Length Dependent Thermal Conductivity Measurements Yield Phonon Mean Free Path Spectra in Nanostructures

Zhang, Hang; Hua, Chengyun; Ding, Ding; Minnich, Austin J.

doi:10.1038/srep09121

Cited by 58 publications

(51 citation statements)

References 45 publications

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“…The length of our system is shorter than the maximum phonon mean free path (PMFP) that has been predicted for Si–Ge nanowires with Monte Carlo simulations. The PMFP in Si–Ge nanowires span the range up to several micrometers (). Therefore, the contribution of long mean free path phonons is neglected in our setup and accordingly, the thermal conductivity is underestimated.…”

Section: Resultsmentioning

confidence: 99%

Molecular dynamics simulations of thermal transport in isotopically modulated semiconductor nanostructures

Frieling

Eon

Wolf

et al. 2016

Physica Status Solidi (a)

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In this paper, we investigate the effect of isotopic modulation on the thermal conductivity of semiconductor nanostructures. The isotope doping is of particular interest for the application of semiconductors as thermoelectric materials as it leaves the electronic properties practically unaffected while the phononic transport is retarded. This approach could increase the figure of merit of thermoelectric generators by decreasing the thermal conductivity of semiconductors. We use non‐equilibrium molecular dynamics simulations to examine thermal transport in isotopically engineered semiconductors. The temperature profiles along the sample region deduced from the simulations allow the extraction of thermal conductivities. The reliability of the MD‐predicted thermal conductivities is studied by analyzing the influence of the input parameters on the results. The first set of samples are isotopically modified silicon samples. The influence of temperature, isotopic composition, and ordering of isotopic defects on the thermal conductivity of silicon is studied. The second material system under investigation is silicon germanium alloys. The influence of isotopic modulation on the thermal conductivity of Si–Ge alloys is examined for varying chemical composition. The thermal conductivities predicted by MD are compared to results derived from the solution of the Boltzmann transport equation in the relaxation time approach.

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Section: Resultsmentioning

confidence: 99%

Molecular dynamics simulations of thermal transport in isotopically modulated semiconductor nanostructures

Frieling

Eon

Wolf

et al. 2016

Physica Status Solidi (a)

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“…Based on the Eq. 2, one can find that for the L= , the k L = k ∞ /2, in this way, the EMFP corresponds to a length at which the system yields a thermal conductivity, half of the length independent thermal conductivity, k ∞ , 29,[64][65][66] . By fitting curves to the NEMD data points, the diffusive or in another word length independent phononic thermal conductivity of single-layer and free-standing C 3 N along the armchair and zigzag directions at room temperature are calculated to be 810±20 W/mK and 826±20 W/mK, respectively.…”

Section: Resultsmentioning

confidence: 99%

Ultra high stiffness and thermal conductivity of graphene like C3N

Mortazavi

2017

Carbon

255

134

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Recently, single crystalline carbon nitride 2D material with a C 3 N stoichiometry has been synthesized. In this investigation, we explored the mechanical response and thermal transport along pristine, free-standing and single-layer C 3 N. To this aim, we conducted extensive first-principles density functional theory (DFT) calculations as well as molecular dynamics (MD) simulations. DFT results reveal that C 3 N nanofilms can yield remarkably high elastic modulus of 341 GPa.nm and tensile strength of 35 GPa.nm, very close to those of defect-free graphene. Classical MD simulations performed at a low temperature, predict accurately the elastic modulus of 2D C 3 N with less than 3% difference with the first-principles estimation. The deformation process of C 3 N nanosheets was studied both by the DFT and MD simulations. Ab initio molecular dynamics simulations show that single-layer C 3 N can withstand high temperatures like 4000 K. Notably, the phononic thermal conductivity of free-standing C 3 N was predicted to be as high as 815±20 W/mK.Our atomistic modelling results reveal ultra high stiffness and thermal conductivity of C 3 N nanomembranes and therefore propose them as promising candidates for new application such as the thermal management in nanoelectronics or simultaneously reinforcing the thermal and mechanical properties of polymeric materials.Corresponding author (BohayraMortazavi):

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“…The influence of size effects on the phonon thermal conductivity of crystalline thin films has been the topic of a wide array of studies [1][2][3][4] that have shaped the direction of fields rooted in nanoscale heat transfer and applications reliant on nanotechnology. It is well known that for films with thicknesses less than the length scale of their phonon mean free paths, thermal conductivity can be reduced due to incoherent boundary scattering of phonons ballistically traversing the film.…”

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confidence: 99%

“…The study of heat carrier mean free path contributions to thermal conductivity has evolved significantly over the past decade 13 through analytical methods like the thermal conductivity accumulation function 14 and experimental methods like Time Domain Thermoreflectance (TDTR) 15 and Broadband Frequency Domain Thermoreflectance (BB-FDTR) 16 . In the approach taken here, we use TDTR to measure the thermal conductivity of amorphous silicon films of varying thicknesses, an approach that Zhang et al 4 analytically demonstrated can provide information regarding the spectral dependence of the phonon thermal conductivity in nanosystems. While our results provide similar insight into the role of long mean free path propagons to the thermal conductivity of amorphous silicon as that reported by Liu et al 17 , our approach is fundamentally different.…”

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confidence: 99%

Size effects on the thermal conductivity of amorphous silicon thin films

et al. 2016

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We investigate thickness-limited size effects on the thermal conductivity of amorphous silicon thin films ranging from 3 -1636 nm grown via sputter deposition. While exhibiting a constant value up to ∼100 nm, the thermal conductivity increases with film thickness thereafter. This trend is in stark contrast with previous thermal conductivity measurements of amorphous systems, which have shown thickness-independent thermal conductivities. The thickness dependence we demonstrate is ascribed to boundary scattering of long wavelength vibrations and an interplay between the energy transfer associated with propagating modes (propagons) and nonpropagating modes (diffusons). A crossover from propagon to diffuson modes is deduced to occur at a frequency of ∼1.8 THz via simple analytical arguments. These results provide empirical evidence of size effects on the thermal conductivity of amorphous silicon and systematic experimental insight into the nature of vibrational thermal transport in amorphous solids.

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Length Dependent Thermal Conductivity Measurements Yield Phonon Mean Free Path Spectra in Nanostructures

Cited by 58 publications

References 45 publications

Molecular dynamics simulations of thermal transport in isotopically modulated semiconductor nanostructures

Molecular dynamics simulations of thermal transport in isotopically modulated semiconductor nanostructures

Ultra high stiffness and thermal conductivity of graphene like C3N

Size effects on the thermal conductivity of amorphous silicon thin films

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