University of Wollongong: Amorphous Alumina, Josephson Junctions, and Bosons
Through the nanoscale looking glass: FLEET researchers determine boson peak frequency in ultra-thin alumina
+ Yet surprisingly, many of the fundamental properties of alumina remain unknown owing to the fact it is thermodynamically unstable at the macroscale.+ The UoW /RMIT team overcame this issue by focusing on nanoscale glasses, in the context of core-shell particles of an aluminium sphere wrapped in a thin skin of its native alumina oxide. You can picture it as an hardboiled egg, with an internal aluminium solid ‘yolk’ surrounded by a thin, external alumina shell.+ Armed with these novel (and slightly explosive) samples, they deployed neutron spectroscopy at ANSTO — one of the FLEET partner organisations — to measure the lattice vibrations in the core shell particles.
Amorphous alumina is an important glass, used in the electronics industry as a dielectric layer, and within the emerging quantum computing sector where it plays the role of the barrier in a Josephson barrier junction.
+ By studying various particle sizes, the relative ratio of the core: shell was varied to allow for the group to separate the contributions of the “yolk” aluminum and from the alumina “shell.”+ Using the small particles to enhance the surface contrast, the group revealed a THz-frequency feature for the boson peak that is in good agreement with theoretical calculations.
+ As lattice vibrations are a leading source of dissipation in electronics, the new measurements are useful to identify methods to control heat transfer through ultra-thin alumina…In a separate development, the group also found clear evidence for hydrogen in the form of H2O and hydroxyl groups whizzing around on the surface of the alumina, and reported a procedure to remove these native surface defects using a heat treatment procedure…Normally hydrogen is nearly invisible to standard techniques, but neutrons scatter ten times more strongly from hydrogen than other elements because they interact with via nuclear forces rather than electromagnetic interactions. At ultra-low temperatures, quantum tunneling of hydrogen in two level systems is a candidate to explain the source of decoherence in leading quantum computing schemes.
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