Date of Award

8-2007

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Physics

Advisor

Daw, Murray S

Committee Member

Rao , Apparao M

Committee Member

Marinescu , Catalina

Committee Member

Ke , Pu Chun

Abstract

First-principles methods enable one to study the electronic structure of solids, surfaces, or clusters as accurately as possible with moderate computational effort.
So we used a first-principles electronic structure method to calculate the electronic structure of free-standing layer of MoS2 with ABA and ABC stacking. Our results suggest MoS2 with ABA stacking which appears as an insulator has an energy gap of 1.64 eV. The covalent bonds between molybdenum and sulfur atoms are strong enough to form this gap. The ABC stacking will break the symmetry and becomes metallic. The valance and impurities calculations show the rigid-band picture of MoS2 with ABA stacking.
For treating larger systems, one can also use the tight-binding method. We applied this method to fit the band structure of single layer of S to the result from the first-principles calculation.
The electronic structure of MoS2 nanotubes has been studied using a first-principles electronic structure method. We investigated MoS2 zigzag (n, 0) nanotubes as well as armchair (n, n) structures. We constructed MoS2 nanotubes with ABA and ABC stacking. The structures have been completely optimized. We compare our results to previous tight-binding calculations by Seifert et al. and find significant differences in configuration, bond lengths and resulting electronic structure in several MoS2 nanotubes. For zigzag structures, almost all the nanotubes with ABA stacking and small tubes with ABC stacking are semiconducting. For armchair structures, all (n, n) tubes with ABA stacking are semiconducting and with ABC stacking are metallic. For armchair and zigzag tubes of a given n, the lowest energy structure is semiconducting.

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