石墨烯在散热及热管理中的应用

由于其优异的机械、光学、电子和热性能,石墨烯引起了全球科技界和工业界的高度关注。其中,石墨烯极高的横向热导率使石墨烯成为电子和光子器件热管理的理想材料。本文介绍石墨烯在电子热管理中的应用,特别关注其产业化方面的进展。本文首先介绍石墨烯的制备和热学性能,然后介绍石墨烯散热片在电子器件热管理中的应用,最后,介绍石墨烯在散热和热管理领域中的机遇、挑战和未来趋势。     

热界面材料对高功率LED热阻的影响

散热不良是制约大功率LED发展的主要瓶颈之一, 直接影响着大高功率LED器件的寿 命、出光效率和可靠性等。本文采用T3ster热阻测试仪和 ANSYS热学模拟的方法对LED器件进行热学分析,以三种热界面材料(金锡,锡膏,银胶)对LE D热阻及芯片结温的影响为例,分析了热界面材料的热导率、厚度对LED器件热学性能的影响 ,实验结果表明界面热阻在LED器件总热阻中所占比重较大,是影响LED结温高低的主要因素 之一;热学模拟结果表明,界面材料的热导率、厚度及界面材料的有效接触率均会影响到LE D器件结温的变化,所以在LED器件界面互连的设计中,需要综合考虑以上三个关键参数的控 制,以实现散热性能最佳化。     

大功率白光LED封装设计与研究进展

封装设计、材料和结构的不断创新使发光二极管(LED)性能不断提高.从光学、热学、电学、机械、可靠性等方面,详细评述了大功率白光LED封装的设计和研究进展,并对封装材料和工艺进行了具体介绍.提出LED的封装设计应与芯片设计同时进行,并且需要对光、热、电、结构等性能统一考虑.在封装过程中,虽然材料(散热基板、荧光粉、灌封胶)选择很重要,但封装工艺(界面热阻、封装应力)对LED光效和可靠性影响也很大.     

基于介质嵌层的热电式微波功率传感器特性研究

为改善热电式MEMS微波功率传感器的电-热-电转换效率,提出了一种新型介质嵌层结构。选用Si₃N₄、新型材料石墨烯分别作为介质嵌层。建立介质嵌层结构的热学模型,采用Ansys软件对热学特性进行了仿真。结果表明,当石墨烯作为介质嵌层时,热电偶热端的温度提高了12 K,有效改善了传热效率,提高了热电堆温差。建立介质嵌层结构的电磁模型,采用Hfss软件对微波性能进行了仿真。结果表明,在8~12 GHz范围内,S参数约为-18 dB,传感器仍具有良好的匹配特性。该介质嵌层结构对热电式MEMS微波功率传感器研究有参考价值。     

一种二极管型红外热探测器热学参数的电学等效测 试方法

红外热探测器的热学参数包括热容、热导、热响应时间,反应了结构信息和器件性能。精确有效地获得这些参数,对探测器的结构优化与性能评估具有指导意义。二极管型红外热探测器是红外热探测器的主要类型之一。基于二极管型红外热探测器的自热效应,提出了一种热学参数的电学等效测试方法,具有测量精度高且实现简单的特点。并对自制的一款二极管型红外焦平面阵列像元进行了测试,测试结果与理论分析相符,验证了方法的可行性。     

微波等离子法在硅上生长碳纳米管

美国珀杜大学报道,在计算机芯片上生长碳纳米管可在芯片与热沉连接部位加速散热。微波等离子法可产生纳米管界面,使热沉拥有起伏不平的表面,从而使导热性能比普通界面材料更佳。     

一种优化的微测热辐射计热学参数性能测试分析方法

优化的微测热辐射计热学参数的测试方法,与传统测试方法相比,能够实现热导和响应时间的精确测量,克服热学参数评估依赖仿真的缺陷,且该方法易于实现,工程应用性强.通过对研制的微测热辐射计性能进行相应的测试,确定了该测试方法准确、可靠.     

石墨烯材料在钙钛矿太阳能电池中的研究进展

石墨烯及其衍生物具有独特的材料结构和光电性质,可作为界面修饰层、电子传输层、空穴传输层应用于新型钙钛矿太阳能电池,以提高电池的光电转换效率和性能稳定性。此外,石墨烯透明电极在柔性、半透明或叠层钙钛矿太阳能电池应用中独具优势。本文综述了石墨烯及其衍生物在钙钛矿太阳能电池中的研究进展,指出了未来发展重点。     

基于石墨烯复合材料的散热结构温度场分布有限元分析

高导石墨烯复合材料具有优异的热物理性能,与铜等传统热管理材料相比,具有密度低、导热性能好的优势,是非常理想的电子封装材料。但由于其高成本、低强度的缺点,严重制约了这类材料的应用。本文以课题组制备的石墨烯高导热复合材料为基础,采用复合材料作为关键散热部件材料,既利用了复合材料的定向高导热特性又解决了成本高、力学强度差的问题,并且通过ANSYS软件进行温度场模拟,成功将热源表面温度降低11.5℃,证明了在特殊区域,采用新型高导热石墨烯复合材料代替传统材料的手段,可以改善整个结构导热性能。研究成果为新型热管理材料在相关领域的应用提供了技术支撑。     

石墨烯基电子学研究进展(续)

4 石墨烯的应用 尽管纳米管具有许多独特的优点,但石墨烯与其相比具有无可比拟的优势,如在制作复杂电路时若采用纳米管,则必须经过仔细筛选和定位,目前还没有开发出有效的方法,而采用石墨烯工艺较为简单和容易得多;石墨烯平面型材料与传统的半导体器件CMOS等的平面化工艺兼容性较好.     

激光诱导碳纳米管制备石墨烯纳米带及其电学性能分析

通过将纳米管解压缩可以很容易地生产石墨烯纳米带,因为碳纳米管结构可以被认为是卷起的石墨烯筒。这是一种特殊的2D石墨结构,具有出色的性能。应用领域广泛,包括晶体管、光学和微波通信设备、生物传感器、化学传感器、电子存储和处理设备以及纳米机电系统和复合材料。通过扫描电子显微镜（SEM）观察薄膜的形貌,通过拉曼光谱法表征石墨烯的性质,并通过半导体参数测量系统测量薄膜的电导率。拉曼光谱表明,通过优化工艺可以增强石墨烯的拉曼特性。碳纳米管制备石墨烯带的两个重要参数是激光能量密度和辐照时间。在这项研究中,通过准分子激光辐照碳纳米管薄膜来生产石墨烯纳米带。实验结果表明,在150 mJ的激光能量下,观察到连接时碳纳米管没有打开。在450 mJ的能量下,可以有效地破坏碳纳米管,并且使其部分地形成石墨烯带。此时,膜的电导率达到最大值。由于蓄热作用,在碳纳米管壁上出现大量的多孔结构。     

Carbide‐Derived Carbons – From Porous Networks to Nanotubes and Graphene

Carbide‐derived carbons (CDCs) are a large family of carbon materials derived from carbide precursors that are transformed into pure carbon via physical (e.g., thermal decomposition) or chemical (e.g., halogenation) processes. Structurally, CDC ranges from amorphous carbon to graphite, carbon nanotubes or graphene. For halogenated carbides, a high level of control over the resulting amorphous porous carbon structure is possible by changing the synthesis conditions and carbide precursor. The large number of resulting carbon structures and their tunability enables a wide range of applications, from tribological coatings for ceramics, or selective sorbents, to gas and electrical energy storage. In particular, the application of CDC in supercapacitors has recently attracted much attention. This review paper summarizes key aspects of CDC synthesis, properties, and applications. It is shown that the CDC structure and properties are sensitive to changes of the synthesis parameters. Understanding of processing–structure–properties relationships facilitates tuning of the carbon material to the requirements of a certain application.     

Graphene: Carbide‐Derived Carbons – From Porous Networks to Nanotubes and Graphene (Adv. Funct. Mater. 5/2011)

Carbide‐derived carbons (CDCs) are a large family of carbon materials derived from carbide precursors that are transformed into pure carbon via physical (e.g., thermal decomposition) or chemical (e.g., halogenation) processes. Structurally, CDC ranges from amorphous carbon to graphite, carbon nanotubes or graphene. For halogenated carbides, a high level of control over the resulting amorphous porous carbon structure is possible by changing the synthesis conditions and carbide precursor. The large number of resulting carbon structures and their tunability enables a wide range of applications, from tribological coatings for ceramics, or selective sorbents, to gas and electrical energy storage. In particular, the application of CDC in supercapacitors has recently attracted much attention. This review paper summarizes key aspects of CDC synthesis, properties, and applications. It is shown that the CDC structure and properties are sensitive to changes of the synthesis parameters. Understanding of processing–structure–properties relationships facilitates tuning of the carbon material to the requirements of a certain application.     

Covalently Bonded Graphene–Carbon Nanotube Hybrid for High‐Performance Thermal Interfaces

The remarkable thermal properties of graphene and carbon nanotubes (CNTs) have been the subject of intensive investigations for the thermal management of integrated circuits. However, the small contact area of CNTs and the large anisotropic heat conduction of graphene have hindered their applications as effective thermal interface materials (TIMs). Here, a covalently bonded graphene–CNT (G‐CNT) hybrid is presented that multiplies the axial heat transfer capability of individual CNTs through their parallel arrangement, while at the same time it provides a large contact area for efficient heat extraction. Through computer simulations, it is demonstrated that the G‐CNT outperforms few‐layer graphene by more than 2 orders of magnitude for the c‐axis heat transfer, while its thermal resistance is 3 orders of magnitude lower than the state‐of‐the‐art TIMs. We show that heat can be removed from the G‐CNT by immersing it in a liquid. The heat transfer characteristics of G‐CNT suggest that it has the potential to revolutionize the design of high‐performance TIMs.     

Graphene–Polymer Nanofiber Membrane for Ultrafast Photonics

A freestanding membrane composed of a nanofiber network of a graphene–polymer nanocomposite is fabricated by electrospinning and applied as an optical element in fiber lasers. The functionalization of graphene with conjugated organic molecules provides a handle for improving mechanical and thermal properties as well as tuning the optical properties. A small loading (0.07 wt%) of functionalized graphene enhances the total optical absorption of poly(vinyl acetate) (PVAc) by 10 times. The electrospun graphene–polymer nanocomposites exhibit wideband saturable absorbance for laser pulse shaping, and attain a larger modulation depth and smaller nonsaturable loss than single‐walled carbon nanotubes. The results show that electrospun graphene nanocomposites are promising candidates as practical and efficient photonic materials for the generation of ultrashort pulses in fiber lasers.     

Thermal joint conductance for flexible graphite materials: analytical and experimental study

Increasingly, thermal interstitial materials (TIMs), such as metallic foils, solder, metallic coatings, polymeric matrices loaded with highly conducting filler particles (e.g., elastomers), greases, and phase-change materials are being employed to a greater extent in power generating systems. With greater use, follow an increased interest in the thermal transport and mechanical properties of these materials. These properties include thermal conductivity, thermal diffusivity, Young's modulus, Poisson's ratio, and the thermal resistance at the interface between the interstitial materials with the substrate material; however, these are just a few of the representative thermophysical properties that might be needed to model these thermal interstitial materials. In addition to these TIMs, a novel material has recently been fabricated, from highly pure graphite flakes, which has shown great promise in enhancing the joint thermal conductance without the limitations experienced by some TIMs (e.g., need for reflow temperatures for phase change materials to achieve good contact conductance). To provide information on the thermal joint conductance of an important interstitial material employed in microelectronic components, an experimental investigation has been undertaken for a class of TIMs called "Flexible Graphite". The experimental data were compared to an analytical model developed for elastic layers that was applicable to this class of thermal interface material. In addition, a comparison between the model, and a paraffin phase-change material deposited onto one surface of the elastic layer was conducted. The model assumes that complete wetting of the paraffin material takes place, therefore, only an additional gap conductance expression was incorporated. The model and data were found to be in good agreement over the pressure range within the investigation. The proposed model can be used to predict the lower bound on the joint conductance.     

二维材料调制的掺铥脉冲光纤激光器的研究进展

2μm波段掺铥脉冲光纤激光器由于在人眼安全、激光雷达、生命科学、光通信和医疗等领域有着重要的应用,近年来成为新型光纤激光器的研究热点。以石墨烯为代表的二维材料因其优良的可饱和吸收特性引起人们的广泛关注。分析了碳纳米管、石墨烯、黑鳞及拓扑材料等二维材料作为可饱和吸收体在掺铥脉冲激光器中的应用和发展。对国内外基于二维材料的掺铥脉冲光纤激光器的研究进展进行了综述,并对其未来的发展前景进行了展望。     

Tailored Assembly of Carbon Nanostructures: Tailored Assembly of Carbon Nanotubes and Graphene (Adv. Funct. Mater. 8/2011)

This Feature Article reviews recent progress in the tailored assembly of carbon nanotubes and graphene into three‐dimensional architectures with particular emphasis on our own research employing self‐assembly principles. Carbon nanotubes and graphene can be assembled into macroporous films, hollow spherical capsules, or hollow nanotubes, via directed assembly from solvent dispersion. This approach is cost‐effective and beneficial for large‐scale assembly, but pre‐requests stable dispersion in a solvent medium. Directed growth from a nanopatterned catalyst array is another promising approach, which enables the control of morphology and properties of graphitic materials as well as their assembly. In addition, the aforementioned two approaches can be synergistically integrated to generate a carbon hybrid assembly consisting of vertical carbon nanotubes grown on flexible graphene films. Tailored assembly relying on scalable self‐assembly principles offer viable routes that are scalable for mass production towards the ultimate utilization of graphitic carbon materials in nanoelectronics, displays, sensors, energy storage/conversion devices, and so on, including future flexible devices.     

Tailored Assembly of Carbon Nanotubes and Graphene

This Feature Article reviews recent progress in the tailored assembly of carbon nanotubes and graphene into three‐dimensional architectures with particular emphasis on our own research employing self‐assembly principles. Carbon nanotubes and graphene can be assembled into macroporous films, hollow spherical capsules, or hollow nanotubes, via directed assembly from solvent dispersion. This approach is cost‐effective and beneficial for large‐scale assembly, but pre‐requests stable dispersion in a solvent medium. Directed growth from a nanopatterned catalyst array is another promising approach, which enables the control of morphology and properties of graphitic materials as well as their assembly. In addition, the aforementioned two approaches can be synergistically integrated to generate a carbon hybrid assembly consisting of vertical carbon nanotubes grown on flexible graphene films. Tailored assembly relying on scalable self‐assembly principles offer viable routes that are scalable for mass production towards the ultimate utilization of graphitic carbon materials in nanoelectronics, displays, sensors, energy storage/conversion devices, and so on, including future flexible devices.     

Ionic Liquid‐Assisted Synthesis of TiO2–Carbon Hybrid Nanostructures for Lithium‐Ion Batteries

Building nanocomposite architectures based on nanocarbon materials (such as carbon nanotubes and graphene nanosheets) and metal‐oxide nanoparticles is of great interests for electrochemical energy storage. Here, an ionic‐liquid‐assisted strategy is presented to mediate the in situ growth of TiO₂ nanocrystals with controlled size on carbon nanotubes and graphene, and also reduce the modified carbon supports to recover the graphitic structure simultaneously. The as‐prepared nanocomposites exhibit a highly porous and robust structure with intimate coupling between TiO₂ nanocrystals and carbon supports, which offers facile ion and electron transport pathway as well as high mechanical stability. When evaluated as electrode materials for lithium‐ion batteries, the nanocomposites manifest high specific capacity, long cycling lifetime, and excellent rate capability, showing their promising application in high‐performance energy storage devices.