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Scheidt, Torsten. "Non-linear optical diagnostics of non-centrosymmetric opto-electronic semiconductor materials." Thesis, Stellenbosch : University of Stellenbosch, 2006. http://hdl.handle.net/10019.1/17332.
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Ghosh, Sujoy. "SYNTHESIS, ELECTRONIC AND OPTO-ELECTRONIC TRANSPORT PROPERTIES OF ATOMICALLY THIN 2D LAYERS OF MoS2, WSe2 and CuIn7Se11." OpenSIUC, 2016. https://opensiuc.lib.siu.edu/dissertations/1308.
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The recent emergence of a new class of two dimensional layered materials (2DLMs) have not only opened up the potential for exciting new technological opportunities but also established a new platform to explore exciting new fundamental physics and chemistry at the limit of atomic thickness. Among several of these newly rediscovered 2DLMs, transition metal dichalcogenides (TMDCs) as well as other elemental combinations of Group III and Group VI represent a large family of 2D layered materials, which can be isolated into few atomic layers. These materials show remarkable promise for future electronic and opto-electronics applications. The scope of this dissertation, thus, broadly covers the electronic and opto-electronic properties of such few layered 2D materials. Extensive investigation of electronic and opto-electronic transport phenomena of charge carriers in few layer MoS2 synthesized using a variety of methods such as Chemical Vapor Deposition (CVD), liquid phase exfoliation and mechanical exfoliation as well as CVT grown mechanically exfoliated WSe2 and ternary alloy of CuIn7Se11 is reported. Specifically, it is shown that in case of MoS2, the ac conductance (σ(ω); measured in the range of 10mHz < ω < 0.1 MHz) of atomically thin 2D layers of chemical vapor deposited (CVD) Molybdenum Disulphide (MoS2) as well as thin films of exfoliated flakes of MoS2, show "universal" power law behavior (with σ(ω) ~ ωs). The temperature dependence of 's' indicate that the mechanism of ac transport in CVD MoS2 is due to electron hopping by quantum mechanical tunneling (QMT) process whereas the ac transport in exfoliated MoS2 films is due to correlated barrier hoping (CBH) mechanism. The ac conductivity also show scaling behavior, manifested by collapse of the ac conductivity data for both the samples at various temperatures to one single master curve. The T-γ dependence of the d.c conductance suggests that in case of the CVD – grown and mechanically exfoliated MoS2, γ=1/3 which corresponds to the Mott’s variable range hopping (VRH) transport where as in case of liquid phase exfoliated MoS2, γ=1 which relates to thermally activated Arrhenius type transport mechanism. Opto-electronic measurements were also performed in a variety of 2DLM samples. From the field effect transport measurements on the mechanically exfoliated samples of few layers of MoS2, WSe2 and CuIn7Se11, we found at room temperature the charge carrier mobility is ~ 47 cm2/V.s, 80 cm2/V.s and 37 cm2/V.s for MoS2, WSe2 and CuIn7Se11 respectively. The photoconductivity measurements performed on these samples show that it is possible to achieve photo-responsivities values~50 μA/W, 0.2 A/W, 1 A/W and 51 A/W at room temperature for liquid exfoliated MoS2, mechanically exfoliated MoS2, WSe2 and CuIn7Se11 based devices respectively. Mechanisms of photoconduction in these materials were explained on the basis of intensity dependent photo-current measurements. From the intensity dependent photo-current along with the low temperature photoconduction measurements we found that in case of liquid phase exfoliated MoS2 thin film devices the trap states are continuously distributed within the mobility gap in these thin film of MoS2, and play a vital role in influencing the overall photo response. On the other hand for CVT grown mechanically exfoliated WSe2 based devices bimolecular recombination mechanism is the most dominant process for photoconduction. The result obtained are discussed and compared with the available literature on the subject.
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Luong, Vu Hai Nam. "Studying optical micro-resonators coupling for future insertion in an opto-electronic oscillator." Phd thesis, École normale supérieure de Cachan - ENS Cachan, 2012. http://tel.archives-ouvertes.fr/tel-00905958.
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The classical structure of an Opto-Electronic Oscillator (OEO) is based on a long fiber loop acting as a delay line and leading to the high spectral purity, or very low phase noise, of the oscillator. Such an OEO has been developed in SATIE/LPQM laboratory at ENS Cachan, operating at 8 GHz frequency. However, this system has some main disadvantages such as a bulky size, the difficulty to control temperature and a wide range of peaks among which it is difficult to select only one mode. In order to eliminate these disadvantages, high quality factor optical resonator can be used instead of the optical fiber loop. In this thesis, two resonator structures are produced and investigated. Microspheres are fabricated based on optical single mode fiber. Whispering gallery modes of these resonators are characterized by tapered fiber -resonator coupling. The experimental results show that the quality factor of the microsphere is up to 106 and FSR depends on the diameter of the resonator. A microsphere with a diameter of 300 µm, presents a FSR of 0.2 nm corresponding to a frequency of 25 GHz. However, for an OEO system which should work at 8 GHz, microsphere with a smaller FSR or with diameter of some millimeters should be fabricated- that is really difficult to obtain. Another add/drop racetrack resonator is designed and investigated. Optical experimental behavior of racetrack is characterized via fiber micro-lens coupling. The transmission spectrum shows resonance dips with average quality factor of 105 and a small FSR of 0.050 ± 0.003 nm (actually corresponding to 6 GHz) for a scanning wavelength range from 1534 nm to 1610 nm. The most promising features of the racetrack resonator are its high quality factor, and its free spectral range, which give it the high suitability for being used in the OEO system. Nevertheless the coupling with fiber lens leads to high losses and it is not possible to fulfill the oscillation conditions. Future work should be conducted for improving the coupling and for controlling the resonance dips position in agreement with the wavelength of the laser used in the OEO.
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Alam, Md Shah. "Additive Nanomanufacturing based on Opto-Thermo-Mechanical Nano-Printing." University of Dayton / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1591871749553767.
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Seyd, Darwish Iyad. "Etude et réalisation d'un automate cellulaire opto-électronique parallèle." Phd thesis, Université Paris Sud - Paris XI, 1991. http://pastel.archives-ouvertes.fr/pastel-00732332.
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Les automates cellulaires, composes d'un grand nombre de processeurs élémentaires, permettent un traitement rapide et efficace de certaines algorithmes. Le présent travail étudie la possibilité d'une implantation parallèle d'un tel automate sur un circuit intégré avec des entrées optiques en utilisant des photodiodes intégrées et un illuminateur de tableaux et des sorties optoélectroniques avec des modulateurs a puits quantiques multiples. Différents composants ont été étudiés et réalisés dans ce but: illuminateur de tableaux réalisé sur un hologramme en utilisant l'effet d'imagerie de talbot. Une amélioration des aberrations chromatiques est proposée en changeant les conditions d'enregistrement; circuit électronique intégrée VLSI contenant un seul processeur élémentaire avec des photodiodes intégrées pour les entrées optiques et les plots de sortie spéciaux pour les modulateurs; modulateurs opto-électroniques a puits quantiques multiples. Un montage expérimental a été réalisé en éclairant une photodiode avec une diode laser a 999 nm. L'estimation des performances de l'automate propose montre sa haute capacité de calcul et de connexion.
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Bocheux, Amandine. "Maîtrise des processus opto-électroniques d'architectures moléculaires π-conjuguées : auto-assemblage et sonde locale". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2011. http://tel.archives-ouvertes.fr/tel-00748715.
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Ce travail de thèse porte sur l'étude des limites physiques requises pour la conception d'une diode organique électroluminescente à l'échelle la plus réduite qui soit, celle d'un faible nombre d'atomes. Nous avons travaillé avec plusieurs systèmes moléculaires organiques π-conjugués afin de déterminer les critères essentiels que doit remplir une molécule pour pouvoir être utilisée comme telle. Dans ce cadre, le Microscope à Effet Tunnel s'avère être un outil particulièrement adapté pour étudier l'auto-assemblage de tous ces systèmes sur une surface ainsi que pour positionner avec une haute précision les électrodes constituées par la pointe et le substrat conducteurs. L'organisation sur graphite de tectons tridimensionnels à pilier central paracyclophane a tout d'abord été étudiée. Ils présentent, au sein d'une même entité moléculaire, l'ensemble des fonctions requises pour obtenir une émission : celles d'organisation structurée par les interactions avec le substrat et celles d'opto-électronique. Le passage à un substrat d'or, mieux adapté pour l'exaltation par les plasmons, a ensuite été examiné. Une autre stratégie quant à l'organisation des molécules reposant sur une modification de leur nature et de leur longueur a été choisie avec l'usage d'oligophénylènes et de poly(3-alkylthiophènes). Leur stabilité, qui constitue le paramètre clef pour l'émission de photons sous pointe, a demandé à être améliorée sur ce même substrat et a motivé le développement d'une troisième architecture afin de consolider l'ensemble de l'édifice moléculaire. Des thiols chimisorbés ont été déposés sur or et des polymères fluorescents s'y sont superposés par création d'une liaison électrostatique. L'obtention d'une émission localisée avec un tel système conclue ce travail qui souligne que le principal obstacle à la réalisation d'une diode de taille minimale sera la stabilité structurale de ses constituants moléculaires.
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Mccafferty, Sean. "Analysis and application of opto-mechanics to the etiology of sub-optimal outcomes in laser corrective eye surgery and design methodology of deformable surface accommodating intraocular lenses." Thesis, The University of Arizona, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=1589573.
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<p> <b>Overview:</b> Optical concepts as they relate to the ophthalmologic correction of vision in corneal laser vision correction and intraocular lens design was examined. </p><p> <b>Purpose:</b> The interaction between the excimer laser and residual corneal tissue in laser vision correction produces unwanted side effects. Understanding the origin of these artifacts can lead to better procedures. Furthermore, accommodating intraocular lenses offer a potential for eliminating presbyopia. Understanding the properties of a new accommodating intraocular lens incorporating a deformable interface may lead to advances in cataract surgery. </p><p> <b>Introduction:</b> Corneal surface irregularities following laser refractive procedures are commonly seen. They regularly result in a patient’s decreased best corrected visual acuity and decreased contrast sensitivity. These changes are only seen in biologic tissue and the etiology has been elusive. A thermal response has been theorized and was investigated in this research. In addition, intraocular lenses using a mechanically deforming interface to change their power in order to duplicate natural accommodation have been developed. The deforming interface(s) induce optical aberrations due to irregular deformations. Design efforts have centered on minimizing these deformations. Both of the ophthalmic applications have been analyzed using finite element analysis (FEA) to understand their inherent optical properties. </p><p> <b>Methods:</b> FEA modeling of thermal theory has been applied to verify that excimer laser induced collagen contraction creates corneal surface irregularities and central islands. A mathematical model which indicates the viability of the theory was developed. The modeling results were compared to post ablation changes in eyes utilizing an excimer (ArF 193 nm), as well as non-ablative thermal heating in eyes with a CO<sub>2</sub> laser. </p><p> Addition modeling was performed on an Intraocular lens prototype measuring of actuation force, lens power, interface contour, optical transfer function, and visual Strehl ratio. Prototype verified mathematical models were utilized to optimize optical and mechanical design parameters to maximize the image quality and minimize the required force. </p><p> Results: The predictive model shows significant irregular central buckling formation and irregular folding. The amount of collagen contraction necessary to cause significant surface changes is very small (0.3%). Uniform scanning excimer laser ablation to corneal stroma produces a significant central steepening and peripheral flattening in the central 3mm diameter. Isolated thermal load from uniform CO<sub>2</sub> laser irradiation without ablation also produces central corneal steepening and paracentral flattening in the central 3mm diameter. </p><p> The iterative mathematical modeling based upon the intraocular lens prototype yielded maximized optical and mechanical performance through varied input mechanical and optical parameters to produce a maximized visual Strehl ratio and a minimized force requirement. </p><p> <b>Conclusions:</b> The thermal load created by laser irradiation creates a characteristic spectrum of morphologic changes on the porcine corneal stromal surface which correlates to the temperature rise and is not seen inorganic, isotropic material. The highly similar surface changes seen with both lasers are likely indicative of temperature induced transverse collagen fibril contraction and stress re-distribution. Refractive procedures which produce significant thermal load should be cognizant of these morphological changes. </p><p> The optimized intraocular lens operates within the physiologic constraints of the human eye including the force available for full accommodative amplitude using the eye’s natural focusing feedback, while maintaining image quality in the space available. Optimized optical and mechanical performance parameters were delineated as those which minimize both asphericity and actuation pressure. The methodology combines a multidisciplinary basic science approach from biomechanics, optical science, and ophthalmology to optimize an intraocular lens design suitable for preliminary trials.</p>
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Snell, Rodney James 1965. "A digital-electronic video-rate reconstruction system for magnetic resonance imaging." Thesis, The University of Arizona, 1992. http://hdl.handle.net/10150/278071.
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A digital-electronic video-rate reconstruction system for Magnetic Resonance Imaging (MRI) has been designed to first order. The maturation of ultra-fast acquisition techniques in MRI has produced the need for a reconstruction system that will enable dynamic processes to be viewed on-line. Conventional reconstruction hardware is not configured for real-time reconstruction and previous developments are limited in accuracy and flexibility. The real-time reconstruction system presented here consists of three main subsystems. A digitizer interfaces with an MR scanner to digitize data matrices of resolutions up to 256 x 256 at arbitrary rates up to video rates. A Fourier processor performs either 2D Fourier transformation or projection filtering on the digitized data at video-rates. A backprojector performs the backprojection operation on filtered-projection data at video-rates. The complete system would be able to reconstruct data acquired from nearly any acquisition technique. True real-time MRI is then possible.
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Saini, Anuj. "FROM APPLICATION OF ORGANIC THIN MULTILAYER FILMS IN 3D OPTICAL DATA STORAGE TO THEIR FABRICATION FOR ORGANIC ELECTRONIC DEVICES." Case Western Reserve University School of Graduate Studies / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=case1459518551.
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Erbing, Axel. "In pursuit of next generation photovoltaics : An electronic structure study of lead-free perovskite solar cells." Licentiate thesis, Stockholms universitet, Fysikum, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-181608.
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The recent development of perovskite-based solar cells have shown a remarkably fast increase in power conversion efficiency making them a promising low-cost alternative to conventional cells. The most successful class of materials however, the lead-halide perovskites, are held back due to toxicity and stability issues significantly limiting their use. Because of this, the investigation of new, lead-free, light-absorber materials as a replacement is an important step towards improved solar cells. The focus of this licentiate thesis is the study of bismuth-based materials and their photovoltaic properties through electronic structure calculations. Specifically, the cubic-phase AgBi2I7 under gradual substitution of either bromine or antimony is investigated using density functional theory under periodic boundary conditions. This enables calculations of the system's energy levels and band structure. Furthermore, the energy variance of the employed model of the system is sampled with respect to its level of ion disorder to obtain a better understanding of the distribution of ions within the crystal. The materials are found to have good optical properties but comparatively low efficiencies. The introduced substitutions allow fine-tuning of the system's band gap and is shown to increase the overall performance of the solar cells. In addition, spin-orbit coupling effects are demonstrated to be important when treating these bismuth-based systems. The crystal structure is found to have a significant preference for separating its silver ions and cation vacancies.
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Gavrilyuk, Sergey. "Molecular electronic, vibrational and rotational motion in optical and x-ray fields." Doctoral thesis, Stockholm : School of Biotechnology, Royal Institute of Technology, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-11386.
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Armakavicius, Nerijus. "Study of novel electronic materials by mid-infrared and terahertz optical Hall effect." Licentiate thesis, Linköpings universitet, Halvledarmaterial, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-142220.
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Development of silicon based electronics have revolutionized our every day life during the last three decades. Nowadays Si based devices operate close to their theoretical limits that is becoming a bottleneck for further progress. In particular, for the growing field of high frequency and high power electronics, Si cannot offer the required properties. Development of materials capable of providing high current densities, carrier mobilities and high breakdown fields is crucial for a progress in state of the art electronics. Epitaxial graphene grown on semi-insulating silicon carbide substrates has a high potential to be integrated in the current planar device technologies. High electron mobilities and sheet carrier densities make graphene extremely attractive for high frequency analog applications. One of the remaining challenges is the interaction of epitaxial graphene with the substrate. Typically, much lower free charge carrier mobilities, compared to free standing graphene, and doping, due to charge transfer from the substrate, is reported. Thus, a good understanding of the intrinsic free charge carriers properties and the factors affecting them is very important for further development of epitaxial graphene. III-group nitrides have been extensively studied and already have proven their high efficiency as light sources for short wavelengths. High carrier mobilities and breakdown electric fields were demonstrated for III-group nitrides, making them attractive for high frequency and high power applications. Currently, In-rich InGaN alloys and AlGaN/GaN high electron mobility structures are of high interest for the research community due to open fundamental questions. Electrical characterization techniques, commonly used for the determination of free charge carrier properties, require good ohmic and Schottky contacts, which in certain cases can be difficult to achieve. Access to electrical properties of buried conductive channels in multilayered structures requires modification of samples and good knowledge of the electrical properties of all electrical contact within the structure. Moreover, the use of electrical contacts to electrically characterize two-dimensional electronic materials, such as graphene, can alter their intrinsic properties. Furthermore, the determination of effective mass parameters commonly employs cyclotron resonance and Shubnikov-de Haas oscillations measurements, which require long scattering times of free charge carriers, high magnetic fields and low temperatures. The optical Hall effect is an external magnetic field induced optical anisotropy in conductive layers due to the motion of the free charge carriers under the influence of the Lorentz force, and is equivalent to the electrical Hall effect at optical frequencies. The optical Hall effect can be measured by generalized ellipsometry and provides a powerful method for the determination of free charge carrier properties in a non-destructive and contactless manner. In principle, a single optical Hall effect measurement can provide quantitative information about free charge carrier types, concentrations, mobilities and effective mass parameters at temperatures ranging from few kelvins to room temperature and above. Further, it was demonstrated that for transparent samples, a backside cavity can be employed to enhance the optical Hall effect. Measurement of the optical Hall effect by generalized ellipsometry is an indirect technique requiring subsequent data analysis. Parameterized optical models are fitted to match experimentally measured ellipsometric data by varying physically significant parameters. Analysis of the optical response of samples, containing free charge carriers, employing optical models based on the classical Drude model, which is augmented with an external magnetic field contribution, provide access to the free charge carrier properties. The main research results of the graduate studies presented in this licentiate thesis are summarized in the five scientific papers. Paper I. Description of the custom-built terahertz frequency-domain spectroscopic ellipsometer at Linköping University. The terahertz ellipsometer capabilities are demonstrated by an accurate determination of the isotropic and anisotropic refractive indices of silicon and m-plane sapphire, respectively. Further, terahertz optical Hall effect measurements of an AlGaN/GaN high electron mobility structures were employed to extract the two-dimensional electron gas sheet density, mobility and effective mass parameters. Last, in-situ optical Hall effect measurement on epitaxial graphene in a gas cell with controllable environment, were used to study the effects of environmental doping on the mobility and carrier concentration. Paper II. Presents terahertz cavity-enhanced optical Hall measurements of the monolayer and multilayer epitaxial graphene on semi-insulating 4H-SiC (0001) substrates. The data analysis revealed p-type doping for monolayer graphene with a carrier density in the low 1012 cm−2 range and a carrier mobility of 1550 cm2/V·s. For the multilayer epitaxial graphene, n-type doping with a carrier density in the low 1013 cm−2 range, a mobility of 470 cm2/V·s and an effective mass of (0.14 ± 0.03) m0 were extracted. The measurements demonstrate that cavity-enhanced optical Hall effect measurements can be applied to study electronic properties of two-dimensional materials. Paper III. Terahertz cavity-enhanced optical Hall effect measurements are employed to study anisotropic transport in as-grown monolayer, quasi free-standing monolayer and quasi free-standing bilayer epitaxial graphene on semi-insulating 4H-SiC (0001) substrates. The data analysis revealed a strong anisotropy in the carrier mobilities of the quasi freestanding bilayer graphene. The anisotropy is demonstrated to be induced by carriers scattering at the step edges of the SiC, by showing that the mobility is higher along the step than across them. The scattering mechanism is discussed based on the results of the optical Hall effect, low-energy electron microscopy, low-energy electron diffraction and Raman measurements. Paper IV. Mid-infrared spectroscopic ellipsometry and mid-infrared optical Hall effect measurements are employed to determine the electron effective mass in an In0.33Ga0.67N epitaxial layer. The data analysis reveals slightly anisotropic effective mass and carrier mobility parameters together with the optical phonon frequencies and broadenings. Paper V. Terahertz cavity-enhanced optical Hall measurements are employed to study the free charge carrier properties in a set of AlGaN/GaN high electron mobility structures with modified interfaces. The results show that the interface structure has a significant effect on the free charge carrier mobility and that the sample with a sharp interface between an AlGaN barrier and a GaN buffer layers exhibits a record mobility of 2332±73 cm2/V·s. The determined effective mass parameters showed an increase compared to the GaN value, that is attributed the the penetration of the electron wavefunction into the AlGaN barrier layer.
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Ouerghemmi, Ezzeddine. "Étude physique des limites en puissance des lasers à cascade quantique." Phd thesis, Ecole Polytechnique X, 2011. http://pastel.archives-ouvertes.fr/pastel-00605931.
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Cette thèse concerne l'étude théorique et expérimentale des limitations de la puissance de sortie des lasers à cascade quantique (LCQ). Nous y exposons une modélisation globale de leurs propriétés électro-optiques. Le fonctionnement du laser est décrit en incluant la structure électronique, les mécanismes de diffusion responsables des transitions non radiatives des électrons et le couplage électron- photon de la cavité. Ce modèle nous a permis de reproduire avec succès l'ensemble des caractéristiques (courant et puissance optique en fonction de la tension appliquée) d'un LCQ sur un large domaine de température de fonctionnement. Dans un premier temps, ce modèle a été utilisé pour le calcul de la température électronique dans les LCQ. Il en ressort que la diffusion par des phonons-LO est le seul mécanisme avec lequel le gaz d'électrons peut transférer son énergie vers le réseau. Les mécanismes élastiques de diffusion sont des sources d'énergie pour le gaz d'électrons. Deux paramètres physiques permettent de décrire complètement le comportement de la température électronique dans le composant : la résistance thermique électronique de l'hétérostructure et le coefficient de couplage courant température électronique. Ensuite, l'étude du couplage des électrons avec les photons de la cavité montre que ce couplage peut modifier notablement la distribution électronique sur les niveaux énergétiques. Le gain de la zone active du laser diminue avec la densité de photons. Cet effet appelé saturation de gain joue un rôle important sur les performances des LCQ. La minimisation de cet effet peut augmenter la puissance maximale de sortie du laser d'un facteur deux. Cette étude nous a permis de proposer de nouveaux dessins de zone active ayant des performances améliorées. La fabrication de certaines de ces structures a permis de valider l'approche que nous avons suivie pour améliorer les performances de ce type de laser.
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Audo, Frédéric. "Opto-alimentation et transmission de données par fibre optique pour les observatoires de fond de mer." Phd thesis, Université de Bretagne occidentale - Brest, 2012. http://tel.archives-ouvertes.fr/tel-00782502.
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Ce mémoire de thèse est consacré à l'étude d'une liaison tout-optique longue de 10 km dédiée à l'extension d'un observatoire câblé de fond de mer existant afin d'atteindre de nouvelles zones d'exploration. Les travaux de recherche qui y sont rapportés démontrent la faisabilité de cette liaison tout-optique entre un instrument déporté et une station terrestre avec une seule fibre optique longue de 10 km, qui transmet simultanément la puissance, nécessaire à l'alimentation de l'instrument (quelques centaines de milliwatts), et des données bidirectionnelles en temps réel.Le contexte de cette thèse est présenté au travers d'un état de l'art sur les observatoires câblés et sur la puissance sur fibre. Le choix de la fibre unique et la présence de fortes puissances optiques complexifient la mise en oeuvre de cette extension tout-optique, et sont à l'origine de l'apparition d'interactions entre l'énergie optique dédiée à l'alimentation (@1480 nm) et les données échangées (@1550 nm). Tout au long de ce document, les choix technologiques retenus sont argumentés et les effets optiques non linéaires tels que les diffusions Raman, Brillouin, Rayleigh, l'Émission Spontanée Amplifiée (ASE) sont décrits, modélisés et analysés expérimentalement. L'extension tout-optique proposée a été caractérisée à la fois en régimes statique et dynamique par des mesures du bilan de liaison, du rapport signal à bruit (SNR) et du taux d'erreur binaire (BER). Les résultats obtenus montrent la possibilité de fournir 160 mW électrique à l'instrument déporté en utilisant une source optique continue de 33 dBm sans dégrader excessivement les données bidirectionnelles transmises simultanément (BER<10-7).
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Lidberg, Gustav, Karl Pontén, and Johan Millberg. "Design of Optical Magnetic Systems for Terahertz Lensing." Thesis, Uppsala universitet, FREIA, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-445114.
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When graphene is subjected to magnetic fields, it can be used as an optical device with light in the terahertz region. The functionality of the graphene depends on which magnetic field profile is influencing it. In this project, magnet configurations producing uniform and quadratic magnetic field profiles were studied. A script was written that allowed the user to place dipoles and ring magnets in the proximity of a graphene disc. The script would then determine the necessary dimensions of the permanent magnets used to produce the target magnetic field. The resulting magnetic configurations have been shown to produce a magnetic field within ±1% of the target profile, on the specified domain. However, further studies are required to establish if the acquired configurations proves reasonable in practise, and if so, how well the corresponding optical devices will perform.
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Khreis, Osama M. "Interdiffusion in III-V opto-electronic materials." Thesis, University of Surrey, 1997. http://epubs.surrey.ac.uk/844237/.
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Photoluminescence coupled with repetitive thermal annealing has been used to study the thermal interdiffusion processes in both InGaAs and GaAsSb grown on GaAs substrates. The effect of growth temperature and group-V to group-III flux ratio were studied in InGaAs MQW wafers. The wells in the MQW stack were grown at different temperatures, one of which was grown well below the standard growth temperature to act as a vacancy source in the MQW stack. Due to this vacancy source we have been able to simultaneously measure the In-Ga interdiffusion coefficient, diffusion coefficient for group-III vacancies in GaAs, and the background concentration of these vacancies. It was shown that the interdiffusion at all temperatures is governed by a constant background concentration of vacancies in the material and that this background concentration is the concentration of vacancies in the substrate material. The measured background concentration of vacancies is about 1017 cm-3. This result showed that the vacancy concentrations in GaAs are not at thermal equilibrium concentrations as has been widely assumed. Rather it has been shown to have a value which is "frozen-in", probably at the GaAs crystal growth temperature. The activation energy found for intermixing of InGaAs/GaAs is shown to be governed solely by the activation term for vacancy diffusion which is calculated to have an activation energy of 3.4+/-0.3 eV. These results provide a mechanism to explain the reduced diffusion coefficient under the Ga rich conditions widely reported. The flux ratio was found not to play any significant role in the interdiffusion process. These results can be explained by the diffusion in all cases being governed by a single vacancy-controlled second-nearest-neighbour bopping mechanism. The interdiffusion process on the group-V sublattice in the GaAsSb material system was shown to obey Pick's second law with an activation energy of 2+/-0.3 eV. This result contradicts earlier reports of non-linear diffusion process in this system.
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Wang, Shouyin. "Characterisation of ZnSe and ZnCdSe/ZnSe opto-electronic devices." Thesis, Heriot-Watt University, 1994. http://hdl.handle.net/10399/1394.
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Foster, Howard Allen Jr. "Opto-electronic Technique For Error Fault Detection In Textile Joining Applications." NCSU, 2002. http://www.lib.ncsu.edu/theses/available/etd-08062002-183215/.
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The purpose of this research has been to develop an opto-electronic method for detecting error faults in textile joining applications. The application of this study would be in on-line determination of skipped stitches in seam sewing operations. The research begins with a selection of materials that covers a range of textile materials commonly used, and then determining several physical parameters based upon industry standards. The next portion of the research is to determine the proper wavelength of light to use for the opto-electronics, using near infrared and visible spectrophotometric techniques for acceptable light reflection levels for qualitative analysis. This study then focuses on using NIR wavelength light at 1550nm, using an InGaAsP laser diode module with optics and corresponding Germanium photodiode detector with a wavelength-matched interference filter, to monitor a stitch line passed by the test apparatus to determine the presence of skipped stitches, or stitches where the top thread and looper thread do not properly catch and hold in the sewing of a seam. Due to the spot size of the manufactured laser diode module, a ½? basting stitch, commonly used to temporarily attach fabric pieces, is selected as the best stitch type to use to verify the hypothesis. After determining the ideal positions of the laser diode and photodiode assemblies using geometric optics arguments and extensive position-related intensity measurements, the assembly is mounted onto a linear slide table, and fabric samples, sewn with the ½? basting stitch to simulate a seam, are aligned and tested for variations in light levels based on the presence of a stitch or a space. It is then shown that this method for detecting skipped stitches is a viable alternative to the current visual inspection performed by factory employees.
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De, Amritanand. "Spin dynamics and opto-electronic properties of some novel semiconductor systems." Diss., University of Iowa, 2009. https://ir.uiowa.edu/etd/352.
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A set of problems pertaining to quantum information processing in semiconductors is investigated. Two schemes for implementing electronic qubits in strong and weak three dimensional quantum confinement regimes are studied along with their related electronic properties. Recent experiments motivated us to calculate electronic properties and g factors for nanowhisker quantum dots. These calculations were done using 8 band strain dependent k.p theory on a 3D grid and are in excellent agreement with experiment. It has been observed that the growth conditions cause the nanowhiskers to crystallize in wurtzite(WZ) form instead of their stable-phase zinc-blende bulk structure. Very little is known about the WZ phase of non-nitride III-V semiconductors as they do not naturally occur. We have therefore also predicted the electronic bandstructure and optical properties of nine III-V semiconductors in the WZ phase using transferable empirical pseudopotentials. Apart from quantum dots, the spin of an electron bound to an atomic impurity is an attractive candidate for quantum information processing as they do not suffer from structural uncertainties. This makes spin of an electron bound to a hydrogenic impurity an attractive candidate for a qubit as it possess the biggest radii of any ionic bound states in the solid and is a natural two state system. We have calculated the electric and magnetic field dependent modulation of the g tensor for a single Silicon donor embedded in a GaAs substrate. The spin dynamics of the weakly bound electron exhibits an unusual nonlinear behavior, which is not seen in structures with strong quantum confinement such as quantum dots.
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Kahn, Mohammed Tariq Ekeramodien. "Miniaturised dedicated application opto-electronic sensors in the evolution of smart systems." Thesis, Peninsula Technikon, 2002. http://hdl.handle.net/20.500.11838/1196.
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Thesis (DTech (Electrical Engineering))--Peninsula Technikon, Cape Town, 2002<br>In the last decade, the South Amcan Electricity Supply Commission would have had
their ability to serve an ever demanding public severely tested. With the dilemma of
providing electricity supply through hazardous environmental conditions, and with
prospects of supplying power even beyond South Afiican borders, the need for a
comprehensive damage and power delivery assessment strategy becomes all the more
relevant. The rapid growth being made in the evolution of so called "intelligent"
structures, with inherent sensor, actuator and control mechanisms built in can have
direct influence on a power distribution network. At least in the foreseeable future, the
impact ofphotonic sensors with inherent miniaturization, a foremost candidate in Smart
System technology, can play a vital role in damage assessment of a potentially large
network such as that found in the supply ofelectricity.
Smart systems are nonliving systems that integrate the functions of sensing, actuation,
logic and control, to respond adaptively to changes in their condition or environment to
which they are exposed, in a useful and usually repetitive manner. Sensors are a
fundamental part of the evolution of such systems and form the basis for the topic of
this dissertation. The use ofoptical fiber sensors is increasing widely mainly due to their
(a) miniature size, (b) remote signal processing ability, and (c) multiplexing capabilities.
Because of the above features a variety of optical fiber sensing techniques has evolved
over the years having potential for a myriad of applications. In this work a systems model and equations was developed for modeling the
propagation of light in a optical waveguide, in order to study a Fabry Perrot sensor
topology for application as a miniaturised sensor in a new type of smart structure,
namely a smart electrical power system.
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Birkett, M. J. "Opto-electronic studies of semiconductor tunnelling structures and quantum wells." Thesis, University of Sheffield, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267179.
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Morris, Randy W. Jr. "PROPEL: Power & Area-Efficient, Scalable Opto-Electronic Network-on-Chip." Ohio University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1244146228.
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Thorat, Ruhi P. "Opto-Electronic Properties of Self-Contacted MoS2 Monolayer Devices." Ohio University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1512731597427663.
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Peggs, Derek William. "Spectroscopic studies of the opto-electronic properties of quantum wells and superlattices." Thesis, University of Sheffield, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.364305.
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Adrados, Claire. "Polaritons en microcavité semi-conductrice : dynamique de fluide quantique, effets de spin et mesures de bruit en régime d'oscillation paramétrique." Phd thesis, Université Pierre et Marie Curie - Paris VI, 2011. http://tel.archives-ouvertes.fr/tel-00789192.
Full textAbstract:
Ce travail est consacré à l'étude des propriétés des polaritons, particules mi-lumière mi-matière, en microcavité semi-conductrice. Leur caractère bosonique autorise l'accès à des régimes de cohérence macroscopique tels la condensation de Bose-Einstein et la superfl uidité que nous avons démontrée expérimentalement. Nous avons également développé une technique permettant de modifier optiquement l'environnement polaritonique par création de défauts arti ficiels, ce qui facilite l'obtention de comportements particuliers du fluide polaritonique comme la turbulence. Les fortes interactions dépendantes du spin entre ces particules, alliées à des vitesses de propagation très élevées du fait de leur composante photonique, nous ont permis de réaliser un interrupteur performant contrôlé optiquement, codé en polarisation et en intensité. Nous avons également réussi à manipuler la distribution spatiale en spin d'un faisceau de polaritons, et notamment à confi ner des états de spin pur sur des zones de quelques microns. Le phénomène de bistabilité présent dans le système nous a amené à reconsidérer le signe de la constante d'interaction entre polaritons de spin opposés. En fin, en régime d'oscillation paramétrique par mélange à quatre ondes, nous avons poursuivi l'étude de génération de photons jumeaux grâce à des mesures de corrélations et des analyses en bruit de la distribution modale transverse, dans diff érents types de cavités planaires puis dans des micropiliers (0D).
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Vettese, Carlo Ettore. "The effects of multi-quantum well inter-mixing on long-wavelength opto-electronic structures and devices." Thesis, University of Nottingham, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387226.
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Chryssou, Costas. "Fabrication, characterisation and modelling of rare-earth doped alumina (A1203) thin films for opto-electronics." Thesis, University College London (University of London), 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299285.
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Celebi, Kemal. "Optical modeling of organic electronic devices." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45431.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Physics, 2008.<br>Includes bibliographical references (p. 51-53).<br>Organic materials, with their superior photoluminescence and absorbance properties have revolutionized the technologies for displays and solar energy conversion. Due to the large transition dipoles, the localization of excited states or excitons in organic materials necessitates optical models that extend beyond classical far field methods. In this thesis we propose an extended near field calculation method using dyadic Green's functions and demonstrate the applications of both our extended model and traditional far field models for different types of devices such as surface plasmon detectors, cavity organic light emitting devices and organic photovoltaics with external antennas.<br>by Kemal Celebi.<br>S.M.
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Rajaniemi, T. (Tatu). "Electronic and optical properties of TiO₂ nanoclusters." Master's thesis, University of Oulu, 2016. http://urn.fi/URN:NBN:fi:oulu-201612103250.
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The electronic and optical properties of the anatase polymorph of titanium dioxide has been studied using software based on density functional theory. In addition, the performance of different methods and approximations in acquiring these properties have been evaluated. The calculated properties include lattice constants and density of states of bulk material and photoabsorption spectra of nanoclusters.
The original goal was to investigate, whether excitonic effects are significant in the optical properties of anatase nanoclusters. It was found that the GPAW software package could not be used to study these effects due to computational limitations.
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Hempel, Martin. "Defect mechanisms in diode lasers at high optical output power." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2013. http://dx.doi.org/10.18452/16834.
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In dieser Arbeit wird der Catastrophic Optical Damage (COD) zeitaufgelöst untersucht um die beteiligten physikalischen Mechanismen zu identifizieren. Der COD Prozess konnte zeitlich in drei Phasen unterteilt werden, die Alterung, der thermische Runaway (selbst verstärkende Rückkopplung) und das Sekundärschadenswachstum. Die erste Phase konnte durch eine neu eingeführte Art der beschleunigten Bauteilalterung auf den Nanosekunden-Bereich reduziert werden. Die Rolle des Laser-Lichtfelds als Energiequelle des COD-Prozesses wurde experimentell bestätigt. Die genutzten thermographischen Techniken erlaubten eine in-situ Verfolgung des Defektwachstums. Diese direkte Messung der Ausbreitung, die Modellierung des Wärmeflusses und eine kristallographische Materialanalyse zeigen, dass das Material, welches von der Defekt-Front passiert wurde, innerhalb von Nanosekunden zu substanziell tieferen Temperaturen zurückkehrt. Verschiedene experimentelle Ansätze bestätigen das Vorhandensein einer Temperatur im Bereich von 1200°C-1500°C an der Schadensfront während des gesamten Degradationsprozesses. Dabei hat sich gezeigt, dass selbst wenn keine Laseremission mehr vorliegt, die verstärkte spontane Emission ausreicht, um den fortschreitenden Degradationsprozessmit Energie zu versorgen. Für den Start des thermischen Runaway muss ein bestimmter Temperaturunterschied zwischen der späteren COD-Position und dem übrigen aktiven Lasermaterial erreicht werden. Die vorliegende Arbeit zeigt verschiedene Mechanismen auf, die zu einer solchen Situation führen können. Dabei spielen auch physikalische Eigenschaften der verwendeten Materialsysteme und Schichtstrukturen eine entscheidende Rolle. Ein neu im Rahmen dieser Arbeit entwickeltes Modell zur Beschreibung der räumlichen Schadensausbreitung nutzt diesen Umstand, um die Defektkinetik ex-post zu rekonstruieren. Dies ermöglicht das Aufzeigen von Schwachstellen im Bauelement.<br>The scope of this thesis is the time-resolved investigation of the catastrophic optical damage (COD) and the identification of the underlying physical mechanisms. The COD has been separated in three temporal phases: the aging, the thermal runaway (self-amplifying feedback mechanism), and the secondary defect growth. It was possible to reduce the first phase to a couple of nano-seconds by applying a new accelerated life test scheme. It was experimentally verified that the laser light is the primary energy source of COD. The applied thermographic technologies allowed an in-situ tracing of the defect growth. A fast thermo cycle during the passage of the defect front was confirmed by this direct measurement, a modeling of the heat flow, and a crystallographic material analysis. Different experimental setups indicate the presence of a temperature in the range of 1200°C-1500°C at the defect front, during the entire COD-degradation. Even if no lasing action is present anymore, the amplified spontaneous emission is sufficient to provide enough energy for further defect growth. In order to initiate the thermal runaway, a specific temperature difference is necessary between the COD-starting location and the remaining active laser material. This thesis provides an analysis of the mechanisms leading to such a situation. This kind of analysis was used to develop a new model of the geometrical defect growth. The ability to re-construct the defect dynamics based on ex-post analysis of the defect pattern allows for the identification of bottlenecks in the investigated device design leading to COD.
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Schediwy, Sascha W. "Optical spring parametric interactions in a macroscopic opto-mechanical resonator." University of Western Australia. School of Physics, 2007. http://theses.library.uwa.edu.au/adt-WU2007.0161.
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[Truncated abstract] The research described in this thesis investigated optical spring interactions and instabilities in a macroscopic opto-mechanical resonator. The thesis describes an experiment designed to model an optical spring `tranquiliser’ cavity which has been proposed to suppress the predicted parametric instabilities in the next generation of interferometric gravitational wave detectors. In a series of experiments, the optical spring effect was observed in macroscopic optical cavities through measured changes in mechanical stiffness, and measured changes in mechanical loss. The optical spring effect was further characterised through investigation of its dependent parameters. Two pairs of identical, low optical loss mirrors were bonded to a mechanical structure using a novel low mechanical loss technique, forming an opto-mechanical composite resonator. The technique uses the naturally occurring resin Yacca gum as a bonding agent. This resulted in the formation of two optical cavities with a length of l = 0.100±0.001m, only one of which was used in experiments. Using finite element modelling, the resonator?s two lowest modes, with frequencies of fm1 = 722.8Hz and fm2 = 747.9Hz, and an effective mass 0.0323±0.0001kg, were found to be subject to the optical spring effect. ... The instabilities are expected to have a parametric gain factor of up to 100 in the frequency range of 15-120kHz. Therefore, if optical spring damping can be made large enough to reduce the Q-factor of the Advanced LIGO test-masses by a factor of 100, all parametric instabilities should be eliminated. For a simple servo loop and an optical cavity with the practically achievable finesse of F = 30,000, a tranquiliser cavity length of 1.3cm was found to produce optimum enhanced damping. This configuration only requires 1.47W of input power, resulting in an intra-cavity power of 5.72kW. The cavity mirrors were assumed to have optical coatings with a damage threshold of 1MW/cm2, which limited the spot size to a minimum area of 0.572mm2, or a radial beam waist of w = 0.427mm. This nearly flat-flat cavity has a stability g-factor of 0.9997. Even given these technical challenges, suppression of the parametric instabilities predicted to occur in the next generation of interferometric detectors is possible to achieve practically using enhanced optical spring damping. A possible design for such a tranquiliser cavity is also suggested.
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Matthews, Manyalibo Joseph 1970. "Electronic and optical properties of novel carbon structures." Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/50006.
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Elfurawi, Umaima. "Optical and electronic properties of PbS colloidal nanocrystals." Thesis, University of Nottingham, 2012. http://eprints.nottingham.ac.uk/12542/.
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This thesis describes the optical and electrical properties of colloidal PbS nanocrystals synthesized in aqueous solution and comprising different capping ligands and/or matrices. Post-synthesis thermal annealing of thiol-capped PbS colloidal quantum dots (QDs) is discussed and shown to provide a novel means of tailoring the morphological and electronic properties of the QDs. Two different regimes are reported: at low annealing temperatures (< 80oC), the annealing provides a simple strategy for controlling and narrowing the QD size distribution and photoluminescence emission. At higher annealing temperatures, the displacement of the thiol-ligands promotes the fusion of nearby quantum dots thus leading to interconnected nanocrystals. A study of the circularly polarized magneto- photoluminescence of colloidal PbS nanocrystals under the influence of a magnetic field up to 30T is presented. A semiclassical model for the population of polarized excitons is used to account for the measured magnetic field and temperature dependence of the degree of circular polarization of the QD photoluminescence. The g-factor, gX, of the exciton and its dependence on the QD size is reported for the first time. The value of gX increases from 0.1 to 0.3 at low temperature with decreasing the nanocrystal diameter from 9 to 4 nm. The transport properties of a PbS QDs thin film deposited between two electrodes are investigated. This study reveals a non-linear dependence of the current on the applied bias. At low temperature (T<100 K), the conduction is limited by the charging energy (~20 meV) of the quantum dot. The fabrication of a solid-state device based on porous TiO2 impregnated with PbS QDs is discussed. The photovoltaic response of the device in the visible and near infrared wavelength range is obtained by exploiting the Schottky junction that forms at the interface between the PbS/TiO2 film and a metallic contact.
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McNamee, Michael Jonathan. "Optical studies of electronic excitations in II-VI semiconductors." Thesis, University of Oxford, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359471.
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Zoryk, Andrew. "The electronic and optical properties of HgTe-CdTe superlattices." Thesis, University of Newcastle Upon Tyne, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244879.
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Gell, Michael A. "Electronic and optical properties of III-V semiconductor superlattices." Thesis, University of Newcastle Upon Tyne, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.352920.
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Warren, Rachel Frances. "Optical, electronic and structural properties of metal halide intercalates." Thesis, University of Cambridge, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333365.
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Vladisavljevic, Milos. "Electronic and Optical Properties of an Artificial Benzene Ring." Thesis, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31724.
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In this thesis, we develop the methodology for exploring the electronic and optical
properties of an artificial benzene ring, both analytically as well as numerically
through direct diagonalization using the configuration interaction method. We
use the extended Hubbard Hamiltonian to model the interactions with different
numbers of electrons, with spin projection and total spin resolved as good quantum
numbers. The focus in this work is on the charged case and the emergence of an
artificial gauge field and how it can be detected optically. We also examine three
other cases of the artificial benzene ring, the single electron case, the charge neutral
or half filled case, and the quarter filled case. Ground state properties, excited
state spectra, and interactions with light are described.
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Reed, Evan J. (Evan John) 1976. "Optical, electronic, and dynamical phenomena in the shock compression of condensed matter." Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/16935.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2003.<br>Includes bibliographical references (leaves 109-113).<br>This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.<br>Despite the study of shock wave compression of condensed matter for over 100 years, scant progress has been made in understanding the microscopic details. This thesis explores microscopic phenomena in shock compression of condensed matter including electronic excitations at the shock front, a new dynamical formulation of shock waves that links the microscopic scale to the macroscopic scale, and basic questions regarding the role of crystallinity in the propagation of electromagnetic radiation in a shocked material. In Chapter 2, the nature of electronic excitations in crystalline solid nitromethane are examined under conditions of shock compression. Density functional theory calculations are used to determine the crystal bandgap under hydrostatic stress, uniaxial strain, and shear strain for pure and defective materials. In all cases, the bandgap is not lowered enough to produce a significant population of excited states. In Chapter 3, a new multi-scale simulation method is formulated for the study of shocked materials. The method allows the molecular dynamics simulation of the system under dynamical shock conditions for orders of magnitude longer time periods than is possible using the popular non-equilibrium molecular dynamics (NEMD) approach. An example calculation is given for a model potential for silicon in which a computational speedup of 10⁵ is demonstrated. Results of these simulations are consistent with some recent experimental observations. Chapters 4 and 5 present unexpected new physical phenomena that result when light interacts with a shock wave propagating through a photonic crystal.<br>(cont.) These new phenomena include the capture of light at the shock wave front and re-emission at a tunable pulse rate and carrier frequency across the bandgap, and bandwidth narrowing of an arbitrary signal as opposed to the ubiquitous bandwidth broadening. Reversed and anomalous Doppler shifts are also predicted in light reflected from the shock front.<br>by Evan J. Reed.<br>Ph.D.
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Xu, Jinsong. "Electronic and Spin Dependent Phenomena in Two-Dimensional Materials and Heterostructures." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1531925662989238.
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Cusack, Mark Alexander. "Electronic and optical properties of semiconductor quantum wells and dots." Thesis, University of Newcastle Upon Tyne, 1996. http://hdl.handle.net/10443/1039.
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The influence of structural size and geometry on the electronic states, optical transitions and nonlinear optical response in semiconductor quantum wells and dots has been investigated. A quantum mechanical theory of optical nonlinearities in semiconductors has been used in conjunction with the empirical pseudopotential band structure method to determine the structural parameters leading to optimum second harmonic generation in p-type asymmetric GaAs/AlxGa₁₋xAs quantum well structures. Maximum confinement of all participating states is of paramount importance for optimising such responses. The multi-band effective mass approximation was adapted for the calculation of the electronic structure and optical transitions in cubic GaAs/AlAs quantum dots and in the recently discovered InAs/GaAs self-assembled structures. The calculation revealed the importance of factors such as the quantum mechanical mixing between bulk basis states, inhomogeneous strain and symmetry in the construction of the optical signatures of these dots.
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Vasheghani, Farahani Sepehr. "Optical and electronic properties of defects and dopants in oxide semiconductors." Thesis, University of Warwick, 2013. http://wrap.warwick.ac.uk/58463/.
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Interest in semiconductor materials has continually grown over the past 60 years due to their potential use in electronic and optoelectronic device structures. Oxide semiconductors are a particular class of materials that also combine conductivity with optical transparency, properties not usually found in the same material. These transparent conducting oxides (TCOs) have been among the first oxide materials to benefit from the availability of improved epitaxial growth techniques, although perovskite oxides and heterostructures have also proved to be opening a new era of high mobility structures based on oxide materials. Optical and electronic properties of binary oxides, specifically, high quality CdO and SnO2 epi- taxial films have been investigated in this thesis. The main band structure quantities, the band gap and band edge effective mass of CdO has long been a subject of controversy due to the degeneracy of this material. The lowest carrier concentration for an as-grown CdO film is 1-2×1019 cm−3. This brings about further difficulties in determining the optoelectronic properties due to conduction band filling and many body effects. The effective mass value is of particular importance in carrier mobility studies. Simulation and analysis of data collected from Hall effect, mid- and near-infrared reflectance measurements together with optical absorption spectroscopy enabled the band gap and band edge effective mass values to be determined at room temperature. Variations of the band gap, band edge effective mass, high frequency dielectric constant and the Fermi level with temperature and carrier concentration, and taking into ac- count the non-parabolicity of the conduction band, the Burstein-Moss shift and band gap renormalization, revealed the 0 K band gap and band edge effective mass values of 2.31 eV and 0.266m0 at the limit of zero carrier concentration in CdO. With the emergence of sophisticated growth techniques (MBE), high quality growth has become a key property in semiconductor research as it enables further investigation into the intrinsic characteristics of these materials. Carrier mobilities in high quality SnO2(101) films grown on r-plane sapphire by molecular beam epitaxy were studied. Transmission electron microscopy revealed a high density of dislocations at the interface due to the large lattice mismatch of -11.3%, along the < 101 > direction, between the films and the substrate, with an exponential decrease towards the surface of the films. Carrier mobility modelling proved to be impossible if a constant density of threading dislocations was assumed, however, by introducing a layer-by-layer model for the simulation of the mobility as a function of carrier concentration, the donor nature of dislocations in epitaxial SnO2 films was revealed. The deformation potential produced by the presence of these defects has been shown to be the dominant scattering mechanism for carrier concentrations above the Mott transition level of SnO2. Finally, the surface electronic structure of antimony-doped SnO2 films has been studied by the Hall effect, infrared reflectance, X-ray photoemission spectroscopy and electrochemical capacitance-voltage measurements. The bulk Fermi level was determined by carrier statistics calculations and used to obtain the degree of surface band bending. Modelling the surface energy bands through the capacitance-voltage spectra, revealed that SnO2 has downward band bending and surface electron accumulation. The respective variations were attained as a function of depth and composition of the samples.
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Biggs, Jason Daniel 1978. "Theoretical studies of the external vibrational control of electronic excitation transfer and its observation using polarization- and optical phase-sensitive ultrafast spectroscopy." Thesis, University of Oregon, 2010. http://hdl.handle.net/1794/11074.
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xvi, 218 p. : ill. (some col.)<br>Our theoretical studies involve the control of electronic energy transfer in molecular dimers through the preparation of specific vibrational coherences prior to electronic excitation. Our control strategy is based upon the fact that, following impulsive electronic excitation, nuclear motion acts to change the instantaneous energy difference between site-excited electronic states and thereby influences short-time electronic excitation transfer (EET). By inducing coherent intramolecular vibration in one of the chromophores prior to short-pulse electronic excitation, we exert external control over electronic dynamics.
As a means to monitor this coherent control over EET, we propose using multidimensional wave-packet interferometry (md-WPI). Two pairs of polarized phase-related femtosecond pulses following the control pulse would generate superpositions of coherent nuclear wave packets in optically accessible electronic states. Interference contributions to the time- and frequency-integrated fluorescence signal due to overlaps among the superposed wave packets provide amplitude-level information on the nuclear and electronic dynamics.
We test both the control strategy and its spectroscopic investigation by calculating pump-probe difference signals for various combinations of pulse polarizations. That signal is the limiting case of the control-influenced md-WPI signal in which the two pulses in the pump pulse-pair coincide, as do the two pulses in the probe pulse-pair. We present calculated pump-probe difference signals for a variety of systems including a simplified model of the covalent dimer dithia-anthracenophane (DTA) in which we treat only the weakly Franck-Condon active ν 12 anthracene vibration at 385 cm -1 . We further present calculated nl-WPI difference signals for an oriented DTA complex, which reveal amplitude-level dynamical information about the interaction of nuclear motion and electronic energy transfer.
We also present pump-probe difference signals from a model system in which a CF 3 group, whose torsional angle is strongly Franck-Condon active, has been added to the anthracene monomers which make up DTA. We make use of electronic structure calculations to find the torsional potential of the monomer, from which we calculate the spectroscopic signals of the dimer. We show that a significant measure of control over short-time EET is achievable in this system.
This dissertation includes previously published coauthored material.<br>Commitee in charge: Dr. Michael E. Kellman, Chair;
Dr. Jeffrey A. Cina, Advisor;
Dr. David R. Herrick;
Dr. Andrew H. Marcus;
Dr. Daniel A. Steck
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Lovering, David James. "Time resolved optical spectroscopy of electronic states in GaAs quantum wells." Thesis, University of Exeter, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305754.
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Haines, Miles J. L. S. "Optical phonons and the electronic magneto density of states of heteroepitaxial semiconductors." Thesis, Heriot-Watt University, 1990. http://hdl.handle.net/10399/905.
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Armstrong, Albert R. "Electronic and Geometric Structure of AlnOm and AlnOm +." VCU Scholars Compass, 2019. https://scholarscompass.vcu.edu/etd/5889.
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Generally, the electronic stability of aluminum clusters is associated with either closed electronic shells of delocalized electrons, or aluminum in the +3 state. To explore alternative routes for electronic stability in aluminum oxide clusters, theoretical methods were used to examine the geometric and electronic structure of AlnOm (2≤n≤7; 1≤m≤10) clusters. Two types of electronically stable clusters with large HOMO-LUMO gaps were identified the first being Al2nO3m clusters with a +3 oxidation state on the aluminum, and the second being planar clusters such as Al4O4, Al5O3, Al6O4, and Al6O5. The structures of the planar clusters have external Al atoms bound to a single O atom. Their electronic stability can be explained by the multiple valence Al sites with the internal Al atoms having an oxidation state of +3, while the external Al atoms have an oxidation state of +1. The formation of AlnOm+ clusters with high concentrations of oxygen were found experimentally. To determine the stability of such clusters theoretical methods were used to examine the geometric and electronic structure of these clusters (2≤n≤7; 1≤m≤10). The structures were found to be below average in terms stability, implying formation in a low collision environment.
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Swanlund, John M. "ELECTRONIC STRUCTURE OF CATHODE MATERIALS IN LITHIUM ION BATTERIES." VCU Scholars Compass, 2019. https://scholarscompass.vcu.edu/etd/5851.
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Lithium ion batteries are ubiquitous in modern life, from powering hand-held electronic devices to electric vehicles. And with the necessary drive toward renewable energy sources like solar and wind, electricity storage for the grid promises to drive up the demand for higher performing, less expensive, safer, and more environmentally friendly secondary batteries. Recent research has theorized that replacing halogens in batteries’ electrolytes with non-halogens can yield desirable performance characteristics while eliminating the most dangerous and problematic chemicals. This thesis explores the possibility that a similar approach can be taken with the cathodes of lithium ion batteries. The active material in a cathode is a salt composed of an alkali cation – the positive lithium ion, and a negative ion – usually a metal oxide. Replacing the negative ion with a superhalogen, which is more electronegative than the most electronegative element, may yield comparable electronic properties to current cathode materials while also opening up opportunities to research materials previously not considered for lithium ion battery cathodes.
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Derrick, Timothy James. "Electronic and optical properties of conjugated oligomers and polymers." Thesis, London South Bank University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367900.
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Amezcua-Correa, Adrian. "Deposition of electronic and plasmonic materials inside microstructured optical fibres." Thesis, University of Southampton, 2007. https://eprints.soton.ac.uk/50201/.
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Optical fibres are the transport medium of today's digital information. Nowadays, modern optical telecommunication systems make use of semiconductor optoelectronic devices to generate, control and detect light. The union of the two technologies, namely fibre photonics and semiconductor electronics is expected to have a major impact on next generation of optoelectronic devices, exploiting both the guiding capabilities of optical fibres and the signal processing properties of semiconductors devices. Only recently, with the advent of microstructured optical fibres and templating material processing methods, it has been possible to create optical fibres with solid-state material inclusions. An experimental investigation on the optical transmission properties of microstructured optical fibres impregnated with silver nanoparticles is also presented. These fibres are shown to be an excellent way of coupling optical guided modes into surface plasmons. As a result, they represent a promising platform technology for fully integrated photonic/plasmonic devices. These fibres have demonstrated the enhancement of Raman signals from molecules adsorbed onto the inner metal surfaces and thus ideally suited for Surface Enhance Raman Scattering molecular detection.
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Nedzinskas, Ramūnas. "Epitaksinių InGaAs kvantinių taškų darinių moduliuoto atspindžio ir fotoliuminescencijos spektroskopija." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2012. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2012~D_20121001_093259-68855.
Full textAbstract:
Saviformuojantys puslaidininkiniai kvantiniai taškai (quantum dots, QDs), kurių charakteringos elektronų subjuostinių (intraband) šuolių energijos yra infraraudonajame spektriniame ruože (3–25 μm), sudaro daugelio fotojutiklių aktyviąją terpę ir yra aktualūs taikymams šiuolaikinėje optoelektronikoje. Disertacijoje nagrinėjami molekulinio pluoštelio epitaksijos būdu užauginti: -- InAs kvantiniai taškai, įterpti į GaAs matricą ir GaAs/AlAs supergardelę; -- InAs kvantiniai taškai be ir su įtempimus sumažinančiuoju InGaAs sluoksniu, įterpti į kompozitinę GaAs/AlAs kvantinę duobę; -- skirtingo aukščio koloniniai InGaAs kvantiniai taškai arba kvantiniai strypeliai (quantum rods, QRs), apsupti dvimačiu InGaAs sluoksniu, ir užauginti naudojant arba As2, arba As4 šaltinį. Taikant moduliacinę atspindžio spektroskopiją ir fotoliuminescenciją, buvo ištirtos šių darinių optinės savybės bei jų elektroninė sandara, o taip pat atskleista auginimo sąlygų įtaka darinių struktūrai. Eksperimentiniai tyrimai buvo interpretuojami atliekant teorinį modeliavimą skaitmeniniu (nextnano3 programa) bei analitiniu (sukurtas algoritmas) metodais.<br>Self-assembled InAs quantum dots (QDs), whose intersublevel transition energies lie in the mid- and far-infrared spectral range (3–25μm), have attracted particular interest as active elements of infrared photodetectors. This interest is mainly due to intriguing atomic-like quantum confinement and unique optical and electronic properties of QDs. Moreover, QD electronic structure can be adjusted by varying the dots size and shape or their environment. These features make QDs to be of importance in creation of photoelectronic devices with a desired spectral range. The dissertation is concerned specifically with molecular beam epitaxy grown InGaAs QD structures with: -- InAs QD stacks embedded in GaAs matrix and GaAs/AlAs superlattice (SL), or alternatively InAs/GaAs QD-SL structures with and without AlAs barriers between the dot layers; -- InAs QDs with and without InGaAs strain-reducing layers, embedded within GaAs/AlAs quantum wells; -- columnar InGaAs QDs, also referred to as quantum rods (QRs) or quantum posts, of different morphology. (The quantum confined structure consists of vertically oriented InGaAs QRs immersed in a two-dimensional InGaAs layer). These QD structures were studied by modulated reflectance and photo- luminescence spectroscopies to reveal their optical properties and the full- extent of electronic structure. Experimental data were interpreted by numerical (nextnano3 software) and analytical (algorithm developed) modelling.