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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Plasma immersion ion implantation of silicon

Chen, Shou-Mian January 1997 (has links)
Plasma Immersion Ion Implantation has several unique advantages over conventional implantation, such as low cost, large area capability, non-line-of-sight features and high dose rate implantation. However, it is still far from use in routine production because of problems such as the ability to control the ion depth profile in targets, the ion dose and contamination. In this thesis, a PIII system has been systematically calibrated, and a computer simulation code for PIII has been developed in order to understand more clearly the physics of the PIII process and to optimise the experimental conditions. In the second part of this thesis, a new application of PIII has been explored, where the PIII technique has been used as a high dose-rate implant treatment to form amorphous silicon nitride/oxide films on both crystalline and amorphous silicon substrates. The electrical properties of these films have been characterized. It shows that low dose nitrogen/oxygen implantation leads to the modification of Schottky barrier heights or the introduction of charged defects in the materials. As the ion dose is increased, alloying effects take over, forming silicon nitride/oxide alloys. The a-SiNx:H films synthesized via PIII have electrical characteristics similar to those grown by PECVD, but a-SiOx:H has different electrical properties from a-SiNx:H.
2

Metal plasma immersion ion implantation and deposition using polymer substrates

Oates, T. W. H January 2003 (has links)
This thesis investigates the application of plasma immersion ion implantation (PIII) to polymers. PIII requires that a high negative potential be applied to the surface of the material while it is immersed in a plasma. This presents a problem for insulating materials such as polymers, since the implanting ions carry charge to the surface, resulting in a charge accumulation that effectively neutralises the applied potential. This causes the plasma sheath at the surface to collapse a short time after the potential is applied. Measurements of the sheath dynamics, including the collapsing sheath, are performed using an electric probe. The results are compared to theoretical models of the plasma sheath based on the Child-Langmuir law for high voltage sheaths. The theoretical model predicts well the sheath dynamics for conductive substrates. For insulating substrates the model can account for the experimental observations if the secondary electron coefficient is modified, justified on the basis of the poly-energetic nature of the implanting ions. If a conductive film is applied to the insulator surface the problem of charge accumulation can be avoided without compromising the effectiveness of PIII. The requirement for the film is that it be conductive, yet transparent to the incident ions. Experimental results are presented which confirm the effectiveness of the method. Theoretical estimates of the surface potential show that a film of the order of 5nm thickness can effectively circumvent the charge accumulation problem. Efforts to produce and characterise such a film form the final two chapters of this thesis. The optimal thickness is determined to be near the percolation threshold, where a marked increase in conductivity occurs. Spectroscopic ellipsometry is shown to be an excellent method to determine the film thickness and percolation threshold non-invasively. Throughout this work cathodic vacuum arcs are used to deposit thin films and as a source of metal plasmas. The design and construction of a pulsed cathodic vacuum arc forms a significant part of this thesis. Investigations of the cathode spots and power supply requirements are presented.
3

The Influence of Plasma Treatment on Microstructure and Surface Properties of CrxNy, DLC and TiO2 Thin Films

Chiu, Sung-mao 20 June 2006 (has links)
This thesis is to study the microstructure and its related surface properties of CrxNy¡BDLC and TiO2 films prepared by different plasma energy processes such as physical vapor deposition (PVD) and plasma immersion ion implantation (PIII) processes. In the first chapter of this thesis, the different Cr-based coatings (Cr, Cr2N and CrN) were prepared by PVD process with lower plasma energy condition (less than 100 eV). The surface energy properties of these Cr-based coating were studied and the relationship between the surface properties and adhesion forces with respect to epoxy molding compound (EMC) were also investigated. It is found that the PVD-Cr2N coating has the largest contact angle of water and the lowest polar components and surface energy. The low surface energy is attributed to the high density of surface reactive sites and the formation of N-H bonds and O-H bonds on the film surface that act as the effective adsorption sites for carbon. The second chapter focuses on the modification of the electrical and mechanical properties of DLC films with high plasma energy (5¡ã45 keV) , PIII post-treatment. It is found that using high ion energy and a short treating time can modify the sp3 content, the nano-hardness and the Young¡¦s modulus of the DLC films. The formation mechanisms of sp3 C-C bonds in the implanted DLC film involve the reaction among compressive stress field, bonds breakage and recombination process induced by hydrogen and carbon ion. The third chapter deals with the structure and photocatalytic properties of nitrogen-doped TiO2 film prepared by PVD process with lower plasma energy condition (less than 100 eV). The TiO2-xNx films are indirect transition type and optical band gap energy is various with increasing nitrogen flow rate. The TiO2-xNx film with high crystallinity and porous surface morphology shows the best degradation rate of methylene blue solution.
4

Fabrication and characterization of nanocrystalline silicon LEDs : a study of the influence of annealing

2014 July 1900 (has links)
This thesis describes the fabrication of a set of bright, visible light-emitting silicon LEDs. These devices were fabricated in-house at the University of Saskatchewan using a custom plasma ion implantation tool, an annealing furnace, and a physical vapour deposition system. A high-fluence (F = 4 × 1015 cm^−2) implantation of molecular hydrogen ions extracted from an RF inductively coupled plasma at an energy of 5 keV was used to create a heavily damaged region in the silicon centered approximately 40 nm below the silicon surface with a width of approximately 56 nm. A matrix of annealing (e.g. thermal processing) processes at 400 ºC and 700 ºC and different durations (30 minutes and 2 hours) as well as an aluminum gettering procedure were tested with the goal of increasing the output electroluminescence intensity. Current-voltage characterization was used to extract information about the defect-rich nanocrystalline, light-emitting layer as well as the Schottky barrier height. This enabled comparison of these new devices with previous silicon LEDs based on porous silicon and other approaches. The processes which were used to fabricate these devices are compatible with standard CMOS processing techniques and could provide one solution to the problem of optical interconnect on multi-core chips. The scientific significance of this work is the demonstration of bright, visible light emission at mean photon energies ∼1.84 eV corresponding to a photon wavelength of λ ≈ 675 nm. This is remarkable given that ordinary crystalline silicon is an indirect bandgap material with a bandgap energy of 1.1 eV, in which band-to-band radiative recombination is forbidden by momentum conservation. The devices fabricated in this thesis have light emission properties similar to previous silicon LEDs based on nanocrystalline or nanoporous silicon. They have the advantage of being easily electrically driven. The nanocrystalline region which is the source of the light emission was nucleated from the ion-implanted layer below the surface of the silicon. This makes these devices mechanically robust and insensitive to environmental conditions. The engineering significance of this work is the production of CMOS compatible light emitters. This study demonstrated increased light emission efficiency at higher annealing temperatures which is likely due to enhanced diffusion and nucleation of silicon nanocrystals in the ion-implant damaged layer.
5

Metal plasma immersion ion implantation and deposition using polymer substrates

Oates, T. W. H January 2003 (has links)
This thesis investigates the application of plasma immersion ion implantation (PIII) to polymers. PIII requires that a high negative potential be applied to the surface of the material while it is immersed in a plasma. This presents a problem for insulating materials such as polymers, since the implanting ions carry charge to the surface, resulting in a charge accumulation that effectively neutralises the applied potential. This causes the plasma sheath at the surface to collapse a short time after the potential is applied. Measurements of the sheath dynamics, including the collapsing sheath, are performed using an electric probe. The results are compared to theoretical models of the plasma sheath based on the Child-Langmuir law for high voltage sheaths. The theoretical model predicts well the sheath dynamics for conductive substrates. For insulating substrates the model can account for the experimental observations if the secondary electron coefficient is modified, justified on the basis of the poly-energetic nature of the implanting ions. If a conductive film is applied to the insulator surface the problem of charge accumulation can be avoided without compromising the effectiveness of PIII. The requirement for the film is that it be conductive, yet transparent to the incident ions. Experimental results are presented which confirm the effectiveness of the method. Theoretical estimates of the surface potential show that a film of the order of 5nm thickness can effectively circumvent the charge accumulation problem. Efforts to produce and characterise such a film form the final two chapters of this thesis. The optimal thickness is determined to be near the percolation threshold, where a marked increase in conductivity occurs. Spectroscopic ellipsometry is shown to be an excellent method to determine the film thickness and percolation threshold non-invasively. Throughout this work cathodic vacuum arcs are used to deposit thin films and as a source of metal plasmas. The design and construction of a pulsed cathodic vacuum arc forms a significant part of this thesis. Investigations of the cathode spots and power supply requirements are presented.
6

Cationic 5-phosphonio-substituted N-heterocyclic carbenes

Schwedtmann, Kai, Schoemaker, Robin, Hennersdorf, Felix, Bauzá, Antonio, Frontera, Antonio, Weiss, Robert, Weigand, Jan J. 05 April 2017 (has links) (PDF)
2-Phosphanyl-substituted imidazolium salts 2-PR2(4,5-Cl-Im)[OTf] (9a,b[OTf]) (4,5-Cl-Im = 4,5-dichloro-1,3-bis(2,6-di-isopropylphenyl)-imidazolium) (a: R = Cy, b: R = Ph) are prepared from the reaction of R2PCl (R = Cy, Ph) with NHC 8 (4,5-dichloro-1,3-bis(2,6-di-isopropylphenyl)-imidazolin-2-ylidene) in the presence of Me3SiOTf. 5-Phospanyl-substituted imidazolium salts 5-PR2(2,4-Cl-Im)[OTf] (10a,b[OTf]) are obtained in quantitative yield when a slight excess of the NHC 8 is used. 5-Phosphonio-substituted imidazolium salts 5-PR2Me(2,4-Cl-Im)[OTf]2 (14a,b[OTf]2) and 5-PR2F(2,4-Cl-Im)[OTf]2 (16a,b[OTf]2) result from methylation reaction or oxidation of 10a,b[OTf] with XeF2 and subsequent fluoride abstraction. According to our quantum chemical studies the Cl1 atom at the 2-position at the imidazolium ring of dication 14b2+ carries a slightly positive charge and is therefore accessible for nucleophilic attack. Accordingly, the reaction of 14a,b[OTf]2 and 16a,b[OTf]2 with R3P (R = Cy, Ph) affords cationic 5-phosphonio-substituted NHCs 5-PR2Me(4-Cl-NHC)[OTf] (17a,b[OTf]) and 5-PR2F(4-Cl-NHC)[OTf] (18a,b[OTf]) via a SN2(Cl)-type reaction. A series of transition metal complexes such as [AuCl(5-PPh2Me(4-Cl-NHC))][OTf] (19[OTf]), [CuBr(5-PPh2Me(4-Cl-NHC))][OTf] (20[OTf]), [AuCl(5-PPh2F(4-Cl-NHC))[OTf] (21[OTf]) and [RhCl(cod)(5-PPh2Me(4-Cl-NHC))][OTf] (23[OTf]) are prepared to prove the coordination abilities of carbenes 17b[OTf] and 18b[OTf]. The isolation of a rare example of a tricationic bis-carbene silver complex [Ag(5-PPh2Me(4-Cl-NHC))2][OTf]3 (22[OTf]3) is achieved by reacting 14b[OTf] with Cy3P in the presence of AgOTf. NHC 17b[OTf] represents a very effective dehydrocoupling reagent for secondary (R2PH, R = Ph, Cy, iBu) and primary (RPH2, R = Ph, Cy) phosphanes to give diphosphanes of type R4P2 (R = Ph, Cy, iBu) and oligophosphanes R4P4, R5P5 (R = Ph, Cy), respectively. Methylation of 17b+ and subsequent deprotonation reaction with LDA affords the cationic NHO (N-heterocyclic olefin) 35+ of which the gold complex 36+ is readily accessible via the reaction with AuCl(tht).
7

Cationic 5-phosphonio-substituted N-heterocyclic carbenes

Schwedtmann, Kai, Schoemaker, Robin, Hennersdorf, Felix, Bauzá, Antonio, Frontera, Antonio, Weiss, Robert, Weigand, Jan J. 05 April 2017 (has links)
2-Phosphanyl-substituted imidazolium salts 2-PR2(4,5-Cl-Im)[OTf] (9a,b[OTf]) (4,5-Cl-Im = 4,5-dichloro-1,3-bis(2,6-di-isopropylphenyl)-imidazolium) (a: R = Cy, b: R = Ph) are prepared from the reaction of R2PCl (R = Cy, Ph) with NHC 8 (4,5-dichloro-1,3-bis(2,6-di-isopropylphenyl)-imidazolin-2-ylidene) in the presence of Me3SiOTf. 5-Phospanyl-substituted imidazolium salts 5-PR2(2,4-Cl-Im)[OTf] (10a,b[OTf]) are obtained in quantitative yield when a slight excess of the NHC 8 is used. 5-Phosphonio-substituted imidazolium salts 5-PR2Me(2,4-Cl-Im)[OTf]2 (14a,b[OTf]2) and 5-PR2F(2,4-Cl-Im)[OTf]2 (16a,b[OTf]2) result from methylation reaction or oxidation of 10a,b[OTf] with XeF2 and subsequent fluoride abstraction. According to our quantum chemical studies the Cl1 atom at the 2-position at the imidazolium ring of dication 14b2+ carries a slightly positive charge and is therefore accessible for nucleophilic attack. Accordingly, the reaction of 14a,b[OTf]2 and 16a,b[OTf]2 with R3P (R = Cy, Ph) affords cationic 5-phosphonio-substituted NHCs 5-PR2Me(4-Cl-NHC)[OTf] (17a,b[OTf]) and 5-PR2F(4-Cl-NHC)[OTf] (18a,b[OTf]) via a SN2(Cl)-type reaction. A series of transition metal complexes such as [AuCl(5-PPh2Me(4-Cl-NHC))][OTf] (19[OTf]), [CuBr(5-PPh2Me(4-Cl-NHC))][OTf] (20[OTf]), [AuCl(5-PPh2F(4-Cl-NHC))[OTf] (21[OTf]) and [RhCl(cod)(5-PPh2Me(4-Cl-NHC))][OTf] (23[OTf]) are prepared to prove the coordination abilities of carbenes 17b[OTf] and 18b[OTf]. The isolation of a rare example of a tricationic bis-carbene silver complex [Ag(5-PPh2Me(4-Cl-NHC))2][OTf]3 (22[OTf]3) is achieved by reacting 14b[OTf] with Cy3P in the presence of AgOTf. NHC 17b[OTf] represents a very effective dehydrocoupling reagent for secondary (R2PH, R = Ph, Cy, iBu) and primary (RPH2, R = Ph, Cy) phosphanes to give diphosphanes of type R4P2 (R = Ph, Cy, iBu) and oligophosphanes R4P4, R5P5 (R = Ph, Cy), respectively. Methylation of 17b+ and subsequent deprotonation reaction with LDA affords the cationic NHO (N-heterocyclic olefin) 35+ of which the gold complex 36+ is readily accessible via the reaction with AuCl(tht).
8

Estudo das propriedades do elastômero termoplástico de copoliéster tratado a plasma / Study of the properties of polyester thermoplastic elastomer treated by plasma

Resende, Renato Carvalho [UNESP] 06 March 2017 (has links)
Submitted by RENATO CARVALHO RESENDE (htc.renato@gmail.com) on 2017-03-30T23:23:31Z No. of bitstreams: 1 Dissertação Mestrado Renato Carvalho Resende.pdf: 9175175 bytes, checksum: 3d504c6ae855f8c5ee734700afd5a7cc (MD5) / Approved for entry into archive by Juliano Benedito Ferreira (julianoferreira@reitoria.unesp.br) on 2017-04-06T14:17:14Z (GMT) No. of bitstreams: 1 resende_rc_me_bauru.pdf: 9175175 bytes, checksum: 3d504c6ae855f8c5ee734700afd5a7cc (MD5) / Made available in DSpace on 2017-04-06T14:17:14Z (GMT). No. of bitstreams: 1 resende_rc_me_bauru.pdf: 9175175 bytes, checksum: 3d504c6ae855f8c5ee734700afd5a7cc (MD5) Previous issue date: 2017-03-06 / Os elastômeros termoplásticos (TPE) têm sido bastante empregados em substituição às borrachas tradicionais, por terem custo reduzido de matéria prima, facilidade no processamento e serem recicláveis. Apresentam propriedades mecânicas semelhantes, porém quando utilizados em componentes de vedação apresentam limitada resistência à corrosão em água clorada. Assim, o desenvolvimento de tratamento superficial que não modifique as características originais, mas tornem o material mais resistente são desejáveis. Para tanto, este trabalho pretende desenvolver uma metodologia a plasma para melhorar esse quesito. O elastômero termoplástico de copoliéster (COPE) foi escolhido por ser o mais empregado em componentes de vedação. O tratamento a plasma de baixa pressão com hexafluoreto de enxofre (SF6) foi empregado visando tornar a superfície do COPE hidrofóbica através da incorporação de grupos fluorados. A implantação iônica por imersão em plasmas (IIIP) de argônio foi utilizada para criar uma camada superficial mais coesa e entrelaçada, além da possibilidade de torná-la hidrofóbica após envelhecimento. Para o tratamento com SF6, os parâmetros de excitação do plasma (12 Pa e 80 W) foram mantidos, variando-se o tempo do tratamento entre 2 e 180 minutos de modo a encontrar uma condição ótima para esse processo. Para a IIIP de Ar os parâmetros de excitação do plasma (5 Pa e 60 min) foram mantidos e a potência da radiofrequência foi variada entre 10 e 150 W. A energia de superfície e ângulo de contato foram obtidos pelo método da gota séssil em um goniômetro automatizado. A morfologia da superfície foi avaliada por microscopia eletrônica de varredura (MEV) e microscopia de força atômica (AFM). Espectroscopia de energia dispersiva (EDS) e espectroscopia de fotoelétrons de raios X (XPS) foram utilizadas para análises da composição química e estrutura molecular. Corrosão por plasma de O2 e imersão em água clorada foram utilizados para avaliar a resistência antes e após os tratamentos a plasma. Os resultados mostram que as amostras tratadas por 90, 120 e 180 minutos em plasmas de SF6 tornam-se hidrofóbica, mesmo após o envelhecimento, apresentando incorporação de flúor, alterando assim a composição química e morfológica da superfície do COPE. Melhorias substanciais foram observadas nessas amostras após os ensaios de corrosão, indicando que um aumento na vida útil do material em situações reais de uso possam ter sido alcançadas. A IIIP de Ar tornou as amostras inicialmente mais hidrofílicas do que a amostra como-recebida, porém após a ação do tempo, algumas amostras permaneceram hidrofóbicas enquanto outras amostras retornaram à condição inicial. Apesar da hidrofobicidade não ter sido alcançada em todas as amostras, alterações na rugosidade e na morfologia foram verificadas, principalmente nas amostras tratada com 100 W de potência do plasma, ocasionando em melhora na resistência do COPE à água clorada. Essa melhora na resistência é atribuída ao aumento da conectividade da estrutura pelo estabelecimento de reticulações geradas pelo processo de IIIP, densificando o material tornando a permeação de íons da solução mais difícil. / Thermoplastic elastomers have been widely used in substitution for conventional rubber, given that the feedstock is cheaper, easier to process and recyclable. Its mechanical properties are similar, but when applied to sealing components its resistance is limited due to the chlorine present in water, therefore, it is interesting to develop a surface treatment that do not alter the original characteristics, but make the material more robust. To achieve such result, we chose to submit the copolyester thermoplastic elastomer (COPE) to plasma. This material was naturally chosen, once it is widely used for sealing purposes in this specific industry. By using low pressure plasma with sulfur hexafluoride, we expect to alter COPEs surface by incorporating fluorine groups, thus making it hydrophobic. We also submitted the sample to a second treatment, by submersion to argon plasma, making the outer layer less defective and more entangled with aging, as observed in previous experiments. For SF6 treatment, the exiting plasma parameters (12Pa and 80W) were kept and the treatment time was varied between 2 to 180 minutes in order to find the optimal treatment time. For Argon IIIP, the plasma exciting parameters (5Pa and 60 min) were maintained, while the radio frequency variation was between 10 to 150W. Surface energy and contact angle were obtained by and automatic goniometer, through the sessile drop method. The surface's morphology was analyzed by electronic scanning microscope and atomic force microscopy. Dispersive energy spectroscopy and X-ray photoelectric spectroscopy were responsible for the chemical composition and molecular structure analyses the new surface's resistance was tested by O2 plasma corrosion and immersed in chlorinated water. Results show the samples treated for 90,120 and 180 minutes in SF6 plasma became hydrophobic, even after aging. The samples were substantially improved and its resistance prolonged its lifespan in conventional usage. Argon IIIP made the surface more hydrophilic. However, after time part of the material restored its original characteristics. Although hydrophobic it was not achieved, the roughness and morphology alteration (especially when treated with 100W of plasma) improved COPE'S resistance. The results are explained by the increase in the structure's ability to connect by the establishment of reticulate one generated by the IIP process, making the component denser and the ionic solution less permeable.
9

Avaliação da resposta imune in vitro induzida por antígeno de Schistosoma mansoni em indivíduos asmáticos.

Cardoso, Luciana Santos 06 December 2005 (has links)
Submitted by Hiolanda Rêgo (hiolandarego@gmail.com) on 2017-05-05T15:28:25Z No. of bitstreams: 1 Dissertação_ISC_Luciana Santos Cardoso.pdf: 4791824 bytes, checksum: adeea3b3d364d4f4df9afdcb3f7f0a53 (MD5) / Approved for entry into archive by Delba Rosa (delba@ufba.br) on 2017-05-23T13:28:10Z (GMT) No. of bitstreams: 1 Dissertação_ISC_Luciana Santos Cardoso.pdf: 4791824 bytes, checksum: adeea3b3d364d4f4df9afdcb3f7f0a53 (MD5) / Made available in DSpace on 2017-05-23T13:28:10Z (GMT). No. of bitstreams: 1 Dissertação_ISC_Luciana Santos Cardoso.pdf: 4791824 bytes, checksum: adeea3b3d364d4f4df9afdcb3f7f0a53 (MD5) / Estudos vêm demonstrando diminuição da reatividade aos testes cutâneos para alérgenos e menor gravidade da asma em indivíduos infectados por helmintos, principalmente Schistosoma mansoni. A inibição da resposta inflamatória na asma em indivíduos infectados pelo S. mansoni parece ser mediada pela IL-10, desde que tem sido observada maior produção desta citocina por células de asmáticos infectados pelo S. mansoni estimuladas com o antígeno 1 do Dermatophagoides pteronyssinus (Der p1) quando comparado a asmáticos não infectados. A IL-10 é capaz de inibir a produção de citocinas do tipo Th2 e a degranulação de mastócitos e liberação de mediadores inflamatórios, fatores envolvidos na patogênese das doenças alérgicas. O principal objetivo deste estudo foi avaliar a capacidade dos antígenos de S. mansoni Sm22.6, Sm14, PIII, P24 e Sm29 de estimular a produção de IL-10 in vitro, por células mononucleares de sangue periférico de asmáticos infectados e não infectados pelo S. mansoni. Foram também avaliadas as produções de IL-5, IL-13 e IFN-g. Foi adicionado Sulfato de Polimixina B às culturas estimuladas com os antígenos recombinantes para bloquear a ação da endotoxina em induzir a síntese de citocinas, desde que as proteínas recombinantes foram clonadas em Escherichia coli. As concentrações das citocinas foram medidas nos sobrenadantes das culturas de células utilizando-se a técnica ELISA sanduiche. Foi demonstrado que todos os antígenos de S. mansoni avaliados neste estudo induziram a produção de IL-10 por células de indivíduos infectados e de asmáticos não infectados. Nas culturas de 24 horas de células de asmáticos não infectados, os antígenos P24 e Sm 29 induziram as mais altas concentrações de IL-10 (828 ± 415 pg/mL e 891 ± 213 pg/mL,respectivamente). Em todos os grupos avaliados e para todos os antígenos usados, foi baixa a produção de IFN-g (valores em torno de 100 pg/mL) e os níveis de IL-5 foram abaixo do limite de detecção (15,6 pg/mL). A produção de IL- 13 induzida pelos antígenos Sm22.6, P24 e PIII foi avaliada no grupo de asmáticos não infectados, e foram observadas concentrações de 68 ± 60 pg/mL, 55 ± 49 pg/mL e 81 ± 67 pg/mL, para os respectivos antígenos. A adição dos antígenos de S. mansoni Sm22.6, P24 e PIII às culturas de asmáticos não infectados estimuladas com o Der p1 resultou em aumento na produção de IL-10. O fato dos antígenos de S. mansoni avaliados neste estudo terem induzido a produção de IL-10 e baixas concentrações de IL-5, IL-13 e IFN-g por células de asmáticos não infectados sugere que os mesmos pode ser futuramente utilizados como vacina para prevenir doenças alérgicas.
10

Simulation numérique de la fragmentation d'un précurseur de dopage au sein d'un réacteur d'implantation ionique par immersion plasma / Numerical simulation of the fragmentation of a doping precursor inside a plasma immersion ion implantation (PIII) reactor

Maury, Mathieu 04 December 2015 (has links)
Cette thèse est centrée sur le développement de modèles numériques pour simuler le comportement physique des plasmas présents dans un réacteur d'implantation ionique à immersion plasma. Ces modèles ont pour but d'estimer l'impact des réglages opérationnels du réacteur sur les paramètres plasma pertinents pour l'implantation, comme le flux ionique sur le substrat et la distribution en énergie des ions. La géométrie complexe du réacteur rend difficile sa modélisation d'un seul tenant, du fait des importants gradients temporels et spatiaux attendus pour les densités ioniques et la température électronique. Une stratégie de simulation en deux étapes a donc été adoptée : - Un modèle quasi-homogène, couplé à un module de chimie en volume élaboré, permet de représenter des deux portions de la source plasma et d'obtenir l'évolution de la composition du plasma en fonction de la puissance radiofréquence injectée. - Un modèle unidimensionnel de type PIC-MC permet de décrire la dynamique de la gaine ionique qui se forme près du substrat du fait du potentiel imposé, ainsi que de déterminer la distribution de l'énergie d'impact des ions et les flux d'implantation correspondants. Au final, ces travaux de recherche ont permis d'aboutir à une meilleure compréhension de l'impact des paramètres opérationnels du réacteur sur le flux ionique et la distribution en énergie des ions arrivant sur le substrat. La connaissance des couplages physiques entre la source plasma et la chambre d'implantation autorise l'optimisation du processus de dopage, puisque les paramètres opérationnels peuvent être réglés de manière à minimiser la profondeur de dopage après implantation. / Numerical models have been developped to simulate the plasma present inside a plasma immersion ion implantation reactor. Their goal is to estimate the impact of the reactor’s settings on the plasma parameters relevant for ion implan-tation. The complex geometry of the reactor renders its modelling difficult, because of the stiff spatial and temporal gradients expected, so a two-step simulation stra-tegy was adopted : – A global model of the plasma source, coupled to a detailed volume chemistry module, allows to determine the time evolution of the plasma composition according to the radio-frequency power injected in the source.– A 1D PIC-MC model of the sheath facing the substrate describes the dyna-mics of the expanding sheath and allows to determine the ion impact energy distribution function and corresponding implantation profiles. Determination of the couplings between the plasma source and the implantation chamber makes possible to optimize the doping process, since the reactor’s opera-tional settings can then be adjusted to minimize the doping depth after implanta-tion.

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