Optical characterisation of anatase: a comparative study of the bulk crystal and the polycrystalline thin film

The optical parameters of crystalline anatase and polycrystalline anatase films prepared by reactive magnetron sputtering were examined by spectroscopic ellipsometry and optical transmittance spectroscopy, respectively. Some films were doped with aluminium or chromium. In general, the values of the optical bandgap for the films are consistently blue-shifted as compared with the crystal. The blue shift is also found for some films doped with Al and Cr. The width of the absorption bands is considerably narrower in the films than in the crystal. These effects are interpreted as resulting from the spatial confinement of electrons and holes in the TiO2 microcrystallites. The average crystallite size determined from the shift of the optical gap was found to be in the range ~5–8 nm, in excellent agreement with the data obtained from small-angle X-ray diffractometry

Near-zero negative real permittivity in far ultraviolet: extending plasmonics and photonics with B1-MoNx

CMOS-compatible, refractory conductors are emerging as the materials that will advance novel concepts into real, practical plasmonic technologies. From the available pallet of materials, those with negative real permittivity at very short wavelengths are extremely rare; importantly, they are vulnerable to oxidation—upon exposure to far-UV radiation—and nonrefractory. Epitaxial, substoichiometric, cubic MoN (B1-MoNx) films exhibit resistivity as low as 250 μΩ cm and negative real permittivity for experimental wavelengths as short as 155 nm, accompanied with unparalleled chemical and thermal stabilities, which are reported herein. Finite-difference time domain calculations suggest that B1-MoNx operates as an active plasmonic element deeper in the UV (100–200 nm) than any other known material, apart from Al, while being by far more stable and abundant than any other UV plasmonic conductor. Unexpectedly, the unique optical performance of B1-MoNx is promoted by nitrogen vacancies, thus changing the common perception on the role of defects in plasmonic materials

Polarimetric studies of polyethylene terephtalate flexible substrates

Polymer sheets are currently used worldwide in a wide range of applications. The manufacturing process of these sheets involves extruding machines that stretch the material in both lateral and longitudinal directions with respect to the machine direction, thus inducing birefringence. In most cases, the film obtained is optically biaxial. Polarimetric spectroscopy (Ellipsometry and Mueller Matrix) combined with conoscopic observation are the methods of choice to study these properties. In this work we report an analysis of commercially available polyethylene terephtalate (PET) films used as substrate for food packaging as well as for embedded electronic devices such as solar cells or flexible displays. Initial observation of these films through polarizing microscope in conoscopic mode reveals first the trace of optical axis plane with respect to the film surface and second, whether the optical axis is acute or not. This preliminary study allows optimal sample positioning for further polarimetric studies. The measurements and modelling are done in both reflection and transmission mode on several spectroscopic polarimetric setups from UV to NIR. The models give as a main result, the dielectric tensor of the film as well as its orientation with respect to the laboratory reference frame

Polarimetric studies of strained biaxially oriented Polyethylene Terephtalate flexible substrates

International audienc

Optical properties of cobalt clusters implanted in thin silica layers

International audienc

Optical and dielectric properties of fluorinated ethylene propylene and tetrafluoroethylene-perfluoro(alkoxy vinyl ether) copolymer films modified by low energy N4+ and C4+ ion beams

Fluorinated ethylene propylene (FEP) and tetrafluoroethylene-perfluoro(alkoxy vinyl ether) (PFA) copolymer films were irradiated in vacuum with 60 key C4+ and N4+ ions to fluences ranging from 1.0 x 10(12) to 5.0 x 10(15) cm(-2). Changes in optical and dielectric properties were analyzed by spectroscopic ellipsometry and ultraviolet-visible (UV-vis), Raman and dielectric relaxation spectroscopies. Direct and indirect energy band gap values were determined from the absorption edge in the 200-800 nm region using Taucs relation. The values of the direct energy gap have been found to be greater than the corresponding values of the indirect energy gap. Significant changes in the index of refraction, and 13 and gamma dielectric relaxations were observed in the case of N4+ irradiated FEP and PFA samples. (C) 2011 Elsevier Ltd. All rights reserved