Residual stresses and Raman shift relation in anatase TiO2 thin film

Anatase TiO₂ film (100-1000 nm thick) grown on glass, sapphire (0001), and Si (100) substrates by pulsed dc-magnetron reactive sputtering were evaluated for stress and strain analysis using Raman spectroscopy and curvature measurement techniques. The X-ray analysis revealed that films prepared for this study were purely anatase, and the measurements indicate that the film exhibit that (101) is the preferred growth orientation of the crystallites, especially for the film thicker than 100 nm. Curvature measurements and Raman spectroscopy, with 514.5 nm excitation wavelength, phonon line shift were used for stress analysis. A comparison between Raman lineshapes and peak shifts yields information on the strain distribution as a function of film thickness. The measurements of residual stresses for crystalline anatase TiO₂ thin film showed that all thin film were under compressive stress. A correlation between Raman shifts and the measured stress from the curvature measurements was established. The behavior of the anatase film on three different substrates shows that the strain in film on glass has a higher value compared to the strain on sapphire and on silicon substrates. The dominant 144 cm^− 1E_g mode in anatase TiO₂ clearly shifts to a higher value by 0.45-5.7 cm^− 1 depending on the type of substrate and film thickness. The measurement of the full width at half maximum values of 0.59-0.80 (2θ°) for the anatase (101) peaks revealed that these values are greater than anatase powder 0.119 (2θ°) and this exhibits strong crystal anisotropy with thermal expansion.