Cryogenic mechanical loss of amorphous germania and titania-doped germania thin films

Abstract

The mechanical loss of amorphous thin films of germania (GeO2) and titania-doped germania (Ti:GeO2) deposited by ion-beam sputtering onto silicon double-paddle oscillators was studied from 10 K to 290 K. Undoped germania was found to show a wide cryogenic mechanical loss peak centered at ∼ 60 K with ϕ = 3.1 × 10 − 3 , which decreases to 1.1 × 10 − 3 as Ti-concentration increases to 44%. In addition to decreasing the height of this low-temperature peak, Ti-doping increases its width, and shifts its position toward lower temperatures. Annealing reduces the room temperature mechanical loss of Ti:GeO2 and increases its cryogenic mechanical loss, which is consistent with trends observed in most amorphous oxides.

Optical properties of germania and titania at 1064 nm and at 1550 nm

“…As a reduction in temperature is also a way to reduce CTN, see equation ( 1), cryogenic operation is considered for future gravitational-wave detectors such as the Einstein Telescope [30] and LIGO Voyager [31]. GeO 2 shows a low-temperature mechanical loss peak very similar to that of SiO 2 , which decreases with increasing TiO 2 content [32], making even higher TiO 2 concentrations particularly interesting for use at low temperatures. For pure TiO 2 , a drop in low temperature loss after crystallisation has been observed [33].…”