Role of oxygen vacancies in the structural phase transformations of granular TiO2 thin films

Year: 2023

Authors: Durante O., Granata V., Fittipaldi R., Neilson J., Carapella G., Chiadini F., De Salvo R., De Simone R., Dinelli F., Fiumara V., Pierro V., Pinto IM., Vecchione A., Bobba F., Di Giorgio C.

Autors Affiliation: Univ Salerno, Dept Phys ER Caianiello, Fisciano, Italy; Natl Inst Nucl Phys INFN, Sez Napoli Grp Collegato Salerno, Naples, Italy; Univ Salerno, Natl Res Council SuPerconducting & other Innovat M, Fisciano, Italy; Univ Sannio, Dept Engn, DING, Benevento, Italy; Univ Salerno, Dept Ind Engn, DIIN, Fisciano, Italy; LLC Co, RicLab, Pasadena, CA USA; Natl Inst Opt, Natl Res Council, CNR INO, Pisa, Italy; Univ Basilicata, Sch Engn, Potenza, Italy; Univ Naples Federico II, Dept Elect & Informat Technol Engn, Naples, Italy; Museo Stor Fis, Mat Foundry Inst, Rome, Italy; Ctr Studi & Ric Enrico Fermi, Rome, Italy.

Abstract: Tailoring the structural phases of titanium dioxide (TiO2) is nowadays highly attracting for diverse applications, ranging from optical coatings, where rutile outperforms anatase, to photocatalysis, where a mix of the two is preferred. In this framework, the very high temperature transformation of anatase to rutile constitutes a big drawback. Here, we investigate the structural transformations of granular TiO2 thin films subjected to thermal treatments in different gaseous environments, such as air, oxygen, and vacuum, with the latter expected to enhance the formation of oxygen vacancies. To this aim, we used a combined approach of X-ray diffraction (XRD), Raman Spectroscopy (RS), Atomic Force Microscopy (AFM) and Field Emission Scanning Electron Mi-croscopy (FESEM), and we demonstrate that the achievement of a crystallization temperature as low as 150 degrees C for the anatase and 250 degrees C for the rutile is possible. By using a Gibbs free energy minimization approach, the combination of granular morphology and oxygen vacancies is proposed to tune both the amorphous to anatase transition and the anatase to rutile transformation. Finally, we explore the possibility of a low-dimensional growth of anatase-TiO2 by studying phonon confinement-like effect and crystallization kinetics thanks to time-dependent RS experiments.

Journal/Review: SURFACES AND INTERFACES

Volume: 37      Pages from: 102698-1  to: 102698-11

KeyWords: Granular TiO 2; Oxygen vacancies; Crystallization; Phonon confinement; Low-dimensional growth
DOI: 10.1016/j.surfin.2023.102698

Citations: 5
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