利用热电桥法研究悬空单层石墨烯的声子热输运性质

Graphene provides perfect test platform for investigating two-dimensional phonon transports due to its unique two-dimensional structure and its ultra-high thermal conductivity. However, the study of heat conduction in graphene is still in its infancy due to the technical challenge in fabricating suspended single layer graphene suitable for thermal measurements. In this proposal, we will utilize thermal-bridge method to study thermal conductivity in suspended single layer graphene by combining suspended MEMS (Microelectromechanical System ) and CVD-grown graphene. We will try to solve the following issues in graphene thermal conduction:(1)what's the intrinsic thermal conductivity value in suspended graphene at room temperature; (2)which branch of acoustic phonons dominate thermal conduction in graphene, LA, TA or ZA phonons; (3)can phonons travel in graphene without being scattered, i.e. ballistic phonon transport; (4)thermal contact resistance issue between graphene and metal.

因为具有独特的二维晶格结构和高热导率，悬空石墨烯是迄今为止研究二维声子热传输的最佳平台。然而，由于制备悬空石墨烯样品存在很大的难度，从而使得对其热学性质的研究仍处于起步阶段。本项目将悬空微机电系统（MEMS）和CVD石墨烯相结合，利用热电桥法测量不同长度下悬空石墨烯的热导率，尝试解决其热学性质中的几个基本问题：（1）室温悬空石墨烯的数值为多少；（2）石墨烯中的三支声学声子(LA，TA和ZA)分别对其热导起着怎样的作用；（3）石墨烯中是否存在无阻声子热传输，即弹道声子热传输；（4）石墨烯与金属的接触热阻问题。

现代集成电路工作时产生的废热如果没有及时扩散出去就会导致热点，可能影响电路的稳定性或最终导致器件烧毁。二维材料（包括石墨烯、氮化硼和硫化钼等）具有很好的导热性能，是散热的绝佳材料。在本项目中，我们通过将多层二维材料与微机电系统（MEMS）结合的方式来研究二维材料热导性能及相关物理机理问题：声子-声子相互作用。本项目系统研究了单层石墨烯、多层氮化硼和硫化钼的热导性能，探讨了其物理机理。我们发现悬空石墨烯中面外ZA声子决定了其热导性能；发现悬空氮化硼热导率具有尺度效应；发现MoS2热输运符合变程跳跃模型。通过该项目的研究，我们提升了对二维材料声子热传导机理的认识，为进一步建立一套全新的二维材料声子热传导理论奠定实验基础。