Formation of crystalline aluminum silicate hydroxide layer during deposition of amorphous alumina coatings by electron beam evaporation

Aluminum oxide films were deposited on fused silica and borosilicate glass substrates by electron beam evaporation, without any substrate heating. Grazing incidence X-ray diffraction measurements found that a layer of crystalline aluminum silicate hydroxide was formed at the interface of the substrate and the amorphous alumina film, the latter transformed to γ-alumina phase on heat treatment at 800 °C. The aluminum silicate hydroxide layer was produced by the chemical reaction between condensing Al and Al–O species, OH− from the residual water vapors in the chamber and Si atoms from the underlying silica and borosilicate glass substrates.

► Growth of interfacial aluminum silicate hydroxide layer during deposition of alumina coatings.
► Silicate layer forms due to reaction between Al–O species and Si atoms in the glass substrates.
► Top layer is amorphous alumina that crystallizes into gamma phase on annealing at 800 °C.
►  Feasibility of growth of mullite layers without high temperature substrate heating.