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1
Puttisong, Yuttapoom. "Spin-dependent Recombination in GaNAs". Thesis, Linköping University, Linköping University, Department of Physics, Chemistry and Biology, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-19355.
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Spin filtering properties of novel GaNAs alloys are reported in this thesis. Spin-dependent recombination (SDR) in GaNAs via a deep paramagnetic defect center is intensively studied. By using the optical orientation photoluminescence (PL) technique, GaNAs is shown to be able to spin filter electrons injected from GaAs, which is a useful functional property for integratition with future electronic devices. The spin filtering ability is found to degrade in narrow GaNAs quantum well (QW) structures which is attributed to (i) acceleration of band-to-band recombination competing with the SDR process and to (ii) faster electron spin relaxation in the narrow QWs. Ga interstitial-related defect centers have been found to be responsible for the SDR process by using the optically detected magnetic resonance (ODMR) technique. The defects are found to be the dominant grown-in defects in GaNAs, commonly formed during both MBE and MOCVD growths. Methods to control the concentration of the Ga interstitials by varying doping, growth parameters and post-growth treatments are also examined.
2
Thomas, Mélissa. "Origins of Cellular Lethality Resulting From a Defect in Homologous Recombination in Human Cells". Thesis, université Paris-Saclay, 2021. http://www.theses.fr/2021UPASL027.
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La recombinaison homologue (RH) est impliquée dans la réparation des cassures double brin à l'ADN, et dans la gestion des fourches de réplication bloquées. Rad51 et BRCA2 en sont deux protéines pivots.J'ai montré que l'inhibition de la RH ainsi que la surexpression de Rad51 sont létales dans les cellules humaines, mais qu'un faible nombre de cellules arrivent à survivre. De plus, dans plusieurs cancers, les gènes de la RH sont mutés (BRCA1/2 dans les cancers du sein et de l'ovaire) ou la surexpression d'un gène de la RH est observée. Mon projet a pour but d'identifier les mécanismes et les causes de la létalité induite par une dérégulation de la RH dans les cellules humaines, ainsi que de comprendre comment certaines cellules arrivent à y survivre. L’analyse du cycle cellulaire et du marquage Histone H3 phosphorylée a révélé que les cellules humaines inactivées pour la RH ou surexprimant RAD51 s’accumulent à la transition G2/M. Parallèlement la vidéomicroscopie a suggéré que les cellules mourraient par apoptose, ce qui a été corroboré par des expériences utilisant l'Annexin-V comme marqueur d’apoptose et par des Western-Blot. Les Western Blots montrent que le checkpoint G2/M est activé, via l'analyse de la cyclineB1 et de cdk1, et que l'apoptose est déclenchée, via l'analyse du clivage de PARP. Mon hypothèse principale de travail étant que la surexpression d'un dominant négatif de Rad51 et possiblement la surexpression du Rad51 WT, entraîne des défauts de réplication dont l'accumulation entraînerait une activation du checkpoint. Des expériences d'incorporation de BrdU et de peignage moléculaire sont venus confirmer mon hypothèse : dans les cellules ayant une dérégulation de la RH, la vitesse de réplication est diminuée et il y a plus de fourches bloquées. Des analyses in-silico ont révélées que les cancers mutés dans la RH sont fréquemment co-mutés dans des gènes impliqués dans le checkpoint G2/M ou dans le redémarrage des fourches. Une liste de gènes candidats, enrichie de résultats de séquençages de fibroblastes de patients FANCD1, a été testée, confirmant l'analyse in-silicoHomologous recombination (HR) is involved in repairing DNA double strand breaks, and in protecting and restarting stalled or collapsed replication forks. Rad51 and BRCA2 are two key proteins of HR. I have showed that inhibiting HR, as well as over expressing Rad51, is lethal in human cells, although a very few cells still survive the inhibition. Moreover, many cancers carry mutations in an HR gene (BRCA1/2 in breast and ovary cancers) or over express an HR gene. My project aims to identify the mechanisms and the causes behind the lethality triggered by a dysregulation of HR, and to understand how a few cells manage to survive it. I have determined, through FACS and phosphorylated histone H3 labeling (IF), that HR deficient human cells, or those over expressing Rad51, accumulate at the G2/M checkpoint.At the same time, time-lapse microscopy experiments seemed to indicate that the cells died from apoptosis, which was confirmed by data from experiments using Annexin-V as an apoptosis marker and from Western-Blots. Western-Blots showed that the G2/M checkpoint is activated, through analysis of CyclinB1 and of cdk1, and that apoptosis is triggered, through analysis of PARP cleavage. My main working hypothesis was that overexpressing a dominant negative form of Rad51, and possibly also overexpressing Rad51 WT, would lead to replication defects, whose accumulation would in turn lead to an activation of the checkpoint. BrdU incorporation experients and use of the molecular combing technique confirmed this hypothesis : in HR-dysregulated cells, replication speed is slowed down and there are more stalled forks. In-silico analyses have showed that HR-mutated cancers often carry a second mutation in another gene, involved in either the G2/M checkpoint or in restarting stalled replication forks. Based on these analyses and on results from RNAseq experiments performed on FANCD1 patients' fibroblasts, candidate genes have already been listed, confirming the in-silico analysis
3
Turcu, Mircea Cassian. "Defect energies, band alignments, and charge carrier recombination in polycrystalline Cu(In,Ga)(Se,S)2 alloys". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2004. http://nbn-resolving.de/urn:nbn:de:swb:14-1086247686828-95497.
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This work investigates the defect energies, band alignments, and charge carrier recombination in polycrystalline Cu(In1-xGax)(Se1-ySy)2 chalcopyrite thin films and the interrelationship with the alloy composition. Photoluminescence spectroscopy of investigated Cu-poor Cu(In,Ga)(Se,S)2 layers generally shows broad emission lines with the corresponding maxima shifting towards higher energies under decreasing temperature or under increasing excitation power. Admittance spectroscopy of Cu-poor ZnO/CdS/Cu(In,Ga)(Se,S)2 chalcopyrite devices shows that the activation energies of the dominant defect distributions involving donors at the CdS/absorber interface and deep acceptors in the chalcopyrite bulk, increase upon alloying CuInSe2 with S. The band alignments within the Cu(In1-xGax)(Se1-ySy)2 system are determined using the energy position of the bulk acceptor state as a reference. The band gap enlargement under Ga alloying is accommodated almost exclusively in the rise of the conduction band edge, whereas the increase of band gap upon alloying with S is shared between comparable valence and conduction band offsets. The extrapolated band discontinuities [delta]EV(CuInSe2/CuInS2) = -0.23 eV, [delta]EC(CuInSe2/CuInS2) = 0.21 eV, [delta]EV(CuInSe2/CuGaSe2) = 0.036 eV, and [delta]EC(CuInSe2/CuGaSe2) = 0.7 eV are in good agreement with theoretical predictions. Current-voltage analysis of Cu-poor ZnO/CdS/Cu(In,Ga)(Se,S)2 devices reveals recombination barriers which follow the band gap energy of the absorber irrespective of alloy composition, as expected for dominant recombination in the chalcopyrite bulk. In turn, the recombination at the active junction interface prevails in Cu-rich devices which display substantially smaller barriers when compared to the band gap energy of the absorber. The result indicates that the Cu-stoichiometry is the driving compositional parameter for the charge carrier recombination in the chalcopyrite heterojunctions under investigations.
4
Turcu, Mircea Cassian. "Defect energies, band alignments, and charge carrier recombination in polycrystalline Cu(In,Ga)(Se,S)2 alloys". Doctoral thesis, Technische Universität Dresden, 2003. https://tud.qucosa.de/id/qucosa%3A24342.
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This work investigates the defect energies, band alignments, and charge carrier recombination in polycrystalline Cu(In1-xGax)(Se1-ySy)2 chalcopyrite thin films and the interrelationship with the alloy composition. Photoluminescence spectroscopy of investigated Cu-poor Cu(In,Ga)(Se,S)2 layers generally shows broad emission lines with the corresponding maxima shifting towards higher energies under decreasing temperature or under increasing excitation power. Admittance spectroscopy of Cu-poor ZnO/CdS/Cu(In,Ga)(Se,S)2 chalcopyrite devices shows that the activation energies of the dominant defect distributions involving donors at the CdS/absorber interface and deep acceptors in the chalcopyrite bulk, increase upon alloying CuInSe2 with S. The band alignments within the Cu(In1-xGax)(Se1-ySy)2 system are determined using the energy position of the bulk acceptor state as a reference. The band gap enlargement under Ga alloying is accommodated almost exclusively in the rise of the conduction band edge, whereas the increase of band gap upon alloying with S is shared between comparable valence and conduction band offsets. The extrapolated band discontinuities [delta]EV(CuInSe2/CuInS2) = -0.23 eV, [delta]EC(CuInSe2/CuInS2) = 0.21 eV, [delta]EV(CuInSe2/CuGaSe2) = 0.036 eV, and [delta]EC(CuInSe2/CuGaSe2) = 0.7 eV are in good agreement with theoretical predictions. Current-voltage analysis of Cu-poor ZnO/CdS/Cu(In,Ga)(Se,S)2 devices reveals recombination barriers which follow the band gap energy of the absorber irrespective of alloy composition, as expected for dominant recombination in the chalcopyrite bulk. In turn, the recombination at the active junction interface prevails in Cu-rich devices which display substantially smaller barriers when compared to the band gap energy of the absorber. The result indicates that the Cu-stoichiometry is the driving compositional parameter for the charge carrier recombination in the chalcopyrite heterojunctions under investigations.
5
Santos, Samantha Fonseca dos. "Theoretical and computational studies of dissociative recombination of H₃⁺ with low kinetic energy electrons time-independent and time-dependent approach /". Orlando, Fla. : University of Central Florida, 2009. http://purl.fcla.edu/fcla/etd/CFE0002668.
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PATRIZI, LAURA. "ANALYSIS OF B LYMPHOCYTES IN MOUSE MODEL LIGASE IV WITH HYPOMORPHIC MUTATION IN VDJ RECOMBINATION ASSOCIATED WITH GROWTH DEFECT". Doctoral thesis, Università degli Studi di Milano, 2010. http://hdl.handle.net/2434/150193.
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The major mechanism for the repair of DNA doublestrand breaks (DSBs) in mammalian cells is non-homologous end-joining (NHEJ), a process that involves the DNA-dependent protein kinase , XRCC4 and DNA ligase IV. Rodent cells and mice defective in these components are radiation-sensitive and defective in V(D)J-recombination, showing that NHEJ also functions to rejoin DSBs introduced during lymphocyte development. We have generated a knock-in mouse model with a homozygous Lig4 arginine to histidine (R278H) mutation that corresponds to the mutation identified in the first LIG4-deficient patient, who developed T cell leukemia associated with increased cellular radiosensitivity. The clinical presentation of the syndrome is complex and heterogeneous and may include varying degrees of lymphopenia, growth retardation and microcephaly. The phenotypic effects of the impaired repair of non programmed DNA damage are more diverse and difficult to study. Although such defects in cell survival and proliferation are likely to have an impact on the immune system, their contribution to the immunodeficiency of the LigIV syndrome remains unknown.
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Lam, N. D., S. Kim, J. J. Lee, K. R. Choi, M. H. Doan y H. Lim. "Enhanced Luminescence of InGaN / GaN Vertical Light Emitting Diodes with an InGaN Protection Layer". Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35210.
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We have investigated the effectiveness of a thin n-In0.2Ga0.8N layer inserted in the bottom n-GaN layer
of InGaN/GaN blue light emitting diodes (LEDs) for the protection of multiple quantum wells during the
laser lift-off process for vertical LED fabrication. The photoluminescence properties of the InGaN/GaN
lateral LEDs are nearly identical irrespective of the existence of the n-In0.2Ga0.8N insertion layer in the
bottom n-GaN layer. However, such an insertion is found to effectively increase the photoluminescence
intensity of the multiple quantum well and the carrier lifetime of the vertical LEDs. These improvements
are attributed to the reduced defect generations in the vertical LEDs during the laser lift-off process due to
the presence of the protection layer.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35210
8
Turcu, Mircea C. [Verfasser]. "Defect energies, band alignments, and charge carrier recombination in polycrystalline Cu(In,Ga)(Se,S)2 alloys / Mircea C Turcu". Aachen : Shaker, 2004. http://d-nb.info/1170529550/34.
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Steingrube, Silke [Verfasser]. "Recombination models for defects in silicon solar cells / Silke Steingrube". Hannover : Technische Informationsbibliothek und Universitätsbibliothek Hannover (TIB), 2011. http://d-nb.info/1015460577/34.
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RUCCI, FRANCESCA. "Murine models of hypomorphic defects of v(d)j recombination". Doctoral thesis, Università degli Studi di Milano, 2009. http://hdl.handle.net/2434/155853.
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V(D)J recombination is the process by which the subgenic elements of T and B cell receptors are assembled. The Rag1 and Rag2 proteins initiate this process by cleaving the DNA, whereas the Non Homologous End-Joining pathway (that includes Ku70/80, XRCC4, LigIV, DNA-PKcs and Cernunnos)mediates DNA joining. Rag1 and Rag2 null mutations cause SCID with complete lack of T and B lymphocytes in humans. Hypomorphic mutations that reduce, but do not abrogate, V(D)J recombination activity, may lead to Omenn syndrome (OS) or to “leaky SCID”, both of which are characterized by activated, anergic and autologous T cells, whereas severe erythroderma and cholitis are typical of OS only.
Hypomorphic LigIV mutations in humans are associated with increased cellular radiosensitivity, microcephaly, facial dysmorphisms, growth retardation, developmental delay, and a variable degree of immunodeficiency. These disorders define the LIGIV syndrome.
The work presented in this thesis focused on the characterization of two murine models with hypomorphic mutations in Rag1 (rag1S723C/S723C) and LigIV (ligIVR278H/R278H) that recapitulate leaky SCID. A minority of rag1S723C/S723C mice (but none of ligIVR278H/R278H mice) showed features of OS without phenotypic features of OS.
Both mouse models show a severe, but incomplete, block in T and B cell development, with residual generation of single-positive thymocytes. However, peripheral T cells are present and show an activated and anergic phenotype, with a restricted repertoire, reminiscent of human leaky SCID. The impaired in vitro proliferation in response to anti-CD3 is mostly due to increased apoptosis, and can be only partially rescued by addition of costimulatory factors such as anti-CD28 or by exogenous IL-2.
Despite a severe block at the pro to pre-B stage of B cell differentiation and of profound B cell lymphopenia, IgG, IgM, IgA and IgE serum levels are maintained, and a high proportion of immunoglobulin-secreting cells was observed in the spleen of both rag1S723C/S723C and ligIVR278H/R278H mice. Antibody responses to T-dependent and T-independent antigens are impaired, however both hypomorphic mouse models spontaneously produce high amounts of low-affinity antibodies that include self-reactive specificities.
The Rag1 and LigIV hypomorphic mouse models show attempts to organize the thymic medulla and are able, to various degrees, to generate nTregs. However, the expression of aire and of tissue-rectricted antigens, required for the maintenance of the central tolerance, is reduced.
Taken together, these data indicate that the stochastic generation of an autoreactive B cell repertoire, associated with defects in central and peripheral T cell tolerance, are an important component of the immunopathology of immunodeficiencies associated with hypomorphic mutation in the V(D)J recombination process. Therefore using these mouse models, it is now possible to elucidate the mechanisms underlying the phenotypic variability between OS and leaky SCID in humans.
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Ferguson, Kyle Akira. "Meiotic defects in infertile men". Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/1228.
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While the introduction of intracytoplasmic sperm injection (ICSI) has revolutionized the treatment of male infertility, concerns have been raised regarding the risk of chromosomal abnormalities in pregnancies derived from ICSI. Studies on sperm from infertile men have suggested that this population may produce higher rates of aneuploid sperm. Thus, we hypothesized that defects in early meiotic events may contribute to both male infertility and the production of aneuploid sperm.
We used immunofluorescent techniques to observe the synapsis and recombination of chromosomes during meiosis, and fluorescent in-situ hybridization (FISH) to assess sperm aneuploidy. We analyzed testicular tissue from thirty-one men (10 fertile and 21 infertile men). We observed that ~36% (5/14) of men with impaired spermatogenesis displayed reduced genome-wide recombination. When all men were pooled, we observed an inverse correlation between the frequency of sex chromosome recombination and XY disomy in the sperm. We combined immunofluorescent and FISH techniques to study recombination patterns on chromosomes 13, 18 and 21 in fifteen men (5 fertile and 10 infertile men). Four of the infertile men displayed altered recombination distributions on at least one of the chromosome arms studied. Finally, we examined early meiotic events in two biopsies from an azoospermic t(8;13) carrier. While global recombination rates were not altered, recombination frequencies were reduced specifically on the rearranged chromosomes. Asynapsed quadrivalents were observed in 90% and 87% of pachytene nuclei from the first and second biopsies, respectively, and were frequently associated with the sex chromosomes. BRCA1 and γH2AX, two proteins implicated in meiotic sex chromosome inactivation, localized along asynapsed regions regardless of whether or not they were associated with the sex chromosomes, suggesting that regions of autosomal chromosomes that fail to synapse undergo transcriptional silencing in humans.
In summary, we observed that a subset of infertile men display alterations in the number and position of meiotic crossovers, which may contribute to both infertility and an increased risk of sperm aneuploidy. The fidelity of synapsis is also a critical factor in determining the outcome of gametogenesis in humans, as the transcriptional inactivation of asynapsed regions may silence meiotic genes, leading to meiotic arrest and infertility.
12
Poolton, N. "ODMR studies of recombination emission bands in ZnSe and ZnS". Thesis, University of Hull, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.381883.
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Mohindra, Atul. "Defects in homologous recombination repair in mismatch repair-deficient tumour cell lines". Thesis, University of Sheffield, 2004. http://etheses.whiterose.ac.uk/6062/.
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MMR-deficiency increases the rate of mutations and often sensitizes cells to DSB-inducing agents (e. g. camptothecin and etoposide) as well as MMC (Jacob et a/., 2001 and Fiumicino et al., 2000). MMR -deficient tumour cell lines are also sensitive to the cytotoxic effects thymidine (Mohindra et al., 2002). This sensitivity is not a direct consequence of MMR -deficiency or alterations of DNA precursor metabolism. Instead, the results described in the present study suggest that MMR -deficient cells are sensitive to thymidine as a result of defects in HRR. The ScNeo recombination reporter substrate was used to determine the integrity of the HRR pathway in several MMR -proficient and -deficient tumour cell lines. Four MMR -deficient tumour cell lines were defective in the production of neo+ recombinants by homology based recombination following the transient expression of a site specific break. Furthermore, all MMR -deficient tumour cell lines tested were sensitive to the cross-linking agent MMC; an effect that is consistent with cells being deficient in HRR (including XRCC2, XRCC3 and BRCAI). To determine the alterations responsible for such HRR defects, genes known to be required for this pathway were screened for mutations in eight tumour cell lines. This revealed a heterozygous frameshift mutation within the RAD51 paralog, XRCC2, (342deIT) in SKUT-1 cells. 342delT was introduced into HRR proficient cells containing the ScNeo substrate. In SW480/SN. 3 transfectants, expression of 342delT conferred sensitivity to thymidine and MMC and suppressed HRR induced at the recombination reporter by thymidine but not by DSBs. In the MRC5VA/SN. 13 transfectants, expression of 342delT was accompanied by a decreased level of the full-length XRCC2. These cells were defective in the induction of HRR by either thymidine or DSBs. Thus 342delT suppresses recombination induced by thymidine in a dominant negative manner while recombination induced by DSBs appears to depend upon the level of wild-type XRCC2 as well as the expression of the mutant XRCC2 allele. These results suggest that HRR pathways responding to stalled replication forks or DSBs are genetically distinguishable. They further suggest a critical role for XRCC2 in HRR at replication forks, possibly in the loading of RAD51 onto gapped DNA.
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Blood, Arabella M. "A study of the electrical properties of defects in silicon". Thesis, University of Oxford, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.298320.
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Crichton, James Hugh. "Dissecting the meiotic defects of Tex19.1-/- mouse spermatocytes". Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/21042.
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The maintenance of genomic stability through suppression of retrotransposon activity is vital for the avoidance of potentially mutagenic genomic disruption caused by retrotransposition. Germline development is a particularly important phase for retrotransposon silencing as retrotransposition events here have the potential for transmission to the entire embryo, threatening the health of offspring. A collection of germline genome defence genes are required for the suppression of retrotransposons in the developing germline of male mice (e.g. Tex19.1, Dazl, Mili, Miwi2, Gasz, Mov10l1, Mael, Dnmt3l), all of which trigger meiotic prophase arrest when mutated. I have analysed the meiotic defects which arise in Tex19.1-/- male mice to contribute to the understanding of the fundamental mechanisms required for successful completion of meiosis and to investigate the involvement of retrotransposon silencing in this process. The absence of TEX19.1 in male mice causes infertility; with failed chromosome synapsis in ~50% of pachytene nuclei and associated apoptosis, as well as individual univalent chromosomes in 67% of remaining nuclei progressing to metaphase I. Where studied, failed chromosome synapsis is a common feature of germline genome defence mutant spermatocytes. One aim of my studies has been to better understand the mechanism responsible for this failed chromosome synapsis. I have demonstrated that unlike Mael-/- spermatocytes, additional SPO11-independent DNA damage potentially attributable to retrotransposition is not detectable in Tex19.1-/- spermatocytes. Rather, the formation of meiotic DNA double strand breaks (DSBs) is dramatically reduced in early prophase to around 50%, resulting in a reduction in nuclear γH2AX signal, production of SPO11- oligonucleotide complexes and foci formation by early recombination proteins RPA, DMC1 and RAD51. Despite this early reduction, DSB frequency recovers to more normal levels shortly after in zygotene. I have shown that defective pairing of homologous chromosomes by meiotic recombination is likely responsible for the asynapsis previously reported. The initial reduction in DSB frequency could be sufficient to cause failed chromosome synapsis in this mutant, assuming that late-forming DSBs cannot participate effectively in promoting homologous pairing. Alternative hypotheses include altered positioning of DSBs in response to altered chromatin organisation relating to retrotransposon upregulation, misguiding the pairing of homologous chromosomes. Such a model of disruption could also extend to other germline genome defence mutants. I have demonstrated that despite successful pairing of homologous chromosomes in a sub-population of Tex19.1-/- spermatocytes, subsequent progression of these cells through pachytene is delayed. Numerous diverse features of progression are all delayed, including recombination, ubiquitination on autosomes and sex chromosomes, expression of the mid-pachytene marker H1t, and chromosome organisation. The delay identified is related to recombination therefore this feature is likely to stem from the initial defect in DSB formation early in prophase. While some delayed features are probably directly related to recombination, others are not. The coordinated delay observed may suggest the presence of a recombination-sensitive cell-cycle checkpoint operating to regulate progression through pachytene. My research has also aimed to establish the cause of elevated univalent chromosomes not connected by chiasmata in metaphase I Tex19.1-/- spermatocytes. I have demonstrated that that absence of chiasmata is not due to failed crossover formation between synapsed chromosomes. Rather, the frequent observation of individual unsynapsed chromosomes during crossover formation suggests that some spermatocytes with low-level asynapsis are leaking through meiotic checkpoints and are unable to form a crossover before reaching metaphase. Therefore, again this later meiotic defect appears to stem from the initial defect in meiotic DSB formation, the consequences of which vary widely in severity. Remarkably the unsynapsed chromosomes present during crossover formation include both sex chromosomes, and autosomes. Tolerance of an unsynapsed autosome from pachytene into metaphase is an unusual observation in mice and this observation may aid the understanding of spermato cyte quality control mechanisms during this progression. Together these findings have greatly advanced the understanding of the infertility incurred during meiosis in Tex19.1-/- male mice. These findings may also extend to benefit the understanding of other germline genome defence mutants. Diverse observations made during my investigations also reveal a potential system of coordinated progression through pachytene relating to meiotic recombination. The variable severity of the synapsis defects incurred in this mutant appears to have variable effects on spermatocyte survival and could also inform the understanding of meiotic checkpoint sensitivity.
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Wilhelm, Therese. "Homologous recombination protects against mitotic defects and unbalanced chromosome segregation caused by spontaneous replication stress". Thesis, Paris 11, 2011. http://www.theses.fr/2011PA112059.
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Les cellules déficientes pour la recombinaison homologue (RH) présentent un ralentissement des fourches de réplication, un nombre aberrant de centrosomes et une aneuploïdie même en absence de stress exogène (Bertrand P 2003, Daboussi F 2005, 2008, Deng 1999, 2002, Griffin 2000, Kraakman-van der Zwet 2002). De plus, la fréquence des mitoses présentant des chromosomes surnuméraires est plus élevée dans ces cellules.L’ensemble des ces résultats suggéraient que le ralentissement des fourches de réplication dans les cellules déficientes pour la RH pourrait avoir un impact direct sur la formation de centrosomes surnuméraires. De plus, nous voulions savoir si cela pouvait également influencer la ségrégation des chromosomes au cours de la mitose. Les résultats que nous avons obtenus sont rassemblés dans l’article intitulé : “Homologous Recombination protects against mitotic defects and unbalanced chromosome segregation caused by spontaneous replication stress”.Le traitement des cellules compétentes pour la RH avec 5µM d’hydroxyurée (HU), un inhibiteur de l’enzyme de synthèse des dNTPs, induit un ralentissement des fourches de réplication parfaitement comparable à celui observé dans les cellules déficientes pour la RH. Après traitement à l’HU des cellules compétentes pour la RH, la fréquence de mitoses présentant des chromosomes surnuméraires augmente et devient similaire à la fréquence de mitoses avec des chromosomes surnuméraires pour les cellules déficientes pour la HR non traitées à l’HU. Nous avons mesuré l’impact de l’HU sur l’apparition des ponts anaphasiques et sur des défauts de ségrégation des chromosomes lors de la mitose. En l’absence de traitement, nous observons une fréquence plus élevée de ponts anaphasiques et de défauts de ségrégation dans des cellules déficientes pour la RH. Des traitements avec 5µM d’HU augmentent la fréquence des ponts anaphasiques et des erreurs de ségrégation dans les cellules compétentes pour la RH, pour atteindre un niveau comparable aux cellules déficientes pour la RH. Ainsi, une altération de la dynamique de réplication consécutive à une déficience de RH ou à un traitment avec de faibles doses d’HU induit des défauts au cours de la mitose. Un lien direct entre une dynamique de réplication anormale et l’apparition d’un nombre aberrant de centrosomes pourrait être la persistance en mitose d’ADN non répliqué ou endommagé. Comme l’ADN non répliqué ou les fourches bloquées induisent la formation d’ADN simple brin couvert par RPA, nous avons compté le nombre de cellules en G2/M présentant des foyers de RPA, et observé que la fraction de cellules ayant plus de 5 foyers de RPA augmente dans des cellules déficientes pour Brca2. En conclusion, nous proposons un lien direct entre des altérations de la cinétique de réplication, l’apparition de centrosomes surnuméraires et des défauts de ségrégation des chromosomes en mitose dans les cellules déficientes pour la RH même non soumises à un stress exogène. L’utilisation de faibles doses d’HU dans des cellules compétentes pour la RH mime les phénotypes observés dans les cellules déficientes pour la RH et confirme notre modèle.Nous avons également cherché à comprendre les causes du ralentissement des fourches de réplication observé dans les cellules déficientes pour la RH. Il est ainsi possible que les arrêts de fourches spontanés soient une conséquence d’un stress oxydatif endogène. Dans les cellules compétentes pour la RH, le redémarrage des fourches bloquées est possible et assure une progression normale de la réplication de l’ADN. Ceci favorise une ségrégation équilibrée des chromosomes, le maintien de la diploïdie et la stabilité du génome. Dans des cellules déficientes pour la RH, les blocages de fourches devraient être délétères puisque les principaux mécanismes de redémarrage des fourches ne sont pas fonctionnels. De plus, l’arrêt prolongé des fourches ainsi que les cassures double brin générées par l’effondrement des fourches devraient activer des voies de signalisation. Nous avons néanmoins observé que les cellules ne sont pas bloquées dans le cycle cellulaire, ce qui suggère qu’un seuil supérieur de dommages doive être atteint pour induire l’arrêt du cycle. Les stress endogènes ne semblent donc pas suffisamment élevés pour atteindre ce seuil : même si l’ensemble des fourches parcourant le génome sont ralenties, l’activation d’origines cryptiques permet de compenser et ainsi de maintenir la progression dans le cycle. Mais puisque les cellules ne sont pas arrêtées dans le cycle, des fourches bloquées, de l’ADN endommagé ou non répliqué pourraient persister jusqu’à la transition G2/M et in fine perturber le déroulement de la mitose. Des centrosomes multipolaires provoquent la formation de fuseaux multipolaires et favorisent la ségrégation déséquilibrée des chromosomes, entraînant l’aneuploïdie, la déstabilisation du génome et le développement de cancersHR deficient cells show slow replication kinetics, aberrant centrosome number and aneuploidy even in the absence of any exogenous stress (Bertrand P 2003, Daboussi F 2005, 2008, Deng 1999, 2002, Griffin 2000, Kraakman-van der Zwet 2002). Frequency of mitosis with extra centrosomes is elevated and replication kinetics decreased in HR deficient compared to HR proficient cells, in the absence of exogenous stress. Thus the question arose, if replication slowing down in HR deficient cells has direct impact on the appearance of supernumerary centrosomes. Furthermore we wanted to know if this might directly impact chromosome segregation. The results we gained are brought together in the paper “Homologous recombination suppression causes spontaneous mitotic alterations through endogenous replication stress”. By treating our HR proficient cells with 5µM HU we found the perfect concentration to mimic replication dynamics of HR deficient cells in an HR proficient background. This concentration was applied to HR proficient cells. After HU treatment the frequency of mitosis with extra centrosomes was elevated in HR proficient cells. Now they showed the same frequency of mitosis with extra centrosomes, than unchallenged HR deficient cells. We measured the impact of HU treatment on occurrence of anaphase bridges or aberrant mitotic segregation. In the absence of treatment higher frequency of anaphase bridges and aberrant mitotic segregation was detected for HR deficient cells. With 5µM HU the frequency of anaphase bridges and aberrant mitosis could be elevated in HR proficient cells. Now they showed aberrant mitotic features with the same frequency than unchallenged HR deficient cells. A direct link between abnormal replication kinetics and aberrant centrosomes might be unreplicated or damaged DNA, that enter mitosis. Unreplicated or blocked DNA might harbour ss DNA bound RPA. Thus we counted G2/M cells with RPA foci. Indeed the fraction of cells that harbour more than 5 RPA foci was elevated in Brca2 deficient in comparison to Brca2 proficient cells. In conclusion we propose a direct link between delayed replication, supernumerary centrosomes and aberrant chromosome segregation in unchallenged HR deficient cells. If we mimicked replication kinetics of HR deficient cells in an HR proficient background, we also mimicked frequency of mitosis with extra centrosome number and aberrant chromosome segregation. Furthermore we investigated the causes of replication slowing down in HR deficient cells. It can be hypothesized that endogenous oxidative stress is implicated in spontaneous fork arrest. In HR proficient cells, reactivation of stalled replication forks and therefore normal replication progression is assured. This favours balanced chromosome segregation, diploidy and genetic stability.In HR deficient cells, replication fork blockage might be detrimental as the main restart mechanism for blocked forks is absent. Prolonged fork blockage or DSB’s arising by fork collapse or resolution of blocked replication forks might activate signalling pathways. However cells are not arrested in cell cycle progression, suggesting that a threshold should be reached to activate cell cycle arrest. Endogenous stress is not sufficient high to reach this threshold. Replication is genome wide slowed down. In this context, the activation of cryptic origins compensates at least partly the slow replication velocity. However, because cells were not arrested in cell cycle progression, some blocked replication forks and damaged or unreplicated DNA regions might persist until G2/M phase and affect centrosome duplication and chromosome segregation. Multipolar centrosomes cause multipolar spindles and favour unbalanced chromosome segregation leading to aneuploidy, genetic instability and cancer development
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Ghosh, Michael. "Defekte im Bodenbereich blockerstarrten Solar-Siliziums". Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2010. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-38493.
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Etwa die Hälfte aller Solarzellen weltweit wird aus blockerstarrtem Silizium hergestellt. Derartige Blöcke weisen in ihren Außenbereichen eine verringerte Diffusionslänge der Minoritätsladungsträger auf. Um die Ursache dafür im Fall des bodennahen Bereichs zu bestimmen wurden zwei Spezialblöcke (ein Block mit reduzierter Bor-Dotierung und ein Block mit Phosphor-Dotierung) - u. a. mittels DLTS und FTIR - auf Kristalldefekte untersucht. Zusätzlich zu Dotierelementen (B, P, Al, As) wurden im Bodenbereich folgende Defekte nachgewiesen:
Metalle: Fe, Cr
Sauerstoffhaltige Defekte: Interstitieller Sauerstoff, Thermische Donatoren (TD), O1, O2
Stickstoffhaltige Defekte: NN-Paar, NNO-Komplex, Shallow Thermal Donors (STD)
Ausgedehnte Defekte: Versetzungen, Ausscheidungen, Korngrenzen.
Die Verteilung der flachen Donatoren (P, TD, STD, As) und Akzeptoren (B, Al) bestimmt den Widerstandsverlauf im bodennahen Bereich des Phosphor dotierten Spezialblocks. Das dortige Diffusionslängenprofil kann im Rahmen der Shockley-Read-Hall-Statistik erst durch eine Erhöhung des Minoritätseinfangquerschnitts für das Cr-Niveau (Faktor 5) bzw. für das STD-Niveau (Faktor 10) nachgezeichnet werden. Eisen, Versetzungen und Korngrenzen haben hier keinen wesentlichen Einfluss. In den untersten Millimetern des Spezialblocks müssen weitere Defekte hinzukommen, die die Diffusionslänge zusätzlich reduzieren; Thermische Donatoren und O1 und eventuell Ausscheidungen kommen dazu in Frage.
Die sinngemäße Übertragung der Konzentrationsverläufe aus den beiden Spezialblöcken auf einen Block mit einer produktionsüblichen Dotierung ([B]≈1016/cm3) ergibt, dass in diesem Fall verschiedene Defekte (TD, STD, CrB und FeB) einen Beitrag zur Diffusionslängenreduktion im bodennahen Blockbereich liefern.
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LORENZON, MONICA. "ROLE OF NONRADIATIVE SURFACE DEFECTS ON EXCITON RECOMBINATION PROCESSES IN SEMICONDUCTOR COLLOIDAL NANOSTRUCTURES". Doctoral thesis, Università degli Studi di Milano-Bicocca, 2018. http://hdl.handle.net/10281/199095.
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Durante la mia tesi di dottorato mi sono occupata dello studio spettroscopico di nanocristalli colloidali di semiconduttore e in particolare della correlazione tra le loro superfici e la fotofisica, che ho studiato per mezzo di spettroelettrochimica (SEC) e spettroscopia ottica in atmosfera controllata. Più precisamente, ho studiato e modellizzato il comportamento di diversi tipi di nanocristalli sottoponendoli a variazioni controllate delle condizioni ossidanti/riducenti dell’ambiente che li circonda, con l’obiettivo di implementarne l’uso in sensori ottici di ossigeno.
L’elevato rapporto superficie-volume tipico dei nanocristalli fa sì che la loro fotoluminescenza sia fortemente influenzata da un’ampia distribuzione di stati introdotti da difetti superficiali. Un portatore catturato da una trappola in superficie, infatti, non è più disponibile per la ricombinazione radiativa, e abbassa la resa quantica del nanocristallo. Tramite SEC, si può applicare una differenza di potenziale elettrochimico (EC) a un sottile film di nanocristalli depositati su un substrato trasparente e conduttivo. La fotolumiscenza del campione viene eccitata e raccolta sia in continua sia temporalmente risolta tramite appositi rivelatori. L’applicazione di una differenza di potenziale EC negativo corrisponde ad aumentare il livello di Fermi del nanocristallo, riempiendone gradualmente i difetti superficiali e attivando l’intrappolamento di lacune. La fotoluminescenza che ne risulta dipende dall’effetto dominante tra lo spegnimento della stessa dovuto all’intrappolamento di lacune e l’aumento derivante dalla soppressione dell’intrappolamento di elettroni. Per ciascun materiale ho effettuato misure di SEC ed esperimenti in atmosfera controllata, per arrivare alla realizzazione di diversi tipi di sensori ottici di ossigeno (Pressure Sensitive Paints, PSPs), usati per monitorare il flusso di ossigeno nei pressi di superfici complesse o miniaturizzate. Tipicamente consistono in un mezzo poroso in cui è disperso un cromoforo organico, la cui emissione cambia in modo inversamente proporzionale alla pressione di ossigeno. Ho utilizzato nanocristalli di perovskite (cesio-piombo-bromo, CsPbBr3) per realizzare un’alternativa completamente inorganica alle PSP tradizionali, basate su un aumento di segnale sotto pressione ridotta. Questo approccio però non è ottimale in applicazioni in cui è necessario rilevare grandi quantità di ossigeno (a pressione ambientale, per esempio). Un avanzamento in questo senso è fornito dalla PSP ‘inversa’ che ho realizzato tramite nanoplatelet di seleniuro di cadmio (CdSe), che diversamente dai materiali tradizionali per PSP sono in grado di illuminarsi maggiormente, invece che di spegnersi, in presenza di ossigeno. Nonostante il vantaggio offerto dal materiale a comportamento inverso, sia le PSP inverse sia quelle tradizionali si basano su una misura radiometrica di intensità luminosa, la quale però può cambiare anche in seguito a variazioni di temperatura, o degradazione indotta da UV, il che comporta la necessità di complesse procedure di calibrazione. Un miglioramento importante che ho introdotto nel corso del mio dottorato è rappresentato dall’impiego di nanocristalli bi-emissivi core/shell di seleniuro di cadmio/solfuro di cadmio (CdSe/CdS), in grado di sostenere contemporaneamente eccitoni di core e di shell, la cui ricombinazione radiativa porta a fotoluminescenza a due colori (rosso e verde) anche con basse potenze di eccitazione. É importante notare che i due canali emissivi presentano una risposta opposta all’ossigeno, il che mi ha permesso di realizzare una PSP raziometrica e intrinsecamente calibrata, con elevata sensibilità sia a livello di ensemble sia di singola particella.The main research theme of my PhD has been the spectroscopic investigation of colloidal semiconductor nanocrystals (NCs), with a focus on the correlation between their surfaces and their photophysics, and was conducted by means of spectroelectrochemistry (SEC) and optical spectroscopy under controlled atmosphere. Specifically, I aimed to understand and model the NCs behavior in a changing oxidative/reducting environment, with the ultimate goal to implement their use as active material in optical oxygen pressure sensors. The high surface-to-volume ratio typical of NCs causes their photoluminescence (PL) efficiency to be strongly affected by a broad distribution of surface defect states. If captured by a surface trap, a photogenerated electron (or hole) becomes unavailable for the radiative recombination, thus lowering the overall PL efficiency of the NCs. By means of SEC, an electrochemical (EC) potential can be applied to a thin film of NCs deposited onto a transparent and conductive substrate, whose PL is excited and collected via dedicated instruments for either continuous or time-resolved measurements. The application of a negative EC potential corresponds to raising the Fermi level of the NCs, thus gradually filling the surface defects and activating their hole-trapping capability. The PL intensity is thus determined by the competition between the quenching effect of hole withdrawal and the brightening effect of suppressed electron trapping. For each material system I performed side-by-side SEC measurements and spectroscopic experiments under controlled atmosphere, and eventually demonstrated different types of optical oxygen pressure sensors, also called pressure-sensitive paints (PSPs), i.e, all-optical probes for monitoring oxygen flows in the vicinity of complex or miniaturized surfaces. They typically consist in a porous binder embedding an oxygen sensitive chromophore, whose PL intensity changes accordingly to the oxygen partial pressure. By employing cesium lead bromide (CsPbBr3) perovskite NCs, I realized an all-inorganic alternative to traditional organic PSPs, based on the increase of their PL intensity under reduced oxygen pressure. This approach relies on the disappearance of the signal in presence of oxygen, which means it may not represent the best approach when high oxygen concentrations (for instance, at atmospheric pressure) need to be detected. In this thesis, I demonstrated how to overcome this issue by realizing a novel-concept, inorganic ‘reverse’ PSP, with cadmium selenide (CdSe) nanoplatelets (NPLs) as active material, since their PL intensity increases with the oxygen concentration. Although the SEC and optical measurements under controlled atmosphere allowed me to understand and model the unusual benefit of an oxidative environment on CdSe NPLs, the PSPs based on them share with the perovskite-based sensors the major drawback of providing a radiometric oxygen detection only, that is, the measurement solely relies on a change in the PL intensity of the chromophore. The PL, however, can also change as a result of a temperature variation or UV-induced degradation. In my work, I introduced a significant improvement by employing dual-emitting, core/shell cadmium selenide/cadmium sulfide (CdSe/CdS) NCs that are capable of simultaneously sustaining core and shell excitons, whose radiative recombination leads to two-color (red and green) luminescence under low-intensity power excitation. Importantly, the two emissive channels exhibit opposite responses to the oxygen pressure, which allowed me to realize an intrinsically calibrated ratiometric PSP whose sensitivity is significantly enhanced with respect to traditional reference-sensor pairs, both in ensemble and at the single particle level.
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Amaku, Afi. "A study of the electrical properties of point and extended defects in silicon". Thesis, University of Oxford, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.339355.
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Luo, Yandi. "Development of new buffer layers and rapid annealing process for efficient Sb₂Se₃ thin-film solar cells". Electronic Thesis or Diss., Université de Rennes (2023-....), 2024. http://www.theses.fr/2024URENS039.
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Dans ce travail de thèse, le comportement de l'interface de l'hétérojonction, le processus de croissance des grains cristallins et la couche tampon des cellules solaires à base de Sb₂2Se₃ ont été étudiés. La qualité de l'absorbeur et l'alignement des bandes d'énergie sont identifiés comme des paramètres clés pour réduire la densité de défauts et pour faciliter la séparation et le transport des porteurs de charge photogénérés. Une stratégie de dopage d'Al³⁺ dans la couche tampon de CdS a été introduite dans les cellules solaires Sb₂2Se₃. L'alignement des bandes d'énergie et la qualité de l'interface p-n ont été considérablement améliorés. Une courbure de bandes type "Spike-like" a été obtenue pour la meilleure cellule solaire avec un rendement de 8,41%. Deuxièmement, un procédé de recuit thermique rapide a également été développé et optimisé afin d'améliorer la qualité de la couche absorbeur de Sb₂2Se₃ avec une densité de défauts réduite. Le rendement des cellules solaires est augmenté à 9,03%. De plus, nous avons essayé de remplacer la couche tampon CdS toxique par un film ZnSnO respectueux de l'environnement avec en plus un band-gap plus large. Un rendement intéressant de 3,44% a été obtenue pour ces cellules solaires de Sb₂2Se₃ sans CdIn this thesis, heterojunction interface behavior, grain growth process and alternative buffer layer of Sb₂Se₃ based solar cells were investigated. The absorber quality and the band alignment are identified as key parameters for reducing defect density and for facilitating the separation and the transport of photogenerated charge carriers. A strategy of Al³⁺ doping into the CdS buffer layer was introduced in Sb₂Se₃ solar cells. The band alignment and the interface quality have been significantly improved. A “spike-like” structure was obtained for the best device with an efficiency of 8.41%. Secondly, a rapid thermal annealing process has also been developed and optimized in order to improve the quality of Sb₂Se₃ absorber film with reduced defect density. The efficiency of the Sb₂Se₃ solar cells is increased to 9.03%. In addition, we have tried to replace the toxic CdS buffer layer with an environmentally friendly ZnSnO film with moreover a wider band gap. An interesting power conversion efficiency of 3.44% was achieved for the Cd-free Sb₂Se₃ thin-film solar cells
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Pang, Shu Koon. "Investigation of recombination lifetime and defects in magnetic czochralski silicon for high efficiency solar cells". Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/13554.
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Jiang, Xianwu. "Hydrocarbon molecules databases for waste treatment applications". Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPAST039.
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Dans cette thèse, nous étudions la (dé)excitation vibronique et la recombinaison dissociative du CH+ par impact d'électrons de faible énergie. Nous développons d'abord une approche théorique de l'excitation (dé)vibronique de CH+ par impact d'électrons. Dans cette approche, la méthode de la matrice R à noyaux fixes est utilisée pour calculer les matrices de diffusion des électrons et des ions dans l'approximation de Born-Oppenheimer. Une transformation vibronique du cadre et la procédure d'élimination à canal fermé dans l'esprit de la théorie des défauts quantiques moléculaires sont utilisées pour construire une matrice de diffusion dépendant de l'énergie décrivant les interactions entre les canaux vibroniques de l'ion cible induits par l'électron incident. La matrice de diffusion obtenue tient compte de la série de résonances vibroniques de Rydberg dans le spectre de collision. Les sections transversales de l'excitation vibronique pour différentes combinaisons d'états vibroniques initiaux et finaux sont calculées. Un bon accord entre les sections transversales d'excitation électronique, obtenu en utilisant la théorie des défauts quantiques et dans un calcul direct de matrice R, démontre que l'approche actuelle fournit un outil fiable pour la détermination des sections transversales d'excitation (dé)vibronique pour des cibles avec des résonances électroniques de faible énergie. De telles cibles étaient difficiles à traiter théoriquement avec les méthodes précédentes. Dans le même cadre que celui appliqué aux excitations (dé)vibroniques, nous calculons en outre la section transversale pour la recombinaison dissociative à basse énergie de CH+ couplant la fonction de base de l'onde sortante définie par le potentiel d'absorption complexe. La contribution des trois états ioniques X 1Σ +, a 3Π et A 1Π les plus bas et la série de Rydberg convergeant vers ces états sont pris en compte. Les sections transversales DR obtenues sont quantitativement en bon accord avec les mesures expérimentales et présentent une caractéristique de résonance analogue à la courbe de la section transversale expérimentale. L'origine des résonances proéminentes dans les résultats calculés est analysée par le calcul des probabilités de DR pour les ondes partielles de l'électron incident. On constate que les ondes partielles de type d, notamment dσ, dπ et dδ, contribuent considérablement à la DR du état de terrain CH+. Cela peut expliquer les écarts observés entre la théorie et l'expérience dans les études précédentesIn this thesis, we investigate the vibronic (de-) excitation and dissociative recombination of CH+ by low-energy electron impact. We first develop a theoretical approach for the electron-impact vibronic (de-) excitation of CH+. In this approach, the fixed-nuclear R-matrix method is employed to compute electron-ion scattering matrices in the Born-Oppenheimer approximation. A vibronic frame transformation and the closedchannel elimination procedure in a spirit of molecular quantum defect theory are employed to construct an energy-dependent scattering matrix describing interactions between vibronic channels of the target ion induced by the incident electron. The obtained scattering matrix accounts for Rydberg series of vibronic resonances in the collisional spectrum. Cross sections for vibronic excitation for different combinations of initial and final vibronic states are computed. A good agreement between electronic-excitation cross sections, obtained using the quantum defect theory and in a direct R-matrix calculation, demonstrates that the present approach provides a reliable tool for determination of vibronic (de-) excitation cross sections for targets with low-energy electronic resonances. Such targets were difficult to treat theoretically using earlier methods. Within the same framework applied for the vibronic (de-) excitations, we further compute the cross section for low-energy dissociative recombination of CH+ coupling the outgoing-wave basis function defined by complex absorbing potential. The contribution of the three lowest X 1Σ +, a 3Π and A 1Π ionic states and the Rydberg series converging to those states are taken into account. The obtained DR cross sections are quantitatively in good agreement with the experimental measurements and exhibit a resonanc feature analogous to the experimental cross-section curve. The origination of the prominant resonances in the computed results are analyzed through computing the DR probabilities for the partial waves of the incident electron. The d-type partial waves including dσ, dπ and dδ are found considerably contributing to the DR of the ground-state CH+. This may explain the discrepancies observed between thoery and experiment in the preceeding studies
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Ringel, S. A. "Growth and process induced defects and recombination mechanisms in AIGaAs/GaAs and CdZnx Te/CdS photovoltaic device structures". Diss., Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/13330.
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Čeponis, Tomas. "Radiation technologies for optimization of Si device parameters and techniques for control of radiation defects". Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2012. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2012~D_20121001_093158-64168.
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In high energy physics experiments the semiconductor particle detectors of pin structure are commonly employed for tracking of the ionising particles. However, ionising radiation creates defects and consequently affects the parameters of particle detectors. Therefore, it is necessary to characterize irradiated detectors and search for the new approaches on how to suppress or control the degradation process. Measurements of current-voltage, capacitance-voltage characteristics as well as deep level transient spectroscopy, thermally stimulated currents spectroscopy are employed for the characterization of irradiated particle detectors. At high irradiation fluences when defects concentration exceeds that of dopants, a generation current increases and, thus, the above mentioned techniques can not be applied for the correct evaluation of defect parameters. In this work, models describing displacement currents in detectors due to redistribution of electric field determined by variations of external voltage or a moving charge in electric field are discussed. These models were applied for creation of the advanced techniques which allow evaluating of charge transport, trapping and recombination/generation parameters in heavily irradiated detectors after irradiation. These techniques were applied for the spectroscopy of deep levels associated with defects, for cross-sectional scans within layered junction structures as well as for examination of defects evolution during irradiation. In... [to full text]Aukštųjų energijų fizikos eksperimentuose plačiai taikomi puslaidininkiniai pin struktūros dalelių detektoriai jonizuojančiosioms dalelėms registruoti. Radiacinė spinduliuotė sukuria defektus medžiagoje ir neigiamai įtakoja detektorių parametrus, todėl būtina charakterizuoti apšvitintus detektorius ieškant būdų, kaip juos patobulinti. Apšvitintų detektorių charakterizavimui taikomi volt-amperinių, volt-faradinių būdingųjų dydžių matavimai ir analizė, giliųjų lygmenų talpinė bei šiluma skatinamų srovių spektroskopija. Tačiau stipriai apšvitintuose detektoriuose, kai defektų koncentracija viršija legirantų koncentraciją bei išauga nuotėkio srovė, šie metodai negali būti taikomi siekiant korektiškai įvertinti radiacinių defektų parametrus. Šiame darbe buvo sukurti modeliai, apibūdinantys slinkties sroves, tekančias detektoriuje dėl elektrinio lauko persiskirstymo keičiantis išorinei įtampai arba elektriniame lauke judant injektuotam krūviui. Šie modeliai buvo pritaikyti naujų metodikų sukūrimui, kurios įgalina įvertinti krūvio pernašos, pagavimo, rekombinacijos/generacijos parametrus stipriai apšvitintuose detektoriuose po apšvitos. Sukurti metodai buvo pritaikyti defektų spektroskopijai ir skersinei žvalgai sluoksninėse struktūrose bei defektų evoliucijos tyrimams apšvitos metu. Disertacijoje pateikti ir aptarti apšvitintų detektorių ir apšvitos metu pasireiškiančios parametrų kaitos rezultatai. Elektronikos grandynuose plačiai naudojami galios pin struktūros diodai, kurie... [toliau žr. visą tekstą]
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Raška, Michal. "Diagnostika PN přechodu křemíkových vysokonapěťových usměrňovacích diod pomocí šumu mikroplazmatu". Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2009. http://www.nusl.cz/ntk/nusl-233496.
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The doctoral thesis deals with diagnostics of local defects in PN junctions and brings new information about microplasma noise behaviour and its usage for the temperature changes detection inside PN junctions. Defects in PN junctions are the source of microplasma noise. There were deviations observed in microplasma noise from the common known rectangle shape pulses during the measurements. These deviations were correlated with the temperature change directly in the defect area and in the defect area surroundings. Generation and recombination coefficients are commonly thought to be constant. However, these coefficients were observed to be not stable with time and this effect is explained in this work. The doctoral thesis then focuses on the PN junction parameters determination in the case when it is not possible to define unambiguously whether it is abrupt or linearly graded PN junction. The most significant parameters which are to be determined are barrier capacity, diffusion voltage and depleted area width in dependence on the voltage. The correlation between local avalanche discharge in PN junction and negative differential resistance appearance on VA characteristics of reverse-biased diode was qualitatively verified. The last important point in the work is computer modelling of temperature behaviour in the defect area and its surroundings during local avalanche breakdown. Thus the method of real diodes heating area parameters determination was introduced.
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Čeponis, Tomas. "Radiacinės Si prietaisų parametrų optimizavimo ir radiacinių defektų kontrolės technologijos". Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2012. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2012~D_20121001_093138-74555.
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Aukštųjų energijų fizikos eksperimentuose plačiai taikomi puslaidininkiniai pin struktūros dalelių detektoriai jonizuojančiosioms dalelėms registruoti. Radiacinė spinduliuotė sukuria defektus medžiagoje ir neigiamai įtakoja detektorių parametrus, todėl būtina charakterizuoti apšvitintus detektorius ieškant būdų, kaip juos patobulinti. Apšvitintų detektorių charakterizavimui taikomi volt-amperinių, volt-faradinių būdingųjų dydžių matavimai ir analizė, giliųjų lygmenų talpinė bei šiluma skatinamų srovių spektroskopija. Tačiau stipriai apšvitintuose detektoriuose, kai defektų koncentracija viršija legirantų koncentraciją bei išauga nuotėkio srovė, šie metodai negali būti taikomi siekiant korektiškai įvertinti radiacinių defektų parametrus. Šiame darbe buvo sukurti modeliai, apibūdinantys slinkties sroves, tekančias detektoriuje dėl elektrinio lauko persiskirstymo keičiantis išorinei įtampai arba elektriniame lauke judant injektuotam krūviui. Šie modeliai buvo pritaikyti naujų metodikų sukūrimui, kurios įgalina įvertinti krūvio pernašos, pagavimo, rekombinacijos/generacijos parametrus stipriai apšvitintuose detektoriuose po apšvitos. Sukurti metodai buvo pritaikyti defektų spektroskopijai ir skersinei žvalgai sluoksninėse struktūrose bei defektų evoliucijos tyrimams apšvitos metu. Disertacijoje pateikti ir aptarti apšvitintų detektorių ir apšvitos metu pasireiškiančios parametrų kaitos rezultatai.
Elektronikos grandynuose plačiai naudojami galios pin struktūros diodai, kurie... [toliau žr. visą tekstą]In high energy physics experiments the semiconductor particle detectors of pin structure are commonly employed for tracking of the ionising particles. However, ionising radiation creates defects and consequently affects the parameters of particle detectors. Therefore, it is necessary to characterize irradiated detectors and search for the new approaches on how to suppress or control the degradation process. Measurements of current-voltage, capacitance-voltage characteristics as well as deep level transient spectroscopy, thermally stimulated currents spectroscopy are employed for the characterization of irradiated particle detectors. At high irradiation fluences when defects concentration exceeds that of dopants, a generation current increases and, thus, the above mentioned techniques can not be applied for the correct evaluation of defect parameters. In this work, models describing displacement currents in detectors due to redistribution of electric field determined by variations of external voltage or a moving charge in electric field are discussed. These models were applied for creation of the advanced techniques which allow evaluating of charge transport, trapping and recombination/generation parameters in heavily irradiated detectors after irradiation. These techniques were applied for the spectroscopy of deep levels associated with defects, for cross-sectional scans within layered junction structures as well as for examination of defects evolution during irradiation. In... [to full text]
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Kreßner-Kiel, Denise. "Wechselwirkung von Kupfer mit ausgedehnten Defekten in multikristallinem Silicium und Einfluss auf die Rekombinationseigenschaften". Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2017. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-229212.
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Die Rekombinationsaktivität von Versetzungen und Korngrenzen in multikristallinem Silicium wird von Kupfer und anderen metallischen Verunreinigungen wie Eisen mitbestimmt. Das Hauptziel der Arbeit war es, die Verteilung von Kupfer und dessen Wirkung auf die Rekombinationsaktivität von Versetzungen und Korngrenzen genauer zu untersuchen. Dazu wurden optische und elektrische Untersuchungen an gezielt mit Metallen verunreinigten Modellmaterialien durchgeführt. Nicht alle Versetzungen sind rekombinationsaktiv. Es konnte gezeigt werden, dass der Anteil rekombinationsaktiver Versetzungen am Gesamtinventar und die Hintergrunddiffusionslänge von der Verunreinigung mit Metallen abhängig sind. Ergebnisse von Untersuchungen an Proben, die Diffusionsexperimenten unterzogen wurden, deuten auf unterschiedliches Ausscheidungsverhalten von Kupfer und Eisen hin sowie auf Wechselwirkungen mit Versetzungen und Korngrenzen, die mit der Diffusionstemperatur und den Abkühlbedingungen in Zusammenhang stehen.
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Aversa, Pierfrancesco. "Primary Defects in Halide Perovskites : Effect on Stability and Performance for Photovoltaic Applications Effect of organic PCBM Electron transport Layers on natural and post-irradiation ageing of optical absorption and emission in methyl ammonium lead triiodide spin –coated on p-i-n Solar Sell Substrates Effect of organic PCBM Electron transport Layers on natural and post-irradiation ageing of optical absorption and emission in triple cation lead mixed halide perovskite spin –coated on p-i-n Solar Sell Substrates Electron Irradiation Induced Ageing Effects on Radiative Recombination Properties of methylammonium lead triiodide layers on p-i-n solar cell substrates Electron Irradiation Induced Ageing Effects on Methylammonium Lead Triiodide Based p-i-n Solar Cells Electron Irradiation Induced Ageing Effects on Radiative Recombination Properties of Quadruple Cation Organic-Inorganic Perovskite Layers". Thesis, Institut polytechnique de Paris, 2020. http://www.theses.fr/2020IPPAX050.
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Ces onze dernières années ont vu apparaitre les pérovskites organiques inorganiques hybrides (HOIPs) comme un passionnant domaine de recherche pour leur application potentielle dans les technologies du photovoltaïque (PV) en raison de leurs exceptionnelles propriétés optoélectroniques et de leur facilité de mise en oeuvre. Cependant, les matériaux HOIPs ont plusieurs inconvénients dont leur manque de stabilité en conditions opérationnelles. Améliorer celle-ci est l'un des plus grands défis à relever avant commercialisation. La formule générale est (A1,A2,A3,A4)Pb(X1,X2)3, où les sites A occupés par une distribution de 1 à 4 cations métalliques/organiques et les sites X par celle d’anions halogénures. Les défauts lacunaires natifs sont considérés comme une cause possible de dégradation des cellules solaires HOIPs. L'objectif de ce travail est de comprendre le rôle des défauts dans la stabilité à long terme des matériaux PV HOIPs. A cette fin, des défauts primaires ont été introduits de manière contrôlée par irradiation avec des électrons de haute énergie (1MeV) dans des lots de couches et cellules solaires (SCs) à base de divers composés HOIPs. Il s'agit notamment du prototype PV HOIPs, MAPbI3 (A1PbX13), et de nouveaux composés mixtes d’halogénures à triple ou quadruple cations, (CsMAFA)Pb(I1-xBrx)3 (A3PbX23) ou (GACsMAFA)Pb(I1-yBry)3 (A4PbX23). Les couches sont fabriquées selon la même procédure que les couches actives SCs et, ensuite, traitées dans des conditions similaires. Pour A1PbX13/A3PbX23, la structure SC est de type p-i-n avec des couches organiques pour le transport des trous et des électrons (HTL/ETL). Les couches sont déposées sur le substrat verre/ITO/HTL (PEDOT:PSS) sans ou avec couche supérieure ETL (PCBM). Pour A4PbX23, la structure SC est de type n-i-p avec des couches ETL inorganiques (TiO2) et HTL organiques (Spiro-OMeTAD). Les couches sont directement déposées sur du verre.La spectroscopie d'annihilation de positons donne une évidence directe de l'existence de défauts lacunaires natifs et induits par irradiation dans chaque composé. Les spectres d’absorbance en fonction de l’énergie montrent que le vieillissement naturel et après irradiation génère différentes populations de défauts dans chaque composé. De plus, celles-ci pour A1PbX13 et A3PbX23 diffèrent selon l'absence ou la présence de la couche supérieure ETL. Les populations de défauts évoluent pendant au moins 3 mois. Le vieillissement modifie (i) la bande interdite, (ii) les queues de bande de conduction/valence et (iii) l'absorption optique via des niveaux électroniques profonds. Les effets d’illumination sous laser varient aussi en fonction du vieillissement. L’asymétrie des pics de photoluminescence (PL) dans chaque composé sous illumination laser continue reflète une superposition de raies d’émission gaussiennes à énergie, FWHM et hauteur évoluant avec le temps d'illumination. Les transitions d'émission impliquent des niveaux électroniques localisés peu profonds dans A3PbX23/A4PbX23 et résonnants dans A1PbX13. De tels effets durent au moins 3 mois dans A4PbX23. Ces niveaux électroniques sont attribués à des populations de défauts spécifiquement induits par illumination. Le vieillissement naturel et après irradiation donne des spectres PL à décroissance temporelle résolue en une ou deux exponentielles. Le nombre et la durée de vie sont fortement influencés par l’irradiation initiale et la composition. Une amélioration frappante du fonctionnement PV pour le type SC p-i-n est induite par le vieillissement dû à l'irradiation. Le rendement quantique externe et les performances PVs ont des valeurs plus élevées pour l’état irradié que de référence durant 6 à 12 mois de vieillissement. Cela prouve que l'ingénierie des défauts par irradiation d'électrons à haute énergie a le potentiel de fournir des voies de traitement innovantes pour améliorer la stabilité à long terme des performances photovoltaïques HOIPsDuring the last eleven years, Hybrid Organic Inorganic Perovskites (HOIPs) materials have emerged as an exciting topic of research for potential application in solar cell technologies due to their outstanding optoelectronic properties and processing advantages. However, HOIPs materials suffer from several drawbacks with, in peculiar, their lack of stability under operational conditions (light, bias, environment…). To improve this stability is one of the biggest challenges to be addressed before commercialization. The general formula for HOIPs is (A1,A2,A3,A4)Pb(X1,X2)3, where the A sites can be occupied by a distribution of 1 to 4 metallic/organic cations and X sites with halide anions. The role of native vacancy defects has been questioned as a possible cause for HOIPs solar cells degradation. The aim of this work is to understand the defect role in long term stability of HOIPs materials for photovoltaics. For this reason, primary defects were introduced in a controlled way via high energy electron irradiation (1MeV) in sets of layers and solar cells (SCs) fabricated using various HOIPs compounds. Those include the photovoltaic HOIPs prototype, MAPbI3 (A1PbX13), and emergent triple or quadruple cation mixed halide HOIPs, (CsMAFA)Pb(I1-xBrx)3 (A3PbX23) or (GACsMAFA)Pb(I1-yBry)3 (A4PbX23). The HOIPs layers are fabricated according to the same procedure as the HOIPs active SC layers and, subsequently, treated in similar conditions. For A1PbX13 and A3PbX23, the solar cells are of the p-i-n structure with organic hole and electron transport layer (HTL/ETL). The HOIPs layers are deposited on the glass/ITO/HTL (PEDOT:PSS) substrate without or with the top ETL layer (PCBM). For A4PbX23, the solar cells are of the n-i-p type with inorganic ETL (TiO2) and organic HTL (Spiro-OMeTAD) layers. The layers are directly deposited on glass without the ETL layer.Positron Annihilation Spectroscopy (PAS) gives direct evidence for native vacancy-type defects and irradiation induced ones in layers of each HOIP compound. The energy dependence of absorbance shows that natural and after irradiation ageing generates different defect populations in each HOIP compound. These populations strikingly also differ depending on the absence or presence of the top ETL layer for the A1PbX13 and A3PbX23 compounds. The defect populations evolve over ageing duration as long as 3 months. The prominent effects of ageing include (i) band gap modification, (ii) tailing of conduction/valence band extrema and (iii) optical absorption via deep subgap electronic levels. Illumination effects under laser also vary with ageing for each HOIP compound. Asymmetric photoluminescence (PL) peaks in each compound under continuous laser illumination reflect that radiative emission involves Gaussian emission rays with energy, FWHM and height evolving with illumination time. The emission transitions involve shallow localized electronic levels in A3PbX23 and A4PbX23 and resonant ones in A1PbX13. These electronic levels are attributed to specifically illumination-induced defect populations. Natural and after irradiation ageing result in PL decay lifetime spectra resolved into one or two exponential decay components. The decay components number and lifetime are strongly affected by the initial production of irradiation defects and HOIPs composition. Such effects last over 3 months at least in A4PbX23. The p-i-n solar cells exhibit most striking irradiation ageing induced photovoltaics performance. The External Quantum Efficiency (EQE versus photon energy) and the photovoltaic performance (I-V under illumination) of the irradiated solar cells have higher values than those in the reference SCs after 6 to 12 months of ageing. This gives evidence that defect engineering via high energy electron irradiation has a potential for providing innovative processing pathways to enhance the long-term stability of HOIPs photovoltaic performance
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Valloggia, Sylvie. "SPECTROSCOPIE DE PHOTOLUMINESCENCE LOCALE DANS LES SEMICONDUCTEURS MASSIFS (Si, InP) ET LES PUITS QUANTIQUES (GaAs/GaAlAs)". Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb37619041b.
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Ait, Saada Anissia. "Mécanismes par lesquels la recombinaison homologue prévient les défauts mitotiques induits par le stress réplicatif". Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS167/document.
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Des stress réplicatifs sont rencontrés à chaque phase S du cycle cellulaire et différents mécanismes permettent leur prise en charge. La recombinaison homologue (RH) tient un rôle important dans le maintien de la stabilité du génome au cours de la réplication. En effet, la RH escorte la progression des fourches et prévient les défauts mitotiques. Toutefois, le lien moléculaire entre le stress réplicatif et les défauts mitotiques n’est pas élucidé. De façon générale, les fourches de réplication bloquées peuvent être sauvées grâce à leur fusion avec la fourche convergente ou au redémarrage de fourche par la RH. Le laboratoire a développé un essai génétique reposant sur l’utilisation d’une barrière de réplication conditionnelle afin d’étudier le mécanisme par lequel la RH contribue au sauvetage des fourches de réplication bloquées. L’équipe a montré que le redémarrage des fourches bloquées par la RH est conditionné par l’exposition d’un ADNsb et non d’une cassure double-brin. Ainsi, les fonctions de la RH au cours de la gestion du stress réplicatif peuvent être adressées indépendamment de sa fonction de réparation des cassures (fonction relativement bien documentée). Les travaux décrits dans ce manuscrit s’inscrivent autour des mécanismes que la RH engage afin d’assurer la stabilité génétique en réponse au stress réplicatif. Plus précisément, je me suis intéressée à l’implication des facteurs de la RH dans la protection des fourches de réplication bloquées au niveau moléculaire et cellulaire. En absence de la recombinase Rad51 ou de son chargeur Rad52, le blocage d’une seule fourche de réplication est suffisant pour induire des défauts mitotiques, incluant des ponts anaphasiques (lien physique entre chromatides sœurs). Il s’avère que les fourches bloquées sont extensivement dégradées par la nucléase Exo1 en absence de Rad51/Rad52. De manière intéressante, l’accumulation excessive d’ADNsb à la fourche est à l’origine de la non-disjonction des chromatides sœurs en mitose et ce malgré l’arrivée de fourches convergente. Ainsi, les fourches de réplication non protégées sont le siège de terminaison pathologique mettant à mal la ségrégation des chromosomes. La RH étant impliquée dans la protection et le redémarrage des fourches de réplication, l’utilisation du mutant de séparation de fonction Rad51-3A a permis de montrer que ces deux fonctions sont génétiquement séparables. Les fourches de réplication protégées et incapables d’être redémarrées par la RH ne présentent pas de symptômes de terminaison pathologique. Ainsi, au-delà de sa capacité à redémarrer les fourches inactivées, les facteurs de la RH assurent la complétion de de la réplication en maintenant les fourches de réplication dans une conformation propice à une fusion avec la fourche convergente. Ces résultats contribuent à une meilleure compréhension des mécanismes moléculaires invoqués par la RH afin de maintenir la stabilité génétique au cours du stress réplicatifAt each cell cycle, cells undertaking the DNA replication process face several sources of replication stress (RS) compromising the progression of the replicating forks and threatening both chromosome duplication fidelity and their correct segregation during mitosis. Replication stresses emerged as a major source of genetic instability and cancer development. Several mechanisms, among which homologous recombination (HR), operate to buffer the deleterious effects of RS. HR acts as an escort to fork progression and prevents mitotic defects. Nonetheless, the molecular connection between replication stress and mitotic defects remains elusive. A conditional replication fork barrier (RFB) acting in a polar manner was developed in the lab to terminally-arrest fork progression. In this system, HR functions handling replication stress can be assessed independently of its well-known function in double strand break repair. The work described here aims to understanding the mechanism that HR performs to ensure genetic stability in response to replication stress. In general, blocked replication forks can be rescued either by fork convergence or by active HR-mediated fork restart. However, in absence of Rad51 recombinase or it loader Rad52, a single activated RFB is sufficient to induce mitotic abnormalities including anaphase bridges. The involvement of HR factors in fork protection was explored at the molecular and cellular levels. It turns out that terminally-arrested forks are extensively resected by the Exo1 nuclease in the absence of Rad51/Rad52. Interestingly, the excess of ssDNA accumulation at the fork triggers sister chromatid non-disjunction in mitosis despite the arrival of an uncorrupted converging fork to rescue replication. Thus, unprotected replication forks are prone to pathological termination threatening chromosome segregation. HR being involved in fork protection and restart, the use of a Rad51 mutant showed that these two functions are genetically separable. Indeed, protected forks unable to restart by HR do not show any pathological termination. Thus, beyond their ability to restart inactivated forks, HR factors ensure replication completion by maintaining the forks in a suitable conformation for a fusion with the converging fork. Overall, these results shed light on the molecular events engaged by RH to ensure genome stability in response to replication stress
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Bell, Abigail. "Photoluminescence of wurtzite GaN and its related alloys grown by MBE". Thesis, University of Nottingham, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325734.
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Andreev, Alexey. "Šumová spektroskopie detektorů záření". Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2008. http://www.nusl.cz/ntk/nusl-233425.
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Kadmium telurid je velmi důležitý materiál jak základního, tak i aplikovaného výzkumu. Je to dáno zejména jeho výhodnými elektronickými, optickými a strukturními vlastnostmi, které ho předurčují pro náročné technické aplikace. Dnes se hlavně používá pro jeho vysoké rozlišení k detekci a X-záření. Hlavní výhodou detektorů na bázi CdTe je, že nepotřebují chlazení a mohou spolehlivě fungovat i při pokojové teplotě. To způsobuje efektivnější interakce fotonů než je tomu u Si nebo jiných polovodičových materiálů. Obsahem této práce byla analýza a interpretace výsledků získaných studiem šumových a transportních charakteristik CdTe vzorků. Měření ukázaly že odpor homogenní části CdTe krystalů mírně klesá při připojení elektrického pole na vzorku. Při změně teploty navíc dochází k odlišné reakci u CdTe typu p a n. Právě těmto efektům je v práci věnována pozornost. Pomocí šumové spektroskopie bylo zjištěno, že při nízkých frekvencích je u vzorků dominantní šum typu 1/f, zatímco při vyšších frekvencích je sledován generačně-rekombinační šum a tepelný šum. Všechny měřené vzorky vykazovaly mnohem vyšší hodnotu šumu na nízkých frekvencích než udává Hoogeova rovnice. Byly nalezeny a popsány zdroje nadbytečného šumu.
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Davies, Matthew John. "Optical studies of InGaN/GaN quantum well structures". Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/optical-studies-of-ingangan-quantum-well-structures(f6c6e59b-8366-44aa-b149-9338d3f03dc0).html.
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In this thesis I present and discuss the results of optical spectroscopy performed on InGaN/GaN single and multiple quantum well (QW) structures. I report on the optical properties of InGaN/GaN single and multiple QW structures, measured at high excitation power densities. I show a correlation exists between the reduction in PL efficiency at high excitation power densities, the phenomenon so-called ``efficiency-droop'', and a broadening of the PL spectra. I also show a distinct change in recombination dynamics, measured by time-resolved photoluminescence (PL), which occurs at the excitation power densities for which efficiency droop is measured. The broadening of the PL spectra at high excitation power densities is shown to occur due to a rapidly redshifting, short-lived high energy emission band. The high energy emission band is proposed to be due to the recombination of weakly localised/delocalised carriers occurring as a consequence of the progressive saturation of the local potential fluctuations responsible for carrier localisation, at high excitation power densities. I report on the effects of varying threading dislocation (TD) density on the optical properties of InGaN/GaN multiple QW structures. No systematic relationship exists between the room temperature internal quantum efficiency (IQE) and the TD density, in a series of nominally identical InGaN/GaN multiple QWs deposited on GaN templates of varying TD density. I also show the excitation power density dependence of the PL efficiency, at room temperatures, is unaffected for variation in the TD density between 2 x107 and 5 x109 cm-2. The independence of the optical properties to TD density is proposed to be a consequence of the strong carrier localisation, and hence short carrier diffusion lengths. I report on the effects of including an InGaN underlayer on the optical and microstructural properties of InGaN/GaN multiple QW structures. I show an increase in the room temperature IQE occurs for the structure containing the InGaN underlayer, compared to the reference. I show using PL excitation spectroscopy that an additional carrier transfer and recombination process occurs on the high energy side of the PL spectrum associated with the InGaN underlayer. Using PL decay time measurements I show the additional recombination process for carriers excited in the underlayer occurs on a faster timescale than the recombination at the peak of the PL spectrum. The additional contribution to the spectrum from the faster recombination process is proposed as responsible for the increase in room temperature IQE.
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Turcu, Mircea Cassian [Verfasser]. "Defect energies, band alignments, and charge carrier recombination in polycrystalline Cu(In,Ga)(Se,S)2 alloys / von Mircea Cassian Turcu". 2004. http://d-nb.info/971826161/34.
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Hvizdoš, Dávid. "Modelování disociační rekombinace lehkých iontů". Doctoral thesis, 2021. http://www.nusl.cz/ntk/nusl-447466.
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The purpose of this work and the project under which it was created is to develop, compare and validate several theoretical approaches and computation methods used to calculate the cross sections of dissociative recombination. For the most part it is con- cerned with the indirect dissociative recombination of molecular ions of H+ 2 in the singlet ungerade channels computed with three distinct approaches. First, the fully numerically solvable two-dimensional approach developed at ÚTF MFF UK as a part of my master's thesis. Second, a vibrational frame transformation method based on the work of Chang and Fano [E. S. Chang and U. Fano, Phys. Rev. A 6, 173 (1972)] and then enhanced into a full energy-dependent form by Gao and Greene [H. Gao and C. H. Greene, J. Chem. Phys. 91, 3988 (1989)], [H. Gao and C. H. Greene, Phys. Rev. A 42, 6946 (1990)], fur- ther improved by our own revisions. Third, a two-dimensional R-matrix method based on matching exact 2D solutions from a small interaction region to asymptotic solutions in the non-interacting region. We thoroughly discuss the various advantages and caveats of these methods and, in the later chapters, present our work on employing them for the realistic recombination of HeH+ + e− . Furthermore, we attempt to extend the presented models to the description of the...
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Lin, Yang-You y 林沇佑. "The Impact on Photovoltaic Efficiency with Regards to Defect Densities of Amorphous Silicon Layers and Carrier Recombination Velocity at Interfaces in a Heterojunction Solar Cell Using Silvaco ATLAS". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/15593378593498140236.
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碩士大葉大學
電機工程學系
98
This study involves the novel heterojunction with intrinsic thin layer (HIT) solar cell structure. Combining the advantages of both crystalline silicon and amorphous silicon, a new structure of silicon-based solar cell was proposed - the heterojunction with an intrinsic thin layer (HIT) solar cell. It has high stability and large light absorption coefficient. It is manufactured under low temperature deposit process, which results in a low cost thin film HIT solar cell with high conversion efficiency. The influence of various layer materials and interfaces on the performance of n-type c-Si based bifacial HIT solar cell has been investigated by using the Silvaco TCAD simulation software. Accordingly, the design optimization of HIT solar cell was proven.
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Sun, Chang. "Recombination Activity of Metal-related and Boron-oxygen Defects in Crystalline Silicon". Phd thesis, 2017. http://hdl.handle.net/1885/122920.
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This thesis aims to improve the understanding of the
recombination activity of some metal-related defects and the
boron-oxygen (BO) defect in crystalline silicon.
First, the recombination parameters of the aluminium-oxygen
(Al-O) complex are reassessed by applying lifetime spectroscopy
on several n- and p-type Al-contaminated samples. The uncertainty
ranges of the recombination parameters have been tightened
significantly by simultaneously fitting the lifetimes measured on
several differently doped samples. The same method is also
applied on several n- and p-type Cr-contaminated samples, to
determine the defect parameters of interstitial Cr and CrB pairs.
Direct experimental comparisons have shown that both the Al-O
defect and Cr have greater negative impacts on carrier lifetimes
in p-type silicon than in n-type silicon at low to intermediate
injection levels.
One approach to reduce the recombination activity of the defects
is via hydrogen passivation. The charge state of monatomic
hydrogen plays a key role in the passivation process. In this
thesis, we describe and apply a rigorous approach to calculating
the charge states of monatomic hydrogen, as well as Fe, Cr and
the BO defect, as a function of both temperature and injection
level. Based on these results, the impact of temperature and
injection on the hydrogenation of the key defects, and other
pairing reactions, are discussed. In the experimental
investigation of the potential hydrogenation of Fe, significant
reductions of interstitial Fe concentration are observed in
samples passivated with hydrogen-rich silicon nitride films, but
not in samples with hydrogen-lean silicon oxide films. We have
measured and modelled the Fe reduction kinetics over a wide
temperature range, assuming that the reduction is caused by
hydrogenation, based on the charge state model. However, a
subsequent study has shown conclusively that Fe is gettered by
the nitride films. Based on this new finding, the kinetics data
are re-analysed in this thesis.
For Cu and Ni precipitates, both photoluminescence (PL) images
and micro-PL maps are taken on several n-type and p-type wafers
in which Cu or Ni has precipitated during the ingot cooling. The
high-injection micro-PL measurements significantly reduce the
carrier diffusion, allowing more highly resolved inspection of
the particles. Markedly different precipitation patterns were
observed in n- and p-type samples. The effects of the intrinsic
point defect on the precipitation behaviour of the metals, and
the dopant effects on the intrinsic point defect concentrations,
are discussed based on the results.
High-injection micro-PL measurements are also valuable to study
the activation kinetics of the BO defect because (a) the
activation is significantly accelerated, allowing it to be
studied in shorter timeframes, and (b) the injection level can be
kept constant over time and in differently doped samples, as the
high-injection lifetime is dominated by Auger recombination. This
allows the activation time constant and defect concentration in
differently doped samples to be compared more directly. Therefore
the micro-PL system is used to measure the activation kinetics of
the BO defect in compensated n- and p-type silicon. The results
obtained under high-injection conditions help to clarify some
unresolved issues related to the defect.
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Sio, Hang Cheong. "Carrier Recombination in Multicrystalline Silicon: A Study using Photoluminescence Imaging". Phd thesis, 2015. http://hdl.handle.net/1885/101930.
Texto completoResumen
This thesis applies photoluminescence imaging technique
to study various carrier recombination mechanisms in
multicrystalline silicon materials. One emphasis of the work has
been recombination at grain boundaries, which is one of the
limiting factors for the performance of multicrystalline silicon
solar cells. An approach for quantifying the recombination
activities of a grain boundary in terms of its effective surface
recombination velocity, based on the photoluminescence intensity
profile across the grain boundary, is developed. The approach is
applied to compare the recombination properties of a large number
of grain boundaries in wafers from different parts of a p-type
boron doped directionally solidified multicrystalline silicon
ingot. The results show that varying impurity levels along the
ingot significantly impact the electrical properties of as-grown
grain boundaries, and also their response to phosphorus gettering
and hydrogenation. The work is then extended to various types of
multicrystalline silicon materials. The electrical properties of
conventionally solidified p-type, n-type and also recently
developed high performance p-type multicrystalline silicon wafers
were directly compared in terms of their electronic behaviours in
the intra-grain regions, the grain boundaries and the dislocation
networks. All studied samples reveal reasonably high diffusion
lengths among the intra-grain regions after gettering and
hydrogenation, suggesting that the main performance limiting
factors are likely to be recombination at crystal defects.
Overall, grain boundaries in the conventional p-type samples are
found to be more recombination active than those in the high
performance p-type and conventional n-type samples. As-grown
grain boundaries and dislocations in the high performance p-type
samples are not recombination active and only become active after
thermal processes. In contrast, grain boundaries in the n-type
samples are already recombination active in the as-grown state,
but show a dramatic reduction in their recombination strength
after gettering and hydrogenation. Apart from recombination
through crystal defects within the bulk, recombination at
surfaces acts as another significant loss mechanism in solar
cells. This thesis also demonstrates the use of the
photoluminescence imaging technique to study surface
recombination in silicon wafers, and provides some examples of
such applications.
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Ghosh, Michael. "Defekte im Bodenbereich blockerstarrten Solar-Siliziums: Identifikation, Verteilung und elektrischer Einfluss". Doctoral thesis, 2008. https://tubaf.qucosa.de/id/qucosa%3A22729.
Texto completoResumen
Etwa die Hälfte aller Solarzellen weltweit wird aus blockerstarrtem Silizium hergestellt. Derartige Blöcke weisen in ihren Außenbereichen eine verringerte Diffusionslänge der Minoritätsladungsträger auf. Um die Ursache dafür im Fall des bodennahen Bereichs zu bestimmen wurden zwei Spezialblöcke (ein Block mit reduzierter Bor-Dotierung und ein Block mit Phosphor-Dotierung) - u. a. mittels DLTS und FTIR - auf Kristalldefekte untersucht. Zusätzlich zu Dotierelementen (B, P, Al, As) wurden im Bodenbereich folgende Defekte nachgewiesen:
Metalle: Fe, Cr
Sauerstoffhaltige Defekte: Interstitieller Sauerstoff, Thermische Donatoren (TD), O1, O2
Stickstoffhaltige Defekte: NN-Paar, NNO-Komplex, Shallow Thermal Donors (STD)
Ausgedehnte Defekte: Versetzungen, Ausscheidungen, Korngrenzen.
Die Verteilung der flachen Donatoren (P, TD, STD, As) und Akzeptoren (B, Al) bestimmt den Widerstandsverlauf im bodennahen Bereich des Phosphor dotierten Spezialblocks. Das dortige Diffusionslängenprofil kann im Rahmen der Shockley-Read-Hall-Statistik erst durch eine Erhöhung des Minoritätseinfangquerschnitts für das Cr-Niveau (Faktor 5) bzw. für das STD-Niveau (Faktor 10) nachgezeichnet werden. Eisen, Versetzungen und Korngrenzen haben hier keinen wesentlichen Einfluss. In den untersten Millimetern des Spezialblocks müssen weitere Defekte hinzukommen, die die Diffusionslänge zusätzlich reduzieren; Thermische Donatoren und O1 und eventuell Ausscheidungen kommen dazu in Frage.
Die sinngemäße Übertragung der Konzentrationsverläufe aus den beiden Spezialblöcken auf einen Block mit einer produktionsüblichen Dotierung ([B]≈1016/cm3) ergibt, dass in diesem Fall verschiedene Defekte (TD, STD, CrB und FeB) einen Beitrag zur Diffusionslängenreduktion im bodennahen Blockbereich liefern.
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"Efficiency-Limiting Recombination Mechanisms in High-Quality Crystalline Silicon for Solar Cells". Doctoral diss., 2018. http://hdl.handle.net/2286/R.I.51599.
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abstract: Recent technology advancements in photovoltaics have enabled crystalline silicon (c-Si) solar cells to establish outstanding photoconversion efficiency records. Remarkable progresses in research and development have been made both on the silicon feedstock quality as well as the technology required for surface passivation, the two dominant sources of performance loss via recombination of photo-generated charge carriers within advanced solar cell architectures.
As these two aspects of the solar cell framework improve, the need for a thorough analysis of their respective contribution under varying operation conditions has emerged along with challenges related to the lack of sensitivity of available characterization techniques. The main objective of my thesis work has been to establish a deep understanding of both “intrinsic” and “extrinsic” recombination processes that govern performance in high-quality silicon absorbers. By studying each recombination mechanism as a function of illumination and temperature, I strive to identify the lifetime limiting defects and propose a path to engineer the ultimate silicon solar cell.
This dissertation presents a detailed description of the experimental procedure required to deconvolute surface recombination contributions from bulk recombination contributions when performing lifetime spectroscopy analysis. This work proves that temperature- and injection-dependent lifetime spectroscopy (TIDLS) sensitivity can be extended to impurities concentrations down to 109 cm-3, orders of magnitude below any other characterization technique available today. A new method for the analysis of TIDLS data denominated Defect Parameters Contour Mapping (DPCM) is presented with the aim of providing a visual and intuitive tool to identify the lifetime limiting impurities in silicon material. Surface recombination velocity results are modelled by applying appropriate approaches from literature to our experimentally evaluated data, demonstrating for the first time their capability to interpret temperature-dependent data. In this way, several new results are obtained which solve long disputed aspects of surface passivation mechanisms. Finally, we experimentally evaluate the temperature-dependence of Auger lifetime and its impact on a theoretical intrinsically limited solar cell. These results decisively point to the need for a new Auger lifetime parameterization accounting for its temperature-dependence, which would in turn help understand the ultimate theoretical efficiency limit for a solar cell under real operation conditions.Dissertation/Thesis
Doctoral Dissertation Materials Science and Engineering 2018
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Koppe, Tristan. "Untersuchungen zum Lumineszenzverhalten des Aluminiumnitrids und der Aufbau einer Kurzzeit-Lumineszenz-Spektroskopie-Apparatur". Doctoral thesis, 2017. http://hdl.handle.net/11858/00-1735-0000-0023-3E9D-F.
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Cutler, Geoffrey Lloyd. "CHARACTERIZING VALPROIC ACID-INDUCED DNA DOUBLE STRAND BREAK REPAIR". Thesis, 2012. http://hdl.handle.net/1974/7597.
Texto completoResumen
The teratogenic effects of valproic acid (VPA) are well known, though its teratogenic mechanism remains unknown. VPA induces oxidative stress, which may lead to double strand breaks (DSBs) in DNA. Though the cell may repair this damage via homologous recombination (HR) and non-homologous end joining (NHEJ), repair is not always error-free; genomic instability may arise from gene deletions, amplifications, rearrangements, and loss of heterozygosity. Such alterations may underpin VPAʼs teratogenicity. The present study evaluated VPAʼs ability to induce NHEJ and HR and characterized the changes in expression of two proteins key to HR (RAD51) and NHEJ (XRCC4).
Using pKZ1 transgenic mice (C57BL/6 genetic background), we sought to measure NHEJ events via X-gal staining. Although consistent staining was observed in adult male brain (positive control), no staining was observed in embryos 12 or 24 hours after in utero exposure to a teratogenic dose of VPA (500 mg/kg, maternal subcutaneous dose) on gestational day 9 (GD9).
To determine whether the lack of staining observed in embryos was due to low/absent expression of key DSB-repair proteins, we measured mRNA/protein expression of RAD51 and XRCC4 in C57BL/6, GD9-exposed embryos and maternal brain. One hour after treatment, XRCC4 was increased at the protein level in brain and embryo. RAD51 was not increased in embryos and not detected in adult brain. These data suggest that embryos do possess the protein mediators of NHEJ and HR and that VPA-induced changes in expression of XRCC4 may influence the type of repair pursued, potentially affecting DSB repair fidelity (accuracy).
Determination of fidelity of VPA-induced HR was attempted with the Chinese hamster ovary cell line (CHO33) using DNA sequencing; low template concentration and purity precluded successful sequencing of DNA from recombinant colonies and the assessment of fidelity.
Overall, these data demonstrate that the lack of X-gal staining observed in pKZ1 embryos is not due to an underexpression of at least one key protein in the NHEJ pathway. Furthermore, a VPA-induced change in the the type of repair pathway pursued by the embryo may have teratological implications.Thesis (Master, Pharmacology & Toxicology) -- Queen's University, 2012-10-15 11:06:30.613
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Kreßner-Kiel, Denise. "Wechselwirkung von Kupfer mit ausgedehnten Defekten in multikristallinem Silicium und Einfluss auf die Rekombinationseigenschaften". Doctoral thesis, 2015. https://tubaf.qucosa.de/id/qucosa%3A23162.
Texto completoResumen
Die Rekombinationsaktivität von Versetzungen und Korngrenzen in multikristallinem Silicium wird von Kupfer und anderen metallischen Verunreinigungen wie Eisen mitbestimmt. Das Hauptziel der Arbeit war es, die Verteilung von Kupfer und dessen Wirkung auf die Rekombinationsaktivität von Versetzungen und Korngrenzen genauer zu untersuchen. Dazu wurden optische und elektrische Untersuchungen an gezielt mit Metallen verunreinigten Modellmaterialien durchgeführt. Nicht alle Versetzungen sind rekombinationsaktiv. Es konnte gezeigt werden, dass der Anteil rekombinationsaktiver Versetzungen am Gesamtinventar und die Hintergrunddiffusionslänge von der Verunreinigung mit Metallen abhängig sind. Ergebnisse von Untersuchungen an Proben, die Diffusionsexperimenten unterzogen wurden, deuten auf unterschiedliches Ausscheidungsverhalten von Kupfer und Eisen hin sowie auf Wechselwirkungen mit Versetzungen und Korngrenzen, die mit der Diffusionstemperatur und den Abkühlbedingungen in Zusammenhang stehen.