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Development and evaluation of nonlinear optical and spectroscopic properties of 2D materials


We aim to investigate the potential of various 2D -materials and specifically 2D- composites of such materials as building blocks for photonic devices. Specifically we will employ femtosecond pulsed laser systems to probe the ultrafast and nonlinear responses of these materials to light.- In a joint effort, the equipment and the expertise available at MackGraphe and at the Universidade Estadual de Campinas (Unicamp) will be utilized. The visiting scientist and his collaboration partners will investigate Nonlinear Optical Properties as well as ultrafast responses to light in 2D systems. Although these two properties are only loosely related, the femtosecond laser equipment available at the involved research facilities at MackGraphe and at Unicamp can, with minor modifications of the detection process, be utilized for probing these different properties in basically the same set of experiments. -There has considerable experimental work been done on optical properties of pure 2D materials that show extraordinary optical and electronic properties. Particularly the remarkably strong light-matter interaction in many 2D materials such as graphene, black phosphorus (BP) and transition metal dichalcogenides (TMDC) seems to be very promising for photonic applications. The broad range of electronic structure, ranging from the bandless dirac cone of graphene to band-gap materials such as BP and TMDC to the insulator Boronitride (BN) provides a broad spectrum of building blocks for composite structures with alterated and fine-tuned optical and electronic properties. That is the principal basis of this proposal. For example, pure 2D layers of TMDC or BP already show extraordinarily strong NLO properties. How are these properties altered by combining different types of such 2D materials, for example due to a change of symmetry Likewise using the same combination of materials, how is the ultrafast response of such combined 2D layers to light? It is feasible to assume that for example the different band gaps cause an ultrafast energy and electron transfer within these layers. For example, using a composite of a TMDC and graphene, the bandgap of the TMDC would cause a longer relaxation time of the excited electron with a higher probability to transfer to graphene, following a rapid relaxation of the electron down the dirac cone of graphene. The effect could be tunable by shifting the Dirac cone crossing point by applying an electrical voltage. Even an insulating spacer of BN could be interesting in terms of energy transfer, but particularly in terms of electron transfer by tunneling. Likewise using heavy transition metals (W) or chalcogenides (Se, Te), the spin -orbit coupling would be enhanced and the polarization of light would become an additional parameter. While the suggested research is in principle fundamental and exploratory work, an emphasis will be put on the perspective for applicability. Potential applications include novel methods of ultrafast light modulation and manipulation, directed energy transfer and collection, the creation of optical metamaterials and nonlinear effects such as second harmonic generation and two photon absorption. (AU)

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