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Séminaire NANO

Mardi 25 novembre à 9h30,
Salle Rémy Lemaire, K223

Oratrice : Nedjma Bendiab (HYBRID)
"Phonons in low dimensional sp2 carbon systems"


Optical phonons, in low dimensional sp2 carbon systems, couple easily with different elementary excitations (electron, acoustic phonon, photon), allowing us to be sensitive to various physical phenomena : mechanical resonances, charge transfer, energy transfer...
To illustrate this aspect, I will show how optical phonons can be used to detect mechanical resonances that involve a coupling between an acoustic phonon and an optical one and thus be used as a probe of motion and strain in different systems.
I will also discuss the electron phonon coupling in these systems, which leads to change our vision of this low dimensional system (we have to consider these systems out of the adiabatic approximation). Moreover, this huge electron-phonon coupling and its dependency with a gate voltage, allows us to detect a small amount of molecules on graphene sheet. In this case, the grafted molecules transfer a small charge to graphene, thus the frequency of the optical mode is shifted due to a change in the strength of the electron-phonon coupling.
More recently, we have grafted optical molecules to nanotubes, and we measure a huge modification of the optical phonons due to an excitation transferred from the molecule to the nanotube under illumination allowing a transduction effect and probably new optoelectronics properties of such a hybrid device.
Finally, I will discuss the strain versus doping effects and how to discriminate these two effects, which is a real issue.

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