Controlled synthesis of Mg(OH)2 thin films by chemical solution deposition and their thermal transformation to MgO thin films

• Published in: Ceramics international 2019-06, Vol.45 (8), p.10356-10363
• Main Authors: Suárez-Campos, G., Cabrera-German, D., García-Valenzuela, J.A., Cota-Leal, M., Fuentes-Ríos, J.L., Martínez-Gil, M., Hu, H., Sotelo-Lerma, M.
• Format: Article
• Language: English
• Subjects: Annealing; Chemical bath deposition; Magnesium hydroxide; Magnesium oxide; Quantitative XPS; Thin film
• ISSN: 0272-8842; 1873-3956
• DOI: 10.1016/j.ceramint.2019.02.093

The chemical solution deposition of Mg(OH)2 thin films on glass substrates and their transformation to MgO by annealing in air is presented. The chemical solution deposition consists of a chemical reaction employing an aqueous solution composed of magnesium sulfate, triethanolamine, ammonium hydroxide, and ammonium chloride. The as-deposited films were annealed at different temperatures ranging from 325 to 500 °C to identify the Mg(OH)2-to-MgO transition temperature, which resulted to be around 375 °C. Annealing the as-deposited Mg(OH)2 films at 500 °C results in homogeneous MgO thin films. The properties of the Mg(OH)2 and MgO thin films were analyzed by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, UV–Vis spectroscopy, and by circular transmission line model. Results by X-ray diffraction show that the as-deposited thin films have a brucite structure (Mg(OH)2), that transforms into the periclase phase (MgO) after annealing at 500 °C. For the as-deposited Mg(OH)2 thin film, a nanowall surface morphology is found; this morphology is maintained after the annealing to obtain MgO, which occurred with the evident formation of pores on the nanowall surface. The assessed chemical composition from X-ray photoelectron spectroscopy yields Mg0.36O0.64 (O/Mg ratio of 1.8) for the as-deposited Mg(OH)2 film, where the expected stoichiometric composition is Mg0.33O0.67 (O/Mg ratio of 2.0); the same assessment yields Mg0.60O0.40 (O/Mg ratio of 0.7) for the annealed thin film, which indicates the obtainment of a MgO material with oxygen vacancies, given the deviation from the stoichiometric composition of Mg0.50O0.50 (O/Mg ratio of 1.0). These results confirm the deposition of Mg(OH)2 films and the obtainment of MgO after the heat-treatment. The energy band gap of the films is found to be 4.64 and 5.10 eV for the as-deposited and the film annealed at 500 °C, respectively. The resistivity of both Mg(OH)2 and MgO thin films lies around 108 Ω·cm.