cfaed Seminar Series

Prof. Christoph Tegenkamp , Leibniz University of Hannover

Functionalization of epitaxially grown graphene nanostructures

11.05.2017 (Thursday) , 13:00 - 14:00
Seminar Room 115 (HAL) , Hallwachsstr. 3 (HAL) , 01187 Dresden

Functionalization of graphene is an essential task for any future carbon based electronics.
In this respect graphene ribbons grown on pre-structured SiC(0001) surfaces are
interesting as they exhibit promising transport properties. Graphene ribbons grown on prestructured
SiC(0001) surfaces exhibit promising transport properties, e.g. high temperature
annealing of appropriately designed SiC-Mesa structures results in growth of sidewall
nanoribbons revealing robust ballistic transport channels with mean free path lengths up
to 16μm at 300K. The existence of edge states on zig-zag oriented ribbons is confirmed by
Raman, STM and STS measurements. Moreover, we have recently fabricated nanoconstrictions
within these wires revealing Fabry-Perot like resonance features.
Npn-structures with ballistic Klein tunneling barriers were realized by functionalizing the
buffer layer on top of the SiC-mesas via Ge-intercalation. Depending on the local Ge
coverage the chemical potential is either shifted above or below the Dirac point correlating
nicely with the morphology as deduced from scanning tunneling microscopy and
spectroscopy. The length of a single pn-junction is around 5 nm as revealed by spatially
resolved STS measurements and therefore, significantly lower than those induced by field
effects. In case of bipolar structures the resistance strongly depends on the inner barrier
length D. For short barriers the second junction appear transparent, a clear signature of
Klein tunneling.


Christoph Tegenkamp works in the field of transport phenomena and collective
excitations in correlated matter and nanoscaled structures on surface and is
currently holder of a professorship for nano-electromechanical quantum systems at
the Leibniz University of Hannover.
He received his PhD in 2000 where he dealt with functionalization of surfaces due
adsorption of organic molecules on epitaxially grown insulating films. After his Post-
Doc time at the University of Maryland he returned to Hannover, where he
introduced novel concepts of nanostructuring to surfaces. The combination of both
top-down and bottom-up techniques is used to fabricate metallic nanostructures with
atomic precision and intriguing transport properties.
Among other systems he works currently on of atomic wires grown by self-assembly
on semiconducting surfaces, graphene nanostructures and topological insulators.
Besides fundamental aspects, e.g spin-orbit coupling in correlated materials,
application-driven and interdisciplinary topics, e.g. molecular electronics, belong to
his interests.
Christoph Tegenkamp is in the editorial board of JPCM and member in various
scientific panels.


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