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Séminaire QUEST

Jeudi 14 Janvier à 9h30,
Salle Rémy Lemaire, K223

Orateur : Stéphane Berciaud (IPCMS)
Titre : Optical spectroscopy of two-dimensional materials and heterostructures.

Abstract :

In the wake of graphene, a large family of layered materials has risen as an outstanding playground to investigate the interplay between photons, electrons and phonons in the (quasi) two-dimensional limit. In particular, graphene, as a 2D semimetal with excellent transport properties and transition metal dichalcogenides (MX2, with M=Mo, W, Re and X=S, Se, Te) as versatile 2D semiconductors are promising candidates for realistic applications in electronic and optoelectronic devices. In this seminar, we will focus on the fundamental properties of i) basic systems composed of a stack of N-layers of graphene or MX2 and ii) hybrid heterostructures composed of a single nano-emitter (e.g. a semiconducting nanostructure) physisorbed on graphene or a MX2-Graphene van der Waals heterostructure.

First, we will demonstrate how Raman (i.e., inelastic light scattering) spectroscopy can be employed to uncover the evolution of the physical properties of layered systems from the 3D (bulk) limit to the 2D (monolayer) limit. The cases of the electronic excitations in N-layer graphene (probed by magneto-Raman spectroscopy of inter Landau level excitations [1,2]) and of the complex manifold of phonon modes in N-layer MX2 (probed by vibration Raman spectroscopy down to ultralow frequencies, below 1 THz) will be discussed [3,4].

Second, we will address Förster-type energy transfer [5] and photo-induced charge transfer in the heterostructures introduced above. These near-field phenomena are investigated by means of time-resolved photoluminescence and Raman spectroscopies. In particular, we will discuss how energy and charge transfer depend on exciton dimensionality and on the distance between the building blocks that compose the heterostructure [5].

Related references
[1] S. Berciaud et al., Nano Letters 14, 4548 (2014)
[2] C. Faugeras et al., PRL 114, 126804 (2015)
[3] G. Froehlicher et al., Nano Letters 15, 6481 (2015)
[4] E. Lorchat et al., arXiv:1512.03842
[5] F. Federspiel et al., Nano Letters 15, 1252 (2015)

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