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Graphene’s exceptional properties make it attractive for technological applications in many areas,
including high-speed electronics. The establishment of processes for producing high quality, large-scale
graphene is necessary for such applications. Large area growth of epitaxial graphene on the Si-face of
hexagonal SiC (0001) wafers exhibits manageable growth kinetics, and most importantly, its azimuthal
orientation is fixed, as it is determined by the structure of the single crystal substrate. Therefore, this is a
viable method for producing graphene with uniform coverage and structural coherence at wafer-scale.[1],[2]
Semi-insulating SiC is a good substrate for graphene RF transistors, however, its cost is so high
that potentially only niche applications of graphene on SiC (e.g. defense or space related) can be viable.
Furthermore, to enable hybrid electronics, where standard circuits built on Si perform digital logic functions
while graphene that does not exhibit a band gap is used for ultrafast analog devices, we would need to
transfer epitaxial graphene onto Si wafers. To address these issues, we have developed a method in which
a graphene film grown on a 4” SiC wafer is exfoliated via the stress induced by an overgrown Ni film and
transferred to other substrates, resulting in a wafer-scale monolayer of graphene that is continuous and has
a single azimuthal orientation.[3] This growth and transfer process can be repeated on the same SiC wafer
hundreds to thousands of times, dramatically reducing the cost per wafer-sized graphene layer. The
characterization of the transferred films shows that they are of quality similar to the pristine films on SiC.
Capitalizing on this new method for single crystal epitaxial graphene transfer, we have initiated a
project to produce bilayers of graphene with deterministically controlled twist angles. The inspiration for
this experimental work is recent theoretical work by Maroudas and coworkers4 that predicts the opening of
substantial band gaps at specific twist angles in bilayer graphene. We will report our methods for producing
twisted bilayers with controlled twist angle, their characterization and device results.
[1] C. Dimitrakopoulos, Y.-M. Lin, A. Grill, D. B. Farmer, M. Freitag, Y. Sun, S.-J. Han, Z. Chen, K. A. Jenkins,
Y. Zhu, Z. Liu, T. J. McArdle, J. A. Ott, R. Wisnieff, Ph. Avouris J. Vac. Sci. Technol. B 28, 985-992, (2010).
[2] Y.-M. Lin, C. Dimitrakopoulos, K. A. Jenkins, D. B. Farmer, H.-Y. Chiu, Ph. Avouris Science 327, 662 (2010).
[3] J. Kim, H. Park, J. B. Hannon, S. W. Bedell, K. Fogel, D. K. Sadana, C. Dimitrakopoulos Science 342, 833-836
(2013).
[4] A. R. Muniz, D. Maroudas Phys. Rev. B 86, 075404 (2012)
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