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1
Jacobs, Clayton Jeffrey. "Influence of catalyst ink mixing procedures on catalyst layer properties and in-situ PEMFC performance." Master's thesis, University of Cape Town, 2016. http://hdl.handle.net/11427/22932.
Full textAbstract:
Despite the benefits of fuel cell technology its advancement to being commercially functional is hindered by a number of crucial factors. These factors are often associated with the lack of appropriate materials or manufacturing routes that would enable the cost of electricity per kWh to compete with existing technology. Whilst most research efforts have been directed towards developing more active catalysts, the amount of catalyst required in the fuel cell can be further reduced by improving the platinum utilisation in the membrane electrode assembly. The platinum utilisation is a strong function of the catalyst layer preparation step and there remains significant scope for optimisation of this step. Whereas significant work has been conducted into the different components of the catalyst ink there is limited work and understanding on the influence of the mixing method of the catalyst ink. This study will focus on the influence of the mixing technique on the catalyst ink properties and on the final fuel cell performance. Specifically, the study will investigate the effect of the three different mixing techniques on (i) catalyst ink quality (ii) the physical properties of the resultant catalyst layer and (iii) the in-situ electrochemical performance of the membrane electrode assembly. A large set of characterisation techniques were chosen to effectively study the step wise processing of the catalyst layer, and fuel cell performance. The results presented here include a comparison of the various mixing techniques and a comprehensive 2 x 2 factorial design into the individual techniques. The results suggest that high energy mixing is required for effective distribution of catalyst layer components, an even catalyst layer topography and a highly functional ionomer network which consequently, enhances performance. The mixing energy referred to involves prolonged mixing time, enhanced mixing intensity or a combination of the two. During bead milling of catalyst inks, high intensity mixing seems to be beneficial however, prolonged mixing time appears to be detrimental to the ionomer film structure. During high shear stirring and ultrasonic homogenisation of catalyst inks, the ink mixture significantly heats up. It has been observed that at higher temperatures, Nafion elongates and the contact with catalyst agglomerates is enhanced. High shear stirring of catalyst inks seems to be most effective at high agitation rates. High mixing energies result in high shear forces and in addition, high mixing temperatures which appear to be beneficial to establishing an effective catalyst/Nafion interface, enhancing the three phase boundary observed during in-situ testing. Ultrasonic homogenisation seems to be more effective at prolonged sonication times. Due to the erosive nature of ultrasonic dispersion, sufficient time is required to establish a well dispersed and distributed catalyst ink. However, the nature of particle size distribution resulting from ultrasonication shows that inks are unstable and is not recommended for high throughput processing. Overall, fuel cell performance is not significantly affected by the mixing step however; mixing does have an observable impact on catalyst layer formulation. Generally, when optimizing membrane electrode assembly fabrication, mixing parameters should be carefully chosen. This goes without saying that parameters need to be effectively studied before foregoing catalyst ink processing.
2
Lutey, Adrian Hugh Alexander <1986>. "High-Speed Laser Processing of Thin Single and Multi-Layer Films." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5741/.
Full textAbstract:
Theoretical models are developed for the continuous-wave and pulsed laser incision and cut of thin single and multi-layer films. A one-dimensional steady-state model establishes the theoretical foundations of the problem by combining a power-balance integral with heat flow in the direction of laser motion. In this approach, classical modelling methods for laser processing are extended by introducing multi-layer optical absorption and thermal properties. The calculation domain is consequently divided in correspondence with the progressive removal of individual layers. A second, time-domain numerical model for the short-pulse laser ablation of metals accounts for changes in optical and thermal properties during a single laser pulse. With sufficient fluence, the target surface is heated towards its critical temperature and homogeneous boiling or "phase explosion" takes place. Improvements are seen over previous works with the more accurate calculation of optical absorption and shielding of the incident beam by the ablation products. A third, general time-domain numerical laser processing model combines ablation depth and energy absorption data from the short-pulse model with two-dimensional heat flow in an arbitrary multi-layer structure. Layer removal is the result of both progressive short-pulse ablation and classical vaporisation due to long-term heating of the sample. At low velocity, pulsed laser exposure of multi-layer films comprising aluminium-plastic and aluminium-paper are found to be characterised by short-pulse ablation of the metallic layer and vaporisation or degradation of the others due to thermal conduction from the former. At high velocity, all layers of the two films are ultimately removed by vaporisation or degradation as the average beam power is increased to achieve a complete cut. The transition velocity between the two characteristic removal types is shown to be a function of the pulse repetition rate. An experimental investigation validates the simulation results and provides new laser processing data for some typical packaging materials.
3
Taddia, Sara <1986>. "Effect of Laser Shock Peening on Fatigue Crack Propagation of Aeronautical Structures." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amsdottorato.unibo.it/7130/.
Full textAbstract:
Laser Shock Peening (LSP) is a surface enhancement treatment which induces a significant layer of beneficial compressive residual stresses up to several mm
underneath the surface of metal components in order to improve the detrimental effects of crack growth behavior rate in it.
The aim of this thesis is to predict the crack growth behavior of thin Aluminum specimens with one or more LSP stripes defining a compressive residual stress area.
The LSP treatment has been applied as crack retardation stripes perpendicular to the crack growing direction, with the objective of slowing down the crack when approaching the LSP patterns.
Different finite element approaches have been implemented to predict the residual stress field left by the laser treatment, mostly by means of the commercial
software Abaqus/Explicit.
The Afgrow software has been used to predict the crack growth behavior of the component following the laser peening treatment and to detect the improvement
in fatigue life comparing to the specimen baseline.
Furthermore, an analytical model has been implemented on the Matlab software to make more accurate predictions on fatigue life of the treated components.
An educational internship at the Research and Technologies Germany- Hamburg department of Airbus helped to achieve knowledge and experience to write this thesis.
The main tasks of the thesis are the following:
-To up to date Literature Survey related to laser shock peening in metallic
structures
-To validate the FE models developed against experimental measurements
at coupon level
-To develop design of crack growth slow down in centered and edge cracked
tension specimens based on residual stress engineering approach using laser
peened patterns transversal to the crack path
-To predict crack growth behavior of thin aluminum panels
-To validate numerical and analytical results by means of experimental tests.
4
Ascari, Alessandro <1974>. "Giunzione mediante laser di materiali difficili, ibridi ed a struttura cellulare." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amsdottorato.unibo.it/6358/.
Full textAbstract:
Lo studio presentato in questa sede concerne applicazioni di saldatura LASER caratterizzate da aspetti di non-convenzionalità ed è costituito da tre filoni principali. Nel primo ambito di intervento è stata valutata la possibilità di effettuare saldature per fusione, con LASER ad emissione continua, su pannelli Aluminum Foam Sandwich e su tubi riempiti in schiuma di alluminio. Lo studio ha messo in evidenza numerose linee operative riguardanti le problematiche relative alla saldatura delle pelli esterne dei componenti ed ha dimostrato la fattibilità relativa ad un approccio di giunzione LASER integrato (saldatura seguita da un post trattamento termico) per la realizzazione della giunzione completa di particolari tubolari riempiti in schiuma con ripristino della struttura cellulare all’interfaccia di giunzione. Il secondo ambito di intervento è caratterizzato dall’applicazione di una sorgente LASER di bassissima
potenza, operante in regime ad impulsi corti, nella saldatura di acciaio ad elevato contenuto di
carbonio. Lo studio ha messo in evidenza come questo tipo di sorgente, solitamente applicata per lavorazioni di
ablazione e marcatura, possa essere applicata anche alla saldatura di spessori sub-millimetrici. In questa fase è stato messo in evidenza il ruolo dei parametri di lavoro sulla conformazione del giunto ed è stata definita l’area di fattibilità del processo. Lo studio è stato completato investigando la possibilità di applicare un trattamento LASER dopo saldatura per addolcire le eventuali zone indurite. In merito all’ultimo ambito di intervento l’attività di studio si è focalizzata sull’utilizzo di sorgenti ad elevata densità di potenza (60 MW/cm^2) nella saldatura a profonda penetrazione di acciai da costruzione. L’attività sperimentale e di analisi dei risultati è stata condotta mediante tecniche di Design of Experiment per la valutazione del ruolo preciso di tutti i parametri di processo e numerose considerazioni relative alla formazione di cricche a caldo sono state suggerite.This dissertation concerns LASER-based joining and welding applications characterized by non-conventional prerogatives. The work is divided into three main topics: LASER joining of hybrid cellular-structured materials, with particular attention to aluminum foam sandwiches and foam-cored tubes, short-pulse LASER micro welding of high carbon steels and high power density continuous wave LASER welding of structural steels. The first topic investigates the role of LASER in joining hybrid components characterized by an external dense skin and an internal foam core. In particular the possibility of achieving both the fusion welding of the skin and the restoration of the cellular structure at the welding interface is assessed and the main guidelines concerning an integrated LASER welding - LASER heat treatment processing cycle are suggested. The second topic deals with the application of a low-power nanosecond pulsed LASER source in welding high carbon steels. The study points out that an accurate selection of pulse-related parameters allows to achieve sound micro-joints characterized by a penetration between 20 and 200 microns. These results point out the possibility to consider the construction of integrated LASER manufacturing cells in which, with the same low-cost source and on the same workpiece positioning, welding, cutting, marking and texturing processes can be performed. The study is completed by the investigation of the possibility to carry out a LASER post welding heat treatment for annealing the eventual hardened zones occurring in the welded material. The last topic deals with high power density LASER welding of carbon steels: by exploiting a high brilliance fiber source, capable of achieving 60 MW/cm^2, high penetration weld beads were obtained. By means of Design of Experiment techniques the role of radiation power, welding speed and beam focal position is assessed and several considerations were made concerning the influence of this kind of process on hot cracks formation.
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Molesini, Ambra <1980>. "Meta-models, environment and layers: agent-oriented engineering of complex systems." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/930/.
Full textAbstract:
Traditional software engineering approaches and metaphors fall short when applied to
areas of growing relevance such as electronic commerce, enterprise resource planning,
and mobile computing: such areas, in fact, generally call for open architectures that
may evolve dynamically over time so as to accommodate new components and meet new
requirements. This is probably one of the main reasons that the agent metaphor and the
agent-oriented paradigm are gaining momentum in these areas.
This thesis deals with the engineering of complex software systems in terms of the
agent paradigm. This paradigm is based on the notions of agent and systems of interacting agents as fundamental abstractions for designing, developing and managing at
runtime typically distributed software systems. However, today the engineer often works
with technologies that do not support the abstractions used in the design of the systems.
For this reason the research on methodologies becomes the basic point in the scientific
activity. Currently most agent-oriented methodologies are supported by small teams of
academic researchers, and as a result, most of them are in an early stage and still in the
first context of mostly \academic" approaches for agent-oriented systems development.
Moreover, such methodologies are not well documented and very often defined and presented only by focusing on specific aspects of the methodology. The role played by meta-
models becomes fundamental for comparing and evaluating the methodologies. In fact a
meta-model specifies the concepts, rules and relationships used to define methodologies.
Although it is possible to describe a methodology without an explicit meta-model, formalising the underpinning ideas of the methodology in question is valuable when checking its
consistency or planning extensions or modifications. A good meta-model must address all
the different aspects of a methodology, i.e. the process to be followed, the work products
to be generated and those responsible for making all this happen. In turn, specifying
the work products that must be developed implies dening the basic modelling building
blocks from which they are built.
As a building block, the agent abstraction alone is not enough to fully model all the
aspects related to multi-agent systems in a natural way. In particular, different perspectives exist on the role that environment plays within agent systems: however, it is
clear at least that all non-agent elements of a multi-agent system are typically considered to be part of the multi-agent system environment. The key role of environment
as a first-class abstraction in the engineering of multi-agent system is today generally
acknowledged in the multi-agent system community, so environment should be explicitly
accounted for in the engineering of multi-agent system, working as a new design dimension
for agent-oriented methodologies. At least two main ingredients shape the environment:
environment abstractions - entities of the environment encapsulating some functions -,
and topology abstractions - entities of environment that represent the (either logical or
physical) spatial structure. In addition, the engineering of non-trivial multi-agent systems requires principles and mechanisms for supporting the management of the system representation complexity. These principles lead to the adoption of a multi-layered description, which could be used by designers to provide different levels of abstraction over
multi-agent systems.
The research in these fields has lead to the formulation of a new version of the SODA
methodology where environment abstractions and layering principles are exploited for en-
gineering multi-agent systems.
6
Sato, Taku. "Laser assisted ink consolidation for Direct Write Component Fabrication." Thesis, University of Liverpool, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.540068.
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Коротенко, Олена Володимирівна. "Технологічне забезпечення якості банкнот під час металографічного друку." Thesis, КПІ ім. Ігоря Сікорського, 2018. https://ela.kpi.ua/handle/123456789/21718.
Full textAbstract:
Дисертаційна робота присвячена встановленню закономірностей впливу технологічних факторів металографічного друку на якість відбитків. Для виконання роботи було використано профілометричні методи дослідження поверхні зразків (механічна, оптична профілометрія); мікроскопічні методи дослідження поверхні та мікротомних зрізів зразків; органолептично-експертний метод тактильної дискримінації зразків; експертний аналіз якості зразків. Розроблено узагальнену ієрархічну модель формування якості відбитків у процесі металографічного друку, розроблено комплекс моделей залежності якості відбитків від технологічних факторів, експериментально підтверджено характер залежності формування фарбового рельєфу від параметрів друкарської форми та факторів друкарського процесу. Також у роботі здійснено моделювання впливу теплообмінних процесів та інерційності процесу на процес формування фарбового шару та моделювання впливу профілю тиску у друкарському контакті та виду профілю гравійованих елементів форми на процес проникнення та розподіл фарби в об’ємі паперу.Intaglio printing is one of the basic methods for protection of the strict accounting documents, in particular banknotes, all over the world. The peculiarity of this printing method is the possibility to form the strokes with different ink layer thickness (up to 320 microns) on the prints. It provides identification of the authenticity of the strict accounting documents by the public, including visually impaired people. But there is the paucity of theoretical and practical developments regarding the intaglio printing. Thus, the determination of the principles of the ink layer formation and its dependence on the influence of technological parameters of the process to provide high quality of intaglio printing is an topical scientific and technical task. The dissertation is devoted to establish the regularities of the influence of the intaglio printing technological factors on the prints quality. The generalized hierarchical model of prints quality forming, based on a detailed analysis of professional literature and scientific sources, was developed. A group of quality indicators and the main technological factors that influence prints quality were determined for the generalized hierarchical model of prints quality forming. The phenomenological model of intaglio ink transferring was developed and a mathematical description of physical processes, occurring during intaglio ink transferring, was made. Thus, the basic technological parameters that influence the prints quality were determined. It was found that the most effective factors that influence the quality of the ink relief forming are the geometric parameters of the plate as well as the technological print parameters, such as print pressure and print speed. The model of intaglio ink penetration and its distribution during intaglio printing was created. It allowed to investigate how the pressure that acts throughout the printing contact can influence the ink penetration depth. The modeling of the influence of heat exchange processes and the inertia of the process on the intaglio ink layer formation was carried out. These models explained the cause of asymmetry of the cross-sectional shape of strokes obtained by the intaglio printing. The results of modeling are confirmed by experimental research which was carried out with using of the developed method of determination of the generalized quality index of intaglio printing. The determination of the index is based on surface profilometric and microscopic analyses as well as on organoleptic and visual analyses of prints. The method allowed to increase the objectivity of quality evaluating and detect the regularities of the influence of the technological process parameters on the intaglio prints quality parameters. Based on the experimental study results, it was recommended to use a printing plate with the engraved elements of a rectangular profile or trapezoidal profile with an angle of 75 degrees and the element width to depth ratio of more than 1.3 times. It was also recommended to use reduced printing speed and high pressure in printing nip. The correlation analysis of the dependence of the generalized quality index on technological factors was made. As a result, the ranking of the factors on the weight of their influence was carried out. These conclusions became the basis for the recommendations given to the NBU Banknote Printing and Minting Works. The recommendations were aimed at ensuring the quality of the intaglio printing which is produced by the plates made by direct laser engraving. The system of technological assurance of banknotes quality in the process of intaglio printing was developed. As a basis for the system, the developed software for determining of the dependence of the quality printing parameters on technological factors as well as the software for determining of the ink layer thickness were used. By using this system in the manufacturing it is possible to improve the autonomy of the prints quality control process and to normalize the reproduction.
Диссертация посвящена установлению закономерностей влияния технологических факторов металлографской печати на качество оттисков. Для выполнения работы были использованы профилометрические методы исследования поверхности образцов (механическая, оптическая профилометрия) микроскопические методы исследования поверхности и микротомальных срезов образцов; органолептическо-экспертный метод тактильной дискриминации образцов; экспертный анализ качества образцов. В результате работы была разработана обобщенная иерархическая модель формирования качества оттисков в процессе металлографской печати, разработан комплекс моделей зависимости качества оттисков от технологических факторов, экспериментально подтвержден характер зависимости формирования красочного рельефа от параметров печатной формы и факторов печатного процесса. Также в работе осуществлено моделирование влияния теплообменных процессов и инерционности процесса на процесс формирования красочного слоя и моделирования влияния профиля давления в печатном контакте и вида профиля гравированных элементов формы на процесс проникновения и распределение краски в структуре бумаги.
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Stavrinou, Paul Nicholas. "A study of InP-based strained layer heterostructures." Thesis, University College London (University of London), 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261711.
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Bonifacio, Rafael Nogueira. "Desenvolvimento de processo de produção de conjuntos eletrodo-membrana-eletrodo para células a combustível baseadas no uso de membrana polimérica condutora de prótons (PEMFC) por impressão a tela." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-29082011-151940/.
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Energia é um recurso que historicamente apresenta tendência de crescimento de demanda. Projeções indicam que, para suprir as necessidades energéticas do futuro, será necessário um uso massivo do hidrogênio como combustível. O uso de sistemas de célula a combustível baseada no uso de membrana polimérica condutora de prótons (PEMFC) tem características que permitem sua aplicação para geração de energia elétrica em aplicações estacionárias, automotivas e portáteis. O uso de hidrogênio como combustível para PEMFC apresenta a vantagem de resultar em baixa emissão de poluentes quando comparado às dos combustíveis fósseis. Para que ocorram as reações em uma PEMFC é necessária a construção de conjuntos eletrodo-membrana-eletrodo (MEA), sendo o processo de produção de MEAs e os materiais utilizados, relevantes no custo final do kW instalado para geração de energia por sistemas de célula a combustível, o que é, atualmente, uma barreira tecnológica e financeira para a aplicação em grande escala desta tecnologia. Nesse trabalho foi desenvolvido um processo de produção de MEAs por impressão a tela que apresenta alta reprodutibilidade, rapidez e baixo custo. Foram desenvolvidos o processo de impressão a tela e a composição de uma tinta precursora da camada catalisadora (TPCC), que permitem o preparo de eletrodos para confecção de MEAs com a aplicação da massa exata de eletrocatalisador adequada para cátodos 0,6 miligramas de platina por centímetro quadrados (mgPt.cm-2) e ânodos 0,4 mgPt.cm-2 em apenas uma aplicação por eletrodo. A TPCC foi desenvolvida, produzida, aplicada e caracterizada, apresentando características semelhantes a de tintas de impressão a tela para outras aplicações. Os MEAs produzidos apresentaram desempenho de até 712 mA.cm-2 a 600 mV para MEAs de 25 cm2 e o custo para produção de MEAs de 247,86 cm2 capazes de gerar 1 kW de energia foi estimado em R$ 13.939,45, considerando custo de equipamentos, materiais e mão de obra.Energy is a resource that presents historical trend of growth in demand. Projections indicate that future energy needs will require a massive use of hydrogen as fuel. The use of systems based on the use of proton exchange membrane fuel cell (PEMFC) has features that allow its application for stationary applications, automotive and portable power generation. The use of hydrogen as fuel for PEMFC has the advantage low pollutants emission, when compared to fossil fuels. For the reactions in a PEMFC is necessary to build membrane electrode assembly (MEA). And the production of MEAs and its materials are relevant to the final cost of kW of power generated by systems of fuel cell. This represent currently a technological and financial barriers to large-scale application of this technology. In this work a process of MEAs fabrication were developed that showed high reproducibility, rapidity and low cost by sieve printing. The process of sieve printing and the ink composition as a precursor to the catalyst layer were developed, which allow the preparation of electrodes for MEAs fabrication with the implementation of the exact catalyst loading, 0.6 milligrams of platinum per square centimeters (mgPt.cm-2) suitable for cathodes and 0.4 mgPt.cm-2 for anode in only one application step per electrode. The ink was developed, produced, characterized and used with similar characteristics to ink of sieve printing build for other applications. The MEAs produced had a performance of up to 712 mA.cm-2 by 600 mV to 25 cm2 MEA area. The MEA cost production for MEAs of 247.86 cm2, that can generate 1 kilowatt of energy was estimated to US$ 7,744.14 including cost of equipment, materials and labor.
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Mosiadz, Mariusz. "Inkjet printing of buffer and superconducting layers for YBa₂Cu₃O₇₋x coated conductors." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610415.
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Naes, Benjamin E. "Elemental Analysis of Glass and Ink by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) and Laser Induced Breakdown Spectroscopy (LIBS)." FIU Digital Commons, 2009. http://digitalcommons.fiu.edu/etd/207.
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The necessity of elemental analysis techniques to solve forensic problems continues to expand as the samples collected from crime scenes grow in complexity. Laser ablation ICP-MS (LA-ICP-MS) has been shown to provide a high degree of discrimination between samples that originate from different sources. In the first part of this research, two laser ablation ICP-MS systems were compared, one using a nanosecond laser and another a femtosecond laser source for the forensic analysis of glass. The results showed that femtosecond LA-ICP-MS did not provide significant improvements in terms of accuracy, precision and discrimination, however femtosecond LA-ICP-MS did provide lower detection limits. In addition, it was determined that even for femtosecond LA-ICP-MS an internal standard should be utilized to obtain accurate analytical results for glass analyses. In the second part, a method using laser induced breakdown spectroscopy (LIBS) for the forensic analysis of glass was shown to provide excellent discrimination for a glass set consisting of 41 automotive fragments. The discrimination power was compared to two of the leading elemental analysis techniques, µXRF and LA-ICP-MS, and the results were similar; all methods generated >99% discrimination and the pairs found indistinguishable were similar. An extensive data analysis approach for LIBS glass analyses was developed to minimize Type I and II errors en route to a recommendation of 10 ratios to be used for glass comparisons. Finally, a LA-ICP-MS method for the qualitative analysis and discrimination of gel ink sources was developed and tested for a set of ink samples. In the first discrimination study, qualitative analysis was used to obtain 95.6% discrimination for a blind study consisting of 45 black gel ink samples provided by the United States Secret Service. A 0.4% false exclusion (Type I) error rate and a 3.9% false inclusion (Type II) error rate was obtained for this discrimination study. In the second discrimination study, 99% discrimination power was achieved for a black gel ink pen set consisting of 24 self collected samples. The two pairs found to be indistinguishable came from the same source of origin (the same manufacturer and type of pen purchased in different locations). It was also found that gel ink from the same pen, regardless of the age, was indistinguishable as were gel ink pens (four pens) originating from the same pack.
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Di, Felice Marco <1980>. "Cross-layer optimizations in multi-hop ad hoc networks." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/915/.
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Unlike traditional wireless networks, characterized by the presence of last-mile, static and
reliable infrastructures, Mobile ad Hoc Networks (MANETs) are dynamically formed by
collections of mobile and static terminals that exchange data by enabling each other's
communication. Supporting multi-hop communication in a MANET is a challenging
research area because it requires cooperation between different protocol layers (MAC,
routing, transport). In particular, MAC and routing protocols could be considered
mutually cooperative protocol layers. When a route is established, the exposed and
hidden terminal problems at MAC layer may decrease the end-to-end performance
proportionally with the length of each route. Conversely, the contention at MAC layer
may cause a routing protocol to respond by initiating new routes queries and routing table
updates.
Multi-hop communication may also benefit the presence of pseudo-centralized virtual
infrastructures obtained by grouping nodes into clusters. Clustering structures may
facilitate the spatial reuse of resources by increasing the system capacity: at the same
time, the clustering hierarchy may be used to coordinate transmissions events inside the
network and to support intra-cluster routing schemes. Again, MAC and clustering
protocols could be considered mutually cooperative protocol layers: the clustering
scheme could support MAC layer coordination among nodes, by shifting the distributed
MAC paradigm towards a pseudo-centralized MAC paradigm. On the other hand, the
system benefits of the clustering scheme could be emphasized by the pseudo-centralized
MAC layer with the support for differentiated access priorities and controlled contention.
In this thesis, we propose cross-layer solutions involving joint design of MAC, clustering
and routing protocols in MANETs.
As main contribution, we study and analyze the integration of MAC and clustering
schemes to support multi-hop communication in large-scale ad hoc networks. A novel
clustering protocol, named Availability Clustering (AC), is defined under general nodes'
heterogeneity assumptions in terms of connectivity, available energy and relative
mobility. On this basis, we design and analyze a distributed and adaptive MAC protocol,
named Differentiated Distributed Coordination Function (DDCF), whose focus is to
implement adaptive access differentiation based on the node roles, which have been
assigned by the upper-layer's clustering scheme. We extensively simulate the proposed
clustering scheme by showing its effectiveness in dominating the network dynamics,
under some stressing mobility models and different mobility rates. Based on these results,
we propose a possible application of the cross-layer MAC+Clustering scheme to support
the fast propagation of alert messages in a vehicular environment.
At the same time, we investigate the integration of MAC and routing protocols in large
scale multi-hop ad-hoc networks. A novel multipath routing scheme is proposed, by
extending the AOMDV protocol with a novel load-balancing approach to concurrently
distribute the traffic among the multiple paths. We also study the composition effect of a
IEEE 802.11-based enhanced MAC forwarding mechanism called Fast Forward (FF),
used to reduce the effects of self-contention among frames at the MAC layer. The
protocol framework is modelled and extensively simulated for a large set of metrics and
scenarios.
For both the schemes, the simulation results reveal the benefits of the cross-layer
MAC+routing and MAC+clustering approaches over single-layer solutions.
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Choi, Woo-Young. "MBE-grown long wavelength InGaAlAs/InP laser diodes." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/34061.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1994.Includes bibliographical references (leaves 107-116).
by Woo-Young Choi.
Ph.D.
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Crosnier, Guillaume. "Nanodiodes laser hybrides InP sur Silicium injectées électriquement." Sorbonne Paris Cité, 2015. http://www.theses.fr/2015USPCC225.
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Face au défi que représente l'interconnect bottleneck, l'industrie microélectronique se doit de mettre en place une nouvelle technologie pour le transfert de données aux échelles inter- et intra-puces. Sur la base des performances démontrées pour les grandes distances de propagation, les interconnexions optiques constituent aujourd'hui la solution la plus étudiée pour résoudre ce défi. Si le transport de l'information au travers d'interconnexions optiques peut profiter de la technologie développée autour des guides d'onde SOI, les fonctionnalités actives n'ont pas encore atteint le même niveau de maturité. Un des points critiques restant à développer est la source laser qui doit répondre à des critères de faible seuil, d'efficacité énergétique, de taille réduite et de bande passante élevée. Au cours de cette thèse, nous avons proposé un nouveau design de nanolaser hybride InP sur SOI reposant sur une cavité rib à cristaux photoniques 1D. Cette nouvelle architecture permet d'injecter efficacement du courant électrique dans des cavités optiques de grands facteurs de qualité couplées à une circuiterie de guides d'onde en silicium. Dans ce travail, nous nous sommes d'abord intéressés à la conception des nanodiodes lasers en mettant en place les simulations électriques et optiques nécessaires. Ceci nous a permis de déterminer un design résolvant le problème du pompage électrique, jalon incontournable pour l'utilisation de tels dispositifs. Nous avons développé la technologie nécessaire à leur fabrication en s'imposant comme contrainte l'utilisation de procédés compatibles avec la technologie CMOS en matière de température. Ces études et ces développements ont abouti à la première démonstration de nanolasers pompés électriquement intégrés sur des guides d'ondes en silicium. Ces lasers émettent autour de 1. 55um et ont pu être opérés en régime continu avec des seuils de l'ordre de 100 uA à 1 V de tensionConfronted with the challenge of the interconnect bottleneck, microelectronics industry must develop a new technology for data transfer over inter- and infra-chip distances. Based on the demonstrated performance for long distances, optical interconnects are right now the most studied solution to take up to this challenge. If data transfer through optical interconnects can benefit from the developed technologies for silicon photonics, active components are still lacking maturity. One of the critical points that needs to be addressed is the development of an ultrasmall, low-power, energy-efficient laser source with high bandwidth. During this PhD, we proposed a new design of hybrid InP on SOI nanolaser relying on a 1D rib Photonic Crystal (PhC) cavity. This new architecture allows us to efficiently inject electrical current in high quality factors optical cavities coupled to silicon waveguides circuitry. In this work, we first looked at the conception of nanolasers by carrying out the required electrical and optical simulations. This allowed us to define a design solving the problem of electrical injection, a necessary step for the use of that kind of components. We also developed the technology needed for their fabrication by limiting us to processes that are CMOS-compatible in terms of temperature. These developments led to the first demonstration of electrically-pumped nanolasers fully integrated on silicon waveguides. Those nanolasers emitting around 1. 55um were operated in continuous regime with threshold values of 100 uA at a voltage of 1 V
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Fu, Liwei. "Laser curing of inks for plastic electronic applications." Thesis, University of Liverpool, 2014. http://livrepository.liverpool.ac.uk/2005999/.
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The development of the plastic electronics industry has drawn great interest and inspired technology innovations in a broad area. This has stimulated the rapid development of flexible circuitry manufacturing technologies, including advances in conductive inks, printing technology and most importantly the novel curing technology - laser based curing (or Laser Direct Write). This has the ability to replace the conventional environmentally damaging and time consuming chemical etching method in current Printed Circuit Board (PCB) manufacturing. The work presented in this thesis is an investigation into a frequency doubled Nd:YAG laser curing process of epoxy-based micro-sized particulate silver inks. This 532nm laser curing process filled the gap as no research reported for solidifying conductive microparticle silver ink using this particular laser wavelength at 532nm. This 532nm laser curing process also extended the curing technology with a fast localized heating process. The composition of the epoxy-based conductive silver ink was studied in this investigation. The laser wavelength of 532nm was selected as the silver microparticles can absorb the laser energy more efficiently without the risk of damaging the material compared to infrared wavelength. Liquid-phase epoxy-based particulate silver inks deposited on flexible substrates were irradiated by laser beam at the wavelength of 532nm. This produced a smooth and cured ink with an effectively reduced electrical resistivity. A new laser curing mechanism theory was proposed based on the presented experimental research. 532nm has shown benefits in protecting the flexible substrate used from thermal damage, owing to the high transmittance of the wavelength through the substrate material. Unlike massive solvent evaporation observed in CO2 laser curing at 10.6µm, laser curing at 532nm, transported the solvent component by expelling solvent liquid from the ink system as a result of a radical change in solvent dynamic viscosity at an increased temperature and the molecular excitation followed by the Marangoni effect. Chemical cross-linking reactions to resin system were evidenced by Fourier Transform Infrared Spectroscopy (FTIR), resulting in a fully cured ink with reduced electrical resistivity. Epoxy-based silver ink's physical properties such as density, thermal conductivity were mathematically defined based on a new temperature evolution for use in a 3-D finite element (FE) modelling. A Time-dependent solver was chosen for modelling the thermal field in a 532nm laser curing process of epoxy-based conductive silver ink within COMSOL Multiphysics 4.3b. The modelling results were compared to the experimental thermal images for FE model validation. The impact to laser curing results by changing the absorption of the epoxy-based conductive silver ink was investigated in this FE model.
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Tefft, John. "The Study of Coating and Ink Penetration into Coating Structures Using a Confocal Laser Scanning Microscope." Fogler Library, University of Maine, 2007. http://www.library.umaine.edu/theses/pdf/TefftJ2007.pdf.
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Agrawal, Ambuj. "Implementation of Application Layer Protocol for an Active RFID System." Thesis, Virginia Tech, 2011. http://hdl.handle.net/10919/34961.
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The emerging technology of active RFID tags has strong potential in the areas of real time health monitoring, sorting of cargo, and large scale inventory management because of their longer communication range and larger data storage capacity. The market of active RFID is growing very rapidly and therefore there has been an increase in the number of companies engaging in this field. But very often it is found that the products available in the market are not always suited to the application at hand. To overcome this problem, off the shelf active RFID products which were reconfigurable and followed a standard PHY and MAC layer protocol were used for this work. By reprogramming the application layer protocol of the RFID hardware, these devices were made suitable for the desired application. This also allowed the RFID tags to extend their functionality by interfacing extra modules with themselves. The work presented in this thesis describes the way in which the microcontroller on board the active RFID tags and readers can be programmed so that the functionality of the RFID hardware can be changed as per requirements. It also shows that extra modules can be added to the tag by successfully interfacing an accelerometer module with the tag.Master of Science
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Borowiec, Andrzej Haugen Harold Kristen. "Ablation and micromachining of INP with femtosecond laser pulses /." *McMaster only, 2004.
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Lutti, Julie. "Optical properties of InP/AlGaInP quantum dot laser heterostructures." Thesis, Cardiff University, 2005. http://orca.cf.ac.uk/56016/.
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Optical characterisation of InP/AlGaInP quantum dot laser structures, involving laser threshold and wavelength, optical modal gain and absorption spectra, and radiative efficiency are presented. The samples were grown by MOVPE in Sheffield University on (100) 10 off and (211)B GaAs substrates, and consist of 5 layers of self-assembled InP dots, with each layer grown on Alo.3Gao.7InP and placed in a GaInP quantum well. A record low threshold current density of 290A/cm2 at a wavelength of 740nm for a 1.6 mm-long device with uncoated facets is obtained from one of the sample grown on (100) 10 off substrate at 690 C. This sample has an internal optical mode loss of 4 1 cm"1 and an internal quantum spontaneous emission efficiency of 30% for current densities corresponding to the threshold. The ground state modal gain is shown to saturate at 17cm"1 at room temperature, which is about lA of the full population inversion limit, and the saturation level increases with decreasing temperature. A sample grown at a lower temperature of 650 C has higher optical mode loss (7.5 1 cm"1) and quantum efficiency under 15%. A sample grown on (211)B substrate exhibits optical transitions at higher photon energies, consistent with smaller dot sizes. The thesis also presents an analysis of the segmented contact technique used to measure gain and absorption spectra, determining criteria for the excitation and detection geometries required to ensure accurate measurement. It is shown that the collection angle and device nearfield should be limited so that rays that intercept the stripe edges are not collected. If this is not satisfied, the measurement underestimates the modal gain. An exponential variation of the measured ASE upon stripe length cannot be taken as evidence for a correct collection geometry.
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Al-Ghamdi, Mohammed Saad. "Optoelectronic properties of InP AlGaInP quantum dot laser diodes." Thesis, Cardiff University, 2009. http://orca.cf.ac.uk/54948/.
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The aim of this thesis is to understand and optimise the optoelectronic properties of InP quantum dot laser diodes which operate in the range around 730nm required for various application such as the photodynamic therapy. The properties of wafers with two barrier widths, 8 and 6nm, each grown at different temperatures, 690, 710, 730 and 750T, and consisting of 5 layers of dots forms from different quantity of deposited material, 2, 2.5 and 3ML, are described and investigated. The laser and multisection devices of these structures are used to determine threshold current density, lasing wavelength, modal absorption, modal gain and spontaneous emission spectra. The modal absorption spectra show three different dot size distributions, small, large and very large dots. Their variation with growth temperature results in a blue shift accompanied by an increasing number of states while the variation with quantity of deposited material shows only an increase to the number of states. The lasing wavelength variation with growth temperature covers a range between 715–745nm. The threshold current density as a function of temperature for 2000/m long laser devices grown at temperature of 750°C exhibits a distinctive dependence on the operating temperature and becomes less pronounced when the growth temperature reduces. This is explained in terms of the carrier distributions in the quantum dot and quantum well states without invoking an effect from Auger recombination. The optimisation of threshold current density can be reached by using structures with higher barrier width grown at low temperature and deposited with high quantity of quantum dot material to minimise both the affect of the very large dot, which contain a number of defects associated with them, and carrier leakage from quantum dot to quantum well states. This reduces the room temperature threshold current density to ISO A/cm 2 for 2mm long lasers with uncoated facets.
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Mladen, Stančić. "Model toplotnih svojstava štampanih odjevnih predmeta." Phd thesis, Univerzitet u Novom Sadu, Fakultet tehničkih nauka u Novom Sadu, 2016. http://www.cris.uns.ac.rs/record.jsf?recordId=96217&source=NDLTD&language=en.
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U disertaciji su predstavljena istraživanja uticajnih parametaradigitalne štampe na toplotna svojstva odjevnih predmeta, pri čemu sukao parametri procesa štampe ispitani uticaji različitog brojananosa boje u štampi i različite tonske pokrivenosti. Odštampaniuzorci podvrgnuti su ispitivanjima toplotnih karakteristikaštampanih tekstilnih materijala. Na bazi analize izabranihparametara razvijen je model toplotnih svojstava štampanih odjevnihpredmeta koji ima poseban značaj za predviđanje toplotno fiziološkeudobnosti odjeće tokom upotrebe.У дисертацији су представљена истраживања утицајних параметарадигиталне штампе на топлотна својства одјевних предмета, при чему сукао параметри процеса штампе испитани утицаји различитог бројананоса боје у штампи и различите тонске покривености. Одштампаниузорци подвргнути су испитивањима топлотних карактеристикаштампаних текстилних материјала. На бази анализе изабранихпараметара развијен је модел топлотних својстава штампаних одјевнихпредмета који има посебан значај за предвиђање топлотно физиолошкеудобности одјеће током употребе.
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Olivier, Laurent. "??tude des propri??t??s physiques du Sr[indice inf??rieur 0,9]Nd[indice inf??rieur 0,1]Cu0[indice inf??rieur 2] en couches minces d??pos??es par ablation laser puls??" Mémoire, Universit?? de Sherbrooke, 2014. http://savoirs.usherbrooke.ca/handle/11143/76.
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Les chercheurs savent depuis longtemps que la supraconductivit?? est engendr??e par le couplage de paires d?????lectrons, appel??es paires de Cooper. Par contre, l???origine de l???inter-action conduisant ?? l???attraction effective entre les ??lectrons formant les paires demeure mal comprise pour certains mat??riaux d??couverts durant les trente derni??res ann??es. Dans ce m??moire, la supraconductivit?? a ??t?? induite dans des cuprates dop??s aux ??lectrons faisant partie de la famille des infinite-layers (IL), ayant la forme Sr[indice inf??rieur 1???x]Nd[indice inf??rieur x]CuO[indice inf??rieur 2]. Les IL ne peuvent ??tre d??pos??s en couches minces par la technique d???ablation laser que depuis tr??s r??cemment. L?????tude syst??matique de ces compos??s reste donc enti??rement ?? accomplir. Les IL ont ??galement une structure cristalline extr??mement simplifi??e qui facilite l???interpr??tation des ph??nom??nes physiques mesur??s en laboratoire.
L?????tude des IL est un v??ritable tour de force. Plusieurs groupes de recherche dans le monde tentent de les synth??tiser en couches minces avec beaucoup de difficult??. Ces mat??riaux sont m??tastables et d???une sensibilit?? d??concertante. Obtenir des couches minces exemptes de phases parasites est un travail de longue haleine. Ce d??fi a non-seulement ??t?? relev??, mais il a ??t?? possible de r??aliser de la microfabrication sur les couches minces crues, rendant toute caract??risation des propri??t??s de transport beaucoup plus pr??cise. L???ablation laser puls??e est la technique qui a ??t?? utilis??e pour faire la croissance des couches minces ??tudi??es. La diffraction des rayons-X a permis l???identification des phases de la structure cristalline, mais surtout l?????tude des propri??t??s structurales des couches minces d??pos??es. Une analyse des param??tres en plan (a) et hors plan (c) de la cellule unit?? de ces couches minces en fonction des conditions de croissance s???est av??r??e essentielle. Il a ??t?? remarqu?? que le param??tre hors plan joue un r??le limitant dans l?????mergence de la supraconductivit??. Des mesures de r??sistivit?? ?? tr??s basses temp??ratures et sous champs magn??tiques intenses ont permis d?????tablir un lien entre l???apparition de la supraconductivit?? et la grandeur du param??tre hors plan de la structure cristalline. Une transition compl??te ne semble ??tre possible que lorsque le param??tre hors plan se trouve sous une grandeur critique, c = 3,41[A rond majuscule].
Des mesures d???effet Hall en fonction de la temp??rature sur des ??chantillons ayant diff??rentes valeurs du param??tre hors plan ont permis de d??terminer l?????volution des porteurs de charges pr??sents en fonction de c. Les ??chantillons supraconducteurs sugg??rent que la pr??sence de trous comme porteurs de charge est essentielle ?? l?????mergence de la supraconductivit??. Leur pr??sence semble diminuer rapidement ?? partir d???un param??tre hors plan plus grand que 3,41[A rond majuscule]. Il est possible d?????tablir un lien fondamental entre le comportement de la densit?? observ?? et celui d???une autre famille de supraconducteurs, les dop??s aux ??lectrons ayant une structure T???.
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Cakmak, Bülent. "Fabrication and characterisation of InP and GaAs based optoelectronic components." Thesis, University of Bristol, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322354.
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Farmer, Corrie David. "Fabrication and evaluation of In0.52Al0.48As/In0.53Ga0.47As/InP quantum cascade laser." Thesis, University of Glasgow, 2000. http://theses.gla.ac.uk/6883/.
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InP-based quantum cascade (QC) lasers were fabricated following the design reported by Faist et al. with the initial aim of applying them in gas sensing applications. The lasers were characterised by our collaborators, Cockburn et al. Unfortunately, the performance of our QC lasers (QCLs) did not live up to expectations, and the gas sensing objectives became replaced with resolving the issues of their poor performance. This was achieved through a mixture of laser fabrication, characterisation, and optical and thermal waveguide modelling. The devices fabricated included mesa-etched QCLs, shallow-etched QCLs, and novel native-oxide defined QCLs.2D thermal modelling using a commercial finite element modelling package was carried out to solve the 2D non-linear thermal diffusion equation for all of the structures listed above, as well as for InP-clad and buried heterostructure configurations. The temperature elevations, distributions and heat flow vectors were calculated under high, but not unrealistic thermal power generation in the active waveguide core. The relative effectiveness at dissipating heat was judged using these results. The modelling indicated the presence of high temperatures and thermal gradients across the active waveguide core under continuous wave (CW) operation. The thermal resistance derived through the use of the thermal modelling agreed very well with that calculated by Faist et al. from experimental data. The optical modelling, which was instrumental in resolving the anomalous behaviour of our QC lasers, comprised of two parts. First, modelling of the dielectric permittivity gave values of n and a for InP, In0.52Al0.48As and In0.53Ga0.47As as a function of the free-carrier density and wavelength. The calculations were made using single and multiple-oscillator models with a free-carrier contribution in the form of a classical Drude expression. The dependencies of the electron mass and electron mobility on the free electron density were taken in the calculations. These values were used to perform 2D optical modelling of the waveguide using a commercial, fully vectorial waveguide mode solver. This yielded the effective index, confinement factor, facet reflectivity, waveguide loss and far-field distribution for each mode. These, in turn, were used to calculate the threshold gain for each mode. Perhaps the most important findings were the prediction of the existence of higher order transverse modes, that these modes can have low values of gth (comparable or better than that of the fundamental mode of the waveguide) and that the collection efficiency will vary dramatically from mode to mode. The modelling also indicated that the performance of the QCLs would suffer greatly with an increase in the InP substrate doping level, even just from 1x1018 cm-3 to 3x1018 cm-3.
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Shakourian, Gelareh. "Enhanced De-inking and Recyclability of Laser Printed Paper by Plasma-Assisted Fiber Coating." Thesis, Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10572.
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Office waste paper is one of the fastest growing segments of the recycled fiber industry. Toner particles are rigid, insoluble and difficult to disperse and detach from fibers. Therefore papers made from recycled office waste having high toner content will contain noticeable ink particles. This work will consider an alternative way of efficient de-inking using plasma polymers which will not affect the fibers chemically or mechanically. The focus is development and characterization of plasma-deposited films to serve as a barrier film for the adhesion of ink toner to the paper fibers and thereby enhance ink lift off from the fibers. The plasma treated paper is coated with fluorocarbon (PFE) and polyethylene glycol (PFE) films, with constant thickness of PFE and varying the thickness of PEG by 1500, from 1500 to 4500, for the three cases studied (PFE greater than PEG, PFE=PEG, PFE less than PEG). Handsheets were made using virgin fibers to eliminate effects of fillers. Once the sheets were coated and printing performed, they were re-pulped and both the slurry and the de-inking surfactant were placed in a flotation cell. Handsheets were made from the collected foam and stock and were scanned for particle count. The results indicated higher ink loss for the cases with increased thickness of polymer films. A handsheet with a 7500 film (PFE = 3000 and PEG = 4500) showed 61% ink removal compared to 38% for handsheets with no film deposited. There was also less material loss for the cases with higher polymer film thickness.
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CALLIGER, OLIVIER. "Etude de l'integration optoelectronique et photonique sur inp : laser-mesfet et laser-convertisseur fm->am." Paris 6, 1994. http://www.theses.fr/1994PA066517.
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L'objet de cette these est l'etude d'une integration optoelectronique (laser-mesfets) et d'une integration photonique (laser fsk-convertisseur fm->am) sur inp. Pour l'integration optoelectronique, des monolithes composes d'un laser brs emettant a 1. 3m et de deux transistors mesfet de materiau gaas ont ete realises. L'heteroepitaxie du gaas sur inp par epitaxie en phase vapeur aux organometalliques (epvom) est utilisee pour deposer les couches necessaires aux transistors. Les monolithes ainsi fabriques montrent une bande passante de 7ghz et un debit de modulation de 8gbit/s. Le monolithe concu pour l'integration photonique est compose d'un laser fsk modulable a 10gbit/s et d'un convertisseur fm->am. Il a pour objectif de compenser la dispersion chromatique de la fibre standard et ainsi de permettre une distance de propagation plus importante sans regeneration du signal a un debit eleve (>=10gbit/s). Un modele simulant le systeme laser-convertisseur-fibre a ete realise, permettant de definir les parametres du convertisseur (bande passante, finesse). A partir de ces caracteristiques, une structure du convertisseur a ete choisie: un resonateur de bragg couple contradirectionnellement avec un second guide. Ses parametres (epaisseur des deux guides, pas et profondeur du reseau) sont calcules via la methode des modes couples afin d'obtenir les caracteristiques desirees pour realiser une transmission sur 100km a 10gbit/s. Les etapes technologiques de fabrication de ce monolithe ont ete definies et celles jugees les plus critiques mises au point: la gravure profonde du reseau (>0. 1m) et du ruban (2-3m)
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Caverhill, James Ross. "Investigation into the use and effects of a Q-switched Nd:YAG laser for the removal of ink from paper." Thesis, Northumbria University, 2004. http://nrl.northumbria.ac.uk/1608/.
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A Q-switched Nd:YAG laser is used to remove ballpoint pen ink from 'Roma', a 100% cotton rag art paper. The laser was operated at 1064 run, pulse duration 87 ns, and using a nominal fluence of 41 ± 12 Jcm-2. By shortening the pulse length (63 and 26 ns), using a Glan-Thompson prism the ink removal threshold was reduced to 24 ± 7 and 20 ± 6 Jcm-2 respectively. The physical damage to the paper is observed under SEM and found to be less disruptive to the surface fibres than contemporary mechanical methods of ink removal; scalpel and eraser. The tensile strength of laser treated paper is measured and found to remain unaffected below ink removal threshold fluences, although there is an increased tendency to tear at laser treatment sites. Repeat testing with artificially aged laser treated samples shows a marked decrease in tensile strength in comparison with an aged reference. Laser treated paper (nominal fluence of 41 ± 12 Jcm2, pulse length 87 ns) is tested for evidence of thermal degradation, via oxidation and depolymerisation. The tests include the Russell effect test for the presence of peroxides (oxidation), the methylene blue test for the presence of carboxyl groups (oxidation), FTIR spectroscopy to determine the presence of carboxyl, carbonyl, and conjugated groups (oxidation), and GC/MS to test for the presence of sugars (depolymerisation). The tests suggest that there is thermal degradation predominantly via depolymerisation. This is supported by repetition of the tests on laser treated samples prepared in an argon atmosphere. The laser treated paper is subjected to accelerated ageing in a humid oven to simulate natural is considered to be a reaction between the sizing agent (gelatin) and sugars formed during depolymerisation The tests are repeated on 'Roma' paper laser treated with shorter laser pulses (nominal fluence 24 ± 7 and 20 ± 6 Jcm-2, pulse durations of 63 and 26 ns), and this is found to have significantly less physical and chemical effect on the paper. Accelerated ageing of short pulse laser treated samples did not result in colour changes with respect to reference samples, indicating a more limited chemical interaction with the paper.
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Trejos, Tatiana. "Evaluation of the Evidential Value of the Elemental Composition of Glass, Ink and Paper by Laser-Based Micro-Spectrochemical Methods." FIU Digital Commons, 2012. http://digitalcommons.fiu.edu/etd/755.
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Elemental analysis can become an important piece of evidence to assist the solution of a case. The work presented in this dissertation aims to evaluate the evidential value of the elemental composition of three particular matrices: ink, paper and glass.
In the first part of this study, the analytical performance of LIBS and LA-ICP-MS methods was evaluated for paper, writing inks and printing inks. A total of 350 ink specimens were examined including black and blue gel inks, ballpoint inks, inkjets and toners originating from several manufacturing sources and/or batches. The paper collection set consisted of over 200 paper specimens originating from 20 different paper sources produced by 10 different plants.
Micro-homogeneity studies show smaller variation of elemental compositions within a single source (i.e., sheet, pen or cartridge) than the observed variation between different sources (i.e., brands, types, batches). Significant and detectable differences in the elemental profile of the inks and paper were observed between samples originating from different sources (discrimination of 87 – 100% of samples, depending on the sample set under investigation and the method applied). These results support the use of elemental analysis, using LA-ICP-MS and LIBS, for the examination of documents and provide additional discrimination to the currently used techniques in document examination.
In the second part of this study, a direct comparison between four analytical methods (µ-XRF, solution-ICP-MS, LA-ICP-MS and LIBS) was conducted for glass analyses using interlaboratory studies. The data provided by 21 participants were used to assess the performance of the analytical methods in associating glass samples from the same source and differentiating different sources, as well as the use of different match criteria (confidence interval (±6s, ±5s, ±4s, ±3s, ±2s), modified confidence interval, t-test (sequential univariate, p=0.05 and p=0.01), t-test with Bonferroni correction (for multivariate comparisons), range overlap, and Hotelling’s T2 tests. Error rates (Type 1 and Type 2) are reported for the use of each of these match criteria and depend on the heterogeneity of the glass sources, the repeatability between analytical measurements, and the number of elements that were measured. The study provided recommendations for analytical performance-based parameters for µ-XRF and LA-ICP-MS as well as the best performing match criteria for both analytical techniques, which can be applied now by forensic glass examiners.
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Takeda, Yoshikazu, Keiji Fujita, Naoteru Matsubara, Naoki Yamada, Satofumi Ichiki, Masao Tabuchi, and Yasufumi Fujiwara. "Layer structure analysis of Er δ-doped InP by x-ray crystal truncation rod scattering." American Institute of Physics, 1997. http://hdl.handle.net/2237/7024.
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Klaime, Kamil. "Laser à blocage de modes à base de boîtes quantiques InAs/InP pour les télécommunications optiques." Phd thesis, INSA de Rennes, 2013. http://tel.archives-ouvertes.fr/tel-00905711.
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L'objectif de la thèse concerne le développement de lasers à semi-conducteur à blocage de modes qui présentent un grand intérêt pour les systèmes de télécommunications optiques à très haut débit (WDM, OTDM, radio sur fibre...).Les nanostructures à base de boites quantiques (BQs) possèdent des propriétés remarquables grâce au confinement 0D des porteurs de charge. Leur utilisation dans les lasers à blocage de modes a donné lieu à des avancées importantes en terme de génération d'impulsions très courtes à haute fréquence et avec un très faible niveau de bruit.Durant la thèse, une optimisation de la croissance des structures lasers à BQs InAs sur substrat InP(113)B a été menée afin d'accroître le nombre de plans de BQs tout en assurant une forte densité pour maximiser le gain modal. Le travail a également porté sur l'utilisation de substrats InP(001) désorienté et l'obtention d'empilement de plans de BQs de faible anisotropie. Une optimisation de la technologie des lasers monomode de type " shallow-ridge " a été réalisée sur substrat conventionnel InP (001). Nous avons confirmé l'intérêt des BQs pour améliorer l'efficacité d'injection grâce à une réduction de la diffusion latérale des porteurs. Le blocage de modes a été obtenue sur des lasers à mono-section et double sections à base de BQs InAs élaborés sur InP (001) désorienté et InP(113))B, à des fréquences de répétitions allant de 20 jusqu'à 83 GHz. Les spectres RF présentent des pics de faibles largeurs (jusqu'à 20 kHz) qui indique un faible bruit de phase. Enfin, une étude a été menée sur le comportement en température des lasers à blocage de modes passif à double sections à base de BQs ou de BatQs InAs/InP.
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Musaev, Omar Wróbel Jerzy. "UV laser assisted processing of InP at different ambient conditions with variable number of pulses and fluences." Diss., UMK access, 2006.
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Thesis (Ph. D.)--Dept. of Physics and School of Computing and Engineering. University of Missouri--Kansas City, 2006."A dissertation in physics and telecommunications networking." Advisor: Jerzy Wrobel. Typescript. Vita. Title from "catalog record" of the print edition Description based on contents viewed Nov. 1, 2007. Includes bibliographical references (leaves 185-190). Online version of the print edition.
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Raja, Sandeep. "The systematic development of Direct Write (DW) technology for the fabrication of printed antennas for the aerospace and defence industry." Thesis, Loughborough University, 2014. https://dspace.lboro.ac.uk/2134/14930.
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Low profile, conformal antennas have considerable advantages for Aerospace and Military platforms where conventional antenna system add weight and drag. Direct Write (DW) technology has been earmarked as a potential method for fabricating low profile antennas directly onto structural components. This thesis determines the key design rules and requirements for DW fabrication of planar antennas. From this, three key areas were investigated: the characterisation of DW ink materials for functionality and durability in harsh environments, localised processing of DW inks and the optimisation of DW conductive ink material properties for antenna fabrication. This study mainly focused on established DW technologies such as micro-nozzle and inkjet printing due to their ability to print on conformal surfaces. From initial characterisation studies it was found that silver based micro-nozzle PTF inks had greater adhesion then silver nano-particle inkjet inks but had lower conductivity (2% bulk conductivity of silver as opposed to 8% bulk conductivity). At higher curing temperatures (>300??C) inkjet inks were able to achieve conductivities of 33% bulk conductivity of silver. However, these temperatures were not suitable for processing on temperature sensitive surfaces such as carbon fibre. Durability tests showed that silver PTF inks were able to withstand standard aerospace environments apart from Skydrol immersion. It was found that DW inks should achieve a minimum conductivity of 30% bulk silver to reduce antenna and transmission line losses. Using a localised electroplating process (known as brush plating) it was shown that a copper layer could be deposited onto silver inkjet inks and thermoplastic PTF inks with a copper layer exhibiting a bulk conductivity of 66% bulk copper and 57% bulk copper respectively. This was an improvement on previous electroless plating techniques which reported bulk copper conductivities of 50% whilst also enabling DW inks to be plated without the need for a chemical bath. One of the limitations of many DW ink materials is they require curing or sintering before they become functional. Conventional heat treatment is performed using an oven which is not suitable when processing DW materials onto large structural component. Previous literature has investigated laser curing as means of overcoming this problem. However, lasers are monochromatic and can therefore be inefficient when curing materials that have absorption bands that differ from the laser wavelength. To investigate this, a laser diode system was compared to a broadband spot curing system. In the curing trials it was found that silver inks could be cured with much lower energy density (by a factor of 10) using the broadband white light source. Spectroscopy also revealed that broadband curing could be more advantageous when curing DW dielectric ink materials as these inks absorb at multiple wavelengths but have low heat conductivity. Themodynamical modelling of the curing process with the broadband heat source was also performed. Using this model it was shown that the parameters required to cure the ink with the broadband heat source only caused heat penetration by a few hundred micro-metres into the top surface of the substrate at very short exposure times (~1s). This suggested that this curing method could be used to process the DW inks on temperature sensitive materials without causing any significant damage. Using a combination of the developments made in this thesis the RF properties of the DW inks were measured after broadband curing and copper plating. It was found that the copper plated DW ink tracks gave an equivalent transmission line loss to a copper etched line. To test this further a number of GPS patch antennas were fabricated out of the DW ink materials. Again the copper plated antenna gave similar properties to the copper etched antenna. To demonstrate the printing capabilities of the micro-nozzle system a mock wireless telecommunications antenna was fabricated on to a GRP UAV wing. In this demonstrator a dielectric and conductive antenna pattern was fabricated on to the leading edge of the wing component using a combination of convection curing and laser curing (using an 808nm diode laser).
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Yip, Raymond Yew-Fai. "Growth, characterization and design of InP-based strained-layer multiple quantum wells for optical modulator devices." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape11/PQDD_0015/NQ46642.pdf.
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Subedi, Kiran. "Elemental Analysis of Printing Inks Using Tandem Laser- Induced Breakdown Spectroscopy and Laser Ablation Inductively Coupled Plasma Mass Spectrometry." FIU Digital Commons, 2015. http://digitalcommons.fiu.edu/etd/2263.
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As a consequence of the widespread use of computers coupled to high-quality printers and different types of papers, forgery, counterfeiting, change of wills, anonymous letter writing and felonious use of the documents have become serious problems. Forensic analysts are always seeking methods that can provide reliable information on whether a specimen collected at the crime scene is linked to the crime or to a source of known origin. Sensitive methods that can provide more detailed characterization of natural or man-made materials or even provide information not previously available to forensic examiners.
Recent advances in rapid solid sampling of materials using laser ablation (LA) coupled to inductively coupled plasma mass spectroscopy (ICP-MS) have led to this analytical method to be regarded as the “gold standard” in the field of elemental analysis for trace level components in solids. Another, emerging, analytical technique that uses the same laser pulse to generate a plasma that can be interrogated with spectroscopy is laser induced break down spectroscopy (LIBS).
The analysis of ink and paper is also possible because of the surface removal effect of laser interactions with the samples. In the present study, printing inks were analyzed using LIBS, LA-ICP-MS and both of them in tandem mode. In the tandem setup, the light generated during the relaxation of the excited species (LIBS) was used to create a spectral signature of the elements, and the mass-to-charge ratio of the ejected particles (ICP-MS) was used to create a mass spectrum.
For a set of 319 printing ink samples, LA-ICP-MS alone provided discrimination greater than 99%. A subset of 43 printing inks, having a very similar elemental profile, was analyzed by tandem LIBS/LA-ICP-MS. The fusion of LIBS and LA-ICP-MS provided additional discrimination through the detection of elements like Ca, Si, Fe, and K by LIBS, that are difficult to detect and confirm using standalone ICP-MS because of the spectral interferences (isobaric and polyatomic) involved. The combination of these two sensors was found to minimize the individual limitations and provide a more complete and representative chemical characterization of printing inks.
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Hazell, John Frederick. "Dielectric-enhanced quantum-well intermixing in [lámbdha] = 1.55 [micron]m InGaAsP/InP laser structures /." *McMaster only, 2000.
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Bennett, Brian R. (Brian Robert). "Molecular beam epitaxial growth and charcterization of mismatched InGaAs and InAlAs layers on InP." Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/33483.
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Elias, Georges. "Epitaxie des boîtes quantiques InAs/InP(001) de hautes performances pour les applications laser." Rennes, INSA, 2009. http://www.theses.fr/2009ISAR0018.
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Cette thèse porte sur l’étude de la croissance des boîtes quantiques (BQs) d’InAs/InP(001), et son application pour la réalisation des composants optoélectroniques émettant à la longueur d’onde des télécommunications optiques (1,55µm). Les BQs sont formées en épitaxie par jets moléculaires selon le mode de croissance Stranski-Krastanow. Le travail de la thèse s’est focalisé sur l’élaboration de BQs sur substrat d’orientation (001) qui est le plus utilisé dans l’industrie mais sur lequel la croissance des BQs apparaît plus complexe. Dans un premier temps nous passons en revue les modèles dits de « nucléation-croissance », qui permettent de rendre compte la plupart des résultats expérimentaux pour les systèmes InAs/GaAs et InAs/InP. La morphologie des nanostructures sur substrat InP(001) est ensuite étudiée en fonction des paramètres de croissance, par des moyens d’analyses structurales et optiques. Nous observons une transition de la forme des nanostructures (de fils à boîtes) qui peut être interprétée dans le cadre du modèle énergétique de Tersoff. Nous mettons en évidence que cette transition est reliée à la différence d’énergie de surface des facettes parallèles à [110] et [1-10] qui dépend fortement du flux d’arsenic Dans une deuxième partie, nous étudions la croissance sur des surfaces vicinales d’InP(001). L’utilisation d’une désorientation spécifique (vers [1-10]) a permis de réduire l’effet de l’anisotropie de la surface (001) et de favoriser la nucléation de BQs isotropes. L’optimisation du flux d’arsenic pour cette désorientation, conduit à une forte densité de BQs, (9. 1010cm-2) et une réduction de leurs dimensions. La fabrication de structures lasers à BQs a permis l’obtention de l’émission laser à température ambiante avec des performances en terme de courant de seuil (141 A/cm2) comparables aux meilleurs résultats reportés dans la littératureInAs quantum dots grown on InP substrate are attractive for optoelectronic devices working at 1. 55 µm used in long haul telecommunication network. This PhD work concerns the formation of QD by molecular beam epitaxy on InP (001) substrates. Such substrate orientation is largely used in industry for device elaboration; however the formation of QD on it appears complex. In a first part the trend of QD structural characteristic changes versus growth parameters are reviewed and discussed in the frame of a classical nucleation and growth model. We show as a function of nanostructure size, a shape change from wires to quantum dots. We evidence the key role of the arsenic pressure on this transition. Calculations based on Tersoff analytical expression of the nanostructure energy show that the shape change can be related to the différence of the surface energy of their facets. In the second part of this work the growth on misoriented InP(001) substrates is investigated. Alter optimization of arsenic pressure during growth and substrates miscut direction, a high density (9 1010 QD/cm2) of small quantum dots has been achieved on InP(001). Further investigations allow us to achieve QD laser on InP (001) vicinal substrates with a threshold current density as low as 141 A/cm2
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GUICHARDON, ANTOINE. "Caracterisation et modelisation du courant de fuite d'un laser ingaasp/inp a ruban enterre." Paris 11, 1995. http://www.theses.fr/1995PA112238.
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Cette these expose une analyse electrique des composants laser a semi-conducteur basee sur le calcul a 2d de la repartition du courant dans la structure a l'aide d'un outil de resolution numerique par elements finis. La modelisation du composant a partir de la description de la structure reelle s'appuie sur l'etude prealable des differentes regions elementaires caracterisees et modelisees independamment. Cette approche est appliquee au laser ingaasp/inp brs dans le cadre de l'optimisation de ses performances statiques. Des caracterisations i(v) sont tout d'abord effectuees sur des diodes test permettant de mesurer le courant a travers la jonction p-n, la region implantee par des protons et la couche active de la structure. Leurs caracteristiques sont etudiees et modelisees par le logiciel de simulation 2d dans le modele de derive/diffusion. Le courant total du composant est calcule en prenant en compte globalement la modelisation des differentes regions. L'analyse debouche sur un modele electrique du fonctionnement du laser en regime d'impulsion, permettant une interpretation des caracteristiques i(v) et p(i) en impulsion. Le courant de fuite est localise et evalue en fonction du courant total a la temperature constante de 20c. Le role de l'interface entre les regions implantees et non implantees est mis en evidence au niveau du courant de seuil et celui de la jonction p-n au niveau de la limitation de la puissance
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Mustaffa, Muhammad Ubaidah Syafiq. "Alternative Uses of CZTS Thin Films for Energy Harvesting." Doctoral thesis, Università degli studi di Trento, 2021. http://hdl.handle.net/11572/315176.
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The search for renewable energy resources and ways to harvest them
has become a global mainstream topic among researchers nowadays,
with solar cells and thermoelectric generators among the energy
harvesting technologies currently being researched in vast. CZTS
(Cu2ZnSnS4), a p-type semiconducting material initially researched to
replace copper indium gallium selenide (CIGS) as the light absorbing
layer in thin film solar cells, was studied in this doctoral work for
alternative uses in energy harvesting. This work aims to systemically
investigate the prospects of CZTS to be used as hole transport layers
and thermoelectric generators.
CZTS thin film was successfully fabricated using a versatile
approach involving hot-injection synthesis of CZTS nanoparticles ink
followed by spin coating and thermal treatment. Results obtained
revealed the possibility to fine control CZTS thin film fabrication based
on ink concentration and spin. Besides that, thermal treatment
temperature was found to affect the film’s overall properties, where an
increase in thermal treatment temperature improved the degree of
crystallinity and electrical properties. In addition, a phase change going
from less stable cubic and wurtzite structures to a more stable tetragonal
structure was also observed. Furthermore, CZTS was found to be a good
candidate to replace the commonly used organic hole transport layer in
perovskite solar cells, with potentials in improving performance and
stability. In addition, CZTS also possessed good transport properties to
be a potential p-type material in a thermoelectric generator, with the
preliminary performance of fabricated CZTS/AZO thermoelectric
generator showing a maximum power output of ~350 nW at ~170 K
ΔT.
These findings provide new perspectives for CZTS in energy harvesting
applications, despite the struggle in its development as the absorber
layer in thin film solar cells. Besides providing a deeper understanding
of CZTS and its vast possibilities in energy harvesting applications,
promising future research stemming from this work is also limitless,
reinventing ways in material studies, in search of alternative
applications which may be of benefit.
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Teixeira, Ana Cristina Coelho Dal Rio. "Estudo da halitose em pacientes com tonsilite cronica caseosa, tratados por criptolise com laser de 'CO IND. 2'." [s.n.], 2007. http://repositorio.unicamp.br/jspui/handle/REPOSIP/309198.
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Orientador: Ester Maria Danielli NicolaTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Ciencias Medicas
Made available in DSpace on 2018-08-08T17:35:33Z (GMT). No. of bitstreams: 1 Teixeira_AnaCristinaCoelhoDalRio_D.pdf: 10054525 bytes, checksum: 9e44ad7f8a52711069574871543224a6 (MD5) Previous issue date: 2007
Resumo: Halitose é um sintoma constrangedor com grande impacto social. Afeta milhões de pessoas, no mundo todo, que gastam muitos recursos em produtos na tentativa de obter a melhora do hálito. Uma abordagem científica da halitose justifica-se, uma vez que esta diminui a qualidade de vida e pode ser indicativa de doenças que necessitam de diagnóstico e tratamento específico. Inicialmente, foi elaborado um protocolo de avaliação da halitose baseado na literatura e na experiência pessoal, com o objetivo de minimizar custos, evitar exames desnecessários e orientar o diagnóstico. A segunda etapa do trabalho consistiu na mensuração objetiva do hálito (através da técnica de Halitometria dos Compostos Sulfurados Voláteis) em uma população com Tonsilite Crônica Caseosa (TCC), pois esta apresenta íntima relação com a queixa de halitose. O perfil halitométrico dos portadores de TCC ainda não havia sido descrito. Observou-se que a presença do cáseo é um fator preditivo de halitometria anormal nessa população. Na terceira etapa, foi estudado o impacto da criptólise por coagulação com laser de CO2 em indivíduos portadores de TCC e queixa de halitose. A técnica demonstrou ser segura e bem tolerada, e os valores das halitometrias foram normalizados após o tratamento, em virtude da diminuição da formação de cáseos
Abstract: Halitosis is a very constraint symptom with a significant social impact. It is estimated that halitosis affects millions of people and these people regularly spend resources in products in order to improve their halitus. The study of halitosis in a scientific approach is justified once halitosis causes social restriction, decreases life quality and can be an indication of serious diseases that need diagnosis and specific treatment. Initially, a halitosis proposal for assessment protocol was elaborated based on the literature and on personal experience, with the objective of minimize costs, avoid unnecessary procedures and orientate diagnosis. The second part was the mensuration of halitosis (through the Volatile Sulphur Compounds Halitometry) in a population with Chronic Caseous Tonsillitis (CCT), since this disease is strongly related to the halitosis complaint. The halitometry profile in patients with CCT had not yet been described. In this study it was observed that caseum presence is a predictive factor for abnormal halitometry. On the third part, the impact of CO2 laser cryptolysis by coagulation in patients with CCT and halitosis complaint was studied. The technique using CO 2 laser ablation demonstrated to be safe, well tolerated, and halitometry values became normal after treatment, due to the decrease in caseum formation
Doutorado
Ciencias Biomedicas
Doutor em Ciências Médicas
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Armistead, C. J. "Far-infrared laser spectroscopy of neutral and negatively charged shallow donors in GaAs and InP." Thesis, University of St Andrews, 1987. http://hdl.handle.net/10023/14167.
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An optically pumped far-infrared laser and superconducting magnet have been used to perform high resolution studies of the energy levels of neutral and negatively charged shallow donors in high purity n-GaAs and n-InP in magnetic fields where the dimensionless magnetic field gamma is approximately one (where gamma=hoc/(2R*), hoc is the cyclotron energy and R* is the Coulomb binding energy). The central cell structure caused by the presence of different shallow donor species has been studied on the 1s-2p+1,0 transitions of neutral shallow donors in undoped GaAs samples grown by molecular beam epitaxy, liquid phase epitaxy and vapour phase epitaxy (VPE). VPE material showed two new shallow donor species with negative central cell shifts. The ls-2p-1 transition at magnetic fields where gamma > 1 shows exceptionally well resolved central cell structure. Detailed structure at magnetic fields below the 1s-2p+2 transition is due to transitions from the is to higher excited states. Samples of undoped high purity InP grown by the VPE, metal organic chemical vapour deposition and bulk growth techniques have been studied. VPE samples always show a strong component related to sulphur though some also show a strong silicon related component, and some show up to 7 components. A bulk, sample showed two strong components shallower than silicon which may have negative central cell shifts. Transitions between the excited states of neutral shallow donors in GaAs have been studied. Recent theoretical work by Makado (1982) describes the transition energies very well. Clearly resolved central cell structure is observed on inter-excited state transitions involving the 2s state. The first unambiguous observation of negatively charged shallow donors (D-states) in GaAs is reported. Simultaneous observations of transitions involving D-states, the cyclotron resonance and inter-excited state transitions of neutral donors over a wide magnetic field range, 0.03 < gamma < 3.5, highlight the differences between the transitions and the relative effects of optical excitation, temperature, magnetic field and electric field bias.
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Ross, Anthony J. III. "Laser Machining and Near Field Microwave Microscopy of Silver Inks for 3D Printable RF Devices." Scholar Commons, 2017. http://scholarcommons.usf.edu/etd/6944.
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3D printable materials for RF devices need improvement in order to satisfy the demand for higher frequency and lower loss performance. Characterization of materials that have shown improvements of conductor conductivity have been performed. By using a laser machining technique the loss of a 3D printed 2.45 GHz microstrip Square Open Loop Resonator (SOLR) bandpass filter has been shown to improve by 2.1dB, along with an increase in bandwidth from 10% to 12.7% when compared to a SOLR filter that has not been laser machined. Both laser machined and microwaved silver inks have been mapped for conductivity using a Near Field Microwave Microscope (NFMM) and have shown improvement of conductivity compared to inks that have been cured using standard methods.
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Lamponi, Marco. "Lasers inp sur circuits silicium pour applications en telecommunications." Phd thesis, Université Paris Sud - Paris XI, 2012. http://tel.archives-ouvertes.fr/tel-00769402.
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La photonique du silicium a connu un développent massif pendant les dix derniers années. Presque toutes les briques technologiques de base ont été réalisées et ont démontrées des performances remarquables. Cependant, le manque d'une source laser intégrée en silicium a conduit les chercheurs à développer de composants basés sur l'intégration entre le silicium et les matériaux III-V.Dans cette thèse je décris la conception, la fabrication et la caractérisation des lasers hybrides III-V sur silicium basés sur cette intégration. Je propose un coupleur adiabatique qui permet de transférer intégralement le mode optique du guide silicium au guide III-V. Le guide actif III-V au centre du composant fourni le gain optique et les coupleurs, des deux cotés, assurent le transfert de la lumière dans les guides silicium.Les lasers mono longueur d'onde sont des éléments fondamentaux des communications optiques. Je décris les différentes solutions permettant d'obtenir un laser mono-longueur d'onde hybride III-V sur silicium. Des lasers mono longueur d'onde ont été fabriqués et caractérisés. Ils démontrent un seuil de 21 mA, une puissance de sortie qui dépasse 10 mW et une accordabilité de 45 nm. Ces composants représentent la première démonstration d'un laser accordable hybride III-V sur silicium.
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Liu, Neng. "Sur l’origine de l’interdiffusion de puits quantiques par laser uv dans des heterostructures de semi-conducteurs iii-v." Thèse, Université de Sherbrooke, 2014. http://savoirs.usherbrooke.ca/handle/11143/5291.
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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.
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Paranthoën, Cyril. "Croissance et caractérisations des boites quantiques InAs sur substrat InP (113) B pour la réalisation d'un laser émettant à 1. 55um." Rennes, INSA, 2001. http://www.theses.fr/2001ISAR0014.
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Grigorieff, Peter Nikolaus. "Electron microscopy of interfaces and thin buried layers in the InGaAs/InP system grown by MOVPE." Thesis, University of Bristol, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386162.
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Paraskevopoulos, Anagnostis-Alexandros. "Modélisation et étude expérimentale du comportement dynamique des lasers InP/InGaAsP de structure "Buried Ridge Stripe" (BRS)." Paris 11, 1988. http://www.theses.fr/1988PA112189.
Full textAbstract:
L'objet de cette thèse est l'étude et l'optimisation des performances en modulation rapide de lasers InP / InGaAsP de structure "Buried Ridge Stripe" (BRS). Un modèle électrique "petit signal" a été développé, qui prend en compte tous les éléments parasites de cette structure sous la forme d'un réseau distribué de résistances et de capacités calculées à partir des caractéristiques physiques et technologiques de la structure. Au voisinage de la région active, ce réseau distribué a été déterminé à partir d'un calcul de potentiel par la méthode des éléments finis à 2 dimensions. Des mesures précises dans la bande 0-8GHz de la réponse en fréquence en modulation "petit signal" de lasers BRS sont ensuite présentées. Un bon accord est obtenu entre les mesures et les prévisions de la simulation. Dans un deuxième temps, quelque solutions permettant l'amélioration des performances des lasers BRS en régime dynamique sont proposées : Faible résistivité de contact, pour minimiser les éléments parasites. Ceci nous a permis d'obtenir des bandes passantes supérieures à 8GHz. - Lasers à cavité courte, augmentation de la puissance optique émise, pour augmenter les capacités intrinsèques de modulation. Nous avons plus particulièrement entrepris l'étude de couches InP rendues semi-isolantes par implantation de fer afin d'améliorer le confinement électrique dans la structure BRS et donc augmenter la puissance optique. Cette étude nous a permis de définir les conditions optimales d'implantation pour obtenir des couches de forte résistivité (p > J0 ⁷ Ω cm) (dans une large plage de tensions (± 4V). High frequency modulation mode and experimental study of InP / InGaAsP "Buried Ridge Stripe" CBRS) lasersThe object of this thesis is the study and optimization of the high speed modulation performances of InP/ InGaAsP "Buried Ridge Stripe" (BRS) lasers. A "small signal" electric model has been developed, which takes into account all the parasitic elements of this structure represented by a distributed network of resistances and capacitances, calculated from the physical and technological structure parameters. In the active region vicinity the distributed network has been defined by a voltage calculation using the finite element method. Precise "small signal" Frequency response measurements of BRS lasers in the 0-8GHz band are then presented. A good agreement has been obtained between the measured and calculated characteristics. In a second part some solutions for the improvement of the BRS lasers modulation performances are proposed : weak contact resistivity, which minimizes the parasitic elements values. Bandwidths higher than 8GHz have been obtained in this way. - Short cavity lasers, optical power increase, which improve the intrinsic modulation characteristics. A systematic study of the electric insulation by Fe implantation in n-doped InP layers has been performed in order to improve the electric confinement in the BRS laser structure. We have, thus been able to define the optimal Fe implantation conditions for high resistivity (p > 107 n cm) in a large voltage zone (± 4V)
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Waddicor, David Alan. "Aerosol in the tropical tropopause layer." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/aerosol-in-the-tropical-tropopause-layer(c68a4252-15dc-4a96-a890-0156719b3a9f).html.
Full textAbstract:
This thesis details the ACTIVE campaign in the tropics of northern Australia during 2005-2006 (based in Darwin). The focus of the campaign was to find the influence of tropical convection on the aerosol and chemical content of the Tropical Tropopause Layer [TTL] and the cirrus cloud cover in the area, which is important for the global energy budget. This study details the background climatology of the Darwin region with statistical categorisation of the trace gases and particles. The TTL had regions of extremely high aerosol number concentration, much higher than that of the PBL. The 10 to 1000 nm particle concentrations were as high as 25,000 cm-3 and 100 to 1000 nm were as high as 1000 cm-3. High aerosol concentrations were usually found in cloud-free conditions; cloudy regions were typically low in aerosol number. Wind data and trajectories (BADC) were used to find the origin of the high particle concentrations. Aerosols were found to be nucleating in outflow regions of convective anvils. SO2 oxidation to H2SO4 is a widely accepted mechanism for nucleation. A binary mechanism (H2O-H2SO4), with SO2 as the precursor, was found to be inadequate in explaining the nucleation and growth rates -- tested using an aerosol sectional model. However, it was found, via back trajectory analysis, that the climatology of Darwin was influenced by local and long-range sources, including advection from Indonesia and the Tropical Warm Pool. These distant sources could have introduced condensable matter, with aerosol precursor properties (certain organic compounds). The aerosol model found a condensable precursor concentration of at least 300 pptv was necessary to replicate the observations.
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Genest, Jonathan. "Interdiffusion de puits quantiques contrôlée par irradiation laser excimère pour l'intégration de composants photoniques." Thèse, Université de Sherbrooke, 2008. http://savoirs.usherbrooke.ca/handle/11143/1824.
Full textAbstract:
L'intégration de composants discrets sur un système unique, tel une puce électronique, augmente les performances totales du système, fait apparaitre de nouvelles fonctionnalités et diminue les coûts associés à la fabrication des dispositifs. Ces améliorations, appliquées au secteur de la microélectronique, sont grandement responsables des avancements importants qu'ont connus les technologies de l'information et des communications au cours des dernières années. Puisque la fabrication de circuits photoniques intégrés nécessite l'intégration de structures ayant des bandes interdites différentes à partir d'une même puce semiconductrice, leur niveau d'intégration est bien inférieur que celui atteint pour un microprocesseur standard. Parmi les techniques ayant le potentiel de fabriquer des circuits photoniques intégrés monolithiquement, l'interdiffusion de puits quantique post-expitaxial contrôlée spatialement augmente la bande interdite d'une hétérostructure semiconductrice à l'intérieur de régions définies. Le processus d'interdiffusion, activé thermiquement, est accéléré par la diffusion d'impuretés et de défauts ponctuels tels que les lacunes et les interstitiels. L'hypothèse de départ de mes travaux de doctorat suppose que la radiation laser ultra-violette module la diffusion et la génération de défauts ponctuels dans les hétérostructures reposant sur les technologies à base de GaAs et d'InP et, conséquemment, contrôle spatialement l'interdiffusion de puits quantiques. Nous avons démontré que lorsque appliquée sur des hétérostructures à base de GaAs, l'irradiation laser excimère l'interdiffusion en favorisant la croissance d'un stresseur de surface qui empêche la diffusion des défauts ponctuels vers les puits quantiques. Nous avons souligné l'influence de la vapeur d'eau physisorbée sur la croissance du stresseur et avons déterminé la résolution spatiale de la technique. Dans les hétérostructures basées sur les technologies InP, même sous le seuil d'ablation, l'absorption des impulsions laser UV favorise la désorption des atomes de surface ce qui génère des défauts ponctuels en concentration excédentaire. Lors d'un recuit thermique, ces défauts ponctuels augmentent la vitesse de l'interdiffusion sous les régions irradiées.
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Schulz, Wolfgang-Michael [Verfasser]. "InP/AlGaInP Quantenpunkte - Design, Epitaxie und Charakterisierung von Halbleiter-Quantenpunkt-Bauelementen für Laser und Einzelphotonenquellen / Wolfgang-Michael Schulz." München : Verlag Dr. Hut, 2011. http://d-nb.info/1013526716/34.
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