Tunneling spectra of graphene on copper unraveled.
Scanning tunneling spectroscopy is often employed to study two-dimensional (2D) materials on conductive growth substrates, in order to gain information on the electronic structures of the 2D material-substrate systems, which can lead to insight into 2D material-substrate interactions, growth mechanisms, etc. The interpretation of the spectra can be complicated, however. Specifically for graphene grown on copper, there have been conflicting reports of tunneling spectra. A clear understanding of the mechanisms behind the variability is desired. In this work, we have revealed that the root cause of the variability in tunneling spectra is the variation in graphene-substrate coupling under various experimental conditions, providing a salutary perspective on the important role of 2D material-substrate interactions. The conclusions are drawn from measured data and theoretical calculations for monolayer, AB-stacked bilayer, and twisted bilayer graphene coexisting on the same substrates in areas with and without intercalated oxygen, demonstrating a high degree of consistency. The Van Hove singularities of the twisted graphene unambiguously indicate the Dirac energy between them, lending strong evidence to our assignment of the spectral features. In addition, we have discovered an O-Cu superstructure that has never been observed before.
Department of Physics, University at Buffalo, the State University of New York, Buffalo, NY 14260, USA.
Xin
X
Zhang
Department of Micro- and Nanotechnology, Center for Nanostructured Graphene (CNG), Ørsteds Plads, Building345E, DK-2800 Kgs. Lyngby, Denmark.
Daniele
D
Stradi
Department of Electrical Engineering and Computer Science, The University of Tennessee, Knoxville, Tennessee 37996, USA. ggu1@utk.edu.
Lei
L
Liu
Department of Physics, University at Buffalo, the State University of New York, Buffalo, NY 14260, USA.
Hong
H
Luo
Department of Micro- and Nanotechnology, Center for Nanostructured Graphene (CNG), Ørsteds Plads, Building345E, DK-2800 Kgs. Lyngby, Denmark.
Mads
M
Brandbyge
Department of Electrical Engineering and Computer Science, The University of Tennessee, Knoxville, Tennessee 37996, USA. ggu1@utk.edu.
Gong
G
Gu