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Alves, Leticia Rodrigues. "Biochemical and structural alterations induced by selenium under cadmium stress in tomato plants /." Jaboticabal, 2019. http://hdl.handle.net/11449/183154.
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Orientador: Priscila Lupino GratãoResumo: As plantas estão expostas a adversidades no ambiente que as circundam, como a contaminação por cádmio (Cd). Este metal pesado tem aumentado na atmosfera devido a atividades humanas. As plantas podem absorver o Cd, causando sérias alterações estruturais, fisiológicas e bioquímicas. As plantas desenvolveram sistemas de defesa complexos, incluindo mecanismos não enzimáticos e enzimáticos para evitar uma cascata de oxidação descontrolada causada pelo estresse oxidativo. Alguns elementos, como o selênio (Se), se utilizados em concentração adequadas, podem induzir uma melhora no sistema antioxidante, no crescimento e nos atributos fotossintéticos. Ainda é pouco conhecido o papel do Se nas respostas das plantas ao estresse. O objetivo deste trabalho foi obter novas informações sobre o papel do selenato e selenito no sistema de desintoxicação das plantas, incluindo a avaliação da nutrição mineral, atividade de enzimas antioxidantes e conteúdo de compostos não enzimáticos, pigmentos, alterações estruturais e o papel do Se na modulação do etileno, com o uso de mutantes hormonais como ferramenta. Nossos dados indicam que o Se é uma estratégia interessante para melhorar o metabolismo da planta sob condições normais ou estressantes. O selênio pode induzir aumento da ação do metabolismo de defesa antioxidante, provavelmente devido a alterações na sinalização do etileno. Além disso, em condições normais, o Se induz alterações estruturais nas células, o que pode contribuir para o desenvolvim... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: Cadmium (Cd) contamination is a worldwide concern and one of the most severe causes of abiotic stress in plants, triggering losses in crop production and contamination risks to human health. This heavy metal increased in atmosphere due to human activities. Plants can uptake Cd, causing serious changes in structural, physiological and biochemical processes. Plants developed a complex defence systems including non-enzymatic and enzymatic mechanism to avoid oxidative stress and prevent an uncontrolled oxidation cascade. Some elements, such as selenium (Se), if used in adequate concentration, may induce an improvement in antioxidant system, growth and photosynthetic attributes. It is still unknown the mechanisms of Se in stress responses. The aim of this work was get new insights about the role of selenate and selenite-mediated detoxification strategies, including the evaluation of mineral nutrition, the activity of antioxidant enzymes and non enzymatic compounds, pigments, structural alterations and the role of Se in modulate ethylene, with the use of hormonal mutants as a tool. Our data indicates that Se is an interesting strategy to improve plant metabolism under normal or Cd stressful-condition. Selenium may induce enhancement in antioxidant defence metabolism, probably due to alterations in ethylene signalling. Moreover, under normal condition Se induce structural alterations in cells, which may contribute to plant development. Thus, the information available in this work is... (Complete abstract click electronic access below)
Doutor
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Wong, Donald Chun Kit. "Toxic effects of selenite and selenate on marine microalgae : a physiological and ultrastructural study." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/29341.
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Seven species of marine phytoplankters assigned to different taxonomic divisions were tested for toxic responses to two different molecular species of selenium known to be prevalent in seawater, selenite and selenate. Selenate proved to be more toxic than selenite, although severe toxicity was only observed at high concentrations
(10⁻² and 10⁻³ M) of both selenate and selenite. At these concentrations, growth was completely or severely inhibited in most species tested. In some of the species that remained viable, both the percentage of motile cells and their swimming speed were drastically reduced. Scanning electron microscopy revealed that, under these circumstances, Dunaliella tertiolecta cells possessed much shorter flagella compared to the controls, while those that became non-motile lacked flagella altogether. Despite these striking alterations in both growth and morphology, cells of Amphidinium carterae, Dunaliella tertiolecta and Pavlova lutheri showed, after prolonged exposures, signs of adaptation to high selenium concentrations. Lower concentrations of selenium were generally non-toxic and frequently even stimulatory to growth. These observations suggest that for meaningful inferences on selenium toxicity
both the concentration range and the length of the studies must be considered and the potential for adaptation to high selenium concentrations taken into consideration.
The main ultrastructural and physiological changes in cells of Dunaliella tertiolecta, Pavlova lutheri and Amphidinium carterae treated with selenite or selenate involved the cell coat, mitochondria, chloroplasts as well as the respiratory and photosynthetic rates. Other changes were observed in the nucleus, lipids, vacuoles, nitrogen and carbon contents, but these showed greater variability among the microalgae studied. The major alterations suggested that energy transducing systems were severely affected by selenium toxicity. These led to significant decreases or even elimination of storage products which were indicative of severe shortage in energy and produced major reductions in growth. These occurred later upon exposure to the toxicant and coincided with the loss of cell coat material, suggesting that the shedding of cell surface material might play a major role in the detoxification and adaptation of the microalgae to toxic concentrations of selenium.Science, Faculty of
Botany, Department of
Graduate
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Barboza, Eliza [UNESP]. "Biofortificação agronômica com selênio em cultivares de repolho." Universidade Estadual Paulista (UNESP), 2018. http://hdl.handle.net/11449/154224.
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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
O objetivo deste trabalho foi avaliar concentrações de selênio (selenato e selenito de sódio) no crescimento, produção e biofortificação de duas cultivares de repolho. Para isso foram realizados dois experimentos em casa de vegetação, em sistema hidropônico, no período de julho a novembro de 2014, na UNESP, campus Jaboticabal-SP. Os experimentos diferiram conforme a fonte de selênio (Se) utilizada (selenato e selenito de sódio). Em ambos os experimentos, avaliaram-se dois fatores, sendo: duas cultivares de repolho (‘Fênix’ e 'Red Dinasty’) e cinco concentrações de Se (0, 5, 15, 30 e 60 µmol L-1) na solução nutritiva. O delineamento experimental utilizado foi o de blocos casualizados, com esquema fatorial 2 x 5 e quatro repetições. As variáveis analisadas foram o teor e acúmulo de Se na raiz e cabeça de repolho, área, diâmetro, comprimento e densidade de raiz, produtividade de repolho, massa seca de raiz, caule e cabeça de repolho e o teor e acúmulo de nitrogênio, fósforo e enxofre na cabeça de repolho. As fontes selenato e selenito promoveram o crescimento das raízes de repolho devido aos aumentos verificados em área, diâmetro, comprimento e densidade de raiz, em baixas concentrações de Se aplicadas. O aumento da produção de massa seca de raiz provavelmente foi devido o maior crescimento da raiz, que foi influenciado pelo fornecimento de Se. A massa seca do caule foi diferente apenas entre as cultivares de repolho com aplicação de selenato ou selenito. O teor de nitrogênio apresentou diferenças apenas entre as cultivares quando utilizada a fonte selenito. Ambas as fontes de Se também proporcionaram aumentos na absorção de fósforo e enxofre quando baixas concentrações de Se foram fornecidas. Observou-se que a aplicação de até 16,77 e 7,54 µmol L-1 de Se com as fontes selenato e selenito, respectivamente, proporcionaram os maiores incrementos na produtividade do repolho, e mesmo com a redução da produtividade com concentrações acima destas, os valores foram maiores que o tratamento controle. Isso indica que o Se foi benéfico ao repolho, pois não reduziu a sua produção. Verificou-se que a biofortificação foi eficiente para ambas as cultivares de repolho, que absorveram e acumularam Se na cabeça de repolho em função do incremento de Se, tanto com selenato como selenito.
The objective of this research was to evaluate concentrations of selenium (sodium selenate and selenite) in the growth, production and biofortification of two cabbage cultivars. Two experiments were carried out in greenhouse under hydroponic system, from July to November, 2014, at UNESP, Jaboticabal-SP campus. The experiments differed according to the source of selenium (Se) used (sodium selenate and selenite). In both experiments two factors were evaluated: two cabbage cultivars ('Fênix' and 'Red Dinasty') and five concentrations of Se (0, 5, 15, 30 and 60 μmol L-1) in the nutrient solution. The experimental was a randomized block design, with 2 x 5 factorial and four replications. The variables analyzed were the content and accumulation of Se in the root and shoot cabbage, evaluating area, diameter, length, density and dry mass in the root, cabbage yield, stem and cabbage head, and the content accumulation of nitrogen, phosphorus and sulfur in the cabbage shoot. Selenate and selenite sources promoted the growth of cabbage roots due to increases in area, diameter, length and root density at low concentrations of Se applied. The increase in root dry mass production was probably due to higher root growth, which was influenced by the supply of Se. The dry mass of the stem was different only between the cabbage cultivars with application of selenate or selenite. The nitrogen content presented differences only among the cultivars when the selenite source was used. Both S sources also provided increases in phosphorus and sulfur absorption when low concentrations of if were provided. It was observed that the application of up to 16,77 and 7,54 μmol L-1 of Se with selenate and selenite sources, respectively, provided the greatest increases in cabbage yield, and even with the reduction of productivity with concentrations above these, the values were higher than the control treatment. These indicate that the Se was beneficial to the cabbage, since it did not reduce its production. It was verified that biofortification was efficient for both cabbage cultivars, which absorbed and accumulated Se in the cabbage head as a function of the increase of Se, with both selenate and selenite.
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Tan, Thatt Yang Timothy School of Chemical Engineering & Industrial Chemistry UNSW. "Photocatalytic reduction of selenate and selenite : water/wastewater treatment and the formation of nano-selenium compounds." Awarded by:University of New South Wales. School of Chemical Engineering and Industrial Chemistry, 2003. http://handle.unsw.edu.au/1959.4/20448.
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The current work investigates the photocatalytic reduction of selenium (Se) ions, selenate Se(VI) and selenite Se(IV), from two perspectives: Se ion removal from water and wastewater and the formation of nano-Se compounds. Se ion pollution has become an environmental issue in recent years, and hence there is an urgent need for an efficient removal technique. In addition, there is increasing interest in the formation of nano-size semiconductors for niche applications. Since Se is a semiconductor, its formation onto the semiconductor TiO2 could lead to the discovery of new composite materials. The current study has successfully elucidated the mechanism of Se ions reduction by photocatalysis. Factors such as the simultaneous adsorption of the Se ions (the electron scavenger in this case) and a suitable organic compound (the hole scavenger), and the chemical properties of the hole scavenger were crucial for effective and efficient Se ions photoreduction. Optimum conditions in relation to pH, concentrations and types of hole scavenger were reported and discussed. It was also found that stoichiometric adsorption ratio of formate and selenate resulted to optimum photoreduction rate. A modified Langmuir-Hinshelwood kinetic model that considered the simultaneous adsorption of both solutes was derived. The current investigation has also seen the successful formation Se deposits of different morphologies onto the TiO2 particles. Discrete Se particles of various sizes in the nano-size range as well as a Se film were deposited onto the TiO2 particles under different initial experimental conditions. The Se-TiO2 composite semiconductor was explored for the removal of cadmium Cd2+ ions, which resulted in the formation of CdSe-TiO2 systems. The photoreduction of Se ions using silver-modified TiO2 showed the enhanced reduction of Se ions to Se2- in the form of H2Se gas. It is suggested that the H2Se gas generated from the current photoreduction process could be used as a safer and cheaper technique in the formation of Se-compounds such copper selenide, cadmium selenide and zinc selenide. All these compounds were widely used in optical and semiconducting devices.
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Ferreira, Raphael Leone da Cruz [UNESP]. "Biofortificação e toxicidade de selênio na cultura da alface em solução nutritiva." Universidade Estadual Paulista (UNESP), 2016. http://hdl.handle.net/11449/144363.
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Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)
As informações sobre fontes de selênio (Se) em alface são incipientes na literatura, sobretudo, com relação ao limite entre biofortificação e toxicidade. Assim, o objetivo deste estudo foi determinar níveis críticos de Se na solução nutritiva e foliar, e a melhor fonte que aumente a biofortificação da alface hidropônica sem causar toxicidade. O delineamento experimental utilizado foi inteiramente casualizado representado por duas fontes de selênio, selenito de sódio (Na2SeO3) e selenato de sódio (Na2SeO4), dez concentrações de selênio (0; 2; 4; 6; 8; 16; 32; 64; 96; 128 μM) com quatro repetições por tratamento, totalizando 80 unidades experimentais. As concentrações adequadas estão entre 5,6 e 16 μM de selênio na forma selenato em solução nutritiva e teores foliares adequados de 10,2 a 41,8 mg kg-1 de selênio.
Information on sources of selenium (Se) in lettuce are scarce in the literature, especially with respect to the boundary between Biofortification and toxicity. The objective of this study was to determine critical levels of Se in the nutrient solution and leaf and the best source to increase biofortification of hydroponic lettuce without causing toxicity. The experimental design was completely randomized represented by two sources of selenium, sodium selenite (Na2SeO3) and sodium selenate (Na2SeO4) ten selenium concentrations (0. 2. 4. 6. 8. 16. 32. 64. 96. 128 M) with four replicates per treatment, totaling 80 experimental units. The concentrations are between 5.6 and 16 M selenium selenate form the nutrient solution and appropriate foliar 10.2 to 41.8 mg kg-1 of selenium.
CNPq: 132361/20159
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Finzer, Brant M. "Detection of Oxyanion Adsorption at the Silica-Aqueous Interface using Total Internal Reflection (TIR)-Raman Spectroscopy." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1417521135.
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King, Ellen Anne. "Structure and Relaxation in Germanium Selenide and Arsenic Selenide Glasses." Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/202735.
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GeₓSe₍₁₋ₓ₎ and AsₓSe₍₁₋ₓ₎ glasses have found use in many technological applications due to their excellent rheological properties and their wide IR transparency window. However, the low glass transition temperatures of these glasses leads to large changes in their properties, due to structural relaxation, over the weeks and months subsequent to their fabrication. Thus, obtaining a more thorough understanding of structural relaxation and its relation to the structure, composition, and processing of these glasses is important in furthering their use. Structural investigations, using NMR and Raman spectroscopies, performed on the GeₓSe₍₁₋ₓ₎ family of glasses show that the structure of these glasses is composed of two distinct microdomains. One corresponds to a rigid GeSe₂-like domain and the other corresponds to a floppy Se domain. These results are compared to other existing structural models for GeₓSe₍₁₋ₓ₎ glasses. Enthalpy measurements on both GeSe₉ and GeSe₄ optical fibers which were aged up to five years demonstrate that both compositions undergo a large amount of enthalpy relaxation in this time period. Raman spectroscopy performed concurrently with enthalpy measurements on the same GeSe₉ and GeSe₄ fibers shows that one of the structural changes taking place within the glass network is the conversion of edgesharing to corner-sharing tetrahedra in the GeSe₂-like phase. Moreover, the rate at which this conversion takes place is shown to be similar to the rate of enthalpy relaxation, suggesting that this structural change is one of the main mechanisms for structural relaxation in GeₓSe₍₁₋ₓ₎ glasses. Implementation of the Tool-Narayanaswamy-Moynihan (TNM) model as a hybrid computer model allowing the prediction of the four relaxation parameters Δh*, log(A), x, and β via optimization of simulated and experimental data was accomplished. It was found that a multi-rate version of the TNM model, which obtains an average set of model parameters via optimization of multiple experimental thermal histories simultaneously, was able to predict relaxation parameters for AsₓSe₍₁₋ₓ₎ glasses within the 2.10 ≤
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Cooper, Matthew A. "Selenium mediated cyclizations and reactions of selenones /." Title page, contents and abstract only, 1994. http://web4.library.adelaide.edu.au/theses/09PH/09phc7776.pdf.
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Stewart, Helen. "Studies into the growth and doping of zinc selenide and zinc cadmium selenide." Thesis, Heriot-Watt University, 1996. http://hdl.handle.net/10399/734.
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Barsova, Zoia. "Właściwości fizykochemiczne spinelu ZnCr₂Se₄ domieszkowanego wybranymi pierwiastkami d- i f-elektronowymi." Doctoral thesis, Katowice : Uniwersytet Śląski, 2020. http://hdl.handle.net/20.500.12128/16785.
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As part of this work, the synthesis of doped poly- and monocrystalline compounds based on ZnCr₂Se₄ was planned and carried out, and then their physicochemical characteristic was determined. The inspiration for the research consisted in its unusual physicochemical properties.
This compound has a spinel structure and is a p-type semiconductor with a spiral magnetic structure. The d- and f-electron elements manganese, holmium and neodymium were chosen as admixtures, guided by different values of effective magnetic moment compared to chromium ions on III oxidation state. The synthesis of poly- and monocrystalline compounds was based on solid phase reactions (ceramic method for polycrystalline compounds and chemical vapour transport for growth of single crystals). X-ray methods (diffraction, SEM, XPS), magnetic measurements (SQUID, strong fields), electric measurements (four-point method), and thermal analysis (DSC/TG) were used to develop the characteristics of the compounds obtained.
In the Zn₁₋ₓMnxCr₂Se₄ polycrystalline system, single-phase compounds in the x = 0.1÷0.5 range were obtained, which was confirmed by an X-ray study. The lattice and anion parameters increase linearly with an increase in the Mn2+ amount, which is consistent with the difference in the radii values between Zn2+ and Mn2+ ions. Magnetic measurements showed an antiferromagnetic ordering in the obtained compounds as well as a superexchange interaction between chromium and manganese ions. XPS studies confirmed the presence of manganese ions on the II oxidation state and chromium ions on the III oxidation state. Thermal analysis showed that the increase in the amount of Mn2+ ions affects the stability and resistance of doped compounds compared to pure ZnCr₂Se₄.
In the ZnCr₂Se₄:Ho system, single crystals with well-formed walls and edges were obtained. The chemical composition of the obtained single crystals and their structural parameters were determined using an X-ray study. Based on these studies, it was found that holmium ions occupy octahedral positions, together with chromium ions, and the general formula for single crystals can be written as Zn[Cr₂₋ₓHoₓ]Se₄. The network parameters increase linearly with the increase in the holmium amount, which is consistent with the difference in the radii values between Cr³⁺ and Ho³⁺ ions. Magnetic measurements have shown that the obtained single crystals exhibit an antiferromagnetic order and a metamagnetic transition. A significant influence of holmium ions on short-range ferromagnetic interactions, effective magnetic moments, and exchange integrals for the first and second coordination zones was observed. Thermal analysis confirmed the thermal stability of the obtained single crystals to about 800°C.
In the ZnCr₂Se₄:Nd system, good quality single crystals were obtained, which were examined using X-ray in order to determine their structure and chemical composition. Based on these studies, it was found that neodymium ions occupy tetrahedral positions, together with zinc ions, and the general formula for single crystals can be written as (Zn₁₋ₓNdₓ)Cr₂Se₄.
The lattice parameters increase linearly with the increasing amount of neodymium, which is consistent with the difference in cation radii of Zn2+ and Ho³⁺ ions. Based on magnetic measurements, it was found that the obtained single crystals are antiferromagnetics and exhibit short-range ferromagnetic interactions. Measurements of electrical conductivity showed semiconductor properties and a metal-insulator transition for single crystals with a lower amount of Nd³⁺ ions, at TMI = 330 K for x = 0.08 and 360 K for x = 0.05. Thermal measurements confirmed the thermal stability of single crystals (Zn₁₋ₓNdₓ)Cr₂Se₄ to a temperature of about 700°C.
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Kamada, Rui. "Copper(indium,gallium)selenide film formation from selenization of mixed metal/metal-selenide precursors." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 226 p, 2009. http://proquest.umi.com/pqdweb?did=1654501631&sid=4&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Waite, Paul. "Deep levels in zinc selenide." Thesis, Durham University, 1986. http://etheses.dur.ac.uk/6773/.
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The main purpose of the work reported in this thesis was to investigate and characterise the deep levels in zinc selenide crystals grown from the vapour phase at Durham, and by the CVD technique at AWRE, Aldermaston. The methods of TSC, TSL and DLTS were applied to samples of Durham-grown and CVD ZnSe. The study revealed the presence of traps at 0.14-0.16,0.23, 0.26, 0.30-0.31, 0.45, -0.60 and 0.70 eV in Durham-grown material, whereas the CVD material was found to contain trapping levels at 0.10, 0.20 and 0.27-0.28 eV. The 0.10 eV level in CVD ZnSe is ascribed to the Na acceptor. The traps occurring at 0.26-0.31 eV in both materials are thought to be due to a vacancy-impurity complex. Examination of the CVD material using the EBIC technique in an SEM revealed that the conductivity was limited by electrically-active grain boundaries which were shown to obey a simple potential barrier model. Cathodoluminescence studies showed that the emission bands at 465 nm (edge emission) and 630 nm (copper-red) were quenched at the grain boundaries. A relationship between the absorption coefficient at 10.6 ym and the intensity of the copper-red emission was demonstrated, which has important implications in the production of low absorption zinc selenide for laseroptics.
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Imai, Takeshi. "Studies on Mammalian Selenite Metabolism." Kyoto University, 2013. http://hdl.handle.net/2433/175070.
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Kyoto University (京都大学)0048
新制・課程博士
博士(農学)
甲第17641号
農博第2003号
新制||農||1012(附属図書館)
学位論文||H25||N4762(農学部図書室)
30407
京都大学大学院農学研究科応用生命科学専攻
(主査)教授 栗原 達夫, 教授 阪井 康能, 教授 平竹 潤
学位規則第4条第1項該当
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Roy, Santanu. "Spectroscopic study of defects in cadmium selenide quantum dots (QDS) and cadmium selenide nanorods (NRS)." Diss., Kansas State University, 2013. http://hdl.handle.net/2097/16118.
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Doctor of PhilosophyDepartment of Chemistry
Viktor Chikan
Ever depleting sources of fossil fuel has triggered more research in the field of alternate sources of energy. Over the past few years, CdSe nanoparticles have emerged as a material with a great potential for optoelectronic applications because of its easy exciton generation and charge separation. Electronic properties of CdSe nanoparticles are highly dependent on their size, shape and electronic environment. The main focus of this research is to explore the effect of different electronic environments on various spectroscopic properties of CdSe nanoparticles and link this to solar cell performance. To attain that goal, CdSe quantum dots (QDs) and nanorods (NRs) have been synthesized and either doped with metal dopants or embedded in polymer matrices. Electronic properties of these nanocomposites have been studied using several spectroscopic techniques such as absorption, photoluminescence, time-resolved photoluminescence, confocal microscopy and wide field microscopy. Indium and tin are the two metal dopants that have been used in the past to study the effect of doping on conductivity of CdSe QDs. Based on the photoluminescence quenching experiments, photoluminescence of both indium and tin doped samples suggest that they behave as n-type semiconductors. A comparison between theoretical and experimental data suggests that energy levels of indium doped and tin doped QDs are 280 meV and 100 meV lower than that of the lowest level of conduction band respectively. CdSe nanorods embedded in two different polymer matrices have been investigated using wide field fluorescence microscopy and confocal microscopy. The data reveals significant enhancement in bandedge luminescence of NRs in the vicinity of a conjugated polymer such as P3HT. Photoactive charge transfer from polymers to the surface traps of NRs may account for the observed behavior. Further study shows anti-correlation between bandedge and trap state emission of CdSe NRs. A recombination model has been proposed to explain the results. The origin of traps is also investigated and plausible explanations are drawn from the acquired data.
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Berestok, T. O., M. M. Ivashchenko, Nadiia Mykolaivna Opanasiuk, and Надежда Николаевна Опанасюк. "Optical investigation of zinc selenide films." Thesis, Видавництво СумДУ, 2010. http://essuir.sumdu.edu.ua/handle/123456789/4075.
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As results we can said that were investigated optical properties of ZnSe thin
films, deposited by CSVS method at different physical and technological
condensation regimes. Established physical and technological
deposition regimes with optimal parameters for using as window layers of the
heterojunction tandem solar cells and in optoelectronic devices.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/4075
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Wang, Zaiqi. "Lens calcium homeostasis and selenite cataract." Diss., This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-05042006-164509/.
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Varanasi, Mohan R. "Geometries of small cadmium selenide (CdSe) clusters." Virtual Press, 2006. http://liblink.bsu.edu/uhtbin/catkey/1349770.
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The sizes, shapes, relaxed atomic positions, eigenvalues, and total energies are calculated for selected ultra-small CdSe clusters using SIESTA, a software package for electronic structure calculations and molecular dynamics simulations of molecules and solids. The properties of these bare clusters with small numbers of constituent atoms are studied using density functional theory (DFT) for energy calculations and the conjugate gradient approximation as well as simulated annealing type of molecular dynamics techniques in relaxing the structure to find the lowest energy configurations.The ab-initio norm-conserving pseudopotentials, the exchange-correlation approximation, and parameters used in the computations by Siesta software is verified using FHI98PP, a package used to generate and test the ab-initio norm-conserving pseudopotentials. The initial position of the atomic co-ordinates is determined using ancillary software written in Matlab.Department of Physics and Astronomy
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Sacra, Ann. "Stark spectroscopy of cadmium Selenide (CdSe) nanocrystallites." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/9892.
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Schriver, Maria C. "Electron transport in lead selenide nanocrystal arrays." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32911.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2005.Includes bibliographical references (p. 49-50).
I have investigated electrical properties of arrays of lead selenide (PbSe) nanocrystals (NC's) of approximately 6nm diameter. The films become substantially more conducting when annealed at 400K, although no chemical changes of the capping layer occur at this low temperature. There is no evidence based on TEM images of annealed and unannealed films that the interparticle spacing changes at 400K. The dependence of the conductance on the voltage applied to a gate separated from the sample by 350nm of SiO2 was also measured. At 77K and 150K, a U-shaped curve is observed with a minimum in conductance near zero gate voltage, indicating that both electrons and holes are injected. At 294K, the conductance falls monotonically with increasing gate voltage, indicating injection of holes only. I calculate the electron and hole mobilities, [mu]e and [mu]h at 77K and 150K and find effective mobilities 10 orders of magnitude smaller than those of bulk PbSe at 77K.
by Maria C. Schriver.
S.B.
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Leatherdale, Catherine A. (Catherine Anne) 1972. "Photophysics of cadmium selenide quantum dot solids." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/8828.
Full textAbstract:
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2000.Includes bibliographical references.
Semiconductor quantum dots or nanocrystals have size dependent optical and electronic properties that arise from quantum confinement. While the quantum size effect is reasonably well understood, the effect of abrupt interface between the nanocrystal and its dielectric environment is not. In this thesis we study how the dielectric environment affects the quantum dot electronic structure, the optical absorption ~ross-section, charge separation, and transport in cadmium selenide colloidal quantum dots. The electronic states and optical absorption cross-section are found to be less sensitive to changes in the dielectric environment than predicted from theory unless screening from the ligand shell is taken into account. The absolute absorption cross section is measured as a function of quantum dot size; excellent agreement with theory is obtained for absorption far above the band edge. Three-dimensional close packed solids of quantum dots are predicted to act as model artificial solids. Optical absorption measurements indicate that the electronic states of CdSe quantum dots separated by 11 angstroms or more are essentially uncoupled. Photoconductivity measurements suggest that photoexcited quantum confined excitons are ionized by the applied field with a rate that depends on both the size and surface passivation of the quantum dots. The charge generation efficiency decreases with increasing temperature as non-radiative and radiative recombination pathways increasingly compete with charge separation. A simple tunneling model for the initial charge separation step is presented that qualitatively reproduces both the size and surface dependence of the photoconductivity as a function of applied electric field. Finally, we report observations of amplified spontaneous emission from quantum dot solids. The stimulated emission is tunable with quantum dot size and does not sensitively depend upon surface passivation. These measurements demonstrate the feasibility of nanocrystal quantum dot lasers and amplifiers.
by Catherine A. Leatherdale.
Ph.D.
21
Nirmal, Manoj. "Photophysics of cadmium selenide (CdSe) semiconductor nanocrystals." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/10715.
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Naval, Victoriano C. "Characterization of zinc selenide-based ultraviolet detectors." Thesis, Monterey, California : Naval Postgraduate School, 2009. http://edocs.nps.edu/npspubs/scholarly/theses/2009/Dec/09Dec%5FNaval.pdf.
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Thesis (M.S. in Applied Physics)--Naval Postgraduate School, December 2009.Thesis Advisor(s): Karunasiri, Gamani. Second Reader: Smith, Craig. "December 2009." Description based on title screen as viewed on January 28, 2010. Author(s) subject terms: Zinc Selenide, photodetectors, ultraviolet, Schottky, responsivity, current-voltage, depletion region, bandgap, melanoma, dark current, forward biased, reverse biased. Includes bibliographical references (p. 39-40). Also available in print.
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Espinosa, Ortiz Erika. "Bioreduction of selenite and tellurite by Phanerochaete chrysosporium." Thesis, Paris Est, 2015. http://www.theses.fr/2015PESC1193/document.
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Le sélénium et le tellurium partagent des propriétés chimiques communes et appartiennent à la colonne des éléments chalcogènes de la classification périodique des éléments. Ces métalloïdes ont des propriétés physico-chimiques remarquables et ils ont été utilisés dans un grand nombre d'applications dans le domaine des hautes technologies (électronique, semi-conducteurs, alliages). Ces éléments, qui se retrouvent généralement sous formes d'oxyanions, sont extrêmement solubles dans l'eau et présentent une forte toxicité. Leur libération dans l'environnement est donc d'un enjeu capital. Différentes méthodes physico-chimiques ont été développées pour la récupération de ces metalloïdes, en particulier pour le sélénium. Néanmoins, ces méthodes requièrent un équipement lourd et couteux et ne sont pas très recommandables sur le plan écologique. Le traitement biologique est donc une bonne alternative pour la récupération de Se et de Te provenant des effluents pollués. Cette approche réside dans la bioréduction des différents oxyanions sous formes métalliques. Ceux-ci sont moins toxiques et d'intérêts commerciales notables surtout lorsqu'ils se présentent sous forme nanométrique. L'utilisation de micro-champignons comme microorganismes catalyseur de la réduction de Se et de Te a été démontrée dans cette étude. La réactivité du champignon responsable de la pourriture blanche, Phanerochaete chrysosporium en présence de sélénite et de tellurite a été évaluée, ainsi que son application potentielle pour le traitement des eaux contaminées et la production de nanoparticules. La présence de Se et de Te a une influence importante sur la croissance et la morphologie du champignon. Il s'avère que P. chrysosporium est très sensible à la présence de sélénites. La synthèse de Se° et de Te° sous forme de nanoparticules piégées dans la biomasse fongique a été observée, ainsi que la formation de nano-composites Se-Te lorsque le champignon était cultivé simultanément en présence des deux métalloïdes. L'usage potentiel de biofilm fongiques pour le traitement des effluents semi-acides (pH 4.5) contenant du Se et du Te a été suggéré. De plus, le traitement en mode continu de sélénite dans un réacteur à biofilm fongique granulaire a été évalué. Le réacteur a montré un rendement d'élimination du sélénium en régime permanent de 70% pour differentes conditions opératoires. Celui-ci s'est montré efficace pendant une période supérieure à 35 jours. La bonne sédimentation du biofilm granulaire facilite la séparation du sélénium de l'effluent traité. L'utilisation du biofilm granulaire contenant du sélénium élémentaire comme bio-sorbant a également été étudiée. Cet adsorbant hybride s'est montré prometteur pour l'immobilisation du zinc présent dans les effluents semi-acides. La plupart des recherches effectuées se sont focalisées sur l'utilisation des biofilms granulaires. Toutefois, la croissance du champignon suite à l'exposition à des concentrations différentes de sélénites a également été étudiée. Des micro-électrodes à oxygène et un microscope confocal à balayage laser ont été utilisées pour évaluer l'effet du sélénium sur la structure des biofilms fongiques. Quel que soit le mode de croissance de P. chrysosporium, le mécanisme de réduction du sélénite semble être toujours le même tout en menant à la formation de sélénium élémentaire. Cependant, l'architecture des biofilms et l'activité en oxygène sont influencées par la présence de séléniumSelenium (Se) and tellurium (Te) are particular elements, they are part of the chalcogens (VI-A group of the periodic table) and share common properties. These metalloids are of commercial interest due to their physicochemical properties, and they have been used in a broad range of applications in advanced technologies. The water soluble oxyanions of these elements (i.e., selenite, selenate, tellurite and tellurate) exhibit high toxicities, thus their release in the environment is of great concern. Different physicochemical methods have been developed for the removal of these metalloids, mainly for selenium. However, these methods require specialized equipment, high costs and they are not ecofriendly. The biological treatment is a green alternative to remove Se and Te from polluted effluents. This remediation technology consists on the microbial reduction of Se and Te oxyanions in wastewater to their elemental forms (Se0 and Te0), which are less toxic, and when synthesized in the nano-size range, they can be of commercial value due to their enhanced properties. The use of fungi as potential Se- and Te-reducing organisms was demonstrated in this study. Response of the model white-rot fungus, Phanerochaete chrysosporium, to the presence of selenite and tellurite was evaluated, as well as their potential application in wastewater treatment and production of nanoparticles. The presence of Se and Te had a clear influence on the growth and morphology of the fungus. P. chrysosporium was found to be more sensitive to selenite. Synthesis of Se0 and Te0 nanoparticles entrapped in the fungal biomass was observed, as well as the formation of unique Se-Te nanocomposites when the fungus was cultivated concurrently in the presence of Se and Te. Potential use of fungal pellets for the removal of Se and Te from semi-acidic effluents (pH 4.5) was suggested. Moreover, the continuous removal of selenite in a fungal pelleted reactor was evaluated. The reactor showed to efficiently remove selenium at steady-state conditions (~70%), and it demonstrated to be flexible and adaptable to different operational conditions. The reactor operated efficiently over a period of 35 days. Good settleability of the fungal pellets facilitated the separation of the selenium from the treated effluent. The use of elemental selenium immobilized fungal pellets as novel biosorbent material was also explored. This hybrid sorbent was promising for the removal of zinc from semi-acidic effluents. The presence of selenium in the fungal biomass enhanced the sorption efficiency of zinc, compared to Se-free fungal pellets. Most of the research conducted in this study was focused on the use of fungal pellets. However, the response of the fungus to selenite in a different kind of growth was also evaluated. Microsensors and confocal imaging were used to evaluate the effects of selenium on fungal biofilms. Regardless of the kind of fungal growth, P. chrysosporium seems to follow a similar selenite reduction mechanism, leading to the formation of Se0. Architecture of the biofilm and oxygen activity were influenced by the presence of selenium
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Rennie, J. H. S. "Photo-dissolution of silver in amorphous germanium selenide." Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383872.
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Berry, Patrick A. "Versatile Chromium-Doped Zinc Selenide Infrared Laser Sources." University of Dayton / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1271776256.
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McDaniel, Sean A. "Seeded, Gain-switched Chromium Doped Zinc Selenide Amplifier." University of Dayton / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1343760359.
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Dacleu, Siewe Vanessa. "Molecular and structural bases of selenoprotein N dysfunction in diverse forms of congenital muscular dystrophies." Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAJ127.
Full textAbstract:
Les Selenoprotéines sont des protéines contenant un résidu sélénocystéine (U) dans leur séquence en acide amines. Vingt-cinq sélénoprotéines constituent le sélénoprotéome humain. Parmi elles, la sélénoprotéine N ou SelenoN ; des mutations dans le gène SELENON donnent lieu à un groupe de dystrophies musculaires congénitales appelées myopathies liées à SELENON. SelenoN est une protéine membranaire glycosylée de 72 kDa localisée dans le réticulum endoplasmique. Sa séquence en acide aminés contient le motif redox SCUG, similaire à celui des thioredoxines réductases. Elle contient de même un domaine EF-hand qui est un domaine de liaison au calcium. Des études ont récemment démontré l’implication de cette protéine dans l’établissement et la maintenance du muscle squelettique. D’autres études ont montré qu’elle joue un rôle dans la protection contre le stress oxydatif et l’homéostasie du calcium. Cependant, le mécanisme catalytique de SelenoN reste inconnu à ce jour. Le projet décrit dans cette thèse s’intéresse à la caractérisation, la cristallisation et la comparaison des SelenoNs d’une bactérie, Candidatus poribacteriae, et du poisson zèbre. Les études bio-informatiques ont démontré que SelenoN bactérienne et du poisson zèbre partagent 37% d’identité et un domaine commun correspondant à un repliement de type thioredoxine de fonction inconnue, contenant le motif redox. Les caractérisations biophysiques ont démontré que les deux protéines sont naturellement bien repliées et riche en hélices α. La protéine bactérienne comportant en C-terminal de sa séquence en acide aminé un domaine thioredoxine additionnel, présente une forme étendue et est sous forme monomérique tandis que la protéine du poisson zèbre est un dimère compact. Des caractérisations biochimiques ont montré que le Ca2+ influence l’oligomérisation ou la conformation de SelenoN du poisson zèbre. Des cristaux initiaux de la protéine eucaryote sous sa forme déglycosylée ont pu être obtenus. La cristallisation de la protéine bactérienne a permis d’obtenir des cristaux appartenant à deux groupes d’espaces, avec des paramètres de cellule différents. Néanmoins, un modèle partiel à 2.3 Å couvrant le domaine C-terminal thioredoxine additionnel de SelenoN bactérienne a été obtenu. L’ensemble de ces résultats permettent de poser les bases de l’étude structure-fonction de SelenoN. L’expression, la purification et la cristallisation ont été optimisées et une stratégie pour résoudre la structure 3D de la protéine est proposéeSelenoproteins are proteins containing a selenocysteine residue (U) in their amino acid sequence. Twenty-five proteins constitute the human selenoproteome. Among them is Selenoprotein N or SelenoN; mutations in the SELENON gene can lead to a group of congenital dystrophies now designated as SELENON-related myopathies. SelenoN is a 72 kDa membrane and glycosylated protein of the endoplasmic reticulum. It handles in its amino acid sequence a redox motif SCUG like the one of thioredoxin reductases, and an EF-hand domain which is a calcium binding site. Recent studies showed the implication of SelenoN in muscle development and maintenance, and position its function at the crossroad between oxidative stress control and calcium homeostasis. However, its catalytic function remains elusive. The research project presented in this thesis concerns the crystallization, characterization and comparison of one bacterial and the zebrafish SelenoNs. Bioinformatics analyses revealed that the two proteins share 37% degree of identity and a common domain which corresponds to a thioredoxin fold of unknown function which includes the redox motif SCUG. From the biophysical characterization, both recombinant proteins are found to be naturally well-folded and enriched in α-helical domains. The bacterial SelenoN which handles an additional C-terminal thioredoxin domain is an extended monomer whereas zebrafish SelenoN is a compact dimer. Biochemical characterization indicated that Ca2+ binding mediates zSelenoN oligomerization. Initial crystals of the zSelenoN in its deglycosylated form were obtained. Bacterial SelenoN crystallization yielded crystals belonging to two different space groups with different cell parameters. An initial partial model covering the C-terminal thioredoxin domain of the bacterial SelenoN was obtained at 2.3Å. Together, these results lay a foundation for the structure-function studies of SelenoN. Conditions for recombinant bacterial and zebrafish SelenoNs expression, purification and crystallization were optimized and strategies for solving the structure are being proposed
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Schmitz, Dieter. "Synthese, Charakterisierung und Bildungsprinzipien von sauren und neutralen Oxoselenaten(IV)- und Oxoselenat(IV)-Hydraten." [S.l.] : [s.n.], 2001. http://deposit.ddb.de/cgi-bin/dokserv?idn=964249820.
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Lowe, Elisabeth Clare. "Resolving electron transport in the selenate respiring bacterium Thauera selenatis." Thesis, University of Exeter, 2008. http://hdl.handle.net/10036/40333.
Full textAbstract:
The Gram negative bacterium Thauera selenatis is able to respire with selenate as the sole terminal electron acceptor, utilising a periplasmic selenate reductase enzyme to reduce selenate to selenite. Previous characterisation of this enzyme has shown that it is a heterotrimeric molybdo-enzyme (SerABC) of the dimethylsulfoxide reductase family, containing a Mo-bis molybdopterin guanine dinucleotide co-factor, Fe-S clusters and a b-type haem (Schroder et al., 1997, J Biol Chem, 272: 23765-68, Dridge et al., 2007, Biochem J, 408: 19-28). In order to elucidate the electron transport pathway to selenate reductase, and how it can generate a proton motive force, detailed study was required. Firstly, the redox potential of the b-haem of SerC was determined by optical redox titration to be +234 mV. The serC gene was cloned and expressed heterologously in E. coli, but the protein was incorrectly folded into inclusion bodies, and attempts to refold and reconstitute SerC with haem were unsuccessful. A profile of c-type cytochromes in T. selenatis was undertaken, and characterisation of a number of cytochromes was carried out. Two cytochromes were purified, cytc7 and cytc4, and cytc4 was shown to be able to donate electrons to SerABC in vitro. Protein sequence was obtained by N-terminal sequencing and LC-MS/MS, and assigned cytc4 to the cytochrome c4 family of dihaem cytochromes. Redox potentiometry combined with UV-visible and electron paramagnetic spectroscopy showed that cytc4 is a dihaem cytochrome with a redox potential of +282 mV and both haems are predicted to have His-Met ligation. To investigate the role of membrane bound cytochromes in selenate respiration, PCR with degenerate primers amplified a partial gene coding for quinol: cytochrome c oxidoreductase (QCR). A microplate growth method was developed to monitor growth of T. selenatis under reproducible conditions, and used to analyse the effect of respiratory chain inhibitors on growth under different conditions. Aerobic metabolism was unaffected by QCR inhibitors, while nitrite reduction was totally inhibited, linking nitrite reduction to the generation of a proton motive force by the QCR. The QCR inhibitor myxothiazol partially inhibited selenate respiration, showing that some electron flux is via the QCR, but total inhibition of selenate respiration was achieved by combining myxothiazol with the more general inhibitor 2-n-heptyl-4-hydroxyquinoline N-oxide (HQNO). These data suggest that electron transfer to selenate reductase occurs via a branched pathway, in which one route is inhibited by myxothiazol and the other by HQNO. Electron transfer via a QCR and a dihaem cytochrome c4 is a novel route for a member of the dimethylsulfoxide reductase family of molybdo-enzymes.
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Heath, Jennifer Theresa. "Electronic transitions in the bandgap of copper indium gallium diselenide polycrystalline thin films /." view abstract or download file of text, 2002. http://wwwlib.umi.com/cr/uoregon/fullcit?p3072587.
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Thesis (Ph. D.)--University of Oregon, 2002.Typescript. Includes vita and abstract. Includes bibliographical references (leaves 143-148). Also available for download via the World Wide Web; free to University of Oregon users.
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Rickman, Sarah. "Growth and characterization of molybdenum disulfide, molybdenum diselenide, and molybdenum(sulfide, selenide) formed between molybdenum and copper indium(sulfide, selenide) during growth." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 0.94 Mb., 85 p, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:1435848.
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Sperança, Adriane. "Síntese de Seleno-Isoxazóis e Seleno-Indóis via Reações de Ciclização Intramolecular mediadas por Cloreto Férrico." Universidade Federal de Santa Maria, 2013. http://repositorio.ufsm.br/handle/1/4241.
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Conselho Nacional de Desenvolvimento Científico e TecnológicoThis work reports the synthesis of a series of 4-organoselenyl-isoxazoles (19 examples), prepared via FeCl3/diorganyl diselenides-promoted intramolecular cyclization of alkynone O-metyloximas. In general, the selenyl-isoxazoles were obtained, in 50 to 70% yield. In addition, an alternative method was developed to promote the intramolecular cyclization reaction of o-alkynyl-N,N-dimethyl-anilines, where FeCl3 and substituted diorganyl diselenides were employed as promoter agents to this process. Through this cyclization protocol a series of N-methyl-3-organoselenyl-indoles could be synthesized (20 examples), in yields varying from 36 to 81%, by using room temperature and ambient atmosphere. In order to evaluate the versatility of the obtained compounds as precursors to the synthesis of functionalized isoxazoles and indoles, the 3,5-diphenyl-4-(phenylselenyl)-isoxazole, N-methyl-2-phenyl-3-(phenylselenyl)-1H-indole and N,5-dimethyl-2-phenyl-3-(phenylselenyl)-1H-indole were submitted to PhSe-Lithium exchange reactions, and the corresponding organolithium intermediates, which were generated by treatment with nBuLi, could be trapped with different electrophiles, affording the functionalized isoxazoles (5 examples) and indoles (4 examples) in good yields (45-80%).
Este trabalho relata a síntese de uma série de 4-organoseleno-isoxazóis (19 exemplos), preparados a partir da reação de ciclização intramolecular de O-metiloximas alquinílicas promovidas por FeCl3 e diferentes disselenetos de diorganoíla. Em geral, os derivados de seleno-isoxazóis foram obtidos de maneira satisfatória, em rendimentos de 50 a 70%. Desenvolveu-se também, um método alternativo para promover a reação de ciclização intramolecular de o-alquinil-N,N-dimetil-anilinas, empregando-se FeCl3 e disselenetos de diorganoíla diferentemente substituídos, como agentes promotores da ciclização. Através deste protocolo de ciclização pode-se sintetizar uma série de N-metil-3-organosseleno-indóis (20 exemplos), em rendimentos que variaram de 36 a 81%, utilizando condições de reação brandas, uma vez que os experimentos foram realizados a temperatura e atmosfera ambiente. A fim de avaliar a versatilidade dos compostos obtidos, como precursores para a síntese de isoxazóis e indóis com diferentes funcionalizações, o 3,5-difenil-4-(fenilselenil)-isoxazol e o N-metil-2-fenil-3-(fenilselenil)-1H-indol e N,5-dimetil-2-fenil-3-(fenilselenil)-1H-indol, foram submetidos à reações de troca PhSe-lítio, e o intermediário litiado correspondente, formado a partir de uma reação utilizando n-BuLi, pôde ser capturado com diferentes eletrófilos, obtendo-se como produtos uma série de isoxazóis (5 exemplos) e indóis (4 exemplos) diferentemente funcionalizados em bons rendimentos (45-80%).
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Colakoglu, Tahir. "The Growth And Characterization Of Galium Selenide Thin Films." Master's thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/4/1085240/index.pdf.
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GaSe thin films were deposited by thermal evaporation technique with and
without Cd doping. X-ray analysis showed that the crystallinity increases in (1014) preferred orientation direction with annealing for doped and undoped films. The room temperature conductivity and mobility values of the samples were found to be for doped and undoped films in between 1.3×101 - 3.4×
102 (&
#8486
-cm)-1, 1.2×
10-6 - 1.5×
10-6 (&
#8486
-cm)-1 and 5.9 &
#8211
20.9 (cm2/V.s) (for doped samples only), respectively. Due to the high resistivity of the undoped samples mobility measurements could not be performed. The dominant conduction mechanisms were determined to be thermionic emission in the high temperature region (250-400 K), tunneling in the range 160-250 K and between 100-150 K variable range hopping mechanism for the doped films. For the undoped films above 250 K thermionic emission was the dominant conduction mechanism. Space charge limited currents in parallel and perpendicular directions of the film surface showed two different localized energy levels with different concentrations for each case, namely, 99.8 meV with concentration 3.5×
1012 cm-3 and 418.3 meV with the concentration 2.2×
105 cm-3 for parallel direction and for perpendicular direction 58.3 meV with concentration 6.2×
1025 cm-3 and 486.1 meV with concentration 3.3×
1022 cm-3. Photocurrentillumination intensity dependences indicated that power exponent of illumination intensity with values n>
1 implied two recombination centers exist in studied samples.
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Sih, Bryan Christian. "Gold and cadmium selenide (CdSe) nanoparticles capped with oligothiophenes." Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/31523.
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The preparation and characterization of hybrid materials composed of oligothiophene-capped Au and CdSe nanoparticles with novel chemical, structural, electronic and optical properties are reported. α-Phosphino-oligothiophenes (12-15 and 23) and thiol-substituted oligothiophenes (26, 29, 32) were prepared by metal-catalyzed coupling reactions and studied using absorption and emission spectroscopy, and cyclic voltammetry. These functionalized oligothiophenes were used to passivate the surface of Au (16-19) and CdSe (CdSe-26, CdSe-29, CdSe-32) nanoparticles. Oligothiophene-capped Au nanoparticles were prepared directly by reducing a Au salt in the presence of the phosphino-oligothiophene. Attachment to the Au nanoparticles has little effect on the electronic structure of the oligothiophene as determined from the absorption spectra. On the other hand, the oligothiophenes appear to affect the electronic structure of the Au nanoparticle, as observed via a red-shift in the surface plasmon absorption. Electrochemical oxidation of the phosphino-terthiophene capped Au nanoparticles lead to crosslinking where the nanoparticles are linked both structurally and electronically by observed increases in conjugation, conductivity and plasmon coupling relative to the unlinked particles. The oligothiophene bridge linking the Au nanoparticles is shown to facilitate plasmon coupling between adjacent nanoparticles. The crosslinked material also demonstrates tunable conductivity where the conductivity in the material can be increased by oxidative doping of the π-conjugated bridge. Oligothiophene-capped CdSe nanoparticles were prepared through an exchange reaction between thiol-substituted oligothiophenes and trioctylphosphine oxide-capped CdSe nanoparticles. Attachment of the oligothiophenes to the CdSe nanoparticle has little effect on the electronic structure of the oligothiophene as determined from the absorption spectra. However, the optical properties are significantly affected where the oligothiophene emission is quenched after attachment to the CdSe surface due to either an energy or electron transfer mechanism. Depending on the number of oligothiophenes attached to the CdSe surface, the optical properties of the CdSe nanoparticles are affected differently. An excess number of thiols act as hole traps leading to quenching of the nanoparticle emission. Attempts to electrochemically crosslink these oligothiophene-capped CdSe nanoparticles were unsuccessful possibly due to the intrinsic resistivity in the particles.[See Thesis for Diagrams]Science, Faculty of
Chemistry, Department of
Graduate
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Philipp, Dean. "Structural and optical properties of small cadmium selenide nanocyrstallites." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/38098.
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Oduor, A. O. "Electronic transport properties in evaporated cadmium selenide thin films." Thesis, Keele University, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.388869.
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Sapkota, Yub Raj. "PHYSICAL PROPERTIES OF TOPOLOGICAL INSULATOR: BISMUTH SELENIDE THIN FILMS." OpenSIUC, 2017. https://opensiuc.lib.siu.edu/theses/2261.
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Topological Insulator (TI) is new classes of materials with gapless surface states and insulating bulk. The topological connection can be traced back to the discovery of Integer Quantum Hall Effect in 1980. In the last decade, new categories of topological insulators were predicted and later discovered, that have gained a lot of attraction for room-temperature applications. Since the experimental observation of single Dirac cone on the surface states of Bismuth selenide (Bi2Se3) in 2009, it has emerged as the prototype. Bismuth Selenide has one of the highest bulk band gaps of 0.3 eV among all TI materials. While its single crystal properties are well documented, thin films are producing equally exciting discoveries. In this work, Bi2Se3 thin films were synthesized using magnetron sputtering method and a diverse set of physical properties, such as structural, optical, and electronic, are investigated. In particular, properties of few-layer (ultra-thin) Bi2Se3 thin films are studied. Optical properties of Bi2Se3 was particularly revealing. We observed a sharp increase (blue shift) in the bulk band gap of Bi2Se3 by almost 0.5 eV as it approached the two-dimensional limit. Strong thickness-dependent structural and transport properties were also observed.
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Kim, Changsu. "Optical, laser spectroscopic, and electrical characterization of transition metal doped ZnSe and ZnS nano- and microcrystals." Birmingham, Ala. : University of Alabama at Birmingham, 2009. https://www.mhsl.uab.edu/dt/2009r/kim.pdf.
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Thesis (Ph. D.)--University of Alabama at Birmingham, 2009.Title from PDF title page (viewed Feb. 3, 2010). Additional advisors: Renato Camata, Derrick Dean, Chris M. Lawson, Andrei Stanishevsky, Sergey Vyazovkin. Includes bibliographical references (p. 133-140).
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Bhardwaj, R. K. "Oxidative deselenation and desulphurisation at pentacovalent phosphorus." Thesis, City University London, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379125.
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Weber, Frank. "Präparative Studien in den Mehrstoffsystemen Selten-Erd-Metall - Selen bzw. - Tellur und Sauerstoff." [S.l.] : Universität Stuttgart , Fakultät Chemie, 1999. http://www.bsz-bw.de/cgi-bin/xvms.cgi?SWB8287476.
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Huang, Donglin. "Heterogeneous reduction of selenite by zero valent iron-steel wool." Morgantown, W. Va. : [West Virginia University Libraries], 2010. http://hdl.handle.net/10450/11233.
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Thesis (Ph. D.)--West Virginia University, 2010.Title from document title page. Document formatted into pages; contains ix, 106 p. : ill. (some col.). Includes abstract. Includes bibliographical references.
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Knight, Edward Joseph 1968. "Cryogenic refractive index of zinc selenide from 8-12 micrometers." Thesis, The University of Arizona, 1992. http://hdl.handle.net/10150/278265.
Full textAbstract:
I have measured the refractive index of zinc selenide for wavelengths between 8 and 12 mum and temperatures from 85 to 300 K. Each measurement was made by finding the deviation angle of a beam perpendicularly incident on a right triangle prism. The resulting data curves are fitted to polynomials for the temperature dependence and to three different dispersion formulae for the wavelength dependence. I achieved accuracies in the refractive index of ±0.0008 and my results agree well with most previously available data. Refinements to the previously established experimental procedure and error analysis are also presented.
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Adamchak, Marsha Ann. "The action of selenite on ATP synthesis in rat lens." Thesis, Virginia Tech, 1986. http://hdl.handle.net/10919/45655.
Full textAbstract:
A subcutaneous injection of sodium selenite (30
umol/kg body weight) in 10â day old rats produced a
cataract within 72 hours. Lens opacification was
preceded by a 15% decrease in ATP content. Lens ATP did
not fully recover to control concentrations by 11 days
postâ injection. A moderate correlation existed between
lens weight and total ATP content in control lenses
Master of Science
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Perera, Jayalath Pathirannehelage Dimuthu Nuwan. "Photocatalytic Properties of Zinc Selenide/Cadmium Sulfide Core-shell Nanoparticles." Bowling Green State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1370994697.
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Beukes, Stewart Eva-Panduleni. "EPR studies of electron transfer in cadmium selenide sensitised titania." Thesis, University of Aberdeen, 2016. http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=232399.
Full textAbstract:
Research into renewable energy sources is crucially increasing to counteract the ever more concerning impact of non-renewable sources. Theoretically, Quantum Dot Solar Cells (QDSCs) can achieve much greater efficiencies than current, commercial solar cells, but its expansion is still in its very early stages of scientific study and development. In this project TiO2, one of the most efficient and cost-effective photocatalysts, is coupled with Cadmium Selenide (CdSe) Quantum Dots (QD) in a study of interfacial charge transfers. Thus far, in other studies, CdSe QDs have shown some of the most promising results of QDSCs. EPR spectroscopy has been used here to study charge transfer processes in CdSe quantum dot (QD) sensitised titania. Visible light excitation of QDs directly adsorbed onto titania surfaces causes electron transfer to the titania, producing characteristic EPR signals of trapped electrons in the titania. Under ultraviolet excitation the trapped electron signals seen in titania alone are suppressed in the presence of directly adsorbed quantum dots, as is the formation of superoxide in the presence of oxygen. These observations suggest that reverse electron transfer from the titania to the QDs can also occur. No visible light excited electron transfer occurs in the case of QDs attached to the titania surface via bi-linker molecules, but under ultraviolet excitation a similar suppression of electron trapping in the titania phase is seen. These results show that the nature of the interface between the QDs and the titania phase is crucially important in the electron transfer processes in both directions. The study also looks at the pitfalls of synthesis techniques used for making the CdSe QDs as well as the method of attaching it to the TiO2. Ionic deposition, which generally resulted in the best photocurrents in other studies, was discovered early on this project produced very impure samples. Direct Adsorption produces low titania surface coverage, which can potentially be improved. Whereas the lack of discussion in literature of clear purification methods in synthesis techniques for attaching QDs via a bi-linker molecule, through ligand exchange, causes a significant drawback in the study of such systems.
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Krügermann, Ina. "Oxo-Selenate (IV/IV) der Selten-Erd-Elemente und ihre Derivate." [S.l. : s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=966624343.
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Guzzo, Julie. "Characterization of Escherichia coli genes whose expression is affected by selenite." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0030/NQ64566.pdf.
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Boscher, Nicolas D. "Atmospheric pressure chemical vapour deposition of transition metal selenide thin films." Thesis, University College London (University of London), 2006. http://discovery.ucl.ac.uk/1444549/.
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This thesis investigates the formation of thin films of metal selenides via atmospheric pressure chemical vapour deposition (APCVD). The films and powders produced were characterised by SEM, EDAX/WDX, XPS, XRD, Raman, SQUID, reflectance and absorbance measurements. The APCVD reaction of TiCl4, V(NMe2)4 and NbCl5 with fBu2Se were respectively found to be a convenient route to stable and crystalline titanium, vanadium and niobium diselenide films. The use of VCI4 and VOCI3 showed that they were both found unsuitable for producing VSe2 from the APCVD reaction with 'Bu2Se. Molybdenum and tungsten diselenide films were respectively synthesised using M0CI5 and WC16 with Et2Se. The WSe2 films produced were highly hydrophobic with contact angles for water droplets in the range of 135 - 145 . Furthermore these surfaces were highly adherent for water droplets that did not roll or slide even at a tilt angle of 90 . The deposition of tin monoselenide and tin diselenide films was achieved by the reaction of SnCU with Et2Se. The deposition temperature, flow rates and position on the substrate determined whether mixed SnSe - SnSe2, pure SnSe or pure SnSe2 thin films could be obtained. The characterisation of the films and powders formed from the APCVD or gas phase reaction of Cr02Cl2 and Et2Se confirmed the formation of an unknown solid solution of Cr2Se3_xOx. Cr2Se3-xOx adopts the hexagonal Cr2C>3 structure for a stoichiometry between Cr2C>3 and Cr2Seo.202.g, and the rhombohedral Cr2Se3 structure for a stoichiometry varying from Cr2Seo.302.7 to Cr2Se2.15O0.85- Magnetic studies showed that all the Cr2Se3.xOx compounds formed with the rhombohedral Cr2Se3 structure had an antiferromagnetic ordering with a Neel temperature lower than the expected one for Cr2Se3.
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Vu, Nhan Trung. "Characterisation of cadmium selenide material for high speed photoconductive switching systems." Thesis, University of Brighton, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310102.
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Jehl, Zacharie. "Realization of ultrathin Copper Indium Gallium Di-selenide (CIGSe) solar cells." Thesis, Paris 11, 2012. http://www.theses.fr/2012PA112058/document.
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Nous étudions la possibilité de réaliser des cellules à base de diséléniure de cuivre, indium et gallium (CIGSe) à absorbeur ultra-mince, en réduisant l’épaisseur de la couche de CIGSe de 2500 nm jusqu’à 100 nm, tout en conservant un haut rendement de conversion.Grâce à l’utilisation d’outils de simulation numérique, nous étudions l’influence de la réduction d’épaisseur de l’absorbeur sur les paramètres photovoltaïques de la cellule. Une importante dégradation du rendement est observée, principalement attribuée à une réduction de la fraction de lumière absorbée par le CIGSe ainsi qu’à une collecte des porteurs de charge réduite dans les dispositifs ultraminces. Des solutions permettant de surmonter ces problèmes sont proposées et leur influence potentielle est numériquement simulée ; nous démontrons qu’une ingénierie de face avant (couche tampon alternative, couche anti-réfléchissante…) et de face arrière (contact arrière réfléchissant, diffusion de la lumière) sur une cellule CIGSe à absorbeur ultramince permet de potentiellement améliorer le rendement de la cellule solaire au niveau de celui d’une cellule à absorbeur référence (2.5 μm).Grâce à l’utilisation de techniques de gravure chimique sur des échantillons standards de CIGSe épais, nous réalisons des cellules solaires avec différentes épaisseurs d’absorbeurs, et nous étudions l’influence de l’épaisseur du CIGSe sur les paramètres photovoltaïques des cellules. Le comportement similaire aux simulations numériques.Une ingénierie du contact avant sur des cellules CIGSe à différentes épaisseurs est réalisée pour spécifiquement améliorer l’absorption dans la couche de CIGSe. Nous étudions l’influence d’une couche tampon alternative de ZnS, de la texturation de la fenêtre avant de ZnO:Al, et d’une couche anti-reflet sur la cellule solaire. D’importantes améliorations sont observées quelque soit l’épaisseur de la couche de CIGSe, ce qui permet d’obtenir des rendements de conversions supérieurs à ceux obtenus dans la configuration standard des dispositifs.Une ingénierie du contact arrière à basse température est également réalisée avec l’utilisation d’un procédé novateur combinant la gravure chimique du CIGSe avec un « lift-off » mécanique de la couche de CIGSe afin de la séparer du substrat de Molybdène. De nouveaux matériaux fortement réflecteur de lumière et précédemment incompatible avec le procédé de croissance du CIGSe sont utilisés comme contact arrière pour des cellules CIGSe ultra-minces. Une étude comparative en fonction de l’épaisseur de CIGSe entre des cellules avec contact arrière réfléchissant en Or (Au) et cellules solaires avec contact arrière standard Mo est effectuée. Le contact Au permet d’augmenter significativement le rendement de conversion des cellules solaires à absorbeur sub-microniques comparé au contact standard Mo avec un rendement de conversion supérieur à 10% obtenu sur une cellule CIGSe de 400 nm (comparé à 7.9% avec Mo).Afin de réduire encore plus l’épaisseur de la couche de CIGSe, jusque 100-200 nm, les modèles numériques montrent qu’il est nécessaire d’utiliser un réflecteur lambertien sur la face arrière de la cellule afin de maximiser l’absorption de la lumière. Un dispositif preuve de concept expérimental est réalisé avec une épaisseur de CIGSe de 200 nm et un réflecteur arrière lambertien, et ce dispositif est caractérisé par spectroscopie de transmission/réflexion. La réponse spectrale est déterminée en combinant des valeurs issues de simulation numérique et la mesure expérimental de l’absorption du dispositif. Nous calculons un courant de court circuit de 26 mA.cm-2 pour ce dispositif avec réflecteur lambertien, bien supérieur à ce qui est calculé pour la même structure sans réflecteur (15 mA.cm-2), et comparable au courant mesuré sur une cellule de référence de 2500 nm (28 mA.cm-2). L’utilisation de réflecteur lambertien pour des cellules CIGSe ultraminces est donc particulièrement adaptée pour maintenir de hauts rendementsIn this thesis, we investigate on the possibility to realize ultrathin absorber Copper Indium Gallium Di-Selenide (CIGSe) solar cells, by reducing the CIGSe thickness from 2500 nm down to 100 nm, while conserving a high conversion efficiency.Using numerical modeling, we first study the evolution of the photovoltaic parameters when reducing the absorber thickness. A strong decrease of the efficiency of the solar cell is observed, mainly related to a reduced light absorption and carrier collection for thin and ultrathin CIGSe solar cells. Solutions to overcome these problems are proposed and the potential improvements are modeled; we show that front side (buffer layer, antireflection coating) and back side (reflective back contact, light scattering) engineering of an ultrathin device can potentially increase the conversion efficiency up to the level of a standard thick CIGSe solar cell.By using chemical bromine etching on a standard thick CIGSe layer, we realize solar cells with different absorber thicknesses and experimentally study the influence of the absorber thickness on the photovoltaic parameters of the devices. Experiments show a similar trends to that observed in numerical modeling.Front contact engineering on thin CIGSe solar cell is realized to increase the specific absorption in CIGSe, including alternative ZnS buffer, front ZnO:Al window texturation and anti-reflection coating. Substantial improvements are observed whatever the CIGSe thickness, with efficiencies higher that the default configuration.A back contact engineering at low temperature is realized by using an innovative approach combining chemical etching of the CIGSe and mechanical lift-off of the CIGSe from the original Molybdenum (Mo) substrate. New highly reflective materials previously incompatible with the standard solar cell process are used as back contact for thin and ultrathin CIGSe solar cells, and a comparative study between standard Mo back contact and alternative reflective Au back contact solar cells is performed. The Au back reflector significantly enhance the efficiency of solar cell with sub-micrometer absorbers compared to the standard Mo back reflector; an efficiency higher than 10 % on a 400 nm CIGSe is obtained with Au back contact (7.9% with standard Mo back contact). For further reduction of the absorber thickness down to 100-200 nm, numerical modeling show that a lambertian back reflector is needed to fully absorb the incident light in the CIGSe. An experimental proof of concept device with a CIGSe thickness of 200 nm and a lambertian back reflector is realized and characterized by reflection/transmission spectroscopy, and the experimental spectral response is determined by combining simulation and experimentally measured absorption. A short circuit current of 26 mA.cm-2 is determined with the lambertian back reflector, which is much higher than what is obtained for the same device with no reflector (15 mA.cm-2), and comparable to the short circuit current measured on a reference 2500 nm thick CIGSe solar cell (28 mA.cm-2). Lambertian back reflectors are therefore found to be the most effective way to enhance the efficiency of an ultrathin CIGSe solar cell up to the level of a reference thick CIGSe solar cell