Thermal Boundary Resistance Values Research Articles

Molecular dynamics study of thermal transport across Ga2O3–diamond interfaces

Integration of β-Ga2O3 with high thermal conductivity materials such as diamond has been considered due to β-Ga2O3's low and anisotropic thermal conductivity, reaching only 27 W m–1 K–1. However, the effect of crystallographic orientation on thermal interface resistance has not been studied extensively, which is relevant for potential device architectures. In this work, we use molecular dynamics simulations to investigate the crystal orientation-dependent thermal boundary resistance (TBR) across van der Waals bonded diamond–β-Ga2O3 and ionicly bonded amorphous Al2O3–β-Ga2O3 interfaces. Al2O3 is often used as interlayer to grow diamond onto Ga2O3. We find that TBR values across the van der Waals interface may vary by up to 70% depending on the orientation of the β-Ga2O3, while the Al2O3–β-Ga2O3 TBR values remain around 0.9 ± 0.3 m2 KGW−1. We, thus, conclude on the optimal direction of β-Ga2O3 to use for reducing the TBR in these heterostructures.

Thermal boundary resistance enhancement through interfacial polarization electric field induced in GaN/InxGa1-xN superlattice

In this paper, we have theoretically investigated the effect of interfacial polarization electric (IPE) field due to interfaces on thermal boundary resistance (TBR) of GaN/InGaN superlattices (SLs). The distribution of temperature in the active region of GaN/InGaN devices determines the TBR including and excluding IPE field induced by the strain of the SL compared with experiments and thermal simulations. The calculated TBR was found to be 9.3 × 10 −9 W −1 m 2 K for devices at room temperature which plays a key role in thermal management of the devices. The determined effective TBR was found to decrease with temperature; but was enhanced by polarization mechanism developed at the interface of GaN/InGaN SL. The contribution of very low thermal conductivity of InGaN layer of the SLs for improved thermoelectric efficiency requires comparatively a large value of TBR and its temperature dependences are also discussed. • Interfacial electric field is exploited to enhance thermal boundary resistance of GaN/In x Ga 1-x N/GaN SLs. • Electric field modifies thermal parameters and phonon properties of SL via inverse piezoelectric effect. • TBR is enhanced from 2.10 to 5. 30 × 10 −9 m 2 KW −1 closer to reported value of InGaAs SL. • TBR is enhanced in presence of field and shows more than 15% ehancement due to enhanced TBR. • k cp in presence (absence) of field for x = 0.1 and 0.9 are 4.652 (5.710) and 6.083 (7.327) Wm −1 K −1 .

Thermal boundary resistance at graphene-pentacene interface explored by a data-intensive approach

As the machinery of artificial intelligence matures in recent years, there has been a surge in applying machine learning (ML) techniques for material property predictions. Artificial neural network (ANN) is a branch of ML and has gained increasing popularity due to its capabilities of modeling complex correlations among large datasets. The interfacial thermal transport plays a significant role in the thermal management of graphene-pentacene based organic electronics. In this work, the thermal boundary resistance (TBR) between graphene and pentacene is comprehensively investigated by classical molecular dynamics simulations combined with the ML technique. The TBR values along the a, b and c directions of pentacene at 300 K are 5.19 ± 0.18 × 10−8 m2 K W−1, 3.66 ± 0.36 × 10−8 m2 K W−1 and 5.03 ± 0.14 × 10−8 m2 K W−1, respectively. Different architectures of ANN models are trained to predict the TBR between graphene and pentacene. Two important hyperparameters, i.e. network layer and the number of neurons are explored to achieve the best prediction results. It is reported that the two-layer ANN with 40 neurons each layer provides the optimal model performance with a normalized mean square error loss of 7.04 × 10−4. Our results provide reasonable guidelines for the thermal design and development of graphene-pentacene electronic devices.

Phonon Transport in Silicon-Diamond Thin Film Pairs: Consideration of Thermal Boundary Resistance Due to Cutoff Mismatch and Diffusive Mismatch Models

Thermal boundary resistance (TBR) generates a temperature drop across the interface of the thin film pairs, which in turn modifies the heat transport rates across the films. This effect magnifies for the dielectric films because of the boundary scattering of phonons during the energy transport. Therefore, investigation into TBR and phonon transport across thin film pairs becomes essential. In the present study, phonon transport across the silicon-diamond thin film pairs due to temperature disturbance is formulated using the first principle solution of the transport equation. The transient and frequency dependent solution of the Boltzmann transport equation is presented numerically for two-dimensional thin film pairs. The TBR at the interface of the thin film pairs is modeled incorporating the cutoff mismatch and diffusive mismatch models. It is found that the value of TBR predicted from the cutoff mismatch model agrees with the results reported in the open literature; in which case, the predictions of the cutoff mismatch model for the TBR are larger than those predicted from the diffusive mismatch model.

Inter-Carbon Nanotube Contact and Thermal Resistances in Heat Transport of Three-Phase Composites

Single-walled carbon nanotubes (SWNTs) tend to aggregate into bundles due to van der Waals forces during the fabrication of the composite. A computational model using an off-lattice Monte Carlo method is developed to systematically investigate the effects of SWNT bundles, the number of SWNTs per bundle and the thermal boundary resistance (TBR) at the SWNT–SWNT interfaces on the effective thermal conductivity (Keff) of three-phase composites. It is found that the aggregation of the SWNTs in bundles can reduce significantly the Keff of the composites with SWNTs oriented parallel or randomly to the heat flux direction, but it enhances slightly the Keff of those with SWNTs perpendicular to the heat flux direction. The Keff of the composites also decreases when more individual SWNTs aggregate in each bundle and with larger SWNT–SWNT TBR values. The thermal transport mechanism within the composites is dominated by a critical SWNT–SWNT TBR of 0.155 × 10–8 m2K/W.

Thermoelectric transport in heterogeneous medium: the role of thermal boundary resistance

To investigate the effect of thermal boundary resistance (TBR) on thermoelectric transport, the discontinuity in temperature is considered at the interface through Kapitza’s definition. The effect depends on two factors: the length of thermoelectric element and the value of TBR. More importantly, it is found that TBR has dramatic impact on the reduction in thermoelectric conversion efficiency, which decays exponentially with increasing TBR. The ratio of thermal boundary resistance to the length of thermoelectric element leading to the decrease of effective Seebeck coefficient largely accounts for the degradation of thermoelectric performance at the micro-scale.

Morphology Effects on Nonisotropic Thermal Conduction of Aligned Single-Walled and Multi-Walled Carbon Nanotubes in Polymer Nanocomposites

Carbon nanotube (CNT)−CNT contact and CNT distribution effects on anisotropic thermal transport in aligned CNT−polymer nanocomposites (PNCs) are studied using an off-lattice Monte Carlo numerical simulation. Inter-CNT contact and the associated thermal boundary resistance are shown here to significantly affect transport properties of PNCs, including anisotropy ratios. Previous studies have considered the effective thermal conductivities of CNT−PNCs using only a very large CNT−CNT thermal boundary resistance (TBR) compared to that of the CNT−matrix TBR as a limiting case. As CNT−CNT TBR is currently an unquantified parameter for CNT−polymer systems, and because it may be reduced by various techniques, heat transport with CNTs in contact is studied for a wide range of CNT−CNT TBR values, varying from 2 to 25 × 10−8 m2 K/W. The degree of CNT−CNT contact, CNT spatial distribution, and CNT−CNT TBR relative to CNT−matrix TBR are considered for 1−20% volume fraction of aligned single-walled and multi-walled CNTs...

Optimized Thermoelectric Refrigeration in the Presence of Thermal Boundary Resistance

Thermoelectric refrigerators (TEMs) offer several advantages over vapor-compression refrigerators. They are free of moving parts, acoustically silent, reliable, and lightweight. Their low efficiency and peak heat flux capabilities have precluded their use in more widespread applications. Optimization of thermoelectric pellet geometry can help, but past work in this area has neglected the impact of thermal and electrical contact resistances. The present work extends a previous 1-D TEM model to account for a thermal boundary resistance and is appropriate for the common situation where an air-cooled heat sink is attached to a TEM. The model also accounts for the impact of electrical contact resistance at the TEM interconnects. The pellet geometry is optimized with the target of either maximum performance or efficiency for an arbitrary value of thermal boundary resistance for varying values of the temperature difference across the unit, the pellet Seebeck coefficient, and the contact resistances. The model predicts that when the thermal contact conductance is decreased by a factor of ten, the peak heat removal capability is reduced by at least 10%. Furthermore, when the interconnect electrical resistance rises above a factor of ten larger than the pellet electrical resistance, the maximum heat removal capability for a given pellet height is reduced by at least 20% and the maximum coefficient of performance at low Ku-infin,u/(NK) values is reduced by at least 50%.

The Kapitza Resistance Across Grain Boundary by Molecular Dynamics Simulation

Nonequilibrium molecular dynamics (NEMD) simulations are performed to calculate thermal boundary resistance that arises from heat flow across Si grain boundary. The environment-dependent interatomic potential (EDIP) on crystal silicon is adopted as a model system. The issues are related to nonlinear response, local thermal equilibrium, and statistical averaging. The tilt grain boundaries Σ5 and Σ13 are simulated, and the values of thermal boundary resistance by nonequilibrium molecular dynamics are compared with those by Maiti et al. (Solid State Communications, vol. 102, 1997). Using the disperse relation of EDIP potential, an average transmission coefficient of thermal conductivity across boundary is calculated.

単層カーボンナノチューブと周辺物質の熱コンダクタンス(オーガナイズドセッション10 ナノ・マイクロスケール伝熱)

Molecular dynamics simulations of heat transfer between carbon nanotubes in a bundle and between a carbon nanotube and surrounding Lennard-Jones fluid were performed. The Brenner potential with the simplified form is employed as the potential function between carbon and carbon within a nanotube. The heat transfer rate can be well expressed by employing the thermal boundary resistance (TBR). The value of thermal boundary resistance is compared for the bundle and nanotube-LJ cases.