Atomic-Layer Dependent Adhesion of Two-Dimensional Transitional Metal Carbides (MXenes)

二维过渡金属碳化物(MXenes)是一类新型的低维材料，它具有优异的电学和光学性能，往往优于其他2D材料。重要的是，与其他2D材料不同的是，这些性质可以在同一个家族中系统地变化和研究，而不会改变材料中的元素组成和原子间键类型。这些独特的功能使MXenes对基础科学和应用开发同样感兴趣，在这些领域，它们可以用于新的平面和灵活的设备，从而带来新技术和重大的经济影响。目前正在研究的这些应用包括健康监测传感器、高性能能量收集和存储系统以及化学-光热癌症治疗。然而，MXenes的粘附性，这在许多这些应用中是关键的，还没有得到系统的研究。到目前为止，对MXenes的粘合行为只有很少的理论研究，几乎没有实验数据。从更广泛的意义上讲，对MXenes粘附性的实验测定将有助于我们理解低维材料的粘附性与原子结构之间的基本关系。该项目的目标是：(I)在原子、纳米和微米尺度上系统地研究MXenes的粘附性；(Ii)利用MXenes提供的独特优势，系统和单独地研究2D材料的表面官能团和单层厚度对其粘附性的影响；以及(Iii)探索环境对MXenes粘附性的影响，包括地表水和氧化过程。为了实现这些目标，我们打算：(1)利用原子尺度的接触实验来研究原子结构和表面终止对粘附性的影响；(2)利用纳米压痕来了解MXenes与自身和其他材料之间的界面牵引力-分离关系；(3)探索利用原位纳米剪切滞后实验来研究MXenes的剪切相互作用的可能性；(4)结合多尺度模拟和实验结果来理解包括表面缺陷、终止、单层厚度、以及(5)探索地表水和氧化过程对MXen附着力影响的可能评估。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。

A novel large family of low dimensional materials, 2D transition metal carbides (MXenes), have shown excellent electronic and optical properties that are often superior compared to other 2D materials. Importantly and in contrast to other 2D materials, these properties can be systematically varied and studied within the same family, without changing elemental composition and type of interatomic bonds in the material. These unique features make MXenes equally interesting for fundamental science and application development, where they can be used in new planar and flexible devices, leading to new technologies and significant economic impacts. Some of these applications that are researched now include health monitoring sensors, high performance energy harvesting and storage systems, and chemo-photothermal cancer therapy. However, the adhesion of MXenes, which is critical in many of these applications, has yet to be systematically investigated. To date, there have only been a few theoretical studies of the adhesive behavior of MXenes, with little to no experimental data. In a broader sense, experimental determination of adhesive properties of MXenes will contribute to our understanding of the fundamental relationships between adhesion and atomic structures for low dimensional materials. This could revolutionize the modern materials and manufacturing industries in harnessing the adhesion for coatings and planar devices made of low dimensional materials.The goals of the project are to: (i) systematically investigate the adhesive interactions of MXenes at the atomistic, nano- and micrometer scales, (ii) using the unique advantages provided by MXenes, systematically and separately examine the effects of surface functional groups and monolayer thickness of 2D materials on their adhesive interactions, and (iii) explore the environmental effects on the adhesion of MXenes including surface water and oxidation process. To achieve the goals, we intend to: (1) utilize the atomistic scale contact-based experiments to investigate the effect of atomic structures and surface terminations on the adhesion, (2) employ nanoindentation to understand the interfacial traction-separation relations of MXenes with themselves and other materials, (3) explore the potential use of in-situ nano-shear-lag experiments to investigate the shear interactions of MXenes, (4) combine the multiscale modeling and the experimental results to understand the coupled adhesive mechanisms involving the surface defects, terminations, monolayer thickness, and (5) explore the possible evaluation of the effects of surface water and oxidation process on the adhesion of MXenes.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.