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The best nanoparticle size distribution for minimum thermal conductivity.

Zhang H, Minnich AJ - Sci Rep (2015)

Bottom Line: Nanoparticles have long been demonstrated to reduce the thermal conductivity of crystals by scattering phonons, but most previous works assumed the nanoparticles to have a single size.Here, we use optimization methods to show that the best nanoparticle size distribution to scatter the broad thermal phonon spectrum is not a similarly broad distribution but rather several discrete peaks at well-chosen nanoparticle radii.For SiGe, the best size distribution yields a thermal conductivity below that of amorphous silicon.

View Article: PubMed Central - PubMed

Affiliation: Division of Engineering and Applied Science California Institute of Technology Pasadena,CA 91125.

ABSTRACT
Which sizes of nanoparticles embedded in a crystalline solid yield the lowest thermal conductivity? Nanoparticles have long been demonstrated to reduce the thermal conductivity of crystals by scattering phonons, but most previous works assumed the nanoparticles to have a single size. Here, we use optimization methods to show that the best nanoparticle size distribution to scatter the broad thermal phonon spectrum is not a similarly broad distribution but rather several discrete peaks at well-chosen nanoparticle radii. For SiGe, the best size distribution yields a thermal conductivity below that of amorphous silicon. Further, we demonstrate that a simplified distribution yields nearly the same low thermal conductivity and can be readily fabricated. Our work provides important insights into how to manipulate the full spectrum of phonons and will guide the design of more efficient thermoelectric materials.

No MeSH data available.


Normalized optimized size distribution of nanoparticles for various Ge concentrations in bulk Si based on the DFT dispersion: for total Ge volumetric percentage of (a) Ge% = 0.1%, (b)Ge% = 12.2%, (c) Ge% = 50.8%.Heights of histogram bars indicate fraction of Ge allocated to each nanoparticle size. The best distribution introduces additional non-adjacent peaks as more Ge is added. Red histogram bars indicate point defects.
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f2: Normalized optimized size distribution of nanoparticles for various Ge concentrations in bulk Si based on the DFT dispersion: for total Ge volumetric percentage of (a) Ge% = 0.1%, (b)Ge% = 12.2%, (c) Ge% = 50.8%.Heights of histogram bars indicate fraction of Ge allocated to each nanoparticle size. The best distribution introduces additional non-adjacent peaks as more Ge is added. Red histogram bars indicate point defects.

Mentions: To gain further insight, we calculate the best distribution for several different volumetric percentages of Ge, shown in Figure 2. We observe additional peaks to appear in the optimal distribution with increasing Ge concentration, and further that these peaks do not form adjacent to each other but with some separation.


The best nanoparticle size distribution for minimum thermal conductivity.

Zhang H, Minnich AJ - Sci Rep (2015)

Normalized optimized size distribution of nanoparticles for various Ge concentrations in bulk Si based on the DFT dispersion: for total Ge volumetric percentage of (a) Ge% = 0.1%, (b)Ge% = 12.2%, (c) Ge% = 50.8%.Heights of histogram bars indicate fraction of Ge allocated to each nanoparticle size. The best distribution introduces additional non-adjacent peaks as more Ge is added. Red histogram bars indicate point defects.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4355732&req=5

f2: Normalized optimized size distribution of nanoparticles for various Ge concentrations in bulk Si based on the DFT dispersion: for total Ge volumetric percentage of (a) Ge% = 0.1%, (b)Ge% = 12.2%, (c) Ge% = 50.8%.Heights of histogram bars indicate fraction of Ge allocated to each nanoparticle size. The best distribution introduces additional non-adjacent peaks as more Ge is added. Red histogram bars indicate point defects.
Mentions: To gain further insight, we calculate the best distribution for several different volumetric percentages of Ge, shown in Figure 2. We observe additional peaks to appear in the optimal distribution with increasing Ge concentration, and further that these peaks do not form adjacent to each other but with some separation.

Bottom Line: Nanoparticles have long been demonstrated to reduce the thermal conductivity of crystals by scattering phonons, but most previous works assumed the nanoparticles to have a single size.Here, we use optimization methods to show that the best nanoparticle size distribution to scatter the broad thermal phonon spectrum is not a similarly broad distribution but rather several discrete peaks at well-chosen nanoparticle radii.For SiGe, the best size distribution yields a thermal conductivity below that of amorphous silicon.

View Article: PubMed Central - PubMed

Affiliation: Division of Engineering and Applied Science California Institute of Technology Pasadena,CA 91125.

ABSTRACT
Which sizes of nanoparticles embedded in a crystalline solid yield the lowest thermal conductivity? Nanoparticles have long been demonstrated to reduce the thermal conductivity of crystals by scattering phonons, but most previous works assumed the nanoparticles to have a single size. Here, we use optimization methods to show that the best nanoparticle size distribution to scatter the broad thermal phonon spectrum is not a similarly broad distribution but rather several discrete peaks at well-chosen nanoparticle radii. For SiGe, the best size distribution yields a thermal conductivity below that of amorphous silicon. Further, we demonstrate that a simplified distribution yields nearly the same low thermal conductivity and can be readily fabricated. Our work provides important insights into how to manipulate the full spectrum of phonons and will guide the design of more efficient thermoelectric materials.

No MeSH data available.