Thesis (MSc)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Trilayered transition metal dichalcogenides such as our sample (1T-TiSe2) have been studied
for many years as systems with strong electron-electron and electron-phonon correlations.
The main attraction to this family of compound is its potential to exhibit ground state phenomena
known as charge density waves whose detailed physical origin has been controversially
determined.
In this study, we have used an ultrafast femtosecond laser based on a pump-probe technique,
namely ultrafast electron diffraction, to investigate these exotic features associated with the
crystal. A pump laser pulse photo-excites the crystal from its ground state and the probe
pulse (ultrashort electron pulse) takes the snapshot of the evolution of the lattice generating
an electron diffraction pattern of the crystal. Hence the dynamical structural behaviour can
be observed in time with a subpicosecond temporal resolution. As a hexagonal close-packed
structure, its signature is expected to be seen in the diffraction pattern in both a steady-state
and electron time-resolved femtosecond electron diffraction.
In addition, simulations of electron diffractions pattern for room and low temperature structural
data via a software called Simulation and Analysis of Electron diffraction (SAED) have
been carried out. Clear signatures of charge density waves were seen at low temperature. / AFRIKAANSE OPSOMMING: Drie-laag oorgangsmetaal dikhalkogeniedes soos ons voorbeeld (1T-TiSe2), word reeds vir
baie jare bestudeer as sisteme met sterk elektron-elektron en elektron-fonon korrelasies. Die
hoof aantrekkingskrag van hierdie sisteme is die verskynsel van ladingdigtheidsgolwe in
die grondtoestand. Die fisiese oorsprong van hierdie ladingdigtheidsgolwe was bepaal te
midde van verskeie teenstrydighede.
In hierdie studie, maak ons gebruik van die ultravinnige femtosekonde laser gebaseerde
aktiveer-interogeer tegniek, genaamd ultravinnige elektron diffraksie (UED) om unicke eienskappe
wat met die kristal geassosieer is te bestudeer. In UED wek ’n ultravinnige laserpuls
(aktivering) die kristal op vanaf die grondtoestand waartydens n ultravinnige elektronpuls
(interogering) ’n foto neem van die evolusie van die elektron diffraksiepatroon wat deur
die kristalrooster gegenereer word. Hierdie wisselwerking van die interogerings elektronpuls
en die sisteem kan gevolglik teen verskeie vasgetelde tye toegelaat word. Dus kan die
dinamiese strukturele gedrag waargeneem word met ’n tydresolusie in die orde van die
elektronpuls (sub-pikosekondes). Siende dat die kristal ’n diggepakte-heksagonale struktuur
vorm, behoort die kenmerkende diffraksiepatroon daarvan waarneembaar te wees in
beide die bestendige diffraksie en femtosekonde elektron diffraksie tegnieke. In hierdie konteks
was duidelike tekens van ladingdigtheidsgolwe waargeneem.
Benewens was daar ook simulasies uitgevoer om die elektron diffraksiepatrone asook die
strukturele data by kamer en lae temperature vas te pen. Die sagteware wat hiervoor gebruik
word is genaamd Simulasie en Ontleding van Elektronendiffraksie (SAED) - Simulation and
Analysis of Electron Diffraction (SAED).
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/95990 |
| Date | 12 1900 |
| Creators | Suleiman, Aminat Oyiza |
| Contributors | Schwoerer, Heinrich P. H., Rohwer, Erich G., Stellenbosch University. Faculty of Science. Dept. of Physics. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | x, 66 p. : col. ill |
| Rights | Stellenbosch University |
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