Interfacial Thermal Transport Research Articles

Boosting thermal energy transport across the interface between phase change materials and metals via self-assembled monolayers.

Thermal energy storage using phase change materials has great potential to reduce the weather dependency of sustainable energy sources. However, the low thermal conductivity of most phase change materials is a long-standing bottleneck for large-scale practical applications. In modifications to increase the thermal conductivity of phase change materials, the interfacial thermal resistance between phase change materials and discrete additives or porous networks reduces the effective thermal energy transport. In this work, we investigated the interfacial thermal resistance between a metal (gold) and a polyol solid-liquid phase change material (erythritol) at various temperatures including temperatures below the melting point (300 and 350 K), near the melting point (390, 400, 410 K, etc.) and above the melting point (450 and 500 K) adopting non-equilibrium molecular dynamics. Since the gold-erythritol interfacial thermal conductance is low regardless of whether erythritol is melted or not (<40 MW m-2 K-1), self-assembled monolayers were used to boost the interfacial thermal energy transport. The self-assembled monolayer with carboxyl groups was found to increase the interfacial thermal conductance most (by a factor of 7-9). As the temperature increases, the interfacial thermal conductance significantly increases (by ~50 MW m-2 K-1) below the melting point but decreases little above the melting point. Further analysis revealed that the most obvious influencing factor is the interfacial binding energy. This work could build on existing composite phase change material solutions to further improve heat transfer efficiency of energy storage applications in both liquid and solid states.

Direct observation of tunable thermal conductance at solid/porous crystalline solid interfaces induced by water adsorbates

Improving interfacial thermal transport is crucial for heat dissipation in devices with interfaces, such as electronics, buildings, and solar panels. Here, we design a strategy by utilizing the water adsorption-desorption process in porous metal-organic frameworks (MOFs) to tune the interfacial heat transfer, which could benefit their potential in cooling or heat dissipation applications. We observe a changeable thermal conductance across the solid/porous MOF interfaces owing to the dense water channel formed by the adsorbed water molecules in MOFs. Our experimental and/or modeling results show that the interfacial thermal conductance of Au/Cu3(BTC)2, Au/Zr6O4(OH)4(BDC)6 and Au/MOF-505 heterointerfaces is increased up to 7.1, 1.7 and 3.1 folds by this strategy, respectively, where Cu3(BTC)2 is referred to as HKUST-1 and Zr6O4(OH)4(BDC)6 is referred to as UiO-66. Our molecular dynamics simulations further show that the surface tension of Au layer will cause the adsorbed water molecules in MOFs to gather at the interfacial region. The dense water channel formed at the interfacial region can activate the high-frequency lattice vibrations and act as an additional thermal pathway, and then enhance heat transfer across the interfaces significantly. Our findings revealed the underlying mechanisms for tailoring thermal transport at the solid/porous MOF heterointerfaces by water adsorbates, which could motivate and benefit the new cooling system design based on MOFs.

Investigation of interfacial thermal resistance between Bi2Te3 thin films and metal electrodes via TDTR

A challenge on promoting thermoelectric application is the low energy conversion efficiency of thermoelectric devices. Reducing the contact thermal resistance of a thermoelectric device can improve efficiency effectively. However, study on interfacial thermal transport is lack due to the difficulty on contact thermal resistance measurement. Herein, a study on contact thermal resistance between thermoelectric and electrode materials was reported. We prepared various heterostructures of Bi2Te3–Cu and Bi2Te3–Ni via magnetron sputtering, and measured the contact thermal resistance using a time-domain thermoreflectance technique. Our results show that the contact thermal resistance is affected by both chemical and physical properties of interface. The chemical and physical stability of interfaces, the surface roughness and porosity of films, as well as electrical properties of Bi2Te3, are all related to the contact thermal resistance. The contact thermal resistance of Bi2Te3–Ni prepared at 400 °C can be reduced to 3.96 × 10−7 m2KW−1. Our work provides important experimental data and theoretical basis for optimizing the interlayer between thermoelectric materials and electrodes, and improving energy conversion efficiency of thermoelectric devices.

Interfacial Thermal Transport between Stacked Functionalized Graphene Nanoflakes

Interfacial Thermal Transport between Stacked Functionalized Graphene Nanoflakes

Enhanced Thermal Boundary Conductance across GaN/SiC Interfaces with AlN Transition Layers.

Heat dissipation plays a crucial role in the performance and reliability of high-power GaN-based electronics. While AlN transition layers are commonly employed in the heteroepitaxial growth of GaN-on-SiC substrates, concerns have been raised about their impact on thermal transport across GaN/SiC interfaces. In this study, we present experimental measurements of the thermal boundary conductance (TBC) across GaN/SiC interfaces with varying thicknesses of the AlN transition layer (ranging from 0 to 73 nm) at different temperatures. Our findings reveal that the addition of an AlN transition layer leads to a notable increase in the TBC of the GaN/SiC interface, particularly at elevated temperatures. Structural characterization techniques are employed to understand the influence of the AlN transition layer on the crystalline quality of the GaN layer and its potential effects on interfacial thermal transport. To gain further insights into the trend of TBC, we conduct molecular dynamics simulations using high-fidelity deep learning-based interatomic potentials, which reproduce the experimentally observed enhancement in TBC even for atomically perfect interfaces. These results suggest that the enhanced TBC facilitated by the AlN intermediate layer could result from a combination of improved crystalline quality at the interface and the "phonon bridge" effect provided by AlN that enhances the overlap between the vibrational spectra of GaN and SiC.

Phonon transport across rough AlGaN/GaN interfaces with varying Al–Ga atomic ratios

Exploring interfacial thermal transport of a heterojunction interface is crucial to achieving advanced thermal management for gallium nitride-based high electron mobility transistor devices. The current research primarily focuses on material enhancements and microstructure design at the interfaces of epitaxial layers, buffer layers, and substrates, such as the GaN/SiC interface and GaN/AlN interface. Yet, the influence of different concentrations of Al/Ga atoms and interface roughness on the interfacial thermal conductance (ITC) of AlGaN/GaN interface, the closest interface to the hot spot, is still poorly understood. Herein, we focus on the rough AlGaN/GaN interface and evaluate the changes in ITC under different Al–Ga atomic concentrations and interface roughness using atomistic simulations. When the interface is completely smooth and AlGaN and GaN are arranged according to common polarization characteristic structures, the ITC gradually increases as the proportion of Al atoms decreases. When the proportion of Al atoms is reduced to 20%–30%, the impact of the interface structure on heat transfer is almost negligible. For interface models with different roughness levels, as the interface roughness increases, the ITC drops from 735.09 MW m−2 K−1 (smooth interface) to 469.47 MW m−2 K−1 by 36.13%. The decrease in ITC is attributed to phonon localization induced by rough interfaces. The phonon modes at the interface are significantly different from those in bulk materials. The degree of phonon localization is most pronounced in the frequency range that contributes significantly to heat flux. This work provides valuable physical insights into understanding the thermal transfer behaviors across the rough AlGaN/GaN interfaces.

Interfacial Thermal Transport and Electrical Performances of Supercapacitors with Graphene/Carbon Nanotube Composite Electrodes

Interfacial Thermal Transport and Electrical Performances of Supercapacitors with Graphene/Carbon Nanotube Composite Electrodes

Molecular dynamics study of thermal transport across diamond/cubic boron nitride interfaces

The thermal transport properties at the interface of diamond and cubic boron nitride (c-BN) heterostructures significantly influence heat dissipation in high-power electronic and optoelectronic devices. However, a fundamental understanding of the various parameters modulating the interfacial thermal conductance is still lacking. In this work, we employ non-equilibrium molecular dynamics (NEMD) simulations to systematically investigate the effects of system size, temperature, and defect density on the interfacial thermal conductance across diamond/c-BN interfaces. The results indicate a positive correlation between system length and interface thermal conductance when below the phonon mean free path threshold, attributable to ballistic phonon transport regimes in smaller domains. Additionally, we observe an incremental enhancement in interface thermal conductance with increasing temperature, stemmed from intensified phonon-phonon interactions and reduced boundary scattering of thermal energy carriers. The introduction of vacancy and twinning defects is found to hinder interfacial thermal transport due to heightened phonon scattering processes that impede phononic transmission. The interatomic interactions and lattice dynamics are analyzed to provide insights into the underlying thermal transport physics at the atomistic scale. By tuning the system length from 4 to 16 nm, temperature from 300 to 500 K, and defect density from 0 to 0.4%, we achieve tunable control of the interfacial thermal conductance. Our study elucidates the multiscale mechanisms governing thermal transport across diamond/c-BN and provides potential pathways to actively tailor interfacial thermal properties through structural and temperature engineering. The fundamental understandings are valuable for optimizing heat dissipation and enabling thermal management solutions in next-generation power electronics leveraging these materials.

Enhancing interfacial thermal transport efficiently in diamond/graphene heterostructure by involving vacancy defects

The enhancement of interfacial thermal conductance is critical to the efficient heat dissipation in micro- and nano- devices. The introduction of defects is a special method to improve the interfacial thermal conductance. For diamond/graphene heterostructure, the effects of defects in graphene and diamond on interfacial thermal conductance are investigated by molecular dynamics simulation. The increasing of defects in graphene causes the interfacial thermal conductance decreasing first and then increasing. The interfacial thermal conductance will remarkably rise with the increasing of the radius and number of vacancy defects in diamond. The thermal transport process at the interface experiences three stages according to the overlap energy of diamond and graphene. The mechanism of vacancy defect effectively enhancing interfacial thermal conductance is explained by interfacial modes of phonon density of states. The progress made so far could provide a special idea and guidance for improving heat dissipation for micro- and nano-devices.

Regulating interfacial thermal conductance with commensurate-incommensurate transitions at atomic-scale silicon/silicon interfaces.

Interfacial thermal conductance (ITC) between two contact surfaces is an important factor in accurately measuring energy transfer and heat dissipation at the interface; however, it is still not fully resolved how to more effectively modulate the ITC and unravel the related inner mechanisms. In this study, the contribution of commensurability and normal load to ITC at the atomic-scale silicon/silicon interface is disclosed. The results manifest that the ITC gradually reduces with the transition from commensurability to incommensurability. This is because the reduced force constant at the incommensurate interface decreases the transmittance of phonons, leading to the suppression of high-frequency phonon excitation and a red shift in the phonon spectrum, thereby weakening the ITC. We further discovered that increasing the normal loads can significantly enhance the ITC in both contact states, and the reason is that the interlayer distance decreases with increasing normal loads, which strengthens the interfacial potential and force constant, consequently resulting in greater heat transfer efficiency. This paper reveals that interfacial thermal transport can be regulated by applying normal loads and changing the interfacial contact states.

Microstructural Welding Engineering of Carbon Nanotube/Polydimethylsiloxane Nanocomposites with Improved Interfacial Thermal Transport

AbstractCarbon nanotube (CNT) reinforced polymer nanocomposites with high thermal conductivity show a promising prospect in thermal management of next‐generation electronic devices due to their excellent mechanical adaptability, outstanding processability, and superior flexibility. However, interfacial thermal resistance between individual CNT significantly hinders the further improvement in thermal conductivity of CNT‐reinforced nanocomposites. Herein, an interfacial welding strategy is reported to construct graphitic structure welded CNT (GS‐w‐CNT) networks. Notably, the obtained GS‐w‐CNT/polydimethylsiloxane (PDMS) nanocomposite with a GS loading of 4.75 wt% preserves a high thermal conductivity of 5.58 W m−1 K−1 with a 410% enhancement as compared to a pure CNT/PDMS nanocomposite. Molecular dynamics simulations are utilized to elucidate the effect of interfacial welding on the heat transfer behavior, revealing that the GS welding degree plays an important role in reducing both phonon scattering in the GS‐w‐CNT structure and interfacial thermal resistance at the interfaces between CNT. The unique welding strategy provides a new route to optimize the thermal transport performance in filler reinforced polymer nanocomposites, promoting their applications in next‐generation microelectronic devices.

Modulation of localized phonon thermal transport at GaN/AlxGa1-xN heterointerface: Polar surface, doping, and compressive Strain

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/AlxGa1-xN 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/AlxGa1-xN 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.

Enhanced interfacial thermal conductance in functionalized boron nitride/polylactic acid nanocomposites: A molecular dynamics study

The relatively low thermal conductivity of biodegradable polylactic acid (PLA) has limited its applications in various fields. To address this issue, the incorporation of nanofillers, such as boron nitride nanosheets (BNNSs), has emerged as an effective method to enhance PLA's thermal properties. However, the thermal conduction of polymer-based nanocomposites is strongly influenced by interfacial thermal resistance. In this study, we investigate the impact of pristine and surface-treated BNNSs on the thermal behavior of PLA using molecular dynamics simulations. To enhance interfacial interactions and reduce chain mobility during heat transfer, we chemically modify the surface of BNNSs by introducing three different functional groups (NH2, OH, and COOH) with varying polarities. Our findings suggest that oxygen-containing groups, namely –OH and –COOH, exhibit stronger interfacial interactions compared to the other cases. We also systematically apply different percentages of these functional groups (i.e., 2.5, 5, and 7.5 %) and observe that a higher number of functional groups leads to a greater improvement in interfacial thermal transport, attributed to the enhanced phonon coupling effect. To complete the discussion, we thoroughly study the influence of random and agglomerated patterns of functional groups distribution.

Reducing interfacial thermal resistance between polyethylene oxide-based solid-state polymer electrolyte and lithium anode by using IVA group two-dimensional materials: A molecular dynamics study

Solid-state lithium-ion batteries, as a new generation of high energy density electrochemical energy storage devices, need to meet more stringent thermal management standards. In this work, the interfacial thermal transport phenomena between a polyethylene oxide based solid electrolyte and a lithium anode in solid-state lithium-ion batteries was investigated by using a non-equilibrium molecular dynamics simulation method. To reveal the internal heat transport mechanism of the batteries at the microscopic level and to enhance the heat dissipation in them, IVA group two-dimensional monolayer materials such as graphene, silicene, and germanene were inserted at the interface and the interfacial thermal resistances were calculated to compared with the pristine interface. It was found that interfacial interactions were enhanced and the lattice vibrations were coupled by inserting the monolayer materials. Also, compared to the pristine interface, the interfacial thermal resistance was reduced by 83.89 %, 76.05 % and 55.99 %, respectively. Thus, this work provides valuable insights into the thermal transport between electrodes and electrolytes in solid-state lithium-ion batteries, and provides methodological references for improving the heat dissipation and thermal management efficiency inside the batteries.

The effect of binding energy on optimizing the interfacial thermal transport in metal-MoS2-dielectric nanostructures

The development of MoS2-based devices presents a significant challenge due to the poor interfacial thermal transport of metal-MoS2-dielectric structures, which results in severe thermal dissipation issues. This work aims to investigate the effects of various strategies, including modifying metal electrodes, adjusting the number of MoS2 layers, and incorporating van der Waals heterostructures, on the enhancement of interface thermal conductance (ITC) of metal-MoS2-dielectric structures. The time-domain thermoreflectance method was applied to characterize the ITC and experimental results demonstrate that the effect of regulating metal electrodes depends on the binding energy between the metal-MoS2 interfaces, which is a matter of controversy due to the large dispersion of published results. Furthermore, the increase in the number of MoS2 layers does not necessarily lead to the enhancement of the ITC of metal-MoS2-dielectric structures, as this is a comprehensive reflection of the number of layers' influence on both thermal conductance of MoS2 itself and the ITC between MoS2 and the surrounding materials. The results from the heterostructures of hBN-MoS2 and Gr-MoS2 were then systematically compared, and the results indicate the potential of Gr-MoS2 heterostructures in augmenting ITC. In addition, the nonequilibrium molecular dynamics simulation was effectively employed to gain deeper insights into the effect of binding energy on optimizing the ITC of metal-heterostructures-dielectric nanostructures. Finally, the effectiveness of these strategies in enhancing thermal properties was discussed through an analysis of interfacial binding energy. This finding provides a valuable direction for enhancing the thermal management of MoS2-based devices.

Phonon non-equilibrium effects on interface thermal resistance between graphene and substrates

Accurate measurement and deep understanding of interfacial thermal transport through interfaces where two-dimensional (2D) materials are involved are crucial for efficient thermal management in nanodevices. However, there is still a large discrepancy in the measurement on the interfacial thermal resistance (ITR) at interfaces between 2D materials and substrates. In this study, two kinds of molecular dynamics techniques are utilized to investigate the ITR of graphene/silicon interfaces under steady-state and transient conditions. Our results indicate that, in both conditions, phonon non-equilibrium phenomena could lead to an overestimation of the interfacial thermal resistance. In the steady state, the overestimation of ITR arises from an exaggerated interfacial temperature difference when using specific vibrational modes as indicators of the sample temperature. In the transient regime, it is attributed to the extended thermal relaxation time of flexural acoustic modes in graphene caused by weak phonon coupling when recording the temperature evolution to extract the ITR. These findings provide a comprehensive understanding of thermal transport across the graphene/silicon interface, aiding in the optimization of graphene-based nanodevices. The study also underlines the necessity of considering the specific experimental setup and physical processes involved when interpreting ITR data obtained from measurements.

Thermal transport across TiO2-H2O interface involving water dissociation: Ab initio-assisted deep potential molecular dynamics.

Water dissociation on TiO2 surfaces has been known for decades and holds great potential in various applications, many of which require a proper understanding of thermal transport across the TiO2-H2O interface. Molecular dynamics (MD) simulations play an important role in characterizing complex systems' interfacial thermal transport properties. Nevertheless, due to the imprecision of empirical force field potentials, the interfacial thermal transport mechanism involving water dissociation remains to be determined. To cope with this, a deep potential (DP) model is formulated through the utilization of abinitio datasets. This model successfully simulates interfacial thermal transport accompanied by water dissociation on the TiO2 surfaces. The trained DP achieves a total energy accuracy of ∼238.8meV and a force accuracy of ∼197.05 meV/Å. The DPMD simulations show that water dissociation induces the formation of hydrogen bonding networks and molecular bridges. Structural modifications further affect interfacial thermal transport. The interfacial thermal conductance estimated by DP is ∼8.54 × 109 W/m2K, smaller than ∼13.17 × 109 W/m2K by empirical potentials. The vibrational density of states (VDOS) quantifies the differences between the DP model and empirical potentials. Notably, the VDOS disparity between the adsorbed hydrogen atoms and normal hydrogen atoms demonstrates the influence of water dissociation on heat transfer processes. This work aims to understand the effect of water dissociation on thermal transport at the TiO2-H2O interface. The findings will provide valuable guidance for the thermal management of photocatalytic devices.

Sustainable epoxy composites with high thermal conductivity using poly(lipoic acid) modified liquid metal as crosslinkers

With the increasing demand for electronics integration and the increasing accumulation of e-waste, thermal management materials combing high conductivity and sustainability is highly desired. Herein, bio-based recyclable epoxy composites with significantly improved thermal conductivity were prepared by utilizing poly(lipoic acid) modified liquid metal (LM) as the crosslinkers. The strong interactions between poly(lipoic acid) and LM enable the formation of a poly(lipoic acid) shell layer coating on the LM droplet core, which facilitates the dispersion of LM droplets as well as interfacial thermal transport in the composites. As a result, the composite with only 25 vol% LM exhibits a thermal conductivity of 0.82 W/(m·K), which is higher than those of the previous studies with randomly filled LM at the same loading. In addition, attributed to the existence of dual dynamic bonds (disulfide bonds and β-hydroxyl ester bonds), the composites are reprocessable and their thermal conductivities are maintained after reprocessing. Moreover, the composites can be degraded under mild reducing conditions. This work presents a novel approach for the preparation of high-performance thermal management materials featuring recyclability and degradability.

Implications of Interfacial Thermal Transport on the Self-Heating of GaN-on-SiC High Electron Mobility Transistors

Implications of Interfacial Thermal Transport on the Self-Heating of GaN-on-SiC High Electron Mobility Transistors

Boltzmann transport equation simulation of phonon transport across GaN/AlN interface

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.