Phonon Behaviour at Advanced Material Interfaces using Electron Energy Loss Spectroscopy

Recent developments in monochromators integrated into scanning transmission electron microscopes (STEM) enable the study of lattice vibrations (phonons) with nanoscale spatial resolution using electron energy loss spectroscopy (EELS). Probing phonons at this spatial resolution provides access to vibrational properties associated with structural features in which the crystal symmetry is broken. Interfaces are a structural feature of particular interest, where localized phonons arise from the interaction between different materials. This thesis presents the characterization of phonons at advanced material interfaces, relevant to technological applications in thermal management, electronics, photonics, energy harvesting, and quantum devices. Using a variety of experimental configurations, this work investigates interfacial phonons between high-temperature cuprate superconductor thin films and dielectric substrates, and between nitride semiconductor thin films. The results show the interplay between surface, bulk, and interface phonons in cuprate superconductors and reveal how these contributions influence the interpretation of vibrational spectra. The momentum transfer inherent to the inelastic scattering process in EELS was used to probe the dispersive behaviour of phonons at group III nitride interfaces, revealing anisotropic long- and short-range vibrational interactions governed by interfacial chemical gradients and fabrication-induced strain. At the nanometre length scale, surface excitations can dominate the overall response of materials and support thermal transport across interfaces and in vacuum. The interaction of evanescent excitations across nanoscale cavities formed between surfaces under thermal gradients was investigated. The measurements isolated surface interactions to understand their contribution to radiative energy transport, which coexists with conductive heat transport influenced by interface and surface phonons. Insights into scattering physics of surface phonon polaritons were also identified. Together, these studies establish experimental frameworks for the characterization of interface and surface phonons using monochromated STEM-EELS.

Department dc:contributor.department

Materials Science and Engineering

Year dc:date.issued

2026

Author dc:creator

• Reyes Gonzalez, Joaquin Eduardo

Advisor dc:contributor.advisor

• Lagos Paredes, Maureen

• electron microscopy
• electron energy loss spectroscopy
• phonons
• nanotechnology
• semiconductor
• superconductor

Language dc:language.iso

en

Identifier URI

https://doi.org/10.71548/2232

OAI record oai:identifier

https://macsphere.mcmaster.ca/server/oai/request?verb=GetRecord&metadataPrefix=dim&identifier=oai%3Amacsphere.mcmaster.ca%3A11375%2F33448