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The sodiation-desodiation process of sputtered amorphous electrochromic tungsten oxide coatings in aqueousbased medium was simultaneously monitored over 99 cycles by cyclic voltammetry and in situ spectroscopic ellipsometry. This allowed extracting the evolution of optical and geometrical parameters upon cycling. The resulting electrochemical coloring-bleaching process was dynamically fitted in the 1.8-2.8 eV optical range with a four-phase model including a constrained spline parametrization of the dielectric function. This allows real time access to thickness, surface roughness and dielectric function of NaxWO3. The temporal evolution of the latter in the fully colored state was used to highlight a porosity extent of the probed coating of opened morphology. The designed spectro-electrochemical approach was applied to map the temporal evolution of the Na content (x in NaxWO3) during and between cycles, taking into account the intricate interplay between charge density, thickness and electrolyte uptake.

ZnO thin films have been prepared by sol gel and deposited by spin coating. The dielectric function has been determined by spectroscopic ellipsometry. Ellipsometric spectra are inverted by a direct numerical method without using the standard fitting procedures. The obtained dielectric function presents a broad excitonic effect. The dielectric function is studied using Elliot excitonic theory including exciton plus band-to-band Coulomb interactions with standard Lorentzian broadening. A modification of this model dielectric function with independent bound and unbound exciton contributions is empirically proposed to improve modelling of the band gap excitonic peak.

Zinc oxide (ZnO) layers consisting of grains closely packed together are grown using a solgel synthesis and spin-coating deposition process. The morphologies are characterized by atomic force microscopy and X-ray diffraction, and their optical properties are investigated by spectroscopic ellipsometry at the different stages of the growth process. The optical observations are correlated with evolution of morphology and orientation. Two remarkable evolutions are observed: gradual evolution of morphology, crystallinity, and excitonic contribution with the first deposition steps; and transformation from a poorly oriented to a c-axis oriented crystalline state featuring a large contribution of bound excitons after thermal annealing. A modified Elliott model is used to obtain the optical parameters of ZnO, including bandgap and exciton energies. A simple growth mechanism is proposed to explain the evolution of the layers in accordance with the different deposition steps.

The coloration mechanism of tungsten trioxide (WO3) upon insertion of alkali ions is still under debate after several decades of research. This Letter provides new insights into the reversible insertion and coloration mechanisms of Na + ions in WO3 thin films sputterdeposited on ITO/glass substrates. A unique model based on a constrained spline approach was developed and applied to draw out ε1+iε2 from spectroscopic ellipsometry data from 0.6 to 4.8 eV whatever the state of the electrochromic active layer, i.e. as-deposited, colored or bleached. It is shown that electrochemically intercalated sodium-tungsten trioxide, NaxWO3 (x=0.1, 0.2, 0.35), exhibits an absorption band centered at ca. 1.14 eV in 2 governing the coloration mechanism.