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Exploring the thermal transport properties of the interface structure of low-dimensional nanomaterials contributes to a deeper understanding of the interface phonon modes and may provide theoretical support for efficient chip cooling devices. In this manuscript, we have simulated in detail the effects of system temperature, substrate location, and heat flow density on the thermal transport at the SWCNT/Si interface using the Non-equilibrium Molecular Dynamics approach and predicted the interfacial thermal conductance of SWCNT/Si for second, third and fourth order phonon using the Anharmonic Inelastic model. The results show that the low-frequency acoustic branch of SWCNT is suppressed by phonon scattering from the substrate, and the low-frequency phonon branch of SWCNT is boosted by about 1 THz. The anharmonic channels and inelastic phonon scattering significantly affect the interface phonon modes at higher temperatures, and the anharmonic interactions could increase additional thermal transport channels, which result in an increased number of additional phonon peaks. The increase in temperature gradually consumes the phonons incident at the interface in SWCNT, which enhances the anharmonic scattering and weakens the nonlinear characteristics of the material heterostructure, while the weakening of the acoustic branch accompanied by the temperature increase makes the LA phonon branch thermal conduction rate slower and the interfacial thermal conductance gradually stabilizes, which leads to the weakening of the thermal rectification effect. [ABSTRACT FROM AUTHOR]

Based on the first-principles calculations of the phonon Boltzmann transport equation (pBTE) under the framework of the three-phonon scattering theory, we characterized the temperature and size dependence of the lattice thermal conductivity of monolayer silicene under the tensile strain. Our research shows that the lattice thermal conductivity of silicene has obvious strain dependence, and demonstrates the great potential of thermal management by applying strain in silicene. The TA phonon mode contributes the most to the thermal conductivity of silicene, while the contribution of the ZA phonon is suppressed. With the increase in tensile strain, the contribution of LA mode phonons to the thermal conductivity increases rapidly, and eventually become the dominant phonon mode of the silicene lattice thermal conductivity. We suspect that this phenomenon is caused by the reduction of the warpage of the silicene and the restoration of the crystal symmetry due to the tensile strain. When the characteristic size is less than 10 nm, the lattice thermal conductivity of silicene is no longer sensitive to temperature, and with the increase in tensile strain, the effective phonon mean free path (MFP) of silicene also increases, and the size effect is more obvious. The characterization of the scattering channel reveals its significant influence on the characteristics of thermal transport capacity of different phonon modes. These findings deepen the understanding of the phonon dynamics of the monolayer silicene-like structure, and provide the reference and theoretical basis for the research on the heat management of the corresponding material combined with strain and size and the development of thermal management technology. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations are employed to investigate the thermal boundary conductance between a horizontally aligned carbon nanotube (CNT) and graphene. The results show that the thermal boundary conductance increases monotonically with the temperature and the interfacial van der Waals interaction strength. It is also found that the thermal boundary conductance demonstrates strong positive correlation not only with the CNT diameter but also with the system length until it reaches an elevated plateau. After incorporating organic molecules into the interface, the thermal boundary conductance is about one order of magnitude higher than that without organic molecules due to the enhanced matching level of phonon density of states. When tensile strain is applied along the transversal direction, the thermal boundary conductance decreases with increasing stretching strain without organic molecules, and the reduction can be prevented with additional organic molecules. Further analysis indicates that larger overlap between the phonon spectra of organic molecules and sp 3 hybridized C atoms can compensate for the softening of high-frequency phonon modes of sp 2 hybridized C atoms in graphene induced by tensile strain. This work provides guidance about tuning the thermal transport of C-based nanomaterials for applications in nanoelectronic devices. [ABSTRACT FROM AUTHOR]

Abstract: The thermal boundary conductance between multilayer structures including Al film, semiconductors with high Debye temperatures (GaN, AlN, Si, diamond) and dielectric substrates (sapphire) has been measured using a two-color femtosecond laser pump-probe system (a variation of transient time-domain thermoreflectance, TDTR). The thermal boundary conductance for the combinations of semiconductors and dielectrics falls within a relatively narrow range, 10–20 MW m−2 K−1, at room temperature. The measured thermal boundary conductance between Al film and semiconductor or dielectric substrates is one order of magnitude larger than that between semiconductor and dielectric substrates. A modified diffuse mismatch model (DMM) is used to interpret the data and extract the phonon transmissivity at the interface. The predicted results of the DMM corrected by attenuation constant agree well with the experimental values. Over a wide phonon velocity, both the measured and predicted results decrease with the increasing average phonon velocity. Both the vibration mismatch and changes in the localized phonon transport near the interface contribute to the reduction in thermal boundary conductance. Other scattering mechanisms are discussed which may explain the failure of the DMM at room temperature. [Copyright &y& Elsevier]

• The interfacial thermal conductance of GaN/AlN is investigated by both MD simulations and Monte Carlo simulations based on first-principles calculations. • Interfacial phonon modes are the additional channels for interfacial thermal transport. • Modal temperature and wave-resolved spectral heat flux provide modal-level and frequency-level acknowledge. Interfacial thermal conductance (ITC) is of critical importance for GaN-based device performance. GaN/AlN is a key component in GaN-based devices. Therefore, systematically investigating the interfacial thermal transport between GaN and AlN is of great significance for the thermal management of GaN-based devices. The temperature dependence of ITC across GaN/AlN interfaces are investigated using nonequilibrium molecular dynamics (NEMD) and Monte Carlo simulations based on first-principles calculations. Interestingly, the calculated ITC is much larger than that of GaN/metal, GaN/Si and GaN/SiC. Structural similarity and interfacial phonon modes are used to reveal the underlying mechanism. Moreover, the modal temperature and wave-resolved spectral heat flux are calculated to understand the interfacial thermal nonequilibrium and the dominant thermal transport channel, respectively. This study explores the modal-level and frequency-level mechanisms for interfacial thermal transport between GaN and AlN, which provides effective understanding in thermal management of GaN-based devices. [ABSTRACT FROM AUTHOR]

• The N-face GaN optical phonon branch is localized more strongly than Ga-face. • The interface phonon of GaN/Al x Ga 1- x N is significantly localized. • The interface phonon dispersion curve is elevated. • Lattice distortion leads to a drift of the interface phonon branch. The phonon transport processes within a few atomic layers near heterointerfaces play a crucial role in thermoelectric applications such as nitride-based high electron mobility transistors (HEMTs) and light-emitting diodes (LEDs). However, a systematic investigation of their localized transport characteristics remains unexplored. This article employs the Interfacial Phonons method based on first-principles calculations to extract interface phonon information for GaN/Al x Ga 1- x N heterostructures. Molecular dynamics simulations are utilized to compare the phonon behaviors between Ga-face and N-face GaN-based heterointerfaces. The research extensively investigates the dependence of interfacial thermal transport on the concentration of Al atoms under ordered substitutional doping and the strength of uniaxial compressive strain. The research revealed that both Ga-face and N-face GaN/Al x Ga 1- x N heterointerfaces exhibit phonon branch drift. The differences in charge distribution at the polar surfaces lead to varying degrees of Brillouin zone distortion. The vibrational modes of the atoms at the N-face GaN interface are more compact and localized than those of Ga-face GaN, resulting in a stronger degree of localization for the optical phonon branches. When varying the doping concentration of Al atoms, some phonon branches at the GaN interface appear outside the band structure of the intrinsic bulk and surface states, exhibiting strong localized characteristics. The introduction of Al atoms at the heterointerface induces additional phonon scattering, and the lattice vibration mismatch between Al and Ga atoms results in a non-uniform residual stress field at the interface, further enhancing phonon-interface scattering. Moderate compressive strain-induced lattice distortion promotes the overlapping of phonon modes at the interface, allowing some localized phonons to serve as interface transport modes. This optimization enhances phonon transport at the heterointerface. This research provides valuable insights into a comprehensive understanding of interfacial thermal transport in GaN-based semiconductors. Moreover, it offers useful theoretical guidance for thermal management through the manipulation of phonon wave properties. [ABSTRACT FROM AUTHOR]

The weakly van der Waals interactions make monolayer TMDCs straightforward to vertically stack to bilayer systems, which have attracted enormous attention because of their potential applications in optoelectronics and electronic devices. In particular, MoS 2 /WS 2 heterostructure exhibits excellent performance in photodetectors. The thermal transport behavior plays a vital role in life and performance of devices, which have been rarely reported. Here, the thermal properties and thermal transport mechanism of monolayer MoS 2 and WS 2 , bilayer MoS 2 and WS 2 and MoS 2 /WS 2 heterostructure are systematically investigated by first-principles calculations and Boltzmann transport theory. The results indicate that the thermal conductivity of bilayer systems is considerably higher than that of correlated monolayer systems. Most interesting, the thermal conductivity of MoS 2 /WS 2 heterostructure is not only much lower than the thermal conductivity of 2L-WS 2 and 2L-MoS 2 , but also much lower than that of monolayer WS 2 and MoS 2. The harmonic properties mainly including phonon dispersion and anharmonic properties mainly including scattering rate and Grüneisen parameters are used to elucidate the corresponding mechanism. Moreover, the underlying electronic properties mainly including interlayer charge transfer and interlayer coupling play an essential role in thermal transport of MoS 2 /WS 2 heterostructure. The results suggest that the thermal conductivity of TMDCs can be largely tunes by various combinations, such as WS 2 /WS 2 or WS 2 /MoS 2 , which provides an effective way for manipulating the thermal transport properties of MoS 2 and WS 2 for future emerging applications. [ABSTRACT FROM AUTHOR]

An electro-thermal coupling simulator for GaN devices based on electron Monte Carlo (e-MC) simulations is established. Taking GaN Metal Insulator Semiconductor High Electron Mobility Transistor (MISHEMT) as example, the non-equilibrium thermal transport processes of self-heating effect in the channel layer are studied. This simulator is mainly coupled by e-MC and the phonon Boltzmann transport equation (pBTE), physical property parameters and electric field parameters are provided by first-principles and Technology Computer Aided Design (TCAD), respectively. We first verify the e-MC program by calculating the electron transport properties of GaN materials, verify the feasibility of the established GaN MISHEMT model by using TCAD and obtained its operating characteristics. Further, the simulator is used to evaluate the non-equilibrium processes inside the channel layer in detail, the results show that there is significant consistency in the peak positions of electric field strength, heat generation and diffusion temperature, the diffusion temperature peak occurs at the secondary peak of heat generation. The frequency distribution of phonon emission under different drain-source bias voltages is revealed by phonon emission spectrum analysis. The strength of the non-equilibrium effect is measured by effective temperature. Increasing the drain-source bias voltage will significantly increase the peak temperature of hotspot and further enhance the non-equilibrium effect. Our study reports an efficient scheme for electro-thermal simulations of GaN MISHEMT, which provides insights for thermal management of GaN-based transistor devices. • A self-consistent electrothermal coupling simulation process is established. • The electronic transport properties of GaN materials are verified in detail by the e-MC program. • A new improvement scheme is proposed to solve the problem of complex dispersion curves and multiple scattering types. • The non-equilibrium thermal transport and phonon emission spectrum based on selective excitation are studied. [ABSTRACT FROM AUTHOR]

[Display omitted] The miniaturization of devices makes interfacial resistance to heat dissipation more and more obvious. Therefore, it is important to study interfacial thermal transport systematically. A modified higher harmonic inelastic model is proposed to describe the inelastic scattering at the interface. Combined with this interface model, the thermal transport of interface structures is studied by the Boltzmann transport equation. The results show that the introduction of inelastic scattering enhances the heat flux contribution of low-frequency phonons, changes the phonon distribution near the interface, and enhances the phonon non-equilibrium. This demonstrates the importance of inelastic interfacial scattering in simulations. By analyzing the phonon distribution, it is found that temperature and thickness affect the interfacial heat transport through the redistribution of phonons. The redistribution has the opposite effect on the contribution of inelastic scattering. By studying ballistic phonons in the interface structure, it is found that the ballistic phonons are mainly concentrated in the low-frequency region. Due to the longer mean free path, the phonons with frequencies below 2.5 THz are more likely to maintain a ballistic transport state. Similar to nanoscale hotspots, strong quasi-ballistic transport hinders heat diffusion. The energy fraction of ballistic phonons increases by 49%, and the local effective thermal conductivity drops by 52%. This work studied the mechanism of interfacial thermal transport, and will be useful for future interface simulation. [ABSTRACT FROM AUTHOR]