Date on Master's Thesis/Doctoral Dissertation

12-2021

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Physics and Astronomy

Degree Program

Physics, PhD

Committee Chair

Yu, Ming

Committee Member

Sumanasekera, Gamini

Committee Member

Jasinski, Jacek

Committee Member

Liu, Shudun

Committee Member

Narayanan, Badri

Author's Keywords

Li intercalation; black phosphorous; blue phosphorous; first-principle study; DFT; black phosphorous under pressure

Abstract

A comprehensive density functional theory calculation has been conducted to seek a potential structural transition from black to blue phosphorene layers, with a focus on the roles played by alkali-metal intercalation in black phosphorene/phosphorus. This study reveals that at sufficiently high Li concentration and specific, well-defined configurations, a phase transition from black to blue phosphorene can take place. The Li atoms intercalated in black phosphorene could act as a “catalyst” in the“reactive region” of the lone pair of P atoms, leading to a P-P bond breaking and, subsequently, a local structural transformation from an orthorhombic lattice to an assembly of parallel narrow nanoribbons with rhombohedra-like symmetry. During Li deintercalation, these nano-ribbons are self-mended and form blue phosphorene layers with interlayer separation of 4.13 ̊A, indicating individual layers can be mechanically exfoliated. Besides Li, we studied intercalation of Sodium (Na), Potassium (K), and cesium (Cs) in multilayer black phosphorene and found that only Li and Cs can induce stable black to the blue phosphorene phase transition. We further extend our study by incorporating the synergetic effect of pressure and Li intercalation on black to the blue phosphorene phase transition. This study shows that pressure indeed can accelerate the phase transition process. We hope our study will guide future experiments in search of a phase transition from black to blue phosphorene. Hydrazine gas adsorption on layered WS2 has been systematically studied using first-principle calculations. The hydrazine molecules were found to be exothermically physisorbed. The layer-dependent adsorption energy and interlayer separation induced by van der Waals interaction exerted by hydrazine molecules lead to the difficulty in desorbing hydrazine molecules from layered WS2 as the number of layers increases. The emergence of localized impurity states below the Fermi level was discovered upon the hydrazine adsorption, which significantly alter the band structure and electrical transport properties of pristine WS2. The existence of defects and the humidity, on the other hand, influences the sensitivity of layered WS2 to hydrazine adsorption. This study shows that a perfectly layered WS2 could be a promising candidate for an efficient nano-sensor to detect hydrazine gas in dry environment.

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