Lu, Mo
(2021).
Plasmon-exciton coupling: from DNA origami to graphene nanoribbons.
PhD thesis, Universität zu Köln.
Abstract
Plasmonic nanostructure can serve as optical antennas that convert freely propagating optical radiation into localized energy. Coupling between plasmon and an exciton leads to a strong modification of the decay rate, emission direction, and quantum efficiency of an emitter. The coupling efficiency varies drastically on a length scale that is much smaller than the incident wavelength. Combined with single-molecule techniques, plasmon-exciton coupling provides a versatile platform for studying nanoscale motions and interactions.
In this dissertation, we have investigated dynamic light-matter interaction nanosystems enabled by the DNA origami nanotechnology. We first studied a dynamic plasmonic walker structure, where a plasmonic nanorod can walk progressively and reversibly on a DNA origami template and interact with a fluorophore assembled along the walking track. We tracked the dynamic motion on individual walker devices by monitoring the change of brightness and fluorescence dynamics, which can not be resolved by the ensemble-level observation reported earlier[1]. Additionally, we demonstrated a dynamic DNA-origami directed nanomachine, where a single fluorophore molecule can autonomously and unidirectionally walk into the hotspot of a plasmonic nanoantenna along a designed origami track. Successive fluorescence intensity increase and lifetime reduction are in situ monitored using single-molecule fluorescence spectroscopy, while the fluorophore walker gradually approaches and eventually enters the plasmonic hotspot. Our approach offers a dynamic platform that can be used to develop functional materials, investigate intriguing light-matter interaction phenomena, and serve as a prototype system for examining theoretical models.
The highly confined plasmonic hotspot also allows probing inherent weak features. By coupling plasmonic nanoantennas to semiconducting armchair graphene nanoribbons (AGNRs), we observed blinking of spectrally narrow photoluminescence from the AGNRs next to the metal nanostructure[2]. Such blinking is a typical signature of emissions from single quantum emitters. In this dissertation, we probe in detail the origin of the blinking. In particular, we clarify the relative roles in field enhancement in the vicinity of a plasmonic nanoantenna. We conclusively demonstrate that the field enhancement alone enables being able to observe photoluminescence blinking. Thus, the blinking is an intrinsic feature of light emission from the graphene nanoribbons and not due to, e.g., contact with the environment. This work has thus provided a key contribution in understanding light emission in seven atom-atom wide
armchair-edge graphene nanoribbons.
[1]C.Zhou, X.Duan and N.Liu, A plasmonic nanorod that walks on DNA origami, Nature communications 6(2015) 1
[2]M.Mfeiffer, B.V.Senkovskiy, D.Haberer, F.R.Fischer, F.Yang, K.Meerholtz, Y.Ando, A.Grüneis and K.Lindfors, Observation of Room-Temperature Photoluminescence Blinking in Armchair-Edge Graphene Nanoribbons, Nano Letters 18 (2018) 7038
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