Synthesis of Thin Magnesium-Aluminate Spinel Films through the Reactive Anodic Evaporation of Aluminum and Magnesium

Abstract

We investigate the structure and properties of magnesium-aluminate spinel films synthesized by the reactive anodic evaporation of Al and Mg from separate crucibles in a low-pressure arc (Ar–O₂ mixture at 0.7–1.2 Pa) and vapor deposition onto a substrate at 400–600°C. A discharge current with a self-heating hollow cathode is distributed between the anode (10–30 A) and the crucibles containing Mg (0.8–1.6 A) and Al (4–16 A), which allows for independent adjustment of the deposition rate of the films, plasma density, partial pressures of metal vapors, and elemental concentrations in the films. A decrease in the oxidation rate of Mg and stabilization of the evaporation process are achieved by increasing the power density of the electron beam on the Mg surface inside the crucible and transitioning from the sublimation mode to the evaporation mode from the liquid state by narrowing the aperture of the Mg crucible. The high vapor-flux density of Mg in the small aperture prevents oxygen from entering the crucible. The crystallization temperature of the spinel under ion bombardment of the growing film, with ions having an energy of 25–100 eV at a current density of 2 mA/cm², is approximately 400°C. The films are characterized using scanning electron microscopy, X-ray phase analysis, and microhardness testing. The cubic spinel films exhibit a strong (100) texture and a crystal-lattice distortion level of ~1%. The deposition rate of nonstoichiometric spinel films, with a relative Al-to-Mg atomic content adjustable within the range of 1.2–2.4, is 1–3 μm/h.