Twinning In Two-Dimensional Materials And Its Application To Electronic Properties

Controlled band gap engineering is crucial to the design of next-generation, flexible, two-dimensional (2D) electronic nanodevices. In 2D materials, defects have shown promise in manipulating electronic properties. Unfortunately, only a small number of topological defects are available in 2D materials, leading to the current open problem of overcoming challenges in tailoring material properties. We propose the exploitation of twin boundaries, as they can, in principle, be generated under controlled circumstances (e.g. by applying shear deformation or by shuffling atoms). Using a recently-developed twin framework, we investigate the use of twin boundaries to modify electronic properties in 2D materials. Taking graphene and molybdenum disulfide as representative materials, we study several twin modes predicted with our framework and compute their nucleation and formation energies, equilibrium positions, and thermal stability using atomistic simulations. We show that many of our predicted twin boundaries are seen in experimental characterization of 2D materials, with their energies being competitive relative to existing grain boundaries. To highlight the possibility of using twin boundaries in nanoscale devices, we compute their respective electronic properties and transmission gaps. By showing that gaps as large as 1.2 eV can be opened up with the introduction of nano-twins, we propose their use in the development of field-effect nano-transistors with tailored properties based on 2D materials.