Large Variations of the Raman Signal in the Spectra of Twisted Bilayer Graphene on a BN Substrate.
We report an unusual enhancement of the Raman signal of the G mode in a twisted graphene bilayer (2-LG) on a hexagonal single-crystalline boron nitride substrate. We used an isotopically engineered 2-LG, where the top layer was composed of (13)C atoms and the bottom layer of (12)C atoms. Consequently, it was possible by Raman spectroscopy to distinguish between the enhancement coming from the top and bottom layers. The enhancement of the G mode was, however, found to be similar for the top and bottom layers, and this enhancement effect was observed only at certain locations on the substrate. The experiment with two different laser excitation energies showed that the location of the enhanced spots is dependent on the laser excitation energy. Therefore our results suggest that the enhancement comes from new states in the electronic structure, which are a consequence of a local specific rotation of the grains in graphene layers.
†J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v.v.i., Dolejškova 3, CZ-18223 Prague 8, Czech Republic.|‡Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
Martin
M
Kalbac
†J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, v.v.i., Dolejškova 3, CZ-18223 Prague 8, Czech Republic.
Otakar
O
Frank
‡Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
Jing
J
Kong
§Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
Javier
J
Sanchez-Yamagishi
∥National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan.
Kenji
K
Watanabe
∥National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki 305-0044, Japan.
Takashi
T
Taniguchi
§Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
Pablo
P
Jarillo-Herrero
‡Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.|§Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
Mildred S
MS
Dresselhaus
Raman spectroscopy; bilayer; graphene