Tantalum oxide and silicon oxide mixture coatings deposited using microwave plasma assisted co-sputtering for optical mirror coatings in gravitational wave detectors

Abstract

This work presents the characterization of the optical and mechanical properties of thin films based on ( T a 2 O 5 ) 1 − x ( S i O 2 ) x mixed oxides deposited by microwave plasma assisted co-sputtering, including post-annealing treatments. The deposition of low mechanical loss materials ( 3 × 10 − 5 ) with a high refractive index (1.93) while maintaining low processing costs was achieved and the following trends were demonstrated: The energy band gap increased as the S i O 2 concentration was increased in the mixture, and the disorder constant decreased when the annealing temperatures increased. Annealing of the mixtures also showed positive effects to reduce the mechanical losses and the optical absorption. This demonstrates their potential as an alternative high-index material for optical coatings in gravitational wave detectors using a low-cost process.

Design of filament-type auxiliary ion source and study on its improvement of thin film parameters

“…Comparing the oxide films of silicon and tantalum, it can be found that the improvement effect of ion source on the density of 𝑆𝑖𝑂 2 film is not as obvious as that of 𝑇𝑎 2 𝑂 5 film, which may be due to the difference in the microstructure of the two films, resulting in the different degree of influence of ion beam on the surface structure of the film. In addition, under the same process conditions, it is more difficult for silicon to react with oxygen [10] , so increasing the inlet flow rate of oxygen may significantly improve the densification of 𝑆𝑖𝑂 2 film. Due to the limited experimental conditions, this conjusion could not be verified.…”

Microwave plasma assisted sputtering of a combined Ta2O5/SiO2 and a-Si:H/SiO2 two stack optical coating design concept for gravitational wave detectors

“…[9], [10] From the fluctuation-dissipation theorem, coating thermal noise (CTN) arises from the internal friction in the coating and substrate, and the thermoelastic loss between the coating and substrate. [11][12] There are several approaches being investigated to reduce CTN whilst matching or improving the optical properties of the current coating including crystalline coatings [13][14], nano-layer coating [15], alternative deposition methods [16], [17], heat treatments, [18] and alternative coating materials. [19] [20] A promising candidate for an alternative high index material is amorphous silicon (a-Si), due to its low mechanical loss at room temperature which can be further decreased at cryogenic temperatures.…”

“…The advantages of this deposition technique are the high degree of control over the deposition parameters, low cost, high deposition rate and good reproducibility. [28], [29]…”