Mrsec Highlights 2009

Chemical Modification of Epitaxial Graphene Elena Bekyarova, Mikhail E Itkis, Palanisamy Ramesh, Robert C Haddon University of California-Riverside Claire Berger, Michael Sprinkle, Walt A de Heer Georgia Institute of Technology NO2

O2 N

N N , BF4 0.1 M [Bu4N] PF6 ACN; RT, Ar, 20 h

Fig. 1 Spontaneous grafting of aryl groups to epitaxial graphene

Advantages: • Extremely mild conditions • Minimum perturbation to electronic structure of EG (conversion of C sp2 to sp3) • Simple, Fast, Versatile

Fig. 2 Temperature dependence of sheet resistance of pristine (EG) and nitrophenyl functionalized graphene (NP-EG).

Sponsored by NSF-MRSEC through contract DMR-0820382 Bekyarova, E.; Itkis, M. E.; Ramesh, P.; Berger, C.; Sprinkle, M.; de Heer, W. A.; Haddon, R. C., Chemical Modification of Epitaxial Graphene: Spontaneous Grafting of Aryl Groups. J. Am. Chem. Soc. 2009, 131, 1336-1337.

First Epitaxial Graphene Workshop

Workshop covered importance and  future of epitaxial graphene.  Advances  described by GT MRSEC investigators  facilitated discussion of future research  directions and promoted additional  international collaborations. Sponsored by NSF-MRSEC through contract DMR-0820382

Georgia Institute of Technology NSF MRSEC Highlight:

Graphene-based Transparent Electrodes for Organic Electronics Samuel Graham, School of Mechanical Engineering, Georgia Tech Robert Haddon, School of Chemistry, University of California Riverside

Before Annealing

After Annealing

Fig. 2 Optical image showing the graphene oxide-carbon nanotube composite prior to annealing

Fig. 3 Transparency data from the electrodes.

This research is developing a low cost, solution processible transparent electrode for use in future flexible electronics. Recent results have suggested that the films will have properties which will surpass the currently used electrode in the electronics industry and will be applicable to a wide range of devices including solar cells and LEDs for next generation light sources.

Fig. 1 Images showing graphene-CNT electrodes on quartz substrates.

Sponsored by NSF-MRSEC through contract DMR-0820382

Georgia Institute of Technology NSF MRSEC Highlight:

High quality graphene grown on silicon carbide Ming Ruan, Yike Hu, Mike Sprinkle, Claire Berger, Walt A. de Heer Researchers at Georgia are the pioneers of graphene based electronics, that has the potential for unprecedented capabilities. They have developed methods to produce the highest quality graphene material in the world. The graphene layer extends over the entire surface of the silicon carbide chip. This is an critical breakthrough in graphene based electronics.

Fig.1 Atomic force microscopy image of a graphene layer grown on an electronics grade silicon carbide crystal. The graphene layer is extremely flat and shows a few pleats (the white lines) that are few nanometers high, much like the pleats on a bed sheet.

Sponsored by NSF-MRSEC through contract DMR-0820382

Georgia Institute of Technology NSF MRSEC Highlight:

New Material Developed for Post Si-CMOS Electronics Michael Sprinkle, Claire Berger, Walt A de Heer, Edward Conrad School of Physics, Georgia Tech

Fig. 2 The expected Dirac Cones for a single graphene sheet.

Fig. 1 Multiple Dirac Cones Measured by Angle Resolved Photoemission.

A new form of graphene was discovered at the GT MRSEC for new electronic materials that makes an all graphene electronics circuit possible. Figure 1 shows multiple Dirac Cones from a 10-layer graphene film. These undoped Dirac Cone shows that multilayer graphene grown on the carbon face of SiC is “effectively” an electronic single graphene sheet. This remarkable results means that controlling graphene thickness to get large single layer films is no longer a requirement in graphene electronics and opens the way to a whole new way of thinking about graphene electronics.

Sponsored by NSF-MRSEC through contract DMR-0820382

Quantization of Zero-Mass Particles in Graphene D. L. Miller*, K. D. Kubista*, M. Ruan, W. A. de Heer, and P. N. First School of Physics, Georgia Institute of Technology G. M. Rutter and J. A. Stroscio NIST Center for Nanoscale Science and Technology * These authors contributed equally to this work.

Tunneling spectroscopy of graphene in magnetic fields from 0-6 T. Background shows predicted Landau level energy spectrum.

K. D. Kubista, Georgia Tech

Foreground: cartoon, Background: STM data. The wave continuity (tailcatching) condition requires an integer number of wavelengths around the orbit. This leads to special orbit sizes and a discrete spectrum of allowed orbit energies. For massless particles in graphene, these “Landau levels” have energies that vary as the square-root of the magnetic field, except for a special field-independent state at zero energy. NSF Support: DMR-0804908 and facilities of the Georgia Tech MRSEC (DMR-0820382).

D. L. Miller, Georgia Tech

Due to the wave nature of matter, the circular "cyclotron" orbits of electrons in a magnetic field must join on to themselves after a full revolution; like a dog catching its tail.

Quantization of Zero-Mass Particles in Graphene D. L. Miller*, K. D. Kubista*, M. Ruan, W. A. de Heer, and P. N. First School of Physics, Georgia Institute of Technology G. M. Rutter and J. A. Stroscio NIST Center for Nanoscale Science and Technology * These authors contributed equally to this work.

Tunneling spectroscopy of graphene in magnetic fields from 0-6 T. Background shows predicted Landau level energy spectrum.

K. D. Kubista, Georgia Tech

Foreground: cartoon, Background: STM data. The wave continuity (tailcatching) condition requires an integer number of wavelengths around the orbit. This leads to special orbit sizes and a discrete spectrum of allowed orbit energies. For massless particles in graphene, these “Landau levels” have energies that vary as the square-root of the magnetic field, except for a special field-independent state at zero energy.

D. L. Miller, Georgia Tech

Due to the wave nature of matter, the circular "cyclotron" orbits of electrons in a magnetic field must join on to themselves after a full revolution; like a dog catching its tail.

1 NSF Support: DMR-0804908 and facilities of the Georgia Tech MRSEC (DMR-0820382).

Due to the wave nature of matter, the circular "cyclotron" orbits of electrons in a magnetic field must join on to themselves after a full revolution; like a dog catching its tail. For electrons in graphene, researchers at the Georgia Institute of Technology (D. L. Miller, K. D. Kubista, M. Ruan, W. A. de Heer and P. N. First) and the NIST Center for Nanoscale Science and Technology (G. M. Rutter and J. A. Stroscio) have resolved the discrete spectrum of electron energies resulting from this wave-matching condition. Their lowtemperature (4.3 K) scanning tunneling microscopy (STM) and spectroscopy measurements allow detailed comparison with the predicted energy structure of graphene, a one-atom-thick honeycomb of carbon atoms. The spectra show two signatures unique to graphene: A sqrt(B) dependence of the magnetic-quantization energy states (Landau levels) and a Landau level that remains fixed at zero energy, independent of the applied magnetic field. The team also developed a new technique based on “tunneling magnetoconductance oscillations,” that was used to determine the energy versus momentum relation in graphene with high precision. All measurements utilized multilayer epitaxial graphene (MEG) synthesized at Georgia Tech; a material whose unusual rotated layerstacking results in electrical decoupling of neighboring graphene sheets. (Left) Cartoon of quantized circular orbits of graphene electrons in a magnetic field. Background honeycomb is an STM image of multilayer epitaxial graphene (MEG). Yellow areas are raised (0.01 nm) regions created by the Moiré alignment of slightly rotated graphene layers. (Right) Tunneling differential conductance (dI/dV) spectra from the top layer of a 10-layer MEG sample taken for magnetic fields from 0-6 T. Background curves show the predicted Landau-level spectrum of graphene. NSF Support: DMR-0804908 and facilities of the Georgia Tech MRSEC (DMR-0820382). Related Publication: D. L. Miller*, K. D. Kubista*, G. M. Rutter, M. Ruan, W. A. de Heer, P. N. First, and J. A. Stroscio, Science 324, 924-7 (2009). * These authors contributed equally to this work.

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Shared Experimental Facilities

Vacuum radio-frequency heated furnaces

Graphene is grown in a high temperature furnace

The GT MRSEC supports the operation of the graphene fabrication and analysis laboratory (Keck Epitaxial Graphene Laboratory located on the Georgia Tech Campus). This lab produces graphene samples and conducts pre- and posttesting of samples for all MRSEC members and collaborators.

Dr. Walt de Heer, Dr. Claire Berger, Dr. Edward Conrad, School of Physics, Georgia Tech Associated with work sponsored by NSF-MRSEC through contract DMR-0820382