Investigating the roles of intrinsic point defects and transition metal doping in monolayer and bulk TiS2

Author

Patrick J. Keeney, University of North FloridaFollow

Year

2025

Season

Summer

Paper Type

Master's Thesis

College

College of Arts and Sciences

Degree Name

Master of Science in Material Science & Engineering (MS)

Department

Physics

NACO controlled Corporate Body

University of North Florida. Department of Physics

Committee Chairperson

Dr. Paula M. Coelho

Second Advisor

Dr. Jason T. Haraldsen

Third Advisor

Dr. Joshua Melko

Fourth Advisor

Dr. T. J. Mullen

Department Chair

Dr. Greg Wurtz

College Dean

Dr. Kaveri Subrahmanyam

Abstract

Within this thesis, the magnetic and electronic properties of various 1T-TiS₂ systems are thoroughly examined using density functional theory (DFT) and scanning tunneling microscopy (STM). Formation energies and electronic implications of intrinsic point defects in bulk TiS₂ and monolayer TiS₂ are analyzed by approximating a computational monolayer of TiS₂ as the surface layer of a bulk sample. This approximation is validated given that intralayer covalent bonding dominates interlayer van der Waals interactions. We conclude that the most energetically favorable intrinsic defects are Ti atoms settling above the outermost S plane and S vacancies. In addition, the change in stoichiometry impacts the band structure by shifting the Fermi level into the conduction band, resulting in a metallic region rather than a semiconducting region, as expected with pristine stoichiometry. Magnetism in bulk TiS₂ is examined through SQUID magnetometry and density functional theory. Magnetism is not expected within pristine TiS₂ due to the symmetry of covalent bonding; however, magnetization data demonstrate a paramagnetic signal. SQUID data are analyzed in conjunction with density functional theory calculations to provide a comprehensive understanding of the possible mechanisms within the sample that induce magnetism. Lastly, magnetic exchange pathways of monolayer TiS₂ are computationally examined through systematic direct substitution of transition-metal atoms (V-, Cr-, Mn-) into Ti sites.

Suggested Citation

Keeney, Patrick J., "Investigating the roles of intrinsic point defects and transition metal doping in monolayer and bulk TiS2" (2025). UNF Graduate Theses and Dissertations. 1359.
https://digitalcommons.unf.edu/etd/1359