(502d) Exploring the Optical Properties of Silicalite (MFI) Thin Films Via Quantum Tunneling Photoacoustic Spectroscopy (QTPAS)

Novel optical material systems have tremendous potential to revolutionize the design, fabrication and performance metrics of micro- and nano-scale integrated optical devices and systems. Nanostructured materials, like zeolites, have unique and complex relationships between structure and physicochemical properties that can be tuned during their synthesis. Zeolites are crystalline minerals with uniform micropores, structural symmetry, and a variety of topologies resulting in desirable physicochemical properties such as high surface area, thermal stability, and shape and size selectivity.  However, many of these materials have yet to be investigated for their optical properties, limiting their use in integrated optical systems.  Here, we synthesize and characterize a model zeolite system, pure-silica MFI, in thin film form to evaluate its potential for integrated optics.  We use SEM, XRD, ellipsometry and FTIR-ATR to determine the crystallinity, film thickness, surface coverage, crystal size, crystal habit, and chemical composition. Additionally, we introduce a new technique to explore the optical properties of thin film materials called quantum tunneling photoacoustic spectroscopy. QTPAS is used to non-destructively determine both film thickness and refractive index of the pure-silica MFI thin films at 532 nm, and compare it to standard ellipsometry and theoretically calculated values of the refractive index.  This work represents the first evaluation of pure-silica MFI for these purposes, and introduces the concept of QTPAS as an accurate, low-cost and non-destructive optical materials characterization technique.