Investigation of microstructure, micro-mechanical and optical properties of HfTiO4 thin films prepared by magnetron co-sputtering

• HfTiO4 thin films were deposited by magnetron co-sputtering.
• As-prepared and annealed at 800 °C thin films were nanocrystalline.
• Optical properties and hardness were investigated in relation to thin films structure.
• Hardness was 3-times higher in the case of as-deposited thin films.
• HfTiO4 thin films are suitable for use as optical coatings with protective properties.

Titania (TiO2) and hafnium oxide (HfO2) thin films are in the focus of interest to the microelectronics community from a dozen years. Because of their outstanding properties like, among the others, high stability, high refractive index, high electric permittivity, they found applications in many optical and electronics domains. In this work discussion on the hardness, microstructure and optical properties of as-deposited and annealed HfTiO4 thin films has been presented. Deposited films were prepared using magnetron co-sputtering method. Performed investigations revealed that as-deposited coatings were nanocrystalline with HfTiO4 structure. Deposited films were built from crystallites of ca. 4–12 nm in size and after additional annealing an increase in crystallites size up to 16 nm was observed. Micro-mechanical properties, i.e., hardness and elastic modulus were determined using conventional load-controlled nanoindentation testing. the annealed films had 3-times lower hardness as-compared to as-deposited ones (∼9 GPa). Based on optical investigations real and imaginary components of refractive index were calculated, both for as-deposited and annealed thin films. The real refractive index component increased after annealing from 2.03 to 2.16, while extinction coefficient increased by an order from 10−4 to 10−3. Structure modification was analyzed together with optical energy band-gap, Urbach energy and using Wemple–DiDomenico model.

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