Spectroscopic ellipsometry from 10 to 700 K

Zollner, Stefan; Abadizaman, Farzin; Emminger, Carola; Samarasingha, Nuwanjula S.

doi:10.1515/aot-2022-0016

Cited by 6 publications

(4 citation statements)

References 62 publications

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“…In fact, the loss angle data points relative to the annealed 21 and 44% samples lie very close to each other, one being slightly lower than the other depending on the considered frequency. This further strengthens our hypothesis that the search for an absolute minimum following postdeposition heat treatment must be sought in the individual study of the best annealing for each type of titania-tantala mixing concentrationa study in which temperature-depentent, in situ SE is a valid research tool. , Furthermore, considering the frequency trend of the loss angle, the search for a minimum after annealing may depend on the frequency range of interest.…”

Section: Discussionmentioning

confidence: 99%

Enhancing Titania-Tantala Amorphous Materials as High-Index Layers in Bragg Reflectors of Gravitational-Wave Detectors

Amato

Magnozzi

Shcheblanov

et al. 2023

ACS Appl. Opt. Mater.

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Amorphous mixed titania-tantala coatings are key components of Bragg reflectors in gravitational-wave detectors (GWDs). Attaining the lowest possible values of optical absorption and mechanical losses in coatings is of paramount importance for GWDs, and this requires a complex optimization of the coating deposition and postdeposition annealing. We present here a systematic investigation of the optical properties and internal friction of amorphous mixed titania-tantala coatings grown by ion beam sputtering. We consider coatings with six different cation mixing ratiosdefined as Ti/(Ti + Ta)and we study them both in the as-deposited and annealed states. All coatings have been subject to the same annealing of 500 °C for 10 h in air, which is the postdeposition treatment adopted so far for Bragg reflectors in GWD applications. By exploiting spectroscopic ellipsometry data and modeling, along with ancillary techniques, we retrieved the dielectric function of the coatings in a wide spectral range. When varying the mixing ratio and performing the annealing, we find monotonicin some cases, almost lineartrends for most of the aforementioned properties. Remakably, the postannealing Urbach energy displays a definite minimum for a mixing ratio around 20%, very close to the composition of the coatings showing the lowest optical absorption for GWD applications. We suggest that the observed minimum in the Urbach energy depends not only on the mixing ratio but also on the annealing parameters. On the other hand, the minimum coating loss angle was found to be weakly dependent on the considered measurement frequency and to lie within a rather broad range of Ti content (cation ratios of 21 and 44%), suggesting that the search for an absolute minimum following postdeposition annealing should be rather sought in the study of the best annealing parameters for each specific cation ratio considered. This work constitutes a reference for the optical properties of the amorphous mixed titania-tantala coatings and highlights the relevance of the Urbach energy as an additional parameter to guide the optimization process of materials for high-performing Bragg reflectors.

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Section: Discussionmentioning

confidence: 99%

Enhancing Titania-Tantala Amorphous Materials as High-Index Layers in Bragg Reflectors of Gravitational-Wave Detectors

Amato

Magnozzi

Shcheblanov

et al. 2023

ACS Appl. Opt. Mater.

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“…Samples were pre-treated with a mild annealing at 373 K overnight to reduce ambient molecular contamination [17], then cooled to 75 K. Pressure inside the cryostat was 1.3 × 10 −5 mbar at the beginning of cooling and became lower than 2.5 × 10 −6 mbar at 75 K. ∆, Ψ and temperature were continuously monitored during the cooling, as exemplified in figure 1(right). The pressure inside the cryostat is higher than that used in KAGRA, the latter being in the order of 10 −8 mbar.…”

Section: Experimental Methodsmentioning

confidence: 99%

“…Spectroscopic ellipsometry (SE) is a well-proven technique to determine the optical properties and thickness of thin and ultrathin films [10][11][12][13], allowing the determination of the thickness with a resolution well below 1 nm in single-layer as well as multi-layer structures [14][15][16]. Moreover, SE can be implemented in cryogenic setups, so that SE data can be acquired while keeping the sample at cryogenic temperatures [9,17], and therefore is an ideal tool to characterize and monitor thin and ultrathin ice layers.…”

Section: Introductionmentioning

confidence: 99%

Detecting ultrathin ice on materials for optical coatings at cryogenic temperatures

Magnozzi,

Bisio,

Gemme

et al. 2023

J. Phys. D: Appl. Phys.

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The performance of optical cavities in Gravitational Wave Detectors (GWD) is negatively affected by the growth of ice layers when operating at cryo temperatures. Loss of performance begins when the ice overlayer is only a few-nm thick. Careful planning is then required to minimize, monitor and take into account the presence of ultrathin ice on cryo-cooled optical surfaces. Here we employed spectroscopic ellipsometry (SE) to study icing on the surfaces of SiO2 and Ti:Ta2O5 thin films, two materials used in the high-reflective mirrors of current GWD. SE measurements were performed at 75 K. The data presented suggest that SE is a most convenienttool to monitor in operando the ice formation on the surfaces of GWD mirrors.Furthermore, ultrathin ice layers can affect the evaluation of the optical properties of materials at low temperatures, a valuable task for those next-generation GWD that will operate at cryogenic temperatures. The characterization of an ultrathin ice overlayer (<10 nm) allowed to determine for the first time the low-temperature optical properties of Ti:Ta2O5. The same approach could be applied to determine the low-temperature optical properties of other dielectric films, thus helping to screen new materials for cryo-operated GWD mirrors.

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“…We have incorporated references to detailed reviews authored by esteemed experts in the field of SE (see, for example [1,2]). This inclusion is meticulously designed for readers who aspire to a profound and advanced understanding of SE technique.…”

Section: Introductionmentioning

confidence: 99%

Spectroscopic Ellipsometry: Advancements, Applications and Future Prospects in Optical Characterization

Politano,

Versace

2023

Spectroscopy Journal

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Spectroscopic ellipsometry (SE), a non-invasive optical technique, is a powerful tool for characterizing surfaces, interfaces, and thin films. By analyzing the change in the polarization state of light upon reflection or transmission through a sample, ellipsometry provides essential parameters such as thin film thickness (t) and optical constants (n, k). This review article discusses the principles of ellipsometry, including the measurement of key values ∆ and Ψ, and the complex quantity ρ. The article also presents the Fresnel equations for s and p polarizations and the importance of oblique angles of incidence in ellipsometry. Data analysis in ellipsometry is explored, including the determination of bandgap and data referencing the electrical properties of materials. The article emphasizes the importance of choosing the appropriate models to fit ellipsometric data accurately, with examples of the Cauchy and Lorentz models. Additionally, the Kramers–Kronig relations are introduced, illustrating the connection between real and imaginary components of optical constants. The review underscores the significance of ellipsometry as a non-destructive and versatile technique for material characterization across a wide range of applications.

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Spectroscopic ellipsometry from 10 to 700 K

Cited by 6 publications

References 62 publications

Enhancing Titania-Tantala Amorphous Materials as High-Index Layers in Bragg Reflectors of Gravitational-Wave Detectors

Enhancing Titania-Tantala Amorphous Materials as High-Index Layers in Bragg Reflectors of Gravitational-Wave Detectors

Detecting ultrathin ice on materials for optical coatings at cryogenic temperatures

Spectroscopic Ellipsometry: Advancements, Applications and Future Prospects in Optical Characterization

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