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Research Papers

Effects of Surface Stress on the Phonon Properties in GaN Nanofilms

[+] Author and Article Information
Haonan Luo

Department of Engineering Mechanics,
School of Aeronautics and Astronautics,
Zhejiang University,
Hangzhou, Zhejiang 310027, China

Linli Zhu

Department of Engineering Mechanics,
School of Aeronautics and Astronautics,
Zhejiang University,
Hangzhou, Zhejiang 310027, China
e-mail: llzhu@zju.edu.cn

1Corresponding author.

Contributed by the Applied Mechanics Division of ASME for publication in the JOURNAL OF APPLIED MECHANICS. Manuscript received May 11, 2015; final manuscript received July 23, 2015; published online August 10, 2015. Assoc. Editor: Daining Fang.

J. Appl. Mech 82(11), 111002 (Aug 10, 2015) (7 pages) Paper No: JAM-15-1239; doi: 10.1115/1.4031150 History: Received May 11, 2015

This work investigates the phonon properties such as phonon dispersion relation, average group velocity, and phonon density of state (DOS) theoretically in GaN nanofilm under various surface stress fields. By taking into account of the surface energy effects, the elasticity theory is presented to describe the confined phonons of nanofilms with different surface stresses. The calculation results show that the influence of surface stress on the phonon properties depends on the thickness of nanofilm. The negative surface stress leads to a higher average group velocity and corresponding lower phonon DOS. The positive surface stress has the opposite effect. The significant modification of thermal properties, e.g., phonon thermal conductivity, in GaN nanofilms is mostly stemmed from the change of phonon average group velocity and DOS by surface stress. These results suggest that the thermal or electrical properties in GaN nanofilms could be enhanced or reduced by tuning the surface stress acting on the films.

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Figures

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Fig. 3

Phonon average group velocity of SH mode (a), (c), (e) and SA and AS mode (b), (d), (f) as the function of the phonon energy with the positive surface stress, natural state, and the negative surface stress

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Fig. 5

Phonon thermal conductivity of GaN nanofilm varied with the surface stress for different thickness. κ0 is the bulk thermal conductivity.

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Fig. 1

Schematic drawings of a GaN nanofilm in which heat flow is along to x1 direction

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Fig. 2

Phonon dispersion relations for the SH polarization (a), (c), (e) and for SA and AS polarization (b), (d), (f) in GaN film under different surface stress

Grahic Jump Location
Fig. 4

Phonon DOS of SH mode (a), (c), (e) and SA and AS mode (b), (d), (f) as the function of the phonon energy with the positive surface stress, natural state, and the negative surface stress

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