Temperature effects on the structure and mechanical properties of vapor deposited a-SiO2

• Published in: Journal of non-crystalline solids 2022-07, Vol.587, p.121588, Article 121588
• Main Authors: Jambur, V., Molina-Ruiz, M., Dauer, T., Horton-Bailey, D., Vallery, R., Gidley, D., Metcalf, T.H., Liu, X., Hellman, F., Szlufarska, I.
• Format: Article
• Language: English
• Subjects: a-SiO2; Mechanical properties; Molecular dynamics; Nanoindentation; PALS; Vapor deposition
• ISSN: 0022-3093; 1873-4812
• DOI: 10.1016/j.jnoncrysol.2022.121588

•Density of vapor deposited a-SiO2 films increases with increasing growth temperature in spite of increasing porosity and size of nanovoids.•Increased density results in higher elastic modulus and hardness in films grown at higher temperatures.•Vapor deposited a-SiO2 films exhibit an anomalous increase in the elastic modulus with increasing indentation temperature, similar to bulk a-SiO2.•Rate of change in elastic modulus with increasing temperature is inversely proportional to the density of the a-SiO2 films. Amorphous silica (a-SiO2) exhibits unique thermo-mechanical behaviors that set it apart from other glasses. However, there is still limited understanding of how this mechanical behavior is related to the atomic structure and to the preparation conditions of a-SiO2. Here, we used electron beam (e-beam) physical vapor deposition (PVD) to prepare a series of a-SiO2 films grown at different substrate temperatures and then combined molecular simulations with Positronium Annihilation Lifetime Spectroscopy and nanoindentation experiments to establish relations among processing, structure, and mechanical response of the films. Specifically, we found that increase in the growth temperature leads to increase in the elastic moduli and hardness of the films. The relative porosity in the films also increases while the a-SiO2 network itself becomes denser, resulting in an overall increase in density despite increased porosity. In addition, we found that the a-SiO2 films exhibit the same anomalous temperature dependence of elastic modulus as bulk a-SiO2. However, the rate of increase in the elastic modulus with the measurement temperature was found to depend on the density of the a-SiO2 network and therefore on the growth temperature. Our findings provide new insights into the influence of the atomic network structure on the anomalous thermomechanical behavior of a-SiO2 and in turn guidance to control the mechanical properties of a-SiO2 films.