 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.
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