Infrared reflectance measurements of zeolite film thickness, refractive index and other characteristics

Abstract

We present a method for the non-destructive measurement of zeolite membrane characteristics by means of infrared (IR) reflectance measurements in the non-absorbing frequency range. A rigorous expression for the IR reflectivity of an isotropic layered structure is combined with a polynomial expansion for the refractive index function, to interpret reflectance measurements from zeolite MFI membranes grown on α-alumina substrates by the seeded growth technique. The optical refractive index function, the membrane thickness, and the RMS roughness of the membrane surface can be extracted from non-linear least squares fitting of the measurement model. The method can also be used to detect the loading of organic species by measuring changes in the optical characteristics. The utility of the method in studying adsorption and transport in zeolite membranes is discussed.