The film thickness was determined b

The film thickness was determined by step measurements using an optical profilometer (Wyko NT 1100), which was also used to obtain a topographic image of the substrate before and after coating for the stress calculations. The values and directions of the principal radii of curvature were obtained by Gwyddion. The film structure was examined by X-ray diffraction (XRD) using a Bruker D8 diffractometer operating in Bragg-Brentano θ/2θ configuration using a Cu Kα wavelength (1.5406 Å), the scan was performed in two angle ranges of 2θ, from 32° to 69° and 72° to 90° to avoid the intense diffraction peak of Si substrate at 2θ= 69.13°. Scanning Electron Microscopy (JEOL JSM- 5900 LV) was used to analyze the microstructure and to confirm the film thickness by cross-section images. The chemical composition of the films was obtained by energy dispersive X-ray spectroscopy. Indentation and recording of force-displacement curves were performed on a CSM Nano Instrument Berkovich Indenter. The elastic modulus was calculated from the unloading part of load-penetration curves using the standard Oliver-Pharr method. Elastic modulus and hardness values were obtained by an average of five measurement runs.