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Ballistic-phonon heat conduction at the nanoscale as revealed by time-resolved x-ray diffraction and time-domain thermoreflectance

2007; American Physical Society; Volume: 76; Issue: 7 Linguagem: Inglês

10.1103/physrevb.76.075337

1550-235X

Matthew J. Highland, Bryan C. Gundrum, Yee Kan Koh, R. S. Averback, David G. Cahill, V.C. Elarde, J. J. Coleman, Donald A. Walko, Eric C. Landahl,

Heat Transfer and Optimization

We use time-resolved measurements of the evolution of surface and buried layer temperatures to quantify the contribution of ballistic phonons to heat transport on nanometer length scales. A laser pulse heats a $100\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ thick Al film which cools by conduction into a GaAs substrate. The top $120--250\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ of the GaAs substrate is doped with In to create a buried layer with a distinct lattice constant. The cooling of the Al film is monitored by time-domain thermoreflectance and, in the second set of experiments, the heating and cooling of the GaAs:In buried layer are monitored by time-resolved x-ray diffraction. The combination of these data shows that thermal transport by ballistic phonons accounts for nearly 20% of the heat flow across the buried layer on nanosecond time scales.