Effects of pressure and bias voltage on the morphology and properties of refractory WNbMoV high entropy thin films coated via magnetron sputtering

Abstract

The synthesis and characterization of thin film materials have garnered significant attention in advanced technological field nowadays. Development of advanced thin film materials with superior properties is crucial for progress in various technological fields. Among these, refractory high entropy thin films have emerged as innovative materials due to their exceptional properties. The deposition of HEAs as thin films has garnered significant attention as it enables the fabrication of advanced functional coatings with tailored properties. Recent research has focused on understanding the influence of deposition parameters on microstructure and properties, exploring various HEA compositions, and developing innovative applications in fields like electronics, energy, and biomedical engineering. High-entropy thin films offer exceptional properties, making them suitable for various applications. These include protective coatings, electronics, biomedical implants, energy technologies, and components for the aerospace and automotive industries. In this study, by using magnetron sputtering technique, equimolar WNbMoV refractory high entropy thin film coatings were deposited on the silicon wafer substrate which had been coated with chromium metal as an intermediate layer between the substrate and the thin film. The effects of bias voltage and pressure of the chamber on the physical and mechanical properties of coated films during the magnetron sputtering process were investigated. X-Ray diffraction experiments were carried out for phase analysis, determining the experimental components and grain sizes were calculated by using the Williamson-Hall method, ORIGINPro and CALPHAD softwares. Scanning electron microscopy (SEM) and EDS mapping analyses were used to evaluate the microstructural properties and XRF analyses were used to investigate elemental distribution, respectively. In addition, we studied the Surface morphology by AFM (Atomic Force Microscopy). Hardness and Electrical Resistance of the samples was measured using nanoindentation and relative equipment. X-ray diffraction (XRD) analysis confirmed a dominant body-centered cubic (BCC) solid solution phase, aligning with expectations for WNbMoV HEAs, but also revealed minor oxide phases due to oxygen contamination. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) showed a dense columnar microstructure with varying surface roughness depending on deposition conditions. Notably, applying a -80V bias voltage resulted in smoother and denser coatings due to increased energy and directionality of sputtered particles. Nanoindentation tests revealed an inverse relationship between film hardness and working pressure, with -80V bias voltage enhancing hardness due to grain refinement. Energy-dispersive X-ray spectroscopy (EDS) confirmed uniform elemental distribution within the film. Electrical conductivity was influenced by phase composition and microstructure, with oxide phases decreasing conductivity and denser microstructures improving it. UV-Vis spectroscopy showed tunable optical properties, with increased working pressure decreasing transmittance. The sample produced at 1.5 Pa pressure and 0V bias exhibited complete transparency, likely due to excessive oxidation or stoichiometry deviations. The results show that by applying bias and pressure, there are alterations in the produced thin films thickness. This suggests a direct correlation between the applied parameters and hardness values. By applying the -80 V bias, the grain size of samples decreased from 10 to 5.2 nm and the hardness of the films increased from 350 to 301 HVs, respectively. Furthermore, when the pressure increased from 0.5 Pa to 1.5 Pa, the thickness of films decreased approximately from 1.26 to 1.11 m. This project offers unique insights into experimental studies. We've gained groundbreaking knowledge about WNbMoV high-entropy alloy thin films, understanding how processing, structure, and properties are interconnected. This allows us to tailor these films for applications like wear-resistant coatings. Future research should focus on optimizing deposition to improve film quality.