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Title: Václav Valeš: Modified graphene in graphene-enhanced Raman scattering
Number: 32/21
Status: Closing date exceeded
Begin: Thursday, 06.05. 2021, 14:00
Tutor: Václav Holý, Milan Dopita
Location: Zoom Meeting ID: 918 4935 7934

nanocent


Nano Seminar

 

Thursday, 6. 5. 2021, 14.00,

Join Zoom Meeting
https://cesnet.zoom.us/j/91849357934

Meeting ID: 918 4935 7934

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Václav Valeš

Department of Low-dimensional Systems, J. Heyrovský Institute of Physical Chemistry, Prague

Modified graphene in graphene-enhanced Raman scattering

The concept of graphene-enhanced Raman scattering (GERS) was proposed and experimentally demonstrated in 2010. It was observed that molecules in very low concentrations exhibit a significant Raman signal when placed on a graphene layer. Furthermore, photoluminescence quenching of molecules on graphene was observed, which helps to measure the GERS signal with a reasonable signal/noise ratio for the molecules with strong photoluminescence. GERS is often related to surface- enhanced Raman scattering (SERS), which is used to obtain Raman scattering signal from an ultralow concentration of measured molecules. SERS is usually explained by the interactions of the light with surface plasmons. This results in high enhancement (up to 10^8), but the enhancement is not homogeneous. In the case of GERS, the enhancement is lower (10–100), but it is expected to be spatially homogeneous, because graphene can be prepared flat and with a high crystal quality. Since the first observation of GERS, several reports on this effect with various probe molecules and even various 2D crystals were carried out. Furthermore, it was shown that the enhancement can be tuned by changing the Fermi energy of graphene (modified by the electrical field effect), by substitutional doping with heteroatoms or by chemical functionalization. Other studies demonstrated that the enhancement is also a function of the phonon energy of the specific vibration and also laser excitation energy. The observed effects were rationalized by a theoretical approach taking into account several different resonance processes.
In this seminar I will discuss various modifications of graphene and their effect on GERS performance. The relation to theoretical model will be also considered.


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