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Ultrafast Heat Flow in Heterostructures of Au Nanoclusters on Thin Films: Atomic Disorder Induced by Hot Electrons

Thomas Vasileiadis, Lutz Waldecker, Dawn Foster, Alessandra Da Silva, Daniela Zahn, Roman Bertoni, Richard Palmer Orcid Logo, Ralph Ernstorfer

ACS Nano, Volume: 12, Issue: 8, Pages: 7710 - 7720

Swansea University Author: Richard Palmer Orcid Logo

Abstract

We study the ultrafast structural dynamics, in response to electronic excitations, in heterostructures composed of size-selected Au nanoclusters on thin-film substrates with the use of femtosecond electron diffraction. Various forms of atomic motion, such as thermal vibrations, thermal expansion, an...

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Published in: ACS Nano
ISSN: 1936-0851 1936-086X
Published: 2018
Online Access: Check full text

URI: https://cronfa.swan.ac.uk/Record/cronfa41123
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Abstract: We study the ultrafast structural dynamics, in response to electronic excitations, in heterostructures composed of size-selected Au nanoclusters on thin-film substrates with the use of femtosecond electron diffraction. Various forms of atomic motion, such as thermal vibrations, thermal expansion, and lattice disordering, manifest as distinct and quantifiable reciprocal-space observables. In photoexcited supported nanoclusters, thermal equilibration proceeds through intrinsic heat flow between their electrons and their lattice and extrinsic heat flow between the nanoclusters and their substrate. For an in-depth understanding of this process, we have extended the two-temperature model to the case of 0D/2D heterostructures and used it to describe energy flow among the various subsystems, to quantify interfacial coupling constants and to elucidate the role of the optical and thermal substrate properties. When lattice heating of Au nanoclusters is dominated by intrinsic heat flow, a reversible disordering of atomic positions occurs, which is absent when heat is injected as hot substrate phonons. The present analysis indicates that hot electrons can distort the lattice of nanoclusters, even if the lattice temperature is below the equilibrium threshold for surface premelting. Based on simple considerations, the effect is interpreted as activation of surface diffusion due to modifications of the potential energy surface at high electronic temperatures. We discuss the implications of such a process in structural changes during surface chemical reactions.
Keywords: Au nanoclusters; diffusion; electron−lattice interactions; expansion; hot electrons; nanoscale heat flow; premelting
College: College of Engineering
Issue: 8
Start Page: 7710
End Page: 7720