Tip-Enhances Raman Spectroscopy, Enabling Spectroscopy at the Nanoscale

The knowledge on the chemical and the structural properties of substances benefits strongly from characterization methods that can provide access to the sample’s nanoscale building blocks. Not only should the sensitivity of these methods approach a high detection limit up to single molecule, but also the accessible spatial resolution must enable chemical imaging of individual nanoscale features of the substances. High resolution imaging is often provided by electron microscopes through methods such as transmission electron microscopy (TEM) and scanning electron microscopy (STM), nevertheless, these methods lack offering chemical information. Surface-enhanced spectroscopy was developed to improve the sensitivity of the chemical measurements through placing the sample onto rough metallic surfaces. However, in SERS, spatially resolved measurements are not possible since an ensemble of nanoscale features give birth to the SERS effect. The challenge of the simultaneous improvement of the spatial resolution and sensitivity was addressed indeed through combining high resolution optical microscopy with high sensitivity of surface-enhanced spectroscopy and was termed as tip-enhanced Raman spectroscopy. In this thesis, the confined electric field in proximity of the nanoscale apex of the metallic TERS tip is first investigated theoretically through conducting finite-difference time-domain calculations. The results were employed in optimization of the experimental TERS setup which is utilized in this thesis. The power of TERS in high resolution detection of nanoscale substances is then evaluated through TERS study of isolated single walled carbon nanotubes. The accessible high resolution is also used to acquire insight into the impact of structural strains on the molecular vibrations in silicon nanowires. The large surface sensitivity and specificity of TERS is also evaluated through TERS mapping of the adsorption sites of osteopontin phosphoprpteins on the surface of calcium oxalate microcrystal which are responsible for the formation of kidney stones in human body

Multi-period, multi-product production planning in an uncertain manufacturing environment

Les travaux de cette thèse portent sur la planification de la production multi-produits, multi-périodes avec des incertitudes de la qualité de la matière première et de la demande. Un modèle de programmation stochastique à deux étapes avec recours est tout d'abord proposé pour la prise en compte de la non-homogénéité de la matière première, et par conséquent, de l'aspect aléatoire des rendements de processus. Ces derniers sont modélisés sous forme de scénarios décrits par une distribution de probabilité stationnaire. La méthodologie adoptée est basée sur la méthode d'approximation par moyenne d'échantillonnage. L'approche est appliquée pour planifier la production dans une unité de sciage de bois et le modèle stochastique est validé par simulation de Monte Carlo. Les résultats numériques obtenus dans le cas d'une scierie de capacité moyenne montrent la viabilité de notre modèle stochastique, en comparaison au modèle équivalent déterministe. Ensuite, pour répondre aux préoccupations du preneur de décision en matière de robustesse, nous proposons deux modèles d'optimisation robuste utilisant chacun une mesure de variabilité du niveau de service différente. Un cadre de décision est développé pour choisir parmi les deux modèles d'optimisation robuste, en tenant compte du niveau du risque jugé acceptable quand à la variabilité du niveau de service. La supériorité de l'approche d'optimisation robuste, par rapport à la programmation stochastique, est confirmée dans le cas d'une usine de sciage de bois. Finalement, nous proposons un modèle de programmation stochastique qui tient compte à la fois du caractère aléatoire de la demande et du rendement. L'incertitude de la demande est modélisée par un processus stochastique dynamique qui est représenté par un arbre de scénarios. Des scénarios de rendement sont ensuite intégrés dans chaque noeud de l'arbre de scénarios de la demande, constituant ainsi un arbre hybride de scénarios. Nous proposons un modèle de programmation stochastique multi-étapes qui utilise un recours complet pour les scénarios de la demande et un recours simple pour les scénarios du rendement. Ce modèle est également appliqué au cas industriel d'une scierie et les résultats numériques obtenus montrent la supériorité du modèle stochastique multi- étapes, en comparaison avec le modèle équivalent déterministe et le modèle stochastique à deux étapes

A Customized ILP-Based Solver for Description Logic Reasoners

Artificial intelligence based systems are known for conveying knowledge through machines. This knowledge is often represented using logic representation languages. One of the well-known families of such languages is called Description Logic (DL) which formally reasons and represents knowledge on the concepts, roles and individuals of an application domain. DL reasoners have been evolving and upgraded through the years, however when it comes to handling more complicated ontologies with big values occurring in number restrictions, the current reasoners mostly fail to perform efficiently. One of the techniques used in DL reasoners is the so-called atomic decomposition technique which combines arithmetic and logical reasoning. This thesis presents a customized CPLEX-based solver for enhancing DL reasoners through optimizing the atomic decomposition technique. Furthermore, we provide evidence on how this method can improve the reasoning performance by optimizing atomic decomposition. For such purpose, an empirical evaluation of our system for a set of synthesized benchmarks is demonstrated

Plasmon-Mediated Drilling in Thin Metallic Nanostructures

Tetrahedral nanopyramids made of silver and gold over ITO/glass surfaces are fabricated. Our protocol is based on nanosphere lithography (NSL) with the deposition of thicker metal layers. After removing the microspheres used in the NSL process, an array of metallic tetrahedral nanostructures of ~350-400 nm height is formed. The reported procedure avoids the use of any stabilizing surfactant molecules that are generally necessary to segregate the individual particles onto surfaces. We focus here on the optical and the physical properties of these plasmonic surfaces using near-field spectroscopy in conjunction with finite difference time domain (FDTD) modeling of the electric field. Remarkably, FDTD shows that the localized surface plasmon resonance is confined in the plane formed by the edges of two facing pyramids that is parallel to the polarization of the impinging excitation laser. The variable gap between the edges of two adjacent pyramids shows a broader localized surface plasmon and larger specific surface as opposed to the usual nanotriangle array. Localized enhancement of the electric field is experimentally investigated by coating the plasmonic surface with a thin film of photosensitive azopolymer onto the surface of the nanopyramids. The reported deformation upon radiation of the surface topography is visualized by atomic force microscopy and suggests the potentiality of these 3D nanopyramids for near-field enhancement. This last feature is clearly confirmed by surface-enhanced Raman scattering measurement with 4-nitrothiophenol molecules deposited on the pyramid platforms. The potentiality of such 3D nanostructures in plasmonics and surface spectroscopy is thus clearly demonstrated

Raman spectroscopy: techniques and applications in the life sciences

Raman spectroscopy is an increasingly popular technique in many areas including biology and medicine. It is based on Raman scattering, a phenomenon in which incident photons lose or gain energy via interactions with vibrating molecules in a sample. These energy shifts can be used to obtain information regarding molecular composition of the sample with very high accuracy. Applications of Raman spectroscopy in the life sciences have included quantification of biomolecules, hyperspectral molecular imaging of cells and tissue, medical diagnosis, and others. This review briefly presents the physical origin of Raman scattering explaining the key classical and quantum mechanical concepts. Variations of the Raman effect will also be considered, including resonance, coherent, and enhanced Raman scattering. We discuss the molecular origins of prominent bands often found in the Raman spectra of biological samples. Finally, we examine several variations of Raman spectroscopy techniques in practice, looking at their applications, strengths, and challenges. This review is intended to be a starting resource for scientists new to Raman spectroscopy, providing theoretical background and practical examples as the foundation for further study and exploration