Vesna Janicki

On the dielectric function tuning of random metal-dielectric nanocomposites for metamaterial applications

The potential of random metal-dielectric nanocomposites as constituent elements of metamaterial structures is explored. Classical effective medium theories indicate that these composites can provide a tunable negative dielectric function with small absorption losses. However, the tuning potential of real random composites is significantly lower than the one predicted by classical theories, due to the underestimation of the spectral range where topological resonances take place. This result suggests that a random mixture consisting of a metal matrix with embedded isolated dielectric inclusions is a promising design guideline for the fabrication of tunable composites for metamaterial purposes.

Optical characterization and reverse engineering based on multiangle spectroscopy

We perform characterization of thin films and reverse engineering of multilayer coatings on the basis of multiangle spectral photometric data provided by a new advanced spectrophotometer accessory. Experimental samples of single thin films and multilayer coatings are produced by magnetron sputtering and electron-beam evaporation. Reflectance and transmittance data at two polarization states are measured at incidence angles from 7 to 40 deg. We demonstrate that multiangle reflectance and transmittance data provide reliable characterization and reverse-engineering results.

Deposition and spectral performance of an inhomogeneous broadband wide-angular antireflective coating

Gradient index coatings and optical filters are a challenge for fabrication. In a round-robin experiment, basically the same hybrid antireflection coating for the visible spectral region, combining homogeneous refractive index layers of pure materials and linear gradient refractive index layers of material mixtures, has been deposited. The experiment involved three different deposition techniques: electron-beam evaporation, ion-beam sputtering, and radio frequency magnetron sputtering. The material combinations used by these techniques were Nb(2)O(5)/SiO(2), TiO(2)/SiO(2), and Ta(2)O(5)/SiO(2), respectively. The spectral performances of samples coated on one side and on both sides have been compared to the corresponding theoretical spectra of the designed profile. Also, the reproducibility of results for each process is verified. Finally, it is shown that ion-beam sputtering gave the best results in terms of deviation from the theoretical performance and reproducibility.

Hybrid optical coating design for omnidirectional antireflection purposes

We present a new design for an omnidirectional antireflection coating for the visible spectral range. In contrast to classical designs, it combines homogeneous layers and linear gradient index layers into one hybrid design with a full thickness of approximately 500 nm. The coating may be practically produced based on silicon dioxide as low index material and niobium pentoxide as high index material, while intermediate indices may be obtained from corresponding mixtures.

General approach to reliable characterization of thin metal films

Optical constants of thin metal films are strongly dependent on deposition conditions, growth mode, and thickness. We propose a universal characterization approach that allows reliable determination of thin metal film optical constants as functions of wavelength and thickness. We apply this approach to determination of refractive index dispersion of silver island films embedded between silica layers.

Optical characterization of hybrid antireflective coatings using spectrophotometric and ellipsometric measurements

A hybrid antireflective coating combining homogeneous layers and linear gradient refractive index layers has been deposited using different techniques. The samples were analyzed optically based on spectrophotometric and spectroscopic ellipsometry measurements under different angles of incidence in order to precisely characterize the coatings. The Lorentz-Lorenz model has been used to calculate the refractive index of material mixtures in gradient and constant index layers of the coating. The obtained refractive index profiles have been compared with the targeted ones to detect errors in processes of deposition.

Electric field assisted dissolution of metal clusters in metal island films for photonic heterostructures

The dissolution of metal clusters in metal island films by the simultaneous application of electric field and temperature is reported. The consequent fading of surface plasmon resonance greatly modifies the optical properties of the samples. The dissolution process is verified in island films of different metals, obtained under different conditions and covered by different dielectric materials, as well as on multilayer dielectric stacks showing interferential properties. The tailoring possibilities of the optical behavior of metal island films combined with the inexpensive technical requirements of this approach open up the possibility to produce low-cost photonic heterostructures.

Tuning the effective dielectric function of thin film metal-dielectric composites by controlling the deposition temperature

Abstract. The influence of the substrate temperature on the effective optical behavior ofAg-SiO 2 composites obtained by electron beam evaporation was studied. Optical characteriza-tion of the composites was performed by means of spectroscopic ellipsometry measurements.Theeffectivedielectricfunctionofthecomposites,modeledusingamultipleoscillatorapproach,could be widely tuned by controlling the deposition temperature. The spectral dependence ofthe composite absorption appeared to be better described with a Gaussian line shape than withthe classical Lorentz oscillator model. The description of the effective dielectric function usingstandard effective medium theories failed and the experimental results could be explained onlyin the general framework of the Bergman spectral density theory. C 2011 Society of Photo-OpticalInstrumentation Engineers (SPIE) . [DOI: 10.1117/1.3590238] Keywords: metal-dielectric composites; metal island films; surface plasmon resonance; opticalconstants; effective medium theory; spectroscopic ellipsometry.Paper 11015SSR received Jan. 28, 2011; revised manuscript received Apr. 15, 2011; acceptedfor publication Apr. 15, 2011; published online May 13, 2011.

Comparison of two techniques for reliable characterization of thin metal–dielectric films

In the present study we determine the optical parameters of thin metal-dielectric films using two different characterization techniques based on nonparametric and multiple oscillator models. We consider four series of thin metal-dielectric films produced under various deposition conditions with different optical properties. We compare characterization results obtained by nonparametric and multiple oscillator techniques and demonstrate that the results are consistent. The consistency of the results proves their reliability.

Refractive index profiling of CeO2 thin films using reverse engineering methods

In some recent papers it was shown that ZrO2 single films can be modeled using inhomogeneous models. A similar modeling approach to analyze CeO2 layers has been used. Films have been produced using a standard reactive evaporation technique. Following the measurement results, obtained by normal incidence transmission and variable angle spectroscopic ellipsometry, reverse engineering of the monolayer with its sub-layers has been performed. Novel in this method is that no assumption of refractive index profile is needed. A very good fit of the experimental data with the reverse engineered multi-layers has been obtained, showing that it is possible to find a fine substructure of analyzed films.