In this work the optical and electrical characteristics of radio frequency sputtered indium tin oxide (ITO), aluminum doped zinc oxide (AZO) and nickel oxide (NiOx) are reported. ITO and AZO films showed very high visible transmittance values, with maxima up to 90-91%, and sheet resistance of 35 and 33 Ω/□, respectively, while non stoichiometric NiO films showed visible transmittance up to 53% and sheet resistance of several tens of KΩ/□. Properties of the films were correlated to their structure and morphology which are strongly dependent on the growth parameters.
Subwavelength periodic nanostructures on metal, dielectric or metal-dielectric-metal coating were fabricated by femtosecond laser. Circular apertures with diameter of ~0.6μm and a lattice period of 1.0 and 2.0 um were fabricated by single laser pulse irradiation. Surface geometries of nanostructure unit on the three kinds of coatings were compared using the scanning electron microscope and atomic force microscope. Moreover, the nanostructure units fabricated by front-side ablation technique and back-side ablation technique were compared. The minimum diameter of the circular aperture fabricated both by front-side ablation technique and back-side ablation technique could reach approximate 300 nm. By studying mechanisms of femtosecond laser interaction with metal films and dielectric films, it’s found that metal layers dominate femtosecond laser interaction with metal-dielectric-metal sandwich type coatings. It’s also found that the edges of apertures fabricated by back-side ablation technique in metal coatings and metal-dielectric-metal coatings are more regular and round than those fabricated by front-side ablation technique. Femtosecond laser fabrication therefore provides possibilities for maskless and speedy fabrication of fishnet structures which exhibit negative refractive index at optical frequencies.
The study of lightning phenomena will be carried out by a dedicated instrument, the lightning imager, that will make use of narrow-band transmission filters for separating the Oxygen emission lines in the clouds, from the background signal. The design, manufacturing and testing of these optical filters will be described here.
Fishnet metamaterials (MM) conceived for optical coating applications have been simulated for metal-dielectric-metal structures based on silver and oxides. Preliminary experimental results on large-scale fabrication are presented here for alumina-silver based structures. Millimeter-size MM layers have been realized by combination of r.f. sputtering and focused-ion-beam writing.
The behaviour of interference optical filters for space applications has been investigated under low- and high-energy
proton irradiation. Low-energy protons are expected to be necessary to prove the effects on the coating, whereas the
high-energy proton tests shall verify mainly the substrate susceptibility to induced damage. The expected interaction of
protons with coating and substrate was simulated by software, to identify the most appropriate conditions for the
irradiation experiments. Two different accelerator facilities were used for low- and high- energy protons: 60 keV protons
with an integrated fluence of 1012 p+/cm2 and 30 MeV protons with an integrated fluence of 108 p+/cm2.
The spectral transmittance of the filters was measured before and after irradiation and, according to simulations, no
significant effects were detected in the visible-near infrared spectrum, while some variations appeared at short
wavelengths with low-energy irradiation.
Many fields of high technology take advantage of conductor-dielectric interface properties. Deeper knowledge of
physical processes that determine the optical response of the structures containing metal-dielectric interfaces is important
for improving the performance of thin film devices containing such materials.
Here we present a study on optical properties of several ultrathin metal oxides deposited over thin silver layers. Some
widely used materials (Al2O3, SiO2, Y2O3, HfO2) were selected for deposition by r.f. sputtering, and the created metal-dielectric
structures with two of them, alumina and silica, were investigated in this work using attenuated total reflectance
(ATR) technique and by variable-angle spectroscopic ellipsometry (VASE). VASE was performed with a help of a
commercial ellipsometer at various incident angles and in a wide spectral range. A home-made sample holder
manufactured for WVASE ellipsometer and operational in Otto configuration has been implemented for angle-resolved
and spectral ATR measurements. Simultaneous analysis of data obtained by these two independent techniques allows
elaboration of a representative model for plasmonic-related phenomena at metal-dielectric interface. The optical constants
of the interface layers formed between metal and ultrathin oxide layers are investigated. A series of oxides chosen for this
study allows a comparative analysis aimed for selection of the most appropriate materials for different applications.
Aluminium-doped zinc oxide films with 91% transmittance in the visible range and electrical resistivity of the order of
10-3 Ωcm were fabricated by radio frequency magnetron sputtering in Ar atmosphere starting from a target of ZnO
mixed with 2% wt Al2O3. A systematic study of the deposition conditions such as substrate temperature, working gas
pressure, radio frequency power, magnetron strength, target to substrate distance, etc., was performed when searching for
improved electrical and optical performances of the films. Several deposition conditions govern the film characteristics,
so that films with same good optical and electrical properties can be obtained by opportunely combining different
deposition parameters.
It is well known that artworks exposed in museums or galleries can be damaged by infrared and ultraviolet radiation.
Moreover, if not properly protected, these precious paintings or sculptures can be also damaged by vandalism acts.
Coated glasses can actually deal with both these problems. They can also improve the artworks viewing if an
antireflection feature is realized. However such optical coatings should not affect color viewing. In this study we
describe a new prototype of coating and investigate, by mean of psychophysical experiments, how it affects color
perception relative to uncoated glass as well as commercial coating products made up by many coating layers (up to
50). Our results show that color discrimination in the condition in which colors were viewed through our coating
prototype turned out in being better than in the experimental condition in which uncoated glass was used and
surprisingly at least as efficient as the more expensive commercial coated glasses.
Multilayer optical devices generally suffer from two main losses sources: absorption of the materials and scattering losses, due both to volume and surface effects. The exact estimation of this latter contribution is of extreme importance for the final assessment and optimization of efficient devices. In particular, when intrinsic absorption of the materials cannot be further reduced, scattering measurements may provide useful information for improving optical device performance.
In this work we investigated single SiO2, Al2O3 and HfO2 layers deposited by r.f. sputtering under different deposition conditions. These materials are being studied for implementation in multilayer dichroic mirrors for laser applications in the range from 260 to 350 nm. To avoid radiation damage, such devices need to be loss-free in the pumping and lasing region; hence, an insightful knowledge of all losses sources is fundamental.
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