Observation of a Correlation Between Internal friction and Urbach Energy in Amorphous Oxides Thin Films - Ondes Gravitationnelles
Article Dans Une Revue Scientific Reports Année : 2020

Observation of a Correlation Between Internal friction and Urbach Energy in Amorphous Oxides Thin Films

Résumé

We have investigated by spectroscopic ellipsometry (SE, 190–1700 nm) the optical properties of uniform, amorphous thin films of Ta$_{2}$O$_{5}$ and Nb$_{2}$O$_{5}$ as deposited and after annealing, and after so-called “doping” with Ti atoms which leads to mixed oxides. Ta$_{2}$O$_{5}$ and Ti:Ta$_{2}$O$_{5}$ are currently used as high-index components in Bragg reflectors for Gravitational Wave Detectors. Parallel to the optical investigation, we measured the mechanical energy dissipation of the same coatings, through the so-called “loss angle” ϕ = Q$^{−1}$, which quantifies the energy loss in materials. By applying the well-known Cody-Lorentz model in the analysis of SE data we have been able to derive accurate information on the fundamental absorption edge through important parameters related to the electronic density of states, such as the optical gap (E$_{g}$) and the energy width of the exponential Urbach tail (the Urbach energy E$_{U}$). We have found that E$_{U}$ is neatly reduced by suitable annealing as is also perceptible from direct inspection of SE data. Ti-doping also points to a minor decrease of E$_{U}$. The reduction of E$_{U}$ parallels a lowering of the mechanical losses quantified by the loss angle ϕ. The correlation highlights that both the electronic states responsible of Urbach tail and the internal friction are sensitive to a self-correlation of defects on a medium-range scale, which is promoted by annealing and in our case, to a lesser extent, by doping. These observations may contribute to a better understanding of the relationship between structural and mechanical properties in amorphous oxides.
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Dates et versions

hal-02483982 , version 1 (04-02-2021)

Identifiants

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Alex Amato, Silvana Terreni, Massimo Granata, Christophe Michel, Benoit Sassolas, et al.. Observation of a Correlation Between Internal friction and Urbach Energy in Amorphous Oxides Thin Films. Scientific Reports, 2020, 10 (1), pp.1670. ⟨10.1038/s41598-020-58380-1⟩. ⟨hal-02483982⟩
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