The objective of this collaborative research is to explore the fracture and fatigue mechanisms of nano ceramic films on polymer substrates under monotonic and cyclic loadings. Functional nano ceramic films on polymer substrates are emerging as key building blocks to enable promising technologies, such as flexible electronics and next generation bioactive implants. The huge mechanical mismatch and large mechanical loads lead to complex and rich fracture behaviors of thin ceramic films on polymer substrates, which are far from well understood. In particular, recent experiments showed fatigue damage of indium tin oxide films on polymer substrates under cyclic loads, a phenomenon that cannot be explained by conventional fatigue mechanisms. The future success of abovementioned promising technologies is contingent to the mechanistic understanding of the fracture and fatigue of nano ceramic films on polymer substrates. In this project, a collaborative research framework (from analytic modeling, simulations to in situ experiments) will be built to investigate the yet-unexplored mechanisms that govern the mechanical reliability of nano ceramic films on polymer substrates. The potential consequence of failure in functional nano ceramic films on polymer substrates is significant in flexible electronics and bioactive implants. The proposed research will offer fundamental insights into the yet-unexplored mechanisms that govern the reliability of flexible devices and bioactive implants, and enable more robust nanomanufacturing strategies of these emerging technologies. By leveraging cyberinfrastructure, the new knowledge from the project will be disseminated to reach much broader audience, and a new generation of students will be equipped with interdisciplinary perspectives.
Functional thin ceramic films on polymer substrates are emerging as critical building blocks to enable promising technologies, such as flexible electronics and next generation bioactive implants. The specific objectives of this project are two folds: first, we aim to establish a better understanding of both structural and electrical failure mechanisms of currently well-established functional ceramic thin films such as indium thin oxide (ITO) on polymer substrates under mechanical loading, combining in-situ experiments and micromechanics modeling; second, we thrive to explore novel low-dimensional materials system such as MoS2, h-BN, graphene atomic layers and thin films of CNT and metal nanowires for their potential eletro-mechanical properties that could lead to next generation of applications. In this project, we have successfully performed in situ mechanical and electrical tests of ITO thin films deposited on polyimide substrates inside a scanning electron microscope (SEM). The crack initiation and propagation, crack density evolution and the corresponding electrical resistance variation were systematically investigated. Our in situ experiments of polyimide-supported thin ITO films reveal buckling-driven film cracking in some samples and buckling-driven interfacial delamination in other samples. Through theoretical analysis and numerical simulations, we delineate a map of competing buckling-driven failure modes of substrate-supported thin brittle films in the parameter space of interfacial adhesion and interfacial imperfection size. Inspired by recent development of inorganic/organic hybrid permeation barriers for flexible electronics, we design and fabricate ITO-based multilayer electrodes with enhanced electro-mechanical durability. A coherent mechanics model is established to determine the driving force for crack propagation in the ITO layer in these electrodes. The findings in this work provide quantitative guidance for the material selection and structural optimization of ITO-based multilayer transparent electrodes of high mechanical durability. Additionally, we also demonstrated large area growth of MoS2 atomic layers, h-BN/graphene in-plane heterostructure by a scalable chemical vapor deposition (CVD) method. The as-prepared samples can either be readily utilized for further device fabrication or be easily transferred to arbitrary substrates. Mechanical properties of metal nanowires, carbon nanotube thin films were also studied using in-situ quantitative nanomechanical testing methods developed at Rice. These emerging low-dimensional materials could become legitimate alternatives for current functional ceramic thin films with more research in the near future. The current results was integrated into the course MSCI 402 "Mechanical Behaviors of Materials", in a special lecture aiming to educate students about the importance of nanomechanical testing for reliability study of nanoscale structures and devices, taught by the PI to 19 students in 2011, to 25 students in 2012 and 23 students in 2013. A graduate level course MSCI 650 "Advanced Topics on Nanomechanics and Nanomaterials" which was taught to 22 students in spring 2012 also benefited from the research performed in this project. The Rice graduate student, Dr. Cheng Peng who graduated in 2013, had become a master user for the clean room fabrication of the samples as well as the in situ operation of both micro-tensile and micro-fatigue testers. He had also been heavily involved in undergraduate students mentoring. Several Rice undergraduate students, Mr. Dan Bianculli, Mr. Henry Neilson, Mr. Isai Ake had worked extensively on various aspects of experiments with Mr. Peng and had gained valuable research experiences through participations in this project. Henry is now a materials science graduate student at Case Western Reserve University. Dan is working as an engineer in Aker Solution in Houston area. Isai is currently applying for graduate school and will graduate in May 2014. The Rice PI has also established and maintained a strong relationship with University of Houston-Downtown, a minority serving institute. The PI’s lab hosted lab tours for UHD professors and students interested in nanoscience and nanotechnology.
