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Studying the structural phase transition of organic Cu(DCNQI)2 with ultrafast electron diffraction
Thesis (MSc)--Stellenbosch University, 2017
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| Format: | Thesis |
| Language: | en_ZA |
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Stellenbosch : Stellenbosch University
2017
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| _version_ | 1867614130995724288 |
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| access_status_str | Open Access |
| author | Payne, Nancy |
| author2 | Schwoerer, Heinrich |
| author_browse | Payne, Nancy Schwoerer, Heinrich |
| author_facet | Schwoerer, Heinrich Payne, Nancy |
| author_sort | Payne, Nancy |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (MSc)--Stellenbosch University, 2017 |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/102697 |
| institution | Stellenbosch University (South Africa) |
| language | en_ZA |
| last_indexed | 2026-06-10T12:47:09.638Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2017 |
| publishDateRange | 2017 |
| publishDateSort | 2017 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/102697 Studying the structural phase transition of organic Cu(DCNQI)2 with ultrafast electron diffraction Payne, Nancy Schwoerer, Heinrich Pflaum, Jens Stellenbosch University. Faculty of Science. Dept. of Physics. Molecular crystals Metal-insulator transitions Ultrafast Electron Diffraction (UED) Microtomes UCTD Crystal cutting Thesis (MSc)--Stellenbosch University, 2017 ENGLISH ABSTRACT : Organic molecular solids combine the richness of molecular and solid state physics. The structure and properties of organic solids can be modified to a great extent—for example, by utilising isotope effects, addition of side chains, and forming alloys—resulting in a highly tailorable group of materials with a wide range of anisotropic electrical, magnetic and optical properties. The radical-ion salts of copper-dicyanoquinonediimine [Cu(DCNQI)2] are an excellent example, exhibiting high one-dimensional electrical conductivities at room temperature and abrupt metal-insulator transitions upon cooling of more than six orders of magnitude. The reverse insulator-metal transition can be photoinduced using an ultrashort optical laser pulse, turning the crystal from a plastic-like insulator to a metal-like conductor within 10−12 seconds. This phase transition is associated with structural changes of the crystal lattice which can be observed using ultrafast electron diffraction (UED). This thesis describes the preparation of high quality 50 nm thick samples of monocrystalline Cu(Me,Br-DCNQI)2 by use of an ultramicrotome, the experimental setup and procedure, and the preliminary results of our UED experiments. The crystal lattice dynamics associated with the insulator-metal transition are studied in two regimes: 1) just below the phase transition temperature, and 2) far below the phase transition temperature. Time-resolved experiments allow direct observation of the structural changes at an atomic level and on the primary timescales of lattice dynamics. This sheds light on the driving forces behind the phase transition in different regimes, and the coupling strengths between electronic and vibrational degrees of freedom and their role in facilitating the insulator-metal transition. AFRIKAANSE OPSOMMING : Die struktuur en eienskappe van organiese vaste stowwe kan tot ’n groot mate verander word, wat hoogs ’n aanpasbare groep materiale met ’n wye verskeidenheid anitroop elektriese, magnetiese en optiese eienskappe moontlik maak. Die radikale ioon soute van Cu(DCNQI)2 is ’n uitstekende voorbeeld. Hierdie sout besit ho¨e een-dimensiA˜ le elektriese geleidingsvermo¨e by kamer temperatuur en die vermo¨e om skielik om te skakel van geleier na nie-geleibare materiaal tydens die verkoeling van ongeveer ses ordes van grote. Die teenoorgestelde verandering kan deur lig ge¨ıduseer word deur middel van ultra-vinnige laser pulse, wat die sout kristal verander van ’n plastiekagtige nie-geleier na ’n metaalagtige geleier binne 10−12 sekondes. Hierdie fase verandering word g¨eassosieer met strukturuele veranderinge van die kristalrooster wat waar geneem kan word deur ultra-vinnige elektron diffraksie (UED). Hierdie teseis beskryf die voorbereiding van ho¨e kwaliteit 50 nm dikte skyfies, van mono-laag Cu(Me,Br-DCNQI)2 deur gebruik te maak van ’n ultra-mikrotoom, die eksperimentele opstelling en prosedure, en die voorlopige resultate van ons UED eksperimente. Die kristalrooster dinamika g¨eassosieer met die nie-geleier-geleier verandering word bestudeer in twee kenmerkende toestande: een, net onder die fase veranderings temperatuure, en twee, vˆer onder die fase veranderings temperatuur. Eksperimente met tyd opgeloste resolusie stel ons in staat om die stukturuele veranderinge direk waar te neem op ’n atomiese vlak en op die primˆere tydskaal van die rooster dinamika. Dit stel ons ook in staat om meer te weet van die dryfkragte agter die fase verandering in die verskillende regimes, en die koppeling tussen elektroniese en vibrasionelegrade van vryheid en hul rol in die fasilitering van die nie-geleier-geleier verandering. 2017-11-10T10:09:13Z 2017-12-11T10:42:51Z 2017-11-10T10:09:13Z 2017-12-11T10:42:51Z 2017-12 Thesis http://hdl.handle.net/10019.1/102697 en_ZA Stellenbosch University v, 62, 3 pages : illustrations (chiefly colour) application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Molecular crystals Metal-insulator transitions Ultrafast Electron Diffraction (UED) Microtomes UCTD Crystal cutting Payne, Nancy Studying the structural phase transition of organic Cu(DCNQI)2 with ultrafast electron diffraction |
| title | Studying the structural phase transition of organic Cu(DCNQI)2 with ultrafast electron diffraction |
| title_full | Studying the structural phase transition of organic Cu(DCNQI)2 with ultrafast electron diffraction |
| title_fullStr | Studying the structural phase transition of organic Cu(DCNQI)2 with ultrafast electron diffraction |
| title_full_unstemmed | Studying the structural phase transition of organic Cu(DCNQI)2 with ultrafast electron diffraction |
| title_short | Studying the structural phase transition of organic Cu(DCNQI)2 with ultrafast electron diffraction |
| title_sort | studying the structural phase transition of organic cu dcnqi 2 with ultrafast electron diffraction |
| topic | Molecular crystals Metal-insulator transitions Ultrafast Electron Diffraction (UED) Microtomes UCTD Crystal cutting |
| url | http://hdl.handle.net/10019.1/102697 |
| work_keys_str_mv | AT paynenancy studyingthestructuralphasetransitionoforganiccudcnqi2withultrafastelectrondiffraction |