The self-assembly of magnesium aluminate spinel as a result of dewetting an
overlaid thin film of (chiefly) gold was investigated. Thin films of gold were
deposited on single-crystalline spinel substrates and were heat-treated to dewet gold film
which led to self-assembly of intricate structures consisting of faceted spherical particles
atop of frustums. The current work was conducted in continuation of previous studies
which reported formation of such intricate structures. The most recent studies had
evidently overruled a pure gold self-assembly scenario as was pointed out in preliminary
investigations. It was in fact proven that these structures consist of three distinct
parts: (i) a single or polycrystalline gold faceted sphere, (ii) quasi-phase interfacial
bilayer, and (iii) a crystalline MgAl2O4 necking structure spontaneously risen from
spinel substrate. In the current work, samples were produced through different film
deposition methods of sputter, thermal evaporation, and e-beam evaporation coating
which underwent thermal annealing to induce dewetting of gold film and subsequent
self-assembly of intricate structures. Several characterization methods such as electron
microscopy, X-ray energy dispersive spectroscopy, electron energy loss spectroscopy,
and atom probe tomography were utilized to survey the different features of the
intricate structures with focus on chemical analysis of the gold-spinel interface. The
results rejected the previous findings about formation of interface complexion at the
boundary of gold-spinel. It was found out that gold-spinel interface is in fact an
ordinary metal-oxide boundary with sharp atomic distinction and no inter-diffusion
or formation of interfacial complexion. It was further discovered that dewetting pure
gold thin films does not result in formation of spinel self-assembly and existence
of elemental impurities of copper (Cu) in the initial film is vital in development of
such structures. Finally, it was concluded that chemical composition of metallic overlayer
and the heat treatment parameters most fundamentally influence formation and
physical characteristics of those self-assembled structures. / Thesis / Master of Applied Science (MASc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/20283 |
| Date | January 2016 |
| Creators | Hosseini Vajargah, Pouya |
| Contributors | Preston, John S., Engineering Physics |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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