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Title: Mechanisms of nonequilibrium electron-phonon coupling and thermal conductance at interfaces

We study the electron and phonon thermal coupling mechanisms at interfaces between gold films with and without Ti adhesion layers on various substrates via pump-probe time-domain thermoreflectance. The coupling between the electronic and the vibrational states is increased by more than a factor of five with the inclusion of an ∼3 nm Ti adhesion layer between the Au film and the non-metal substrate. Furthermore, we show an increase in the rate of relaxation of the electron system with increasing electron and lattice temperatures induced by the laser power and attribute this to enhanced electron-electron scattering, a transport channel that becomes more pronounced with increased electron temperatures. The inclusion of the Ti layer also results in a linear dependence of the electron-phonon relaxation rate with temperature, which we attribute to the coupling of electrons at and near the Ti/substrate interface. This enhanced electron-phonon coupling due to electron-interface scattering is shown to have negligible influence on the Kapitza conductances between the Au/Ti and the substrates at longer time scales when the electrons and phonons in the metal have equilibrated. These results suggest that only during highly nonequilibrium conditions between the electrons and phonons (T{sub e} ≫ T{sub p}) does electron-phonon scattering at anmore » interface contribute to thermal boundary conductance.« less
Authors:
; ; ; ;  [1] ;  [2] ; ;  [3]
  1. Department of Mechanical and Aerospace Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States)
  2. Department of Mechanical Engineering, United States Naval Academy, Annapolis, Maryland 21401 (United States)
  3. Sandia National Laboratories, Albuquerque, New Mexico 87123 (United States)
Publication Date:
OSTI Identifier:
22399269
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 117; Journal Issue: 10; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ADHESION; ELECTRON TEMPERATURE; ELECTRON-PHONON COUPLING; ELECTRONS; GOLD; INTERFACES; LAYERS; NONMETALS; PHONONS; RELAXATION; SCATTERING; SUBSTRATES; THERMAL CONDUCTIVITY; THIN FILMS; TITANIUM; VIBRATIONAL STATES