Network Topology of Hafnia-Based Amorphous Optical Coatings by Grazing-Incidence X-ray Total Scattering and Atomic Modeling

K. Prasai; B. LaBell; K. H. Lee; A. Mehta; B. Shyam; M. M. Fejer; R. Bassiri

paper

Network Topology of Hafnia-Based Amorphous Optical Coatings by Grazing-Incidence X-ray Total Scattering and Atomic Modeling

arXiv:2608.15011

Abstract

Amorphous hafnia-based films are promising optical-coating materials for cryogenic GW detectors, but their performance depends on how doping and annealing modify the atomic network. We combine grazing-incidence X-ray total scattering measurements with experimentally constrained atomic modeling to study the as-deposited HfO $_{2}$ and 27% SiO $_{2}$ -doped HfO $_{2}$ films annealed at 150 $^{\circ}$ C and 400 $^{\circ}$ C. Pure amorphous HfO $_{2}$ is a dense, high-coordination network of Hf-centered polyhedra with substantial edge- and face-sharing connectivity. Incorporating SiO $_{2}$ introduces stable SiO $_{4}$ tetrahedra, lowers the Hf and O coordination, and replaces highly connected Hf-rich oxygen environments with mixed Si--O--Hf bridges. This produces a chemically mixed network rather than isolated SiO $_{2}$ -rich regions, and shifts the cation topology toward corner-sharing connectivity. Annealing to 400 $^{\circ}$ C produces only modest additional structural relaxation. These results provide an atomic-scale description of how SiO $_{2}$ modifies the topology of amorphous HfO $_{2}$ -based coatings and suggest structural descriptors relevant to understanding their mechanical-loss behavior.