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Title: Ilya Degtev: Polarized Raman spectroscopy for studying two-dimensional materials
Number: 29/21
Status: Closing date exceeded
Begin: Thursday, 29.04. 2021, 14:00
Tutor: Václav Holý, Milan Dopita
Location: Zoom Meeting ID: 962 6152 0529

nanocent


Nano Seminar

 

Thursday, 29. 4. 2021, 14.00,

Join Zoom Meeting
https://cesnet.zoom.us/j/96261520529

Meeting ID: 962 6152 0529

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Ilya Degtev

Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, Prague, Czech Republic

Polarized Raman spectroscopy for studying two-dimensional materials

Raman spectroscopy is a conventional experimental technique for studying two-dimensional materials (2DMs), such as graphene, transitional metal chalcogenides (TMDs), and layered magnetic materials (2D magnets). It has historically played an important role in nondestructively characterizing the lattice structure and electronic, optical, and phonon properties of 2DMs with high resolution. In particular, this technique allows identifying the number of layers, i.e., the thickness. One can find a noticeable shift of one or more Raman peaks as a function of the number of layers due to variation in the interlayer interaction [1,2].
Moreover, if the polarization of the incident and scattered light is properly controlled, Raman spectroscopy (which is called polarized Raman spectroscopy) becomes an even more powerful tool [3]. By controlling the polarization of light, one can easily assign the Raman active vibrational modes such as A, B, and E modes directly related to the structure. Furthermore, this method can be used to determine the crystallographic orientation of isotropic 2DMs with in-plane strain or anisotropic 2DMs.
In the study of 2D magnets, the Raman spectrum of optical phonons has been widely used to study the magnetic phase transition through some indirect phenomena, such as spin−phonon coupling [4], the structural phase transition, and the Brillouin zone folding. Recently, the discovery of the magneto-optic Raman effect in CrI3 proved that the magnetic order could significantly affect the Raman scattering of phonons which implies that Raman spectroscopy could be used to probe the magnetic phase transition directly through the polarization properties of phonon scattering. The last findings in this area demonstrate that helicity-resolved Raman spectroscopy is an effective tool to probe ferromagnetism in 2D magnets directly.
The presentation will cover the basic principles of Raman and polarized Raman spectroscopy techniques and the application of this method to studying various 2DMs.

References:

[1] Ferrari A C et al 2006 Raman spectrum of graphene and graphene layers Phys. Rev. Lett. 97 187401, https://doi.org/10.1103/PhysRevLett.97.187401

[2] Lee C, Yan H, Brus L E, Heinz T F, Hone J and Ryu S 2010 Anomalous lattice vibrations of single- and few-layer MoS2 ACS Nano 4 2695–700, https://doi.org/10.1021/nn1003937

[3] Chen S, Zheng C, Fuhrer M S and Yan J 2015 Helicity-resolved Raman scattering of MoS2, MoSe2, WS2, and WSe2 atomic layers Nano Lett. 15 2526–32, https://doi.org/10.1021/acs.nanolett.5b00092

[4] Tian, Y.; Gray, M. J.; Ji, H.; Cava, R. J.; Burch, K. S. Magneto-elastic coupling in a potential ferromagnetic 2D atomic crystal 2D Mater. 2016, 3 (2), No. 025035 https://doi.org/10.1088/2053-1583/3/2/025035


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