Yingchun Jiang1,Srividhya Sridhar2,Zihan Liu1,Dingli Wang1,Jia Deng1,Huck Beng Chew2,Changhong Ke1
Binghamton University, The State University of New York1,University of Illinois at Urbana-Champaign2
Yingchun Jiang1,Srividhya Sridhar2,Zihan Liu1,Dingli Wang1,Jia Deng1,Huck Beng Chew2,Changhong Ke1
Binghamton University, The State University of New York1,University of Illinois at Urbana-Champaign2
Bending/flexural rigidity is one of the fundamental mechanical properties of mono- and few-layered two-dimensional (2D) van der Waals crystals (e.g., graphene, molybdenum disulfide (MoS<sub>2</sub>) and hexagonal boron nitride (hBN)) that are of great importance to the pursuit of a variety of their applications. Continuum mechanics break down in bending stiffness calculations of these 2D crystals because their layered atomistic structures are uniquely characterized by strong intralayer bonding coupled with weak interlayer interactions. The lack of experimental measurements and the wide scattering of reported values in the literature pose additional challenges to scientific understanding and practical applications of these 2D materials. In this talk, we will present our recent research on quantitative measurements of bending stiffness of pristine monolayer or few-layer graphene, hBN, and MoS<sub>2</sub> flakes and elucidate how the bending rigidities of these 2D crystals are governed by their structural geometry, and intra- and inter-layer bonding interactions. Atomic force microscopy (AFM) experiments on the self-folded conformations of these 2D materials on flat substrates show that the bending rigidity of MoS<sub>2 </sub>significantly exceeds those of graphene or hBN of comparable layers, despite its much lower tensile modulus. Even on a per-thickness basis, MoS<sub>2</sub> possesses similar bending stiffness to hBN and is much stiffer than graphene. Density functional theory (DFT) calculations reveal that this high bending rigidity of MoS<sub>2</sub> is due to its large interlayer thickness and strong interlayer shear, which prevail over its weak in-plane bonding. The high bending rigidity of ultrathin MoS<sub>2</sub> is of particular significance for its electronic applications, as it is less prone to out-of-plane structural instabilities, such as wrinkles and ripples, which can impact the material's electrical properties. The superior bending rigidity of MoS2 makes it a promising building block for robust nanoelectronics and sensors.