We experimentally demonstrate propagation of surface plasmon polaritons in the near-IR window $\lambda ∊(1.45\mu \mathrm{m},1.59\mu \mathrm{m})$ at the interface of indium-tin-oxide films with different thicknesses deposited on glass. Dispersion of such polaritons is strongly dependent on the film thickness, putting into evidence a regime in which polaritons at both films’s interfaces are coupled in surface supermodes. The experimental data are shown to be in good agreement with the analytical model for thin and absorbing conducting films. Measurements on aluminum-doped zinc oxide, characterized by a redshifted plasma resonance, do not show any surface plasmon polariton excitation in the same wavelength window.

The effect of the order-disorder transition on the band gap of kesterite Cu₂ZnSnS₄, an interesting material for solar cells, has been investigated by optical spectroscopy. The band gap energy (E_g) decreases continuously with increasing annealing temperature, T_a, and reaches its minimum at T_a ∼ 273 °C. E_g is about 200 meV higher in the most ordered state, than in the fully disordered state. Its value and the transition kinetic depend on the sample stoichiometry. A simplified model able to explain the order degree and stoichiometry effects on the E_g value is developed. Ordering results in narrower Raman peaks without affecting the shape of the photoluminescence spectrum—except for the change in E_g—or the characteristic energy of the exponential tail below the fundamental absorption edge. Although a prolonged annealing increases the order degree, the material properties are still influenced by residual disorder as well as by defects related to the off-stoichiometry composition.

Optical materials and coatings are exposed to the flux of energetic particles when used in either space applications or nuclear energy plants. The study of their behavior in such an environment is important to avoid failure of the optical components during their operation. The optical performance of several thin-film materials (${\mathrm{HfO}}_2$, ${\mathrm{Ta}}_2{\mathrm{O}}_5$, ${\mathrm{Nb}}_2{\mathrm{O}}_5$, ${\mathrm{TiO}}_2$, ${\mathrm{SiO}}_2$) and coatings, under irradiation with high-dose gamma rays (5.8 MGy) and exposure to low-energy (60 keV) protons, has been investigated. Some variations of optical properties have been detected in silicon oxide after irradiation, while the other materials are stable in such conditions.

Highly conductive and transparent NiO _x films can be very useful as buffer layers for the optimization of the p-type contacts of optoelectronic devices. Thin NiO _x films were fabricated by reactive radio frequency (RF) sputtering at room temperature starting from a Ni target. A systematic study of the influence of oxygen partial pressure, RF power and sputtering gas pressure on the films’ properties was carried out. The structural, microstructural, optical and electrical properties were affected differently by the sputtering parameters. Resistivity decreased by increasing the oxygen partial pressure and the sputtering total pressure and by decreasing the RF power, while transmittance increased by decreasing the oxygen partial pressure and by increasing the RF power and sputtering pressure. Minimum resistivity of 1.6 × 10 ⁻² Ωcm and a visible transmittance of 40% were achieved for a film grown in a pure oxygen atmosphere, while a higher transmittance of 54% and a resistivity of ρ = 1.1 × 10 ⁻¹ Ωcm were obtained for a film grown at 30% oxygen partial pressure. The trends of transmittance and resistivity as a function of the oxygen pressure during the sputtering process can be explained in terms of the amount of Ni ³⁺ defects deduced by x-ray photoelectron spectroscopy (XPS) measurements. The full interpretation of the other results is less straightforward and highlights the relevance of the samples’ structural properties.