Heat Dissipation Mechanism at Carbon Nanotube Junctions on Silicon Oxide Substrate

Journal of Applied Physics

et al. 2016

In this work, we investigate the temperature-dependent thermal conductivities of few nanometer thick alternating stacks of amorphous dielectrics, specifically SiO2/Al2O3 and SiO2/Si3N4. Experiments using steady-state Joule-heating and electrical thermometry, while using a micro-miniature refrigerator over a wide temperature range (100–500 K), show that amorphous thin-film multilayer SiO2/Si3N4 and SiO2/Al2O3 exhibit through-plane room temperature effective thermal conductivities of about 1.14 and 0.48 W/(m × K), respectively. In the case of SiO2/Al2O3, the reduced conductivity is attributed to lowered film density (7.03 → 5.44 × 1028 m–3 for SiO2 and 10.2 → 8.27 × 1028 m–3 for Al2O3) caused by atomic layer deposition of thin-films as well as a small, finite, and repeating thermal boundary resistance (TBR) of 1.5 m2 K/GW between dielectric layers. Molecular dynamics simulations reveal that vibrational mismatch between amorphous oxide layers is small, and that the TBR between layers is largely due to imperfect interfaces. Finally, the impact of using this multilayer dielectric in a dash-type phase-change memory device is studied using finite-element simulations.

Section: Discussion and MD Simulationsmentioning

confidence: 99%

Thermal conductivity measurement of amorphous dielectric multilayers for phase-change memory power reduction

Fong

Sood

Journal of Applied Physics

et al. 2016

“…The VDOS g( ω ) is calculatedfrom the sampling of atom velocities in equilibrium MD simulations at room temperature 42 : where N a is the number of atoms, and v j,α is the velocity of atom j in direction α. The mean square displacement (MSD) of the mass center translation is given by where is the position of the mass center of the molecule l , and the summation is over all the M molecules.…”

Section: Methodsmentioning

confidence: 99%

Thermal Transport in Fullerene Derivatives Using Molecular Dynamics Simulations

Wang

Kumar

2015

Sci Rep

Self Cite

In order to study the effects of alkyl chain on the thermal properties of fullerene derivatives, we perform molecular dynamics (MD) simulations to predict the thermal conductivity of fullerene (C60) and its derivative phenyl-C61-butyric acid methyl ester (PCBM). The results of non-equilibrium MD simulations show a length-dependent thermal conductivity for C60 but not for PCBM. The thermal conductivity of C60, obtained from the linear extrapolation of inverse conductivity vs. inverse length curve, is 0.2 W m−1 K−1 at room temperature, while the thermal conductivity of PCBM saturates at ~0.075 W m−1 K−1 around 20 nm. The different length-dependence behavior of thermal conductivity indicates that the long-wavelength and low-frequency phonons have large contribution to the thermal conduction in C60. The decrease in thermal conductivity of fullerene derivatives can be attributed to the reduction in group velocities, the decrease of the frequency range of acoustic phonons, and the strong scattering of low-frequency phonons with the alkyl chains due to the significant mismatch of vibrational density of states in low frequency regime between buckyball and alkyl chains in PCBM.

“…Then, the CNT and PEK matrix composite system is relaxed for 500ps in NVE. The frequency dependent energy distribution g() during this process is calculated by Fourier transform of velocities of atoms as follows [50,85] : written as:…”

Section: Spectral Temperature Analysismentioning

confidence: 99%

“…, where z a is lattice constant along CNT axial direction [85,86]. SED is averaged over all CNT atoms and the discreteness in dispersion curve is due to the finite size of the CNT in the simulation.…”

Section: Sed Analysis For (2020) Swcntmentioning

confidence: 99%

See 1 more Smart Citation

Investigation of phonon transport and thermal boundary conductance at the interface of functionalized SWCNT and poly (ether-ketone)

Huang

Journal of Applied Physics

Varshney

et al. 2016

Self Cite

Carbon nanostructures such as carbon nanotube (CNT), graphene, and carbon fibers can be used as fillers in amorphous polymers to improve their thermal properties. In this study, the effect of covalent bonding of CNT with poly(ether ketone) (PEK) on interfacial thermal interactions is investigated using non-equilibrium molecular dynamics simulations. The number of covalent bonds between (20, 20) CNT and PEK is varied in the range of 0–80 (0%–6.25%), and the thermal boundary conductance is computed. The analysis reveals that covalent functionalization of CNT atoms can enhance the thermal boundary conductance by an order of magnitude compared to the non-functionalized CNT-PEK interface at a high degree of CNT functionalization. Besides strengthening the thermal coupling, covalent functionalization is also shown to modify the phonon spectra of CNT. The transient spectral energy analysis shows that the crosslinks cause faster energy exchange from CNT to PEK in different frequency bands. The oxygen atom of hydroxyl group of PEK contributes energy transfer in the low frequency band, while aromatic and carbonyl carbon atoms play a more significant role in high frequency bands. In addition, by analyzing the relaxation time of the spectral temperature of different frequency bands of CNT, it is revealed that with increasing number of bonds, both lower frequency vibrational modes and higher frequency modes efficiently couple across the CNT-PEK interface and contribute in thermal energy transfer from CNT to the matrix.