@ J. Heyrovsky Institute of Physical Chemistry
Spectroelectrochemistry at individual SWCNT
Individual single walled carbon nanotubes were prepared by CVD method (see SEM and AFM images). The SWCNT were electrochemically doped and at the same time Raman spectra were loaded. The work demonstrates bleaching of the intensity of the Raman bands of individual SWCNT in dependence on doping. The bleaching speed was shown to be a function of the laser excitation energy.
Ref.: M. Kalbac, H. Farhat, L. Kavan, J. Kong, K. Sasaki, R.Saito and M. S. Dresselhaus: ACS Nano, 3 (8), 2320-2328 (2009).
Direct addressing of top and bottom layer in BLG
Using CVD method 12C and 13C graphene samples were prepared. These isotopically labeled layers were combined to form graphene bilayer. As the mass of the carbon isotope is different for each individual layer the frequencies of their Raman modes also differ and the layers can be clearly distinguished (top).The graphene bilayer can be further electrochemically doped and the doping of each layer can be addressed at any doping level (bottom).
Ref.:M. Kalbac, H. Farhat, J. Kong, P. Janda, L. Kavan, and M. S. Dresselhaus: Nanoletters, 11(5),1957-1963 (2011).
Tuning quantum interference in graphene
The CVD graphene has been electrochemically doped and the Raman spectra were measured at the same time. At high electrode potentials an unusual increase of the intensity of the G mode has been observed. The effect has been explained by canceling of a fraction of destructively interfering electronic transitions.
Ref.: M. Kalbac,A. Reina-Cecco, H. Farhat, J. Kong, L. Kavan, and M. S. Dresselhaus: ACS Nano, 4 (10), 6055-6063 (2010).
Observation of van Hove singularities in twisted BLG
Graphene bilayers were placed on BN flake and the Raman maps were measured. At some points corresponding to specific twist angle a strong signal enhancement of the G mode was observed due to resonance with van Hove singularities (top). The location of the ‘hot’ spot depends on the laser excitation energy because the energy split of van Hove singularity is dependent on a twist angle (bottom).
Ref.: M. Kalbac, O. Frank, J. Kong, J. D. Sanchez-Yamagishi, K. Watanabe, T. Taniguchi, P. Jarillo-Herrero, M. S. Dresselhaus. J. Phys. Chem. Lett. 3, 796-799 (2012).
Our joint work
M. Kalbac, L. Kavan, L. Dunsch and M.S. Dresselhaus: Development of the tangential mode in the Raman spectra of SWCNT bundles during electrochemical charging, Nanoletters, 8, 1257-1264 (2008).
M. Kalbac, H. Farhat, L. Kavan, J. Kong, M.S. Dresselhaus: Competition of a spring force constant and a phonon energy renormalization in electrochemically doped semiconducting single walled carbon nanotubes, Nanoletters, 8 (10), 3532-3537 (2008).
M. Kalbac, L. Kavan, H. Farhat, J. Kong, M.S. Dresselhaus: A Large Variety of Behaviors for the Raman G' Mode of Single Wall Carbon Nanotubes upon Electrochemical Gating Arising from Different (n,m) of Individual Nanotubes, J. Phys. Chem C. 113(5), 1751-1757 (2009).
H. Farhat, K. Sasaki, M. Kalbac, M. Hofmann, R. Saito, M. S. Dresselhaus and J. Kong: Softening of the Radial Breathing Mode in Metallic Carbon Nanotubes, Phys. Rev. Lett. 102, 126804 (2009).
J.S. Park, K. Sasaki, R. Saito, W. Izumida, M. Kalbac, H. Farhat, G. Dresselhaus, and M. S. Dresselhaus: Fermi energy dependence of the G-band resonance Raman spectra of single-wall carbon nanotubes, Phys. Rev. B, 80, 081402-1-4(R) (2009).
M. Kalbac, H. Farhat, L. Kavan, J. Kong, K. Sasaki, R.Saito and M. S. Dresselhaus: Electrochemical Charging of Individual Single-Walled Carbon Nanotubes, ACS Nano, 3 (8), 2320-2328 (2009).
Y.-p. Hsieh, M. Hofmann, H. Farhat, E. B. Barros, M. Kalbac, J. Kong, C.-t. Liang, Y.-f. Chen, and M. S. Dresselhaus: Chiral angle dependence of resonance window widths in (2n+m) families of single-walled carbon nanotubes, Applied Physics Letters 96, 103118 (2010).
M. Kalbac,A. Reina-Cecco, H. Farhat, J. Kong, L. Kavan, and M. S. Dresselhaus: The Influence of Strong Electron and Hole Doping on the Raman Intensity of CVD Graphene. ACS Nano, 4 (10), 6055-6063 (2010).
M. Kalbac, Y-P. Hsieh, H. Farhat, L. Kavan, M. Hofmann, J. Kong, and M.S. Dresselhaus: Defects in Individual Semiconducting Single Wall Carbon Nanotubes: Raman Spectroscopic and in Situ Raman Spectroelectrochemical Study. Nanoletters, 10 (11),4619-4626 (2010).
M. Kalbac, H. Farhat, J. Kong, P. Janda, L. Kavan, and M. S. Dresselhaus: Raman spectroscopy and in situ Raman spectroelectrochemistry of bi-layer 12C/13C graphene Nanoletters, 11(5),1957-1963 (2011).
H. Farhat, S. Berciaud, M. Kalbac, R. Saito, T. F. Heinz, M. S. Dresselhaus, and J. Kong: Observation of Electronic Raman Scattering in Metallic Carbon Nanotubes, Phys. Rev. Lett,107, 157401 (2011).
M. Kalbac, O. Frank, J. Kong, J. D. Sanchez-Yamagishi, K. Watanabe, T. Taniguchi, P. Jarillo-Herrero, M. S. Dresselhaus. Large Variations of the Raman Signal in the Spectra of Twisted Bilayer Graphene on a BN Substrate: J. Phys. Chem. Lett. 3, 796-799 (2012).
M. Kalbac, J. Kong., M. S. Dresselhaus. Raman Spectroscopy as a Tool to Address Individual Graphene Layers in Few Layer Graphene J. Phys. Chem. C, 116 (35), 19046–19050 (2012).
M. Kalbac, J. Kong, L. Kavan, and M.S. Dresselhaus: Raman spectroscopy of isotopically labeled two-layer graphene Physica status solidi (b), 249 (12), 2500-2502 (2012).
W. Fang, A. L. Hsu, R. Caudillo, Y. Song, A.G.Birdwell, E. Zakar, M. Kalbac, M. Dubey, T. Palacios, M. S. Dresselhaus, P. T. Araujo, and J. Kong: Rapid Identification of Stacking Orientation in Isotopically Labeled Chemical-Vapor Grown Bilayer Graphene by Raman Spectroscopy: Nano Lett., 13 (4),1541–1548 (2013).
P. T. Araujo, O. Frank, D. L. Mafra, W. Fang, J. Kong, M. S. Dresselhaus and M. Kalbac: Mass-related inversion symmetry breaking and phonon self-energy renormalization in isotopically labeled AB-stacked bilayer graphene: Sci. Rep. 3 : 2061 (2013)
M. Kalbac, J. Kong, and M. S. Dresselhaus: Doping of bi-layer graphene by gradually polarizing a ferroelectric polymer. Physica status solidi (b), 250 (12), 2649-2652 (2013).
O. Frank, Mildred S. Dresselhaus, M. Kalbac: Raman spectroscopy and In-situ Raman spectroelectrochemistry of isotopically engineered graphene systems. Accounts of chemical research. 48, 111-118 (2015).
V. Valeš, P. Kovaříček, X. Ji, X. Ling, J. Kong, M. S. Dresselhaus and M. Kalbáč: Quenching of photoluminescence of Rhodamine 6G molecules on functionalized graphene Physica status solidi (b), 253, 2347-2350 (2016).
V. Valeš, P. Kovaříček, M. Fridrichová, X. Ji, X. Ling, J. Kong, M. S Dresselhaus and Martin Kalbáč: Enhanced Raman scattering on functionalized graphene substrates: 2D Materials, 4, 025087 (2017).graphene and a substitution of fluorine with phenyl sulfonyl group. The approach using exchange reaction can be used also for other substituents as shown on examples of other moieties.
Acknowledgment: The cooperation was supported by several projects: Czech Science Foundation (15-01953S), project of the Ministry of Education, Youth and Sports of the Czech Republic ERC-CZ (LL1301), Czech-USA cooperation projects (LH13022, ME09060), NSF/DMR-07-04197, U.S.
Department of Energy ( DE-SC0001088), NSF-CHE 0111370 and NIHRR02594.
We are all grateful to prof. Jing Kong for a generous help and support of the collaboration and research work.