Fundamental insight into control of thermal conductivity in silicon-germanium alloy nanowires

2014 ◽  
Vol 1707 ◽  
Author(s):  
Yongjin Lee ◽  
Gyeong S. Hwang
Keyword(s):  
Thermal Conductivity ◽  
Silicon Germanium ◽  
Nonequilibrium Molecular Dynamics ◽  
Boundary Scattering ◽  
Alloy Scattering ◽  
Scattering Effect ◽  
Germanium Alloy ◽  
Alloy Nanowires ◽  
Fundamental Insight ◽  
Insight Into

ABSTRACTWe present a computational analysis of thermal transport in Silicon-Germanium alloy nanowires (SiGeNWs), particularly focusing on the relative roles of alloy scattering and boundary scattering to the significant reduction of thermal conductivity (κ). Our nonequilibrium molecular dynamics (NEMD) simulations confirm the strong dependence of κ on Si:Ge ratio, as observed in previous experimental studies. Interestingly, as the amount of impurity increases, the difference in κ between SiGe bulk and SiGeNW becomes smaller. Especially, κSiGeNW and κSiGe have similar κ values when the Ge content is 20-80 %. From a nonequilibrium Green’s function (NEGF)-density functional theory (DFT) analysis, it is suggested that the most reduction in transmission channels is attributed to the strong alloy scattering effect for both Si0.8Ge0.2 bulk and Si0.8Ge0.2 NW. The boundary scattering effect in the SiGe alloy system seems to be unimportant as alloy scattering is dominant. The improved understanding provides fundamental insight into how to modify Si-based materials to enhance their thermoelectric (TE) properties through nanostructuring and alloying.

Thermal Conductivity of One-Dimensional Silicon-Germanium Alloy Nanowires

2009 ◽  
Author(s):  
Yunki Gwak ◽  
Vinay Narayanunni ◽  
Sang-Won Jee ◽  
Anastassios A. Mavrokefalos ◽  
Michael T. Pettes ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Energy Conversion ◽  
Silicon Germanium ◽  
Figure Of Merit ◽  
Mean Free Path ◽  
Thermoelectric Efficiency ◽  
One Dimensional ◽  
Thermoelectric Energy ◽  
Germanium Alloy ◽  
Alloy Nanowires

Thermal properties of one dimensional nanostructures are of interest for thermoelectric energy conversion. Thermoelectric efficiency is related to non dimensional thermoelectric figure of merit, ZT = (S^2 σT)/k where S, σ, k are the Seebeck coefficient, electrical conductivity and thermal conductivity respectively. These physical properties are interdependent, and hence making ZT of a material high is very challenging work. However, when the size of nanostructure is comparable to the wavelength and mean free path of energy carriers, it is feasible to avoid such interdependence to enhance ZT energy conversion. [1–3]

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

2012 ◽  
Vol 134 (10) ◽  
Author(s):  
Xiaoliang Zhang ◽  
Ming Hu ◽  
Konstantinos P. Giapis ◽  
Dimos Poulikakos
Keyword(s):  
Thermal Conductivity ◽  
Energy Conversion ◽  
Conversion Efficiency ◽  
Longitudinal Direction ◽  
Energy Conversion Efficiency ◽  
Nonequilibrium Molecular Dynamics ◽  
Boundary Scattering ◽  
Nanowire Surface ◽  
Simulation Results ◽  
Nanocomposite Structures

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.

scholarly journals Experimental Investigation of Size Effects on the Thermal Conductivity of Silicon-Germanium Alloy Thin Films

2012 ◽  
Vol 109 (19) ◽  
Author(s):  
Ramez Cheaito ◽  
John C. Duda ◽  
Thomas E. Beechem ◽  
Khalid Hattar ◽  
Jon F. Ihlefeld ◽  
...  
Keyword(s):  
Thin Films ◽  
Thermal Conductivity ◽  
Experimental Investigation ◽  
Silicon Germanium ◽  
Size Effects ◽  
Germanium Alloy

Phonon boundary scattering effect on thermal conductivity of thin films

2011 ◽  
Vol 110 (4) ◽  
pp. 046102 ◽  
Author(s):  
G. H. Tang ◽  
Y. Zhao ◽  
G. X. Zhai ◽  
C. Bi
Keyword(s):  
Thin Films ◽  
Thermal Conductivity ◽  
Boundary Scattering ◽  
Scattering Effect ◽  
Conductivity Of Thin Films

scholarly journals Molecular Dynamics Modeling of Thermal Conductivity of Silicon/Germanium Nanowires

2019 ◽  
Vol 19 (3) ◽  
pp. 222-225
Author(s):  
A. Kishkar ◽  
V. Kurylyuk
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Silicon Germanium ◽  
Nonequilibrium Molecular Dynamics ◽  
Dynamics Modeling ◽  
Si Nanowires ◽  
Germanium Nanowires ◽  
Molecular Dynamics Modeling ◽  
Phonon Spectra ◽  
Dynamics Method

The thermal conductivity of silicon/germanium nanowires with different geometry and composition has beenstudied by using the nonequilibrium molecular dynamics method. The thermal conductivity of the Si1-xGexnanowire is shown to firstly decrease, reaches a minimum at x=0.4 and then to increase, as the germaniumcontent x grows. It was found that in the tubular Si nanowires the thermal conductivity decreases monotonouslywith increasing radius of the cylindrical void. The phonon spectra were calculated and the mechanisms of phononscattering in the investigated nanowires were analyzed.

scholarly journals Molecular Dynamics Simulations of the Thermal Conductivity of Silicon-Germanium and Silicon-Germanium-Tin Alloys

2021 ◽  
Vol 2021 ◽  
pp. 1-7
Author(s):  
Zan Wang ◽  
X. Y. Cai ◽  
W. K. Zhao ◽  
H. Wang ◽  
Y. W. Ruan
Keyword(s):  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Silicon Germanium ◽  
Nonequilibrium Molecular Dynamics ◽  
Tin Alloys ◽  
Penetration Distance ◽  
Germanium Tin ◽  
Dynamics Simulations ◽  
Thermal Conductivities

In this work, we investigate the thermal conductivity properties of Si 1 − x Ge x and Si 0.8 Ge 0 Sn 2 y alloys. The equilibrium molecular dynamics (EMD) is employed to calculate the thermal conductivities of Si 1 − x Ge x alloys when x is different at temperatures ranging from 100 K to 1100 K. Then nonequilibrium molecular dynamics (NEMD) is used to study the relationships between y and the thermal conductivities of Si 0.8 Ge 0.2 Sn 2 y alloys. In this paper, Ge atoms are randomly doped, and tin atoms are doped in three distributing ways: random doping, complete doping, and bridge doping. The results show that the thermal conductivities of Si 1 − x Ge x alloys decrease first, then increase with the rise of x , and reach the lowest value when x changes from 0.4 to 0.5. No matter what the value of x is, the thermal conductivities of Si 1 − x Ge x alloys decrease with the increase of temperature. Thermal conductivities of Si 0.8 Ge 0.2 alloys can be significantly inhibited by doping an appropriate number of Sn atoms. For the random doping model, thermal conductivities of Si 0.8 Ge 0.2 Sn y alloys approach the lowest level when y is 0.10. Whether it is complete doping or bridge doping, thermal conductivities decrease with the increase of the number of doped layers. In addition, in the bridge doping model, both the number of Sn atoms in the [001] direction and the penetration distance of Sn atoms strongly influence thermal conductivities. The thermal conductivities of Si 0.8 Ge 0.2 Sn y alloys are positively associated with the number of Sn atoms in the [001] direction and the penetration distance of Sn atoms.

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