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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Real-time measurement of the water-insoluble aerosol size distribution: instrument development and implementation

Greenwald, Roby 02 August 2005 (has links)
This thesis concerns various aspects of the influence of atmospheric particulate matter on the terrestrial system. In Part I, the radiative influence of particulate matter on the production of crops is explored using the CERES crop model. It is known that the presence of aerosols in the atmosphere simultaneously reduces the amount of sunlight reaching the surface and increases the fraction of that light which is diffuse. Reduction of the total amount of sunlight tends to slow the rate of photosynthesis occurring in plants while increasing the fraction which is diffuse tends to increase the net rate of photosynthesis by more evenly distributing sunlight throughout all layers of a plant canopy. The CERES crop model was modified to estimate the influence of both a reduction in total sunlight and an increase in the diffuse fraction. Model simulations were performed for rice, maize and wheat at a variety of locations and found the likely influence of aerosols on crop production to be a 0-10% reduction in yield compared to the base case. In Part II, the concentration and size distribution of water-insoluble aerosols (WIA) is explored. It has been well-established that atmospheric particulate matter influences the planetary radiation budget both directly and indirectly. The magnitude of these influences is related to particle solubility. A new technique was developed to provide these measurements in real-time. This instrumentation was evaluated in a laboratory setting and implemented into several field studies. Results from these sampling campaigns indicate that in areas heavily influenced by motor vehicle traffic, the WIA concentration is dominated by particulate soot. Many episodes of high levels of crustal dust were also observed. At these times, the WIA size distribution shifted toward larger sizes in a characteristic manner. This suggests that this method is useful for detecting insoluble mineral aerosols as well as particulate soot and that examination of the WIA size-distribution may provide a basis to distinguish between the two.
42

Fabrication of Sb-doped CIGS by selenization of stacked elemental layer and thin solar cell

Jian, Chong-Yao 27 August 2012 (has links)
This study is using selenization of stacked elemental layers to form Cu(In,Ga)Se2(CIGS). In the process, use Cu/Sb/In/Ga/Se precursor to heat to 550 oC at Se vapor in vacuum chamber. From the result of XRD¡BRaman and EPMA, that show of the precursor do not form to CIGS. After that, The result of using different layers precursor to form CIGS show that only Cu/In/GaSe/Se reach to form CIGS, but it still has second phase. According to the literature¡Athe reason for the formation of CIGS selenide process due to interdiffusion caused the formation of ternary solid phase, the solid phase diffusion reaction could be hampered.And then change to use rapid thermal selenization to form CIGS with two step of heating (hold at 300 oC and 650 oC) at N2 atmosphere. The laminated follow the best results in the selenide process Cu/In/GaSe/Se precursors in Se atmosphere, the (112) preferred orientation is 26.8o-26.9o in the XRD results of the fixed process conditions. EPMA composition analysis and comparison of Ga actual amount will increase with the estimated value of the amount of increase(Estimated value 4atom% actual value 2atom%¡FEstimated value 9.2tom% actual value 10atom%¡AGa/¢»=0.32), but the composition has yet to amend. Then will join Sb on CIGS observed from the SEM results Sb does improve the CIGS thin film flatness as well as to help grain growth in rapid thermal selenization, grain size of about 1 to 3£gm.
43

Exploration of s-process elemental abundances in globular cluster stars using medium- and high-resolution spectra.

Worley, Charlotte Clare January 2009 (has links)
This thesis has used medium- and high-resolution spectral data to derive elemental abundances, in particular light and heavy s-process elemental abundances, for groups of giant stars in the globular clusters 47 Tuc, NGC 6388 and NGC 362. These analyses were undertaken using both curve-of-growth and spectrum synthesis techniques. The techniques were calibrated with respect to the metal-poor giant star Arcturus in order to reduce systematic errors in the analysis process. A feasibility study was undertaken that compared synthetic spectra at different resolutions throughout the colour-magnitude diagram (CMD) of a metal-rich ([Fe/H] = -0.5 dex) globular cluster. This study identified where on the CMD light and heavy s-process elemental abundances could be derived at medium resolution (R ~ 10,000). Abundance analyses could be undertaken on the giant branches down to just below the horizontal branch and then again on the main sequence below Teff ~ 4500 K. At all other places on the CMD high-resolution spectra (R ~ 30,000) are required to derive these abundances. Performance verification data at R ~ 5,000$ was obtained using the Robert Stobie Spectrograph (RSS) on the Southern African Large Telescope (SALT) and showed that there were no large scale s-process elemental abundance variations in 47 Tuc giant branch stars. The level of precision in this preliminary data was [X/Fe] ~ 0.5dex. A resolution of R ~ 10,000 should be achievable with SALT RSS in the future which will improve this limit. The AAOmega survey of 47 Tuc stars at R ~ 6,500 was more promising in certain aspects of elemental abundance determination. The observed wavelengths included the key features of CN and CH molecular bands, and light (Z < 30) and heavy (38 < Z < 63) element spectral lines. CN indices were measured and calibrated to previous results. The well-known CN bimodality was observed in the 47 Tuc stars, as well as a radial gradient in CN strength. A preliminary subset of ten of the survey stars have undergone an abundance analysis for which the abundances of Fe, Si, and Ca were found to be homogeneous within this cluster. The Na abundances had a large range in values that were observed to correlate with CN strength. The s-process elemental abundance results were inconclusive. The Zr abundances showed little to no enhancement in the sample and the Ba abundances varied considerably due to strong lines of Ba II being extremely sensitive to microturbulence. Various high-resolution studies were carried out using spectra of giant stars in 47 Tuc, NGC 6388 and NGC 362 observed on the Australian National Observatory (ANO) 2.3 m echelle spectrograph and the Ultra-Violet Echelle Spectrograph (UVES) on the Very Large Telescope (VLT). The high-resolution analysis of 47 Tuc giant star Lee 2525 found an enhanced Zr abundance in this star which resolved a discrepancy between two previous 47 Tuc elemental abundance studies (Brown & Wallerstein 1992; Wylie et al. 2006). The stars in the VLT dataset that were analysed here included five giant branch stars in 47 Tuc, two in NGC 6388 and thirteen in NGC 362. The low temperatures and gravities of these stars caused departures from local thermodynamic equilibrium in low excitation potential neutral species, particularly Fe and Zr, that needed to be taken into account before reliable stellar parameters and elemental abundances could be determined for these stars. Veiling effects due to circumstellar dust were postulated to have produced artificially low metallicities for the infra-red excess stars in this sample, particularly for the 47 Tuc stars. The element abundance analyses of 47 Tuc, NGC 6388 and NGC 362 stars found the derived metallicities to be homogeneous for each cluster (<[Fe/H]>(47Tuc) = -0.88 +/- 0.09 dex; <[Fe/H]>(NGC6388) = -0.60 +/- 0.06 dex; <[Fe/H]>(NGC362) = -1.21 +/- 0.08 dex). The 47 Tuc sample included Lee 2525 and the five VLT stars. The derived metallicities were in reasonable agreement with previously reported values. The light (ls) and heavy (hs) s-process element abundances were enhanced and homogeneous in the stars of each cluster. The abundances determined for 47 Tuc and NGC 6388 were in good agreement, reflecting the similarity in metallicity of the stars in these two clusters (<[ls/Fe]>(47Tuc) = +0.53 +/- 0.02 dex; <[hs/Fe]>(47Tuc) = +0.40 +/- 0.06 dex; <[ls/Fe]>(NGC6388) = +0.58 +/- 0.13 dex; <[hs/Fe]>(NGC6388) = +0.39 +/- 0.07 dex). The more metal-poor cluster NGC 362 was less enhanced in ls elemental abundances and slightly more enhanced in hs elemental abundances (<[ls/Fe]>(NGC362) = +0.32 +/- 0.10 dex, <[hs/Fe]>(NGC362) = +0.46 +/- 0.09 dex). The clear enhancement in the s-process elemental abundances and homogeneity in the results for each globular cluster is evidence that these stars have been enhanced extrinsically in s-process elements. Pollution events in the history of each cluster has resulted in the abundance distribution in both the light elements and the heavy elements that has been observed in the stars analysed in this thesis. The enhancements in Na, ls and hs elemental abundances favours intermediate mass AGB stars as the source of the pollution.
44

Análisis de la influencia de la metodología de la intervención psicomotriz sobre el desarrollo de las habilidades motrices en niños de 3 a 4 años

Terry Andrés, Jaime 14 October 2014 (has links)
Esta tesis tiene como propósito establecer las preferencias metodológicas en la intervención en las clases de psicomotricidad con los alumnos de 1º curso de educación infantil. Principalmente se intenta determinar si hay diferencias en el desarrollo de las aptitudes motrices del niño en función de emplear diferentes metodologías de intervención. La intención es demostrar que las aptitudes motrices de los niños de 3 años se desarrollan con mejores resultados mediante la utilización de sesiones de psicomotricidad con una metodología funcional que mediante una metodología vivencial. El objetivo de esta tesis es determinar si existen diferencias entre los métodos de intervención en psicomotricidad en cuanto al desarrollo psicomotor que generan y cuáles pueden ser los resultados de la aplicación de uno y otro estilo. Para ello planteamos la siguiente hipótesis: los niños que han seguido un programa psicomotriz con sesiones estructuradas mediante una metodología de intervención funcional y directiva presentan mejores resultados en la evaluación de la aptitud motriz que otros que han tenido un modelo de intervención vivencial y no directivo. Para poder establecer los valores del desarrollo de las aptitudes motrices de los niños antes de la intervención y los que tendrán después de la intervención, aplicaremos las Escalas McCarthy de Aptitudes y Psicomotricidad para Niños (MSCA). El estudio se distribuye a lo largo de un curso escolar, llevando a cabo una primera toma de datos mediante la aplicación de las escalas McCarthy antes de comenzar con la intervención metodológica que tiene una duración de 4 meses. Al finalizar ésta, se aplicarán de nuevo las escalas MSCA para comprobar si hay diferencia con respecto a los datos obtenidos 4 meses antes. Para la recogida de datos se utilizaron las tres subescalas de la Batería McCarthy, pertenecientes a la escala motora, que evalúan la motricidad gruesa y que son las tres únicas subescalas que no se incluyen en la Escala General Cognitiva (GC) de la batería: subescala número 9; coordinación de piernas; subescala número 10, coordinación de brazos y subescala número 11, de acción imitativa. El tratamiento de los datos fue llevado a cabo mediante la aplicación del SPSS19. Las variables independientes que se analizaron fueron la edad, el sexo, la metodología aplicada y la temporalización de los tests. Las variables dependientes fueron la coordinación de piernas, la coordinación de brazos, la acción imitativa y la psicomotricidad gruesa. Se distribuyó a los niños en dos grupos escogidos azarosamente. El grupo experimental estuvo compuesto por los alumnos de dos clases de 1º de educación infantil (3 años). En este grupo, el profesor especialista de psicomotricidad, llevó a cabo las clases de psicomotricidad mediante una metodología funcional, utilizando como referencia las líneas psicopedagógicas de Le Boulch, Picq y Vayer. El grupo de control estuvo formado por los alumnos de las otras 3 clases de 1º de infantil del mismo centro educativo, y las clases de psicomotricidad correspondieron a una metodología vivencial en relación con los criterios metodológicos de Lapierre y Aucouturier. Estas clases fueron impartidas por el profesor especialista de psicomotricidad y la profesora tutora de cada grupo. La diferencia en el modelo de intervención determinaría si la metodología influye en el desarrollo de las aptitudes motrices de los niños de 3 años en el entorno escolar. Los resultados obtenidos nos revelaron que la metodología funcional mejora el desarrollo de la habilidad motriz en niños de 3 a 4 años de edad. / This thesis aims to establish the methodological preferences intervention psychomotor classes with students of 1st year of early childhood education. The study is primarily to determine if there are differences in the development of motor skills of the children in terms of the use of different methods of intervention. The intention is to show that the driving skills of children 3 years to develop better results using psychomotor sessions with a functional methodology through experiential methodology. The objective of this thesis is to determine whether there are differences between the methods of intervention in terms of psychomotor psychomotor development and generate what may be the results of the application of either style. To do this we propose the following hypothesis: children who have followed a psychomotor program with sessions structured through a methodology of practical and policy intervention have better results in the evaluation of motor ability that others who have had a model of experiential intervention and non-directive. To set the values of the development of motor skills of children before surgery and those who have after surgery, apply the McCarthy Scales of Children s Abilities (MSCA). The study was spread over a school year, performing a first data by applying the McCarthy scales before starting methodological intervention that lasts for 4 months. At the end of it, apply again the MSCA scales to check for difference from the data obtained 4 months ago. For data collection the three subscales of the McCarthy battery, belonging to the motor scale, which assesses gross motor and are the only three subscales that are not included in the General Cognitive Scale (GC) battery used subscale number 9; coordinating legs; Number 10 subscale, and subscale arm coordination number 11 of imitative action. The data processing was carried out by applying the SPSS19. The independent variables analyzed were age, sex, the methodology and the timing of the tests. The dependent variables were the coordination of legs, arm coordination, and imitative action psychomotor thick. It was distributed to the children into two groups chosen randomly. The experimental group consisted of students from two classes of 1st nursery school (3 years). In this group, psychomotor specialist teacher held classes psychomotor by a functional approach, using as reference lines psychoeducational Le Boulch, Picq and Vayer. The control group consisted of students from the other 3 classes of 1st degree in the same school, and psychomotor classes corresponded to an experiential methodology in relation to the methodological criteria about Aucouturier and Lapierre. These classes were taught by a specialist teacher and psychomotor teacher tutor for each group. The difference in the intervention model would determine whether the methodology influences the development of motor skills of children 3 years in the school environment. The results showed us that the methodology improves functional motor skill development in children 3-4 years old.
45

Further Development of Atmospheric Pressure, Self-Igniting Microplasma Devices (MPDs) for Elemental Analysis of Liquid Microsamples Using Atomic Emission Spectrometry (AES)

Weagant, Scott Richard January 2011 (has links)
The present elemental analysis workhorse worldwide is Inductively Coupled Plasma (ICP) Atomic Emission Spectrometry (AES) and Mass Spectrometry (MS). Due to the high power requirements, large gas consumption and the more obvious attribute, size, the ICP is tethered to the lab. Usually, samples must be collected, bottled, sometimes stabilized by acids and then shipped back to the lab for analysis (hours to days to weeks turnover rate). Due to the demand for a portable analyzer this thesis will focus on further development of microplasma devices (MPDs) for portable on-site analysis, in (near) real-time. Mini-In-Torch Vapourization (mini-ITV) is the sample introduction method for MPDs which removes the need for sample preparation (further necessitates portability). Mini-ITV introduces the sample into the MPD via electrothermal vapourization of a dry (water-free) nano- to micro- volume sample. Pneumatic nebulization, the commercially available ICP sample introduction method would extinguish the microplasma. Microplasma stability is the first issue addressed by confining the microplasma to a quartz tube (“wall-stabilized”) in hopes of a more stable MPD background emission. Once stabilized MPD conditions were found key microplasma parameters were studied including MPD power, HVac frequency, operating mode, inter-electrode distance (IED) and observation location, in hopes of improved MPD analytical performance. Microplasma excitation mechanism and maximum energy available in the microplasma for analyte are discussed. Some fundamental characteristics such as excitation temperature (Texc) and changes in atom/ion population with variation in some of the key MPD parameters were also determined.
46

Vitamin B-6 status, energy and protein intakes, and amino acids in the diets and plasma of school-aged patients with Phenylketonuria : implications for an improved nutritional treatment

Prince, Annie 28 November 1990 (has links)
Dietary intake data of 15 treated patients with phenylketonuria (PKU) (7-17 years) and six control siblings (6-14 years) were used to evaluate the effectiveness of medical foods to balance energy, protein, vitamin B-6, and individual amino acids from natural foods and to evaluate vitamin B-6 status. Four-day diet records were computer-analyzed and the contribution of medical foods and natural foods to the total diets of the patients was determined. A fasting blood sample and two 24-hour urine collections were obtained from each subject. In eight patients consuming a strict diet, natural foods provided 0.9 g protein and 39 mg phenylalanine (phe)/100 calories, a significant reduction from control intakes of 3.3 g protein and 153 mg phe/100 calories. However, plasma phe levels were above the acceptable treatment range. Medical foods were consumed in less than the recommended quantities to meet approximately 120% of the Recommended Dietary Allowances (RDAs) for protein. These foods contributed 73% of the total protein RDAs but only met 22% of the energy RDAs of patients consuming the strict diet. Taste qualities of certain L-amino acids (L-AAs; Lmethionine, L-glutamic and L-aspartic acids), which constitute the protein in elemental medical foods (EMFs) for school-aged patients, make acceptance of these products difficult. Intakes of each of these L-AAs were above nutritional standards and suggested that their levels could be safely lowered in EMFs. Natural foods and medical foods provided 0.057 and 0.046 mg vitamin B-6/g protein, respectively, above the 0.020 RDA standard and the mean control intake of 0.018 mg vitamin B-6/g protein. The mean plasma pyridoxal 5'- phosphate (PLP) concentration for the patients with PKU was over twice that of the mean control concentration and above literature values. However, more than half of the patients excreted less than 30% of their vitamin B-6 as 4-pyridoxic acid; values below the criterion suggested for inadequate status. This work provides data for a better understanding of vitamin B-6 metabolism and status in PKU and supports the design and testing of a new EMF to balance energy, protein, and amino acids from natural foods and which may improve dietary adherence. / Graduation date: 1991
47

Exploration of s-process elemental abundances in globular cluster stars using medium- and high-resolution spectra.

Worley, Charlotte Clare January 2009 (has links)
This thesis has used medium- and high-resolution spectral data to derive elemental abundances, in particular light and heavy s-process elemental abundances, for groups of giant stars in the globular clusters 47 Tuc, NGC 6388 and NGC 362. These analyses were undertaken using both curve-of-growth and spectrum synthesis techniques. The techniques were calibrated with respect to the metal-poor giant star Arcturus in order to reduce systematic errors in the analysis process. A feasibility study was undertaken that compared synthetic spectra at different resolutions throughout the colour-magnitude diagram (CMD) of a metal-rich ([Fe/H] = -0.5 dex) globular cluster. This study identified where on the CMD light and heavy s-process elemental abundances could be derived at medium resolution (R ~ 10,000). Abundance analyses could be undertaken on the giant branches down to just below the horizontal branch and then again on the main sequence below Teff ~ 4500 K. At all other places on the CMD high-resolution spectra (R ~ 30,000) are required to derive these abundances. Performance verification data at R ~ 5,000$ was obtained using the Robert Stobie Spectrograph (RSS) on the Southern African Large Telescope (SALT) and showed that there were no large scale s-process elemental abundance variations in 47 Tuc giant branch stars. The level of precision in this preliminary data was [X/Fe] ~ 0.5dex. A resolution of R ~ 10,000 should be achievable with SALT RSS in the future which will improve this limit. The AAOmega survey of 47 Tuc stars at R ~ 6,500 was more promising in certain aspects of elemental abundance determination. The observed wavelengths included the key features of CN and CH molecular bands, and light (Z < 30) and heavy (38 < Z < 63) element spectral lines. CN indices were measured and calibrated to previous results. The well-known CN bimodality was observed in the 47 Tuc stars, as well as a radial gradient in CN strength. A preliminary subset of ten of the survey stars have undergone an abundance analysis for which the abundances of Fe, Si, and Ca were found to be homogeneous within this cluster. The Na abundances had a large range in values that were observed to correlate with CN strength. The s-process elemental abundance results were inconclusive. The Zr abundances showed little to no enhancement in the sample and the Ba abundances varied considerably due to strong lines of Ba II being extremely sensitive to microturbulence. Various high-resolution studies were carried out using spectra of giant stars in 47 Tuc, NGC 6388 and NGC 362 observed on the Australian National Observatory (ANO) 2.3 m echelle spectrograph and the Ultra-Violet Echelle Spectrograph (UVES) on the Very Large Telescope (VLT). The high-resolution analysis of 47 Tuc giant star Lee 2525 found an enhanced Zr abundance in this star which resolved a discrepancy between two previous 47 Tuc elemental abundance studies (Brown & Wallerstein 1992; Wylie et al. 2006). The stars in the VLT dataset that were analysed here included five giant branch stars in 47 Tuc, two in NGC 6388 and thirteen in NGC 362. The low temperatures and gravities of these stars caused departures from local thermodynamic equilibrium in low excitation potential neutral species, particularly Fe and Zr, that needed to be taken into account before reliable stellar parameters and elemental abundances could be determined for these stars. Veiling effects due to circumstellar dust were postulated to have produced artificially low metallicities for the infra-red excess stars in this sample, particularly for the 47 Tuc stars. The element abundance analyses of 47 Tuc, NGC 6388 and NGC 362 stars found the derived metallicities to be homogeneous for each cluster (<[Fe/H]>(47Tuc) = -0.88 +/- 0.09 dex; <[Fe/H]>(NGC6388) = -0.60 +/- 0.06 dex; <[Fe/H]>(NGC362) = -1.21 +/- 0.08 dex). The 47 Tuc sample included Lee 2525 and the five VLT stars. The derived metallicities were in reasonable agreement with previously reported values. The light (ls) and heavy (hs) s-process element abundances were enhanced and homogeneous in the stars of each cluster. The abundances determined for 47 Tuc and NGC 6388 were in good agreement, reflecting the similarity in metallicity of the stars in these two clusters (<[ls/Fe]>(47Tuc) = +0.53 +/- 0.02 dex; <[hs/Fe]>(47Tuc) = +0.40 +/- 0.06 dex; <[ls/Fe]>(NGC6388) = +0.58 +/- 0.13 dex; <[hs/Fe]>(NGC6388) = +0.39 +/- 0.07 dex). The more metal-poor cluster NGC 362 was less enhanced in ls elemental abundances and slightly more enhanced in hs elemental abundances (<[ls/Fe]>(NGC362) = +0.32 +/- 0.10 dex, <[hs/Fe]>(NGC362) = +0.46 +/- 0.09 dex). The clear enhancement in the s-process elemental abundances and homogeneity in the results for each globular cluster is evidence that these stars have been enhanced extrinsically in s-process elements. Pollution events in the history of each cluster has resulted in the abundance distribution in both the light elements and the heavy elements that has been observed in the stars analysed in this thesis. The enhancements in Na, ls and hs elemental abundances favours intermediate mass AGB stars as the source of the pollution.
48

"Alchemy of Desire/Dead Man's Blues": To Tree Or Not To Tree

Larson, Heidi Elaine 01 August 2015 (has links)
The subjects of grief and of the afterlife are ones that have been discussed and analyzed for centuries, with no conclusive answers as to where we go or how we should go on. In “Alchemy of Desire/ Dead Man’s Blues”, Caridad Svich continues this discussion through a narrative, centered around a group of women dealing with the aftermath of a loss. She uses the term alchemy as an allegory for one’s ability to transcend and transform, and in turn, come to know the meaning of life…and death. This paper serves as a documentation of the SIUC Theater Department’s process and results in bringing this conversation to the stage, and this story to life.
49

Synthesis of Multiple Constituent Ferecrystal Heterostructures

Westover, Richard 23 February 2016 (has links)
The ability to form multiple component heterostructures of two-dimensional materials promises to provide access to hybrid materials with tunable properties different from those of the bulk materials or two-dimensional constituents. By taking advantage of the unique properties of different constituents, numerous applications are possible for which none of the individual components are viable. The synthesis of multiple component heterostructures, however, is nontrivial, relying on either the cleaving and stacking of bulk materials in a “scotch tape” type technique or finding coincidentally favorable growth conditions which allow layers to be grown epitaxially on each other in any order. In addition, alloying of miscible materials occurs when the modulation wavelength is small. These synthetic challenges have limited the ability of scientists to fully utilize the potential of multiple component heterostructures. An alternative synthetic route to multiple component heterostructures may be found through expansion of the modulated elemental reactant technique which allows access to metastable products, known as ferecrystals, which are otherwise inaccessible. This work focuses on the expansion of the modulated elemental reactants technique for the formation of ferecrystals containing multiple constituents. As a starting point, the synthesis of the first alloy ferecrystals (SnSe)1.16-1.09([NbxMo1-x]Se2) will be discussed. The structural and electrical characterization of these compounds will then be used to determine the intermixing of the first three component ferecrystal heterojunction ([SnSe]1+δ)([{MoxNb1-x}Se2]1+γ)([SnSe]1+δ)({NbyMo1-y}Se2). Then, by synthesizing ([SnSe]1+δ)m([{MoxNb1-x}Se2]1+γ)1([SnSe]1+δ)m({NbxMo1-x}Se2)1 (m = 0 - 4) compounds with increasing thicknesses of SnSe, the interdiffusion of miscible constituents in ferecrystals will be studied. In addition, by comparison of the ([SnSe]1+δ)m ([{MoxNb1-x}Se2]1+γ)1([SnSe]1+δ)m({NbxMo1-x}Se2)1 (m = 0 - 4) compounds to the ([SnSe]1+δ)m(NbSe2)1 (m = 1 - 8) compounds the electronic interactions of the MoSe2 and NbSe2 layers will be determined. Finally, the effects of different alloying strategies and the interdiffusion of miscible constituents will be further examined by the synthesis of ordered ([SnSe]1.15)1([TaxV1-x]Se2)1([SnSe]1.15)1([VyTa1-y]Se2)1 and ([SnSe]1+δ) ([TaxV1-x]Se2) compounds with the effect of isoelectric doping on the charge density wave transition in (SnSe)1.15(VSe2) also being explored. This work contains previously published and unpublished co-authored material.
50

Improving Doping and Minority Carrier Lifetime of CdTe/CdS Solar Cells by in-situ Control of CdTe Stoichiometry

Evani, Vamsi Krishna 07 April 2017 (has links)
Cadmium Telluride (CdTe) is a leading thin film photovoltaic (PV) material due to its near ideal bandgap of 1.45 eV and its high optical absorption coefficient. Advancements in efficiencies of CdTe/CdS solar cells over the past few decades have come from improving the short circuit current (JSC) and Fill Factor (FF) but the Open Circuit Voltage (VOC) has been stagnant. Further improvements in efficiencies should come from increased VOC’s. VOC’s can be improved by increasing the acceptor concentration and minority carrier lifetime. Both these parameters can be controlled by manipulating the native defect concentration in CdTe which can be achieved by varying CdTe stoichiometry. In this study, a deposition system called Elemental Vapor Transport was used to vary the CdTe stoichiometry with an intent to change the native defect concentration and therefore pave way to increase acceptor concentration and lifetimes. Elemental cadmium and tellurium were heated in dedicated zones and their vapors were transported to the substrate using a carrier gas. By varying the temperatures and flowrates of the carrier gas through the zones, the gas phase Cd/Te ratio was varied to deposit Cd-rich, Te-rich and stoichiometric films. Structural properties were investigated using Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD), and Transmission Electron Microscopy (EDS). Electrical characterization of completed devices was carried out by Current-Voltage (J-V), Capacitance-Voltage (C-V), and Spectral Response (SR) and Deep Level Transient Spectroscopy (DLTS) measurements. Cd-rich films showed smaller grain sizes and lesser degree of preferential orientation. Te-rich films showed increased acceptor concentration and carrier lifetimes and solar cells fabricated using these films showed higher VOC’s compared to Cd-rich and stoichiometric films .Higher degree of CdTe-CdS mixing was observed at the interface for films deposited at increased substrate temperatures.

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