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Wafer-sized multifunctional polyimine-based two-dimensional conjugated polymers with high mechanical stiffness
One of the key challenges in two-dimensional (2D) materials is to go beyond graphene, a prototype 2D polymer (2DP), and to synthesize its organic analogues with structural control at the atomic- or molecular-level. Here we show the successful preparation of porphyrin-containing monolayer and multilayer 2DPs through Schiff-base polycondensation reaction at an air-water and liquid-liquid interface, respectively. Both the monolayer and multilayer 2DPs have crystalline structures as indicated by selected area electron diffraction. The monolayer 2DP has a thickness of∼0.7 nm with a lateral size of 4-inch wafer, and it has a Young's modulus of 267±30 GPa. Notably, the monolayer 2DP functions as an active semiconducting layer in a thin film transistor, while the multilayer 2DP from cobalt-porphyrin monomer efficiently catalyses hydrogen generation from water. This work presents an advance in the synthesis of novel 2D materials for electronics and energy-related applications.
The influence of plasma treatment on the elasticity of the in situ oxidized gradient layer in PDMS: towards crack-free wrinkling
Controlled surface wrinkling is widely applied for structuring surfaces in the micro- and nano-range. The formation of cracks in the wrinkling process is however limiting applications, and developing approaches towards crack-free wrinkles is therefore vital. To understand crack-formation, we systematically characterized the thickness and mechanics of thin layers formed by O2-plasma-oxidation of polydimethyl siloxane (PDMS) as a function of plasma power and pressure using Atomic Force Microscopy Quantitative Nano-mechanical Mapping (AFM-QNM). We found a nearly constant layer thickness with simultaneously changing Young's moduli for both power and pressure screenings. We determined the respective crack densities, revealing conditions for crack-free wrinkling. Thus we could identify correlations between the intensity of plasma treatment and the cracking behavior. The primary cause for crack-suppression is a continuous elasticity gradient starting within the soft bulk PDMS, and rising up to several hundred MPa at the oxidized layer's surface. With mechanical simulations via the Finite Elements Method (FEM) we were able to demonstrate a noticeable difference in maximal stress intensity σmax between a comparable, but theoretical single layer and a gradient interface. A threshold in tensile stress of σcrit = 14 MPa distinguishes between intact and cracked layers.