Journal
ULTRASONICS
Volume 56, Issue -, Pages 116-121Publisher
ELSEVIER
DOI: 10.1016/j.ultras.2014.02.016
Keywords
Silicon membranes; Thickness resonances; Phonon lifetime; Surface specularity; Q-factor
Funding
- S3TEC Energy Frontier Research Center - US. Department of Energy, Office of Basic Energy Sciences [DE-SC0001299/DE-FG02-09ER46577]
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Femtosecond laser pulses are used to excite and probe high-order longitudinal thickness resonances at a frequency of similar to 270 GHz in suspended Si membranes with thickness ranging from 0.4 to 15 mu m. The measured acoustic lifetime scales linearly with the membrane thickness and is shown to be controlled by the surface specularity which correlates with roughness characterized by atomic force microscopy. Observed Q-factor values up to 2400 at room temperature result from the existence of a local maximum of the material Q in the sub-THz range. However, surface specularity would need to be improved over measured values of similar to 0.5 in order to achieve high Q values in nanoscale devices. The results support the validity of the diffuse boundary scattering model in analyzing thermal transport in thin Si membranes. (C) 2014 Elsevier B.V. All rights reserved.
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