Controlling Adhesion Between Stiff Surfaces by Tailoring Interface Geometry

坚硬、表面平整、清洁的材料，即使在最小压力下接触时，也会自发粘连。这种“直接键合”工艺用于连接超平板玻璃光学元件和大直径半导体晶圆。它在基于晶片规模的半导体层转移工艺和微转移印刷的新兴技术中也是必不可少的，包括3D集成电路、微电子机械系统(MEMS)和柔性混合电子产品。本项目的重点是了解通过将相对坚硬的材料与含有导致不完全粘合的工程特征的表面粘合而形成的界面的粘附性。假设表面图案化可以用来实现刚性材料之间可控的和方向相关的粘接。尽管几乎所有的界面都有不完全的粘接，但从科学和工程的角度来看，对不完全粘接的机理仍然存在根本的不完整的理解。因此，目前设计具有理想附着力和韧性的表面主要是基于试错法。该项目将促进粘着科学的发展，并将加强软硬电子和MEMS的制造，影响国家的健康、繁荣和福利，保障国防安全。从教育和外联的角度来看，这个项目将产生关于不完全粘合的新模块和动手演示，将被广泛用于各级教育：研究生和本科生、K-12学生和公众。通过结合实验和严格的力学分析，结合物理激励和实验校准的牵引-分离定律，将进行研究，以设计控制界面韧性的方法。将研究(1)各种几何形状的微米和纳米图案硅表面以及(2)具有工程波纹度的表面的粘附性。基于原子力显微镜的测量将被用来表征牵引-分离粘着规律，并确定诸如粘着功和相互作用长度尺度等参数。微米和纳米涂层将被用来引入附着力各向异性和不对称性，产生根据加载方向和裂纹扩展而具有显著不同韧性的界面。通过AFM测量和波状界面上的实验以及详细的分析，将获得控制附着力的牵引-分离规律的准确表征，这是预测韧性所必需的。此外，将开发和使用USE模拟工具，将实验验证的附着力定律纳入参数研究，以设计表面图案以满足特定目标。这项工作将产生允许设计具有受控、各向异性和非对称韧性的界面的模型。对不完美附着力的理解将使微纳图形的进步能够被利用，以实现通过几何控制界面韧性的创新方法。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。

Stiff and hard materials with flat and clean surfaces can spontaneously adhere when contacted even under minimal pressure. This "direct bonding" process is used to join ultra-flat glass optics and to bond large-diameter semiconductor wafers. It is also essential in emerging technologies based on wafer-scale semiconductor layer transfer processes and micro-transfer printing, including 3D integrated circuits, microelectromechanical systems (MEMS), and flexible hybrid electronics. This project focuses on understanding adhesion of interfaces formed by bonding relatively stiff materials with surfaces containing engineered features that give rise to imperfect adhesion. The hypothesis is that surface patterning can be used to realize controlled and directionally-dependent adhesion between stiff materials. Even though nearly all interfaces have imperfect adhesion, there remains a fundamentally incomplete understanding of the mechanics of imperfect adhesion, both from scientific and engineering points of view. Consequently, at present the design of surfaces with desired adhesion and toughness is mostly trial and error based. This project will advance the science of adhesion and will enhance the fabrication of soft and hard electronics as well as MEMS, impacting national health, prosperity, and welfare and securing national defense. From an education and outreach standpoint, this project will lead to new modules and hands-on demos on imperfect adhesion that will be broadly used to educate at all levels: graduate and undergraduate students, K-12 students, and the public. Through a combination of experiments and rigorous mechanics analyses incorporating traction-separation laws that are physically motivated and experimentally calibrated, research will be conducted to design methodologies to control interfacial toughness. The adhesion of (1) micro- and nano-patterned silicon surfaces with various geometries, and (2) surfaces with engineered waviness will be investigated. Atomic force microscopy-based measurements will be used to characterize the traction-separation adhesion law and determine parameters such as the work of adhesion and interaction length scale. Micro- and nanopatterning will be used to introduce adhesion anisotropy and asymmetry, yielding interfaces that have dramatically different toughness depending on the direction of loading and crack propagation. An accurate characterization of the traction-separation law governing adhesion, which is required to predict toughness, will be obtained from a combination of AFM measurements and experiments on wavy interfaces coupled with detailed analyses. In addition, use simulation tools will be developed and used to incorporate the experimentally-verified adhesion laws in parametric studies to design surface patterns to meet specific objectives. The work will lead to models that allow for the design of interfaces with controlled, anisotropic, and asymmetric toughness. The understanding of imperfect adhesion will enable advances in micro- and nano-patterning to be exploited to realize innovative approaches to control interface toughness through geometry.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.