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Research Papers: Micro/Nanoscale Heat Transfer

Excitation of Single Phonon Modes in Nanoscale Waveguides

[+] Author and Article Information
Drew A. Cheney, Jennifer R. Lukes

Department of Mechanical Engineering and Applied Mechanics,  University of Pennsylvania, Philadelphia, PA 19104dcheney@seas.upenn.edu

J. Heat Transfer 134(4), 042403 (Feb 14, 2012) (9 pages) doi:10.1115/1.4005097 History: Received December 01, 2010; Revised August 22, 2011; Published February 14, 2012; Online February 14, 2012

We present a new computational method that excites guided phonon modes in nanoscale waveguides at a specific frequency and wavenumber. The method uses nonequilibrium molecular dynamics and Fourier analysis of particle displacements to extract mode shapes from single frequency excitations consisting of superposed spatial modes. These mode shapes are used to excite the waveguide inlet boundary so that single phonon modes are generated in the structure. Mode shapes and phonon spectra for a silicon planar waveguide with rigid wall boundaries are calculated to demonstrate the viability of the technique. This method improves upon molecular dynamics techniques that activate all possible phonon modes and are thus not able to isolate the contribution of any single phonon excitation. Application of our method will enable the computational investigation of single phonon mode propagation in nanostructures of varying geometry.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Computational geometry of planar waveguide used to excite single frequency phonons. Actual length is much larger than that shown in the figure.

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Figure 2

Schematic of relationship between rectangular grid points and equilibrium atomic positions. Dashed circle shows maximum distance within which an atom is included in the interpolation.

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Figure 3

Full x-direction dispersion relation of planar waveguide calculated using MD. The low frequency, low wavenumber regime is enlarged and shown in Fig. 4.

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Figure 4

(a) Wavenumber spectral amplitude for plate waveguide excited with randomly generated mode shapes and (b) location of spectral peaks on plate dispersion relation

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Figure 5

Idealized geometry of planar waveguide used in SPW analysis

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Figure 6

Wavenumber spectral amplitude for single mode excitations. Each line represents an individual simulation.

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Figure 7

x-component of displacement resulting from single frequency boundary excitations with random lateral mode shape and phase difference

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Figure 8

x-component of displacement of single (S1) mode extracted from Fourier analysis of randomly excited displacement field

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Figure 9

Normalized mode shapes of possible modes at 1.75 THz. Wavenumbers are divided by 2π/a.

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