• Open Access

Boson peak in ultrathin alumina layers investigated with neutron spectroscopy

D. L. Cortie, M. J. Cyster, T. A. Ablott, C. Richardson, J. S. Smith, G. N. Iles, X. L. Wang, D. R. G. Mitchell, R. A. Mole, N. R. de Souza, D. H. Yu, and J. H. Cole
Phys. Rev. Research 2, 023320 – Published 11 June 2020

Abstract

Bulk glasses exhibit extra vibrational modes at low energies, collectively known as the boson peak. The vibrational dynamics in nanoscale alumina glasses have an impact on the performance of qubits and other superconducting devices; however, the frequency of the boson peak has not been previously measured. Here we report neutron spectroscopy experiments on Al/Al2O3 nanoparticles consisting of spherical metallic cores with a radii from 20 to 1000 nm surrounded by a 3.5-nm-thick alumina glass. A low-energy peak is observed at ωBP = 2.8 ± 0.6 meV for highly oxidized particles, indicating an excess in the density of states. The intensity of the peak scales inversely with particle size and oxide fraction, indicating a surface origin, and is redshifted by 3 meV with respect to the van Hove singularity of γ-phase Al2O3 nanocrystals. Molecular-dynamics simulations of αAl2O3, γAl2O3 and αAl2O3 show that the observed boson peak is a signature of the ultrathin glass surface and the characteristic frequency is reduced compared to the peak in the bulk glass.

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  • Received 1 August 2019
  • Accepted 30 April 2020

DOI:https://doi.org/10.1103/PhysRevResearch.2.023320

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

D. L. Cortie1,*, M. J. Cyster2, T. A. Ablott3, C. Richardson3, J. S. Smith2, G. N. Iles4, X. L. Wang1, D. R. G. Mitchell5, R. A. Mole6, N. R. de Souza6, D. H. Yu6, and J. H. Cole2,†

  • 1The Institute for Superconducting and Electronic Materials, University of Wollongong, NSW 2522, Australia
  • 2Chemical and Quantum Physics, School of Science, RMIT University, Melbourne, Victoria 3000, Australia
  • 3School of Chemistry and Molecular Bioscience, University of Wollongong, NSW 2522, Australia
  • 4Space Physics, School of Science, RMIT University, Melbourne, Victoria 3000, Australia
  • 5Electron Microscopy Centre, University of Wollongong, NSW 2522, Australia
  • 6Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW 2232, Australia

  • *dcortie@uow.edu.au
  • jared.cole@rmit.edu.au

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Vol. 2, Iss. 2 — June - August 2020

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