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Second Thermal and Fluids Engineering  Conference

ISSN: 2379-1748
ISBN: 978-1-56700-430-4

THERMAL CONDUCTIVITY OF SINGLE AND DOUBLE SILICON NANORIBBONS




Abstract

We report on the thermal conductivities of individual single and double silicon nanoribbons of different dimensions to explore the effects of free surfaces and van der Waals interfaces on thermal transport. The thermal conductivities were measured along the in-plane direction using a micro-thermal bridge method. Results show that while the data for ~30 nm thick ribbons can be well explained by the classical size effect, i.e., phonon-boundary scattering, the measured thermal conductivities for the ~20 nm thick ribbons deviate from the prediction remarkably, and size effects beyond phonon-boundary scattering must be considered. Measurements of the Young's modulus of the ribbons yield significantly lower values than the corresponding bulk value, which could lead to reduced phonon group velocity, and subsequently lower thermal conductivity. For silicon double ribbons formed with two identical ribbons stuck together via van der Waals interfaces, the measured thermal conductivity is higher than that of single ribbons of the same dimension as each of the ribbon in the double ribbon sample. This result confirms that even for an interface of weak van der Waals interactions, a significant portion of phonons transmit ballistically through the interface without being diffusely scattered. By exposing the hydrofluoric acid etched double ribbon stack in the ambient environment, an oxide layer can grow at the interface over an extended storage time. In this case, the measured thermal conductivity shows a continuously decreasing trend with the storage time, and eventually becomes the same as that of a single ribbon.

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