantly small compared to non-fluorinated films. In-plane transport characteristics of GFETs displayed two minima (or Dirac points) for short CF4 exposures possibly attributed by both ionic and covalent doping effects simultaneously. Longer exposures result in a single minimum conductivity point possibly due to dominant covalent functionalization effects.
References
1. J.P Eisenstein and A.H MacDonald, Nature 432 691-694 (2004)
2. V. Georgakilas, M. Otyepka, A. B. Bourlinos, V. Chandra, N. Kim, K. C. Kemp, P. Hobza, R. Zboril and
K. S. Kim, Chemical Reviews 112 (11), 6156-6214 (2012).
3. F. Karlicky, R. Zboril and M. Otyepka, Journal of Chemical Physics 137 (3) (2012).