The effect of thickness on surface structure of rf sputtered TiO2 thin films by XPS, SEM/EDS, AFM and SAM

In the current study, silicon was utilized as the substrate material and, then, the TiO2 depositions with 100 nm, 300 nm, 500 nm and 700 nm were done onto substrates as thin films at room temperature by a radio frequency (rf) magnetron sputtering method. The binding energy, the surface roughness, elemental analysis and the specific acoustic impedance have been determined via X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) and scanning acoustic microscopy (SAM), respectively. AFM analysis represented that the root mean square roughness values changed in the range of 0.72 nm-1.22 nm, gradually by the increase in thickness. Two-dimensional acoustic images were recorded by SAM with 80 MHz transducer. The mean and standard deviation values of acoustic impedance were found as 3.151 +/- 0.080 MRayl for 100 nm, 3.366 +/- 0.080 MRayl for 300 nm, 3.379 +/- 0.067 MRayl for 500 nm and, 3.394 +/- 0.065 MRayl for 700 nm. SAM results pointed out that the hardness of films increased with increasing thickness. Moreover, the surface defects at the micrometer level were demonstrated. The success of imaging films indicated the potential of SAM in monitoring as well as the inspection of flat two-dimensional surfaces.