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Synthesizing strontium cobaltite-based oxyfluoride heterostructures
Thesis   Open access

Synthesizing strontium cobaltite-based oxyfluoride heterostructures

Zongmin Yang
Master of Science (M.S.), Drexel University
Mar 2023
DOI:
https://doi.org/10.17918/00001766
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Abstract

Fluorination Superlattices as materials Topochemical reactions Thin Films
Thin films have been utilized in numerous applications, such as solar cells and semiconductors. Motivated by the aim of realizing more complex materials in thin film form, the reductive fluorination of SrCoO_[2.5] was investigated in this thesis. Its fluorination conditions were identified by varying the reaction temperature and time to enable fluorine incorporation throughout the film. Moreover, initial fluorination results from a superlattice of SrCoO_[2.5] and SrFeO_[2.5] are presented, confirming fluoride incorporation within both constituent materials at a reaction temperature of 200 °C carried out for 3 hours. The chemical composition in the thin films was measured by x-ray photoemission spectroscopy. The crystal structures of the thin films were determined by x-ray diffraction, with the c-axis parameters calculated from the diffraction data. Resistivity measurements carried out as a function of temperature confirm that the films are semiconductors. The optical properties of the thin films were evaluated by ellipsometry, and the absorption coefficient and bandgap energies of the thin films were extracted from the thin films' optical spectra. A blue shift of the bandgap energy of SrCoO_[2.5] occurs upon fluorine incorporation. This work demonstrates the feasibility of synthesizing epitaxial cobaltite oxyfluoride films and superlattices.

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