Theoretical Phonon Thermal Conductivity of Si/Ge Superlattice Nanowires

2003 ◽  
Author(s):  
Chris Dames ◽  
Gang Chen
Keyword(s):  
Thermal Conductivity ◽  
Radiative Heat ◽  
Interface Condition ◽  
Segment Length ◽  
Phonon Thermal Conductivity ◽  
Quantum Confinement Effects ◽  
Frequency Independent ◽  
Side Walls ◽  
The Common ◽  
20 Nm

The net-radiation method of radiative heat transfer has been combined with the diffuse mismatch interface condition to develop a model for the phonon thermal conductivity of superlattice nanowires. The important size effect is increased classical scattering at interfaces and side walls, which is treated as diffuse and gray (frequency independent). Coherence and quantum confinement effects are neglected, which should be appropriate for typical nanowires at room temperature. An isotropic, sine-type dispersion relation is used which is a significant improvement over the common Debye dispersion. Without any adjustable parameters, the model captures the effects of diameter, segment length, and transmissivity. A simpler picture is offered in terms of Matthiessen’s rule and effective mean free paths. The limitations of the model are also discussed. For a model Si/Ge superlattice nanowire at 300 K, the thermal conductivity is reduced below the alloy limit (7.0 W/m-K) when the diameter is less than 15 nm and/or the segment length is less than 20 nm.

Thermal Conductivity and Specific Heat Measurements of Single Nanowires

2005 ◽  
Author(s):  
Chris Dames ◽  
Gang Chen
Keyword(s):  
Thermal Conductivity ◽  
Specific Heat ◽  
Bulk Material ◽  
Si Nanowires ◽  
Quantum Confinement Effects ◽  
Single Nanowires ◽  
Effective Use ◽  
20 Nm ◽  
Theory And Experiments ◽  
Good Agreement

For the effective use of nanowires and nanotubes in their many possible applications in sensing, computation and memory, optoelectronics, and energy conversion, it is important to understand their thermal properties, which may differ considerably from bulk [1]. For example, there is good agreement between theory and experiments on Si nanowires showing that the classical size effect of phonon boundary scattering may reduce the thermal conductivity by up to several orders of magnitude for diameters of 40 nm and up [2, 3, 12, 13]. However, more experiments are needed at 20 nm and smaller diameters. There is also a need for experiments on the specific heat of single nanowires, which is intimately related to thermal conductivity by kinetic theory, and may be altered by quantum confinement effects. We have previously measured the specific heat of a pellet of TiO2 nanotubes of ∼3 nm wall thickness and found it similar to the bulk material at temperatures above ∼80 K [4]; however, questions remain about the possible interactions between adjacent tubes, which single-tube studies would resolve.

scholarly journals Lattice vibrational modes and phonon thermal conductivity of single-layer GaGeTe

2020 ◽  
Vol 6 (4) ◽  
pp. 723-728
Author(s):  
Jingyu Li ◽  
Peng-Fei Liu ◽  
Chi Zhang ◽  
Xiaobo Shi ◽  
Shujuan Jiang ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Single Layer ◽  
Vibrational Modes ◽  
Phonon Thermal Conductivity

Sensitivity of Thermal Conductivity of Carbon Nanotubes to Defect Concentrations and Heat-Treatment

2012 ◽  
Author(s):  
Michael F. P. Bifano ◽  
Jungkyu Park ◽  
Vikas Prakash
Keyword(s):  
Thermal Conductivity ◽  
Heat Treatment ◽  
Interatomic Potential ◽  
Side Wall ◽  
Chemical Vapor ◽  
Md Simulations ◽  
Heat Treated ◽  
Side Walls ◽  
Non Equilibrium Molecular Dynamics ◽  
Vacancy Concentrations

In the present study, classical MD simulations using reverse non-equilibrium molecular dynamics with the AIREBO interatomic potential are used to investigate the sensitivity of thermal conductivity in SWCNTs to side-wall defect concentration and heat-treatment. Two types of defects are investigated. First, the thermal conductivity of (6,6) SWCNTs is obtained as a function of concentration of chemisorbed hydrogen adatoms. Secondly, the thermal conductivity is obtained as a function of point-vacancy concentrations. The results of the studies show that 2 atom% of hydrogenation and 1.5–2% vacancy concentrations have very similar detrimental effects on the thermal conductivity of SWCNT. Vacancy repair is evident with heat treatment, and heat-treatments at 3000°C for up to 22 ns are found to transform point vacancies into various types of non-hexagonal side-wall defects; this vacancy repair is accompanied by a ca. 10% increase in thermal conductivity. Thermal conductivity measurements in both heat-treated and non-heat treated chemical vapor deposition grown MWCNTs are also reviewed. The results suggest that CNT thermal conductivity can be drastically increased if measures are taken to remove common defects from the SWCNT side-walls.

Evaluation of Thermal Characterization Techniques and Tools for Thermal Conductivity Measurement of Sub 100 Angstrom Thick Silicon Layers

2007 ◽  
Author(s):  
Keivan Etessam-Yazdani ◽  
Mehdi Asheghi
Keyword(s):  
Thermal Conductivity ◽  
Conductivity Measurement ◽  
Thermal Characterization ◽  
Phonon Transport ◽  
Thermal Conductivity Measurement ◽  
Great Success ◽  
Silicon Structures ◽  
Thin Silicon ◽  
20 Nm

Experimental measurement of thermal conductivity is considered the most reliable tool for the study of phonon transport in ultra-thin silicon structures. While there has been a great success in thermal conductivity measurement of ultra-thin silicon layers down to 20 nm over the past decade, it is not clear if the existing techniques and tools can be extended to the measurements of sun 100 Angstrom layers. In this paper, an analytical study of the feasibility of electrical Joule heating and thermometry in patterned metal bridges is presented. It is concluded that thermal conductivity of silicon layers as thin as 5 nm can be obtained (uncertainty 20%) by performing steady-state measurements using an on-substrate nanoheater structure. The thermal characterization of silicon layers as thin as 1 nm may be possible using frequency domain measurements.

scholarly journals Synthesis of polymer-grafted gold nanoparticles via gamma radiation

Polimery ◽  
2021 ◽  
Vol 66 (11-12) ◽  
pp. 584-588
Author(s):  
Abdul Khaliq Mokhtar ◽  
Norsyahidah Mohd Hidzir ◽  
Irman Abdul Rahman ◽  
Faizal Mohamed ◽  
Nur Ain Mohd Radzali
Keyword(s):  
Gold Nanoparticles ◽  
Gamma Radiation ◽  
Nanoparticle Size ◽  
Absorbed Doses ◽  
The Common ◽  
20 Nm ◽  
Higher Doses

The research focused on the synthesis of poly(tetrafluoroethylene) (PTFE) grafted with gold nanoparticles (AuNP). The Turkevich method, one of the common techniques of AuNP synthesis, was used to obtain an AuNP solution with a nanoparticle size of 20 nm. The PTFE-AuNP samples were subsequently irradiated and the absorbed doses were 0.5, 2, 5, 10 and 20 kGy. It was noticed that samples irradiated with 0.5 and 2 kGy were less stable and less concentrated than samples irradiated with higher doses due to aggregation and formation of precipitation after 30 days.

scholarly journals Experimental determination of phonon thermal conductivity and Lorenz ratio of single-crystal bismuth telluride

2017 ◽  
Vol 7 (4) ◽  
pp. 922-927 ◽  
Author(s):  
Mengliang Yao ◽  
Cyril Opeil ◽  
Stephen Wilson ◽  
Mona Zebarjadi
Keyword(s):  
Thermal Conductivity ◽  
Single Crystal ◽  
Experimental Determination ◽  
Bismuth Telluride ◽  
Phonon Thermal Conductivity ◽  
Image Position

Abstract

scholarly journals Change in Conductive–Radiative Heat Transfer Mechanism Forced by Graphite Microfiller in Expanded Polystyrene Thermal Insulation—Experimental and Simulated Investigations

Materials ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2626
Author(s):  
Aurelia Blazejczyk ◽  
Cezariusz Jastrzebski ◽  
Michał Wierzbicki
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Thermal Resistance ◽  
Thermal Insulation ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Expanded Polystyrene ◽  
Transfer Mechanism ◽  
Total Thermal Conductivity ◽  
Heat Transfer Mechanism

This article introduces an innovative approach to the investigation of the conductive–radiative heat transfer mechanism in expanded polystyrene (EPS) thermal insulation at negligible convection. Closed-cell EPS foam (bulk density 14–17 kg·m−3) in the form of panels (of thickness 0.02–0.18 m) was tested with 1–15 µm graphite microparticles (GMP) at two different industrial concentrations (up to 4.3% of the EPS mass). A heat flow meter (HFM) was found to be precise enough to observe all thermal effects under study: the dependence of the total thermal conductivity on thickness, density, and GMP content, as well as the thermal resistance relative gain. An alternative explanation of the total thermal conductivity “thickness effect” is proposed. The conductive–radiative components of the total thermal conductivity were separated, by comparing measured (with and without Al-foil) and simulated (i.e., calculated based on data reported in the literature) results. This helps to elucidate why a small addition of GMP (below 4.3%) forces such an evident drop in total thermal conductivity, down to 0.03 W·m−1·K−1. As proposed, a physical cause is related to the change in mechanism of the heat transfer by conduction and radiation. The main accomplishment is discovering that the change forced by GMP in the polymer matrix thermal conduction may dominate the radiation change. Hence, the matrix conduction component change is considered to be the major cause of the observed drop in total thermal conductivity of EPS insulation. At the microscopic level of the molecules or chains (e.g., in polymers), significant differences observed in the intensity of Raman spectra and in the glass transition temperature increase on differential scanning calorimetry(DSC) thermograms, when comparing EPS foam with and without GMP, complementarily support the above statement. An additional practical achievement is finding the maximum thickness at which one may reduce the “grey” EPS insulating layer, with respect to “dotted” EPS at a required level of thermal resistance. In the case of the thickest (0.30 m) panels for a passive building, above 18% of thickness reduction is found to be possible.

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