Enhanced Medium Range Order in Vapor Deposited Germania Glasses at Elevated Temperatures

TL;DR

This study demonstrates that vapor deposition at elevated temperatures enhances medium-range atomic order in Germania glasses, leading to reduced internal friction, which is crucial for designing low-noise optical coatings.

Contribution

It reveals how vapor deposition temperature influences medium-range order in GeO2 glasses and links this structural change to internal friction reduction.

Findings

Increased 6-membered GeO4 rings at higher deposition temperatures

Enhanced medium-range order correlates with lower internal friction

Deposition near the glass transition temperature is more effective than annealing

Abstract

Glasses are nonequilibrium solids with properties highly dependent on their method of preparation. In vapor-deposited molecular glasses, structural organization could be readily tuned with deposition rate and substrate temperature. Herein, we show the atomic arrangement of strong network forming GeO2 glass is modified at medium range (< 2 nm) through vapor deposition at elevated temperatures. Raman spectral signatures distinctively show the population of 6-membered GeO4 rings increases at elevated substrate temperatures. Deposition near the glass transition temperature is more efficient than post-growth 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.