Measurement of Residual Stress In TiO2 Sol-Gel Thin Films Using Raman Spectroscopy

Abstract

AbstractThe deposition of thin films can result in residual stresses that affect film properties such as optical properties, phase stability, chemical durability, and film adhesion. There are many components to the total residual stress measured in a film. These include interfacial stress, volume changes associated with phase transitions, film thickness, and film microstructure. For sol-gel films, some contributors to residual stress can be controlled by such variables as the precursor chemistry and gelation time or heat-treatment following deposition. Measurements of the state of stress during crystallization or as a function of processing conditions and sol-gel chemistry allows optimization of film deposition parameters that promote minimal residual stress. We have constructed a three-dimensional surface in Raman shift-pressure-temperature space from spectroscopic measurements on single crystal anatase at high pressure and temperature. Location of the Raman shift of the two Eg modes of anatase on this surface the state of stress (pressure) and temperature of the film can be determined. For materials with large Raman scattering cross-sections, such as anatase, time-resolved crystallization experiments on films as thin as 100 nm are possible. Using this technique, the evolution of the state of stress during isothermal thermal and laser-induced crystallization processes can be monitored in real time and compared to the residual stress upon cooling.