Atomistic and continuum simulations of 2D materials with environmental effects

Abstract

Two-dimensional materials that are only a few atoms thick have been extensively studied due to their distinct properties, which set them apart from their bulk crystalline materials. This opens up a wide range of engineering applications that are not possible with bulk materials. Furthermore, due to the large surface area, the properties of two-dimensional materials are affected by surrounding environments. Understanding the physics of these interactions and how they alter the properties of two-dimensional materials is crucial to take advantage of these characteristics and expedite the testing process. This thesis focuses on my research into examining the environmental effects that include the substrate, inter-layer, and gas reservoir on two-dimensional materials through multi-scale simulations. For the substrate effect, strain-engineering of the MoS2 mono and bilayers driven by the non-flat Si3N4 substrate is examined via the Lennard-Jones potential, and continuum models have been developed by information from atomistic simulations. These results are validated by the bend-contour lines in experimental transmitted electron microscopy images. The demonstration of the de- formation of twisted bilayer graphene, where two graphene layers interact and affect each other, is also demonstrated. We characterize the deformation of twisted bilayer graphene in relaxation and dynamics using an elastic basis derived from the normal mode of continuum elastic 2D plate, and the results are validated by an experimental electron diffraction image. Finally, the gas reservoir effect on two-dimensional mate- rial is examined. Atomistic simulation of the gas reservoir is developed based on the ideal gas law and Maxwell-Boltzmann distribution, and the statistical mechanics of a two-dimensional material in the gas reservoir is studied. We also measure the thermal conductivity of the graphene layer, which depends on time-dependent statistical mechan- ics, and compare it with the thermal conductivity of the graphene layer in canonical ensemble via Langevin and Nos ́e-hoover thermostats.