Author
Chow, Philippe K.
Other Contributors
Koratkar, Nikhil A. A.; Gall, Daniel; Shi, Yunfeng; Terrones, H. (Humberto); Lu, T.-M. (Toh-Ming), 1943-;
Date Issued
2015-12
Subject
Materials engineering
Degree
PhD;
Terms of Use
This electronic version is a licensed copy owned by Rensselaer Polytechnic Institute, Troy, NY. Copyright of original work retained by author.;
Abstract
The ever-evolving symbiosis between mankind and nanoelectronics-driven technology pushes the limits of its constituent materials, largely due to the dominance of undesirable hetero-interfacial physiochemical behavior at the few-nanometer length scale, which dominates over bulk material characteristics. Driven by such instabilities, research into two-dimensional (2D) van der Waals-layered materials (e.g. graphene, transition metal dichalcogenides (TMDCs), boron nitride), which have characteristically inert surface chemistry, has virtually exploded over the past few years. The discovery of an indirect- to direct-gap conversion in semiconducting group-VI TMDCs (e.g. MoS2) upon thinning to a single atomic layer provided the critical link between metallic and insulating 2D materials. While proof-of-concept demonstrations of single-layer TMDC-based devices for visible-range photodetection, light-emission and solar energy conversion have showed promising results, the exciting qualities are downplayed by poorly-understood defectinduced photocarrier traps, limiting the best-achieved external quantum efficiencies to approximately ~1%.; The results in this thesis shed light on the role of defects on atomically-thin TMDC optical behavior and point to yet-unexplored opportunities for further fundamental study and practical use of defects, which will expectedly benefit the development of scalable TMDC-based optoelectronic devices.; This thesis explores the behavior of defects in atomically-thin TMDC layers in response to optical stimuli using a combination of steady-state photoluminescence, reflectance and Raman spectroscopy at room-temperature. By systematically varying the defect density using plasma-irradiation techniques, an unprecedented room-temperature defect-induced monolayer PL feature was discovered. High-resolution transmission electron microscopy correlated the defect-induced PL with plasma-generation of sulfur vacancy defects while reflectance measurements indicate defect-induced sub-bandgap light absorption. Excitation intensity-dependent PL measurements and exciton rate modeling further help elucidate the origin of the defect-induced PL response and highlights the role of non-radiative recombination on exciton conversion processes.;
Description
December 2015; School of Engineering
Department
Dept. of Materials Science and Engineering;
Publisher
Rensselaer Polytechnic Institute, Troy, NY
Relationships
Rensselaer Theses and Dissertations Online Collection;
Access
Restricted to current Rensselaer faculty, staff and students. Access inquiries may be directed to the Rensselaer Libraries.;