Graduate Student Seminar

Novel materials, including two-dimensional (2D) materials, ferroelectric materials, as well as hybrid perovskites materials have been attracting tremendous attention in recent years. Among them, 2D materials, such as graphene and transition metal dichalcogenides (TMDCs), have great potentials for nanoelectronics and optical applications, especially under strain, since strain has huge impact on semiconductors and 2D materials can sustain much larger strain than their bulk counterparts. Ferroelectrics are fairly useful in applications such as transistors and memories. When coming to 2D, off-plane ferroelectric ordering in ultrathin films has been pursued for decades due to depolarization effect. Hybrid perovskites materials are well known for being easily fabricated and controlled in structures, as well as excellent performances in emerging photovoltaic technologies. Due to the lack of inversion symmetry, second-order nonlinear optical properties should emerge in such materials. In this thesis, with the implementation of first-principles, we study the strain-induced quasiparticle band gaps and optical spectra variation of monolayer TMDCs. Besides, we will explore the off-plane polarization ordering in metal chalcogen diphosphates (MCDs) under different layers. We will also study the second-order nonlinear optical properties, such as second harmonic generation (SHG) and linear electro-optic (LEO) effects of organic-inorganic hybrid halide perovskites.