二维堆叠材料导热的范德华界面效应研究

Two-dimensional materials and their stacked structures hold excellent thermal properties, which show great application prospects in the energy field and can be promising thermal functional materials. In addition, thermal issues have a significant influence on the performance and reliability of the stacked two-dimensional material-based electronic devices. Regarding those two points above, it becomes urgently needed to carefully study the heat transport in the stacked two-dimensional materials. In fact, Van der Waals interfacial effects are of critical importance for the emergence of stacked two-dimensional materials’ unique thermal transport properties. When comparing to the interfaces with much stronger chemical bonds, Van der Waals interface’s properties can be easily affected by surroundings, and thus the Van der Waals interfacial effects on heat conduction are switchable. Moreover, the influence of ballistic transport and out-plane phonons is involved in Van der Waals interfacial effects on heat conduction in stacked two-dimensional materials. In the present project, the thermal transport process involving Van der Waals interfacial effects in the stacked two-dimensional materials, such as transition metal dichalcogenides and graphene, is planned to be systematically studied by experiments, simulations, as well as theoretical modeling. In details, a new measurement scheme will be developed for the small-area and irregular stacked materials to achieve an efficient and accurate measurement of their thermal properties; secondly, considering the multi-scale characteristics of the heat transport process involving Van der Waals interfacial effects in the stacking structures, a multi-scale method with the combination of first principle, molecular dynamics, and Monte Carlo techniques, will be utilized in simulations, as the comparison of experiments, to shed light on the underlying mechanism; furthermore, a predictive model for thermal conductivity in this case will be derived based on the Boltzmann transport theory, and then the reliability of the model is planned to be verified through experiment and simulation results; finally, on the basis of the above investigations, this project will explore the tuning techniques of thermal transport properties of stacked two-dimensional materials.

二维材料及其堆叠结构是充满希望的热功能材料，同时，热问题对二维堆叠材料器件的可靠性也有着重要影响，两者都迫切需要对二维堆叠材料的导热规律有更深入的了解。在二维堆叠材料中，范德华界面效应是导致特殊热输运性质的重要原因，其具有明显的可调控性，并受到弹道输运和面外声子模式的显著影响。本课题以过渡族金属二硫族化和物与石墨烯等二维堆叠材料导热的范德华界面效应为研究对象；发展针对小面积形状非规则二维堆叠材料的热物性测量方案，实现相关材料热物性的高效准确测量；针对二维堆叠材料导热的多尺度特性，使用结合第一性原理、分子动力学，和蒙特卡罗等技术的多尺度方法进行数值模拟，用于预测和解释实验结果，并揭示范德华界面的作用机制和热输运性质调控原理；基于玻尔兹曼输运理论，构建热输运预测模型，并通过实验和模拟进行模型的可靠性验证；最后，在上述研究的基础上，探索二维堆叠材料的热物性调控技术。

本项目以二维堆叠材料导热的范德华界面效应及相关物理现象为研究对象，涉及实验测量、数值模拟，理论及模型构建三个方面。具体内容如下：在实验测量方面，基于电学测量的锁相放大技术、有限元模拟、及反问题方法，开发了一系列热物性测量方法，包括3ω-2ω双电极法、应用反问题法的3ω方法，和测量基底上纳米片热导率的电学法，它们不仅可以处理小面积且形状不规则的二维堆叠材料纳米片的热物性测量问题，还被扩展到界面热阻及芯片内部材料热物性的测量。在数值模拟方面，开发了以声子蒙特卡罗方法为核心的多尺度热物性模拟方案，可以把从经验公式、第一性原理、或分子动力模拟获得的纳观尺度声子信息（如色散关系、弛豫时间，和界面透射率等）输入到介观尺度的声子蒙特卡罗模拟中，从而计算包括二维堆叠材料纳米薄膜、纳米线、和纳米界面在内的各种纳米结构的热输运性质；并将该方法应用于声子穿透纳米结构界面的机制的研究。在理论及模型构建方面，基于玻尔兹曼输运理论和层状结构的弹性理论，推导得到了能够考虑层状结构声子各向异性质和边界散射影响的等效热导率模型，可以用于实验数据的机理分析，并可以根据模型的预测，来探索二维堆叠材料热物性的调控方案；此外，理论研究还扩展到了与二维堆叠材料应用紧密相关的非平衡热力学问题：理清了二维堆叠材料热电转换中的开尔文关系的成立条件；对包括热输运在内的不可逆输运过程的最小作用量原理进行了研究。根据上述研究内容，已完成学术论文8篇，国家专利授权1项。其中，申请的国家专利《一种测量界面热阻的方法及系统》，可用于电子器件材料（包括硅，氮化镓，碳化硅，堆叠材料等）等效热导率和界面热阻的测量，从而促进芯片热管理技术的发展。