Temperature-Dependent 4‑, 5- and 6‑Fold Coordination of Aluminum in MOCVD-Grown Amorphous Alumina Films: A Very High Field 27Al-NMR studyReport as inadecuate




Temperature-Dependent 4‑, 5- and 6‑Fold Coordination of Aluminum in MOCVD-Grown Amorphous Alumina Films: A Very High Field 27Al-NMR study - Download this document for free, or read online. Document in PDF available to download.

1 CEMHTI - Conditions Extrêmes et Matériaux : Haute Température et Irradiation 2 CIRIMAT - Centre interuniversitaire de recherche et d-ingenierie des matériaux

Abstract : The only easy way to prepare amorphous alumina is via thin film deposition. For this reason, the disorder in amorphous alumina has not yet been fully investigated. We have used very high-field 20 T solid state 27Al NMR spectroscopy to analyze the structural modifications of amorphous alumina thin films with deposition temperature Td. The films were deposited by metalorganic chemical vapor deposition in the Td range of 360−720 °C. Depending on Td, film composition is either AlO1+xOH1−2x 0 ≤ x ≤ 0.5 or Al2O3. From 27Al 1D magic angle spinningMAS and 2D multiple-quantum magic angle spinning MQMAS NMR analyses, the films grown between 360 and 600 °C contain between 38 and 43 atom % of 5-fold coordinated aluminum sites 5Al. The percentages of 6Al and 4Al sites vary spectacularly, reaching their respective minimum 5 atom % and maximum 54 atom% around 515 °C. The analysis of a very thin film 85 nm of Al2O3 reveals the presence of metallic aluminum at the interface with the substrate and suggests that the respective percentages of nAl sites slightly differ from those in thicker films. The observed Td dependence of amorphous alumina structure can be correlated with that of film properties previously reported,namely, Young’s modulus, hardness, and corrosion protection.

Keywords : MOCVD-Grown Amorphous Alumina Films 27Al-NMR





Author: Vincent Sarou-Kanian - Alain Gleizes - Pierre Florian - Diane Samélor - Dominique Massiot - Constantin Vahlas -

Source: https://hal.archives-ouvertes.fr/



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