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Effective medium theory to the description of plasmonic resonances: Role of Au and Ti nanoparticles embedded in MoO3 thin films
摘要： The growing interest in functional transition metal oxides for efficient energy consumption or in the bio-sensing process; indicates that is necessary to develop a new theoretical method that describes experiments. This article presents a new theoretical methodology to characterize molybdenum trioxide (MoO3) thin films doped with resonant gold – nanoparticles (Au – NPs) and non-resonant titanium – nanoparticles (Ti – NPs). The modulation of surface plasmon resonance (SPR) and the implications in the MoO3 transmittance spectrum is described by applying an effective medium theory. The transmittance modulation was modified by variating three parameters, the radius of the NPs, the concentration of the NPs as well as the variation of the MoO3 thin films thickness. It was found that the nanoparticles concentration is the most important parameter in the transmittance modulation. Additionally, the orthorhombic and monoclinic structure of MoO3 was studied, from which it was obtained that the monoclinic structure of the MoO3 doped with Au – NPs favors the reduction in the transmittance values in the visible region which is associated with the increase of the SPR signal. Similar analyses are performed for non-resonant nanoparticles such as Ti, where it was found that optical modulation is not as marked as the case of gold nanoparticles.
关键词： optical modulation,plasmonic resonances,Au and Ti nanoparticles,surface plasmon resonance,MoO3 thin films,effective medium theory
更新于2025-09-23 15:19:57
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Vacuum-annealed and oxygen plasma treated ellipsometric investigations on molybdenum bronzes and measurements of their thermo optic coefficients and electronic polarizability coefficients
摘要： In this investigation, we have measured the optical constants (n, k) of vacuum evaporated MoO3 thin films and of ZxMoO3 (Z = H+, Li+) bronze thin films being annealed at different temperatures and with different concentrations (x) over the range 298–453 K without and within an oxygen plasma environment using manual ellipsometry. We have also measured mass densities, thermo optic coefficients (TOCs), electronic polarizability coefficients (EPCs) and the coefficients of temperature dependence of density of MoO3 thin film and of its bronzes over the same temperature range. It was found that the change in density and porosity of MoO3 thin film (when annealed at 453 K for 36 h) was not more than 6.4% and 15% respectively from the room temperature data. In the case of bronzes, when the samples H0.203MoO3, Li0.076MoO3 and Li0.133MoO3 were annealed at 453 K within an oxygen plasma over different periods of times, it was found that the overall increase in mass density and decrease in the porosity was not more than 4% and 11%, respectively from the initial data at room temperature. Comparably, when the samples H0.211MoO3 and Li0.27MoO3 were annealed at 453 K within an oxygen plasma over different periods of time, the respective decrease in density and increase in porosity was found not more than 3.4% and 6% from the room temperature data. All these results are mostly due to evolution of H2O which causes diffusion of oxygen leading to shallow and deep localised states in the oxide bronze layers. TOCs and EPCs of samples HxMoO3 (x = 0.203) and LixMoO3(x = 0.076, 0.133) upon annealing at 453 K (without and within an oxygen plasma) over different periods of times have an increase in TOCs and in EPCs, and that increase is from 0.10 × 10?4 K?1 to 13.5 × 10?4 K?1 and 0.13 × 10?27 cm3 K?1 to 3.2 × 10?27 cm3 K?1, respectively. On the other hand, the thermo optic coefficient and the coefficient of temperature dependence of density of MoO3 thin films decrease from ? 1.2 × 10?4 K?1 to ? 8.86 × 10?4 K?1 and ? 1.86 × 10?4 g cm?3 K?1 to ? 15.13 × 10?4 g cm?3 K?1, respectively. In the case of H0.211MoO3 and Li0.27MoO3 when annealed at 453 K over different periods of time within oxygen plasma, the overall decrease in TOC is from ? 0.3 × 10?4 K?1 to ? 4.62 × 10?4 K?1, and the decrease in coefficient of temperature dependence of density is from ? 0.45 × 10?4 g cm?3 K?1 to ? 8.9 × 10?4 g cm?3 K?1. These results are due to linear thermal expansion effect.
关键词： ellipsometry,thermo optic coefficients,electronic polarizability coefficients,MoO3 thin films,molybdenum bronzes
更新于2025-09-11 14:15:04