Collaborative Research: Control of Contact Friction of Van der Waals Heterostructures

二维材料能够通过垂直、逐层堆叠产生一类新的纳米级材料系统，从而产生“货车德瓦尔斯”异质结构。本计画旨在研究货车德瓦耳斯异质结构的结构-机械-电子耦合，最终目标是在奈米级接触下实现摩擦控制。这些知识将推动纳米和微机电设备的设计，服务于商业和美国的安全需求，消除高摩擦的限制，作为其功能的长期障碍，以及新兴的制造方法的基础上货车德瓦尔斯组装。该领域的进展将提高制造工艺的可持续性和效率，从而提高美国工业生产力和竞争力。该研究合作项目将通过培训两名研究生研究助理来促进美国劳动力的发展。加州尔湾大学的学生人口统计数据为扩大力学和纳米技术的参与提供了理想的机会，并为多元化STEM劳动力的教育做出了贡献。该团队将利用这个机会招募学生参与各级研究，并将为两个实验室的学生交流提供机会。这项研究的结果将被整合为两所大学研究生课程的一部分。据推测，调整“货车德瓦尔斯”异质结构中的结构-机械-电子耦合将提供摩擦控制。这是预期的，因为目标过渡金属二硫属化物单层之间的电荷转移诱导的层间激子影响滑动界面处的势能景观。本课题的目标是为摩擦力可调和可控的货车德瓦耳斯异质结构的研究奠定实验和理论基础。该团队将研究（1）货车德瓦尔斯异质结构的内在结构（二维材料组合，堆叠顺序，扭曲角，层间耦合）如何影响耦合和摩擦;以及（2）确定应变和电场等外在因素如何影响货车德瓦尔斯异质结构的结构，机械和电子特性，从而影响摩擦。实验工具集依赖于一个可扩展的方法来组装货车德瓦尔斯异质结构与扭转角控制;表征光致发光/拉曼光谱和二次谐波产生;和纳米摩擦测量与表面形貌，粘附力和刚度图。层间电荷转移的影响也将使摩擦对氧化不那么敏感，这将在故意氧化的样品上进行测试。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Two-dimensional materials enable creating a new class of nanoscale material systems by vertical, layer-by-layer stacking, resulting in ‘van der Waals’ heterostructures. This project aims to investigate the structural-mechanical-electronic coupling of van der Waals heterostructures with the ultimate goal of enabling friction control at nanoscale contacts. This knowledge will advance the design of nano- and microelectromechanical devices serving commercial and U.S. security needs by removing constraints of high friction as a long-standing hurdle for their functionality, as well as emerging manufacturing methodologies based on van der Waals assembly. The progress in this field will improve the sustainability and efficiency of manufacturing processes and thus increase U.S. industrial productivity and competitiveness. The researched collaborative project will contribute to the development of the work force in the U.S. by training two graduate student research assistants. The student demographics at University of California Irvine provide an ideal opportunity for broadening participation in mechanics and nanotechnology and contributing to the education of a diverse STEM work force. The team will take advantage of this opportunity in recruitment of students for engagement with the research at all levels and will provide opportunities for student exchanges in both labs. Findings of this research will be integrated as part of graduate courses at the two universities.It is hypothesized that tuning the structural-mechanical-electronic coupling in ‘van der Waals’ heterostructures will afford control of friction. This is expected because the charge transferred-induced interlayer excitons between the targeted transition metal dichalcogenides monolayers influence the corrugation of the potential energy landscape at the sliding interface. The objective of this hypothesis-driven project is thus to establish experimental and theoretical foundation for van der Waals heterostructures with tunable and controllable friction. The team will investigate (1) how the intrinsic structure (two-dimensional materials combination, stacking order, twist angle, interlayer coupling) of van der Waals heterostructures influences the coupling and friction; and (2) determine how extrinsic factors like strain and electric field affect structural, mechanical and electronic properties of van der Waals heterostructures, and thereby friction. The experimental toolset relies on a scalable approach to assemble van der Waals heterostructures with twist angle control; characterization by photoluminescence/Raman spectroscopy and second harmonic generation; and nanoscale friction measurements correlated with surface topography, adhesion, and stiffness maps. It is also expected that the effect of interlayer charge transfer will make friction less sensitive to oxidation, which will be tested on deliberately oxidized samples.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.