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NPEG - NanoPatterened Epitaxial Graphite

Claire Berger, Zhimin Song, Tianbo Li, Xuebin Li, Asmerom Y. Ogbazghi, Rui Feng, Zhenting Dai, Alexi N. Marchenkov, Edward H. Conrad, Phillip N. First, and Walt A. de Heer.

There has been much excitement in recent years over the properties of carbon nanotubes. Nanotubes display ballistic conduction, and their conductance may be controlled by a simple electrostatic gate. This makes them attractive for applications in electronics where the limitations of conventional devices threatens to impede the exponential growth in computing power. Unfortunately, nanotubes are very cumbersome to manipulate and large scale integration would be extremely difficult using modern techniques.

Many of the attractive electronic properties of nanotubes are shared by graphene (a single sheet of graphite). For example, graphene ribbons may be either metallic or semiconducting depending on the crystallographic direction of the ribbon axis. A major difference is the presence of dangling bonds on a graphitic ribbon (which are closed in a nano-tube). Normally these bonds are terminated with Hydrogen, but it may be possible to bind donor / acceptor atoms to them providing a way to modify the electronic properties of the graphene ribbon.

From K. Nakada, M. Fujita, G. Dresselhaus, and M. Dresselhaus, Phys Rev. B 54, 17954 (1996)

The substrate for our graphene layers is single crystal Silicon Carbide. A pass of hydrogen etching dramatically improves the surface quality making it suitible for growth of graphene layers by thermal desorbtion of the Silicon.

Hydrogen etching of Silicon Carbide.

The quality of the Graphene layers was tested by the use of Low Energy Electron Diffraction (LEED).

LEED images show the epitaxial growth of graphene on SiC. The graphene diffraction spots are aligned with the SiC spots. The satellites are due to reconstruction at the interface.

These thin layers of graphene may be patterned into devices using standard lithographic methods. As a demonstration, we fabricated a first attempt at a NPEG based field effect transistor. The pattern and an AFM image of the device is shown below.

The gates of the device are made from a conductive coating applied to a 100nm thick aluminum oxide layer. The conductance as a function of the gate voltage is shown below. While the leakage for this "device" is large - it clearly demonstrates the potential of NPEG for use in electronics.

Conductance as a function of gate voltage for a sample at 4K. The top gate is only partially effective due to the open geometry. Nevertheless, a 2% change in conductance is observed.

See our publications page for more information related to this research. This project was funded by a grant from NIRT.