Ce travail de thèse est consacré au développement de mécanismes pratiques pour le guidage de chaleur dans des nanostructures de silicium de faible dimension. Les applications vont du domaine de la gestion thermique des circuits intégrés aux technologies et matériaux thermoélectriques émergents à base de Si, dans lesquels le guidage thermique de la chaleur peut jouer un rôle important. L'objectif est d'étudier expérimentalement la faisabilité d'une anisotropie de conductivité thermique (κ) dans le plan, induite artificiellement, des membranes nanostructurées en Si. En combinant la thermométrie Raman, la modélisation optique et la modélisation par éléments finis (FEM), il a été possible de mesurer le gradient thermique, la conductance de la membrane et de déterminer les conductivités thermiques effectives. Cette expérience confirme la possibilité d’induire artificiellement une anisotropie élevée de κ dans des membranes en silicium. Un modèle FEM paramétré conçu à dessein a démontré la mise en œuvre possible des effets anisotropes induits dans le domaine de la gestion thermique des circuits intégrés. / This thesis work is devoted to the development of practical mechanisms for the heat guiding in silicon low-dimensional nanostructures. The motivation comes from both the field of IC thermal management and emerging technology of Si-based thermoelectric devices, where directional heat guiding can play an important role. A series of micrometre-sized thermal characterisation platforms was designed and fabricated. The objective is to study experimentally the feasibility of artificially-induced in-plane anisotropy of effective thermal conductivity (κ) in Si nanopatterned membranes. By the combined use of micro Raman Thermometry, Rigorous Coupled Wave Analysis and Finite Element Modelling (FEM) it was possible to measure the thermal gradient, membrane conductance and determine effective thermal conductivities. This experiment confirms the possibility to induce artificially high anisotropy of κ in Si phononic membranes. Finally, purposefully designed parameterized FEM model demonstrated the possible implementation of the induced anisotropic effects in the area of IC thermal-management.

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Plasmonics have been used to enhance the interaction of light with metallic nanostructures and lanthanide-doped upconversion nanocrystals. This enhancement can be achieved by using specific structures, materials, and plasmonic resonators at the emission and absorption wavelengths of the particles. This dissertation is based on four projects, which are mainly about the interaction of light and matter in metallic nanostructures and the up-conversion of nanocrystals using plasmonic resonators. In metal-insulator-metal systems, the cavity's resonant length is determined by the plasmon wavevector and the phase of reflection from the end faces. In general, the resonance length is not a simple multiple of the half-wavelength due to the significant reflection phase. As a result, in order to have a better understanding of MIM cavity resonances, the reflection phase must be calculated correctly. In the first project, the reflection phase obtained by SPPs upon reflection off the slit end-faces is calculated analytically using a simple mode matching model for real metals showing both dispersion and loss. The technique is similar to previous works, with the exception that we use the unconjugated version of the orthogonality relation. The results show good agreement with the experimental data. By having a strong grasp of the SPP dispersion, this technique aids in the design of plasmonic devices for operation at a specific wavelength. Single-photon sources are optical sources capable of emitting a single photon. A single lanthanide ion within a plasmonic nano structure with a large emission enhancement is one technique to generate a single-photon source at 1550 nm, which is a low-loss band used in fibre optics. In the second project, plasmonic double nanohole resonators are fabricated using colloidal lithography. These structures have been used to enhance the emission from low-concentration erbium emitters. The results indicate that different levels of emissions exist based on the amount of Er contained inside the nanocrystals. These findings would be an excellent starting point for developing a single-photon source operating at a 1550 nm wavelength employing erbium. Because not only can it increase the emission rate from erbium emitters, but it also helps to find and isolate a single emitter, which gives a stable single photon source. Because the surface plasmon resonance is exponentially coupled to the surface, it exhibits excellent sensitivity to changes in the refractive index near the surface. This is the underlying principle of commercially available surface plasmon resonance biosensors. Due to the wide range of applications in water quality testing and biosensing, it is critical to developing highly sensitive sensors that are compatible with commercial sensors. In the third project, we develop a design for SRSP sensing using a rectangular stripe grating and a 10 nm thick gold film. The 10 nm gold layer is sufficiently thick to enable continuous films to be formed using standard deposition procedures. We demonstrate that by employing rigorous coupled-wave analysis, the surface sensitivity of these films to an adlayer is increased by 3.3 times in angle units and the resolution is increased by fourfold while working at the commercial SPR system wavelength of 760 nm. Before trapping a particle in double nanohole apertures, we must first locate the double nanohole on the sample (gold on glass with apertures) and compare the scanning electron microscopy images with the image on the camera in the optical setup using certain markers. In the fourth project, to make DNH aperture trapping easier, we provide a polarization and transmission dependency approach for localizing and orienting DNHs on a substrate. This method provides a time and cost-effective way to ease the experimental process. This technique may also be used to localize different aperture clusters and single holes. / Graduate

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Thesis (Ph.D.(Physics)) -- University of Limpopo, 2020 / We employ molecular dynamics simulations, using DL_POLY code, to study the structural behaviour of β-MnO2 cathode material during discharging through lithium-ion intercalation into the bulk, nanoparticle, nanorod, nanosheet, and nanoporous β-MnO2. It is shown that lithium-ions have an average coordination number of about 5.70 and prefer surface sites with high oxygen coordination. The average lattice parameter values at intercalation of 0.85 Li/Mn are found to be under 4% relative to the experimental values obtained at 0.92 Li/Mn. Moreover, all the lithiated β-MnO2 structures did not collapse at 0.85 Li/Mn as observed in the β-MnO2 mesoporous in experimental work. As lithium is limited, sodium is a good alternative charge carrier in lithium-ion batteries. As a result, we have also performed studies on sodium intercalation into bulk, nanoparticle, nanorod, nanosheet and nanoporous β-MnO2. The microstructures and radial distribution functions show that the β-MnO2 structures could be intercalated up to 0.24 Na/Mn without any obvious structural degradation. Beyond this sodium concentration, the microstructure collapses and become amorphous thus predicting a potentially lower capacity for Na-MnO2-β batteries. Also, as the voltage is an important factor in the energy density of lithium-ion batteries, we have studied the trends in the average intercalation potentials in relation to the various nano architectures. The trend, in increasing value of average intercalation potentials, were found to be bulk structure, nanorod, nanosheet, nanoporous and nanoparticle. This suggests that nanostructuring can enhance cell voltage. Mechanical properties studies on the pure and lithiated bulk and nanorod β-MnO2 were also performed through uniaxial compressive and tensile strain application. The results show that under compressive strain the bulk structure and nanorod mitigate stress through the contraction and collapse of the inherent tunnel structures, known to cause electrochemical inactivity, and also through the shifting of the MnO6 octahedral planes. The collapsing of tunnels was found to occur more on the bulk structure and less on the nanorod, while the MnO6 octahedral plane shifts were found to occur more on the nanorod and less on the bulk structure. Unoccupied 1x2 or conjoined 1x2 were found to result in structural collapse irrespective of the host nanoarchitecture. The X-ray diffraction pattern (v) plots suggest that lithium intercalation and compressive stress application have a similar impact on the underlying structure of the various nanostructures. The microstructure analysis for bulk β-MnO2 under tensile strain reveals that fracture occurred in the brookite region and along the dislocation/stacking fault. The nanorod β-MnO2 mitigated stress through a rutile-to-brookite phase transition which occurred in the unstrained Li0.73MnO2-β and under tensile strain in LixMnO2-β for x = 0.00, 0.03, 0.12, and 0.24. In both the bulk and nanorod β-MnO2 the brookite phase was succeeded by structural breakdown leading to fracture and served as an indicator for imminent structural failure upon more tensile strain application. / National Research Foundation (NRF)

This dissertation aims to both deepen and broaden our understanding of copolymers with pendent benzophenone (BP) in relation to both established applications and novel directions in materials science. Photo-reaction of these BP copolymers is explored in attempts to achieve three distinct goals: (1) robust and efficiently photo-crosslinkable solid polymer films, (2) photo-reacted polymer blends with disordered bicontinuous nanostructures, and (3) photo-patterned hydrogel materials with environmental UV stability. We begin by investigating the fundamental gelation behavior of solid polymer films, finding BP copolymers to be particularly effective crosslinkable materials. Gelation efficiency can be tuned according to comonomer chemistry, as BP hydrogen abstraction on the main polymer chain increases chain scission, reducing crosslinking efficiency. This knowledge is then applied in Chapter 3, wherein we discuss two potential methods for preparing nanostructured polymer blends from these copolymers, namely spinodal decomposition of a photo-crosslinked polymer blend and solution-state photografting to create interfacially active species. While each technique shows promise, the ultimate goal of a disordered bicontinuous morphology will require further tuning of materials systems and protocols. Finally, chemical deactivation of BP photo-crosslinker in copolymers for use as photo-patternable and environmentally stable hydrogel materials is investigated. Reduction of BP by sodium borohydride proves a feasible route toward deactivating residual photo-crosslinker in patterned hydrogel films. These results confirm the utility of copolymers with pendent benzophenone photo-crosslinkers as useful tools for complex material systems.

Le présent mémoire porte sur le développement d'une approche générale en vue de la préparation et de l'utilisation de canaux ioniques artificiels pour la réalisation de biosenseurs. Cependant, l'utilisation de ces nanostructures peptidiques dans des dispositifs pratiques nécessite des modifications. Nous rapportons ici la modification sélective des extrémités de nos canaux ioniques par des groupements permettant leur attachement à une surface électro-attractive et la reconnaissance d'analytes biologiques. La première partie consiste en une description générale des biosenseurs, ainsi qu'en une revue des principaux modèles proposés dans la littérature de protéines «canal» d'origine naturelle ou artificielle comme composantes des ces outils de biodétection. Le second chapitre présente notre approche générale, les molécules cibles utilisées pour faire l'ingénierie de notre système modèle, de même que les méthodes de synthèse employées pour l'élaboration et la modification sélective des extrémités de nos nanostructures peptidiques. La troisième partie est consacrée à l'attachement du peptide à des surfaces d'or. La quatrième partie présente les différentes techniques utilisées pour la caractérisation des canaux ioniques et des nanoparticules d'or.

The main objectives of the research presented in this thesis were to understand mechanistic aspects of the photochemistry of ferritin (Ftn) and bioconjugates that consisted of Ftn linked to gold nanoparticles (AuNPs). The photochemistry investigated in this thesis repurposed Ftn from its role in biological systems as an iron-sequestration protein to potential applications in photocatalysis and nanobiomedicine. The first phase of the thesis research developed a mechanistic understanding of the underlying mechanisms involved in the photochemistry of Ftn with relevance to photocatalysis. In particular, research was designed to determine whether the light-induced bandgap excitation of the semiconductor core of horse-spleen ferritin (HSFtn) resulted in electron transfer from the inorganic core to aqueous redox active reactant via electron transport through the 2 nm thick shell of HSFtn. To investigate this mechanistic pathway, 4-5 nm copper (hydr)oxide nanoparticles were mineralized within the internal volume of HSFtn (CuFtn). It was shown that, unlike the native iron oxyhydroxide-bearing (Ferrihydrite; Fh) Ftn, the visible light photoexcitation of the inorganic core of CuFtn (measured optical bandgap to be 3.65 eV) did not exhibit any release of redox-active metal cation from the HSFtn cage into solution. By photoexciting CuFtn in the presence of aqueous chromate (Cr(VI)) it was shown that the Cr(VI) underwent reduction to Cr(III) in solution. The research strategy eliminated the possibility that metal cations escaping from the HSFtn during photoexcitation could be responsible for Cr(VI) reduction. Hence, the research showed for the first time that electrons resulting from a photoexcited metal oxide core of Ftn could transfer through the protein shell to reduce an aqueous redox active reactant. The research also investigated the wavelength-dependent photochemistry of CuFtn to show that bandgap excitation was indeed responsible for the electrons that transfer across the protein shell. In a second project, the research investigated the bioconjugation of anisotropic AuNPs—gold nanorods (AuNRs) and gold nanostars (AuNSs)—to human H-type ferritin (HFtn). After attaching the AuNRs or AuNSs to HFtn, it was shown that the near-infrared (NIR) radiation excitation of the localized surface plasmon resonance (LSPR) of the AuNR or AuNS conjugated to HFtn led to the activation of the Fh core of the protein. This NIR photochemistry (λ = 850 nm light) resulted in the release of Fe(II) from the Ftn and also led to the reduction of Cr(VI) when it was present in the aqueous phase. The novel synthetic protocols to synthesize the bioconjugates focused on attaching the AuNRs and AuNSs to the solvent-exposed cysteines (Cys) on HFtn. The research also developed techniques for the removal of colloidal stabilizing surfactants, such as cetyltrimethyl ammonium bromide (CTAB), and TritonX-100 (TX-100), from anisotropic AuNPs (AuNR/AuNS) before their attachment to HFtn. The removal of the surfactant was not only important for attachment to the HFtn, but it also removed a cytotoxic species so that the bioconjugates could be used in research that had applications to biomedicine. Research also investigated synthetic strategies to form bioconjugates that consisted of spherical gold nanoparticles (AuNSps) attached to HSFtn. In contrast to HFtn, HSFtn contains a few solvent exposed Cys groups. Hence, a challenge that was overcome in this research was to populate the outer surface of HSFtn with thiol groups (-SH) so that AuNSps could be attached. To meet this challenge, the surface primary amine-containing amino acids (Lysine) in HSFtn were modified to active Cys using N-succinimidyl S-acetylthioacetate (SATA). After this chemical modification of HSFtn, it was shown that a relatively high density of AuNSps could be attached to HSFtn. This SATA-modified HSFtn bioconjugate system (AuNSp-HSFtn) exhibited the release of Fe(II) at wavelengths of light where λ > 475 nm. In the absence of AuNSp, HSFtn released Fe(II) during exposure to light at wavelengths of light where λ < 475 nm. The activation of the bandgap at longer wavelengths of light (λ > 475 nm) was due to the excitation of the 532 nm plasmon resonance of AuNSp and the presumed transfer of hot electrons to the inner Fh core of HSFtn. A final project investigated the use of the AuNR-HFtn bioconjugates as a photodynamic strategy utilizing NIR to suppress the growth of cancer cells with the expectation that this process will occur through the mechanism of ferroptosis. We carried out experiments that exposed prostate cancer cells (PC3) to AuNR-HFtn, and during NIR irradiation, they showed the ability to limit the growth of the cells compared to experiments where the cells were exposed to just HFtn or AuNRs. The results suggested that Fe(II) released from the HFtn led to cancer cell death through a process that might be ferroptosis. Future studies will need to investigate this possibility and whether the bioconjugates developed in this thesis will offer a novel therapeutic strategy for cancer/tumor suppression. / Chemistry

Silver-gold nanocages have attracted considerable research interest recently due to their excellent performance in the fields of biomedicine and photocatalysis. These applications oftentimes manipulate at elevated temperatures and therefore impose demands on the thermal stability of the cage structures. To better understand this subject, in this work, we systematically evaluated the thermal stability of two nanocages with different wall thicknesses of 3.8 nm and 13 nm, both in the solution-phase (diethylene glycol) and solid-phase (in-situ STEM). The results revealed that the nanocages with thicker walls exhibited better thermal stabilities in both phases. By monitoring and analyzing the morphology changes of the nanocages, we determined that the nanocages with thin and thick walls undergo deformation processes differently. Nevertheless, they both deformed into more thermodynamically stable structures eventually. The plasmonic properties of the nanocages were also examined.