Molecular Dynamics Simulation on In-Plane Thermal Conductivity of Graphene/Hexagonal Boron Nitride van der Waals Heterostructures

Thermal Rectification Modulation of Parallel Multiple Carbon/Boron Nitride Heteronanotubes

Thermal rectification (TR) efficiency has always been an important concern for thermal rectifiers. However, in practical terms, the amount of heat conduction is equally not negligible. To get high values on both of them, the carbon nanotube arrays with high thermal conductivity and large heat conduction areas were considered, along with carbon/boron nitride heteronanotubes (CBNNTs) with excellent TR property. In our work, multiple CBNNT models are constructed, and the TR ratio under different conditions is investigated using nonequilibrium molecular dynamics, with double CBNNTs (D-CBNNTs) aligned in parallel as the main analytical object. It is shown that weakening the intertube coupling is an available way to enhance the TR ratio, and adjusting the heteronanotube length and spacing can also effectively regulate the TR. In the process of changing the coupling coefficient, we analyzed both phonon changes and atomic vibrations and got a good correspondence, and the BN region is more variable in D-CBNNTs. In addition, the covariation of phonon localization and intertube phonon exchange with the coupling coefficient results in an invariant backward heat flux in the D-CBNNT. Furthermore, by adjusting the carbon proportion and lowering the coupling coefficient in the model, an excellent TR ratio in four CBNNTs was obtained and its heat flux is even larger than the value at a carbon percentage of 50% in larger coupling. We fully utilized the phonon density of states, phonon participation rate, and mean square displacement. Our results demonstrate the possibility of multiple CBNNTs as thermal rectifiers and provide theoretical guidance for heteronanotube arrays to be applied.

One-Dimensional van der Waals Heterojunction Comprising Carbon Nanotube Half-Wrapped in Boron Nitride Nanotube: Deep Investigation of Thermal Rectification

One-dimensional van der Waals (vdWs) heterostructures are celebrated for their exceptional thermal management capabilities, garnering significant research interest. Consequently, our research focused on the one-dimensional vdWs heterojunction comprising carbon nanotube half-wrapped in boron nitride nanotube (BNCNT), specifically their thermal rectification (TR) properties. We employed non-equilibrium molecular dynamics to explore the TR mechanism and assess the impacts of temperature, strain, and coupling strength on heat flux and TR ratio. Our findings reveal that the backward heat flux demonstrates greater atomic vibration instability, as indicated by mean square displacement (MSD), compared to forward heat flux. This instability leads to a higher concentration of localized phonons, thereby diminishing the backward heat flux and enhancing TR. Additionally, we utilized MSD to shed light on the negative differential thermal resistance phenomenon and the influence of stress on forward and backward heat fluxes. Remarkably, TR ratios reached 344% at 3% strain and 400% at -1% strain. Calculations of phonon density of states revealed a competitive mechanism between in-plane and out-of-plane phonons coupling in the inner carbon nanotube and an overlap degree of out-of-plane phonon spectra between the inner carbon nanotube and outer boron nitride nanotube. This accounts for the differing trends in forward and backward heat fluxes as coupling strength χ increases, with TR ratios exceeding 1000% at χ = 7.5. This study provides vital insights for advancing one-dimensional vdWs thermal rectifiers.

Molecular dynamics investigation on the interfacial thermal resistance between annealed pyrolytic graphite and copper

Modern highly integrated microelectronic products often face the challenge of internal heat dissipation, leading to a significant decrease in their operational efficiency. Annealed Pyrolytic Graphite (APG), due to its superior thermal conductivity, has garnered attention from researchers. The interface thermal resistance between APG and supporting materials like copper significantly affects heat transfer during APG's operation. Existing studies rarely delve into the influence of factors such as the shape of APG material interfaces on thermal resistance from a microscopic perspective. In this paper, utilizing transient thermo-reflectance method and non-equilibrium molecular dynamics simulations, the interface thermal resistance of the APG-Cu structure was investigated under different conditions. The impact of parameters such as copper thickness, interface micro-surface morphology, and APG thickness on the calculated interface thermal resistance was examined. Simulation results revealed that copper thickness had a minor effect on the interface thermal resistance. This is because the phonon participation ratio remains unaffected by changes in the thickness of the copper layer. The interfacial thermal resistance beneath microscopically cylindrical copper surfaces was considerably lower than that of rectangular copper surfaces. This is because beneath the cylindrical surface, the enlarged interface contact area facilitates enhanced thermal transport between the interfaces. The computed results of the radial distribution function in the paper also indirectly validate this viewpoint. The magnitude of interfacial thermal resistance for different APG layers was influenced by the coupling effect of intermolecular forces and the layered stacking structure of APG. The interfacial thermal resistance under the condition of three layers of APG reaches its minimum value, which is 2.2 × 10-9 (K m2 W-1). Furthermore, from the phonon perspective, it is found that the interfacial thermal resistance with different numbers of APG layers is closely related to the localization or delocalization state of phonons. As the number of APG layers increased, the interface thermal resistance showed a trend of initial decrease followed by an increase, this is because the average phonon participation ratio increases and then decreases with the number of APG layers. The average phonon participation ratio reaches its maximum value of 0.45778 under the condition of three layers of APG.

Nanobubble-induced significant reduction of the interfacial thermal conductance for few-layer graphene

The heat transport properties of van der Waals layered structures are crucial for ensuring the reliability and longevity of high-performance optoelectronic equipment. Owing to the two-dimensional nature of atomic layers, the presence of bubbles is commonly observed within these structures. Nevertheless, the effect of bubbles on the interfacial thermal conductance remains unclear. Based on the elastic membrane theory and the improved van der Waals gas state equation, we develop an analytical formula to describe the influence of bubble shape on the interfacial thermal conductance. It shows that the presence of bubbles has a considerable impact on reducing the interfacial thermal conductance across graphene/graphene interfaces. More specifically, the presence of nanobubbles can result in a reduction of up to 53% in the interfacial thermal conductance. The validity of the analytical predictions is confirmed through molecular dynamic simulations. These results offer valuable insights into the thermal management of van der Waals layered structures in the application of next-generation electronic nanodevices.

Advances and mechanisms in polymer composites toward thermal conduction and electromagnetic wave absorption

Polymer composites have essential applications in electronics due to their versatility, stable performance, and processability. However, with the increasing miniaturization and high power of electronics in the 5G era, there are significant challenges related to heat accumulation and electromagnetic wave (EMW) radiation in narrow spaces. Traditional solutions involve using either thermally conductive or EMW absorbing polymer composites, but these fail to meet the demand for multi-functional integrated materials in electronics. Therefore, designing thermal conduction and EMW absorption integrated polymer composites has become essential to solve the problems of heat accumulation and electromagnetic pollution in electronics and adapt to its development trend. Researchers have developed different approaches to fabricate thermal conduction and EMW absorption integrated polymer composites, including integrating functional fillers with both thermal conduction and EMW absorption functions and innovating processing methods. This review summarizes the latest research progress, factors that affect performance, and the mechanisms of thermal conduction and EMW absorption integrated polymer composites. The review also discusses problems that limit the development of these composites and potential solutions and development directions. The aim of this review is to provide references for the development of thermal conduction and EMW absorption integrated polymer composites.