572 research outputs found
Nonlinear thermal transport and negative differential thermal conductance in graphene nanoribbons
We employ classical molecular dynamics to study the nonlinear thermal
transport in graphene nanoribbons (GNRs). For GNRs under large temperature
biases beyond linear response regime, we have observed the onset of negative
differential thermal conductance (NDTC). NDTC is tunable by varying the manner
of applying the temperature biases. NDTC is reduced and eventually disappears
when the length of the GNR increases. We have also observed NDTC in triangular
GNRs, where NDTC exists only when the heat current is from the narrower to the
wider end. These effects may be useful in nanoscale thermal managements and
thermal signal processing utilizing GNRs.Comment: 5 pages, 4 figure
Compressive mechanical response of graphene foams and their thermal resistance with copper interfaces
We report compressive mechanical response of graphene foams (GFs) and the
thermal resistance () between copper (Cu) and GFs, where GFs were
prepared by the chemical vapor deposition (CVD) method. We observe that Young's
modulus () and compressive strength () of GFs have a power
law dependence on increasing density () of GFs. The maximum
efficiency of absorbed energy () for all GFs during the compression
is larger than ~0.39. We also find that a GF with a higher shows a
larger . In addition, we observe that the measured of
Cu/GFs at room temperature with a contact pressure of 0.25 MP applied increases
from ~50 to ~90 when increases from 4.7 to 31.9
Prediction of Spectral Phonon Mean Free Path and Thermal Conductivity with Applications to Thermoelectrics and Thermal Management: A Review
We give a review of the theoretical approaches for predicting spectral phonon mean free path and thermal conductivity of solids. The methods can be summarized into two categories: anharmonic lattice dynamics calculation and molecular dynamics simulation. In the anharmonic lattice dynamics calculation, the anharmonic force constants are used first to calculate the phonon scattering rates, and then the Boltzmann transport equations are solved using either standard single mode relaxation time approximation or the Iterative Scheme method for the thermal conductivity. The MD method involves the time domain or frequency domain normal mode analysis. We present the theoretical frameworks of the methods for the prediction of phonon dispersion, spectral phonon relaxation time, and thermal conductivity of pure bulk materials, layer and tube structures, nanowires, defective materials, and superlattices. Several examples of their applications in thermal management and thermoelectric materials are given. The strength and limitations of these methods are compared in several different aspects. For more efficient and accurate predictions, the improvements of those methods are still needed
Tuning the thermal conductivity of graphene nanoribbons by edge passivation and isotope engineering: a molecular dynamics study
Using classical molecular dynamics simulation, we have studied the effect of
edge-passivation by hydrogen (H-passivation) and isotope mixture (with random
or supperlattice distributions) on the thermal conductivity of rectangular
graphene nanoribbons (GNRs) (of several nanometers in size). We found that the
thermal conductivity is considerably reduced by the edge H-passivation. We also
find that the isotope mixing can reduce the thermal conductivities, with the
supperlattice distribution giving rise to more reduction than the random
distribution. These results can be useful in nanoscale engineering of thermal
transport and heat management using GNRs.Comment: 4 pages, 4 figure
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