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In this research, we utilized density functional theory (DFT) computations to perform ab initio molecular dynamics simulations and static calculations on graphene, hexagonal boron nitride, and their heterostructures, subjecting them to strains, perturbations, twist angles, and defects. The gathered energy, force, and virial information informed the creation of a training set comprising 1253 structures. Employing the Neural Evolutionary Potential framework integrated into Graphics Processing Units Molecular Dynamics, we fitted a machine learning potential (MLP) that closely mirrored the DFT potential energy surface. Rigorous validation of lattice constants and phonon dispersion relations confirmed the precision and dependability of the MLP, establishing a solid foundation for subsequent thermal transport investigations. A further analysis of the impact of twist angles uncovered a significant reduction in thermal conductivity, particularly notable in heterostructures with a decline exceeding 35%. The reduction in thermal conductivity primarily stems from the twist angle-induced softening of phonon modes and the accompanying increase in phonon scattering rates, which intensifies anharmonic interactions among phonons. Our study underscores the efficacy of the MLP in delineating the thermal transport attributes of two-dimensional materials and their heterostructures, while also elucidating the micro-mechanisms behind the influence of the twist angle on thermal conductivity, offering fresh perspectives for the design of advanced thermal management materials. [ABSTRACT FROM AUTHOR]

The thermal transport of Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) nanofiber is contributed by the electronic component of thermal conduction and the phonon component of thermal conduction. The relationship between the electrical conductivity and thermal conductivity of these conducting polymers is of great interest in thermoelectric energy conversation. In this work, we characterized the axial electrical conductivities and thermal conductivities of the single PEDOT:PSS nanofibers and found that the Lorenz number L is larger than Sommerfeld value L0 at 300 K. In addition, we found that the L increased significantly in the low-temperature region. We consider that this trend is due to the bipolar contribution of conducting polymers with low-level electrical conductivity and the increasing trend of the electronic contribution to thermal conductivity in low-temperature regions. [ABSTRACT FROM AUTHOR]

Abstract The cage structure and low lattice thermal conductivity κ L make the schwarzites a suitable candidate for building the host-guest system favorable for thermoelectric applications. In host-guest system, the guest atoms in cages play a crucial role for reducing κ L. However, the underlying mechanism on the thermal conductivity reduction remains unclear. In this work, the authors unveil, through atomic simulations, the working principles of guest atoms in schwarzites by highlighting the relationship between thermal transport properties and rattling motions of guest atoms. It has been found that local vibration of the "on-center" guest atoms at low temperatures gives rise to a single hybridized mode, while the positions of guest atoms at high temperatures deviate severely from the center of cages yielding blue-shifted hybridized modes. These blue-shifted hybridized modes are responsible for the reduction of the phonon relaxation time in a wide range of frequencies. Based on these findings, the authors propose guidelines for reducing κ L in schwarzites by properly tuning the frequency of one hybridized mode. Further reduction of κ L can be achieved by simultaneously introducing multiple hybridized modes with different characteristic frequencies. This study provides insights to the controllable thermal transport properties in schwarzites by engineering the hybridized phonon modes. Graphical abstract Image [ABSTRACT FROM AUTHOR]

Aiming at developing high thermal conductivity copper/diamond composite, an unconventional approach applying self-assembled monolayer (SAM) prior to the high-temperature sintering of copper/diamond composite was utilized to enhance the thermal boundary conductance (TBC) between copper and diamond. The enhancement was first systematically confirmed on a model interface system by detailed SAM morphology characterization and TBC measurements. TBC significantly depends on the SAM coverage and ordering, and the formation of high-quality SAM promoted the TBC to 73 MW/m2-K from 27 MW/m2-K, the value without SAM. With the help of molecular dynamics simulations, the TBC enhancement was identified to be determined by the number of SAM bridges and the overlap of vibrational density of states. The diamond particles of 210 μm in size were simultaneously functionalized by SAM with the condition giving the highest TBC in the model system and sintered together with the copper to fabricate isotropic copper/diamond composite of 50% volume fraction. The measured thermal conductivity marked 711 W/m-K at room temperature, the highest value among the ones with similar diamond-particles volume fraction and size. This work demonstrates a novel strategy to enhance the thermal conductivity of composite materials by SAM functionalization. The precisely-controlled scalable nanointerface by the organic monolayer was firstly implemented in the fabrication of pronounced high thermal conductive composite through the high-temperature plasma sintering process. Image 1 • Self-assembled monolayer is firstly applied in the fabrication of high thermal conductive composite material by sintering. • The number of chains and the phonon transmission via each chain molecule determines the interfacial thermal conductance. • The nanointerface with extensive area in the composite can be precisely controlled by the scalable experimental process. • A marked thermal conductivity is realized for the copper/diamond composite. [ABSTRACT FROM AUTHOR]

The newly synthesized two-dimensional polyaniline (C 3 N) of graphene family attracted extensive research attention due to extraordinary electrical and electron-related properties, but its thermal properties have still been in its infancy although the thermal management is of critical importance for the performance and reliability of electron-related devices. Herein, we investigated the thermal transport properties of single-layer C 3 N with different system size by utilizing non-equilibrium molecular dynamics simulations. Compared with the graphene, the analysis of lattice dynamics and electron density distribution revealed that the lower thermal conductivity of single-layer C 3 N stems from the disorders from mass difference and the polarization from asymmetric electrical difference density. Moreover, the temperature dependence of thermal conductivity of single-layer C 3 N approaches κ ∼ T−1 when the system size increases. Our studies provide more physical insights into the thermal transport of emerging two-dimensional polymeric carbon nitride materials. Image 1 [ABSTRACT FROM AUTHOR]

Recently, single-layer MoS 2 has increasingly promised a great potential in both thermoelectric and thermal management application due to its high Seebeck coefficient and intrinsic band gap. Herein, we investigate thermal conductivity of single-layer MoS 2 sheet and the effect of atomic-scale lattice defects and temperature on thermal conductivity using non-equilibrium molecular dynamics simulations (NEMD). Simulations results indicate the thermal conductivity can be suppressed by lattice defects and the increase in the range of temperature from 100 K to 400 K. Moreover, the physical mechanism of the thermal conductivity reduction was analyzed based on the phonon group velocity, participation ratio and phonon spectral transmission coefficient. Interestingly, it is revealed that the reduction of thermal conductivity results from the decreased phonon group velocity induced by defects, and phonon localization around lattice defects. Furthermore, the contributions from various frequency range of phonons to the thermal conductivity of pristine and defective structure were quantified. Especially, it is found that the coupling strength of between low-frequency and high-frequency phonons gradually increases due to the introduction of atomic-scale defects. This study is beneficial for thermal management of nanodevices and optimizing the thermoelectric properties of MoS 2 based materials. • The effect of atomic-scale defects and temperature on thermal conductivity in single-layer MoS 2 are explored. • Phonon localization around atomic-scale lattice defects results in the reduction of thermal conductivity. • The defect scattering enhances the coupling between low-frequency and high-frequency phonons. [ABSTRACT FROM AUTHOR]

Abstract Active control of heat flow is one of the important concepts in phononic devices, among which thermal diode is a fundamental building block. The long-standing bottleneck is the relevant experiments lagging far behind theoretical results. In this paper, we experimentally demonstrated considerable thermal rectification in the Y-junction carbon nanotube (CNT) bundle with suspended thermal bridge method. The thermal rectification ratio is up to ∼8.3% ± 0.5% with a relatively low temperature difference (Δ T = 4K). Molecular dynamics simulation results show that asymmetric phonon transmission in different (forward and backward) directions is responsible for the thermal rectification observed in the asymmetric CNT structure. Graphical abstract Thermal rectification in Y-junction carbon nanotube is demonstrated in Y-junction CNT. The observed thermal rectification of ∼8.3% ± 0.5% with △ T = 4K and ∼12.0% ± 0.4% with △ T = 17.5K in the Y-junction CNT bundle is the highest among the carbon materials, which is attributed to asymmetric phonon transmission in different (forward and backward) directions as suggested by our molecular dynamics (MD) simulation. Image [ABSTRACT FROM AUTHOR]

• The coherent phonon transport can be destroyed and rebuilt through adjusting the density of MoSe 2 nanodot arrays. • Significant phonon localization induced by the destruction of correlation is visualized based on the spatial energy distribution and anharmonic analysis. • The crossover from incoherent to coherent phonon transport is directly observed in atomic scale. Recently, massive efforts have been done on controlling thermal transport via coherent phonons in the various periodic nanostructures. However, the intrinsic lattice difference between the constituent materials inevitably generates the disorder at the interfaces, thus limiting the opportunity of directly observing the coherent phonon transport. Here, we investigate the controllability and visualization of the coherent phonon transport in a periodic MoS 2 /MoSe 2 arrayed heterostructure with minimum lattice mismatching using non-equilibrium molecular dynamics simulation. It is found that the coherent phonon transport can be destroyed and rebuilt through adjusting the density of MoSe 2 nanodot arrays. The phonon localization induced by the destruction of correlation is visualized based on the spatial energy distribution and anharmonic analysis. Furthermore, the eigen vector diagrams provide a distinct visualization of the localized phonon modes. Besides, the correlation of phonon can be rebuilt by reducing the period length, which is verified by the enhanced group velocities extracted from phonon dispersion curves. Interestingly, the crossover from incoherent to coherent phonon transport is directly observed by the spatial energy distributions and the spectral phonon transmission coefficients. Finally, the size and temperature dependence of thermal conductivity are also discussed. This study of the phonon coherence and its visualizing manipulation on thermal conductivity will be beneficial to fine heat control and management in the real applications. [Display omitted] [ABSTRACT FROM AUTHOR]