Composite structures consisting of two-dimensional (2D) materials deposited on elastic substrates have a wide range of potential applications in flexible electronics. For such devices, robust 2D film/substrate interfacial adhesion is essential for their reliable performance when subjected to external thermal and mechanical loads. To better understand the strength and failure behavior of the 2D film/substrate interfaces, two types of graphene/polymer samples with distinct interfacial adhesion properties are fabricated and tested by uniaxially stretching the substrates. Depending on the interfacial adhesion, two drastically different debonding rates are observed, i.e., rapid snap-through debonding and more progressive crack propagation. Motivated by the experimental observation, we propose an improved shear-lag model with a trapezoidal-shaped cohesive zone to derive an analytical solution for the decohesion behavior. The theoretical model reveals that the decohesion behavior of the frictional adhesive interface is governed by three dimensionless parameters. Particularly, the dimensionless length of the film essentially determines the decohesion rate; while the other two parameters affect the critical substrate strain to initiate debonding. By fitting the experimental data with the theoretical model, the intrinsic adhesion properties of the two samples are obtained with physically meaningful values. This work offers an analytical solution to describing the decohesion behavior of general thin film/substrate systems with a frictional adhesive interface, which is beneficial for characterizing and optimizing the mechanical properties of various thin film/polymer devices.

Atomic-layered hexagonal boron nitride (hBN) is expected to be the best two-dimensional (2D) anti-oxidation layer on metals for its incomparable impermeability, insulativity, and stability, as well as the progressive bottom-up growth techniques to ensure fast coating on metal surface in large area. However, its real anti-oxidation ability in practice is found to be unsatisfactory and nonuniform, and the main obstacle to achieving ideal anti-oxidation performance lies in unclear anti-oxidation behavior at special interface between 2D hBN and three-dimensional (3D) metals. Herein, system of monolayer hBN grown on copper (Cu) foils with various lattice orientations was grown to investigate the anti-oxidation behavior of different interlayer configurations. By using structural characterizations together with analysis of topography, we surprisingly found that stronger interlayer coupling led to worse anti-oxidation performance owing to fast diffusion of O₂ through higher hBN corrugations generated at the commensurate hBN/Cu(111) configuration. In view of this, we developed the approach of cyclic reannealing that can effectively flatten corrugations and steps, and therefore improve the anti-oxidation performance to a great extent. This work provides a more in-depth understanding of anti-oxidation behavior of 2D materials grown on 3D metals, and a practical method to pave the way for its large-scale applications in future.

Mechanical vibration, as an alternative of application of solid/liquid lubricants, has been an effective means to modulate friction at the macroscale. Recently, atomic force microscopy (AFM) experiments and model simulations also suggest a similar vibration-induced friction reduction effect for nanoscale contact interfaces, although an additional external vibration source is typically needed to excite the system. Here, by introducing a piezoelectric thin film along the contact interface, we demonstrate that friction measured by a conductive AFM probe can be significantly reduced (more than 70%) when an alternating current (AC) voltage is applied. Such real-time friction modulation is achieved owing to the localized nanoscale vibration originating from the intrinsic inverse piezoelectric effect, and is applicable for various material combinations. Assisted by analysis with the Prandtl–Tomlinson (P–T) friction model, our experimental results suggest that there exists an approximately linear correlation between the vibrational amplitude and the relative factor for perturbation of sliding energy corrugation. This work offers a viable strategy for realizing active friction modulation for small-scale interfaces without the need of additional vibration source or global excitation that may adversely impact device functionalities.