Collaborative Research: Cross-plane Heat Conduction in 2D Materials under Large Compressive Strain

合作研究：大压缩应变下二维材料的横向热传导

• 批准号: 2211696
• 负责人: Yan Wang
• 金额: $ 11.73万
• 依托单位: Board of Regents, NSHE, obo University of Nevada, Reno
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-06-15 至 2025-05-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2211696&HistoricalAwards=false
• 关键词: Collaborative; Research; Cross; plane; Heat

Heat conduction highly depends on the strength of bonding among atoms and molecules. Typical interatomic forces include the weak Van Der Waals forces (e.g., in liquids) and the strong ionic and covalent forces (e.g., in solids). 2D materials, such as graphite, are peculiar in that individual layers are coupled via Van Der Waals forces while within the layer, atoms are bonded via covalent forces. Heat conduction along the in-plane direction could be hundreds of times faster than the cross-plane direction. The strength of the Van Der Waals force across layers can be tuned to a great extent by compressing the material. In graphite, under extreme compression, atoms from different layers could even form strong, covalent-like bonds. 2D materials provide a good model to study how heat conduction is associated with interatomic bonding. A high-pressure diamond anvil cell will be used to apply compressive strain in 2D materials. Pressure produced in the diamond anvil cell can be as high as 100~200 GPa, similar to the pressure inside Earth core, and can reduce the distance between the 2D layers by about 30%, hence increasing the strength of interlayer bonds substantially. Fundamental understanding of heat conduction across 2D layers under compression will facilitate the realization of parallel strain tuning of thermal, structural, and electrical properties of 2D materials for novel functionalities with improved thermal stability and performance. This research will also provide opportunities to improve diversity in science and engineering through research training of underrepresented groups and various outreach activities.Classical kinetic theory predicts that cross-plane phonon mean free paths in 2D materials are extremely short, leading to low thermal conductivity. This paradigm was challenged by several recent studies that suggest phonon mean free paths orders of magnitude longer, which indicates the lack of understanding about the nature of heat conduction across 2D layers. The hypotheses are that long phonon mean free paths across 2D layers require both weak interlayer force and periodicity, and that phonon scattering and heat conduction depend strongly on the strength of interlayer force. In this proposed research, the large compressive strain generated in a high-pressure diamond anvil cell will tune the interlayer force over a wide range of strength. A comprehensive study of cross-plane thermal transport will be conducted with optical spectroscopies (e.g., x-ray diffraction, transient thermoreflectance) and advanced computational techniques (e.g., ab initio, machine learning-enhanced molecular dynamics). Three material systems will be studied: (i) pristine ReS2, which possesses the weakest interlayer force in the transition metal dichalcogenides family at the ambient condition; (ii) twisted ReS2, which has broken periodicity along the cross-plane direction; and (iii) graphite, which could experience interlayer buckling via sp2-sp3 bond transition under high pressure.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

热传导在很大程度上取决于原子和分子间的成键强度。典型的原子间作用力包括弱的范德华作用力(例如，在液体中)和强的离子作用力和共价力(例如，在固体中)。2D材料，如石墨，是独特的，因为单独的层通过范德华力耦合，而在层内，原子通过共价力结合。沿平面内方向的热传导可能比跨平面方向快数百倍。跨层的范德华力的强度可以通过压缩材料在很大程度上进行调整。在石墨中，在极度压缩的情况下，来自不同层的原子甚至可以形成强大的共价键。2D材料提供了一个很好的模型来研究热传导如何与原子间的成键相关联。高压金刚石压腔将被用来在2D材料中施加压缩应变。在金刚石压腔中产生的压力可高达100~200 Gpa，与地核内部的压力相似，并可将2D层之间的距离减少约30%，从而大大提高层间结合的强度。对压缩下2D层间热传导的基本了解将有助于实现2D材料的热、结构和电学属性的并行应变调节，以实现具有更高热稳定性和性能的新功能。这项研究还将提供机会，通过对未被充分代表的群体进行研究性培训和各种推广活动来提高科学和工程方面的多样性。经典动力学理论预测，二维材料中的跨平面声子平均自由程极短，导致导热系数较低。这一范式受到了最近几项研究的挑战，这些研究表明，声子的平均自由程要长几个数量级，这表明人们对2D层之间的热传导本质缺乏了解。我们的假设是，通过2D层的长声子平均自由程需要弱的层间力和周期性，而声子散射和热传导强烈地依赖于层间力的强度。在这项拟议的研究中，高压金刚石压腔中产生的大压缩应变将在很大的强度范围内调节层间力。将利用光学光谱学(例如X射线衍射、瞬时热反射)和先进的计算技术(例如从头算、机器学习增强的分子动力学)对跨平面热传输进行全面研究。将研究三种材料系统：(I)原始的ReS2，它在环境条件下具有过渡金属二卤化物家族中最弱的层间作用力；(Ii)扭曲的ReS2，它沿跨平面方向具有破坏的周期性；以及(Iii)石墨，它可以在高压下通过sp2-sp3键转变经历层间屈曲。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。