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<p>Cellulose is the most abundant biopolymer on earth, derived from a variety of living species. An attractive source to obtain cellulose is from agriculture wastes, for instance, potato peel. Potato is one of the most important crops for human consumption, but in recent years its consumption in raw form has decreased, especially in developed countries. Many potatoes are processed into value-added products to meet the demand of fast food industries. So far the main use of the potato peel is sold for animal feed at very low prices. In addition, there are significant quantities of rotten potatoes generated during the years of heavy rain fall, which represent a substantial financial loss to the farmers unless an alternative industrial use can be found for the biomass. Therefore, extracting cellulose from potato peel and processing them into a higher valuable product is not only an environment-friendly solution to the disposal issues but also creates a non-food based economy for potatoes.</p> <p>Cellulose nanocrystals (CN) are a promising material and have been widely studied over the past two decades. This material is interesting as nanofiller due to its nanoscale dimensions, high specific area, and highly rigid crystalline structure. In comparison to mineral or metal nanofillers that are industrially available, cellulose nanocrystals are prepared from renewable feedstocks, feature low density, are relatively low cost, and remain biodegradable.</p> <p>This study investigated the effectiveness of cellulose nanocrystal derived from potato peel waste to improve the mechanical and barrier properties of a polymer. The nanocrystals were chemically derived from the cellulosic material in potato peel waste by alkali treatment and subsequently acid hydrolysis with sulfuric acid. Infrared spectroscopy indicated sufficient removal of lignin and hemicellulose from the raw potato peel biomass whereas X-ray diffraction confirmed that the prepared nanocrystals maintained their original crystalline lattice structure as the extracted cellulose, with a crystallinity of 85%. TEM images showed that the average fiber length of the nanocrystals was 410 nm with a diameter of 10 nm (aspect ratio of 41). Cellulose nanocrystal-filled polyvinyl alcohol (PVA) and thermoplastic starch (TPS) were prepared by solution casting method to maintain uniform dispersion of the 1-2% (w/w) fibers. An increase of 19% and 38% (starch composite) and 32% and 54% (PVA composite) in Young’s modulus was observed for the 1% and 2% CN-reinforced composites, respectively. Water vapor transmission rate measurements showed a reduction of water permeability for the PVA nanocomposite, whereas no effect was observed for starch nanocomposite.</p> / Master of Applied Science (MASc)

<p> The need for higher bandwidth and people's desire to be "always connected" have spurred a new era of silicon photonics. The traditional integrated electrical transmission lines have been an obstacle preventing ultra high speed communication. Using monolithic chips of integrated optoelectronic circuits from silicon provides an economic way to realize Tetra Byte/Second bandwidth in a variety of areas such as "fiber to the home" and the buses linking chips inside computer.</p> <p> The heart of such optoelectronics-silicon laser-is still in pursuit. One of the most promising approaches is the erbium doped silicon nanocrystals embedded in silica system. External photon or hot electrons injection excites the silicon nanocrystals, which then transfer their energies to nearby erbium ions to emit light at 1.55 μm wavelength range.</p> <p> In this thesis, we investigate the effects of cavity and electric field on energy transfer from Si nanocrystals (Si-nc's) to Er ions, and simulate material gain in such systems. Our results show that microcavity can enhance the Forster energy transfer and material gain, reducing the requirements for Si-nc pumping. The electric field will hinder the radiation decay of Si-nc, but we have to further explore the tunneling mechanism before concluding the overall effect of electric field. Some future work needs to be done, which will shine some light on the design of the silicon laser.</p> / Thesis / Master of Applied Science (MASc)

Polymeric bone scaffolds are a promising tissue engineering approach for the repair of critical-size bone defects. Porous three-dimensional (3D) scaffolds play an essential role as templates to guide new tissue formation. However, there are critical challenges arising from the poor mechanical properties and low bioactivity of bioresorbable polymers, such as poly(epsilon-caprolactone) (PCL) in bone tissue engineering applications. This research investigates the potential use of cellulose nanocrystals (CNCs) as multi-functional additives that enhance the mechanical properties and increase the biomineralization rate of PCL. To this end, an in vitro biomineralization study of both sulfuric acid hydrolyzed-CNCs (SH-CNCs) and surface oxidized-CNCs (SO-CNCs) has been performed in simulated body fluid in order to evaluate the bioactivity of the surface functional groups, sulfate and carboxyl groups, respectively. PCL nanocomposites were prepared with different SO-CNC contents and the chemical/physical properties of the nanocomposites were analyzed. 3D porous scaffolds with fully interconnected pores and well-controlled pore sizes were fabricated from the PCL nanocomposites with a 3D printer. The mechanical stability of the scaffolds were studied using creep test under dry and submersion conditions. Lastly, the biocompatibility of CNCs and 3D printed porous scaffolds were assessed in vitro. The carboxyl groups on the surface of SO-CNCs provided a significantly improved calcium ion binding ability which could play an important role in the biomineralization (bioactivity) by induction of mineral formation for bone tissue engineering applications. In addition, the mechanical properties of porous PCL nanocomposite scaffolds were pronouncedly reinforced by incorporation of SO-CNCs. Both the compressive modulus and creep resistance of the PCL scaffolds were enhanced either in dry or in submersion conditions at 37 degrees Celsius. Lastly, the biocompatibility study demonstrated that both the CNCs and material fabrication processes (e.g., PCL nanocomposites and 3D printing) were not toxic to the preosteoblasts (MC3T3 cells). Also, the SO-CNCs showed a positive effect on biomineralization of PCL scaffolds (i.e., accelerated calcium or mineral deposits on the surface of the scaffolds) during in vitro study. Overall, the SO-CNCs could play a critical role in the development of scaffold materials as a potential candidate for reinforcing nanofillers in bone tissue engineering applications. / Ph. D.

Tandem solar cells are potentially much more efficient than the silicon solar cells that currently dominate the market but require materials with different bandgaps. This thesis presents work on silicon nanocrystals (Si-NC) embedded in silicon carbide (SiC), which are expected to have a higher bandgap than bulk Si due to quantum confinement, with a view to using them in the top cell of a tandem cell. The strong photoluminescence (PL) of precursor films used to prepare Si-NC in SiC (Si-NC/SiC) was markedly reduced upon Si-NC formation due to simultaneous out-diffusion of hydrogen that passivated dangling bonds. This cannot be reversed by hydrogenation and leads to weak PL that is due to, and limited by, non-paramagnetic defects, with an estimated quantum yield of ≤5×10^-7. Optical interference was identified as a substantial artefact and a method proposed to account for this. Majority carrier transport was found to be Ohmic at all temperatures for a wide range of samples. Hydrogenation decreases dangling bond density and increases conductivity up to 1000 times. The temperature-dependence of conductivity is best described by a combination of extended-state and variable-range hopping transport where the former takes place in the Si nanoclusters. Furthermore, n-type background doping by nitrogen and/or oxygen was identified. In the course of developing processing steps for Si-NC-based tandem cells, a capping layer was developed to prevent oxidation of Si-NC/SiC, and diffusion of boron and phosphorus in nanocrystalline SiC was found to occur via grain boundaries with an activation energy of 5.3±0.4 eV and 4.4±0.7 eV, respectively. Tandem cells with a Si-NC/SiC top cell and bulk Si bottom cell were prepared that exhibited open-circuit voltages V_oc of 900 mV and short-circuit current densities of 0.85 mAcm^-2. Performance was limited by photocurrent collection in the top cell; however, the V_oc obtained demonstrates tandem cell functionality.

L'objectif de ce travail de thèse est de participer à l'élaboration de nanocristaux (NCs) de germanium et de mettre en évidence certaines propriétés de structures Si(n)/SiO2 contenant ces NCs non recouverts sur leur surface par l'utilisation de la technique nano-EBIC (courant induit par bombardement électronique et collecté par un nano-contact). La particularité de cette technique basée le même principe que l'EBIC classique est l'utilisation d'une pointe AFM conductrice à la place de l'électrode standard. Nous avons particulièrement ciblé le comportement d'un NC (ou d'un nombre très réduit de NCs) à piéger et émettre des porteurs de charge suite à un bombardement électronique non continu. La structure contenant les NCs peut être polarisée sous une tension nulle (alignement des niveaux de Fermi) ou sous une tension faible. Suite à cette procédure, des durées de charge ont été mesurées et les valeurs se trouvent dépendre de la taille moyenne des NCs. En effet, le processus de charge est plus long dans un NC de petite taille du fait de sa faible efficacité de stockage. D'un autre côté, le courant collecté présente une valeur de saturation plus élevée dans le cas des petits NCs. Ces deux effets (durée élevée et courant de saturation élevé dans les petits NCs) ont été expliqués par l'abaissement de la barrière d'énergie au niveau du contact pointe/NC qui résulte de l'élargissement du gap du NC et de l'augmentation du champ électrique dans la couche d'oxyde et dans la zone de désertion du substrat de silicium sous une tension de polarisation donnée. Enfin, la procédure, par son originalité, a aussi permis d'accéder à la résistivité électrique de la couche d'oxyde mince (5 nm). / The objective of this work is to contribute to the production of germanium nanocrystals (NCs) and to highlight some electronic properties of Si(n)/SiO2 structures containing those uncovered NCs on top thanks to the nano-EBIC technique (electron beam induced current collected by a nano-contact). The distinctive feature of this technique based on classic EBIC is the use of an AFM conducting probe instead of the standard electrode. Our study focuses on the capability of a single NC (or a few number of NCs) to trap and to release charge carriers as a result of a non-continuous electronic irradiation. The structure containing NCs can be connected to the ground (ensuring the Fermi levels alignment) or polarized under a low voltage. With this procedure, carriers charging times had been measured and their values depend on the mean diameter of the NCs. Indeed, the charging process takes more time in small NCs due to their weak storage efficiency. Nonetheless, the collected current reaches a higher saturation value in small NCs. Both of these effects (large charging time and high saturation current for small NCs) are explained by the lowering of the energy barrier at the AFM-tip/NCs contact, which results from the widening band-gap of NCs and the increase of the electric field across the oxide and in the Si depletion zone at a given bias voltage for small NCs. At last, this novel procedure allows measuring the electric resistivity of the 5 nanometers thin oxide.

<p>Cellulose nanocrystals (CNCs) and its composite coatings may impart many benefits in packaging, electronic, optical, etc. applications; however, large-scale coating production is a major engineering challenge. To fill this knowledge gap, a potential large-scale manufacturing technique, roll-to-roll reverse gravure processing, has been described in this work for the manufacture of CNC and CNC-poly(vinyl alcohol) (PVA) coatings on a flexible polymer substrate. Various processing parameters which control the coating structure and properties were examined. The most important parameters in controlling liquid transfers were gravure roll, gravure speed, substrate speed, and ink viscosity. After successful fabrication, coating adhesion was investigated with a crosshatch adhesion test. The surface roughness and morphology of the coating samples were characterized by atomic force microscopy and optical profilometer. The Hermans order parameter (S) and coating transparency were measured by UV–Vis spectroscopy. The effect of viscosity on CNC alignment was explained by the variation of shear rate, which was controlled by the micro-gravure rotation. Finally, the CNC alignment effect was investigated for gas barrier and thermal management applications.</p> <p>In packaging applications, cellulose nanomaterials may impart enhanced gas barrier performance due to their high crystallinity and polarity. In this work, low to superior gas barrier pristine nanocellulose films were produced using a shear-coating technique to obtain a range of anisotropic films. Induction of anisotropy in a nanocellulose film can control the overall free volume of the system which effectively controls the gas diffusion path and hence, controlled anisotropy results in tunable barrier properties. The highest anisotropy materials showed a maximum of 900-fold oxygen barrier improvement compared to the isotropic arrangement of nanocellulose film. The Bharadwaj model of nanocomposite permeability was modified for pure nanoparticles, and the CNC data were fitted with good agreement. Overall, the oxygen barrier performance of anisotropic nanocellulose films was 97 and 27 times better than traditional barrier materials such as biaxially oriented poly(ethylene terephthalate) (BoPET) and ethylene vinyl alcohol copolymer (EVOH), respectively, and thus could be utilized for oxygen-sensitive packaging applications. </p> The in-plane thermal conductivity of CNC - PVA composite films containing different PVA molecular weights, CNC loadings and varying order parameters (S) were investigated for potential application in thermal management of flexible electronics. Isotropic CNC - PVA bulk films with 10-50 wt% PVA solid loading showed significant improvement in thermal conductivity compared to either one component system (PVA or CNC). Furthermore, anisotropic composite films exhibited in-plane thermal conductivity as high as ~ 3.45 W m-1 K-1 in the chain direction, which is higher than most polymeric materials used as substrates for flexible electronics. Such an improvement can be attributed to the inclusion of PVA as well as to a high degree of CNC orientation. The theoretical model was used to study the effect of CNC arrangement (both isotropic and anisotropic configurations) and interfacial thermal resistance on the in-plane thermal conductivity of the CNC-PVA composite films. To demonstrate an application for flexible electronics, thermal images of a concentrated heat source on both neat PVA and CNC-PVA composite films were taken that showed the temperature of the resulting hot spot was lower for the composite films at the same power dissipation.

Cette thèse est consacrée à l'étude des propriétés électroniques de nanostructures par microscopie à force atomique (AFM) en ultra-vide. La première partie de ce travail a consisté à caractériser localement des nanofils de silicium par technique d'AFM conducteur. Les expériences de conduction locale sur nanofils inclinés montrent que la conduction des nanofils intrinsèques est dominée par un transport en surface, associé à la présence de résidus catalytiques métalliques. Cette conduction peut être partiellement supprimée (par désoxydation) ou exaltée (par traitement thermique). Une caractérisation qualitative du dopage de ces nanostructures est présentée, par technique de microscopie à sonde de Kelvin. La deuxième partie de la thèse a consisté à étudier le transfert de charges et les propriétés d'ionisation de nanocristaux de silicium passivés hydrogène, dopés de type n (P) ou p (B), fabriqués par dépôt plasma. L'analyse des images de microscopie à sonde de Kelvin en modulation d'amplitude sous ultra-vide montre que le transfert de charges des nanocristaux de silicium correspond à un mécanisme de compensation d'énergie, exalté par le confinement quantique. Les résultats expérimentaux fournissent une mesure de l'ouverture de la bande interdite des nanocristaux due au confinement quantique, dans la gamme 2-50 nm, en accord quantitatif avec des calculs en liaisons fortes. Ils mettent en avant la possibilité d'utiliser des nanocristaux dopés comme sources d'électrons pour réaliser un dopage sélectif contrôlé de nanostructures ou nanodispositifs, avec des densités dans les gammes de 2×10^11-10^14 cm^-2 ou 8×10^5-2×10^7 cm^-1.

X-ray crystallography has been around for 100 years and remains the preferred technique for solving molecular structures today. However, its reliance on the production of sufficiently large crystals is limiting, considering that crystallization cannot be achieved for a vast range of biomolecules. A promising way of circumventing this problem is the method of serial femtosecond imaging of single-molecules or nanocrystals utilizing an X-ray free-electron laser. In such an approach, X-ray pulses brief enough to outrun radiation damage and intense enough to provide usable diffraction signals are employed. This way accurate snapshots can be collected one at a time, despite the sample molecule exploding immediately following the pulse due to extreme ionization. But as opposed to in conventional crystallography, the spatial orientation of the molecule at the time of X-ray exposure is generally unknown. Consequentially, assembling the snapshots to form a three-dimensional representation of the structure of interest is cumbersome, and normally tackled using algorithms to analyze the diffraction patterns. Here we explore the idea that the explosion data can provide useful insights regarding the orientation of ubiquitin, a eukaryotic regulatory protein. Through two series of molecular dynamics simulations totaling 588 unique explosions, we found that a majority of the carbon atoms prevalent in ubiquitin are directionally limited in their respective escape paths. As such we conclude it to be theoretically possible to orient a sample with known structure based on its explosion pattern. Working with an unknown sample, we suggest these discoveries could be applicable in tandem with X-ray diffraction data to optimize image assembly.

In this study, silicon nanocrystals (NC) were synthesized in silicon dioxide matrix by ion implantation followed by high temperature annealing. Annealing temperature and duration were varied to study their effect on the nanocrystal formation and optical properties. Implantation of silicon ions was performed with different energy and dose depending on the oxide thickness on the silicon substrate. Before device fabrication, photoluminescence (PL) measurement was performed for each sample. From PL measurement it was observed that, PL emission depends on nanocrystal size determined by the parameters of implantation and annealing process. The peak position of PL emission was found to shifts toward higher wavelength when the dose of implanted Si increased. Two PL emission bands were observed in most cases. PL emission around 800 nm originated from Si NC in oxide matrix. Other emissions can be attributed to the luminescent defects in oxide or oxide/NC interface. In order to see electroluminescence properties Light Emitting Devices (LED) were fabricated by using metal oxide semiconductor structure, current-voltage (I-V) and electroluminescence (EL) measurements were conducted. I-V results revealed that, current passing through device depends on both implanted Si dose and annealing parameters. Current increases with increasing dose as one might expect due to the increased amount of defects in the matrix. The current however decreases with increasing annealing temperature and duration, which imply that, NC in oxide behave like a well controlled trap level for charge transport. From EL measurements, few differences were observed between EL and PL results. These differences can be attributed to the different excitation and emission mechanisms in PL and EL process. Upon comparision, EL emission was found to be inefficient due to the asymmetric charge injection from substrate and top contact. Peak position of EL emission was blue shifted with respect to PL one, and approached towards PL peak position as applied voltage increased. From the results of the EL measurements, EL emission mechanisms was attributed to tunneling of electron hole pairs from top contact and substrate to NC via oxide barrier.