A flexible hard coating for foldable displays is realized by the highly cross-linked siloxane hybrid using structure-property relationships in organic-inorganic hybridization. Glass-like wear resistance, plastic-like flexibility, and highly elastic resilience are demonstrated together with outstanding optical transparency. It provides a framework for the application of siloxane hybrids in protective hard coatings with high scratch resistance and flexibility for foldable displays.

Density–strength tradeoff appears to be an inherent limitation for most materials and therefore design of cell topology that mitigates strength decrease with density reduction has been a long‐lasting engineering pursue for porous materials. Continuum‐mechanics‐based analyses of mechanical responses of conventional porous materials with bending‐dominated structures often give the density–strength scaling law following the power‐law relationship with an exponent of 1.5 or higher, which consequentially determines the upper bound of the specific strength for a material to reach. In this work, a new design criterion capable of significantly abating strength degradation in lightweight materials is presented, by successfully combining the size‐induced strengthening effect in nanomaterials with the architectural design of cellular porous materials. Hollow‐tube‐based 3D ceramic nanoarchitectures satisfying such criterion are fabricated in large area using proximity field nano‐patterning and atomic layer deposition. Experimental data from micropillar compression confirm that the strengths of these nanoarchitectural materials scale with relative densities with a power‐law exponent of 0.93, a hardly observable value in conventional bending‐dominated porous materials. This discovery of a new density–strength scaling law in nanoarchitectured materials will contribute to creating new lightweight structural materials attaining unprecedented specific strengths overcoming the conventional limit.

Any transition toward an era of flexible electronics will have to overcome the mechanical limitations of materials. Specifically, the attainment of both strength and flexibility, which are generally mutually exclusive, is required including glass-like wear resistance, plastic-like compliance, and a high level of strain. Here, we fabricate a urethane−methacrylate−siloxane hybrid (UMSH) material. It is found that UMSH, with molecule-level hybridization of urethane linkage and methacrylate−siloxane conetworks, demonstrates ceramic-like high strength (574 MPa), yet polymer-like low modulus (8.42 GPa), and even high strain (6.3%) at fracture with excellent optical transparency. This combination of high strength, flexibility, and optical transparency indicates that this is a suitable material for glass substitution and can be used as a transparent flexible cover window for foldable display.

Recent progress in nanotechnology enables us to utilize the elastic strain engineering, the emerging technology capable of controlling the physio-chemical properties of materials via externally-imposed elastic strains, for hard materials. Because the range of accessible properties by imposing elastic strains are set by materials' elasticity limits, it is of great importance to suppress the occurrence of any inelastic deformations and failure, and thereby the fundamental knowledge on fracture behavior at nanoscale is highly required. The conventional Weibull theory, which has been widely used for last a few decades to explain the failure statistics of brittle bulk materials, has a limitation to be directly applied to the samples of nanometer dimensions because the baseline assumption on statistical equivalence becomes intractable for small samples. In this study, we suggest an integrated equation presenting the sample size effect on fracture strength for brittle nanomaterials by further considering the confinement of the flaw size distribution. This new approach is applicable to any homogeneous brittle nanomaterials whose failure is governed by linear elastic fracture mechanics, and shows good agreement with experimental data collected from literatures. We expect that this theoretical study offers new guideline to employ brittle nanomaterials in designing and fabricating the advanced strain engineering system.

Most monolithic brittle materials are vulnerable to the failure by cracks because of a lack of intrinsic toughening mechanisms, such as the plasticity in the vicinity of the crack front. As a result, most of the efforts to mitigate the sudden failure of brittle ceramics have been focused on developing the extrinsic toughening mechanisms that hinder crack propagation behind the tip, such as the fiber bridging. In this work, we experimentally demonstrate that the intrinsic toughening arises even in the brittle monolithic ceramic material such as diamond-like carbon (DLC) when its external dimension reduces down to sub-micron scales. This unique phenomenon owes its origin to the decrease of the crack driving force in the small samples, which in turn enables them to bear high enough stresses to activate the local atomic plasticity. Through nanomechanical tensile and bending experiments, electron energy loss spectroscopy analysis, and finite element method for stress distribution calculation, we confirmed that the local atomic plasticity associated with sp 3 to sp 2 rehybridization is responsible for the intrinsic toughening.