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Development of an ultrafast low-energy electron diffraction setup

dc.contributor.advisorRopers, Claus Prof. Dr.
dc.contributor.authorGulde, Max
dc.date.accessioned2014-12-11T10:50:41Z
dc.date.available2014-12-11T10:50:41Z
dc.date.issued2014-12-11
dc.identifier.urihttp://hdl.handle.net/11858/00-1735-0000-0023-9959-5
dc.identifier.urihttp://dx.doi.org/10.53846/goediss-4821
dc.language.isoengde
dc.rights.urihttp://creativecommons.org/licenses/by-nc-nd/3.0/
dc.subject.ddc530de
dc.titleDevelopment of an ultrafast low-energy electron diffraction setupde
dc.typedoctoralThesisde
dc.contributor.refereeSalditt, Tim Prof. Dr.
dc.date.examination2014-10-15
dc.subject.gokPhysik (PPN621336750)de
dc.description.abstractengQuasi two-dimensional systems such as surfaces and atomically thin films can exhibit drastically different properties relative to the material's bulk, including complex phases and transitions only observable in reduced dimensions. However, while methods for the structural and electronic investigation of bulk media with ultrahigh spatio-temporal resolution have been available for some time, there is a striking lack of methods for resolving structural dynamics at surfaces. Here, the development of an ultrafast low-energy electron diffraction setup is presented, offering a temporal resolution of a few picoseconds in combination with monolayer structural sensitivity. In particular, a detailed account is given on the defining beam properties of the electron source, based on a nonlinearly driven nanometric photocathode. The emitter parameters within an electrostatic lens assembly are studied by means of a finite element approach. In particular, the optimal operation regime as well as achievable temporal resolution are determined. A prototype emitter comparable to the one used in the simulation is designed, characterized and applied within an ultrafast low-energy diffraction experiment. Specifically, the superstructure dynamics of an ultrathin bilayer of polymer crystallites adsorbed on free-standing graphene are investigated upon strong out-of-equilibrium excitation. Different processes in the superstructure relaxation are identified together with their respective timescales between 40 and 300 ps, including the energy transfer from the graphene to the polymer, the loss of crystalline order and the formation of extended amorphous components. The findings are subsequently discussed in view of an ultrafast melting of the superstructure. To conclude, the contribution of the approach to time-resolved surface science is discussed and an outlook is given in terms of future systems to investigate and further developments of the apparatus.de
dc.contributor.coRefereeSokolowski-Tinten, Klaus Dr.
dc.subject.engUltrafast Low-Energy Electron Diffractionde
dc.subject.engElectron Pulsede
dc.subject.engSurface Sciencede
dc.subject.engStructural Analysisde
dc.subject.engSuperstructure Dynamicsde
dc.subject.engUltrathin Polymer Filmde
dc.subject.engGraphenede
dc.subject.engPMMAde
dc.subject.engLEEDde
dc.subject.engULEEDde
dc.subject.engpolymer dynamicsde
dc.identifier.urnurn:nbn:de:gbv:7-11858/00-1735-0000-0023-9959-5-7
dc.affiliation.instituteFakultät für Physikde
dc.identifier.ppn812600789


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