Fracture behavior and advanced transfer methods of nanofilms

Abstract

Transferring functional nanofilms onto target substrates is a cornerstone to developing nanofilm-based applications. Conventional nanofilm transfer technologies, which can be categorized into following three methods: wet-etching transfer, electrochemical delamination, and mechanical transfer, have been established successfully. However, selective transfer of a target nanofilm pattern, nanofilm transfer to a tubular substrate, and damage-free nanofilm transfer have remained challenges. Here, advanced transfer methods are presented by exploiting fracture mechanics based approaches and unique properties of a water surface. First, capillary-force-driven switchable delamination of nanofilms and its application to a green selective transfer process which can integrate sophisticated nanofilm patterns without recourse to lithographic techniques were demonstrated. Second, a method for transferring nanofilms onto tubular substrates was developed by using the technique for free-standing of nanofilm on water surface and the controlled rolling manner. Diverse applications including an electroactive polymer tube actuator for steerable microcatheter, a super-elastic nanofilm tube, and a tubular stretchable sensor were demonstrated by this method. Third, it was investigated that the adhesion energy of nanofilm can be quantitatively controlled by using various liquid environments. The liquid-assisted adhesion control achieved effective reduction of structural defects in a transferred nanofilm. Finally, nanofilm cracking behavior in the mechanical transfer process was explored by controlling several factors such as thickness of a target substrate, loading angle, and loading rate. Moreover, the mechanism of cracking was explained by considering crack deflection effect, and a guideline for crack-free transfer was provided. I expect that the advanced transfer methods presented here would contribute to development and commercialization of many novel applications.