Volume 11, Issue 3-4

This view highlights a revolutionary change in IR ellipsometry, namely, the incorporation and application of tunable lasers. The presented instrumental developments beyond classical FTIR-based approaches are coming precisely at the right time for today’s demands for in situ, operando and hyperspectral characterization methods required in bioanalytics, catalysis and surface science.

The Mueller matrix is a mathematical description of how light is altered by an optical element or a sample under study. It describes both intensity (irradiance) and polarization changes, including a reduction of the total polarization. Mueller matrix spectroscopic ellipsometry has gained recent popularity in the optics and semiconductor communities as an effective means to characterize complex sample structures and anisotropic materials. While this method is not new, its recent expansion to new fields has left many users with only a pedestrian understanding of the data they collect. This tutorial provides an overview of Mueller matrix spectroscopic ellipsometry with focus on practical aspects for those new to the technique.

Dielectric function representation by a variety of polynomial spline functions provides a consistent and efficient method for accurate modeling of the material optical properties in the context of spectroscopic ellipsometry data interpretation. Splines as an elegant and purely mathematical way for such modeling task were introduced about three decades ago. In the following years the use of splines in the area of ellipsometric data analysis became widely utilized. The goal of this review is to provide a self-contained presentation on the current status of the dielectric function modeling by splines for advanced industrial ellipsometry users but, hopefully, it can be useful for some scholarly users as well. It is also intended to promote more extended recognition of the spline-based modeling among optical metrology professionals. Here, a brief description of different ways, – ordinary polynomials, piecewise polynomials (splines), and B(asis)-spline functions, – is presented to parameterize an arbitrary function which can be used as an analytic representation of the dielectric-function curves. A number of particular polynomial-based models for the optical functions of materials and how they may be used in applications are also discussed. Particular attention is paid to different concepts of the efficient and optimal spline construction.

The temperature dependence of the optical constants of materials (refractive index, absorption and extinction coefficients, and dielectric function) can be determined with spectroscopic ellipsometry over a broad range of temperatures and photon energies or wavelengths. Such results have practical value, for example for applications of optical materials at cryogenic or elevated temperatures. The temperature dependence of optical gaps and their broadenings also provides insight into the scattering of electrons and holes with other quasiparticles, such as phonons or magnons. This review presents a detailed discussion of the experimental considerations for temperature-dependent ellipsometry and selected results for insulators, semiconductors, and metals in the infrared to ultraviolet spectral regions.

Catalysts are important components in chemical processes because they lower the activation energy and thus determine the rate, efficiency and selectivity of a chemical reaction. This property plays an important role in many of today’s processes, including the electrochemical splitting of water. Due to the continuous development of catalyst materials, they are becoming more complex, which makes a reliable evaluation of physicochemical properties challenging even for modern analytical measurement techniques and industrial manufacturing. We present a fast, vacuum-free and non-destructive analytical approach using multi-sample spectroscopic ellipsometry to determine relevant material parameters such as film thickness, porosity and composition of mesoporous IrO x –TiO y films. Mesoporous IrO x –TiO y films were deposited on Si wafers by sol–gel synthesis, varying the composition of the mixed oxide films between 0 and 100 wt% Ir . The ellipsometric modeling is based on an anisotropic Bruggeman effective medium approximation (a-BEMA) to determine the film thickness and volume fraction of the material and pores. The volume fraction of the material was again modeled using a Bruggeman EMA to determine the chemical composition of the materials. The ellipsometric fitting results were compared with complementary methods, such as scanning electron microscopy (SEM), electron probe microanalysis (EPMA) as well as environmental ellipsometric porosimetry (EEP).