Pull-to-Peel of Two-Dimensional Materials for the Simultaneous Determination of Elasticity and Adhesion

Abstract

The flexible and clinging nature of ultrathin films requires an understanding of their elastic and adhesive properties in a wide range of circumstances from fabrications to applications. Simultaneously measuring both properties, however, is extremely difficult as the film thickness diminishes to the nanoscale. Here we address such difficulties through peeling by pulling thin films off from the substrates (we thus refer to it as “pull-to-peel”). Particularly, we perform in situ pull-to-peel of graphene and MoS2 films in a scanning electron microscope and achieve simultaneous determination of their Young’s moduli and adhesions to gold substrates. This is in striking contrast to other conceptually similar tests available in the literature, including indentation tests (only measuring elasticity) and spontaneous blisters (only measuring adhesion). Furthermore, we show a weakly nonlinear Hooke’s relation for the pull-to-peel response of two-dimensional materials, which may be harnessed for the design of nanoscale force sensors or exploited in other thin-film systems.

Adhesion of 2D MoS2 to Graphite and Metal Substrates Measured by a Blister Test

“…Some devices are measured at several increasing values of p 0 and undergo multiple delaminations to larger delaminated radii, a , and these are shown as identically colored data points (Figure d). We find an average Γ sep = 0.28 ± 0.04 J/m 2 (Figure d), which agrees closely with previous work (0.27–0.67 J/m 2 ) . The difference in the work of separation within each device may be caused by several factors, including local roughness differences due to the etching process of the wells where the rim of the well may be rougher than other nearby surfaces, carbon-based contamination on the surface, or local differences in the chemical reactivity of the surface .…”

Large and Pressure-Dependent c-Axis Piezoresistivity of Highly Oriented Pyrolytic Graphite near Zero Pressure

“…Adding the measured resistivity and the corresponding pressure shown in Figure b to the equation presented above, we obtained the apparent modulus for different pressures, as shown in Figure d. One can see that when the pressure increases to ∼200 MPa, the apparent modulus increases with pressure from <1 to ∼20 GPa, which is a reasonable value for the c- axis modulus of HOPG in previous experiments. , − The apparent modulus under high pressure is much larger than that near zero pressure, showing a significant stiffening effect in the c -axis electromechanical properties. The small apparent modulus near zero pressure and the significant stiffening effect of electromechanical properties are thought to be responsible for our measured large c- axis piezoresistivity near zero pressure and its decrease by a large magnitude with pressure.…”

Mechanical Mapping of Nanoblisters Confined by Two-Dimensional Materials Reveals Complex Ridge Patterns

“…Here, we focus our study on blisters that meet the membrane limit. This can be justified by the Föppl–von Kármán (FvK) number Kh 2 / D , which compares the stretching energy to the bending energy. ,, Here, K = Et is the stretching stiffness where E = 1.06 TPa is the Young’s modulus as we adopted from ref , and D is the bending rigidity. Since the bending rigidity of multilayer van der Waals materials is not well-known, , here we justify the assumption experimentally by focusing on blisters whose shapes conform to the membrane-like form of a pressurized sheet, , as we show below.…”