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| Author(s): |
Francisco Mateus Cirilo da Silva
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | Campinas, SP. |
| Institution: | Universidade Estadual de Campinas (UNICAMP). Instituto de Física Gleb Wataghin |
| Defense date: | 2020-04-22 |
| Examining board members: |
Helio Cesar Nogueira Tolentino;
Harry Westfahl Junior;
Mônica Alonso Cotta
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| Advisor: | Helio Cesar Nogueira Tolentino |
| Abstract | |
In this work, advanced multitechnique setups for synchrotron light were studied and implemented, allowing experiments to be carried out for correlative characterization methods that will be available in the Carnaúba beamline, the new Sirius X-ray nanoscopy beamline. This was applied to thin films of two classes of functional materials: hybrid photovoltaic perovskites (PVSK) ($Cs¬_{x}A_{1-x}PbBr_{x}I_{1-x}$, where $A$ is an organic group, methylammonium or formolmidium) and piezoelectric (PZT) perovskites ($PbZr_{x}Ti_{1-x}O_3$). Initially, the coherent x-ray diffraction (CDI) imaging technique was studied in an exploratory way in an experimental configuration at the SXS/LNLS beamline, which doesn’t allow to achieve the potential of the technique, but it was essential in the study of coherent diffraction main parameters and tests of scientific instrumentation for the Carnaúba beamline in the tender x-ray range ($3$keV). The characterization of the SXS beamline regarding coherence parameters, a discussion of experimental parameters and CDI reconstructions images, among which are shown as photovoltaic perovskites, are used in order to elucidate the main points to follow during a coherent diffraction experiment. This served to indicate the procedures for the design, commissioning and use of a beamline dedicated to the CDI technique. Hybrid perovskites were further studied with respect to their structural and optoelectronic responses in different environments (N$_2 $ and air) when subjected to different stimuli (x-ray and visible LED light) through simultaneous x-ray diffraction (XRD - X-ray diffraction) and optical luminescence excited by x-rays (XEOL - optical luminescence excited by x-rays) experiments. This experimental arrangement mimics combined nanodiffraction and XEOL studies that will be available in Carnaúba. The results strongly indicate the effect of environmental conditions in the optical responses and the samples: in the atmosphere of N$_2$ the samples are always more resilient, while in the air they show accentuated and distinct degradation according to the stimulus that is submitted. The simultaneous optical and structural characterization in controlled environmental conditions allowed to clarify that the material optical emissions changes, commonly associated with a chemical segregation in the material, takes place without any structural transition from the cubic phase or the tetragonal phases, and not even with a chemical segregation, which has not been described in the literature so far. Finally, to elucidate the relationship of crystalline with ferroelectric structure in the vortex, we present the experiments carried out at the NanoMax beamline (synchrotron MaxIV, Sweden), which combined nanodiffraction and nanofluorescence to study micrometric ferroelectric vortexes of PZT materials with controlled electric field conditions. The nanofluorescence clearly indicates titanium segregation in the central regions of the vortexes in which the diffraction signals are less evident. The nanodiffraction itself shows that there exist an observable lattice parameter gradient even though it depends on the diffracting region. This would not be observed with conventional diffraction experiments. In addition, it was observed a variation in the lattice parameters at the different field conditions applied and a change in the shape from one region to the other. The presented preliminary results already bring us relevant pieces of information about the functional materials and demonstrate the power of using correlative synchrotron techniques (AU) | |
| FAPESP's process: | 18/08848-2 - Coherent X-ray imaging applied to the study of functional materials |
| Grantee: | Francisco Mateus Cirilo da Silva |
| Support Opportunities: | Scholarships in Brazil - Master |