Morphological and chemical dynamics upon electrochemical cyclic sodiation of electrochromic tungsten oxide coatings extracted by in situ ellipsometry.

The sodiation-desodiation process of sputtered amorphous electrochromic tungsten oxide coatings in an aqueous-based 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.

Wavelength-by-wavelength Kramers-Kronig consistent inversion of ellipsometry data.

The wavelength-by-wavelength (point-by-point) inversion process consists of solving the ellipsometric equations for each wavelength of the considered spectrum regardless of the other points. It provides the refractive index (${n}$n) and extinction coefficient (${k}$k) of an unknown absorbing material inside a multilayer stack from ellipsometry measurements. A revision of the wavelength-by-wavelength ${n}/{k}$n/k extraction is presented to overcome its two main deficiencies, which are (i) multiple solution possibilities and (ii) lack of Kramers-Kronig consistency.

Semi-analytical method for n-k inversion of ellipsometry data.

A semi-analytical method is presented to unambiguously perform the wavelength-by-wavelength extraction of the optical constants (refractive index n and extinction coefficient k) in a thin film from the ellipsometry measurement. It works by recasting the ellipsometric equations under a parametric polynomial form and drawing parametric curves from the polynomial solutions, whose intersections at zero define solutions of the ellipsometry problem. The interest of the method is the possibility to extract all the solutions of the considered ellipsometric problem in a given range of n and k values, in contrast to the standard least-squares fitting, which provides a single unsure solution conditioned by initial guess values.

Coloration mechanism of electrochromic NaWO thin films.

The coloration mechanism of tungsten trioxide (WO) 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 WO thin films sputter-deposited on ITO/glass substrates. A unique model based on a constrained spline approach was developed and applied to draw out ε+iεfrom spectroscopic ellipsometry data from 0.

Inversion of ellipsometry data using constrained spline analysis.

Ellipsometry is a highly sensitive and powerful optical technique of thin film characterization. However, the indirect and nonlinear character of the ellipsometric equations requires numerical extraction of interesting information, such as thicknesses and optical constants of unknown layers. A method is described to perform the inversion of ellipsometric spectra for the simultaneous determination of thickness and optical constants without requiring particular assumptions about the shape of a model dielectric function like in the traditional method of data fitting.

Dielectric function of very thin nano-granular ZnO layers with different states of growth.

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.

Etching of a-Si:H thin films by hydrogen plasma: a view from in situ spectroscopic ellipsometry.

When atomic hydrogen interacts with hydrogenated amorphous silicon (a-Si:H), the induced modifications are of crucial importance during a-Si:H based devices manufacturing or processing. In the case of hydrogen plasma, the depth of the modified zone depends not only on the plasma processing parameters but also on the material. In this work, we exposed a-Si:H thin films to H2 plasma just after their deposition.