Interlayer Binding Energy of Hexagonal MoS₂ as Determined by an <i>In Situ</i> Peeling-to-Fracture Method

Abstract

Although interlayer binding energy (IBE) is a key parameter relevant to the electronic properties and device performances of hexagonal MoS2, a promising two-dimensional (2D) semiconductor, it has never been determined experimentally. Herein, we report a novel peeling-to-fracture method for measuring the interlayer binding energy of a two-dimensional hexagonal MoS2. In the method, a few upper layers of a multilayer MoS2 nanoflake are in situ radially peeled off to form a circular truncated cone by lifting up a metal disk deposited on it in a scanning electron microscope (SEM), until the peeled layers fracture at the perimeter of the metal disk. By analyzing the peeling-to-fracture process using a continuum mechanical model, the interlayer binding energy of MoS2 is obtained in terms of its Young’s modulus, fracture strength, and geometric parameters of the circular truncated cone. By employing well-determined Young’s modulus and fracture strength of hexagonal MoS2 from previous literatures, the interlayer binding energy of a mechanically exfoliated MoS2 is determined to be 0.55 ± 0.13 J m–2. The interlayer binding energy of hexagonal MoS2 is calculated to be about 0.422 J m–2 by density function theory calculations. Our results give a quantitative knowledge of the van der Waals interlayer interactions of hexagonal MoS2 and provide a general method for measuring the interlayer binding energy of two-dimensional materials.