87 research outputs found
Phonon transport and thermal conductivity in two-dimensional materials
Two-dimensional materials, such as graphene, boron nitride and transition
metal dichalcogenides, have attracted increased interest due to their potential
applications in electronics and optoelectronics. Thermal transport in
two-dimensional materials could be quite different from three-dimensional bulk
materials. This article reviews the progress on experimental measurements and
theoretical modeling of phonon transport and thermal conductivity in
two-dimensional materials. We focus our review on a few typical two-dimensional
materials, including graphene, boron nitride, silicene, transition metal
dichalcogenides, and black phosphorus. The effects of different physical
factors, such as sample size, strain and defects, on thermal transport in
Two-dimensional materials are summarized. We also discuss the environmental
effect on the thermal transport of two-dimensional materials, such as substrate
and when two-dimensional materials are presented in heterostructures and
intercalated with inorganic components or organic molecules.Comment: 67 pages, 18 figures. Submitted to Annual Review of Heat Transfe
Phonon Transport in Single-Layer Transition Metal Dichalcogenides: a First-Principles Study
Two-dimensional transition metal dichalcogenides (TMDCs) are finding
promising electronic and optical applications due to their unique properties.
In this letter, we systematically study the phonon transport and thermal
conductivity of eight semiconducting single-layer TMDCs, MX2 (M=Mo, W, Zr and
Hf, X=S and Se), by using the first-principles-driven phonon Boltzmann
transport equation approach. The validity of the single-mode relaxation time
approximation to predict the thermal conductivity of TMDCs is assessed by
comparing the results with the iterative solution of the phonon Boltzmann
transport equation. We find that the phononic thermal conductivities of 2H-type
TMDCs are above 50 W/mK at room temperature while the thermal conductivity
values of the 1T-type TMDCs are much lower, when the size of the sample is 1
{\mu}m. A very high thermal conductivity value of 142 W/mK was found in
single-layer WS2. The large atomic weight difference between W and S leads to a
very large phonon bandgap which in turn forbids the scattering between acoustic
and optical phonon modes and thus resulting in very long phonon relaxation
time.Comment: 21 pages, 7 figure
Lattice Thermal Conductivity of Organic-Inorganic Hybrid Perovskite CH3NH3PbI3
Great success has been achieved in improving the photovoltaic energy
conversion efficiency of the organic-inorganic perovskite-based solar cells,
but with very limited knowledge on the thermal transport in hybrid perovskites,
which would affect the device lifetime and stability. Based on the potential
developed from the density functional theory calculations, we studied the
lattice thermal conductivity of the hybrid halide perovskite CH3NH3PbI3 using
equilibrium molecular dynamics simulations. Temperature-dependent thermal
conductivity is reported from 160 K to 400 K, which covers the tetragonal phase
(160-330 K) and the pseudocubic phase (>330K). A very low thermal conductivity
(0.50 W/mK) is found in the tetragonal phase at room temperature, whereas a
much higher thermal conductivity is found in the pseudocubic phase (1.80 W/mK
at 330 K). The low group velocity of acoustic phonons and the strong
anharmonicity are found responsible for the relatively low thermal conductivity
of the tetragonal CH3NH3PbI3
A relaxation time model for efficient and accurate prediction of lattice thermal conductivity
Prediction of lattice thermal conductivity is important to many applications
and technologies, especially for high-throughput materials screening. However,
the state-of-the-art method based on three-phonon scattering process is bound
with high computational cost while semi-empirical models such as the Slack
equation are less accurate. In this work, we examined the theoretical
background of the commonly-used computational models for high-throughput
thermal conductivity prediction and proposed an efficient and accurate method
based on an approximation for three-phonon scattering strength. This
quasi-harmonic approximation has comparable computational cost with many
widely-used thermal conductivity models but had the best performance in regard
to quantitative accuracy. As compared to many models that can only predict
lattice thermal conductivity values, this model also allows to include Normal
processes and obtain the phonon relaxation time.Comment: The supplementary materials exceed the size limit of arXiv and could
be available after this paper is publishe
First-Principles Prediction of Phononic Thermal Conductivity of Silicene: a Comparison with Graphene
There has been great interest in two-dimensional materials, beyond graphene,
for both fundamental sciences and technological applications. Silicene, a
silicon counterpart of graphene, has been shown to possess some better
electronic properties than graphene. However, its thermal transport properties
have not been fully studied. In this paper, we apply the first-principles-based
phonon Boltzmann transport equation to investigate the thermal conductivity of
silicene as well as the phonon scattering mechanisms. Although both graphene
and silicene are two-dimensional crystals with similar crystal structure, we
find that phonon transport in silicene is quite different from that in
graphene. The thermal conductivity of silicene shows a logarithmic increase
with respect to the sample size due to the small scattering rates of acoustic
in-plane phonon modes, while that of graphene is finite. Detailed analysis of
phonon scattering channels shows that the linear dispersion of the acoustic
out-of-plane (ZA) phonon modes, which is induced by the buckled structure,
makes the long-wavelength longitudinal acoustic (LA) phonon modes in silicene
not as efficiently scattered as that in graphene. Compared with graphene, where
most of the heat is carried by the acoustic out-of-plane (ZA) phonon modes, the
ZA phonon modes in silicene only have ~10% contribution to the total thermal
conductivity, which can also be attributed to the buckled structure. This
systematic comparison of phonon transport and thermal conductivity of silicene
and graphene using the first-principle-based calculations shed some light on
other two-dimensional materials, such as two-dimensional transition metal
dichalcogenides.Comment: To appear in J. Appl. Phys. (2015) Vol.117 Issue 3. 50 pages, 11
figure
Phonon transport in single-layer Mo1-xWxS2 alloy embedded with WS2 nanodomains
Two-dimensional (2-D) transition metal dichalcogenides (TMDs) have shown
numerous interesting physical and chemical properties, making them promising
materials for electronic, optoelectronic, and energy applications. Tuning
thermal conductivity of two-dimensional (2-D) materials could expand their
applicability in many of these fields. In this paper, we propose a strategy of
using alloying and nanodomains to suppress the thermal conductivity of 2-D
materials. To predict the thermal conductivity of 2-D alloy embedded with
nanodomains, we employ the Green's function approach to assess the phonon
scattering strength due to alloying and nanodomain embedding. Our
first-principles-driven phonon Boltzmann transport equation calculations show
that the thermal conductivity of single-layer MoS2 can be reduced to less than
one-tenth of its intrinsic thermal conductivity after alloying with W and
introducing nanodomains due to the strong scattering for both high- and
low-frequency phonons. The strategies to further reduce the thermal
conductivity are also discussed.Comment: 20 pages, 6 figure
Measurement Techniques for Thermal Conductivity and Interfacial Thermal Conductance of Bulk and Thin Film Materials
Thermal conductivity and interfacial thermal conductance play crucial roles
in the design of engineering systems where temperature and thermal stress are
of concerns. To date, a variety of measurement techniques are available for
both bulk and thin film solid-state materials with a broad temperature range.
For thermal characterization of bulk material, the steady-state absolute
method, laser flash diffusivity method, and transient plane source method are
most used. For thin film measurement, the 3{\omega} method and transient
thermoreflectance technique including both frequency-domain and time-domain
analysis are employed widely. This work reviews several most commonly used
measurement techniques. In general, it is a very challenging task to determine
thermal conductivity and interface contact resistance with less than 5% error.
Selecting a specific measurement technique to characterize thermal properties
need to be based on: 1) knowledge on the sample whose thermophysical properties
is to be determined, including the sample geometry and size, and preparation
method; 2) understanding of fundamentals and procedures of the testing
technique and equipment, for example, some techniques are limited to samples
with specific geometrics and some are limited to specific range of
thermophysical properties; 3) understanding of the potential error sources
which might affect the final results, for example, the convection and radiation
heat losses.Comment: 48 pages, 20 figures. Accepted by ASME Journal of Electronic
Packagin
Thermal conductivity of intrinsic semiconductor at elevated temperature: role of four-phonon scattering and electronic heat conduction
While using first-principles-based Boltzmann transport equation approach to
predict the thermal conductivity of crystalline semiconductor materials has
been a routine, the validity of the approach is seldom tested for
high-temperature conditions. Most previous studies only focused on the phononic
contribution, and neglected the electronic part. Meanwhile, the treatment on
phonon transport is not rigorous as a few ingredients, such as four-phonon
scatterings, phonon renormalization and thermal expansion, are ignored. In this
paper, we present a Boltzmann transport equation study on high-temperature
thermal conduction in bulk silicon by considering the effects of both phonons
and electrons, and explore the role of the missing parts in the previous
studies on the thermal conductivity at elevated temperature. For the phonon
transport, four-phonon scattering is found to considerably reduce the thermal
conductivity when the temperature is larger than 700 K, while the effects of
phonon renormalization and thermal expansion on phononic thermal conductivity
are negligible. Bipolar contribution to the electronic thermal conductivity
calculated from first-principles is implemented for the first time. More than
25% of heat is shown to be conducted by electrons at 1500 K. The computed total
thermal conductivity of silicon faithfully reproduces the measured data. The
approach presented in this paper is expected to be applied to other
high-temperature functional materials, and the results could serve as
benchmarks and help to explain the high-temperature phonon and electron
transport phenomena.Comment: 6 figures, 23 page
How does the accuracy of interatomic force constants affect the prediction of lattice thermal conductivity
Solving Peierls-Boltzmann transport equation with interatomic force constants
(IFCs) from first-principles calculations has been a widely used method for
predicting lattice thermal conductivity of three-dimensional materials. With
the increasing research interests in two-dimensional materials, this method is
directly applied to them but different works show quite different results. In
this work, classical potential was used to investigate the effect of the
accuracy of IFCs on the predicted thermal conductivity. Inaccuracies were
introduced to the third-order IFCs by generating errors in the input forces.
When the force error lies in the typical value from first-principles
calculations, the calculated thermal conductivity would be quite different from
the benchmark value. It is found that imposing translational invariance
conditions cannot always guarantee a better thermal conductivity result. It is
also shown that Gr\"uneisen parameters cannot be used as a necessary and
sufficient criterion for the accuracy of third-order IFCs in the aspect of
predicting thermal conductivity.Comment: 26 pages, 9 figure
Phonon transmission across Mg2Si/Mg2Si1-xSnx interfaces: A first-principles-based atomistic Green's function study
Phonon transmission across interfaces of dissimilar materials has been
studied intensively in the recent years by using atomistic simulation tools
owing to its importance in determining the effective thermal conductivity of
nanostructured materials. Atomistic Green's function (AGF) method with
interatomic force constants from the first-principles (FP) calculations has
evolved to be a promising approach to study phonon transmission in many not
well-studied material systems. However, the direct FP calculation for
interatomic force constants becomes infeasible when the system involves atomic
disorder. Mass approximation is usually used, but its validity has not been
tested. In this paper, we employ the higher-order force constant model to
extract harmonic force constants from the FP calculations, which originates
from the virtual crystal approximation but considers the local force-field
difference. As a feasibility demonstration of the proposed method that
integrates higher-order force constant model from the FP calculations with the
AGF, we study the phonon transmission in the Mg2Si/Mg2Si1-xSnx systems. When
integrated with the AGF, the widely-used mass approximation is found to
overpredict phonon transmission across Mg2Si/Mg2Sn interface. The difference
can be attributed to the absence of local strain field-induced scattering in
the mass approximation, which makes the high-frequency phonons less scattered.
The frequency-dependent phonon transmission across an interface between a
crystal and an alloy, which often appears in high efficiency "nanoparticle in
alloy" thermoelectric materials, is studied. The interfacial thermal resistance
across Mg2Si/Mg2Si1-xSnx interface is found to be weakly dependent on the
composition of Sn when the composition x is less than 40%, but increases
rapidly when it is larger than 40% due to the transition of high-frequency
phonon DOS in Mg2Si1-xSnx alloys.Comment: 44 pages, 11 figure
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