Ultrafast low-energy electron diffraction at surfaces

Vogelgesang, Simon

Probing transitions and phase-ordering of charge-density waves

dc.contributor.advisor	Ropers, Claus Prof. Dr.
dc.contributor.author	Vogelgesang, Simon
dc.date.accessioned	2019-02-22T09:10:00Z
dc.date.available	2019-02-22T09:10:00Z
dc.date.issued	2019-02-22
dc.identifier.uri	http://hdl.handle.net/11858/00-1735-0000-002E-E5A1-F
dc.identifier.uri	http://dx.doi.org/10.53846/goediss-7305
dc.identifier.uri	http://dx.doi.org/10.53846/goediss-7305
dc.language.iso	eng	de
dc.rights.uri	http://creativecommons.org/licenses/by-nc-nd/4.0/
dc.subject.ddc	530	de
dc.title	Ultrafast low-energy electron diffraction at surfaces	de
dc.title.alternative	Probing transitions and phase-ordering of charge-density waves	de
dc.type	doctoralThesis	de
dc.contributor.referee	Ropers, Claus Prof. Dr.
dc.date.examination	2018-12-05
dc.subject.gok	Physik (PPN621336750)	de
dc.description.abstracteng	Due to their reduced dimensionality, surfaces and quasi two-dimensional materials exhibit numerous intriguing physical phenomena that drastically differ from the bulk. To resolve these effects and the associated dynamics at their intrinsic timescales requires experimental methodologies combining a high surface sensitivity with the essential temporal resolution. However, to date, there are still very few methods that facilitate investigation of the structural degrees of freedom of surfaces on the atomic scale along with a temporal resolution of femtoseconds or picoseconds. Addressing these challenges, this thesis covers the development and application of ultrafast low-energy electron diffraction in a backscattering geometry to study structural dynamics at surfaces. In this context, a central aspect is the development of a miniaturized and laser-driven electron source based on a nanometric needle photocathode. Using such a sharp metal tip, the photoemitted electron bunches offer a particularly high coherence and remarkably short pulse durations, which were also successfully implemented recently in ultrafast transmission electron microscopy, as well as in time-resolved transmission low-energy electron diffraction. Employing the capabilities of this novel technique, so-called transition metal dichalcogenides constitute an ideal prototype system. Specifically, in the present work, the transient structural disorder of charge-density waves at the surface of 1T-TaS2 has been examined. Following the optically induced transition between two temperature-dependent charge-density wave phases, this method enables the observation of a highly disordered transient state and the subsequent phase-ordering kinetics. More precisely, the temporal evolution of the growing charge-density correlation length is traced over several hundreds of picoseconds and found to obey a power-law scaling behavior. Due to the particular properties of the charge-density wave system at hand, the observed transient disorder can be explained by the ultrafast formation of topological defects and their subsequent annihilation. These results are complemented by a numerical modeling using a timedependent Ginzburg-Landau approach. Finally, two different excitation schemes demonstrating the possibility to study the relaxation of the investigated sample on the nanosecond and microsecond timescale are presented, as well as future prospects of ultrafast low-energy electron diffraction, including other promising surface sample systems.	de
dc.contributor.coReferee	Mathias, Stefan Prof. Dr.
dc.subject.eng	ultrafast low-energy electron diffraction	de
dc.subject.eng	ULEED	de
dc.subject.eng	structural dynamics	de
dc.subject.eng	surface science	de
dc.subject.eng	laser-driven electron source	de
dc.subject.eng	nanoscale photoemitter	de
dc.subject.eng	ultrashort electron pulses	de
dc.subject.eng	1T-TaS2	de
dc.subject.eng	transition metal dichalcogenide	de
dc.subject.eng	charge-density wave	de
dc.subject.eng	CDW	de
dc.subject.eng	phase transition	de
dc.subject.eng	phase ordering kinetics	de
dc.subject.eng	topological defects	de
dc.identifier.urn	urn:nbn:de:gbv:7-11858/00-1735-0000-002E-E5A1-F-1
dc.affiliation.institute	Fakultät für Physik	de
dc.identifier.ppn	105463758X

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