Thesis (MTech (Chemistry))--Cape Peninsula University of Technology, 2016. / The synthesis of water soluble CdTe, CdTe/CdSe and CdTe/CdSe/ZnSe nanoparticles (NPs) and their optical, cytotoxicity as well as imaging properties are presented. The synthesis was carried out under ambient conditions in the absence of an inert environment and involved the use of potassium tellurite (K2TeO3) and sodium selenosulphate (Na2SeSO4) as a stable tellurium and selenium precursor respectively, while mercaptopropanoic acid (MPA) was used as capping agents. In this method, the CdTe NPs were prepared by the addition of tellurium source solution to MPA-cadmium complex solution at different pH while keeping other parameters constant. The formation of the shell (CdSe) and multi shell (CdSe/ZnSe) were achieved by adding desired precursors to the growing CdTe core NPs at one hour interval. The temporal evolution of the optical properties and stability of the growing nanocrystals was monitored in detail by varying the refluxing time, pH and storing the NPs under ambient condition for several days. The as-prepared NPs were characterised using UV-Vis absorption and photoluminescence (PL) spectroscopy, transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). The formation of the shells was indicated by an immediate change in the colour of the reaction solutions after the addition of the desired precursor and the shift in the absorption wavelength towards red-region. The optical analyses showed an enhancement in the fluorescent intensity after the addition of the shell solution accompanied by red-shifting of the absorption and emission maximum. The stability study revealed an increase in the emission intensity as the ageing days increased. The stability study of the NPs in air at room temperature show highly improved stability of the core-shell NPs than the core. The TEM analysis showed that the materials are small, monodispersed, spherical and highly crystalline. The cytotoxicity of the NPs was investigated on LM 8 and KM-Luc/ GFP cell line using an MTT protocol at different concentrations. The cell viability show significant improvement after the shell formation with CdTe/CdSe/ZnSe core multi shell NPs having the highest cell viability at higher concentration (60 μg/mL). Furthermore a decrease in cytotoxicity is revealed with increase in reaction time, thus NPs prepared at longer (7 h) reaction time showed lower cytotoxicity compared with those prepared at shorter (0.5 h) reaction time. The confocal laser microscope image of the cells after the addition of the as-synthesised NPs confirmed the transfection of the NPs by KM-Luc/GFP cell line, indicating that the NPs have been endocytosis. This study demonstrates the great potential of the as-synthesised core-multi shell nanoparticles for biological and any applications that require efficiency, high fluorescence intensity and stability.

No description available.

Thesis (M.S.)--California Polytechnic State University, 2009. / Title from PDF title page; viewed on January 13, 2010. Major professor: William Ahlgren, Ph.D. "Presented to the Electrical Engineering faculty of California Polytechnic State University, San Luis Obispo." "In partial fulfillment of the requirements for the degree [of] Master of Science in Electrical Engineering." "December 2009." Includes bibliographical references (p. 81-87).

This work has analyzed the complex interfaces of GaN and InGaN grown by sputter deposition and GaN grown by metal-organic chemical vapor deposition (MOCVD) with CdTe and CdS. First, the GaN and InGaN films were characterized by AFM and XRD, and it has been shown that the MOCVD samples have a very smooth surface and are single crystalline with growth in the (002) direction. On the other hand, the sputter deposited samples have rougher surfaces and are polycrystalline. Furthermore, complete interface studies have been performed using in-situ XPS and deposition between GaN grown by sputter deposition and MOCVD and CdTe and CdS to determine the band alignments, conduction and valence band offsets, and Fermi level positions. These interface studies will help determine basic properties to see if these GaN films can be incorporated in a CdTe solar cell to improve its efficiency. It was determined that all the interfaces between the sputtered GaN/InGaN and CdTe/CdS have small conduction band offsets of less than 0.1 eV that do not significantly prevent electron flow across the interface. However, the valence band offsets were much more significant, as they ranged from 0.43 eV to over 1.8 eV. For purposes of the desired positions of the GaN in the CdTe solar cell, the conduction band offsets are much more crucial, and very small conduction band offsets are desired. An interesting effect was that the interfaces between InGaN/CdTe and InGaN/CdS showed In migration into the CdTe and CdS, causing a rise in the Fermi level for the CdTe and CdS, which has been known to worsen the performance of the CdTe solar cell. The MOCVD GaN/CdTe and CdS interfaces showed a slightly higher conduction band offset of about 0.15 eV, but this barrier still should not significantly prevent current flow. / Master of Science

For the theory of electrochemical analysis, a kinetic model that considers the ion transport limitations near the cathode of electrode is based upon a generalized Butler-Volmer equation and has been modified in theory and developed. The subjects of this study are the investigation of the kinetics mechanism of CdTe electrodeposition from an aqueous solution containing CdSO4, TeO2, and H2SO4 in cyclic voltammetry and applied to the optimal control of the composition and stoichiometric deviation of CdTe thin film by electrodeposition. The computer simulation is performed to understand the influences of electrodeposited parameters in the process, such as deposition temperature, pH value and concentrations of Cd2+ and HTeO2+ ions, is one of the focuses in this study. In this investigation, a novel electrochemical method for simultaneously measuring diffusion coefficient and ion transference number is applied in the simulation of CdTe electrodeposition for the first time. From the fitting of the experimental data, the values of the thermodynamic, kinetic and mass transport parameters of the electrodeposition process are obtained. In addition, the modified Butler-Volmer model predicts the potential of perfect stoichiometry (PPS) for electrodeposition of CdTe thin film, and a good agreement has been found between the calculated and experimental results. It also predicts the composition of electrodeposits for the electrodeposition of CdTe and other II-VI and III-V compounds from solutions containing reducible ions. Furthermore, the one that is worth mentioning in this investigation, a novel algorithm of stoichiometric deviation is also developed and applied to the electrodeposition for the first time. With the change of the parameter, the deviation of stoichiometry can be estimated accurately. The simulated results of mathematical model are verified experimentally using electrodeposition and can obtain two aspects. They are the accurate potential perfect stoichiometry (PPS) in which the intrinsic CdTe thin film can be electrodeposited and the stoichiometric deviation which can be dominated accurately in the adjustment of electrodeposited potential. Besides, the native non-degenerate p-type and n-type CdTe thin film can also be deposited. At PPS, well-connected granular CdTe thin films can be deposited and are predicted to be intrinsic, but are slightly p-type due to cadmium vacancies (VCd). The conversion of conductive type occurs only by defect redistribution and local defect reactions after annealing; the converted n-type layer shows lower resistivity and higher mobility. A film annealed at 350oC exhibits excellent crystallization.

Title from PDF of title page. / Document formatted into pages; contains 71 pages. / Thesis (M.S.E.E.)--University of South Florida, 2003. / Includes bibliographical references. / Text (Electronic thesis) in PDF format. / ABSTRACT: The CdTe solar cell is a leading candidate for cost-effective thin-film solar cells having demonstrated small area cell effciencies of 16.4%. A Key issue associated with CdTe thin film photovoltaic modules is the analysis of degradation behavior of the device. The analysis is complicated as changes due to degradation may be reversible. Solar cell measurement techniques were used to understand the changes in device parameters after light soaking for 1000 hours. An automated measurement setup was implemented as part of this thesis work. The main objective of this thesis was to study the effect of CdCl&esc;b2&esc;s heat treatment on the device stability. The temperature for this heat treatment was varied from 360oC to 400oC. Cells were stressed under illumination at both short circuit and open circuit conditions. It was found that the increase CdCl&esc;b2&esc;s heat treatment temperature slowed down the degradation rate.This was true for both short and open circuit stress conditions. Also short circuit stress condition slowed down the degradation of the device when compared with the open circuit condition. It became evident that the recombination current mainly got affected when the device was said to be degraded. / System requirements: World Wide Web browser and PDF reader. / Mode of access: World Wide Web.

No description available.

The aim of this study was to understand the properties of glass/TCO/CdS/CdTe/metal solar cells, the CdS and CdTe being grown by aqueous electrodeposition. Deposited films and completed cells were characterised using electrical, structural and optical techniques. This report describes the production of well-formed polycrystalline CdS and CdTe with well defined XRD peaks and band gap. Experiments were performed to investigate the pre-conditioning of the CdTe bath on the overall cell performance. Pre-conditioning the CdTe deposition bath was found to improve the Voc value of the completed devices. It has been known for some time that treating the CdTe layer of a CdS/CdTe solar cell with chlorine brings about significant improvements in the efficiency of these devices. This report presents results on a systematic variation of the chlorine concentration within a CdTe deposition bath. Solar simulated I-V measurements of completed devices clearly show that the addition of CdCl[2] to the CdTe deposition bath significantly improved the efficiency values for the glass/TCO/CdS/CdTe/metal devices. The electrical parameter most significantly affected by the addition of chlorine is the J[sc] value. In terms of the Voc performance of the device, this investigation showed that there was a trend of improving Voc with increasing chlorine concentration. Addition of chlorine also produces improvements in the preferred orientation of CdTe films as measured by XRD. Optical absorption results showed a correlation that the minima of the band gap vs. chlorine concentration graph for annealed samples matches up with the maximum in the efficiency and J[sc] graphs. To investigate whether this phenomenon was specific to chlorine or was displayed by other elements, similar experiments were performed with no chlorine inclusion but varying the indium concentration in the deposition bath. Solar simulated I-V measurements of completed devices clearly show that the addition of In[2](SO[4])[3] to the CdTe deposition bath significantly reduced the efficiency values for the glass/TCO/CdS/CdTe/metal devices. The electrical parameter most significantly affected by the addition of indium is the J[sc] value. The addition of indium also had a detrimental effect on the preferred orientation measured by XRD.

No description available.

Le travail présenté dans ce manuscrit a été effectué au sein de l’équipe de microélectronique de l’Institut de Recherche sur les lois Fondamentales de l’Univers (IRFU) du CEA. Il s’inscrit dans le contexte de la spectro-imagerie X et gamma pour la recherche en Astrophysique. Dans ce domaine, les futures expériences embarquées à bords de satellites nécessiteront des instruments d’imagerie à très hautes résolutions spatiales et énergétiques.La résolution spectrale d’une gamma-camera est dégradée par l’imperfection du détecteur lors de l’interaction photon-matière lui-même et par le bruit électronique. Si on ne peut réduire l’imprécision de conversion photon-charge du détecteur, on peut minimiser le bruit apporté par l’électronique de lecture. L’objectif de cette thèse est la conception d’une électronique intégrée de lecture de détecteur semi-conducteurs CdTe pixélisés pour gamma-caméra(s) compacte(s) et aboutable(s) sur 4 côtés à résolution spatiale « Fano limitée ». Les objectifs principaux de ce circuit intégré sont: un très bas bruit pour la mesure d’énergie des rayons-X, une très basse consommation, et une taille de canal de détection adaptée au pas des pixels CdTe. Pour concevoir une telle électronique, chaque paramètre contribuant au bruit doit être optimisé. L’hybridation entre l’électronique de lecture et le détecteur est également un paramètre clef qui fait généralement la résolution finale de l’instrument : en imposant une géométrie matricielle à l’ASIC adaptée au pas de 300 µm des pixels de CdTe, on peut espérer, réduire d’un facteur 10 la capacité parasite amenée par la connexion détecteur-électronique et améliorer d’autant le bruit électronique tout en conservant une densité de puissance constante. Une bonne connaissance des propriétés du détecteur nous permet alors d’extraire ses paramètres électroniques clefs pour concevoir l’architecture électronique de conversion et de filtrage optimale. Dans le cadre de cette thèse j’ai conçu deux circuits intégrés en technologies CMOS XFAB 0.18 µm. Le premier, Caterpylar, est destiné à caractériser cette nouvelle technologie, y compris en radiation, identifier un étage d’entrée pour le pixel adapté au détecteur, et valider par la mesure les résultats théoriques établis sur deux architectures de filtrage, semi gaussien et « Multi-Correlated Double Sampling » (MCDS), approchant l’efficacité du filtrage optimal et adaptées aux applications finales. Le deuxième circuit, D2R1, est un système complet, constitué de 256 canaux de lecture de détecteur CdTe, organisés dans une matrice de 16×16 pixels. Chaque canal comprend un préamplificateur de charge adapté à des pixels de 300 μm×300 μm, un opérateur de filtrage de type MCDS de profondeur programmable, d’un discriminateur auto-déclenché à bas seuil de détection programmable par canal. L’ASIC a été caractérisé sans détecteur et est en voie d’être hybridé à une matrice de CdTe très prochainement. Les résultats de caractérisations de la puce nue, en particulier en terme de produit puissance × bruit, sont excellents. La consommation de la puce est de 315 µW/ canal, la charge équivalente de bruit mesurée sur tous les canaux est de 29 électrons rms. Ces résultats valident le choix d’intégration d’un filtrage de type MCDS, qui est, à notre connaissance une première mondiale pour la lecture de détecteurs CdTe. Par ailleurs, ils nous permettent d’envisager d’excellentes résolutions spectrales de l’ensemble détecteur+ASIC, de l’ordre de 600 eV FWHM à 60 keV. / The work presented in this thesis is part of a project where a new instrument is developed: a camera for hard X-rays imaging spectroscopy. It is dedicated to fundamental research for observations in astrophysics, at wavelengths which can only be observed using space-borne instruments. In this domain the spectroscopic accuracy as well as the imaging details are of high importance. This work has been realized at CEA/IRFU (Institut de Recherche sur les lois Fondamentales de l’Univers), which has a long-standing and successful experience in instruments for high energy physics and space physics instrumentation. The objective of this thesis is the design of the readout electronics for a pixelated CdTe detector, suitable for a stacked assembly. The principal parameters of this integrated circuit are a very low noise for reaching a good accuracy in X-ray energy measurement, very low power consumption, a critical parameter in space-borne applications, and a small dead area for the full system combining the detector and the readout electronics. In this work I have studied the limits of these three parameters in order to optimize the circuit.In terms of the spectral resolution, two categories of noise had to be distinguished to determine the final performance. The first is the Fano noise limit. related to detector interaction statistics, which cannot be eliminated. The second is the electronic noise, also unavoidable; however it can be minimized through optimization of the detection chain. Within the detector, establishing a small pixel pitch of 300 μm reduces the input capacitance and the dark current. This limits the effects of the electronic noise. Also in order to limit the input capacitance the future camera is designed as a stacked assembly of the detector with the readout ASIC. This allows to reach extremely good input parameters seen by the readout electronics: a capacitance in range of 0.3 pF - 1 pF and a dark current below 5 pA.In the frame of this thesis I have designed two ASICs. The first one, Caterpylar, is a testchip, which enables the characterization of differently dimensioned CSA circuits to choose the most suitable one for the final application. It is optimized for readout of the target CdTe detector with 300 μm pixel pitch and the corresponding input parameters. With this circuit I have also analyzed possible filtering methods, in particular the semi-Gaussian shaping and the Multi-Correlated Double Sampling (MCDS). Their comparison is preceded by the theoretical analysis of these shapers. The second ASIC D2R1 is a complete readout circuit, containing 256 channels to readout CdTe detector with the same number of pixels, arranged in 16×16 array. Each channel fits into a layout area of 300 μm × 300 μm. It is based on the MCDS processing with self-triggering capabilities. The mean electronic noise measured over all channels is 29 electrons rms when characterized without the detector. The corresponding power consumption is 315 μW⁄channel. With these results the future measurements with the detector give prospects for reaching an FWHM spectral resolution in the order of 600 eV at 60 keV.