Journal
THIN SOLID FILMS
Volume 692, Issue -, Pages -Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.tsf.2019.137641
Keywords
Active site; Paramagnetic defect; Zinc oxide; Thin film; Reactive sputtering; Oxygen vacancy
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Funding
- Instituto de Investigaciones Interdisciplinarias in the University of Puerto Rico at Cayey
- NSF CREST [1736093]
- NSF [EPS-01002410]
- National Aeronautics and Space Administration (NASA) Training Grant [NNX15AI11H]
- Division Of Human Resource Development
- Direct For Education and Human Resources [1736093] Funding Source: National Science Foundation
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Zinc oxide thin films were prepared under oxygen-deficient and oxygen-rich conditions by changing the oxygen to argon ratio (O-2/Ar) during the reactive sputtering deposition at room temperature. The effects of increasing the partial pressure of oxygen in the sputtering gas from 20 to 70% O-2/Ar on the thin film composition, crystallinity and defects that can act as active sites for gas reactions were studied using X-rays diffraction, X-rays photoelectron spectroscopy (XPS), Raman scattering and electron paramagnetic resonance (EPR). All the films exhibited a textured (0002) wurtzite phase and a crystallite size that increases as the partial pressure of oxygen in the sputtering gas increases. The XPS analysis showed that the number of oxygen vacancies decreases as the oxygen percent in the sputtering gas increases. The Raman spectra of the samples contained a band related to a hydroxide, OH, bond in addition to the vibrational modes associated with the wurtzite structure. A strong EPR signal, consistent with the OH acting as a paramagnetic center, was detected in all the films. An additional, but very weak EPR peak, was observed in the film grown at 20% O-2/Ar, which was assigned to singly ionized oxygen vacancies located in the crystallite lattice. These paramagnetic centers are highly reactive because of their unpaired electrons and their formation will have important effects on the physical and chemical properties of the thin films.
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