Recent progress in ellipsometry instrumentation permits precise measurement and characterization of optical coating materials in the deep-UV wavelength range. Dielectric coating materials exhibit their first electronic interband transition in this spectral range. The Tauc-Lorentz model is a powerful tool with which to parameterize interband absorption above the band edge. The application of this model for the parameterization of the optical absorption of TiO2, Ta2O5, HfO2, Al2O3, and LaF3 thin-film materials is described.

Interfacial phase transitions like wetting and prewetting transitions are of considerable interest in physics and chemistry of condensed matter since they represent phase transitions in reduced dimensionality. Besides this interfacial properties are of profound practical and technological interest. Most systems studied experimentally in this respect are characterized by Van der Waals intermolecular interactions. However, in the last few years it was shown that Coulomb liquids like liquid alloys or metal molten salt solutions exhibit interfacial phase transitions similar to those known in Van der Waals systems. In order to get more insight into these phenomena the fluid‐vapor interface of two different alloy systems have been studied using ellipsometry. Gallium‐bismuth is a binary alloy with large positive deviations from Raoult's law, exhibiting a distinct miscibility gap. Approaching liquid‐liquid coexistence a Bi‐rich film completely wets the fluid‐vapor interface. As can be estimated from the ellipsometric results the film thickness jumps at the monotectic temperature to a value of about 50 Å. In contrast, gallium‐germanium shows continuous miscibility and deviates much less from ideal mixing. As the Ge concentration in liquid Ga increases along the solid‐liquid coexistence curve the optical properties at the surface also vary continuously, which can be modelled within a simple effective medium approach.

We report optical absorption spectra of Kx(KI)1−x, Csx(CsI)1−x, and Csx(CsCl)1−x solutions at temperatures around 800 °C and in the saltrich concentration range up to metal mole fractions of xM⩽0.04 for energies 0.5⩽ℏω⩽5 eV. Employing a high-temperature electrochemical cell, we were able to change and determine the alkalimetal activity and the alkalimetal mole fraction in situ simultaneously with the optical absorption spectra. The high quality of the absorption spectra allows to distinguish spectral contributions to localized electronic states and mobile electrons. Together with previously measured spectra of Nax(NaI)1−x melts a systematic investigation of the alkali iodide melts reveals differences in the nature of the strongly localized electronic states with varying cation. Interpretation of the spectroscopic results with the aid of a chemical defect model shows that the formation of localized dimeric electron states (bipolarons) is pronounced in melts of smaller cations. The analysis of the optical contribution due to mobile electrons has been performed with a simple Drude model for nearly free electrons and the results are in good agreement with independent measurements of electronic transport properties.

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At elevated temperatures (about 10 3 K) liquid alkali metal-alkali halide solutions transform continuously from the nonmetallic to the metallic state (NM-M transition) as a function of the metal mole fraction x M . In this study we present results of new experiments on spectroscopic ellipsometry and on absorption spectroscopy across the transition regime. The data indicate that on both sides of the NM-M transition localized and mobile electronic states may coexist