Developing photo-μSR spectroscopy to investigate optical excitations in materials
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PhD Thesis
Embargoed until: 2025-01-06
Reason: Author request
Embargoed until: 2025-01-06
Reason: Author request
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The μSR technique is used to probe material properties, with major research on superconductors, magnetic materials, semiconductors and organic materials. This thesis is concerned with developing the photo-μSR technique (designing, building and commissioning) to investigate photophysical and photochemical processes in organic and inorganic materials. To enable photoexcitation studies, the high field muon spectrometer (HiFi) at the pulsed muon source at ISIS, Rutherford Appleton Laboratory was upgraded with a high-power laser system in 2013-14. The upgraded spectrometer now can be used to investigate the photoexcited states in a variety of materials including organic semiconductors, biologically active molecules and inorganic semiconductors. As a part of designing and building of the photo-μSR spectrometer, sample cells for photo-μSR experiments were prepared to allow muons and photons to enter the sample from opposite directions. A Monte Carlo toolkit - GEANT (GEometry ANd Tracking), which can provide accurate predictions of a muon spectrometer, was used to simulate sample cells. Capabilities of the upgraded spectrometer were demonstrated on two semiconductors- Silicon and 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-Pentacene). In the first photo-μSR experimental results on silicon, it has been interpreted that the photo-generated carriers diffuse into the bulk of silicon and interact with muonium either at bond-centre (Mu0 BC) or at tetrahedral (Mu0T ) site. This experiment offers the proof of principle of the spectrometer. Before moving on to investigations on the second experiment, a general method to optimise the experimental conditions for photo-μSR experiment on organic semiconductors is discussed. Based on this method, a second photo-μSR experiment was performed on TIPSPentacene dissolved in dichloromethane. In this part, photo-μSR technique as a probe for spatial and temporal resolution of photochemical and the dynamics of molecular excited states are discussed.
Authors
Murahari, PCollections
- Theses [4225]