Structural dynamics in DCNQI salts and transition metal dichalcogenides studied by electron diffraction simulation

Olaoye, Olufemi Opeyemi (2015-12)

Thesis (PhD)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: An in-depth understanding of the working principles of and phenomena governing strongly correlated condensed matter materials has paved way for technological advancement in electronics in the recent decades. The discovery and characterisation of many functional materials ranging from superconductors to insulators are hinged on the progressive understanding of the driving mechanisms behind macroscopic properties like superconductivity and magneto-resistance. Stemming from the nature of structural transitions in highly correlated solids and the corresponding abrupt changes in their conductivity or resistivity, various degrees of order parameters have been investigated using different experimental techniques such as angle resolved photoelectron spectroscopy, optical reflectivity measurements, X-ray crystallography and pump-probe spectroscopy, among others. One major technique that could be used to gain further understanding of these correlated systems is electron diffraction analysis. In this dissertation, we demonstrate a qualitative working relationship between electron diffraction simulation and the corresponding X-ray and electron diffraction experiments. These structural analysis techniques are used to investigate metal-insulator structural transitions in strong electron-lattice correlated charge density wave compounds of the radical anion organic molecular crystals of Cu-DCNQI and two members of transition metal dichalcogenides, namely, 4Hb-TaSe2 and 1T-TiSe2 single crystals. This study contributes to the observation and dynamics of charge density waves on the atomic spatial and temporal resolutions. A systematic analysis of electron diffraction patterns obtainable from femtosecond electron diffraction experiments opens up new perspectives on the interpretation of structural evolution in solids.

AFRIKAANSE OPSOMMING: ’n In-diepte begrip van die werkingsbeginsels en verskynsels van sterk gekorreleerde gekondenseerde materie het die pad oopgemaak vir tegnologiese deurbrake in elektronika in die afgelope dekades. Die ontdekking en karakterisering van vele funksionele materiale, vanaf super geleiers tot isolators, is afhanklik van ’n voortdurende dryf om die meganismes agter hierdie makroskopiese eienskappe van materiaal te verstaan. Vanuit die natuur van strukturele transisies in hoogs gekorreleerde vastestowwe en die ooreenstemmende skielike verandering in hulle geleidings vermoë en weerstand, kan verskeie vryheidsgrade en orde parameters ondersoek word deur gebruik te maak van verskillende eksperimentele tegnieke soos hoek opgelosde foto-elektron spektroskopie, optiese weerkaatsings metings, X-straal kristallografie en aktiveer interrogeer spektroskopie onder andere. Een van die hoof tegnieke wat gebruik kan word om hierdie hoogs gekorreleerde sisteme te ondersoek is elektron diffraksie analise. In hierdie skripsie demonstreer ons ’n kwalitatiewe verhouding tussen ’n elekron diffraksie simulasie en die ooreenstemmende X-straal en elektron diffraksie eksperimente. Hierdie struktuur ontledings tegnieke word gebruik om metaal-tot-insulator struktuur oorgange in sterk elektronrooster gekorreleerde ladings digtheid golf stowwe van radikale anioon organiese molekulere kristalle van Cu-DCNQI en twee lede van die oorgang metale 4Hb-TaSe2 en 1T-TiSe2 se kristalle te ondersoek. Hierdie studie dra by tot die waarneming en dinamika van ladings digtheid golwe op ruimtelike en tydelike atoomskaal resolusies. ’n Sistematiese analise van elektron diffraksie patrone verkrygbaar van femtosekonde elektron diffraksie eksperimente stel ons in staat daartoe om nuwe interpretasies van die strukturele veranderings in vastestowwe te maak.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98009
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