Comparison of thin films of titanium dioxide deposited by sputtering and sol-gel methods for waveguiding applications

In this work, TiO$_2$ thin films were deposited onto glass substrate by two different techniques: sol-gel dip-coating (SG) and reactive DC magnetron sputtering (Sput). The prepared samples have been characterized by means of micro-Raman, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) measurements, scanning electron microscopy (SEM), UV-Visible spectrophotometry, and M-Lines spectroscopy (MLS). The micro-Raman results showed an amorphous TiO$_2$-SG phase and the vibrational mode of TiO$_2$-Sput is anatase phase. DSC-TGA analysis was used to investigate the thermal properties of the TiO$_2$ material. SEM spectroscopy has shown that TiO$_2$-SG has a disordered and more porous surface, TiO$_2$-Sput sample is homogeneous and shows uniform distribution of densely packed well-defined grains. The obtained films have an optical transmittance varying from 60 to 88% in the visible region. The optical band gaps deduced from the transmittance are 3.48 and 3.53 eV for TiO$_2$-SG and TiO$_2$-Sput, respectively. The optical waveguiding measurements carried out on TiO$_2$-SG and TiO$_2$-Sput films show single guided modes behavior (TE$_0$ and TM$_0$). These measurements have allowed deducing the refractive index and thickness values that are 2.06 at 216 nm for TiO$_2$-SG and 2.26 at 204 nm for TiO$_2$-Sput thin films. The analysis of waveguiding properties indicates that amorphous TiO$_2$ may prove to be more efficient in photonic device as compared to crystalline TiO$_2$.