Spectroscopic analysis of photochromic films

Sol-gel processing was used to dope photochromic dyes into three matrices: metal alkoxide, metal alkoxide-polymer, and pure polymeric materials. The f ilms on silicon and quartz substrates were examined, with and without ultra violet (UV) irradiation, by ellipsometry, UV-visible transmission spectrosc opy, and Fourier transform infrared (FTIR) transmission spectroscopy. Varia ble angle spectroscopic ellipsometry (VASE) data were analyzed for film thi ckness and optical constants, and in some cases thickness nonuniformity. A modified Cauchy and a combined Cauchy-Lorentz model were used to fit the un irradiated and irradiated film optical constants, respectively. The optical constants of the films showed significant changes upon irradiation. This m eans that the absorption coefficient and hence the emissivity of the films is being modulated with UV irradiation. The VASE-fitted thicknesses of the films were in the range of 1-6 mu m. In the FTIR spectra, the spiropyran do ped samples have shown IR transmission changes in the two spectral regions (6-7 and 7.5-8.5 mu m) where changes are expected due to bond opening. The transmission ratio for UV irradiated and unirradiated samples decreased by as much as about 24% at a particular IR wavelength. (C) 1999 American Vacuu m Society. [S0734-2101(99)00501-1].