The optical properties of Cu island films, in particular their plasmonic behaviour, are investigated. The films are fabricated by electron beam evaporation using different deposition parameters (deposited mass thickness and substrate temperature).The optical response can be tuned from a metal-like behaviour to well-defined localized surface plasmon resonances and is well correlated with the structural and morphological properties of the samples. Significant changes of optical properties take place with sample aging, including quenching and non-monotonic frequency shift of the plasmon resonance. These changes are interpreted in terms of Cu oxidization process, that appears to strongly depend on the initial morphology of samples.Theoretical calculations in the framework of effective medium theories qualitatively explain the experimental observations. Overall, the results give a detailed insight on the morphology dependence and time evolution of the optical response of Cu island films that may provide useful guidelines for applying these nanostructures in plasmonic applications.

Application of electric field and moderately elevated temperature is depleting the side facing anode from alkali present in glasses. The change of composition of the treated glass results in variation of refractive index depth profile within the treated glass. Spectroscopic ellipsometry is employed for characterization of optical properties of glass treated in different conditions. The results of optical characterization are verified by secondary ion mass spectroscopy. It is found that the refractive index profile obtained from ellipsometry has maximum value higher than the one of untreated glass. Obtained refractive index profiles are in very good agreement with concentration profiles.

The strong dispersion in the effective optical constants of plasmonic nanocomposite films is used to generate interference effects that are highly sensitive to changes in the dielectric environment of particles. Numerical simulations show that reflectance measurements on metal nanoparticle systems close to a metallic substrate have larger sensitivities to changes in the surrounding refractive index than the standard transmittance measurements of the same system when placed on a transparent substrate. The scheme is particularly advantageous in case of disordered nanoparticle systems, where the difference between reflectance and transmittance‐based sensing approaches is enhanced due to local‐field fluctuations that modify the effective optical constants dispersion. Exceptional to most plasmonic applications, in the present case, a disordered system provides larger sensitivity and figure of merit than its ordered counterpart. The key concepts suggested from numerical calculations are verified by the fabrication of metal island films coated with different dielectric layers, that confirm the superiority of the reflectance‐based sensing scheme. Overall, the present approach profits from the disorder to improve refractive index sensitivity in metal nanoparticle systems that are produced with industrially appealing techniques. Thus, the proposed scheme may be valuable for the broad implementation of low‐cost and highly efficient plasmonic sensors.

In both engineering and physics communities, it is believed that approximation of a realistic non-Foster negative capacitor (within its operating bandwidth) with an ideal dispersionless negative capacitor is acceptable for practical purposes. However, the ideal negative capacitor is not causal and, therefore, not compatible with basic physics. Its use in the design process is misguiding since it often predicts entirely non-physical behaviour. Here, we show that a realistic negative capacitor can always be modelled as a dispersive voltage-controlled source, the internal impedance of which is an ordinary positive capacitor. This equivalent circuit clearly explains the origin of negative conductance that always accompanies negative capacitance, as well as the background physics of previously reported counter-intuitive phenomena in non-Foster metamaterials. Theoretical analysis was verified by simulations and measurements on an experimental low-frequency (100 Hz-25 kHz) negative capacitor demonstrator. Measurement results agreed well with theoretical predictions, showing that the proposed model is indeed physically sound.

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