A theoretical study of strained monolayer transition metal dichalcogenides based on simple band structures

buir.advisorBulutay, Ceyhun
dc.contributor.authorAas, Shahnaz
dc.date.accessioned2019-11-26T08:31:50Z
dc.date.available2019-11-26T08:31:50Z
dc.date.copyright2019-10
dc.date.issued2019-10
dc.date.submitted2019-11-25
dc.departmentDepartment of Physicsen_US
dc.descriptionCataloged from PDF version of article.en_US
dc.descriptionThesis (Ph.D.): Bilkent University, Department of Physics, İhsan Doğramacı Bilkent University, 2019.en_US
dc.descriptionIncludes bibliographical references (leaves 52-66).en_US
dc.description.abstractThis doctoral thesis deals with optoelectronic and geometric band properties of two-dimensional transition metal dichalcogenides (TMDs) under applied strain. First, we analyze various types of strain for the K valley optical characteristics of a freestanding monolayer MoS2, MoSe2, WS2 and WSe2 within a two-band k p method. By this simple bandstructure combined with excitons at a variational level, we reproduce wide range of available strained-sample photoluminescence data. According to this model strain affects optoelectronic properties. Shear strain only causes a rigid wavevector shift of the valley without any alternation in the bandgap or the effective masses. Also, for exible substrates under applying stress the presence of Poisson's effect or the lack of it are investigated individually for the reported measurements. Furthermore, we show that circular polarization selectivity decreases/increases by tensile/compressive strain for energies above the direct transition onset. TMDs in addition to their different other attractive properties have rendered the geometric band effects directly accessible. The tailoring and enhancement of these features by strain is an ongoing endeavor. In the second part of this thesis, we consider spinless two and three band, and spinful four band bandstructure techniques appropriate to evaluate circular dichroism, Berry curvature and orbital magnetic moment of strained TMDs. First, we establish a new k p parameter set for MoS2, MoSe2, WS2 and WSe2 based on recently released ab initio and experimental band properties. For most of these TMDs its validity range extend from K valley edge to several hundreds of millielectron volts for both valence and conduction band. We introduce strain to an available three band tight-binding Hamiltonian to extend this over a larger part of the Brillouin zone. Based on these we report that by applying a 2:5% biaxial tensile strain, both the Berry curvature and the orbital magnetic moment can be doubled compared to their unstrained values. These simple bandstructure tools can be suitable for the device modeling of the geometric band effects in strained monolayer TMDs.en_US
dc.description.degreePh.D.en_US
dc.description.statementofresponsibilityby Shahnaz Aasen_US
dc.format.extentxiii, 66 leaves : charts ; 30 cm.en_US
dc.identifier.itemidB160199
dc.identifier.urihttp://hdl.handle.net/11693/52731
dc.language.isoEnglishen_US
dc.publisherBilkent Universityen_US
dc.rightsinfo:eu-repo/semantics/openAccessen_US
dc.subjectk - p Hamiltonianen_US
dc.subjectExcitonsen_US
dc.subjectTransition metal dichalcogenidesen_US
dc.subjectStrainen_US
dc.subjectPhotoluminescenceen_US
dc.subjectCircular dichroismen_US
dc.subjectBerry curvatureen_US
dc.subjectOrbital magnetic momenen_US
dc.titleA theoretical study of strained monolayer transition metal dichalcogenides based on simple band structuresen_US
dc.title.alternativeTek katmanlı gerinimli geçiş metali kalkojenitleri için basit bant yapısına dayalı kuramsal bir çalışmaen_US
dc.typeThesisen_US
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