Enhancement of Thermal Energy Transport Across Graphene/Graphite and Polymer Interfaces: A Molecular Dynamics Study

Understanding thermal energy transport in polymeric nanocomposite materials is important to the engineering of polymer composites with better engineered heat transfer properties. Interfacial thermal resistance between the filling particles and the polymer matrices is a major bottleneck for the thermal conductivity improvement of polymer composite materials. Here, thermal energy transport in graphene/graphite‐polymer (paraffin wax‐C₃₀H₆₂) composite systems are systematically studied using molecular dynamics simulations. The influences of graphene size, interfacial bonding strength, and polymer density on the interfacial thermal transport are studied. According to the simulation results, approaches to improve interfacial thermal transport are proposed. Spectral analysis is performed to explore the mechanism of thermal transport. It is found that thermal energy transport across graphene/graphite‐polymer interfaces can be enhanced by increasing the polymer density and graphene size or forming covalent bonds between the graphite edges and polymer molecules. The results offer valuable guidance on improving thermal transport properties of polymeric nanocomposite.     

Tuning Thermal Transport Through Atomically Thin Ti3C2Tz MXene by Current Annealing in Vacuum

Heat transport across vertical interfaces of heterogeneous 2D materials is usually governed by the weak Van der Waals interactions of the surface‐terminating atoms. Such interactions play a significant role in thermal transport across transition metal carbide and nitride (MXene) atomic layers due to their hydrophilic nature and variations in surface terminations. Here, the metallicity of atomically thin Ti₃C₂T_z MXene, which is also verified by scanning tunneling spectroscopy for the first time, is exploited to develop a self‐heating/self‐sensing platform to carry out direct‐current annealing experiments in high (<10^?8 bar) vacuum, while simultaneously evaluating the interfacial heat transport across a Ti₃C₂T_z/SiO₂ interface. At room temperature, the thermal boundary conductance (TBC) of this interface is found, on average, to increase from 10 to 27 MW m^?2 K^?1 upon current annealing up to the breakdown limit. In situ heating X‐ray diffraction and X‐ray photo‐electron spectroscopy reveal that the TBC values are mainly affected by interlayer and interface spacing due to the removal of absorbents, while the effect of surface termination is negligible. This study provides key insights into understanding energy transport in MXene nanostructures and other 2D material systems.     

Enhanced Thermal Transport across Self-Interfacing van der Waals Contacts in Flexible Thermal Devices

Minimizing the thermal contact resistance (TCR) at the boundary between two bodies in contact is critical in diverse thermal transport devices. Conventional thermal contact methods have several limitations, such as high TCR, low interfacial adhesion, a requirement for high external pressure, and low optical transparency. Here, a self-interfacing flexible thermal device (STD) that can form robust van der Waals mechanical contact and low-resistant thermal contact to planar and non-planar substrates without the need for external pressure or surface modification is presented. The device is based on a distinctive integration of a bioinspired adhesive architecture and a thermal transport layer formed from percolating silver nanowire (AgNW) networks. The proposed device exhibits a strong attachment (maximum 538.9 kPa) to target substrates while facilitating thermal transport across the contact interface with low TCR (0.012 m² K kW⁻¹) without the use of external pressure, thermal interfacial materials, or surface chemistries.     

Thermal Transport in 2D Semiconductors—Considerations for Device Applications

The discovery of graphene has stimulated the search for and investigations into other 2D materials because of the rich physics and unusual properties exhibited by many of these layered materials. Transition metal dichalcogenides (TMDs), black phosphorus, and SnSe among many others, have emerged to show highly tunable physical and chemical properties that can be exploited in a whole host of promising applications. Alongside the novel electronic and optical properties of such 2D semiconductors, their thermal transport properties have also attracted substantial attention. Here, a comprehensive review of the unique thermal transport properties of various emerging 2D semiconductors is provided, including TMDs, black‐ and blue‐phosphorene among others, and the different mechanisms underlying their thermal conductivity characteristics. The focus is placed on the phonon‐related phenomena and issues encountered in various applications based on 2D semiconductor materials and their heterostructures, including thermoelectric power generation and electron–phonon coupling effect in photoelectric and thermal transistor devices. A thorough understanding of phonon transport physics in 2D semiconductor materials to inform thermal management of next‐generation nanoelectronic devices is comprehensively presented along with strategies for controlling heat energy transport and conversion.     

Thermal Conductivity of Amorphous Materials

Thermal conductivity is one of the most fundamental properties of solid materials. The thermal conductivity of ideal crystal materials has been widely studied over the past hundreds years. On the contrary, for amorphous materials that have valuable applications in flexible electronics, wearable electrics, artificial intelligence chips, thermal protection, advanced detectors, thermoelectrics, and other fields, their thermal properties are relatively rarely reported. Moreover, recent research indicates that the thermal conductivity of amorphous materials is quite different from that of ideal crystal materials. In this article, the authors systematically review the fundamental physical aspects of thermal conductivity in amorphous materials. They discuss the method to distinguish the different heat carriers (propagons, diffusons, and locons) and the relative contribution from them to thermal conductivity. In addition, various influencing factors, such as size, temperature, and interfaces, are addressed, and a series of interesting anomalies are presented. Finally, the authors discuss a number of open problems on thermal conductivity of amorphous materials and a brief summary is provided.     

Visualizing Energy Transfer at Buried Interfaces in Layered Materials Using Picosecond X‐Rays

Understanding the fundamentals of nanoscale heat propagation is crucial for next‐generation electronics. For instance, weak van der Waals bonds of layered materials are known to limit their thermal boundary conductance (TBC), presenting a heat dissipation bottleneck. Here, a new nondestructive method is presented to probe heat transport in nanoscale crystalline materials using time‐resolved X‐ray measurements of photoinduced thermal strain. This technique directly monitors time‐dependent temperature changes in the crystal and the subsequent relaxation across buried interfaces by measuring changes in the c‐axis lattice spacing after optical excitation. Films of five different layered transition metal dichalcogenides MoX₂ [X = S, Se, and Te] and WX₂ [X = S and Se] as well as graphite and a W‐doped alloy of MoTe₂ are investigated. TBC values in the range 10–30 MW m^?2 K^?1 are found, on c‐plane sapphire substrates at room temperature. In conjunction with molecular dynamics simulations, it is shown that the high thermal resistances are a consequence of weak interfacial van der Waals bonding and low phonon irradiance. This work paves the way for an improved understanding of thermal bottlenecks in emerging 3D heterogeneously integrated technologies.     

Advanced Materials for High‐Temperature Thermal Transport

High temperature processes are widely used in a variety of existing and emerging industrial and aerospace applications. The thermal properties of high‐temperature materials thus play an important role in controlling the thermal energy, as highlighted by successful applications of thermal barrier coating and aerogels. While thermal transport processes at room and low temperature have witnessed tremendous progress in the past two decades, particularly on the fronts of understanding basic heat transfer properties at the micro‐ and nanoscale, the understanding at high temperature is still at the nascent stage, owing to several unique features at high temperature, such as the dominant Umklapp scattering effect that can render a crystalline material amorphous‐like thermal properties, and the important radiation contribution at high temperature. This lack of systematic understanding, coupled with the challenges in maintaining high‐temperature stability in a large number of materials, has limited the development of materials to meet the thermal transport properties pertaining to several current and emerging high‐temperature applications. This Review is aimed at providing an overview of the basic mechanisms governing thermal transport processes at high temperature, to identify their unique features and challenges, and to explore opportunities in material research for high‐temperature thermal materials.     

Anomalous Low Thermal Conductivity of Atomically Thin InSe Probed by Scanning Thermal Microscopy

The ability of a material to conduct heat influences many physical phenomena, ranging from thermal management in nanoscale devices to thermoelectrics. Van der Waals 2D materials offer a versatile platform to tailor heat transfer due to their high surface-to-volume ratio and mechanical flexibility. Here, the nanoscale thermal properties of 2D indium selenide (InSe) are studied by scanning thermal microscopy. The high electrical conductivity, broad-band optical absorption, and mechanical flexibility of 2D InSe are accompanied by an anomalous low thermal conductivity (κ). This can be smaller than that of low-κ dielectrics, such as silicon oxide, and it decreases with reducing the lateral size and/or thickness of InSe. The thermal response is probed in free-standing InSe layers as well as layers supported by a substrate, revealing the role of interfacial thermal resistance, phonon scattering, and strain. These thermal properties are critical for future emerging technologies, such as field-effect transistors that require efficient heat dissipation or thermoelectric energy conversion with low-κ, high electron mobility 2D materials, such as InSe.     

Thermal and Thermoelectric Properties of Molecular Junctions

Molecular junctions (MJs) represent an ideal platform for studying charge and energy transport at the atomic and molecular scale and are of fundamental interest for the development of molecular‐scale electronics. While tremendous efforts have been devoted to probing charge transport in MJs during the past two decades, only recently advances in experimental techniques and computational tools have made it possible to precisely characterize how heat is transported, dissipated, and converted in MJs. This progress is central to the design of thermally robust molecular circuits and high‐efficiency energy conversion devices. In addition, thermal and thermoelectric studies on MJs offer unique opportunities to test the validity of classical physical laws at the nanoscale. A brief survey of recent progress and emerging experimental approaches in probing thermal and thermoelectric transport in MJs is provided, including thermal conduction, heat dissipation, and thermoelectric effects, from both a theoretical and experimental perspective. Future directions and outstanding challenges in the field are also discussed.     

近场热辐射的最新研究进展

主要从理论数值模拟和近场辐射实验研究的角度介绍了近几年在近场热辐射传热方面的最新研究成果。理论研究的焦点主要集中在石墨烯复合材料、人工加工或合成超材料等方面的传热研究。实验研究的焦点是实验室基于纳米尺度近场热辐射测量的设备制造与方法创新。目前实验上已经实现了最小距离仅为2 nm的极近场热辐射测量。近场热辐射的进一步研究可为热光伏、辐射制冷以及高效能源收集应用提供理论基础。     

Antioxidant-Based Phase-Change Thermal Interface Materials with High Thermal Stability

This work provides phase-change thermal interface materials (TIMs) with high thermal stability and high heat of fusion. They are based on antioxidants mainly in the form of hydrocarbons with linear segments. The thermal stability is superior to paraffin wax and four commercial phase-change materials (PCMs). The use of 98.0 wt.% thiopropionate antioxidant (SUMILIZER TP-D) with 2.0 wt.% sterically half-hindered phenolic antioxidant (GA80) as the matrix and the use of 16 vol.% boron nitride particles as the solid component give a PCM with a 100°C lifetime indicator of 5.3 years, in contrast to 0.95 year or less for the commercial PCMs. The heat of fusion is much higher than those of commercial PCMs; the values for antioxidants with nonbranched molecular structures exceed that of wax; the value for one with a branched structure is slightly below that of wax. The phase-change properties are degraded by heating at 150°C much less than those of the commercial PCMs. The stability of the heat of fusion upon phase-change cycling is also superior. The viscosity is essentially unaffected by heating at 150°C. Commercial PCMs give slightly lower values of the thermal contact conductance for the case of rough (12 μm) mating surfaces, in spite of the lower values of the bond-line thickness.     

A Review on Principles and Applications of Scanning Thermal Microscopy (SThM)

As the size of materials, particles, and devices shrinks to nanometer, atomic, or even quantum scale, it is more challenging to characterize their thermal properties reliably. Scanning thermal microscopy (SThM) is an emerging method to obtain local thermal information by controlling and monitoring probe–sample thermal exchange processes. In this review, key experimental and theoretical components of the SThM system are discussed, including thermal probes and experimental methods, heat transfer mechanisms, calibration strategies, thermal exchange resistance, and effective heat transfer coefficients. Additionally, recent applications of SThM to novel materials and devices are reviewed, with emphasis on thermoelectric, biological, phase change, and 2D materials.     

Thermal Transport in Conductive Polymer–Based Materials

The demand for flexible conductive materials has motivated many recent studies on conductive polymer–based materials. However, the thermal conductivity of conductive polymers is relatively low, which may lead to serious heat dissipation problems for device applications. This review provides a summary of the fundamental principles for thermal transport in conductive polymers and their composites, and recent advancements in regulating their thermal conductivity. The thermal transport mechanisms in conductive polymer–based materials and up‐to‐date experimental approaches for measuring thermal conductivity are first summarized. Effective approaches for the regulation of thermal conductivity are then discussed. Finally, thermal‐related applications and future perspectives are given for conductive polymers and their composites.     

封装中的界面热应力分析

随着电子封装集成度的不断提高,集成电路的功率容量和发热量也越来越高,封装体内就产生了越来越多的温度分布以及热应力问题。文章建立了基板-粘结层-硅芯片热应力分析有限元模型,利用有限元法分析了芯片/基板的热应力分布,封装体的几何结构参数对应力的影响,重点讨论了芯片与粘结层界面上和基板与粘结层界面上的层间应力分布     

Thermal Properties of Lipid Bilayers Determined Using Upconversion Nanothermometry

Luminescent nanomaterials have shown promise for thermal sensing in bio‐applications, yet little is known of the role of organic coatings such as supported lipid bilayers on the thermal conductivity between the nanomaterial and its environment. Additionally, since the supported lipid bilayer mimics the cell membrane, its thermal properties are fundamentally important to understand the spatial variations of temperature and heat transfer across membranes. Herein, a new approach is described that enables direct measurement of these thermal properties using a LiYF₄:Er³⁺/Yb³⁺ upconverting nanoparticle encapsulated within a conformal supported lipid bilayer and dispersed in water as a temperature probe yielding the temperature gradient across the bilayer. The thermal conductivity of the lipid bilayer is measured as a function of the temperature, being 0.20 ± 0.02 W m^?1 K^?1 at 300 K. For the uncapped nanoparticles dispersed in water, the temperature dependence of the thermal conductivity is also measured in the 300–314 K range as [0.63–0.69] ± 0.11 W m^?1 K^?1. Using a lumped elements model, the directional heat transfer is calculated at each of the system interfaces, namely, nanoparticle–bilayer and bilayer–nanofluid, opening a new avenue to understand the membrane biophysical properties as well as the thermal properties of organic and polymer coatings.     

非金属基导热材料对HPLED散热性能影响

由于光电转换效率较低,产生的多余熬已成为提升单位体积下大功率LED (HPLED)灯光输出量的主要瓶颈,使有效减少HPLED灯热流回路上各界面接触热阻成为重要课题.研究了不同的非金属基导热界面材料在不同环境温度条件下,应用于HPLED灯具模型中的第二界面处时对灯具散热情况的影响.结果表明,具有相变特征的非金属基导热界面材料.在其相变转化点位置之上的某一特定临界点后的热传导性能优于导热系数相对更高的非金属石墨基的界面材料.第二界面材料之间的接触热阻对发挥其导热能力有重要影响.     

脉冲激光二极管端面抽运固体激光器中晶体的热弛豫时间

在脉冲激光二极管(LD)端面抽运固体激光器中,存在热效应瞬态过程,即晶体的温度分布具有时变性,晶体温度的时变过程受到热弛豫时间的影响.从热传导方程出发,采用解析法和数值法分别对晶体降温过程中温度的时变性进行计算;采用有限元方法,对晶体热弛豫时间及其影响因素进行数值计算,分析了晶体直径、密度、热传导系数和比热等热物性参数对热弛豫时间的影响;采用流体流动换热理论,充分考虑了冷却水流温度和速度对晶体温度分布的影响.结果表明,通过调整晶体尺寸、冷却系统可以实现对热弛豫时间的控制.根据有限元软件ANSYS的计算结果,分析了晶体抽运端面上径向温度的时变分布,晶体边缘与中心的温差和光程差;初步计算了晶体热透镜不同径向位置处的焦距差.结果表明,晶体冷却过程中,不同径向位置与中心的温差和相对光程差具有时变性,晶体热透镜的聚焦特性也是随时间变化的.     

大功率LED路灯叉排式散热器的热学特性研究

本文结合有限体积数值模拟建立散热器热学模型,可准确计算散热器系统中温度场以及流体场分布,为有效评价散热器的散热效率提供重要参考依据。基于散热器热学模型．分析比较叉排式以及顺排式散热器的温度场以及流体场分布,发现又排式散热器中交错分布翅片可有效破坏散热器层流底层,增强了流体扰动,加大了换热效果,为优化叉排式散热器结构提供了可靠依据,进而通过分析优化散热器系统送风方向、粘结层材料、散热器材料对总体散热性能以及重量的交叉影响。     

Polyol-based phase-change thermal interface materials

Polyol-based phase-change thermal interface materials that exhibit high thermal contact conductance and thermal stability have been developed for microelectronic cooling. By using a diol (polycaprolactone or polyester diol in the form of 2-oxepanone) of molecular weight 1,000–2,000 amu, along with 4 vol.%-hexagonal boron nitride particles, this work attained thermal contact conductance (at 70°C, across copper surfaces) that is higher than that attained by using paraffin wax, polyether glycol, polyethylene glycol, or tetradecanol (in place of the diol) and that attained by commercial phase-change thermal interface materials. The thermal stability of the diol is superior to the other phase change materials mentioned above, although the heat of fusion is lower. Boron nitride is more effective than carbon black (also 4 vol.%) for enhancing the conductance, but carbon black diminishes the heat of fusion less than does boron nitride.