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Direct Measurement of Room-Temperature Nondiffusive Thermal Transport Over Micron Distances in a Silicon Membrane

Authors
Journal
Physical Review Letters
0031-9007
Publisher
American Physical Society
Publication Date
Volume
110
Issue
2
Identifiers
DOI: 10.1103/physrevlett.110.025901

Abstract

The ‘‘textbook’’ phonon mean free path of heat carrying phonons in silicon at room temperature is 40 nm. However, a large contribution to the thermal conductivity comes from low-frequency phonons with much longer mean free paths. We present a simple experiment demonstrating that room-temperature thermal transport in Si significantly deviates from the diffusion model already at micron distances. Absorption of crossed laser pulses in a freestanding silicon membrane sets up a sinusoidal temperature profile that is monitored via diffraction of a probe laser beam. By changing the period of the thermal grating we vary the heat transport distance within the range 1–10 m. At small distances, we observe a reduction in the effective thermal conductivity indicating a transition from the diffusive to the ballistic transport regime for the low-frequency part of the phonon spectrum.

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