Abstract
Transfer printing, as one of crucial smart manufacturing technologies, is emerging for manufacturing large-area, deterministic, layered structures down to the nanoscale with a well-defined order in a broad range of materials, for attractive applications in wearable electronics, in particular, in flexible and stretchable electronics and devices. With this technique, thin film that is processed on a donor substrate prior (e.g. as-fabricated wafers, and as-growth metals) will be picked up through a stamp and is then released onto another desirable target substrate.
In fundamental, both steps of transfer and printing can be considered as a crack competing process along the interface of stamp-film or film-substrate, which is a grand challenge to achieve a controllable and stable manner over the past decades. In this PhD dissertation, I explored series of novel strategies of transfer printing technique by investigating fundamental interfacial debonding behavior in a liquid environment, referred to as extreme mechanics-driven transfer printing technique, where I use the adjective “extreme” to highlight the underlying fundamental mechanics mechanism.
Specially, I first present a transfer printing technology in a liquid environment and it is underpinned by a synergistic effect of both external mechanical loading and interior hydrolysis chemical reaction at interfaces, defined as the chemomechanics-driven transfer printing in Chapter 2. The establishment of hydrolysis-based chemomechanics theory and its implementation into the finite element simulation model for a multiscale-multiphysics computational framework will be discussed. The established theoretical and computational models were validated by the results of peeling experiments. At last, the guided applications in the transfer printing of a variety of functional materials, including silicon nanomembrane and three-dimensional plasmonic nanoarchitectures were demonstrated.
In Chapter 3, this hydrolysis-based chemomechanics theory was extended to an electrochemomechanics theory with the introducing of an electric field and its applications in electrical voltage controlled transfer printing technique were explored. In the electrochemomechanics theoretical model, first, a bubble transfer model for the interface delamination driven by bubble force from solvent electrolysis was developed and it can be used to predict the interface delamination rate in this bubble transfer method. Besides, an electrochemical etching model for the interface delamination driven by etching reaction between electrolyte and solid bonds at interface was also developed and it can be used to predict the interface delamination rate in this electrochemical etching transfer method. The finite element method via interfacial cohesive zone model (CZM) was used to simulate the interfacial delamination process and to calculate the delamination rate and to validate the theory model.
Afterward, the development of the capillary theory enabled transfer printing of films was presented in Chapter 4. The effect of surface wettability of film and substrate, thickness and layer number of film, and interfacial sliding are elucidated and incorporated into the theoretical model. Molecular dynamic (MD) simulations were used to simulate the peeling of single layer and multilayered 2D materials in both dry and liquid environments. The peeling force obtained from MD simulations was used to validate the theory. Moreover, theory and MD simulations were used to show the applications in selective peeling of desired layer number of multilayered films by introducing a liquid environment. And the applications in film assembling by self-delamination was also demonstrated.
Further, when the native substrate is liquid, a dynamic capillary mechanics-driven transfer printing approach was explored to directly transfer the films from the surface of a liquid in Chapter 5. This capillary transfer is underpinned by the physical transfer front of contact among substrate, liquid and film and can be well controlled by a selectable moving direction of receiver substrates--push-down or pull-up. Theoretical analysis was used to propose the criterion for selecting transfer direction and the criterion for successful transfer, which are verified by the transfer experiments. Extensive experiments, together with comprehensive theoretical models and computational simulations, on a broad material diversity of film, liquid, and substrates have been given to demonstrate the robust capabilities of this capillary transfer printing in the manufacturing of flexible electronics, surface wetting structures and optical structures.
The fundamental mechanics theories, multiscale-multiphysics computation models and experimental validations and demonstrations in the enabled transfer printing techniques established are expected to lay a foundation for quantitative exploration and control of transfer printing of films for manufacturing flexible/stretchable electronics, surface wetting structures and optical devices, and more importantly provide a new view insight that mechanics can play a critical role in the exploration of new approaches in manufacturing that are beyond the current ones.
