Date on Master's Thesis/Doctoral Dissertation

12-2018

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Physics and Astronomy

Degree Program

Physics, PhD

Committee Chair

Yu, Ming

Committee Co-Chair (if applicable)

Jayanthi, Chakram

Committee Member

Jayanthi, Chakram

Committee Member

Sumanasekera, Gamini

Committee Member

Fu, Xiao-An

Author's Keywords

2D materials; DFT; SCED; phosphorene; phosphide binary compounds

Abstract

In this thesis, a comprehensive computational simulation was carried out for predicting, characterizing, and applications of two-dimensional (2D) materials. The newly discovered GaP and InP layers were selected as an example to demonstrate how to explore new 2D materials using computational simulations. The performance of phosphorene as the anode material of Lithium-ion battery was discussed as the example of the application of 2D material. Furthermore, the semi-empirical Hamiltonian for phosphorous and lithium elements have been developed for our future work on the application of phosphorus and lithium-based systems. The novel 2D materials of GaP and InP binary compounds were found to possess unique anisotropic structural, electronic, and mechanical properties. Their crystalline structures show orthorhombic lattices symmetry and high buckling of 2.14 Å-2.46 Å. They have strong directional dependence of Young’s moduli and effective nonlinear elastic moduli. They have wide fundamental bandgaps which were also found to be tunable under the strain. In particular, a direct-indirect bandgap transition was found under certain strains, reflecting their promising applications for the strain-induced bandgap engineering in nanoelectronics and photovoltaics. To completely understand the performance of phosphorene as the anode material of Li-ion battery, the lithium adsorption energy landscape, diffusion mobility, intercalation, and capacity of phosphorene were studied. The calculations show the anisotropic diffusivity and the ultrafast diffusion mobility of lithium along the zigzag direction. Phosphorene could accommodate up to the ratio of one Li per P atom (i.e., Li16P16). In particular, there was no lithium clustering even at the high Li concentration. The structure of phosphorene, when it was fractured at high concentration, is reversible during the lithium intercalation. The theoretical value of the lithium capacity for a monolayer phosphorene is predicted to be above 433 mAh/g. The SCED-LCAO Hamiltonians for phosphorus and lithium were developed in this thesis. The optimized parameters were obtained by fitting the structural and electronic properties of small clusters and bulk phases, which were calculated by the ab-initial methods. The robustness tests of phosphorus parameters were executed by relaxing the back phosphorus, phosphorene, and blue phosphorene with SCED-LCAO-MD code. The energy order and band gap of black phosphorus, phosphorene and blue phosphorene are all consistent with the DFT calculations and experimental measurements. The robustness tests of Li parameters were executed for the BCC bulk of Li and its stability was proved.

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