The research performed aims to develop a deeper understanding and prediction of behaviour of complex chemical and physical systems using density functional theory
(DFT) modelling complemented by experimental techniques. We focus on phenomena
relevant to practical applications of semiconducting materials.
Semiconductor nanowires, produced by the vapor-liquid-solid method are being considered for applications in photo sensors, field effect transistors, light emitting diodes
(LEDs) and energy harvesting devices. In particular, semiconductor nanowire based
photovoltaic devices show potential for lower cost due to less material utilization and
greater energy conversion efficiency arising from enhanced photovoltage or photocurrent due to hot carrier or multiexciton phenomena enhanced light absorption, compared
to conventional thin film devices. Further, freedom from lattice matching requirements
due to strain accommodation at the nanowire surfaces enable compatibility with a wide
variety of substrates including Silicon. Thus understanding and improving the optoelectronic properties of nanowires is of great interest. In the first paper, we study the
effect of planar defects on optoelectronic properties of nanowire based semiconductor
devices. Specifically, we were interested in investing the origin of various features observed in the photoluminisence (PL) spectrum of GaP nanowire using density functional
modelling, which are not well understood.
In the second paper, we work to model bonding characteristics during a chemical
synthesis. We focus on the synthesis of nanoparticles for supercapacitor application. In
the past decade, comprehensive research has been emphasized on manganese oxides for electrochemical supercapacitor (ECS) applications. Mn3O4 has gained significant interest due to its compatibility with capping agents and the unique spinel structure allows
for potential modifications with other cations. Many metal oxide synthesis techniques
are based on aqueous processing. The synthesized particles are usually dried and redispersed in organic solvents to incorporate water-insoluble additives such as binders to
fabricate films and devices. However, during the drying step nano-structures are highly
susceptible to agglomeration, which can be attributed to the condensation reactions occurring between particles and reduction in surface energy. Poor electrolyte access due
to agglomeration and low intrinsic conductivity of Mn3O4 are detrimental to the performance of Mn
3O4 electrode especially at high active mass loadings. Numerous attempts
have focused on controlling size and morphology of Mn3O4 nanostructures using capping agents, which have strong adhesion to particles surface to inhibit agglomeration.
Catechol containing molecules have been used for dispersion of metallic nanoparticles
and fabrication of composite thin films, resulted in narrow size distribution of nanoparticles and strong adhesion to substrates. Despite the experimental results showing good
adsorption of catechol group to metal atoms, the mechanism is unclear since it is highly
influenced by synthesis parameters. We use Infrared spectroscopy in conjugation with
density functional modelling to understand the binding mechanism of 3,4 dihydroxy
benzaldehyde onto Mn3O4 surface. / Thesis / Master of Applied Science (MASc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/24893 |
| Date | January 2019 |
| Creators | Gupta, Divyanshu |
| Contributors | Rubel, Oleg, Materials Science and Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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