Generalized ellipsometry and quartz crystal nanogravimetry are combined to determine adsorption isotherms and changes in the optical properties of biaxial TiO2 thin films by monitoring changes in the Mueller matrix. Individual Mueller matrix elements, corresponding to a variety of polarization states, exhibit dramatically different sensitivities to the adsorption of toluene. While some elements are sensitive to structural anisotropy and orientation, others report uniquely on the refractive index. The fast (n a) optical axis reflects the greatest change in refractive index due to the adsorption, leading to a decrease from δn800nm = 0.4 to 0.1. This change is discussed in terms of the Bragg-Pippard (B-P) effective medium approximation, which is shown to accurately describe changes in optical behavior in response to adsorption. The integration of generalized ellipsometry with quartz crystal nanogravimetry establishes a highly sensitive technique for acquiring adsorption isotherms and for chemical optical sensing of structurally anisotropic thin films.
ASJC Scopus subject areas
- General Materials Science
- Physical and Theoretical Chemistry