No description available.

When Colossal Magnetoresistance films are grown on lattice mismatched substrates, the strain on the film/substrate interface induces a strong strain that altered the intrinsic properties on transport and magnetic measurements. The transition temperatures of La0.7Ca0.3MnO3(LCMO) and La0.7Sa0.3MnO3(LSMO) thin films are lowered by both tensile and compress strains, while La0.8Ba0.2MnO3(LBMO) films may be increased or decreased dependent on the type of strains. When La0.8Ba0.2MnO3(LBMO) films were grown on SrTiO3 (STO) substrate by a standard off-axis RF sputtering technique, the compressed strain enhanced the transition temperatures. When La0.8Ba0.2MnO3(LBMO) films were further annealed at higher temperature, the transition temperature was increased up to temperature that was never been achieved, and this phenomena can not be explained solely by the strain effect. In this study, Secondary ion mass spectroscopy and X-ray reciprocal mapping were used to investigate the possible cause of the extra enhancement in transition temperatures. It is found that under a fixed annealing condition the substrate element, Sr, diffuses partially into the film that separated the films into the top layer and the bottom layer acting as La1-x(SryBa1-y)xMnO3 with higher transition temperature. The TC enhancement can be attributed to the combination of the strain and interdiffusion effects.

With the rapid spread in use of polymers the study of diffusion in them is becoming increasingly important. For a number of industrial processes diffusion coefficients and elemental distributions need to be quantified precisely. From a more scientific approach accurate models need to be devised to describe the various diffusion mechanisms involved as well as the concentration and temperature dependencies of the diffusion coefficients. Using ion beam analysis techniques (Rutherford Backscattering and Nuclear Reaction Analysis) three systems were studied. The first was an industrially relevant system of relatively small dye molecules diffusing into a number of different polymer matrices. For fixed diffusion settings, diffusion coefficients were measured and found to correlate with the matrix glass transition temperatures. Surface dye concentrations, on the other hand, were independent of matrix properties. The other two systems studied involved polymer interdiffusion. Based on different assumptions, two contradictory theories have been developed to describe the concentration dependence of the mutual diffusion coefficient; the 'slow' and 'fast' theories. In one system, blends of low molecular weight (unentangled) polystyrene and poly(methyl methacrylate) our data followed the 'slow' theory at low temperatures and the 'fast' theory at high temperatures. An equation describing the concentration dependence of the mutual diffusion coefficient at all intermediate annealing temperatures (hence linking the 'slow' and 'fast' theories) was developed and found to describe the data accurately. In the second system, blends of entangled poly(methyl methacrylate) of several molecular weights, the mutual diffusion coefficient was found to follow the 'fast' theory at all studied temperatures. In all three systems the temperature dependence of the tracer diffusion coefficients of the various components were accurately described by the semi-empirical equations of the Free Volume theory.

Universiẗat, Diss., 2000--Göttingen.

A physico-chemical approach (theory of dissociation and reaction) is developed, which can be used in binary diffusion couple to determine diffusion parameters of the product phases with wide homogeneity range, as well as phases with narrow homogeneity range. It is demonstrated that this approach is basically equivalent to the diffusion based treatment. However, physico-chemical approach pedagogically sheds light on the chemical reactions occurring during interdiffusion at the interphase interfaces and morphology develops in the interdiffusion zone. This theory can be used in any binary systems for any end-member condition to explain single phase or multiphase diffusion controlled growth. Ni-Al and Ag-Zn systems are considered here to calculate diffusion parameters following physico-chemical approach. It is evident from our theoretical analysis and experimental evidence that in the presence of a stable Kirkendall marker plane one should expect duplex grain morphology in a particular phase layer. On the other hand, there is another model which is used rather frequently, is the theory of partitioning of flux. Although, the theory of partitioning of flux is used several times, we found that this theory does not count the mobility of both the species and therefore is not suitable to use in most of the interdiffusion systems. We have first modified this theory to take into account the mobility of both the species and then further extended to develop the relations for the integrated diffusion coefficient and the ratio of diffusivities of the species. The versatility of these two different models (that is the theory dissociation and reaction and the partitioning of flux) is examined in the Co-Si system with respect to different end-member compositions. From our analysis, we found that the applicability of the theory of partitioning of flux is rather limited but the theory of dissociation and reaction can be used in any binary systems. The theory of dissociation and reaction is then used to elucidate this behaviour in a single phase of β-NiAl and to calculate the diffusion parameter at the Kirkendall marker planes in the interdiffusion zone. To apply the physico-chemical approach, Ni-and Al-rich part of the phase is treated as two different phases and the plane corresponding to eqiatomic composition is considered as virtual interface between them. Possible dissociation and reaction equations are considered to combine with the flux equations to derive the relation for diffusion coefficient. Further experiments are conducted in the Cu-Sn, Au-Sn and Ni-Sn systems, which are important for flip chip bonding related to micro electronics industry. Different diffusion parameters, such as integrated diffusion coefficient, tracer diffusion coefficient of elements and the ratio of diffusivities are determined, which shed lights on the atomic mechanism of diffusion. Subsequently, the theory of dissociation and reaction is used when possible to explain the growth of the phases in the interdiffusion zone.

University, Diss., 2004--Köln.

No description available.

Sizings, a thin polymer coating applied to the surface of the carbon fiber before impregnation with the matrix, have been shown to affect the mechanical performance of the composite. These sizings affect the processability of the carbon fiber that translates into a composite with less fiber breakage and improved fiber/matrix adhesion. In addition, the interdiffusion of the sizing and the bulk matrix results in the formation of an interphase. This interphase can alter damage initiation and propagation that can ultimately affect composite performance. The overall objective of the work detailed in this thesis is to ascertain the effects that thermoplastic sizing agents have on composite performance and determine the phenomenological events associated with the effects. All of the thermoplastic sizings had improved processability over the traditional G' sizing. These improvements in processability translated into a composite with less fiber damage and improved surface quality. In addition, all of the thermoplastic sizings outperformed the industrial benchmark sizing G' by at least 25% in static tensile strength, 11% in longitudinal flexure strength, and 30% in short beam shear strength. All moduli were found to be unaffected by the addition of a sizing. The interphase formed in K-90 PVP sized carbon fiber composites was fundamentally predicted from the constitutive properties of K-90 PVP/Derakane™ interdiffusion and fundamental mass transport equations. The K-90 PVP sizing material interdiffusing with the Derakane™ matrix was found to be dissolution controlled. The dissolution diffusion coefficient had an exponential concentration dependence. Fundamental mass transport models were utilized to predict the interphase profile. The predicted K-90 PVP interphase concentration profile displayed steep gradients at the fiber/matrix interface but essentially no gradients at points distant from the fiber surface. The predicted mechanical property profile was essentially flat for the modulus but did show a steep gradient in the strain-to-failure and shrinkage properties. However, the K-90 PVP interphase compared to the unsized/pure Derakane™ interphase showed improvements in strength and strain-to-failure and a reduction in cure shrinkage without significantly affecting the interphase tensile or shear moduli. / Ph. D.

An in depth study of the performance of thermally interdiffused concentration gradient polymer photovoltaic devices is carried out with particular attention to the effect of the thickness and the thermal treatments on the power conversion efficiency, short circuit current, open circuit voltage and other key electrical properties. Bilayer films of sequentially spin-cast donor and acceptor materials are exposed to various heat treatments in order to induce the interdiffusion. The depth profiles show concentration gradients in the donor and acceptor as a result of interdiffusion and these devices show an order of magnitude increase in the device performance compared to the bilayer devices. Dual spin-cast poly (3-octylthiophene-2,5-diyl) (P3OT)- [6,6] phenyl C61 butyric acid methyl ester (PCBM) and poly (3-hexylthiophene-2,5-diyl) (P3HT)-PCBM interdiffused devices are studied in detail by varying the thickness of the donor and acceptor layers as well as the annealing conditions for initial polymer layer and the time and temperature of the interdiffusion process. Auger spectroscopy and X-ray photoelectron spectroscopy along with ion beam milling are used to investigate the concentration gradient formed as a result of the interdiffusion. The sulfur signal present in the P3OT and P3HT backbone is detected to identify the concentration profiles in the P3OT-PCBM and P3HT-PCBM devices. The interdiffusion conditions and thickness of the active layers have been optimized to obtain the highest power conversion efficiency. The best device performance of the P3OT-PCBM interdiffused devices is achieved when the interdiffusion is carried out at 150°C for 20 minutes and the P3OT thickness is maintained at 70 nm and the PCBM thickness at 40-50 nm. The highest efficiency achieved for P3OT-PCBM interdiffused devices is 1.0% under AM1.5G solar simulated spectrum. In order to further increase the efficiency, P3OT is replaced by (P3HT) which has higher hole mobility. P3HT- PCBM based concentration gradient devices show improved device performance over P3OT-PCBM devices. Power conversion efficiency of the order of ~3.0% is obtained for P3HT-PCBM interdiffused devices when the interdiffusion is carried out at 150°C for 20 minutes. For both P3OT:PCBM and P3HT:PCBM devices, the optimum performance occurs when the concentration gradient extends across the entire film and is correlated with an increase in the short circuit current density and fill factor as well as a decrease in the series resistance. The results demonstrate that an interdiffused bilayer fabrication approach is a novel and efficient approach for fabrication of polymer solar cell devices. In addition, porphyrin derivative 5, 10, 15, 20-Tetraphenyl-21H, 23H-porphine zinc (ZnTPP) is studied as a new donor material for organic solar cells. ZnTPP: PCBM blend devices are investigated in detail by varying the weight ratio of the donor and acceptor materials in blend devices. The devices with ZnTPP: PCBM in 1:9 ratios showed the best device performance and the efficiency of the order of 0.2% is achieved under AM1.5G solar simulated conditions. Trimetallic Nitride Tempelated (TNT) endohedral fullerenes are also examined in this thesis as the novel acceptor materials. Bulk heterojunction or blend devices are fabricated with P3HT as the donor material and several TNT endohedral fullerenes as the acceptor material. Y3N@C₈₀PCBH based devices which are annealed both before and after the electrode deposition show improvement in the device performance compared to devices that are only annealed before the electrode deposition. The highest power conversion efficiency achieved for TNT endohedral fullerene devices is only 0.06%, suggesting that substantial additional work must be done to optimize the compatibility of the donor and acceptor as well as the device fabrication parameters. / Ph. D.

Les superalliages monocristallins à base de nickel sont couramment utilisés dans la fabrication des aubes de turbines à gaz aéronautiques. En service, ces pièces mécaniques sont soumises à des sollicitations mécaniques et thermiques sévères. La composition chimique et la microstructure de ces superalliages monocristallins ont été optimisées à travers différentes générations d'alliages dans le but de résister au fluage à des températures supérieures à 1100°C. Pour protéger ces matériaux des agressions environnementales (oxydation isotherme et cyclique à très haute température, corrosion à moyenne et haute température), les aubes de turbine sont généralement revêtues d'une couche de NiAlPt ou de MCrAlY (M=Ni, Co). Le procédé de dépôt et les traitements thermomécaniques entrainent la formation d'une zone d'interdiffusion entre le revêtement et le substrat. De plus, la microstructure des différentes zones (le superalliage, le revêtement et la zone d'interdiffusion) évolue en service du fait de l'effet combiné des sollicitations mécaniques et thermiques. De telles évolutions sont susceptibles d'affecter localement les propriétés mécaniques des aubes de turbine. Les revêtements MCrAlY ont fait l'objet de nombreuses études portant sur l'oxydation et la corrosion à haute température. L'abattement des propriétés mécaniques du superalliage du fait de la présence du revêtement a été largement étudié sur le système complet, c'est à dire le superalliage revêtu. Ces études ont eu pour but d'estimer une épaisseur de superalliage qui soit considérée comme non porteuse de la charge, et ce indépendamment de la taille de la zone d'interdiffusion. L'affinement des modèles prédictifs de comportement mécanique et de durée de vie des matériaux requiert une base de données relative aux propriétés locales et à leur évolution au cours du vieillissement. Ces données n'étaient pas disponibles jusqu'à ce jour. Ce travail a donc porté sur la caractérisation microstructurale et mécanique de la zone d'interdiffusion du système MC2 revêtu de NiCoCrAlYTa par co-déposition électrolytique. Des éprouvettes de traction ont été extraites des différentes zones de ce système à gradient de propriétés à l'état de réception et aussi dans des états vieillis avec ou sans contrainte appliquée. Elles ont été ensuite testées mécaniquement à haute température dans des conditions environnementales optimisées de façon à limiter les effets induits par l'oxydation sur le comportement mécanique d'éprouvettes aussi minces. Ces échantillons de 20 à 400 μm d'épaisseur ont été obtenus en utilisant une machine de rodage afin de limiter l'impact de la méthode d'usinage sur l'état de contrainte résiduel. Deux bancs d'essais mécaniques ont spécialement été développés dans le cadre de cette étude pour réaliser des essais de fluage et de traction sur ces échantillons ultra-minces sous atmosphère contrôlée jusqu'à 1200°C. Les résultats obtenus sur ces échantillons minces ont été comparés aux résultats d'essais conduits sur des éprouvettes massives. L'effet « paroi mince » a été exploré parallèlement afin de statuer sur la possibilité d'utiliser ces données pour décrire le gradient de comportement du système. / Monocrystalline nickel based superalloys are the most suitable materials for the design of high performance turbine blades. In service, these mechanical parts undergo both harsh mechanical and thermal solicitations. The chemical composition and also microstructure of these superalloys have been optimized through different generations to resist creep deformation at temperature higher than 1373K. To protect these materials from environment stresses (isothermal and cyclic oxidation at high temperature, intermediate temperature corrosion) blades are generally coated with a NiAlPt or MCrAlY layer (M=Ni, Co). Both deposition process and thermomechanical treatment generate an interdiffusion zone (IDZ) between the coating and the substrate. Moreover, the microstructure of the different strata (superalloy, coating and interdiffusion zone) evolve in service due to the combine effect of high temperature and stress. Such evolutions may locally affect the mechanical properties of turbine blades. MCrAlY coatings have been studied extensively from an oxidation and hot corrosion point of view. The drop of mechanical properties of superalloys because of the presence of coating has been investigated on full system, so that to say the coated superalloy. These study aims to estimate a none bearing thickness of the superalloy independently from the size of the interdiffusion zone. Refinement of predictive models on mechanical behaviour and lifetime of materials require data relative to local properties and their evolution when ageing. These data were not available until now. Hence, this work deals with microstructural and mechanical characterisation of the interdiffusion zone of the system MC2 coated with NiCoCrAlYTa by electrochemical codeposition. Tensile specimens were extracted from the different zones of this functionally graded material on “as received” state and after ageing with and without applied stress. Then, these specimens were mechanically tested at high temperature in optimised controlled atmosphere in order to prevent ultrathin specimens from oxidation effects on the mechanical behaviour. These specimens in a range of 20 to 400μm thick were obtained by use of a lapping machine in order to limit the impact of gritting on residual stress. Two mechanical test rigs were especially designed for this study to perform creep and tensile testing on these ultrathin specimens under controlled atmosphere at temperature up to 1473K. Results obtained from these ultrathin specimens were compared with testing conducted on bulk materials. The “size effect” was explored in parallel so that to conclude on the feasibility of using these data to quantify the behaviour gradient of this system.