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dc.rights.licenseRestricted to current Rensselaer faculty, staff and students. Access inquiries may be directed to the Rensselaer Libraries.
dc.contributorTerrones, H. (Humberto)
dc.contributorMeunier, Vincent
dc.contributorShi, Sufei
dc.contributorZhang, Shengbai
dc.contributor.authorBeach, Kory
dc.date.accessioned2021-11-03T09:16:35Z
dc.date.available2021-11-03T09:16:35Z
dc.date.created2020-08-10T12:03:59Z
dc.date.issued2019-12
dc.identifier.urihttps://hdl.handle.net/20.500.13015/2511
dc.descriptionDecember 2019
dc.descriptionSchool of Science
dc.description.abstractThe central aim of this thesis is to explore the various ways in which the optical and electronic properties of 2D and nanostructured materials are modified by tunable degrees of freedom. These are degrees of freedom, which include the application of strain, alloying, curvature, and defects are all parameters that can be tuned externally to modify physical properties to obtain a desired outcome. In short, these are the knobs that the nano-engineer can turn, and it is the goal of this work to provide a deeper understanding into what exactly those knobs do. In particular, much of this work concerns the nonlinear optical properties of these materials, which is largely unexplored terrain from a theoretical perspective. Throughout this work I explore these nonlinear optical properties both in depth and breadth, gaining a deeper knowledge of the physics of nonlinear optics in 2D materials in relation to these degrees of freedom, as well as exploring and discovering a wide range of new materials with strong nonlinear optical properties.
dc.description.abstractIn Chapter 4, this TDDFT technique is further applied to a filtered database of 2D materials to identify several previously unreported high-intensity nonlinear optical materials. It is found that certain symmetries are highly conducive to strong second harmonic generation. A bond charge model is discussed as a potential heuristic predictor of strong nonlinear optical susceptibility. In Chapter 5, a deeper exploration into more computationally intensive calculations of nonlinear optical properties in TMDs using the TDDFT-BSE method is then presented. The inclusion of spin-orbit coupling (SOC) and its effects on the C-exciton are discussed. The effects of alloying in TMDs with larger unit cells are also explored with the inclusion of excitonic effects. Furthermore, by significantly increasing the smearing in the TDDFT method, which is analogous to lowering the temperature, it is shown that excited excitonic peaks can be resolved in the second harmonic spectrum that agree with experimental reports.
dc.description.abstractIn the first study (Chapter 2), the nonlinear optical properties of a wide range of semiconducting nanostructures and alloys are examined using a Density Functional Perturbation Theory (DFPT) approach. The materials considered are transition metal dichalcogenide (TMD) and boron nitride (BN) nanostructures and alloys with various geometries including monolayers, few-layered systems, nanotubes, Haeckelites, and porous Schwarzites. It is found that alloying, curvature, and the formation of exotic symmetries in these materials can all have a strong enhancing effect on the nonlinear susceptibility. In the next study (Chapter 3), the effects of strain on the second harmonic generation of TMDs is studied using a Time-Dependent Density Functional Theory (TDDFT) approach with the inclusion of correlation effects with the time-dependent Bethe-Salpeter Equation (BSE). High tunability of the nonlinear response as a function of strain is found in these materials. It is also shown that distinct subpeaks of the C-exciton in TMDs can be observed which, when compared with the electronic structure, can be attributed to specific transitions in the Brillouin zone. It is demonstrated that these transitions can be manipulated and differentiated by the application of strain.
dc.description.abstractLastly, the effects of iron doping in WS2 are explored experimentally in Chapter 6 using several experimental techniques. These characterization techniques include Raman Spectroscopy, Photoluminescence (PL) Spectroscopy, Atomic Force Microscopy (AFM), Kelvin Probe Force Microscopy (KPFM), and Tip-Enhanced Raman and PL Spectroscopy (TERS and TEPL). It is shown that hexagonal flakes of Fe-doped WS2 grow distinct doping domains with vastly different optical, mechanical, and electronic properties. These domains are a result of differences in the chemical potential between tungsten and sulfur exposed growth edges. It is further shown that the most likely defects involve three iron substitutions of tungsten atoms. This agrees with several experimental results and theoretical calculations.
dc.language.isoENG
dc.publisherRensselaer Polytechnic Institute, Troy, NY
dc.relation.ispartofRensselaer Theses and Dissertations Online Collection
dc.subjectPhysics
dc.titleNonlinear optics and characterization of layered and nanostructured materials
dc.typeElectronic thesis
dc.typeThesis
dc.digitool.pid180008
dc.digitool.pid180009
dc.digitool.pid180010
dc.rights.holderThis electronic version is a licensed copy owned by Rensselaer Polytechnic Institute, Troy, NY. Copyright of original work retained by author.
dc.description.degreePhD
dc.relation.departmentDept. of Physics, Applied Physics, and Astronomy


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