Understanding and Controlling Subcritical Crack Growth in Large Freestanding Metallic Nanosheets

金属薄膜已成为许多住宅和工业应用的关键特征。它们覆盖着窗户，使我们的家保持凉爽和节能，使电子设备和电器中的集成电路成为可能，使涡轮机发动机能够更有效地运行，并且是无数其他产品的基础。然而，它们的使用受到以下事实的限制，即用于产生一种膜的加工条件通常与制造其它膜或甚至将它们存款在某些类型的材料上所需的加工条件不相容。这个问题是有问题的，因为薄膜是极其脆弱的，并且到目前为止，通常不可能将它们从一个基底移除并将它们转移到另一个基底而不将它们撕开。这项研究计划将建立如何控制裂纹生长的薄膜，使他们可以坚持其他材料后，他们的生产。这项工作将使新材料的制造和现有的整合，创造新一代的产品和设备。这些新的科学见解将与研究生的教育，谁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纳米）金属薄膜有各种各样的应用，但它们的使用是有限的事实，独立的金属薄膜容易破裂和撕裂。因此，除非它们在基板上，否则它们通常不能经受处理和组装。然而，如果可以在不损坏它们的情况下制造和处理独立的金属薄膜，则它们的纳米光学，机械和电学特性可以与通常被认为不相容的材料相结合。这种新的能力将导致更丰富地利用这些薄膜的特殊性能。这项研究计划将使这些金属薄膜的集成，通过使用激光微加工，小规模的机械测试系统，电子显微镜，和有限元建模，以建立独立的金属Au薄膜的亚临界裂纹生长机制。该程序的一个独特之处在于，使用大片材（5 mm平面内范围）来评估微米级试样无法捕获的超大工艺区域。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，扫描电子显微镜和透射电子显微镜。 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抗撕裂膜的抗撕裂性。此外，薄板撕裂裂纹尖端参数的发展将使断裂力学为基础的耐久性和寿命计算。由此产生的设计耐损伤独立金属薄膜的能力将允许工程师从几乎任何金属薄膜材料创建设备。

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.