Enhanced medium-range order in vapor-deposited germania glasses at elevated temperatures

Abstract

Glasses are nonequilibrium solids with properties highly dependent on their method of preparation. In vapordeposited molecular glasses, structural organization could be readily tuned with deposition rate and substrate temperature. Here, we show that the atomic arrangement of strong network-forming GeO 2 glass is modified at medium range (<2 nm) through vapor deposition at elevated temperatures. Raman spectral signatures distinctively show that the population of six-membered GeO 4 rings increases at elevated substrate temperatures. Deposition near the glass transition temperature is more efficient than postgrowth annealing in modifying atomic structure at medium range. The enhanced medium-range organization correlates with reduction of the room temperature internal friction. Identifying the microscopic origin of room temperature internal friction in amorphous oxides is paramount to design the next-generation interference coatings for mirrors of the end test masses of gravitational wave interferometers, in which the room temperature internal friction is a main source of noise limiting their sensitivity.

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

“…All the DPOs used in this study were fabricated in a single batch and one uncoated DPO was used as a control sample. Thin films ∼500 nm in thickness of GeO 2 and Ti:GeO 2 (26% and 44% (cation ratio) Ti were deposited using ion-beam sputtering, described in detail in [6,7]. Temperature-dependent mechanical loss measurements were carried out on each of the coatings in an as-deposited (no annealing) and post-deposition annealed state at various temperatures.…”

“…Recent investigations have shown that GeO 2 -based films are one of the promising materials for room temperature GWDs, as the measured mechanical loss of undoped GeO 2 films at room temperature is significantly lower than that of any other known amorphous oxides other than SiO 2 [6,7]. Thus, a solution currently under investigation is to replace the current Ti:Ta 2 O 5 with GeO 2 -based layers.…”

“…While data are available for the temperature-dependent losses in bulk GeO 2 [17], no temperature-dependent data are available for the mechanical loss of GeO 2 thin films. In addition when GeO 2 is co-sputtered with high-index oxides as is necessary for the LIGO coating design, the mechanical loss is expected to exhibit a complex dependence on composition, as does the atomic structure of mixed films [5,7]. In order to further reduce the mechanical loss, the films are subjected to post-deposition heat treatment at temperatures below their crystallization point.…”

Phase-Change Materials, 1/f Noise, and Phase Synchrony

“…It would then be interesting to see how this shows up in the context of 1/f ficker noise, which dominates the low-frequency region. Noise is important today due to its relevance to gravitational wave detection [4], Casimir torque experiments [5], and infrasound detection [6], among others. On the technological front, noise impacts the integrity of stored data, and for multibit phase-change devices, about 80% of the noise originates from current fuctuations [7].…”

“…r being the amplitude, using equations. ( 5) and ( 6) one derives equation (4) where Kr is replaced by 2t/Z It is convenient to regard K as the interaction coupling while r(T) ∈ [0, 1] is interpreted as a measure of phase coherence or degree of synchrony. If all oscillators move in phase, then r � 1; if the phases are scattered and no recognizable rhythm prevails, r ≈ 0.…”