Understanding and Controlling Subcritical Crack Growth in Large Freestanding Metallic Nanosheets

非技术摘要薄金属薄膜已成为许多住宅和工业应用的重要特征。它们覆盖窗户以保持我们家的凉爽和节能，使电子设备和家用电器中的集成电路得以实现，使涡轮发动机能够更高效地运行燃料，并且是无数其他产品的基础。然而，它们的使用受到这样一个事实的限制，即制作一种薄膜的工艺条件往往与制作其他薄膜所需的工艺条件不兼容，甚至无法将它们沉积在某些类型的材料上。这个问题是有问题的，因为薄膜是极其脆弱的，到目前为止，通常不可能在不撕裂它们的情况下将它们从一种衬底上移除并转移到另一种衬底上。这项研究计划将建立如何控制超薄膜中的裂纹扩展，以便它们在生产后可以附着在其他材料上。这项工作将使新材料得以制造，现有材料得以整合，创造出新一代产品和器件。这些新的科学见解将与研究生的教育相结合，研究生将准备使用它们来解决关键的工业和社会问题。技术摘要超薄(100 Nm)金属薄膜有各种应用，但由于独立的金属薄膜容易破裂和撕裂，其使用受到限制。因此，它们通常不能在搬运和组装中存活下来，除非它们在基板上。然而，如果可以制造和处理独立的超薄金属薄膜而不损坏它们，那么它们的纳米光学、机械和电学特性就可以与通常被认为不相容的材料集成在一起。这一新的能力将使这些薄膜的特殊性质得到更丰富的利用。这项研究计划将通过激光微机械加工、小规模机械测试系统、电子显微镜和有限元模拟来集成这些超薄金属薄膜，以建立自支撑超薄Au薄膜的亚临界裂纹扩展机制。该程序的一个独特功能是使用大薄板(5 mm面内范围)来评估微米级样品无法捕获的异常大的加工区。实验将在配备原位光学系统的低力机械测试系统上进行，以量化变形和损伤累积。相关的损伤累积机制将使用光学、扫描电子和透射电子显微镜进行识别。在这些见解的指导下，热处理和近单层厚度的金属层将被用来设计超薄膜的抗撕裂性能。此外，薄板撕裂裂纹尖端参数的开发将使基于断裂力学的耐久性和寿命计算成为可能。由此产生的设计耐损伤独立金属薄膜的能力将使工程师能够用几乎任何金属薄膜材料制造设备。

Non-technical AbstractThin metallic films have become a critical feature of many residential and industrial applications. They coat windows to keep our homes cool and energy efficient, enable the integrated circuits in electronic devices and appliances, allow for turbine engines to run more fuel efficiently, and are the basis of countless other products. However, their use is limited by the fact that the processing conditions for creating one film are often incompatible with those needed to make others, or even to deposit them on certain types of materials. This issue is problematic because thin films are extremely fragile, and thus far it has generally not been possible to remove them from one substrate and transfer them to another without tearing them apart. This research program will establish how to control crack growth in ultrathin films, so that they can be adhered to other materials after their production. This work will enable new materials to be fabricated and existing ones to be integrated to create a new generation of products and devices. These new scientific insights will be developed in concert with the education of graduate students, who will be prepared to use them to solve critical industrial and societal problems.Technical AbstractUltrathin ( 100 nm) metal films have a variety of applications, but their use is limited by the fact that freestanding metallic films are prone to crack and tear. As a result, they generally cannot survive handling and assembly unless they are on substrates. However, if freestanding, ultrathin metal films could be fabricated and handled without damaging them, their nanoenabled optical, mechanical, and electrical properties could be integrated with materials that are usually considered incompatible. This new capability would lead to a richer use of the special properties of these films. This research program will enable the integration of these ultrathin metal films by using laser micromachining, small-scale mechanical testing systems, electron microscopy, and finite element modeling to establish the subcritical crack growth mechanisms of freestanding ultrathin Au films. A unique feature of this program is that large sheets ( 5 mm in-plane extent) are used to evaluate the anomalously large process zones that micrometer-scale specimens cannot capture. Experiments will be conducted on low force mechanical testing systems equipped with in situ optical systems to quantify deformation and damage accumulation. The relevant damage accumulation mechanisms will be identified using optical, scanning electron, and transmission electron microscopy. Guided by these insights, heat treatments and near-monolayer thickness metal layers will be used to engineer the tearing resistance of the ultrathin films. Furthermore, the development of thin sheet tearing crack tip parameters will enable fracture mechanics-based durability and life calculations. The resulting ability to engineer damage-tolerant freestanding metal films will allow engineers to create devices from virtually any metallic thin film material.