By combining reflectance spectroscopy and spectroscopic ellipsometry, the complex dielectric function of SrTiO, in the frequency range 40-5000 cm-' at 20, 100, 200, and 300 K has been determined. Using a factorized description, analytical expressions for the optical quantities were derived, giving excellent agreement with the experimental data. These can be used for two-layer fits of films on SrTiOs, e.g., of high-T, superconductors. The fit parameters complement very well those found at higher temperatures. 0 1995 American Institute of Physics.

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Current Fourier transform infrared spectroscopy (FTIR) systems have very good spectral resolution, but are bulky, sensitive to vibrations, and slow. We developed a new FTIR system using a microelectromechanical system (MEMS)-based lamellar grating interferometer that is fast, compact, and achromatic (i.e., does not require a beam splitter). The MEMS device has >10  mm² active surface area, up to ±325  μm mechanical displacement, and a 343 Hz resonant operation frequency. The system uses a 5 MHz bandwidth custom infrared (IR) detector and a small emission area custom blackbody source to achieve fast interferogram acquisition and compact form factor. Effects of lamellar grating period, detector size, laser reference, apodization, and averaging of data on the spectral resolution are discussed. The measurement time ranges from 1.5 to 100 ms depending on the averaging time. In the target range of 2.5-16 μm (625-4000  cm^-1) a spectral resolution of 15-20  cm^-1 is demonstrated. The measurements are shown to be stable over a long time.

The photorefractivity of an indole derivative and of its polymer blends has been studied at room temperature. The indole derivative 3-[2-(4-nitrophenyl)ethenyl]-1-(2-ethylhexyl)-2-methylindole (NPEMI-E) is a typical low-molecular-weight glass-forming molecule having peculiar nonlinear optics characteristics. It is unconditionally soluble in the photoconductive poly-(N-vinyl-2,3-dimethylindole) so that all the possible blends can be studied for a weight percent (wt. %) content of NPEMI-E ranging from zero to 100. A very high and sharp maximum of the photorefractive optical gain Gamma(2) approximately 2000 cm(-1) was obtained for a NPEMI-E wt. % content of about 90. On the basis of recently published theoretical calculations, we have made the hypothesis that the rapid change of Gamma(2) can also be ascribed to a correspondingly quick variation of the molecular electro-optic parameters of the dissolved chromophore for some well distinguished values of its concentration in the polymer matrix. Differential scanning calorimetry measurements were made and the results carefully analyzed with the aim of obtaining information on the intermolecular interactions. These last measurements also allowed rationalizing the unconditionally stable glass appearance of the obtained blends. Measurements of spectroscopic ellipsometry were also made on blends with different NPEMI-E content.

Vanadium pentoxide (V2O5) raised much interest, in several fields, especially relating to thin film lithium microbatteries. Yet, literature mentioned different results about a variation of electrochemical performance of these films with thickness. The present work is focused on the use of spectroscopic ellipsometry on V2O5 crystalline thin film during growth. Optical properties were determined in the near‐IR‐visible range (0.25‐2 µm). Effective media approximation based model was developed and was used to determine the optical constants of thin films. Thickness and roughness obtained corresponded well to respectively SEM and AFM results. Based on optical refractive index evolution, a density gradient was identified through the film thickness. These results could explain in parts the thickness influence on the electrochemical performance of V2O5 thin films. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)