Topological effects on the quantum properties of magnetic nanographene molecules
<p>Graphenoids are nanometer-sized flakes that share the same honeycomb framework of graphene. Novel chemistry has allowed the bottom-up synthesis of molecular graphenoids with atomic-like control of their structure. The electronic properties of these finite-sized graphene nanoislands actively...
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| Format: | Thesis |
| Language: | English |
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2021
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| _version_ | 1797107979818893312 |
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| author | Lombardi, F |
| author2 | Bogani, L |
| author_facet | Bogani, L Lombardi, F |
| author_sort | Lombardi, F |
| collection | OXFORD |
| description | <p>Graphenoids are nanometer-sized flakes that share the same honeycomb framework of graphene. Novel chemistry has allowed the bottom-up synthesis of molecular graphenoids with atomic-like control of their structure. The electronic properties of these finite-sized graphene nanoislands actively depend on the topology of their edges and their pi-electron network. Rational design of the topology in terms of size, conjugation, and presence of defects, has highlighted exotic magnetic properties that were predicted for quantum confined graphene structures. The presence of free spins, and the similarity to the graphene lattice would render them promising materials for all carbon-based spintronic and quantum devices. While a large number of structures are being synthetised by chemists everywhere, the quantum properties of these molecules remain widely unexplored.</p>
<p>In this work, we study the quantum properties of three categories of graphenoids: units with pentagonal defects, segments with zigzag edges, and ring-shaped molecules. Defects have been observed in graphene and are expected to play a key role in its optical, electronic, and magnetic properties. However, because most of the studies focused on the structural characterization, the implications of topological defects on the physicochemical properties of graphene remain poorly understood. Zigzag segments of carbon edges are a fundamental ingredient for most proposals of graphene nanostructures: they allow nontrivial topologies, where spin states can be used for quantum information processing and new communication pathways. Ring structures are intriguing for their aromatic and antiaromatic properties, and because they could show compelling quantum interference patterns.</p>
<p>In this thesis, we use EPR to study the quantum properties of ensemble of isolated molecules. We measure coherence times at different temperatures and in different hosting matrices in order to evaluate structural and environmental effects on the properties. The molecular graphenoids obtain large coherence times up to room temperature that we compare to metal-based molecular systems and inorganic systems. We use advanced decoupling sequences to increment the coherence of the systems. Finally, we suggest synthetic strategies to remove the main channels of decoherence. These results shine new light on the fundamental quantum properties of topological defects and edge states in nanographene structures.</p> |
| first_indexed | 2024-03-07T07:21:30Z |
| format | Thesis |
| id | oxford-uuid:8ebb1845-4166-428c-9ce1-4ef28e43f238 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-07T07:21:30Z |
| publishDate | 2021 |
| record_format | dspace |
| spelling | oxford-uuid:8ebb1845-4166-428c-9ce1-4ef28e43f2382022-10-18T14:43:55ZTopological effects on the quantum properties of magnetic nanographene moleculesThesishttp://purl.org/coar/resource_type/c_db06uuid:8ebb1845-4166-428c-9ce1-4ef28e43f238MaterialsPhysicsPhysical organic chemistryEnglishHyrax Deposit2021Lombardi, FBogani, LPorfyrakis, KSmith, J<p>Graphenoids are nanometer-sized flakes that share the same honeycomb framework of graphene. Novel chemistry has allowed the bottom-up synthesis of molecular graphenoids with atomic-like control of their structure. The electronic properties of these finite-sized graphene nanoislands actively depend on the topology of their edges and their pi-electron network. Rational design of the topology in terms of size, conjugation, and presence of defects, has highlighted exotic magnetic properties that were predicted for quantum confined graphene structures. The presence of free spins, and the similarity to the graphene lattice would render them promising materials for all carbon-based spintronic and quantum devices. While a large number of structures are being synthetised by chemists everywhere, the quantum properties of these molecules remain widely unexplored.</p> <p>In this work, we study the quantum properties of three categories of graphenoids: units with pentagonal defects, segments with zigzag edges, and ring-shaped molecules. Defects have been observed in graphene and are expected to play a key role in its optical, electronic, and magnetic properties. However, because most of the studies focused on the structural characterization, the implications of topological defects on the physicochemical properties of graphene remain poorly understood. Zigzag segments of carbon edges are a fundamental ingredient for most proposals of graphene nanostructures: they allow nontrivial topologies, where spin states can be used for quantum information processing and new communication pathways. Ring structures are intriguing for their aromatic and antiaromatic properties, and because they could show compelling quantum interference patterns.</p> <p>In this thesis, we use EPR to study the quantum properties of ensemble of isolated molecules. We measure coherence times at different temperatures and in different hosting matrices in order to evaluate structural and environmental effects on the properties. The molecular graphenoids obtain large coherence times up to room temperature that we compare to metal-based molecular systems and inorganic systems. We use advanced decoupling sequences to increment the coherence of the systems. Finally, we suggest synthetic strategies to remove the main channels of decoherence. These results shine new light on the fundamental quantum properties of topological defects and edge states in nanographene structures.</p> |
| spellingShingle | Materials Physics Physical organic chemistry Lombardi, F Topological effects on the quantum properties of magnetic nanographene molecules |
| title | Topological effects on the quantum properties of magnetic nanographene molecules |
| title_full | Topological effects on the quantum properties of magnetic nanographene molecules |
| title_fullStr | Topological effects on the quantum properties of magnetic nanographene molecules |
| title_full_unstemmed | Topological effects on the quantum properties of magnetic nanographene molecules |
| title_short | Topological effects on the quantum properties of magnetic nanographene molecules |
| title_sort | topological effects on the quantum properties of magnetic nanographene molecules |
| topic | Materials Physics Physical organic chemistry |
| work_keys_str_mv | AT lombardif topologicaleffectsonthequantumpropertiesofmagneticnanographenemolecules |