{"id":{"repo_id":"cambridge","oai_identifier":"oai:www.repository.cam.ac.uk:1810/374109"},"canonical_url":"https://search.dev.ndltd.org/etd/cambridge/oai:www.repository.cam.ac.uk:1810/374109","repository":{"repo_id":"cambridge","name":"Cambridge University","base_url":"https://api.repository.cam.ac.uk/server/oai/request"},"display":{"title":"Photoluminescence from Defects in Two-Dimensional Transition Metal Dichalcogenides","abstract":"Atomic defects in monolayer transition metal dichalcogenides (TMDs) such as chalcogen vacancies significantly affect their properties. In this thesis, I provide a reproducible and facile strategy to rationally induce chalcogen vacancies in monolayer MoS<sub>2</sub> by annealing at 600 °C in an argon/hydrogen (95 vol.%/5 vol.%) atmosphere. At sulfur vacancy densities of ~1.8×10<sup>14</sup> cm<sup>−2</sup>, I observe defect-mediated photoluminescence (PL) at ~1.72 eV (referred to as LX<sub>D</sub>) at room temperature. The LX<sub>D</sub> emission is attributed to excitons trapped at defect-induced in-gap states and is typically observed only at low temperatures (≤77 K). Time-resolved PL measurements reveal that the lifetime of defect-mediated LX<sub>D</sub> emission is longer than band edge excitons, both at room and low temperatures (~2.44 ns at 8 K). My results provide insight into how excitonic and defect-mediated PL emission in MoS<sub>2</sub> are influenced by sulfur vacancies at room and low temperatures. I also show that the LX<sub>D</sub> peak can be suppressed by annealing the defective MoS<sub>2</sub> in sulfur or selenium vapor, which indicates that it is possible to passivate the vacancies. At annealing temperatures ≥600 °C in selenium vapor, I observed the filling of sulfur vacancies by selenium. I extended the defect generation strategy to monolayer MoS<sub>2</sub> on various dielectric substrates to investigate the influence of dielectric substrates on defect-mediated emission. The LX<sub>D</sub> emission after annealing was observed on SiO<sub>2</sub> and hBN, but not on HfO<sub>2</sub>. When the MoS<sub>2</sub> is first annealed on SiO<sub>2</sub> and then transferred onto HfO<sub>2</sub>, the LX<sub>D</sub> emission is present on untreated HfO<sub>2</sub>, but not on annealed HfO<sub>2</sub>. These results suggest that surface states in dielectric substrates can influence the defect-mediated emission.","abstract_html":"Atomic defects in monolayer transition metal dichalcogenides (TMDs) such as chalcogen vacancies significantly affect their properties. In this thesis, I provide a reproducible and facile strategy to rationally induce chalcogen vacancies in monolayer MoS&lt;sub&gt;2&lt;/sub&gt; by annealing at 600 °C in an argon/hydrogen (95 vol.%/5 vol.%) atmosphere. At sulfur vacancy densities of ~1.8×10&lt;sup&gt;14&lt;/sup&gt; cm&lt;sup&gt;−2&lt;/sup&gt;, I observe defect-mediated photoluminescence (PL) at ~1.72 eV (referred to as LX&lt;sub&gt;D&lt;/sub&gt;) at room temperature. The LX&lt;sub&gt;D&lt;/sub&gt; emission is attributed to excitons trapped at defect-induced in-gap states and is typically observed only at low temperatures (≤77 K). Time-resolved PL measurements reveal that the lifetime of defect-mediated LX&lt;sub&gt;D&lt;/sub&gt; emission is longer than band edge excitons, both at room and low temperatures (~2.44 ns at 8 K). My results provide insight into how excitonic and defect-mediated PL emission in MoS&lt;sub&gt;2&lt;/sub&gt; are influenced by sulfur vacancies at room and low temperatures. I also show that the LX&lt;sub&gt;D&lt;/sub&gt; peak can be suppressed by annealing the defective MoS&lt;sub&gt;2&lt;/sub&gt; in sulfur or selenium vapor, which indicates that it is possible to passivate the vacancies. At annealing temperatures ≥600 °C in selenium vapor, I observed the filling of sulfur vacancies by selenium. I extended the defect generation strategy to monolayer MoS&lt;sub&gt;2&lt;/sub&gt; on various dielectric substrates to investigate the influence of dielectric substrates on defect-mediated emission. The LX&lt;sub&gt;D&lt;/sub&gt; emission after annealing was observed on SiO&lt;sub&gt;2&lt;/sub&gt; and hBN, but not on HfO&lt;sub&gt;2&lt;/sub&gt;. When the MoS&lt;sub&gt;2&lt;/sub&gt; is first annealed on SiO&lt;sub&gt;2&lt;/sub&gt; and then transferred onto HfO&lt;sub&gt;2&lt;/sub&gt;, the LX&lt;sub&gt;D&lt;/sub&gt; emission is present on untreated HfO&lt;sub&gt;2&lt;/sub&gt;, but not on annealed HfO&lt;sub&gt;2&lt;/sub&gt;. These results suggest that surface states in dielectric substrates can influence the defect-mediated emission.","abstract_has_math":false,"creators":["Zhu, Yiru"],"institution":"University of Cambridge","degree_name":"Doctor of Philosophy (PhD)","degree_level":"Doctoral","degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Chhowalla, Manish"],"committee_chairs":[],"committee_members":[],"year":2024,"date_issued":"2024-03-30","date_published":"2024-03-30","updated_at":"2026-07-22T22:24:10Z","subjects":["Defect","Photoluminescence","Two-Dimensional Transition Metal Dichalcogenides"],"languages":["eng"],"rights":[],"rights_urls":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/22cbeee4-d36f-4553-add2-54fe7cab4326/download","https://www.rioxx.net/licenses/all-rights-reserved/"],"identifier_entries":[]},"links":{"outbound_url":"https://doi.org/10.17863/CAM.112297","outbound_label":"DOI","outbound_source":"dc:identifier.doi"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Chhowalla, Manish"]},{"key":"dc:creator","label":"Author","values":["Zhu, Yiru"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.issued","label":"Date","values":["2024-03-30"]},{"key":"dc:publisher.institution","label":"Dc Publisher Institution","values":["University of Cambridge"]},{"key":"dc:relation.isreferencedby.uri","label":"Dc Relation Isreferencedby URI","values":["https://www.repository.cam.ac.uk/handle/1810/374109"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]},{"key":"dc:type.qualificationlevel","label":"Dc Type Qualificationlevel","values":["Doctoral"]},{"key":"dc:type.qualificationname","label":"Dc Type Qualificationname","values":["Doctor of Philosophy (PhD)"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Defect","Photoluminescence","Two-Dimensional Transition Metal Dichalcogenides"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["eng"]},{"key":"dc:rights","label":"Dc Rights","values":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/22cbeee4-d36f-4553-add2-54fe7cab4326/download","https://www.rioxx.net/licenses/all-rights-reserved/"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.doi","label":"DOI","values":["https://doi.org/10.17863/CAM.112297"]},{"key":"dc:identifier.uri","label":"Identifier URI","values":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/eedc9bdc-919e-45c2-bc90-73b064695c52/download"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Atomic defects in monolayer transition metal dichalcogenides (TMDs) such as chalcogen vacancies significantly affect their properties. In this thesis, I provide a reproducible and facile strategy to rationally induce chalcogen vacancies in monolayer MoS<sub>2</sub> by annealing at 600 °C in an argon/hydrogen (95 vol.%/5 vol.%) atmosphere. At sulfur vacancy densities of ~1.8×10<sup>14</sup> cm<sup>−2</sup>, I observe defect-mediated photoluminescence (PL) at ~1.72 eV (referred to as LX<sub>D</sub>) at room temperature. The LX<sub>D</sub> emission is attributed to excitons trapped at defect-induced in-gap states and is typically observed only at low temperatures (≤77 K). Time-resolved PL measurements reveal that the lifetime of defect-mediated LX<sub>D</sub> emission is longer than band edge excitons, both at room and low temperatures (~2.44 ns at 8 K). My results provide insight into how excitonic and defect-mediated PL emission in MoS<sub>2</sub> are influenced by sulfur vacancies at room and low temperatures. I also show that the LX<sub>D</sub> peak can be suppressed by annealing the defective MoS<sub>2</sub> in sulfur or selenium vapor, which indicates that it is possible to passivate the vacancies. At annealing temperatures ≥600 °C in selenium vapor, I observed the filling of sulfur vacancies by selenium. I extended the defect generation strategy to monolayer MoS<sub>2</sub> on various dielectric substrates to investigate the influence of dielectric substrates on defect-mediated emission. The LX<sub>D</sub> emission after annealing was observed on SiO<sub>2</sub> and hBN, but not on HfO<sub>2</sub>. When the MoS<sub>2</sub> is first annealed on SiO<sub>2</sub> and then transferred onto HfO<sub>2</sub>, the LX<sub>D</sub> emission is present on untreated HfO<sub>2</sub>, but not on annealed HfO<sub>2</sub>. These results suggest that surface states in dielectric substrates can influence the defect-mediated emission."]},{"key":"dc:format.checksum.md5","label":"Dc Format Checksum Md5","values":["87eda9de84448d1f82354d60eee3eb5f","b1d41e3267599a4dfb3d1c96803ffd4e"]},{"key":"dc:title","label":"Title","values":["Photoluminescence from Defects in Two-Dimensional Transition Metal Dichalcogenides"]}]}],"canonical_facts":{"dc:contributor.advisor":["Chhowalla, Manish"],"dc:creator":["Zhu, Yiru"],"dc:date.issued":["2024-03-30"],"dc:description.abstract":["Atomic defects in monolayer transition metal dichalcogenides (TMDs) such as chalcogen vacancies significantly affect their properties. In this thesis, I provide a reproducible and facile strategy to rationally induce chalcogen vacancies in monolayer MoS<sub>2</sub> by annealing at 600 °C in an argon/hydrogen (95 vol.%/5 vol.%) atmosphere. At sulfur vacancy densities of ~1.8×10<sup>14</sup> cm<sup>−2</sup>, I observe defect-mediated photoluminescence (PL) at ~1.72 eV (referred to as LX<sub>D</sub>) at room temperature. The LX<sub>D</sub> emission is attributed to excitons trapped at defect-induced in-gap states and is typically observed only at low temperatures (≤77 K). Time-resolved PL measurements reveal that the lifetime of defect-mediated LX<sub>D</sub> emission is longer than band edge excitons, both at room and low temperatures (~2.44 ns at 8 K). My results provide insight into how excitonic and defect-mediated PL emission in MoS<sub>2</sub> are influenced by sulfur vacancies at room and low temperatures. I also show that the LX<sub>D</sub> peak can be suppressed by annealing the defective MoS<sub>2</sub> in sulfur or selenium vapor, which indicates that it is possible to passivate the vacancies. At annealing temperatures ≥600 °C in selenium vapor, I observed the filling of sulfur vacancies by selenium. I extended the defect generation strategy to monolayer MoS<sub>2</sub> on various dielectric substrates to investigate the influence of dielectric substrates on defect-mediated emission. The LX<sub>D</sub> emission after annealing was observed on SiO<sub>2</sub> and hBN, but not on HfO<sub>2</sub>. When the MoS<sub>2</sub> is first annealed on SiO<sub>2</sub> and then transferred onto HfO<sub>2</sub>, the LX<sub>D</sub> emission is present on untreated HfO<sub>2</sub>, but not on annealed HfO<sub>2</sub>. These results suggest that surface states in dielectric substrates can influence the defect-mediated emission."],"dc:format.checksum.md5":["87eda9de84448d1f82354d60eee3eb5f","b1d41e3267599a4dfb3d1c96803ffd4e"],"dc:identifier.doi":["https://doi.org/10.17863/CAM.112297"],"dc:identifier.uri":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/eedc9bdc-919e-45c2-bc90-73b064695c52/download"],"dc:language":["eng"],"dc:publisher.institution":["University of Cambridge"],"dc:relation.isreferencedby.uri":["https://www.repository.cam.ac.uk/handle/1810/374109"],"dc:rights":["https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/22cbeee4-d36f-4553-add2-54fe7cab4326/download","https://www.rioxx.net/licenses/all-rights-reserved/"],"dc:subject":["Defect","Photoluminescence","Two-Dimensional Transition Metal Dichalcogenides"],"dc:title":["Photoluminescence from Defects in Two-Dimensional Transition Metal Dichalcogenides"],"dc:type":["Thesis"],"dc:type.qualificationlevel":["Doctoral"],"dc:type.qualificationname":["Doctor of Philosophy (PhD)"]},"updated_at":"2026-07-22T22:24:10Z"}