Investigation of the dynamic bending properties of MoS2 thin films by interference colours

Hoop compression driven instabilities in spontaneously formed multilayer graphene blisters over a polymeric substrate

The blistering of elastic membranes is prone to elastic-solid as well as substrate-based mechanical instabilities. The solid-based instabilities have been well-explored in the mechanically indented blisters of elastic membranes over the rigid/solid substrates, but an integrated study illustrating the underlying mechanism for the onset of solid as well as substrate-based instabilities in the spontaneous blistering of a 2D material is still lacking in the literature. In this article, an extensive experimental as well as analytical analysis of the spontaneous blister-formation in the multilayer graphene (MLG) flakes over a polymeric substrate is reported, which elucidates the involved mechanism and the governing parameters behind the development of elastic-solid as well as viscoelastic-substrate based instabilities. Herein, a 'blister-collapse model' is proposed, which infers that the suppression of the hoop compression, resulting from the phase-transition of the confined matter, plays a crucial role in the development of the instabilities. The ratio of blister-height to flake-thickness is a direct consequence of the taper-angle of the MLG blister and the thickness-dependent elasticity of the upper-bounding MLG flake, which shows a significant impact on the growth-dynamics of the viscous fingering pattern (viscoelastic-substrate based instability) under the MLG blister.

Manipulating three-dimensional bending to extraordinarily stiffen two-dimensional membranes by interference colors

We have provided a no-touch and inexpensive technique to present the three-dimensional (3D) structure of two-dimensional (2D) films, based on the equal thickness interference fringes. In these experiments, the interference colors were obtained by an optical microscope without contact with the sample, and the 3D structures of curved 2D membranes were reconstructed by MATLAB programs in real time. The theoretical model and experimental results both showed that natural bending can improve the stiffness of 2D materials by more than 10 times. By using micro-droplets as the workbench, the 3D bending orientation and curvature of the 2D material could be manipulated and detected at the same time. The selected 3D curved shapes of cylindrical, ellipsoid and saddle surfaces can increase the bending stiffness over 10 000 times based on theoretical calculation. A saddle-shaped 3D structure (classic crisps shape) is predicted to obtain the maximum bending stiffness. Herein, a simple and practical method to comprehensively detect the basic deformation of 2D membranes is proposed, which should be promoted to explore the out-of-plane mechanical properties of 2D materials under external fields.

Effects of surface defects on the mechanical properties of ZnO nanowires

The elastic modulus of ZnO nanowires was measured using a resonance method based on laser Doppler effect and their fracture strains were determined via two-point bending with the aid of optical nanomanipulation. The elastic moduli of ZnO nanowires with diameters of 78 to 310 nm vary from 123 to 154 GPa, which are close to the bulk value of 140 GPa and independent of the diameters and surface defects. However, the fracture strains of the ZnO nanowires depend significantly on their diameters, increasing from 2.1% to 6.0% with the decrease in diameter from 316 to 114 nm. Post-mortem TEM analysis of the ends of the fractured nanowires revealed that fracture initiated at surface defects. The Weibull statistical analysis demonstrated that a greater defect depth led to a smaller fracture strain. The surface-defect dominated fracture should be an important consideration for the design and application of nanowire-based nanoelectromechanical systems.

The effect of surface texture on the kinetic friction of a nanowire on a substrate

The friction between Al2O3 nanowires and silicon substrates of different surface textures was characterised by use of optical manipulation. It was found that surface textures had significant effect on both the friction and the effective contact area between a nanowire and a substrate. A genetic algorithm was developed to determine the effective contact area between the nanowire and the textured substrate. The frictional force was found to be nearly proportional to the effective contact area, regardless of width, depth, spacing and orientation of the surface textures. Interlocking caused by textured grooves was not observed in this study.

Broadband spatial self-phase modulation of black phosphorous

Spatial self-phase modulation (SSPM) experiments on two-dimensional (2D) black phosphorus (BP) nanoflake suspensions are performed with focused femtosecond pulsed lasers at 350-1160 nm. In the broadband region, the slope of the SSPM ring number versus laser intensity varies from 0.99 to 0.34, which is larger than 0.25 in MoS2. We deduce the portion of the fluid globe (ξ) to be 0.0067, which is a constant independent of laser intensity, when the laser intensity is above 10 W/cm2. The nonlinear refractive index of BP is measured to be ∼10(-5) cm2 W(-1), and the third-order nonlinear susceptibility is χ(3)∼10(-8) esu at multiple wavelengths.