This study focuses on the application of 193-nm excimer laser (ArF) photodissociation to tandem time-of-flight mass spectrometry. In particular, it focuses on identifying the optimal experimental conditions for peptide sequencing and applying the technology to interesting systems. The early focus is on optimizing the sample preparation conditions that define the initial internal energy state of MALDI-produced ions. Subsequent chapters investigate the effect of changing photodissociation laser conditions and define conditions under which the information content of the spectrum is maximized. Later chapters compare the photodissociation experiment to technologies that represent the current state of the art in tandem mass spectrometry, illustrating both the advantages and shortcoming of photodissociation TOF methodology. Finally, we apply photodissociation to the study of interesting systems of biological relevance, including (1) peptides derived from enzymatic digestion, (2) post-translationally modified peptides, and (3) peptide-transition metal ion complexes. In the final chapter we consider the analytical implications of the work as a whole and comment on the analytical viability of the methodology and look forward to new directions for the experiments.

In this paper, we discuss the effect of the hydrogen-bonding on the photoluminescent(PL) properties of 1-pyrenecarboxylic acid (PCA)/ poly(methyl methacrylate) (PMMA). Isolated fluorophore can be obtained when PCA molecules were blended and septrated by PMMA, i. e. excimer emission can be more efficiently prevented. With the use of non-solvent, toluene, in the preparation step, excimer emission of PCA can be more effeiciently prevented as compared to the good solvent, tetrahydrofuran(THF). With a high PMMA/PCA ratio of 1000/1, emission spectra show no sign of excimer formation. Intermolecular hydrogen bonding between PMMA and PCA helps to prevent the excimer formation. Solvents used in the preparative state play important role on the final PL properties of the solid film. In the blend, partial carbonyl groups in PMMA band with carboxylic acid group in PCA, this causes the appearance of a stretching band at 1718 cm-1 in infrared spectroscopy. The hydrogen-bond interactions help to the prevention of excimer formation in the PMMA/PCA blending systems.

This study focuses on the application of 193-nm excimer laser (ArF) photodissociation to tandem time-of-flight mass spectrometry. In particular, it focuses on identifying the optimal experimental conditions for peptide sequencing and applying the technology to interesting systems. The early focus is on optimizing the sample preparation conditions that define the initial internal energy state of MALDI-produced ions. Subsequent chapters investigate the effect of changing photodissociation laser conditions and define conditions under which the information content of the spectrum is maximized. Later chapters compare the photodissociation experiment to technologies that represent the current state of the art in tandem mass spectrometry, illustrating both the advantages and shortcoming of photodissociation TOF methodology. Finally, we apply photodissociation to the study of interesting systems of biological relevance, including (1) peptides derived from enzymatic digestion, (2) post-translationally modified peptides, and (3) peptide-transition metal ion complexes. In the final chapter we consider the analytical implications of the work as a whole and comment on the analytical viability of the methodology and look forward to new directions for the experiments.

Η παρούσα διπλωματική εργασία χωρίζεται σε έξι κεφάλαια, καθένα από τα οποία περιγράφεται παρακάτω. Στο πρώτο κεφάλαιο , που ονομάζεται "Θεωρία του laser", περιγράφονται οι γενικές αρχές λειτουργίας του laser. Επιπλέον αναφέρονται τα κύρια μέρη του καθώς και οι τρόποι δημιουργίας του φαινομένου laser. Ενώ τέλος γίνεται αναφορά στα χαρακτηριστικά της δέσμης laser. Στο δεύτερο κεφάλαιο, "Θεωρία του πλάσματος", γίνεται λόγος για τον τρόπο δημιουργίας του πλάσματος, τις εφαρμογές του και μελετόντε κάποια ιδιαίτερα χαρακτηριστικά του. Το τρίτο κεφάλαιο αναφέρεται στα excimer laser, την λειτουργία τους και τις ιδιαιτερότητές τους συγκρινόμενα με άλλους τύπους laser. Επιπλέον δίνεται μεγαλύτερη έμφαση στο laser XeCl όπου μελετάται το μόριο του XeCl* καθώς και ο τρόπος δημιουργίας του. Στο τέταρτο κεφάλαιο γίνεται εκτενής αναφορά σε ένα απλοποιημένο θεωρητικό μοντέλο το οποίο δημιουργήθηκε για μελέτη της προσομοίωσης μιας εκκένωσης που πραγματοποιείται μέσα στο ενεργό μέσο προκειμένου να γίνει η αντιστροφή πληθυσμού. Αυτό το θεωρτικό μοντέλο περιλαμβάνει το ηλεκτρικό κύκλωμα που παρέχει ενέργεια στο ενεργό μέσο και στην συνέχεια γίνεται ανάλυση της συμπεριφοράς της εκκένωσης ώστε να επιλυθούν οι εξισώσεις συνέχειας. Στο πέμπτο κεφάλαιο, που ονομάζεται "Αριθμητικό μοντέλο" παρουσιάζονται οι μαθηματικές διεργασίες που χρησιμοποιήθηκαν με στόχο να επιλυθεί το θεωρητικό μοντέλο το οποίο αναπτύχθηκε στο κεφάλαιο τέσσερα. Τέλος στο έκτο κεφάλαιο παρουσιάζονται τα αριθμητικά αποτελέσματα που είναι προϊόν της επίλυσης του αριθμητικού μοντέλου του πέμπτου κεφαλαίου. Επίσης γίνεται σχολιασμών αυτών των αποτελεσμάτων και σύγκρισή τους με αναμενόμενα ή πειραματικά άλλων μελετών. / -

The present study concerns the application of LSM using an excimer laser to enhance the corrosion resistance of rare-earth Elektron 21 magnesium alloy. The alloy has been treated by an excimer laser to produce a highly homogeneous and refined microstructure for improvement of corrosion resistance. The laser surface treatment was applied on two different prepared surfaces of the alloy; i) a ground surface up to 1200 SiC grit; ii) a chemically cleaned surface using CrO3 +AgNO3 boiling solution. The intermetallic phases within the α-matrix that are believed to initiate corrosion have been dissolved by two methods. The first is by the excimer laser, where they were dissolved in the melted layers. The second is by a chemical dissolution prior LSM. Variation of the laser parameters such as changed laser influence (low, medium and high) and increased number of pulses, resulted in formation of thicker melted layers, but promoted the formation of porosity and micro-cracks particularly at overlap regions. The initial stage of this study was aimed at optimising the laser conditions for production of a uniform microstructure, with an increase in the corrosion resistance of the alloy being determined by potentiodynamic polarization measurements in sodium chloride solution. A laser fluence of 6 and 7 J/cm2 with 10, 20, 25, 40 and 50 pulses with a different overlap ratio of 7%, 20% and 50% were subsequently selected as the optimum condition to treat the surface of the alloy. After laser treatment, the top surfaces and the cross-sections of the alloy showed a relatively homogenous melted layer and a significant reduction in the number of large intergranular Mg-Zn-RE phase was achieved resulting in a significant improvement of the corrosion resistance of the alloy. This work also investigated the mechanism of corrosion and the interaction between the intergranular Mg-Zn-RE phase, the Zr-rich regions within the grains and the bulk Mg-rich matrix. The results obtained by scanning electron microscopy (SEM) / energy-dispersive X-ray (EDX) and scanning Kelvin prop forced microscopy (SKPFM) potential map measurements as well as transmission electron microscopy (TEM) / energy-dispersive X-ray (EDX) have shown the importance of the microstructure in the initiation of corrosion in 3.5 wt% NaCl solution, where the Zr-rich regions played a distinct role in the early stages of corrosion in this alloy. However, the obtained results have demonstrated that such laser melted layers improved the corrosion resistance of the alloy, but further work is still needed to obtain the fully understanding of such behaviour which can better the research results, particularly the selectively chemical dissolution of the second phases prior LSM.

Laser surface melting (LSM) of aluminium alloys with high power continuous wave (CW) CO2 and Nd:YAG lasers has been shown to produce dendritic/cellular microstructures with refined second-phase particles distributed along the dendritic boundaries. Although refinement of the microstructure and extension of the solute solubility in the matrix can be achieved, the refined second-phase particles still act as preferential sites to initiate localized corrosion. In contrast to a CW laser, an excimer laser with a UV wavelength and pulses width in the range of nanoseconds, resulting in extremely high cooling rate up to 1011 K/s, is expected to generate a further refining of the near-surface microstructure and hence, improved corrosion performance. In this project, a Lumonics IPEX 848 KrF excimer laser, with a wavelength of 248 nm and pulse width of 13 ns, has been used for surface melting of an AA2024-T351 alloy. The aim is to investigate the microstructure and the resultant corrosion behaviour of the laser treated surface, and its contribution to alloy performance. The laser fluence was fixed at 7 J/cm2 and the number of pulses per unit area was varied as 10, 25 and 50 pulses respectively. Microstructural characterisation and compositional analysis have been performed by SEM/EDX, TEM/EDX and XRD to disclose solidification phenomena and phase transformations. The results show that the melted layers, with a melt depth from 3 to 7 µm, have been achieved, that is far more chemically uniform than the bulk alloy. In particular, the relatively fine precipitates and dispersoids in the matrix have been dissolved, while large constituent intermetallic particles at the melted layer/matrix interface have been partially melted. In addition, solute-rich bands, containing particularly copper, were formed within the melted layers, especially at the melted layer/matrix interface. SKPFM also reveals that the laser-melted layers exhibit a uniform surface potential distribution. The corrosion performance of AA2024-T351 alloy before and after LSM has been evaluated by anodic polarisation in deaerated and aerated 0.1 M NaCl solution, and immersion tests in 0.1 NaCl solutions. Exfoliation corrosion immersion test ASTM G34- 01 (EXCO test) was also carried out to evaluate the intergranular corrosion (IGC)/exfoliation resistance of the alloy. The results show that the untreated alloy exhibits severe pitting corrosion and IGC. After LSM, significant improvement of corrosion resistance has been achieved. However, delamination of the laser melted layer from the matrix was evident after an EXCO test for 6 hours. The absence of significant corrosion product may suggest a stress-related mechanism. In order to investigate the effect of LSM on anodising of AA2024-T351 alloy and its influence on the corrosion resistance, excimer LSM has been applied as a pre-treatment method prior to anodising in 0.46 M H2SO4 solution. The results show that LSM significantly improved the corrosion performance following anodising compared with the alloy anodised without LSM and LSM alone.

Laser cleaning is a non contact, highly controllable process for the removal of contaminants from a surface with minimum or no damage to the substrate material. Laser cleaning has been applied mainly on flat and curved surfaces. Little is known on the phenomena and feasibility of laser cleaning of slotted structures. Slots are common structures in engineering, and can be found in many components. In this PhD work, the feasibility of laser cleaning of alpha case on flat titanium alloy surfaces was initially explored, and then an investigation was made on the use of a pulsed laser for the cleaning of micro to macro slots in silicon and metallic materials. The effects of laser processing parameters on the contaminant removal from these slots were experimentally studied. Laser cleaning thresholds and cleanliness was examined. Meanwhile, finite element modelling (FEM) and time domain finite difference modelling techniques were used to simulate the processes involved to aid the understanding of the technique for process optimisation. The experiments were undertaken to verify if such models are able to accurately predict the cleaning thresholds. The surface and sub-surface characteristics before and after laser cleaning were examined using optical microscopy and scanning electron microscopy (SEM). It has been shown that the slot structure and its material properties were not damaged or changed by laser cleaning process. A novel contribution is that surface morphology after the laser ablation could be used as a diagnostic method to indentify the presence of alpha case and measure its thickness due to the specific characteristics of the surface roughness and generated cracks on the ablated surface after laser irradiation. Besides, it has been found that an axial beam which propagates into the narrow slots can successfully clean the tiny particles on the slot sidewalls whose width ranges from 3.5 mm to 13mm. These phenomena had never been reported before.

In this experiment, fluorescent N- (1-pyrenyl) iodoacetamide modified the two reactive thiols, SH1 (Cys 707) and SH2 (Cys 697) on myosin to detect SH1-SH2 a -helix melting. The excimer forming property of pyrene is well suited to monitor the dynamics of the SH1 and SH2 helix melting, since the excimer should only form during the melted state. Decreased anisotropy of the excimer relative to the monomeric pyrene fluorescence is consistent with the disordering of the melted SH1-SH2 region in the atomic model. Furthermore, nucleotide analogs induced changes in the anisotropy of the excimer, suggesting that the nucleotide site modulates the flexibility of SH1-SH2 region.

No description available.

Résumé : Les circuits photoniques intégrés qui combinent des dispositifs photoniques pour la génération, la détection, la modulation, l'amplification, la commutation et le transport de la lumière dans une puce, ont été rapportés comme étant une innovation technologique importante qui simplifie la conception du système optique et qui réduit l'espace et la consommation de l'énergie en améliorant ainsi la fiabilité. La capacité de modifier la bande interdite des zones sélectives des différents dispositifs photoniques à travers la puce est la clé majeure pour le développement de circuits photoniques intégrés. Comparé à d'autres méthodes d’épitaxie, l’interdiffusion de puits quantiques a attiré beaucoup d'intérêt en raison de sa simplicité et son efficacité en accordant la bande interdite durant le processus de post-épitaxie. Cependant, l’interdiffusion de puits quantiques a subi des problèmes reliés au manque de précision pour modifier convenablement la bande interdite ciblée et à l’incontrôlabilité de l’absorption des impuretés au cours du processus qui peut dégrader la qualité du matériel interdiffusé. Dans cette thèse, nous avons utilisé les lasers excimer pour créer des défauts à proximité de la surface (~ 10 nm) des microstructures à base de puits quantiques III-V (par exemple InP et GaAs) et pour induire l’interdiffusion après le recuit thermique. L'irradiation par les lasers excimer (ArF et KrF) des microstructures à puits quantiques a été réalisée dans différents environnements, y compris l'air, l'eau déionisée, les couches diélectriques (SiO2 et Si3N4) et les couches d’InOx. Pour proposer un bon contrôle de la technique d’interdiffusion de puits quantiques par laser excimer, nous avons étudié la génération et la diffusion de défauts de surface en utilisant différentes méthodes de caractérisation de surface/interface, comme l'AFM, SEM, XPS et SIMS qui ont été utilisées pour analyser la modification de la morphologie de surface/interface et la modification chimique de la microstructure de ces puits quantiques. La qualité des microstructures à puits quantiques étudiées a été représentée par des mesures de photoluminescence et de luminescence des diodes lasers ainsi fabriqués. Les résultats montrent que le laser excimer induit des quantités d'oxydes de surface dans les surfaces des microstructure à puits quantiques InP/InGaAs/InGaAsP dans l'air et des impuretés d'oxygène des couches d'oxydes diffusées dans la région active de la microstructure lors du recuit, ce qui améliore l’interdiffusion, mais réduit l'intensité de la photoluminescence. Par contre, l’irradiation dans un environnement d'eau déionisée n’a pas démontré de diffusion des impuretés évidentes d'un excès d'oxygène vers les régions actives, mais la stœchiométrie de surface a été restaurée après l’interdiffusion. L’InOx a été trouvé avec un grand coefficient de dilatation thermique dans la microstructure interdiffusée qui était supposée d’augmenter la contrainte de compression dans la région active et ainsi d’augmenter l'intensité de photoluminescence de 10 fois dans l’échantillon irradié dans l'eau déionisée. Concernant les microstructures avec une couche diélectrique, la modification de la bande interdite a été toujours réalisée sur des échantillons dont les couches diélectriques ont été irradiées et la surface de InP a été modifiée par le laser excimer. Pour l'échantillon avec une couche de 243 nm de SiO2, les variations de la photoluminescence ont été mesurées sans l’ablation de cette couche de SiO2 lors de l'irradiation par le laser KrF. Cependant, la morphologie de l'interface d’InP a été modifiée, les oxydes d'interface ont été générés et les impuretés d'oxygène se sont diffusées à l'intérieur des surfaces irradiées. Les améliorations de l’interdiffusion dans les deux surfaces non irradiées et irradiés de l'échantillon couvert de couche d’InOx ont démontré l'importance des oxydes dans l’interdiffusion des puits quantiques. Les diodes laser fabriquées à partir d’un matériau interdiffusé par un laser KrF ont montré un seuil de courant comparable à celui des matériaux non interdiffusés avec un décalage de photoluminescence de 100 nm. En combinant un masque d'aluminium, nous avons créé un déplacement uniforme de photoluminescence de 70 nm sur une matrice rectangulaire de 40 μm x 200 μm ce qui présente un potentiel d’application de l’interdiffusion des puits quantiques par les lasers excimer dans les circuits photoniques intégrés. En outre, les lasers excimer ont été utilisés pour créer des structures de nano-cônes auto-organisées sur des surfaces de microstructure de InP/InGaAs/InGaAsP en augmentant l'intensité de PL par ~ 1.4 fois. Les lasers excimer ont été aussi utilisés pour modifier la mouillabilité sélective des zones d’une surface de silicium par une modification chimique de surface induite par laser dans différents milieux liquides. Ainsi, la fluorescence des nanosphères a été réussie pour des fonctions de configuration spécifique avec une surface de silicium. // Abstract : Photonic integrated circuits (PICs) which combine photonic devices for generation, detection, modulation, amplification, switching and transport of light on a chip have been reported as a significant technology innovation that simplifies optical system design, reduces space and power consumption, improves reliability. The ability of selective area modifying the bandgap for different photonic devices across the chip is the important key for PICs development. Compared with other growth methods, quantum well intermixing (QWI) has attracted amounts of interest due to its simplicity and effectiveness in tuning the bandgap in post-growth process. However, QWI has suffered problems of lack of precision in achieving targeted bandgap modification and uncontrollable up-taking of impurities during process which possibly degrade the quality of intermixed material. In this thesis, we have employed excimer laser to create surface defects in the near surface region (~ 10 nm) of III-V e.g. InP and GaAs, based QW microstructure and then annealing to induce intermixing. The irradiation by ArF and KrF excimer lasers on the QW microstructure was carried out surrounded by different environments, including air, DI water, dielectric layers (SiO2 and Si3N4) and InOx coatings. To propose a more controllable UV laser QWI technique, we have studied surface defects generation and diffusion with various surface/interface characterization methods, like AFM, SEM, XPS and SIMS, which were used to analyse the QW surface/interface morphology and chemical modification during QWI. The quality of processed QW microstructure was represented by photoluminescence measurements and luminescence measurements of fabricated laser diodes. The results shows that excimer laser induced amounts of surface oxides on the InP/InGaAs/InGaAsP microstructure surface in air and the oxygen impurities from oxides layer diffused to the active region of the QW microstructure during annealing, which enhance intermixing but also reduce the PL intensity. When irradiated in DI water environment, no obvious excessive oxygen impurities were found to diffuse to the active regions and the surface stoichiometry has been restored after intermixing. InOx with large coefficient of thermal expansion was found inside the intermixed QW microstructure, which was supposed to increase the compressive strain in active region and enhance the PL intensity to maximum 10 times on sample irradiated in DI water. On microstructure coated with dielectric layers, bandgap modifications were always found on samples whose dielectric layers were ablated and InP surface was modified by excimer laser. On sample coated with 243 nm SiO2 layer, the PL shifts were found on sample without ablation of the SiO2 layer when irradiated by KrF laser. However, the InP interface morphology was modified, interface oxides were generated and oxygen impurities have diffused inside on the irradiated sites. The enhancements of interdiffusion on both non irradiated and irradiated sites of sample coated with InOx layer have verified the importance of oxides in QWI. The laser diodes fabricated from KrF laser intermixed material have shown comparable threshold current density with as grown material with PL shifted by 133 nm. Combined aluminum mask, we have created uniform 70 nm PL shifts on 40 μm x 200 μm rectangle arrays which presents UV laser QWI potential application in PICs. In addition, excimer lasers have been used to create self organized nano-cone structures on the surface of InP/InGaAs/InGaAsP microstructure and enhance the PL intensity by ~1.4x. Excimer lasers have selective area modified wettability of silicon surface based on laser induced surface chemical modification in different liquid environments. Then the fluorescence nanospheres succeeded to specific pattern functions with silicon surface.