Dissertations / Theses on the topic 'Photo-Scanning'

2009 - 2010
La ricerca si applica allo studio di decorazioni compositive a matrice geometrica originate dalle mutevoli combinazioni di forme elementari: la divisione regolare del piano con forme chiuse che lo ricoprono completamente, senza sovrapporsi e senza mai lasciare spazi vuoti. Operando su di esso, si inizia a quantificarlo, individuando ogni sua singola parte: la misurazione conduce alla scomposizione in forme elementari di figure complesse. Nello sviluppo di tali configurazioni, il problema della replica è sempre presente, dalla mera idea progettuale fino alle azioni di restauro, in quanto dalla ripetitività delle singole parti – fondamento del suo stesso esistere – prende origine l’intera composizione. Si è cercato, quindi, a partire da un’attenta analisi delle leggi simmetriche che dettano le logiche generative del disegno ornamentale, per una ben precisa canonizzazione di temi e motivi, di identificare gli schemi geometrici che consentano il controllo razionale della decorazione tramite l’individuazione dei procedimenti della iterazione in serie. Non si restituisce semplicemente il dettaglio così come ci appare, ma la scomposizione teorica dell’opera permette di individuare, nella successiva ricomposizione grafica, la natura e la posizione di ogni singolo elemento: uno sguardo critico che guida a una corretta e realistica riproduzione. I modelli formali tendono a divenire così modelli geometrici, simbolo di una struttura più profonda, che è possibile cogliere con l’aiuto di precisi schemi topologici. Attraverso i casi studio esaminati, ed in particolare in funzione del sistema decorativo riscontrato, è stato possibile individuare procedure metodologiche di rilievo ritenute idonee ad esplicitare il processo geometrico di base al fine di facilitare la successiva fase di replica sia in ambiente digitale che fisico e di favorire una funzionale sistematizzazione dell’ornato. In particolare si è ricorso ad un’innovativa metodologia, detta di photo scanning, che permette l’acquisizione simultanea di nuvole di punti e di texture. E così, nota la legge armonica che domina l’intera composizione, definita dal movimento rigido di un modulo predefinito su di un reticolo piano, la decorazione può facilmente riprodursi partendo dalla semplice unità quale entità che può essere, con l’utilizzo di macchine a controllo numerico, reiterata meccanicamente. La procedura è stata applicata a casi studi idonei per analizzare i principi della ripetibilità in serie e delle operazioni di laboratorio; ciò ha consentito, grazie alla ri-progettazione digitale e alla produzione con gli strumenti della tecnologia a controllo numerico, di codificare la riproducibilità tecnica, immateriale e materiale, del decoro architettonico. Le procedure e le strumentazioni descritte possono essere un potente metodo per il controllo, la verifica e il monitoraggio del decoro architettonico, permettendo di realizzare database metrici interattivi in grado di fornire in qualsiasi momento informazioni sull’oggetto rilevato. Impostare un modello di schedatura dei rivestimenti geometrici costituisce uno strumento di catalogazione funzionale sia alla tutela e alla fruizione del bene immobile, sia alla definizione di un metodo di approccio allo studio dei gruppi di simmetria. Si sarà così in grado di stabilire l’origine degli schemi decorativi, i percorsi di distribuzione, lo sviluppo di tendenze locali. [a cura dell'autore]
IX n.s.

It was found that laser modified wood surfaces can be bonded together to create a wood composite without the need of any additive. This bonding method removes the need of applying adhesive, potentially lowers cost, and eliminates off gassing of petroleum resins, creating a wood product with many eco-friendly attributes. This body of work outlines a) initial chemical analysis of the laser modified surface b) its bond strength and c) the optimization of factors that control the strength of the bond. Surface chemical analysis on laser modified wood was conducted using photo acoustic Fourier transform infrared spectroscopy (PA-FTIR) and X-Ray photoelectron spectroscopy (XPS). Light microscopy and scanning electron microscopy were utilized for surface topology analysis.Differential scanning calorimetry (DSC) quantified the thermal properties of the modified wood surface. Screening of multiple factors that would contribute to surface modification and adhesion was performed utilizing mechanical testing. Optimization of significant factors that affect bond strength was determined statistically utilizing a design of experiment approach. Chemical analysis of the laser modified surface revealed changes in the carbonyl and aromatic regions indicating modification of the hemicellulose and lignin components, intensifying with increasing laser modification.The C1/C2 ratios found via XPS revealed that one or more of the following is occurring: more extractives have moved to the surface, condensation reactions among lignin units, and the loss of methoxy and breakage of aryl ether linkages occurred.Microscopy images showed color changes to a darker caramel color with a smoothing of surface topology, suggesting the occurrence of the softening and/or melting of wood polymers. DSC verified chemical and/or physical changes in the wood with the modified material now having a glass transition temperature between 130-150°C.DOE found that laser parameters (power and focus) as well as hot press parameters (temperature and pressure) were significant in optimizing the bond. The impact of the study is the first documentation of the ability to laser modifies wood surfaces and subsequently bond them together. The ability of the wood polymers at the surface to undergo flow at elevated temperature is implicated in the adhesion mechanism of the laser modified wood.
Master of Science

La mise en place, l'étalonnage et l'utilisation d'un nouveau banc expérimental basses températures basé sur une technique photothermique appelée photo pyroélectricité (PPE) sont décrits dans ce manuscrit. Les échantillons que nous avons étudiés en utilisant ce nouvel instrument sont le glycérol, le 1,2 propanediol et leurs mélanges binaires avec l'eau. Ce sont des cryoprotecteurs bien connus (CPAs) utilisés dans la cryoconservation, qui est une technique de préservation des cellules et tissus vivants en les refroidissant à des très basses températures. Le but ultime de la cryoconservation est d'éviter ou de maîtriser la formation de glace et d'atteindre un état vitreux ou amorphe. La vitesse de refroidissement, de chauffage et la concentration des CPAs utilisés sont les paramètres clés qui déterminent la formation de la glace. Par conséquent, l'étude des propriétés thermiques, en particulier près de la transition vitreuse (Tg) des solutions binaires des CPAs avec de l'eau est très importante pour comprendre leur comportement lors du refroidissement. La PPE a été utilisée pour étudier l'effusivité et le temps de relaxation ∝ caractéristique de la transition vitreuse. Le Tg et la fragilité (m) ont été déterminés à partir des données de la PPE en utilisant le modèle d'Havriliak Negami. L'état vitreux présente une très grande viscosité, de l'ordre de 10¹² Pa.s au voisinage du Tg. Le Tg et m peuvent être calculés à partir de l'évolution de la viscosité en fonction de la température ou par calorimétrie différentielle à balayage (DSC). Ainsi, des études à l'aide de ces deux techniques ont été menées et les résultats ont été comparés avec les données de la PPE
The construction, calibration and application of a new low temperature instrument based on a photothermal technique called photo pyroelectricity (PPE) is described in this manuscript. The samples we studied using the new PPE instrument were glycerol, 1,2 propanediol and their binary mixtures with water. These liquids are well known cryoprotectants (CPAs) used in cryopreservation, which is a technique to preserve the living cells and tissues from biological degradation by cooling to sub zero temperatures. The ultimate goal in cryopreservation is to avoid or control the ice formation and attain a glassy or amorphous state.The rate of cooling and heating and the concentration of the CPAs used are the key parameters that determine the ice formation. Therefore, studying the temperature dependent thermal properties especially near their glass transition temperature (Tg) of the binary solutions of CPAs with water at different concentrations are highly important to understand their behavior while cooling. The PPE technique was used to study the effusity and the ∝ relaxation time near the glass transition phenomenon. The Tg and fragility (m) were determined from the PPE data using the Havriliak Negami model. The glassy state has a characteristic property of very high viscosity, of the order of 10¹² Pa.s at Tg. The Tg and m can be calculated from the temperature evolution of viscosity or from Differential Scanning Calorimetry (DSC) measurements. Therefore, viscosity and DSC studies were conducted on the samples and were compared with PPE data

Light-addressable potentiometric sensors (LAPS) and scanning photo-induced impedance microscopy (SPIM) have been extensively applied as chemical sensors and biosensors. This thesis focuses on the investigation of LAPS and SPIM for electrochemical imaging based on two different semiconductor substrates, silicon on sapphire (SOS) and indium tin oxide (ITO) coated glass. Firstly, SOS substrates were modified with 1,8-nonadiyne self-assembled organic monolayers (SAMs), which served as the insulator. The resultant alkyne terminals provided a platform for the further functionalization of the sensor substrate with various chemicals and biomolecules by Cu(I)-catalyzed azide alkyne cycloaddition (CuAAC) 'click' reactions. The CuAAC reaction combined with microcontact printing (μCP) was successfully used to create chemical patterns on alkyne-terminated SOS substrates. The patterned monolayers were found to be contaminated with the copper catalyst used in the click reaction as visualized by LAPS and SPIM. Different strategies for avoiding copper contamination were tested. Only cleaning of the silicon surfaces with an ethylenediaminetetraacetic acid tetrasodium salt (EDTA) solution containing trifluoroacetic acid after the 'click' modification proved to be an effective method as confirmed by LAPS and SPIM results, which allowed, for the first time, the impedance of an organic monolayer to be imaged. Furthermore, the 1,8-nonadiyne modified SOS substrate was functionalized and patterned with an RGD containing peptide, which was used to improve the biocompatibility of the substrate and cell adhesion. By seeding cells on the peptide patterned sensor substrate, cell patterning was achieved. Single cell imaging using LAPS and SPIM was attempted on the RGD containing peptide modified SOS substrate Finally, an ITO coated glass substrate was used as a LAPS substrate for the first time. The photocurrent response, the pH response, LAPS and SPIM imaging and its lateral resolution using ITO coated glass without any modification were investigated. Importantly, single cell images were obtained with this ITO-based LAPS system.

L’intérêt croissant pour l’étude de la morphogénèse des côtes à falaises a permis de mieux appréhender les environnements méso/macrotidaux, mais en délaissant les environnements microtidaux. Pour cette raison, nous proposons d’étudier, à partir d’une approche exploratoire multi-échelle, la dynamique érosive des côtes à falaises en Méditerranée à travers l’exemple de la région Provence-Alpes-Côte d’Azur. Le choix de ce territoire s’est justifié en réponse à une problématique relative à la gestion des risques côtiers identifiée par le Conseil-Régional-PACA qui a financé ce travail doctoral. Les principaux objectifs visent à caractériser d’une part l’ampleur relative des occurrences érosives en fonction de la variabilité temporelle des forçages météo-climatiques, et d’autre part le degré du contrôle géologique sur la morphologie côtière. Toute la difficulté de l’étude réside donc dans l’optimisation des fenêtres d’observation afin de distinguer les comportements érosifs. Nous proposons donc de tester l’apport de quatre méthodes permettant de définir si l’érosion se produit de manière (1) continue à l’échelle annuelle (levés LiDAR embarqués depuis un bateau), (2) chronique à l’échelle séculaire (orthophotographies aériennes) et (3) exceptionnelle voir (4) catastrophique sur les temps propres à l’Holocène et au Quaternaire (datations aux cosmogéniques in situ 36Cl et analyses morphométriques). Au regard des résultats mesurés et interprétés, il apparaît que l’activité gravitaire produite au cours du XXe siècle (érosion moyenne de l’ordre du cm.an-1) est très faible par rapport aux environnements méso/macrotidaux
Increasing interest in studying rocky cliff coastline morphogenesis allowed a better understanding of meso/macrotidal environments, but let microtidal environments apart. Thus we propose studying the dynamic of cliff coastlines erosion in Mediterranean in the South-East of France, through a multi-scale explorative approach. This doctoral work was supported by the region Provence-Alpes-Côte d’Azur, which identified a problematic in relation with coastal hazard management. The main objectives aim at characterizing on one hand how the temporal variability of meteorologic and climatic forcings affects the magnitude of erosion, and on other hand to which extent the geological setting controls the coastline morphology. The great challenge of this work therefore consists in optimizing the observation range in order discriminate erosive behaviours. Thus we propose assessing the contribution of four methods in determining whether erosion takes place (1) continuously at annual scale (boat-borne laser scanning surveys), (2) chronic at secular scale (aerial orthophographies)and (3) exceptional even (4) catastrophic over the characteristic timescales of Holocene and Quaternary (cosmic ray exposure dating from in-situ 36Cl and morphometric analysis). The interpretation of the results shows that erosion rate observed through the XXth century (order of magnitude of cm.y-1) is very low compared to meso/macrotidal environments. However at timescales ranging from pluri-secular (0.29 ka BP) to pluri-millenar (6.8 ka BP), exceptional storms surges of +3 NGF could initiate an erosion process resulting in the formation of horizontal shore platforms

Jádrem této disertační práce bylo studovat optické a elektrické charakteristiky tenkovrstvých elektroluminiscenčních součástek řízených střídavým proudem (ACTFEL) a zejména vliv procesu stárnutí luminiforů na jejich optické a elektrické vlastnosti. Cílem této studie měl být příspěvek ke zvýšení celkové účinnosti luminoforů, vyjádřené pomocí jasu, účinnosti a stability. Vzhledem k tomu, že současnou dominantní technologií plochých obrazovek je LCD, musí se další alternativní technologie plošných displejů porovnávat s LCD. Výhodou ACTFEL displejů proti LCD je lepší rozlišení, větší teplotní rozsah činnosti, větší čtecí úhel, či možnost čtení při mnohem vyšší intenzitě pozadí. Na druhou stranu je jejich nevýhodou vyšší energetická náročnost, problém s odpovídající barevností tří základních barev a podstatně vyšší napětí nutné pro činnost displeje. K dosažení tohoto cíle jsme provedli optická, elektrická a optoelektrická měření ACTFEL struktur a ZnS:Mn luminoforů. Navíc jsme studovali vliv dotování vrstvy pomocí KCl na chování mikrostruktury a na elektroluminiscenční vlastnosti (zejména na jas a světelnou účinnost) ZnS:Mn luminoforů. Provedli jsme i některá, ne zcela obvyklá, měření ACTFEL součástek. Vypočítali jsme i rozptylový poměr nabitých barevných center a simulovali transportní charakteristiky v ACTFEL součástkách. Studovali jsme vliv stárnutí dvou typů ZnS:Mn luminoforů (s vrstvou napařenou či získanou pomocí epitaxe atomových vrstev) monitorováním závislostí svítivost-napětí (L-V), velikost vnitřního náboje - elektrické pole luminoforu (Q-Fp) a kapacitance-napětí (C-V) ve zvolených časových intervalech v průběhu stárnutí. Provedli jsme krátkodobá i dlouhodobá měření a pokusili jsme se i o vizualizaci struktury luminoforu se subvlnovým rozlišením pomocí optického rastrovacího mikroskopu pracujícího v blízkém poli (SNOM). Na praktickém případu zeleného Zn2GeO4:Mn (2% Mn) ACTFEL displeje, pracujícího při 50 Hz, jsme také studovali stabilitu svítivosti pomocí měření závislosti svítivosti na napětí (L-V) a světelné účinnosti na napětí (eta-V). Přitom byl zhodnocen význam těchto charakteristik. Nezanedbatelnou a neoddělitelnou součástí této práce je i její pedagogický aspekt. Předložený text by mohl být využit i jako učebnice pro studenty na mé univerzitě v Lybii.

碩士
國立中興大學
物理學系所
102
Sample preparation for scanning capacitance microscopy (SCM) significantly influences the accuracy of SCM measurements. Especially, the quality of the oxide layer on sample surface including surface roughness of the oxide layer, interface traps, and charges in the oxide layer is decided by sample preparation. These factors influencing the oxide qualities induce capacitor-voltage curve distortion and shift, and hence lead to exceptional differential capacitor (dC/dV) signal intensity. In this article, a short-wavelength semiconductor laser was employed to investigate the improvements of irradiation treatment on the surface oxide layer of a silicon substrate. The specimens were treated by laser illumination with different power and duration. With scanning capacitance spectroscopy (SCS), one can observe the changes in the stability of the surface oxide layers. Experimental results indicated that increasing the illumination power improves the quality of the surface oxide layer, resulting in dC/dV curves with a small flat-band voltage shift and higher signal intensities. Changing the illumination duration leads to changes in the full width at half maximum (FWHM) of SCS curves, but flat-band voltage shift. The main influence of illumination duration is to reduce the trapped charges in the surface oxide layer. For the sample preparation without illumination treatment, the SCS curves of the samples exhibited a high flat-band shift, implying that there are more oxide defects, i.e., low oxide quality. This results in low dC/dV signal intensities. The experimental approach provides a reference for enhancing the dC/dV signal intensities and the stability of SCM measurements on the micro-analysis of electronic materials and surface/interface analysis.

碩士
國立中正大學
物理所
96
In the past, the photoreactive polymer was studied by the all-optical experiment system. However, there are some shortcomings in the all-optical experiment system. For example, the space resolution limits by optical diffraction limit and the destruction of direction of molecular during the all-optical analysis. So we propose a novel approach based on the scanning probe microscopy (SPM). Local poling was made by the probe of AFM beyond diffraction limit, then measured directly by the electric force microscopy which can avoid the optical destruction. The polymer film (DR1-PMMA) was spin-coated on the ITO glass. The local poling of polymer was made by the probe of Atomic force microscopy which is coating a Ti-Pt film and giving a poling bias with the photo-assisted poling (PAP). The polarization was detected by the electric force microscopy (EFM). The laser beam is focused at the AFM tip with an inverted optical microscopy. We successed to made the poling dots of one or two dimensions which the period is 5μm and the diameter of the dot is between 500nm to 1μm. The behavior of PAP was expressed by a biexponential function with two response time t1 and t2; t1 is the respond time of trans to cis, which is proportion to the inversion of laser power and t2 is the respond time of orientational distribution of molecular, which is proportion to the inversion of effectively mobility. We also know that the cis life-time is about 53 seconds and the decay time of the poling dot with a 3μw irradiation is 8 min. The population of saturation of cis state is proportion to the laser power.

An important question with respect to radiation therapy is to what degree of accuracy, dose delivery can be achieved in clinical practice. It is well understood that accurate delivery of a specific radiation dose to a target volume is critical to the success of radiation therapy. The use of portal imaging in radiotherapy for verification of field size, shape, orientation and patient setup is of vital importance in delivering successful radiation treatment. One of the modalities used in improving tumor localization and geometric verification of field sizes is the on-line electronic portal imaging device (EPID). In this thesis, the dosimetric characteristics of a scanning liquid - filled ionization chamber electronic portal imaging device (SLIC-EPID) have been investigated. To assess the system's response in relation to radiation beam intensity, a series of characteristic curves were obtained for various field sizes and energies. It was shown that the response of the imaging system was dependent on incident radiation intensity and could be characterized by a square root function to within 1% accuracy. Exit dose measurements with the SLIC - EPID on the central axis of the beam using homogeneous attenuating phantom materials revealed that the Portal Vision™ is capable of measuring the transmission dose to within 3% of standard dosimeters, such as the ionization chamber. For dosimetry applications, additional build-up material on top of the detector cassette of the portal imager is required to calibrate the system prior to dose measurements. Open field and wedged dose profiles of the portal imager show an accuracy of better than 3.5% when compared with those obtained using an ionization chamber in regions near field edges. SLIC-EPIDs, when configured appropriately have the potential of being used as exit dosimeters. They are capable of determining the relative dose at the exit surface of the patient with an accuracy of better than 3.5%.

博士
國立臺灣科技大學
機械工程系
87
The purpose of this research is to develop a new Line Scanning Mask Base Photo-curing System (LSM) using visible light. The approach of this new developed system is using a photo mask to shadow a layer which the area under the shadow will not be cured in the process of line scanning. Besides, the area where the light could pass through will be cured. The light source used in this project is a high power Xe lamp. Optical fiber is used to guide the light and to form a uniform energy line type light. In order to reduce the photo polymer wasted during part building, the light scanning is from the bottom of the working plane. Furthermore, Taguchi Method is used in this research to find the near optimized combination of process parameters in LSM system within a limited experiment work. The result has given a suggestion of a set of process parameters for layer and solid part build. Based on the above LSM system, the low speed and high cost laser point scanning technique used in conventional sterolithography RP systems could be replaced by the high speed and low cost ling scanning technique.

碩士
國立臺灣師範大學
物理學系
104
The recent studies show that intermixing quantum crystal PbS with the active light-absorber (〖CH〗_3 〖NH〗_3 〖PbI〗_(3-x) 〖Cl〗_x) film in perovskite solar cell enlarges the grain size, which can be exceeded to 4µm. The quantum crystal in perovskite increases not only power conversion efficiency over 17.4%, but also the diffusion length. In order to investigate the variation of the electronic properties of the perovskite solar cell film in dark and under illumination condition, scanning tunneling microscopy (STM) was utilized to study the topography images and localized electronic properties of the perovskite active light-absorber. In this work, the electronic dI/dV spectroscopy measurement of perovskite intermixing PbS in dark demonstrates n-type semiconductor behavior. Moreover, the increase of density of states at valence band of perovskite film reveals the augment of hole carrier concentration under illumination. The shift of electronic dI/dV spectroscopy of perovskite with PbS compared to that of the perovskite without PbS shows that the magnitude of carriers separation is associated with the grain size. Also the grain size enlarged is beneficial for power conversion efficiency (PCE).

Strong underwater bonds between polycarbonate sheet and various other substrates were achieved using ethyl 2-cyanoacrylate gel cured with an anionic photoinitiator (dibenzoylferrocene). The gel reacts quickly with water on contact and forms a protective polyethyl cyanoacrylate (PECA) skin. This provides a diffusion barrier that protects the inner monomer from further reaction with or polymerisation by water (hydroxide ions). The PECA skin is, however, permeable to water and the inner monomer slowly reacts as water diffuses through the PECA skin. The application procedure for this adhesive is critical because of the fast reaction with water. The adhesive should be applied at the centre of the bond area in such a way as to cover the smallest exposed surface area and that it should not be spread out over the entire surface area. The PECA skin will rupture when the substrates are pressed together, exposing unreacted monomer to the fresh new surface between the two substrates. The adhesive displaces water as it propagates towards the joint edges. In this way it is able to form a strong underwater bond. Without a photoinitiator, ethyl cyanoacrylate adhesives will form strong bonds to smooth underwater surfaces. The addition of a photoinitiator (dibenzoylferrocene), however, increases the rate at which the bond strength develops. Photo differential scanning calorimetric (photo-DSC) analysis was used to determine the optimum photoinitiator concentration. A concentration of between 0.3% (m/m) and 0.1% (m/m) was found to be optimum for adhesive films between 0.5 and 1.2 mm thick. Epoxy-based underwater adhesives have the disadvantage that the cure rate is very slow at low water temperatures. In contrast, the current system features a negative temperature dependence. Therefore, the curing rate is faster at lower water temperatures, making it highly suitable for very cold environmental conditions. The underwater bonding properties of cyanoacrylate adhesive were measured on a wide range of metallic and non-metallic materials. Bond strengths ranged from 1 to 5 MPa respectively. Bond strength (0.2 mm film thickness) develops in a very short time (less than a minute) using a 5 mW/cm2 blue LED light source as trigger for the photo initiator. Water temperatures between 1.5 and 40 °C did not influence the ultimate bond strength achieved following 50 seconds of illumination. The reduction in bond strength due to the ethyl cyanoacrylates reacting with water was measured in artificial sea water and potable water. A 20% reduction in bond strength was found after 10 minutes of water exposure. The underwater bond should therefore be made as soon as possible following exposure to water. Bond ageing studies on both steel and polycarbonate showed an initial decrease in bond strength (during the first 50 hours); thereafter the bond strength stabilises.
Dissertation (MEng)--University of Pretoria, 2011.
Chemical Engineering
unrestricted

abstract: In this dissertation research, conventional and aberration-corrected (AC) transmission electron microscopy (TEM) techniques were used to evaluate the structural and compositional properties of thin-film semiconductor compounds/alloys grown by molecular beam epitaxy for infrared photo-detection. Imaging, diffraction and spectroscopy techniques were applied to TEM specimens in cross-section geometry to extract information about extended structural defects, chemical homogeneity and interface abruptness. The materials investigated included InAs1-xBix alloys grown on GaSb (001) substrates, InAs/InAs1-xSbx type-II superlattices grown on GaSb (001) substrates, and CdTe-based thin-film structures grown on InSb (001) substrates. The InAsBi dilute-bismide epitaxial films were grown on GaSb (001) substrates at relatively low growth temperatures. The films were mostly free of extended defects, as observed in diffraction-contrast images, but the incorporation of bismuth was not homogeneous, as manifested by the lateral Bi-composition modulation and Bi-rich surface droplets. Successful Bi incorporation into the InAs matrix was confirmed using lattice expansion measurements obtained from misfit strain analysis of high-resolution TEM (HREM) images. Analysis of averaged intensity line profiles in HREM and scanning TEM (STEM) images of the Ga-free InAs/InAs1-xSbx type-II strained superlattices indicated slight variations in layer thickness across the superlattice stack. The interface abruptness was evaluated using misfit strain analysis of AC-STEM images, electron energy-loss spectroscopy and 002 dark-field imaging. The compositional profiles of antimony across the superlattices were fitted to a segregation model and revealed a strong antimony segregation probability. The CdTe/MgxCd1-xTe double-heterostructures were grown with Cd overflux in a dual-chamber molecular beam epitaxy with an ultra-high vacuum transfer loadlock. Diffraction-contrast images showed that the growth temperature had a strong impact on the structural quality of the epilayers. Very abrupt CdTe/InSb interfaces were obtained for epilayers grown at the optimum temperature of 265 °C, and high-resolution imaging using AC-STEM revealed an interfacial transition region with a width of a few monolayers and smaller lattice spacing than either CdTe or InSb.
Dissertation/Thesis
Doctoral Dissertation Materials Science and Engineering 2017