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Strong light-matter interactions and exciton-polaritons in carbon nanotubes

Graf, Arko

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Abstract

Exciton-polaritons are quasiparticles with hybrid light-matter character, offering a unique combination of photonic properties, such as a light mass, with those of excitons, for example strong nonlinearities and fast relaxation. Strong light-matter coupling enables a rich set of polaritonic quantum phenomena as well as applications. While originally observed in inorganic materials, organic semiconductors have recently attracted tremendous attention since their large oscillator strength facilitates particularly strong light-matter coupling and enabled polariton formation at room temperature. In particular, electrical excitation is pursued to apply these quantum-mechanical effects in practical polariton devices. However, a lack of organic materials with sufficiently high charge-carrier mobility and suitable device architectures impede their full utilization. Nanomaterials, in particular low-dimensional materials, present a novel material class that combines the excitonic properties of organic and electric characteristics of inorganic materials. In this thesis, single-walled carbon nanotubes (SWCNTs) were employed to demonstrate, for the first time, exciton-polariton formation in the near infrared (nIR) at room temperature. SWCNTs are identified as an ideal material facilitating strong light-matter coupling due to their high oscillator strength. Moreover, by implementing a strongly coupled microcavity into a light-emitting field effect transistor (LEFET), electrically pumped polariton emission at high current density was observed. These practical polariton devices emit in ranges relevant for telecommunication and support high currents due to the excellent optoelectronic properties of SWCNTs. Pumping polaritons at high rates presents a major step towards electrical lasing with carbon-based materials. For the realization of these experiments it was crucial to overcome current limitations in post-growth sorting of SWCNTs, which are intrinsically restricted to low-volume and damage the nanotubes. For this purpose, selective polymer wrapping by high-speed shear-force mixing, which can be easily scaled up, was developed. By using shear forces, the SWCNT-yield was drastically increased while, at the same time, the SWCNT-quality could be improved. In addition to strong light-matter coupling and polariton emission, the selected SWCNTs were employed in organic light-emitting diodes. These devices showed pure nIR emission with narrow linewidth at efficient electrical performance. This work paves the way for fundamental investigations as well as advanced applications of SWCNT-based optoelectronic devices.

Item Type: Dissertation
Supervisor: Zaumseil, Prof. Dr. Jana
Date of thesis defense: 26 April 2019
Date Deposited: 04 Jun 2019 05:16
Date: 2019
Faculties / Institutes: Fakultät für Chemie und Geowissenschaften > Institute of Organic Chemistry
Fakultät für Chemie und Geowissenschaften > Institute of Physical Chemistry
The Faculty of Physics and Astronomy > Institute of Physics
The Faculty of Physics and Astronomy > Kirchhoff Institute for Physics
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