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

二维材料可以通过垂直、逐层堆叠创建一类新的纳米级材料系统，从而产生“范德华”异质结构。本项目旨在研究范德华异质结构的结构-机械-电子耦合，最终目标是实现纳米级接触的摩擦控制。所创造的知识将推进(1)纳米和微电子机械设备的设计，通过消除作为其功能长期障碍的高摩擦限制，服务于商业和美国安全需求；(2)基于范德华组装的新兴制造方法。这一领域的进步将提高制造过程的可持续性和效率，从而提高美国工业生产率和竞争力。该合作项目将培养两名研究生研究助理。加州大学欧文分校的学生人口统计为扩大力学和纳米技术的参与提供了理想的机会，并为培养多样化的STEM劳动力做出了贡献。该团队将利用这一机会，招募学生参与各级别的研究，并为学生在实验室之间的交流提供机会。这项研究的结果将作为两所大学研究生课程的一部分进行整合。假设调整范德华异质结构中的结构-机械-电子耦合将提供对摩擦的控制。这是预期的，因为目标过渡金属二硫族化合物单层之间的电荷转移诱导的层间激子影响了滑动界面上势能景观的波纹。因此，这个假设驱动的项目的目标是建立具有可调谐和可控摩擦的范德华异质结构的实验和理论基础。该团队将研究(1)范德华异质结构的内在结构（二维材料组合、堆叠顺序、扭转角、层间耦合）如何影响耦合和摩擦；(2)确定应变和电场等外在因素如何影响范德华异质结构的结构、力学和电子性能，从而影响摩擦。实验工具集依赖于一种可扩展的方法来组装具有扭转角控制的范德华异质结构；利用光致发光/拉曼光谱和二次谐波进行表征；纳米尺度的摩擦测量与表面形貌、附着力和刚度图相关。我们还预计层间电荷转移的作用将使摩擦对氧化的敏感性降低，这将使用故意氧化的样品进行测试。该奖项反映了美国国家科学基金会的法定使命，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. Created knowledge will advance (1) the design of nano- and microelectromechanical devices serving commercial and U.S. security needs by removing the constraints of high friction as a long-standing hurdle for their functionality, and (2) emerging manufacturing methodologies based on van der Waals assembly. Progress in this field will improve the sustainability and efficiency of manufacturing processes and thus increase U.S. industrial productivity and competitiveness. The collaborative project will train two graduate research assistants. 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 by recruiting students for research engagement at all levels and will provide opportunities for student exchanges between their 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 effect 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 using 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.