Understanding and Predicting Properties of Low-dimensional Functional Materials from First-principles

Author

• Naseem Ud Din, University of Central Florida

Keywords

First-principles calculations; Transition metal-organic chains; Density functional theory; Optical properties; Charge dynamics

Abstract

A periodic network with uniform single metal active site, in coordination with redox-active organic ligands, is a promising class of materials for next generation single atom catalysts. Towards this quest, in this dissertation I have carried out first-principles density functional theory (DFT) based calculations of the geometrical and electronic structure and magnetic properties of several transition-metal-organic-chains (TM-C) both in gas phase as well as on Au(111) surface. Of particular interest are dipyridyltetrazine (DT), Bis-pyrimidine (BP), and 1,10-phenanthroline5,6-dione, (PDO) ligands used to design the TM-C with several single TM atoms as the coordination center. I have screened several TM atoms to get their coordination geometry (stable structure ) as well as analyzing their chemical activity through adsorption of small molecules on the TM center. Our results suggest that TM atoms with partially occupied d-orbitals exhibit strong affinity, while the TM atoms with fully occupied d-orbitals show weak affinity to the CO and O2 molecule. We also investigate the effect of support (Au(111)) on geometry and charge state in case of V-BP and V-PDO systems, and found that the support not only alters the local coordination of TM-Cs, but also has significant charge transfer from TM-C to Au(111). The tetrazine-based ligand, DT is only able to undergo a two-electron reduction, which limits the complexation to one metal per ligand. We studied the complexation of tetraethyltetraaza- anthraquinone (TAAQ) with elemental Fe, leading to complex metal–organic chains. We utilized the multiple binding pockets of TAAQ and achieve higher metal:ligand (M:L) ratios. Our results of various Fe:TAAQ ratio, suggests that thermodynamically one cannot create FeTAAQ species with higher than 2:1 M:L ratio. The second part of this dissertation deals with electronic structure and excitation spectrum of hydrogenated single layer and clean bilayer MoS2. We calculate the excitation spectrum of single-layer MoS2 at several hydrogen coverages by using Density-Matrix Time-Dependent Density-Functional Theory (TDDFT). Binding energies of the excitons of the hydrogenated MoS2 are relatively large (few tens of meV), making their experimental detection facile and suggesting hydrogenation as a knob for tuning the optical properties of single-layer MoS2. To examine ultrafast charge dynamics in bilayer MoS2, we applied DFT+Liouville equation approach and found that in conjunction with electron-phonon interaction ultrafast charge dynamics has a strong effect on the calculated emission spectrum. Our results reveal the importance of ultrafast charge dynamics in understanding photoemissive properties of a few-layer transition-metal dichalcogenide.

Notes

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Graduation Date

2020

Semester

Fall

Advisor

Rahman, Talat

Degree

Doctor of Philosophy (Ph.D.)

College

College of Sciences

Department

Physics

Degree Program

Physics

Format

application/pdf

Identifier

CFE0008393; DP0023830

URL

https://purls.library.ucf.edu/go/DP0023830

Language

English

Release Date

December 2020

Length of Campus-only Access

None

Access Status

Doctoral Dissertation (Open Access)

Subjects

Low-dimensional semiconductors; Nanostructured materials--Optical properties; Transition metal complexes--Analysis; Time-dependent density functional theory; Nanostructured materials--Magnetic properties

STARS Citation

Ud Din, Naseem, "Understanding and Predicting Properties of Low-dimensional Functional Materials from First-principles" (2020). Electronic Theses and Dissertations, 2020-2023. 422.
https://stars.library.ucf.edu/etd2020/422