The Growth of Oxygen Vacancy Controlled Hfxti1-Xoy Films Deposited by Gas Injection Magnetron Sputtering Technique

Abstract

HfxTi1-xOy coatings (0.3≤x≤0.86, and 2.04≤y≤2.09) were grown by the Gas Injection Magnetron Sputtering  (GIMS) technique. Hf-Ti targets (1/4, 2/3, 3/2, and 4/1 Hf/Ti) were employed for reactive sputtering in Ar/O2 gas mixture.  The initial growth of the HfxTi1-xOy coatings was characterized by amorphous structure that tended to crystallize along the oxide growth direction when Hf content was sufficient (x>0.74). A non-equilibrium mixture of monoclinic and rhombohedral HfO2 phases was created when x=0.74. The oxide coatings structure with x≤0.86 exhibited monoclinic crystallization. Although y>2 for all the obtained coatings, the formed oxide lattices were O-deficient, indicating that the HfxTi1-xOy growth is controlled by the formation of oxygen vacancies. The optical properties of fabricated coatings changed as their composition was modified. An increase in the Hf fraction reduced refractive index and extinction coefficient from 2.3 to 2.45 in visible range and from 1 to 0.2 at 250 nm. We indicated that O-vacancies created the mid-band states, shifting the absorption toward lower energies. As the x value was increased from 0.30 to 0.86, the corresponding absorption shifted from 3.20 to 2.55 eV. In addition, Hf-rich coatings revealed an increase in hardness and Young's modulus by 81% and 27%. All layers were also hydrophobic.

Keywords: Magnetron Sputtering, Gas Injection Magnetron Sputtering, TiO2 layers, HfO2 layers, XPS, optical properties