Modulating the Adhesion, Friction and Lubrication Characteristics of Few-Atom Thick Materials in Aqueous Environment over Several Length Scales

二维（2D）材料引起了人们的极大关注，因为它们的原子大小导致了独特的材料特性。虽然水通常存在于这些系统中，并且它显著地影响微机电系统或器件性能，但是关于在水存在下的2D材料的界面性质知之甚少。这部分是由于高质量2D材料的无污染、受控加工所面临的挑战，这限制了基础研究和应用。该项目将研究与2D材料的界面特性相关的科学。由于该技术直接适用于微米和纳米级器件，因此该研究有可能影响汽车，消费电子，航空航天和国防部门，因此直接影响经济福利和国家安全。 该研究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。此外，PI？综合教育计划旨在激发K-12学生对STEM的早期兴趣，并激励本科生和研究生进一步提高他们对2D材料和表面科学与工程的兴趣。此外，PI将通过暑期研究机会和实地考察，吸引退伍军人学生、高中生和少数民族学生参与，重点扩大纳米工程教育。研究员亦会积极进行外展活动，包括互动讲座及亲身实践活动。为填补水环境中二维材料界面性质的知识空白，研究员会进行两大方向的研究：（1）建立单层和少层石墨烯和二硫化钼（MoS 2）的制造方法，以控制其质量，层的数量和衬底诱导的掺杂特性在几个长度尺度和（2）从根本上理解，测量和模型的摩擦，粘附，和润滑的几个原子厚的材料在水环境中。研究假设是，衬底诱导掺杂可以是一种手段，以调制的少原子厚材料与水和离子的相互作用，以及它们的界面迁移率，因此，它可以用来控制双电层，摩擦，粘附和润滑机制。制备无污染的单晶石墨烯和具有受控衬底诱导掺杂的MoS 2层将能够仔细研究水性环境中2D材料的界面性质。用表面力装置（SFA）的测量将提供界面力的全面数据，这些数据将被精确建模以量化衬底诱导掺杂的影响。原子力显微镜（AFM）样品的制备容易，也将能够通过金属薄膜，更高数量的离子组合物研究衬底诱导的掺杂，并定性比较MoS 2和石墨烯与其他几种（剥离）2D材料和大块晶体的界面行为。最终，将建立一个关于二维材料的基质诱导掺杂与其在水存在下的粘合和摩擦特性之间关系的理论。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 (2D) materials are drawing significant attention because their atomic size results in unique material properties. Although water is often present in these systems and it significantly affects the microelectromechanical system or device performance, very little is known about the interfacial properties of 2D materials in the presence of water. This is partially due to the challenges involved in contamination-free, controlled processing of high quality 2D materials, which limits fundamental studies and applications. This project will study the science associated with the interfacial properties of 2D materials. Since the technology has direct applicability to micro and nano-scale devices, the research has the potential to impact the automotive, consumer electronic, aerospace and defense sectors, and therefore directly impacts economic welfare and national security. The research will contribute to the development of work force in the U.S. by training two graduate students research assistants. Further, the PIs? integrated education plan is designed to spark the early interest of K-12 students in STEM and inspire undergraduate and graduate students to further advance their interests in the intersection of 2D materials and surface science and engineering. In addition, the PIs will focus on broadening nano-engineering education by engaging student veterans and high school and minority students via summer research opportunities and field trips. The PIs will also actively pursue outreach activities, including interactive lectures and hands-on activities.In order to fill the knowledge gap of interfacial properties of 2D materials in aqueous environment, two major lines of research will be followed: (1) establish manufacturing methods for single- and few-layer graphene and molybdenum disulfide (MoS2) that afford control of their quality, the number of layers and substrate-induced doping characteristics over several length scales and (2) fundamentally comprehend, measure and model friction, adhesion, and lubrication by few-atomic thick materials in aqueous environment. The research hypothesis is that substrate-induced doping can be a means to modulate the interactions of few-atomic thick materials with water and ions, as well as their interfacial mobility, and therefore, it can be used to control electrical double layer, friction, adhesion and lubrication mechanisms. Preparation of contamination-free, single-crystalline graphene and MoS2 layers with controlled substrate-induced doping will enable careful study of interfacial properties of 2D materials in aqueous environment. Measurements with a surface forces apparatus (SFA) will provide thorough data of interfacial forces, which will be precisely modeled to quantify the effects of the substrate-induced doping. The ease of preparing samples for atomic force microscopy (AFM) will enable to also investigate substrate-induced doping via metal thin films, a higher number of ionic compositions and also to qualitatively compare the interfacial behavior of MoS2 and graphene with several other (exfoliated) 2D materials and with the bulk crystals. Ultimately, a theory for the relation between substrate-induced doping of 2D materials and their adhesive and frictional characteristics in the presence of water will be established.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.