0
Micro/Nanoscale Heat Transfer

Schemes for and Mechanisms of Reduction in Thermal Conductivity in Nanostructured Thermoelectrics

[+] Author and Article Information
Xiaoliang Zhang1

Laboratory of Thermodynamics in Emerging Technologies, Department of Mechanical and Process Engineering, ETH Zürich, 8092 Zürich, Switzerland

Ming Hu2

Laboratory of Thermodynamics in Emerging Technologies, Department of Mechanical and Process Engineering, ETH Zürich, 8092 Zürich, Switzerlandhum@ethz.ch

Konstantinos P. Giapis

Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA 91125giapis@cheme.caltech.edu

Dimos Poulikakos

Laboratory of Thermodynamics in Emerging Technologies, Department of Mechanical and Process Engineering, ETH Zürich, 8092 Zürich, Switzerlanddimos.poulikakos@ethz.ch

1

Permanent address: Center for Heat and Mass Transfer, Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, China; Graduate School of Chinese Academy of Sciences, Beijing 100049, China.

2

Corresponding author.

J. Heat Transfer 134(10), 102402 (Aug 07, 2012) (7 pages) doi:10.1115/1.4006750 History: Received June 22, 2011; Revised April 21, 2012; Published August 06, 2012; Online August 07, 2012

Nonequilibrium molecular dynamics (NEMD) simulations were performed to investigate schemes for enhancing the energy conversion efficiency of thermoelectric nanowires (NWs), including (1) roughening of the nanowire surface, (2) creating nanoparticle inclusions in the nanowires, and (3) coating the nanowire surface with other materials. The enhancement in energy conversion efficiency was inferred from the reduction in thermal conductivity of the nanowire, which was calculated by imposing a temperature gradient in the longitudinal direction. Compared to pristine nanowires, our simulation results show that the schemes proposed above lead to nanocomposite structures with considerably lower thermal conductivity (up to 82% reduction), implying ∼5X enhancement in the ZT coefficient. This significant effect appears to have two origins: (1) increase in phonon-boundary scattering and (2) onset of interfacial interference. The results suggest new fundamental–yet realizable ways to improve markedly the energy conversion efficiency of nanostructured thermoelectrics.

FIGURES IN THIS ARTICLE
<>
Copyright © 2012 by American Society of Mechanical Engineers
Your Session has timed out. Please sign back in to continue.

References

Figures

Grahic Jump Location
Figure 1

(Top) Side and cross-sectional view of the Si–W nanowire with 6 × 6 × 307 unit cells of Si nanowire covered by 10 W particles. Color coding: gray, Si; dark, W. (Bottom) The corresponding temperature profiles for the Si core and W particles. The solid line is a linear fit to the temperature profile of the Si core.

Grahic Jump Location
Figure 2

Thermal conductivity of 6 × 6 × 307 u.c. (167 nm long) Si core in Si–W nanowire as a function of W coverage percentage with 0% denotes pure Si NW. The right axis is the reduction percentage of the thermal conductivity of the Si core in the Si/W NW relative to that of pure Si NW, as indicated by the arrow. Filled and empty symbols are for Si–W NW with regular and random W particles, respectively.

Grahic Jump Location
Figure 3

Comparison of vibrational density of states of Si atoms on the surface of Si–W nanowire with different W coverages

Grahic Jump Location
Figure 4

Participation ratio (a) and mode weight factor (b) of each vibrational eigen-mode for Si–W nanowires with different W coverages. Color code in (b): red: Si core, blue: Si–W interface, pink: W interior.

Grahic Jump Location
Figure 5

Thermal conductivity of 9 × 9 × 302 u.c. and 16 × 16 × 302 u.c. (164 nm long) Si nanowire with Ge inclusions as a function of Ge volume percentage with 0% denotes pure Si nanowire. The right axis is the reduction percentage of the thermal conductivity of the Si nanowire with Ge inclusions relative to that of pure Si nanowire, as indicated by the arrow. Filled and open symbols are for the case of 9 × 9 × 302 u.c. and 16 × 16 × 302 u.c., respectively. (Inset) A segment of Si nanowire with Ge inclusions. Color coding: gray, Si; dark, Ge.

Grahic Jump Location
Figure 6

Thermal conductivity of Si nanowires with different types of inclusions. For all cases, the Si nanowire is 9 × 9 × 302 unit cells with nine inclusions and the radius of all inclusions is 2 Si unit cells. “m1”: pure Si nanowire; “m2”, “m4,” “m8”: atom mass in inclusions is 2, 4, and 8 times larger than normal Si, respectively; “m4x” and “m4xy”: same atom mass as “m4” but inclusions are randomly placed in x direction (also y direction for the later) to block the perfect lattice vibrations in that direction; “dia”: normal Si mass but interatomic interaction strength inside inclusions is eight times larger than normal Si (to mimic diamond inclusions); “Ge”: normal Ge inclusions; “voids”: remove atoms in inclusions.

Grahic Jump Location
Figure 7

Thermal conductivity of Si-based core–shell nanowires with different shell structures. For all cases, the Si core is 6 × 6 × 307 unit cells. Si_NW: pure Si nanowire; SiC crystal: Si–core/crystalline-SiC-shell nanowire; SiC amphs: Si-core/amorphous-SiC-shell nanowire; GaN: Si-core/GaN-shell nanowire; AlN: Si-core/AlN-shell nanowire; SiO2 amphs: Si-core/amorphous-SiO2 -shell nanowire; Si3 N4 amphs: Si-core/amorphous-Si3 N4 -shell nanowire.

Grahic Jump Location
Figure 8

Comparison of vibrational density of states of Si atoms on the surface of Si core in Si-based core-shell nanowires with different shell structures

Grahic Jump Location
Figure 9

Calculated thermal conductivity of Si-core/SiO2 -shell nanowire versus nanowire length at 300 K with comparison to that of a pure Si nanowire. The right axis is the reduction percentage of the thermal conductivity of the Si-core relative to that of the pure Si nanowire, as indicated by the arrow. The dotted lines are fitting to the MD results and the dashed lines denote the upper limit of the thermal conductivity of an infinitely long Si nanowire with same cross-sectional size.

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In