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The direct application of heavy metal- and quaternary ammonium-based antibacterial agents can cause inconvenience such as irritation, short-term applicability, discoloration of the tissue, and environmental concerns. The immobilization of these agents on montmorillonite (Mnt) was expected to diminish these effects by hindering direct contact of the ions with the target tissues. The objective of the present study was, therefore, to prepare inorgano(I)- and organo(O)-montmorillonites (I/O-Mnt) and to determine their potential uses in such biomedical applications. Na-montmorillonite (Mnt-Na) was modified by hydrothermal and microwave irradiation methods using Cu2+/Zn2+, and quaternary ammonium and/or anionic surfactants. The effect of the structures formed by immobilization on Mnt surfaces on antibacterial activity was investigated. Quaternary ammonium surfactants were cetyltrimethyl ammonium bromide (CTAB) with a linear alkyl chain, cetylpyridinium chloride (CPC) with a single aromatic ring, and benzethonium chloride (BZT) with double aromatic rings. N-lauroyl sarcosinate (SR) was the anionic surfactant. The samples were subjected to thermogravimetric (TGA) and scanning electron microscopy (SEM) analyses. Desorption tests showed that the antibacterial efficacy against Streptococcus mutans stemmed from I/O-Mnt and not from the ions released from the material surfaces to the aqueous phase. The results of the antibacterial studies showed that the existence of a linear alkyl chain and a double aromatic ring were the structural factors causing the greatest antibacterial effect. The time-kill tests revealed that Mnt-CTA, Mnt-BZT, and Mnt-CP-SR were effective against Streptococcus mutans within 5 min of contact. With the new findings, they were identified as possible selective and potent bactericidal agents and promising candidates for biomedical applications., Scientific Research Projects of Ege University (BAP) [FGA-2019-20715], The authors gratefully acknowledge the support of Scientific Research Projects of Ege University (BAP) through the project number FGA-2019-20715 and proofreading assistance to Enago, Crimson Interactive Inc, New York.

Graphene/copper matrix composites have a wide range of application prospects, but the mechanical properties of the interface have been one of the key problems restricting their wide application. In this paper, the mechanical behaviors at the interface of graphene/copper matrix composites, such as pulling up, pulling out, and cohesion, and the effects of temperature and graphene content on them were studied by the molecular dynamics method. The results show that the pull-up force and cohesiveness show two stages in the whole process. The pulling force increases rapidly and then decreases to 0 slowly. The pull-out force shows three stages: it rises rapidly at first, then fluctuates continuously, and finally drops to 0. The mechanical properties of the interface deteriorated with the increase in temperature. When the temperature increased from 0 K to 1100 K, the interface normal strength, shear strength, and cohesion strength of the interface decreased by 26.3%, 32.9%, and 24.8%, respectively. In addition, with the increase in graphene content, the normal strength of the interface increases, the shear strength decreases, and the cohesion strength almost stays the same. When the graphene content increases from 6.71 at% to 11.75 at%, the normal strength increases by 6.8%, while the shear strength decreases by 37.4%. The influence mechanism of temperature and content is explained from the aspects of the influence of atomic thermal motion and the hindering effect of graphene on the dislocation motion of the copper matrix. The relevant results have certain reference values for the engineering application and theoretical research of graphene/copper composites.

Phosphorus oxide (PO x ) capped by aluminum oxide (Al2O3) has recently been discovered to provide excellent surface passivation of crystalline silicon (c-Si). In this work, insights into the passivation mechanism of PO x /Al2O3 stacks are gained through a systematic study of the influence of deposition temperature (Tdep = 100-300 °C) and annealing temperature (Tann = 200-500 °C) on the material and interface properties. It is found that employing lower deposition temperatures enables an improved passivation quality after annealing. Bulk composition, density, and optical properties vary only slightly with deposition temperature, but bonding configurations are found to be sensitive to temperature and correlated with the interface defect density (Dit), which is reduced at lower deposition temperature. The fixed charge density (Qf) is in the range of + (3-9) × 1012 cm-2 and is not significantly altered by annealing, which indicates that the positively charged entities are generated during deposition. In contrast, Dit decreases by 3 orders of magnitude (∼1013 to ∼1010 eV-1 cm-2) upon annealing. This excellent chemical passivation is found to be related to surface passivation provided by hydrogen, and mixing of aluminum into the PO x layer, leading to the formation of AlPO4 upon annealing.

Chitosan (CS) and pea protein isolate (PPI) were used as raw materials to prepare nanoparticles. The structures and functional properties of the nanoparticles with three ratios (1:1, 1:2 1:3, CS:PPI) were evaluated. The particle sizes of chitosan–pea protein isolate (CS–PPI) nanoparticles with the ratios of 1:1, 1:2, and 1:3 were 802.95 ± 71.94, 807.10 ± 86.22, and 767.75 ± 110.10 nm, respectively, and there were no significant differences. Through the analysis of turbidity, endogenous fluorescence spectroscopy and Fourier transform infrared spectroscopy, the interaction between CS and PPI was mainly caused by electrostatic mutual attraction and hydrogen bonding. In terms of interface properties, the contact angles of nanoparticles with the ratio of 1:1, 1:2, and 1:3 were 119.2°, 112.3°, and 107.0°, respectively. The emulsifying activity (EAI) of the nanoparticles was related to the proportion of protein. The nanoparticle with the ratio of 1:1 had the highest potential and the best thermal stability. From the observation of their morphology by transmission electron microscopy, it could be seen that the nanoparticles with a ratio of 1:3 were the closest to spherical. This study provides a theoretical basis for the design of CS–PPI nanoparticles and their applications in promoting emulsion stabilization and the delivery of active substances using emulsions.

In order to study the influencing factors of the tensile properties of axial braided C/C composites, the interfacial shear strength of the fiber rod and matrix was studied and ejecting tests of the fiber rod were carried out. The ejecting test specimens were formed with different thicknesses to obtain the changing rule of the interface shear strength with the thickness of the sample, and the testing method for the interface shear strength of the axial braided C/C composite material. The results show that the recommended thickness of the ejecting test specimens for the interface shear strength of is four times the diameter of the fiber rod. The interface shear strength distribution law of two different batches of materials was obtained through the interface ejecting test. The mesoscopic structure characteristics and pore statistical distribution law of the hole surface after ejecting were analyzed by scanning electron microscopy (SEM), and the mechanism of the difference of the interface shear strength was obtained. The tensile properties of two different batches of materials were obtained by tensile tests. The results show that the tensile properties of the two batches of materials differ greatly. The analysis suggests that the reason for this difference is the differences in interfacial bonding strength between the fiber rod and matrix. The higher the interface shear strength, the better the tensile property of the material will be.

In this work, we apply a molecular dynamics simulation of Ag-nanoparticle-doped epoxy resin to analyze in depth the micro-mechanisms in this nanodielectric. The simulation results show that when Ag nanoparticles with a radius of 10Å are used as dopants, the periodically arranged atoms in a ~4.5-Å-thick surface layer of the nanoparticles have become amorphous. This modification of the interface depends on temperature and nanoparticle size and leads to an interface polarization layer that changes the relative permittivity of the epoxy matrix. Moreover, a simulation indicates that doping with Ag nanoparticles can improve certain thermal and mechanical properties. However, the interface properties have little effect on the thermal and mechanical properties of nanodielectrics, which may depend only on the thermal and mechanical properties of the doped material itself, the doping concentration, or the microstructure of the nanodielectrics. The innovation of this article lies in the study of the microstructure characteristics of the nanodielectric and the changes of some key physical parameters at the nanoscale by means of molecular simulation. It provides a more efficient research idea for the traditional, experimental-based nanodielectric field. Our results may help in the analysis of nanodielectrics and insulating materials, and they suggest that doping with Ag nanoparticles may improve the thermal and mechanical performance of dielectrics.

Nanocarbon materials (carbon nanotubes, graphene, graphene oxide, reduced graphene oxide, etc.) are considered the ideal toughening phase of ceramic matrix composites because of their unique structures and excellent properties. The strengthening and toughening effect of nanocarbon is attributed to several factors, such as their dispersibility in the matrix, interfacial bonding state with the matrix, and structural alteration. In this paper, the development state of nanocarbon-toughened ceramic matrix composites is reviewed based on the preparation methods and basic properties of nanocarbon-reinforced ceramic matrix composites. The assessment is implemented in terms of the influence of the interface bonding condition on the basic properties of ceramic matrix composites and the methods used to improve the interface bonding. Furthermore, the strengthening and toughening mechanisms of nanocarbon-toughened ceramic matrix composites are considered. Moreover, the key problems and perspectives of research work relating to nanocarbon-toughened ceramic matrix composites are highlighted.

Vapor–liquid equilibria and fluid interface properties of binary mixtures containing either methane or cyclohexane representing fuel and nitrogen or oxygen are reported. The mixtures are studied at different temperatures and pressures, which are chosen such that the temperature of the fuel component is subcritical, while that of the gaseous component is mainly supercritical. Data are obtained from molecular dynamics (MD) simulation, as well as density functional theory and density gradient theory in combination with the PC-SAFT equation of state (EOS). The studied interface properties include surface tension, interface thickness, enrichment, and relative adsorption. Furthermore, bulk vapor–liquid equilibrium properties are computed with two distinct MD methods as well as the PC-SAFT EOS. All approaches are compared to data from highly accurate empirical EOS. Despite the fundamental differences between these methods, very good agreement between the results of MD, density functional theory, and density gradient theory and EOS data is observed for the phase equilibria and interface properties, reinforcing the present predictions. It is found that the equivalence of nitrogen to oxygen is rather limited, in particular for the methane propellant. The disparities are particularly pronounced for low temperatures, where the compositions of the bulk phases differ significantly. As a result, enthalpy of vaporization as well as surface tension attains much higher values for mixtures containing oxygen.

We report the improvement in photoelectrochemical water splitting (PEC-WS) by controlling migration kinetics of photo-generated carriers using InGaN/GaN hetero-structure nanowires (HSNWs) as a photocathode (PC) material. The InGaN/GaN HSNWs were formed by first growing GaN nanowires (NWs) on an Si substrate and then forming InGaN NWs thereon. The InGaN/GaN HSNWs can cause the accumulation of photo-generated carriers in InGaN due to the potential barrier formed at the hetero-interface between InGaN and GaN, to increase directional migration towards electrolyte rather than the Si substrate, and consequently to contribute more to the PEC-WS reaction with electrolyte. The PEC-WS using the InGaN/GaN-HSNW PC shows the current density of 12.6 mA/cm2 at −1 V versus reversible hydrogen electrode (RHE) and applied-bias photon-to-current conversion efficiency of 3.3% at −0.9 V versus RHE. The high-performance PEC-WS using the InGaN/GaN HSNWs can be explained by the increase in the reaction probability of carriers at the interface between InGaN NWs and electrolyte, which was analyzed by electrical resistance and capacitance values defined therein.

CO2 adsorption and activation on a catalyst are key elementary steps for CO2 conversion to various valuable products. In the present computational study, we screened different Cu–ZrO2 interface structures and analyzed the influence of the interface structure on CO2 binding strength using density functional theory calculations. Our results demonstrate that a Cu nanorod favors one position on both tetragonal and monoclinic ZrO2 surfaces, where the bottom Cu atoms are placed close to the lattice oxygens. In agreement with previous calculations, we find that CO2 prefers a bent bidentate configuration at the Cu–ZrO2 interface and the molecule is clearly activated being negatively charged. Straining of the Cu nanorod influences CO2 adsorption energy but does not change the preferred nanorod position on zirconia. Altogether, our results highlight that CO2 adsorption and activation depend sensitively on the chemical composition and atomic structure of the interface used in the calculations. This structure sensitivity may potentially impact further catalytic steps and the overall computed reactivity profile. peerReviewed

The limited long-term stability of metal halide perovskite-based solar cells is a bottleneck in their drive toward widespread commercial adaptation. The organic hole-transport materials (HTMs) have been implicated in the degradation, and metal oxide layers are proposed as alternatives. One of the most prominent metal oxide HTM in organic photovoltaics is MoO3. However, the use of MoO3 as HTM in metal halide perovskite-based devices causes a severe solar cell deterioration. Thus, the formation of the MoO3/CH3NH3PbI3-xClx (MAPbI3-xClx) heterojunction is systematically studied by synchrotron-based hard X-ray photoelectron spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Raman spectroscopy. Upon MoO3 deposition, significant chemical interaction is induced at the MoO3/MAPbI3-xClx interface: substoichiometric molybdenum oxide is present, and the perovskite decomposes in the proximity of the interface, leading to accumulation of PbI2 on the MoO3 cover layer. Furthermore, we find evidence for the formation of new compounds such as PbMoO4, PbN2O2, and PbO as a result of the MAPbI3-xClx decomposition and suggest chemical reaction pathways to describe the underlying mechanism. These findings suggest that the (direct) MoO3/MAPbI3-xClx interface may be inherently unstable. It provides an explanation for the low power conversion efficiencies of metal halide perovskite solar cells that use MoO3 as a hole-transport material and in which there is a direct contact between MoO3 and perovskite.

This study aims to understand the effects of confinement on the rheology and molecular dynamics in multilayer polymeric structures fabricated by the forced-assembly multilayer coextrusion of polyethylenes (PE) and confined polymers (PS and PC). The originality of our approach deals with coextrusion of these high mismatched viscoelastic systems. Through this work, PEs with varying macromolecular architectures, with short-chain branching (SCB) and long-chain branching (LCB), were used. Various nano-structured multilayer structures with stable flow and layered architecture were then obtained. Hitherto, various characterization techniques such as WAXS, SEM or TEM, and rheology were used to probe the structure and molecular dynamics of the PE chains. Micro and nanolayered instabilities were observed depending on the viscoelastic mismatched properties and interfacial tensions. The layer multiplication strongly affects the crystallization microstructure/morphology and molecular orientations of PEs. Interestingly, we found that macromolecular and geometrical confinements further influence the final morphology. Subsequently, they remarkably influence the rheology and molecular dynamics of PEs depending on the amount of LCB. From micro- to nanolayers, strain hardening properties in the extensional measurements are strongly dependent on the number of layers, architecture, compositions and confinement. Relevant mechanisms involving molecular rheology theories are proposed to elucidate the reasons underlying the changes. Meanwhile, we were able to model interfacial tension properties especially in the case of nanolayered polymeric systems. Hence, this work clearly demonstrates how the multiscale structural evolution during the micro-/nano-layer coextrusion process can control the final properties of multilayered products. Our findings are aimed at a better understanding of the interfacial properties towards controlling the interface/interphases in the present micro-nanostructured model multilayers polymers including their recyclability for advanced applications ranging from ultra-barrier films from cast extrusion to flexible and high transparency sheets for thermoforming process. Finally, and in the context of circular economy, a future-oriented approach from eco-design to a recycling strategy of the studied multi-micro/nanolayered systems was investigated. Therefore, a novel route is purposed to decrease the number of constituents, control the thickness of the layers, avoid using tie layers, and enhance the recyclability of the studied systems., L’objectif de la présente thèse consiste en l’étude fondamentale pour la compréhension de l’ultra-confinement des polymères sur les propriétés rhéologiques et la dynamique des chaines lors de l’élaboration des multi-micro/nanocouches par le procédé de coextrusion. Pour ce faire, les travaux ont été menés sur des couples modèles à base de polyéthylènes (PE) et de polymères confineurs de type (PS et PC). L'originalité de notre approche concerne la coextrusion de ces polymères ayant un fort contraste des propriétés rhéologiques. Dans ce cadre, différents grades de PEs ayant des architectures macromoléculaires avec des ramifications courtes (SCB) et des ramifications longues (LCB) ont été utilisés. Outre l’étude rhéologique, les systèmes élaborés ont été analysés par diverses techniques de caractérisation telles que le MEB, MET et 2D-WAXS, afin de sonder les propriétés morphologiques, la structure cristalline et la dynamique des chaînes PEs à différentes échelles. Des instabilités ont été observées en fonction du contraste viscoélastique des polymères stratifiés et de la tension interfaciale. Des cartes de stabilités ont été établies. Dans certaines conditions, différentes structures multi-nano-couches nano-architecturées présentant un écoulement stable et ayant une architecture complexe ont été alors obtenues. Lors de la mise en œuvre, la démultiplication des couches influence fortement la microstructure/morphologie et l’orientation cristalline des PE. En outre, nous avons constaté que le confinement moléculaire des PE présente un effet notoire sur la morphologie et la microstructure des multicouches, en fonction de la nature du polymère confineurs. De surcroit, le comportement la rhéologique et de ces PE se révélait être influencé en fonction du type et la longueur de branchements. Quant au comportement rhéologique en élongation, le phénomène de Strain hardening dépend fortement du nombre de couches, de l’architecture et de la composition. Des mécanismes moléculaires ont été proposés pour élucider les manifestations observées. Parallèlement et malgré le fort contraste rhéologique, nous avons pu modéliser à partir des mesures élongationnelles les propriétés de la tension interfaciale, en particulier dans le cas des nanocouches. Par ailleurs, ce travail démontre clairement comment l'évolution structurelle multi-échelle au cours du processus de coextrusion micro-/nano-couche peut contrôler les propriétés finales et notamment le processus de « Strain-hardening ». En outre, les résultats obtenus visent à une meilleure compréhension des propriétés interfaciales pour contrôler l'interface/les interphases dans ces polymères multicouches modèles, tout en intégrant leur recyclabilité. A cet égard, et dans le contexte de l'économie circulaire, une approche prospective allant de l'éco-design à l’élaboration des systèmes multi-micro/nano couches facilement recyclable a été étudiée.

International audience; The adsorption of carbon monoxide and nitrogen molecules at the surface of four forms of solid water is investigated by means of grand canonical Monte Carlo simulations. The trapping ability of crystalline Ih and low-density amorphous ices, along with clathrate hy-drates of structures I and II, are compared at temperatures relevant for astrophysics. It is shown that, when considering a gas phase that contains mixtures of carbon monoxide and nitrogen, the trapping of carbon monoxide is favored with respect to that of nitrogen at the surface of all solids, irrespective of the temperature. The results of the calculations also indicate that some amounts of molecules can be incorporated in the bulk of the water structures and the molecular selectivity of the incorporation process is investigated. Again, it is shown that the incorporation of carbon monoxide is favored with respect to that of nitrogen in most of the situations considered here. In addition, the conclusions of the present simulations emphasize the importance of the strength of the interactions between the guest molecules and the water network. They indicate that the accuracy of the corresponding interaction potentials is a key point, especially for simulating clathrate selectivity. This highlights the necessity of having interaction potential models that are transferable to different water environments.

The use of high-performance polymeric microfibres in enhancing the ductility of cementitious composites is widespread. A vivid example is the application of strain-hardening cement-based composites (SHCCs) in the construction industry. However, there are a few challenges which need to be addressed with respect to material design. For instance, the ductility of SHCC diminishes under alternating tension&ndash, compression loading, where the fibres lose their crack-bridging capacity due to specific damage mechanisms. The damage development and its influence on crack-bridging capacity have been studied in previous works by the authors. The paper at hand focuses on the influence of crack width on the crack-bridging capacity of polymeric microfibres in conjunction with the number of cycles in an alternating tension&ndash, compression regime with different cyclic compressive force levels. It shows that bridging capacity can be markedly influenced by crack width: an increase in crack width leads to more severe damage to the fibres and thus to lower crack-bridging capacity. Then, after analysing the specimens by means of electron microscopy, a hypothesis is presented to address the effect of crack width on damage development. Finally, a simple approach is proposed for estimating the influence of different parameters on fibre degradation.

The transport properties of novel device architectures depend strongly on the morphology and the quality of the interface between contact and channel materials. In silicon nanowires with nickel silicide contacts, NiSi2-Si interfaces are particularly important as NiSi2 is often found as the phase adjacent to the silicide-silicon interface during and after the silicidation. The interface orientation of these NiSi2-Si interfaces as well as the ability to create abrupt and flat interfaces, ultimately with atomic sharpness, is essential for the properties of diverse emerging device concepts. We present a combined experimental and theoretical study on NiSi2-Si interfaces. Interfaces in silicon nanowires were fabricated using silicidation and characterized by high-resolution (scanning) transmission electron microscopy. It is found that {111} interfaces occur in ⟨110⟩ nanowires. A tilted interface and an arrow-shaped interface are observed, which depends on the nanowire diameter. We have further modeled NiSi2-Si interfaces by density functional theory. Different crystallographic orientations and interface variations, e.g., due to interface reconstruction, are compared with respect to interface energy densities. The {111} interface is energetically most favorable, which explains the experimental observations. Possible ways to control the interface type are discussed.

Composite materials are widely used in aircraft industry as they have high specific strengths. To increase the delamination resistance of layered composites, tough particles, films or fibers at different length scales can be interleaved between composite layers. Until now, electrospun nanofibers from homopolymers such as polycaprolactone (PCL), polyacrylonitrile (PAN), polyvinylidene difloruide (PVDF), polysulfone (PS), nylon 6,6, have been used to investigate their effects on the interlaminar fracture toughness. Besides the use of homopolymers, physically mixed polymer systems have also been used. In such systems, alternatives like; spinning of alternating layers of two polymers, co-electrospinning of different polymers at the same time from different needles, or core-shell configurations have been tried. Another category which could be named as, ‘hybrids’ were formed between different polymers and carbon based materials such as multi wall carbon nanotube (MWCNT), graphene (G) or graphene-oxide (GO) flakes. Nanofibers from polymer blends mixed in molecular chain level could bring certain advantages in improving the interlaminar toughness of layered composites. In addition, these blends can be hybridized with externally sprayed-on G or GO to trigger multiple toughening mechanisms. In this study, nylon 6 (N6), PCL and their blends with different mass ratios (N6/PCL: 100/0, 80/20, 60/40, 40/60 and 0/100) were electrospun and interleaved between carbon fiber reinforced polymer composites (CFRP). In addition, GO flakes were sprayed between the nanofiber layers to investigate the effect of these hybrid interleaves on Mode I interlaminar fracture toughness of CFRPs. With Differential Scanning Calorimetry (DSC) analyses, it was identified that weight ratios of polymers affect the phase separation characteristic of polymer blends. In Scanning Electron Microscope (SEM) analyses which were carried out after Double Cantilever Beam (DCB) test, it was observed that the specific phase separation behaviors facilitates the activation of different toughening mechanisms. N6/PCL with 60/40 ratio showed the best result with respect to the unmodified reference sample with a 69% improvement on the Mode 1 G1c initiation and 59% on that of G1c propagation. At 60/40 ratio, a phase separation between PCL and N6 was observed and this lead to a cooperative synergistic increase in the resistance against crack progression by activating the debonding and fiber bridging mechanisms simultaneously. GO flakes that were synthesized in different sizes were electrosprayed between elektrospun nanofiber veils and hybrids with different sandwich structures were produced. Due to the problems in optimization of electropsraying process parameters and dispersion of GO flakes in the spray solvent, the improvements in GIC were insignificant. However, load-displacement behavior of the composites were significantly altered. The reasons of this change were discussed. The main reason behind the poor mechanical performance was the dissolution of the veil layers by the spray solvent. Losing the structural integrity of base layer formed an asymmetry in the sandwiches’ mechanical behavior, which in turn lead to a crack diversion from tough veil layers to the brittle epoxy layers. However, it can be anticipated that, upon rectification of process parameters in spraying the GO component, the already observed significant changes in the load-displacement behavior can be utilized in favor of building structures with even higher interlaminar toughness. TÜBİTAK 214M110 numaralı proje İÇİNDEKİLER ETİK iii ÖZET i ABSTRACT iv İÇİNDEKİLER viii ÇİZELGELER x ŞEKİLLER xi 1. GİRİŞ 1 2. LİTERATÜR ÖZETİ 6 2.1. Elektroeğirme 6 2.2 Kompozit Malzemeler 7 2.3 Kompozit Malzemelerle Metalik Malzemelerin Farkı 8 2.4 KFTP’de Hasar Mekanizmaları ve Hata Modları 10 2.5 Delaminasyon Direncini Arttırma Yöntemleri 14 3 DENEYSEL ÇALIŞMALAR 25 3.2 Malzemeler 25 3.2.1 Malzeme Seçim Prensipleri 25 3.2.2 Polimerler ve Çözücüler 27 3.2.3 Grafen Oksit (GO) Parçacıkları 27 3.2.4 Prepreg 30 3.3 Arayüz Eklentilerinin Üretimi 30 3.4 Test Numunesi Üretimi 37 3.5 Mekanik Testler 38 3.6 Karakterizasyon Çalışmaları 40 3.6.1 Taramalı Elektron Mikroskobu (SEM) 40 3.6.2 Geçirimli Elektron Mikroskobu (TEM) 40 3.6.3 Differansiyel Tarama Kalorimetresi (DSC) 40 4 BULGULAR VE TARTIŞMA 43 4.1 Referans Plakalar 43 4.2 Elektroeğirme Plakaları 46 4.3 Elektropüskürtme Çalışmaları 62 5 SONUÇLAR 69 KAYNAKLAR 71 EKLER 75 EK 1: Sıcak Pres Sıcaklık Kontrolü 75 EK2: Kompozit plakalarındaki fiber-reçine oranlarının hesaplanması 76 EK3: ASTM-D5528’e göre incelenen örnek bir DCB test verisi 81 EK 4: DSC Verileri tepe ayrıştırması yöntemiyle incelenmesi 87 Kompozit malzemeler yüksek mukavemet ve düşük ağırlık avantajları sebebi ile özellikle havacılık sektöründe sıklıkla tercih edilmekte ve kullanım oranları giderek artmaktadır. Tabakalı kompozitlerde gözlenen düşük tabakalar arası tokluk ve buna bağlı delaminasyon problemlerinin çözümüne yönelik olarak, kırılgan yapıdaki tabaka ara yüzlerine; toklaştırıcı partiküller, filmler veya farklı boyutlarda fiber yapıların eklenmesiyle çatlak ilerlemesine karşı daha iyileştirilmiş özellikler kazandırılabilmektedir. Bugüne kadar, elektroeğirme yöntemi kullanılarak elde edilmiş polikaprolakton (PCL), poliakrilonitril (PAN), polivinilidin florür (PVDF), polisülfon (PS), naylon 6,6 (N6,6) gibi tekil polimer nanofiberlerinin tabakalararası kırılma tokluğuna etkileri farklı kompozit sistemlerinde incelenmiştir. Bunun yanında, tekil polimerler yerine, birden fazla polimerin gerek tabakalar halinde, gerek çoklu nozul kullanılarak aynı anda elektroeğirilmesiyle, gerekse çekirdek kabuk yöntemi ile bir araya getirilmesi ile elde edilen polimer karışımlarının kullanımına da rastlanmaktadır. Tekil bir polimerin veya kopolimerlerin çok duvarlı karbon nanotüp (ÇKDN) eklentileriyle elektroeğirilerek tabakalar arasına eklendiği ve grafen (G) veya grafen oksit (GO) gibi iki boyutlu karbon bazlı eklentilerin bir polimer matrisi içinde kullanıldığı, “melez” toklaştırıcılara dayalı çalışmalar ise diğer bir kategoriyi oluşturmaktadır. Polimerlerin zincir seviyesinde karıştırılmasıyla elde edilecek nanofiberler ve bu polimer karışımı halindeki nanofiber tabakaların arasına harici olarak püskürtülecek GO parçacıklarıyla oluşturulabilecek yeni “melez” malzemeler, epoksi bazlı KFTP’lerin tabaka ayrışması sırasındaki etkin toklaşma mekanizmalarının sayısını arttırmakta kullanılabilecek ve literatürde henüz örneği olmayan malzemelerdir. Bu çalışmada, naylon 6 (N6) ve PCL belirli kütle oranlarında (N6/PCL: 100/0, 80/20, 60/40, 40/60 ve 0/100) ortak bir çözücüde karıştırıldıktan sonra elektroeğrilmiş ve elde edilen nanofiber tüller KFTP prepreg arayüzlerine aktarılmıştır. Polimer karışımlarından elde edilen sonuçlar ışığında, tül arayüzlerine harici olarak GO parçacıkları eklenmiş ve kompozitlerin Mod I arayüz toklukları belirlenmiştir. Üretilen nanofiberler Diferansiyel Taramalı Kalorimetre (DSC) ile incelenmiş ve polimerlerin birleşme oranlarının polimerlerin karışma karakteristiğini etkilediği tespit edilmiştir. Çift Ankastre Kiriş (DCB) testi sonrası ayrılma yüzeylerinin Taramalı Elektron Mikroskobu (SEM) görüntüleri incelendiğinde; oluşan farklı karışımların, çatlak ilerlemesine karşı farklı toklaşma mekanizmalarını etkinleştirdiği görülmüştür. En iyi artışların sağlandığı, kütlece 60/40 N6/PCL oranında, karışım arayüz eklentisi yapılmamış referans numunesine göre Mod 1 yönünde GIC başlangıç değerinde %69, GIC ilerleme değerinde %59 artış göstermiştir. 60/40 karışımında, N6 ve PCL polimerlerinin nanofiber içinde faz ayrışması sonucu birbirlerinden ayrı bölgelerde bulunduğu ve bu bölgelerin, arayüzde oluşan çatlağın ilerleyişine karşı direnç oluşturacak bağaçımı, sıyrılma ve köprüleme mekanizmalarını işbirliği içerisinde aynı anda devreye soktuğu tespit edilmiştir. Harici GO eklentisi yapılan çalışmalarda ise, farklı boyutlarda hazırlanmış GO yaprakçıklar kullanılmış, yaprakçıklar nanofiber tüllerinin arasına bir sandviç yapı oluşturacak şekilde püskürtülmüştür. Fakat gerek elektropüskürtme işleminin parametrelerinin optimizasyonunda, gerekse GO parçacıklarını homojen dağıtımı konusunda yaşanılan problemlerden dolayı bu setlerden beklenilen performans elde edilememiştir. Ancak kompozitlerin yük-uzanım davranımında GO eklenmemiş tüllere göre çarpıcı farklılıklar elde edilmiş ve nedenleri tartışılmıştır. Performans düşüklüğünün temel nedeni püskürtme işlemi sırasında GO’i dağıtmak için kullanılan çözücünün elektroeğirilmiş nanofiber katmanlarını çözerek, o bölgedeki nanofiber yapısını bozmuş olmasıdır. Bu şekilde bozulan sandviç yapısında ilerleyen çatlağın, tok tül tabaka yerine gevrek epoksi katmana doğru geçebileceği belirlenmiştir. Tabaka asimetrisi sorunlarının çözümüyle, hem başlangıç hem de ilerleme bölgesinde elde edilmiş dikkat çekici davranım değişikliklerinin mekanik performansı pozitif yönde etkileyecek şekilde kullanılabileceğine dair ön veriler elde edilmiştir.

Graphene based nano-composites are relatively new materials with excellent mechanical, electrical, electronic and chemical properties for applications in the fields of electrical and electronic devices, mechanical appliances and chemical gadgets. For all these applications, the structural features associated with chemical bonding that involve other components at the interface need in-depth investigation. Metals, polymers, inorganic fibers and other components improve the properties of graphene when they form a kind of composite structure in the nano-dimensions. Intensive investigations have been carried out globally in this area of research and development. In this article, some salient features of graphene–noble metal interactions and composite formation which improve hydrogen gas sensing properties—like higher and fast response, quick recovery, cross sensitivity, repeatability and long term stability of the sensor devices—are presented. Mostly noble metals are effective for enhancing the sensing performance of the graphene–metal hybrid sensors, due to their superior catalytic activities. The experimental evidence for atomic bonding between metal nano-structures and graphene has been reported in the literature and it is theoretically verified by density functional theory (DFT). Multilayer graphene influences gas sensing performance via intercalation of metal and non-metal atoms through atomic bonding.

Waste tires have excellent mechanical performance and have been used as reinforcing material in geotechnical engineering; however, their interface properties are poorly understood. To further our knowledge, this paper examines the pull-out characteristics of waste tire strips in a compacted sand, together with uniaxial and biaxial geogrids also tested under the same conditions. The analysis of the results shows that the interlocking effect and pull-out resistance between the tire strip and the sand is very strong and significantly higher than that of the geogrids. In the early stages of the pull-out test, the resistance is mainly provided by the front portion of the embedded tire strips, as the pull-out test continues, more and more of the areas towards the end of the tire strips are mobilized, showing a progressive failure mechanism. The deformations are proportional to the frictional resistance between the tire-sand interface, and increase as the normal stresses increase. Tire strips of different wear intensities were tested and presented different pull-out resistances; however, the pull-out resistance mobilization patterns were generally similar. The pull-out resistance values obtained show that rubber reinforcement can provide much higher pull-out forces than the geogrid reinforcements tested here, showing that waste tires are an excellent alternative as a reinforcing system, regardless of the environmental advantages.

Waste tires have excellent mechanical performance and have been used as reinforcing material in geotechnical engineering; however, their interface properties are poorly understood. To further our knowledge, this paper examines the pull-out characteristics of waste tire strips in a compacted sand, together with uniaxial and biaxial geogrids also tested under the same conditions. The analysis of the results shows that the interlocking effect and pull-out resistance between the tire strip and the sand is very strong and significantly higher than that of the geogrids. In the early stages of the pull-out test, the resistance is mainly provided by the front portion of the embedded tire strips, as the pull-out test continues, more and more of the areas towards the end of the tire strips are mobilized, showing a progressive failure mechanism. The deformations are proportional to the frictional resistance between the tire-sand interface, and increase as the normal stresses increase. Tire strips of different wear intensities were tested and presented different pull-out resistances; however, the pull-out resistance mobilization patterns were generally similar. The pull-out resistance values obtained show that rubber reinforcement can provide much higher pull-out forces than the geogrid reinforcements tested here, showing that waste tires are an excellent alternative as a reinforcing system, regardless of the environmental advantages.

To reveal the potential and limits of multi-material three-dimensional (3D) printed parts in droplet-based additive manufacturing, a study combining tensile experiments and 3D imaging technique is proposed. A polymeric composite structure made of acrylonitrile butadiene styrene and thermoplastic polyurethane is manufactured using a two extrusion head printer. The quality of the interface between the two thermoplastics is quantified by adjusting the number of intertwining droplets at the interface. Tensile experiments assisted with digital image correlation are performed with two-interface orientation to discriminate shearing and traction at the interface. The 3D imaging results, which are based on X-ray micro-tomography, show the distinct features of droplet-based additive manufacturing in terms of porosity content and connectivity. Interface properties are found to control, in an incomparable way, the mechanical response. It is found that the interface quality is determinant for enhancing the ultimate performance whereas the interface orientation is found to be the perfect leverage for varying the slope of the linear part.

Günümüzde mobil telefonlar, gelişimlerini giderek akıllı mobil telefonlara devretmekte, bilgisayarların işlevlerini de yerine getirmeye başlamaktadırlar. Akıllı telefonların hızlı gelişimi bu telefonlar için geliştirilen mobil uygulamaların önemini arttırmakta olup, hızlı bir şekilde mobil uygulama pazarına girmektedir. Akıllı telefonların teknolojilerinin ve özelliklerinin gelişmesi, mobil uygulama geliştiricileri için farklı tarz ve çeşitlerde uygulamalara olanak sağlamaktadır.Akıllı telefonların gelişmiş özelliklerinden biri olan 'GPS' konum özelliklerini kullanan mobil telefon uygulamaları, kullanıcıları genellikle istedikleri yerlere yönlendirmesi amacı ile kullanılmaktadır. Günümüzdede mobil aygıtlarda kullanılan GPS teknolojisi yardımı ile mobil uygulamalara farklı bir bakış açısı sunulması hedeflemektedir.Uygulama çalışmasının teorik alt yapısı ilk üç bölümde araştırılan literatür taraması sonucunda hazırlanmıştır. Tezin dördüncü bölümünde anlatılan 'Voyager Art and History' mobil uygulamasında alışılagelmiş mobil uygulama yöntemlerinden farklı bir yaklaşım tarzı sergilenerek, akıllı cihaz kullanıcılarının seçtikleri zaman aralığı içerisinde akıllı telefonlarının gezi rotasını otomatik olarak hesaplaması ve ortaya çıkan rotayı mobil uygulama kullanıcıları ile paylaşmayı ve böylelikle alternatif bir kullanıcı deneyimi yaşatmayı hedeflemektedir. Today mobile phones have started to fulfill the functions of computer by transferring their progress to smart phones increasingly. The rapid development of smart phones has increased the importance of the applications progressed for them and has entered the mobile application marketing quickly. The progress in smart phones' technology and specification has made it possible for mobile application developers to create different styles and varieties.Mobile applications using GPS location property, which is one of the most developed features of smart phones, have been used to direct the users to desired locations. Today a different perspective is aimed to be presented by the help of GPS technology used in mobile applications.Mobile application has been prepared as the result of literature review of which theoretical infrastructure has been researched in the first three chapters. The 'Voyager Art and History' Application, which is explained in the fourth chapter, tries to calculate the trip route of smart phones automatically in a time interval chosen by the users and prepare the resulting route with smart phone users as an alternative user experience. 121

Orientador: Prof. Dr. Fabio Leandro de Souza Tese (doutorado) - Universidade Federal do ABC, Programa de Pós-Graduação em Nanociências e Materiais Avançados, 2017. Esta tese de doutorado é divida em três partes, (i) definição dos parâmetros de síntese de fotoanodos de óxidos de ferro na fase hematita; modificação dos filmes de hematita com (ii) Sn e (iii) W. (i) Na primeira parte do trabalho foram sintetizados filmes de hematita de 2 a 24 horas, tendo sua fase confirmada por difração de raios x após o tratamento térmico a 750 ºC. Alem disso, os filmes após o tratamento térmico as 750 °C apresentaram a orientação preferencial no plano de maior condutividade da hematita, o plano (110). Todos os filmes exibiram uma boa estabilidade eletroquímica, sendo o filme de 2 horas o de maior fotocorrente. (ii) Na segunda os fotoanodos de hematita tiveram sua superfície modificada com solução contendo Sn4+. A modificação com Sn4+ aumentou a fotocorrente de todos os fotoanodos de hematitas quando comparados com os puros, mantendo a melhor fotocorrente nos filmes de 2 horas. A melhoria na fotocorrente pela adição de Sn4+ foi atribuída a maior área superficial decorrente da superfície mais hidrofílica, favorecendo a reação química na interface sólido/líquido e provavelmente reduzindo pontos de recombinação. No entanto, resultados ainda superiores poderiam ser alcançados se o Sn4+ atuasse como dopante, ao invés de ter formando uma fase adicional identificada pela análise MET/EDX. Esses resultados abrem caminho para novas perspectivas para explicar o efeito da adição de Sn4+ como uma sobre camada na superfície de eletrodos de hematita. (iii) Na terceira parte foi adicionado pela primeira vez W6+ diretamente na síntese dos filmes de hematita tratados a 550 ou 750 ºC. A modificação com W6+ aumentou a fotocorrente e mantendo-se a mesmas estáveis em ambas as temperaturas de tratamento térmico. Por outro lado, a adição de W6+ fez com que os nanobastões perdem-se o leu alinhamento perpendicular ao substrato e a orientação preferencial no plano (110). Os resultados de XPS mostraram a presença de W6+, possível somente na forma de óxido, sugerindo que o tungstênio tenha segregado de forma a estabilizar na superfície da hematita. A segregação na superfície também corrobora com as medidas eletroquímicas, a densidade de carga (ND) praticamente inalterada e a melhora no desempenho catalítico evidenciado pelas medidas fotoeletroquímica com H2O2. This doctoral thesis is divided into three parts, (i) synthesis parameters definition of iron oxide photoanodes in hematite phase and modification of the hematite with (ii) Sn and (iii) W. (i) In the first part, hematite photoanodes were synthesized from 2 to 24 hours, this phase was confirmed by x-ray diffraction after annealing at 750 ° C. In addition, the photoanodes showed a preferred orientation in the hematite higher conductivity plane, (110), after annealing at 750 ° C. All photoanodes were electrochemical stable, with the 2 hour photoanode having the highest photocurrent. (ii) In the second part, the hematite photoanodes had their surface modified with Sn4+ containing the solution. The Sn modification increased the photocurrent of all hematite photoanodes when compared to the pure ones, maintaining the 2 hours photoanode as the best photocurrent. The Sn4+ photocurrent improvement was attributed to the larger surface area resulting from the more hydrophilic surface (high water affinity), favoring the chemical reaction at the solid/liquid interface and probably reducing recombination sites. However, even higher results could be achieved if the Sn4+ can act as a dopant, rather than forming an additional phase identified by the TEM / EDX analysis. These results pave the way for new perspectives to explain the effect of Sn4+ addiction as an overlayer on the hematite electrodes surface. (iii) In the third part, W6+ was first added directly during the hematite synthesis by the first time and annealed at 550 or 750 ºC. The W modification increased the photocurrent keeping it stable at both annealing temperatures. On the other hand, the W6+ addition made the nanorods lose their substrate perpendicular alignment and the (110) plane preferential orientation. The XPS results confirmed the W6+ presence, possible only in the oxide form, suggesting that the tungsten has segregated in order to stabilize on the hematite surface. Surface segregation also corroborates with electrochemical measurements, the almost unchanged charge density (ND) values and its catalytic performance improvement shown on the electrochemical measurements with H2O2.

We have revised classical micromechanics by accounting for the effect of interface to predict the effective anisotropic elastic properties of heterogeneous materials containing nano-inhomogeneities. In contrast to sharp interface between the matrix and inhomogeneity, we introduce the concept of interphase to account for the interfacial-stress effect at the nano-scale. The interphase’s constitutive properties are derived from atomistic simulations and then incorporated in a micromechanics-based interphase model to compute effective properties of nanocomposites. This scale transition approach bridges the gap between discrete atomic level interactions and continuum mechanics. An advantage of this approach is that it combines atomistic with continuum models that consider inhomogeneity and interphase morphology. It thereby enables us to account simultaneously for both the shape and the anisotropy of a nano-inhomogeneity and interphase at the continuum level when we compute material’s overall properties. In so doing, it frees us from making any assumptions about the interface characteristics between matrix and the nano-inhomogeneity.

The performance of modern a-Si/c-Si heterojunction (HIT) solar cells is dictated by a complex interplay of multiple device parameters. A single characterization experiment [e.g., light current–voltage ( I–V )] can be fitted with a set of parameters, but this set may not be unique and is, therefore, questionable as the basis for future design/optimization. In this paper, we use multiple (quasi-orthogonal) measurement techniques to uniquely identify the key parameters that dictate the performance of HIT cells. First, we study the frequency, voltage, and temperature response of inversion charge ( $Q_{{\bf Inv}} $ ) to create the theoretical basis for characterization of key device parameters, namely, the thickness of the i-layer at the front interface ( $t_{{\rm a - S{\it i}}}^{\it i} $ ), a-Si/c-Si heterojunction valence band discontinuity ( $\Delta E_V $ ), built-in potentials in a-Si ( ${\bm \phi} _{{\bf a - S{\it i}}} $ ) and c-Si ( $\phi _{{\bf c - Si}} $ ) regions, etc. Next, we simulate various characterization measurements, such as capacitance–voltage ( C–V ) and impedance spectroscopy, which probe $Q_{{\rm Inv}} $ and explain the parameter extraction procedure from these measurements. Subsequently, we use the algorithm/procedure just developed to extract the aforementioned parameters for an industrial-grade HIT sample. Finally, we extend this quasi-orthogonal characterization framework by correlating the C–V characteristics with the ubiquitous light and dark I–V characteristics to demonstrate the consistency of the developed theory and uniqueness of the parameter extracted. The unique parameter set thus obtained can simultaneously provide a basis for the interpretation of the experimental measurements and can also be used for the design/optimization of these solar cells.

Many people would like to learn how to play a musical instrument. Unfortunately, many of them never do. There are numerous reasons for that: lack of time, lack of motivation, absence of music school in near area, etc. Computer technology can be used to overcome some of these issues. In this paper the answers on questions about which features and properties user interface of adaptive drum kit learning system should have are presented and elaborated. Research results, along with possible solutions based on previous research, are presented and discussed.

International audience; The thermal conductivity and the interface thermal contact resistance of four different in thickness CuO films, obtained by PVD on a tungsten carbide substrate were investigated with a developed modulated photothermal method based on infrared measurement. According to the knowledge of the substrate thermophysical properties, the gain between the thermal perturbation and the response of the sample was used as the experimental data. The results show the dependence of the effective longitudinal thermal conductivity on the film thickness. Scanning electron microscopy observations reveal the strong anisotropy and columnar structure of the deposits. Moreover, the chemical composition of films was tested. A similar composition for each film was also verified.

International audience; The equilibrium of coherent and incoherent mismatched interfaces is reformulated in the context of continuum mechanics based on the Gibbs dividing surface concept. Two surface stresses are introduced: a coherent surface stress and an incoherent surface stress, as well as a transverse excess strain. The coherent surface stress and the transverse excess strain represent the thermodynamic driving forces of stretching the interface while the incoherent surface stress represents the driving force of stretching one crystal while holding the other fixed and thereby altering the structure of the interface. These three quantities fully characterize the elastic behavior of coherent and incoherent interfaces as a function of the in-plane strain, the transverse stress and the mismatch strain. The isotropic case is developed in detail and particular attention is paid to the case of interfacial thermo-elasticity. This exercise provides an insight on the physical significance of the interfacial elastic constants introduced in the formulation and illustrates the obvious coupling between the interface structure and its associated thermodynamics quantities. Finally, an example based on atomistic simulations of Cu/Cu2O interfaces is given to demonstrate the relevance of the generalized interfacial formulation and to emphasize the dependence of the interfacial thermodynamic quantities on the incoherency strain with an actual material system.

International audience; A process of co-curing of composite/aluminium structures is presented. Several surface treatments from chromate conversion to several anodizing processes have been tested to improve the interface properties between the polymer matrix of the composite and the aluminum substrate during the process. Methods for monitoring and characterizing surface treatments are presented. To assess the interface properties, single lap joint testing has been performed. The ultimate force at breaking has been found to be highly dependant of the treatment. The highest ultimate failure force has been obtained with treatments based on phosphoric acid anodizing. The manufacturing of hybrid materials (composite / aluminum) has been performed, showing that it is possible to co-cure composite/aluminium structures. Non destructive evaluation has been used to monitor the delamination areas between composite and aluminium.

This study deals with the membrane and interface electrical properties investigation by electrochemical impedance spectroscopy (EIS). The EIS is a powerful technique for characterizing electrical behavior of systems in which coupled electrical processes occur at different rates.A systematics tudy on the effect of solution concentration,temperature and velocity, on the electrical resistance of anion-and cation- exchange membranes (AEMs and CEMs) and their interfaces (electrical double layer and diffusion boundary layer), was carried out. At the best of our knowledge, for t he first time electrolyte concentrations up to 4 M were used for the study of membranes and interface by EIS. Moreover, Pulsed Gradient Spin Echo Nuclear Magnetic Resonance (PGSE-NMR)technique was used to measure the water self-diffusion coefficients in swelled membrane as a function of the solution concentration and temperature.These measurements gave additional important insights about the effect of the electrolyte solution and fixed charges concentration in membrane,on membrane microstructure and its transport and electrical properties. & 2014TheAuthors.PublishedbyElsevierB.V.ThisisanopenaccessarticleundertheCCBY This study deals with the membrane and interface electrical properties investigation by electrochemical impedance spectroscopy (EIS).

Interfaces are elements of the product architecture that facilitates innovation and enables an organization to leverage the trade-off between cost and performance of its products. Despite the importance of interfaces for organizations, little is known about their genesis and evolution. In this study, we make one of the initial attempts to define the attributes of interdependencies managed by interfaces, which we call as interface properties, to gain a deeper insight about how interfaces emerge. By relying on secondary case data, we define four interface properties. We discuss the congruence of these properties with Herbert Simon's notion of near decomposability.

SiOxNy films with a low nitrogen concentration (< 4%) have been prepared on Si substrates at 400°C by atmospheric-pressure plasma oxidation-nitridation process using O2 and N2 as gaseous precursors diluted in He. Interface properties of SiOxNy films have been investigated by analyzing high-frequency and quasistatic capacitance-voltage characteristics of metal-oxide-semiconductor capacitors. It is found that addition of N into the oxide increases both interface state density (Dit) and positive fixed charge density (Qf). After forming gas anneal, Dit decreases largely with decreasing N2/O2 flow ratio from 1 to 0.01 while the change of Qf is insignificant. These results suggest that low N2/O2 flow ratio is a key parameter to achieve a low Dit and relatively high Qf, which is effective for field effect passivation of n-type Si surfaces.

Tez (doktora) - Anadolu Üniversitesi, Anadolu Üniversitesi, Eğitim Bilimleri Enstitüsü, Bilgisayar ve Öğretim Teknolojileri Eğitimi Anabilim Dalı, Kayıt no: 619118, Hiper ortamların öğrenen kontrollü yapısı öğretim için sağladığı en önemli üstünlüklerden biri olarak görülmektedir. Ancak hiper ortamların öğrenenlere sunduğu bu esneklik beraberinde kaybolma, aşırı bilişsel yüklenme, dikkat bölünmesi ve zaman kaybı gibi gezinim problemlerini de ortaya çıkarmıştır. Bu noktada öğrenenlerin bu problemlerle başa çıkabilmesi için yeni ve karmaşık bir kavram, sistem veya modelin anlaşılmasında ipuçları sağlayabilen yapılar olarak metaforlardan oluşturulan metaforik arayüzlerden yararlanılabileceği düşünülmektedir. Bu bağlamda araştırmada, metaforik arayüzlerin Bilişim Teknolojileri öğretmen adaylarının eğitsel hiper ortamlardaki gezinim performansına etkilerinin belirlenmesi amaçlanmıştır. Nitel ve nicel verilerin bir arada toplandığı bu araştırma karma yöntem araştırması olarak desenlenmiştir. Araştırmanın nitel boyutunda fenomenoloji nicel boyutunda ise gerçek deneme modellerinden son-test kontrol gruplu modelden yararlanılmıştır. Araştırmanın katılımcılarını 2011-2012 öğretim yılının bahar döneminde Anadolu Üniversitesi, Eğitim Fakültesi, Bilgisayar ve Öğretim Teknoloji Eğitimi Bölümü 2. ve 4. sınıfta öğrenim gören 76 Bilişim Teknolojileri öğretmen adayı oluşturmaktadır. Verilerinin toplanmasında araştırma kapsamında geliştirilen ve iç tutarlılık katsayısı ?=.90 olan Hiper Ortamlarda Gezinim Performansı Ölçeğiyle birlikte gözlem ve odak grup görüşmesinden yararlanılmıştır. Araştırma kapsamında toplanan nicel verilerin analizinde bağımsız iki örneklem t-testi, tek yönlü ANOVA ve iki yönlü ANOVA testleriyle birlikte yüzde (%), ortalama (X), frekans (f) gibi betimsel istatistiklerden yararlanılmıştır. Elde edilen nitel verilerin analizinde ise betimsel içerik analizi ve tematikanalizden yararlanılmıştır. Araştırmadan elde edilen verilerin analizi sonucunda, metaforik arayüzlerin Bilişim Teknolojileri öğretmen adaylarının gezinim performansı üzerinde “yüksek” düzeyde anlamlı bir etkiye sahip olduğu görülmüştür (?2=.16). Metaforik arayüze sahip eğitsel hiper ortamlarda verilen görevleri yerine getiren 2. ve 4. sınıf Bilişim Teknolojileri öğretmen adayları metaforik olmayan arayüzde verilen görevleri yerine getiren öğretmen adaylarından daha yüksek gezinim performansı göstermişlerdir. Cinsiyet, internet kullanım sıklığı ve internet kullanım yeterliği gibi bağımsız değişkenlerin ise Bilişim Teknolojileri öğretmen adaylarının eğitsel hiper ortamlardaki gezinim performansı üzerinde yeterli etkiye sahip olmadığı belirlenmiştir. Bununla birlikte 2. sınıf Bilişim Teknolojileri öğretmen adaylarının ortama ilişkin daha az hareket ve davranışlarda bulunup gezinim yollarını kısa tutarak zayıf gezinim stilini yansıttıkları, 4. sınıf Bilişim Teknolojileri öğretmen adaylarının ise daha uzun sürede ve ortama ilişkin daha fazla hareket ve davranışlarda bulunarak yorucu gezinim stilini yansıttıkları belirlenmiştir. Araştırmada elde edilen diğer bir sonuca göre eğitsel hiper ortamlarda gezinim performansının Bilişim Teknolojileri öğretmen adayları tarafından gezinilen ortamın tasarımı, içerik yapısı, niteliği ve güvenirliğinden etkilenen; hız, doğruluk, çaba, motivasyon ve memnuniyet değişkenlerinin bir bütünü olarak algılandığı sonucuna varılmıştır. Ayrıca Bilişim Teknolojileri öğretmen adaylarının sıklıkla kullandıkları eğitsel hiper ortamlarda ortamın karmaşıklığı ve yönlendirme eksikliğinden dolayı aşırı bilişsel yüklenme ve kaybolma problemleriyle karşılaştıkları sonucuna varılmıştır. Karşılaşılan bu durumun ise Bilişim Teknolojileri öğretmen adaylarının istenilen bilgiye ulaşmaktan vazgeçmesiyle sonuçlanabildiği görülmüştür. Araştırmadan elde edilen sonuçlara dayalı olarak uygulamaya ve gelecekte yapılabilecek araştırmalara yönelik öneriler sunulmuştur.

Supervisor:Tatsuya Shimoda, マテリアルサイエンス研究科, 博士

Neopentilglikol (NPG)?% [x] ağ.Dikamfor (DK), x=0, 4, 30, 46, 70 ve 96 alaşımlarında katı fazların termal iletkenliklerinin bileşime ve sıcaklığa bağlılığı, radyal ısı akış sistemi kullanılarak incelenmiştir. NPG?% [x] ağ. DK , x=0, 4, 30, 46, 70 ve 96 alaşımları için erime sıcaklıklarında katı fazlarının termal iletkenlikleri ve sıcaklık katsayıları, katı fazların termal iletkenliklerinin sıcaklığa karşı değişen grafiklerinden belirlendi. Aynı alaşımlar için erime sıcaklıklarında katı fazın termal iletkenliğinin sıvı fazın termal iletkenliğine oranı bir Bridgman tipi doğrusal katılaştırma fırını ile elde edildi. Bu yüzden, NPG?% [x] ağ. DK , x=0, 4, 30, 46, 70 ve 96 alaşımlarının erime sıcaklıklarındaki sıvı fazlarının termal iletkenlikleri, katı fazın termal iletkenliğinin sıvı fazın termal iletkenliğine oranı ve katı fazların termal iletkenlik değerleri kullanılarak ölçüldü.NPG-DK ötektik sıvısı (NPG-% 46 ağ. Dikamfor) ile dengeye gelmiş katı neopentilglikol (NPG) çözeltisi (NPG-% 4 ağ. Dikamfor) için tane arayüzey oluk şekilleri yatay bir lineer sıcaklık gradyenti sistemi kullanılarak gözlendi. Gözlenen tane arayüzey oluk şekillerinden Gibbs-Thomson katsayısı (?), katı NPG çözeltisinin katı-sıvı arayüzey enerjisi elde edildi. Katı NPG çözelti fazının da tane arayüzey enerjisi gözlenen tane arayüzey oluk şekillerinden elde edilmiştir. Dependency of thermal conductivity of solid phases on temperature and composition of D-Camphor (DC) in the Neopentylglycol (NPG)?[x] wt.% D-Camphor (DC), x=0, 4, 30, 46, 70 and 96 alloys have been investigated by using radial heat flow apparatus. From graphs of the solid phases thermal conductivity variations versus temperature, the thermal conductivities of the solid phases at their melting temperature and temperature coefficients for NPG?[x] wt.% DC, x=0, 4, 30, 46, 70 and 96 alloys have been determined. The ratios of thermal conductivity of liquid phase to thermal conductivity of solid phase for the same alloys at their melting temperature were obatined with a Bridgman type directional solidification apparatus. Thus, the thermal conductivities of liquid phases for NPG?[x] wt.% DC, x=0, 4, 30, 46, 70 and 96 alloys at their melting temperature have also been evaluated by using the values of thermal conductivity of solid phases and the ratios of thermal conductivity of liquid phase to thermal conductivity of solid phase.The grain boundary groove shapes for equilibrated solid neopentylglycol (NPG) solution (NPG-4 wt. % D-camphor) in equilibrium with the NPG-DC eutectic liquid (NPG-46 wt. % D-camphor) have been directly observed by using a horizontal linear temperature gradient apparatus. From the observed grain boundary groove shapes, the Gibbs-Thomson coefficient (?), solid-liquid interfacial energy (?SL) of NPG solid solution have been determined. The grain boundary energy of solid NPG solution phase has also been determined from the observed grain boundary groove shapes. 193

Recent decades, numerous studies on cerium-based oxides have been realized and have revealed that cerium-based oxides were materials of choice in the field of heterogeneous catalysis. The aim now is therefore to increase the reactivity of these oxides, while expanding their range of optimal temperatures of Use. In this particular context, it seems possible to modulate the properties of cerium-based oxides by controlling the morphology of the crystallites. This thesis has been devoted to the identification, development and characterization of materials based on cerium oxides of controlled morphology. We first determined possible morphologies for the studied system, by hydrothermal synthesis by micro-wave assisted heating we have synthesized these morphologies and we characterized reactivity of these materials by infrared thermography and TGA. We have optimized these materials first, by extrinsic doping (deposition of precious metals) and then by intrinsic doping (Yttrium and Iron). New morphologies have been synthesized so we have studied the processes of nucleation-growth set in. The high reactivity of iron-doped materials has led us to a detailed characterization of the microstructure of these materials. Finally correlation reactivity/morphologies of crystallites have been achieved., Les oxydes à base de Cérium, ont fait l'objet de nombreuses études ces dernières décennies et se sont révélés des matériaux de choix, dans le domaine de la catalyse hétérogène. L'objectif à l'heure actuelle, est donc d'accroître la réactivité de ces oxydes, tout en élargissant leur gamme de températures optimales d'utilisation. Dans ce contexte particulier, il semble possible de moduler les propriétés des oxydes à base de cérium en contrôlant la morphologie des cristallites. Ce travail de thèse a donc été consacré à la détermination, l'élaboration et à la caractérisation de matériaux oxydes à base de cérium de morphologies contrôlées. Nous avons tout d'abord déterminé cristallographiquement et thermodynamiquement les morphologies accessibles au système étudié puis par traitement hydrothermale assistée par chauffage micro-ondes nous avons synthétisé les dites morphologies. Après caractérisation de la réactivité par ATG et thermographie Infrarouge nous avons optimisé ces matériaux par un dopage extrinsèque tout d'abord (dépôt de métaux précieux), puis par un dopage intrinsèque ensuite (Yttrium et Fer). Enfin, l'obtention de morphologies non accessibles cristallographiquement nous a amené à approfondir le(s) processus de germination croissance de ces particules et la forte réactivité des matériaux dopés fer nous a poussé à une caractérisation fine de la microstructure de ces matériaux. Au final nous avons pu corréler l'influence de la morphologie des cristallites sur la réactivité propre de l'ensemble des familles de matériaux étudiés.

The aim of this work was to better understand the surface and interface properties of sputtered ferroelectric BaTiO3 thin films. They are typically used as dielectrics in integrated capacitors, electromechanical sensors and so. This thesis studies the chemical and electronic structures of the interface of BaTiO3 in order to understand basic mechanisms of contact formation with the substrate and the electrode like the Schottky barrier height. Furthermore, the surface stoichiometry of such films has been investigated under different thermal preparation revealing significant instability through segregation phenomenon. Finally, the doping effect with niobium is studied regarding compensation mode, dopant solubility and dielectric properties. The experimental setup allows for in-situ analysis of surface and interface properties using photoelectron spectroscopy.; Cette thèse porte sur l'étude de couches minces ferroélectriques à base de BaTiO3 déposées par pulvérisation cathodique. Ces matériaux permettent par exemple de réaliser des condensateurs accordables ou encore des mémoires non-volatiles pour le stockage d'informations. Cependant, leurs propriétés diélectriques sont considérablement dégradées par des effets extrinsèques d'interfaces; film/substrat ou encore film/électrode. Dans ce contexte, la spectroscopie de photoémission (XPS) a été utilisée pour quantifier les états électroniques et chimiques de ces interfaces avec une approche in-situ. L'étude sur la formation du contact film/électrode a permis de mesurer la hauteur de barrière de Schottky partiellement responsable des caractéristiques capacités – tensions des couches. Des phénomènes de ségrégation ont été mis en évidence révélant une profonde instabilité de la stoechiométrie de surface. Enfin, la conséquence d'un dopage au niobium dans les couches minces de BaTiO3 est discutée du point de vue des modes de compensation, de la solubilité du dopant et des propriétés diélectriques.

Bu çalışmada, alt yarısı gözenekli ortam dolu dikdörtgen kesitli bir kanalda daimi, sıkıştırılamaz ve laminar bir akış oluşturularak; berrak akışkan bölgesi ile gözenekli ortam dolu bölge arasındaki kalan sınırda arayüzey hızı DPIV yöntemi kullanılarak deneysel olarak incelenmiştir.Deneysel çalışmadan önce, kısmi gözenekli ortam dolu dikdörtgensel kesitli bir kanalda akış için yapılan daimi, laminar ve uniform akış kabullerinden sonra sınır şartları belirlenmiştir. Matematik model ve analitik çözümler elde edilmiştir. Berrak akışkan bölge için Stokes denklemi kullanılırken gözenekli ortam dolu bölgede Brinkman-Forchheimer düzeltmeli Darcy denklemi kullanılmıştır. Bu iki bölge sınırı olan arayüzey geçiş bölgesinde ise bu denklemlerin ortak çözümü kullanılmıştır. Matematik model ve analitik çözüm üzerinde çalışılırken mühendislik bilgisayar yazılımlarından Fortran ve Matlab programlama dilleri ve Grapher grafik programları kullanılmıştır. Sayısal çözümlemede Gridgen ve Fluent mühendislik bilgisayar programları kullanılmıştır. Sayısal çözümler sonucu elde edilen u-hız bileşeni değer verilerinin aritmetik ortalaması düzlemde belirlenmiş alanlar için alınarak kanalın belirli noktalarında kanal yüksekliği boyunca ortalanmış hız dağılımı bulunmuştur. Deneysel çalışmada arayüzey hızının tespiti farklı debi değerleri için gerçekleştirilip DPIV yöntemiyle veri toplanmıştır. Veriler işlenerek arayüzey hızının tespiti için düzlemsel hız alanları elde edilmiştir. Düzlemsel hız alanlarının maskeleme ve kötü vektörlerden ayrıklaştırma işlemleri sonucunda hız verilerinin ortalaması alınarak hız-kanal yüksekliği grafikleri çizdirilmiştir.Çalışmanın konusu, arayüzey hızının deneysel olarak bulunması ile analitik ve sayısal çalışmalarla bu çalışmanın desteklenmesidir. Çalışmanın önemi, güncel ve gelişime açık olup tam açıklanamayan noktalarının bulunmasıdır. Buna örnek olarak kayma gerilmesi sıçrama koşulu sabiti verilebilir. Bu yüzden gözenekli ortam ile akışkan bölge arasındaki geçiş olaylarının bilimsel açıklaması günümüzde hala tam olarak anlaşılmış değildir. Arayüzeydeki hız dağılımlarının incelenmesi gözenekli ortamlardaki yeni ve temel çalışmalar grubuna girmektedir. Çalışmanın ve konunun önemlerinden bir diğeri ise farklı mühendislik disiplinlerinde olduğu kadar, uçak ve uzay mühendisliğinde özel uygulama alanlara sahip olmasıdır.Deneyler İstanbul Teknik Üniversitesi Trisonik Laboratuarı'nda, sıfırdan tasarlanıp üretilen deney düzenekleri ile gerçekleştirilmiştir. Gözenekli ortam oluşturmak için dairesel kesitli silindirik pleksiglas çubuklar yatay ve dikey olarak belirli aralıklara sahip gridler halinde kanal tabanına düzgün bir şekilde yerleştirilmiştir. Akışkan olarak ise deneylerde su kullanılmıştır. Deneyler debi değerlerinin değiştirilmesi ile tekrarlanmıştır.Çalışma sonucunda, deneysel veriler özetlenmiştir. Arayüzey hız tespitinden sonra sonuçlar bölümünde analitik ve sayısal çalışma ile deneysel veriler tartışılmıştır. In this study, by creating steady, laminar and incompressible flow in a rectangular cross-sectioned channel which is filled with porous medium located at the bottom, the interface velocity profile on the boundary between the clear fluid region and the porous medium region is observed experimentally using DPIV method.Earlier than experimental study, the boundary conditions are assigned after assuming the flow conditions as steady, laminar and uniform in the partially porous medium filled rectangular cross-sectioned channel. Mathematical model is found out and the analyitical solutions are determined. For the clear fluid region, Stokes equation is used, and for the porous medium region Brinkman-Forchheimer extended Darcy Equation is used. On the boundary of these two regions, the common solution for these equations which are told above are used. During working on the mathematical model and the analytical solution, engineering softwares such as Fortran and Matlab-programming languages and Grapher are used. For the numerical solution of the problem Gridgen and Fluent engineering softwares are used. After the data acquisition of numerical study, by averaging u-velocity component magnitudes arithmetically over a specific area in plane, average velocity profiles is figured out for all channel height in the specific points. In the experimental study, the velocity profile in the interface is examined for different mass flow rates and data acquisition is done by using DPIV method. By data processing, planar velocity maps are found out in order to determine the velocity profile at the interface. After discretization of bad vectors from planar velocity maps and masking, velocity-channel height graphes are plotted by taking the averaged velocity data.The subject of this study is determining the interface velocity experimentally and supporting this work with analytical and numerical solutions. The importance of this study is new and evolving, and there are some points which could not be explained exactly. Shear stress jump condition constant can be given as an example for this argument. That?s why, the scientific explanations to the transition phenomena between the saturated porous medium region and clear fluid region haven?t understood yet fully today. Investigations of the interface velocity profiles are included in the new and basic studies category for porous media. Another importance of the study is that as well as different engineering disciplines, aeronautic and astronautic engineering have specific application areas about this topic.Experiments are done in the Trisonic Research Center at Istanbul Technical University with producing and developing the whole experimental setup from beginning to the end. For preparing the porous medium, circular cross-sectioned cylinderical plexiglass parallel located at the bottom of the channel with specific horizontal and vertical distances like in grid lines homogenously. As fluid, liquid water is used during the flow for the experiments. Experiments are repeated by changing mass flow rates.At the end of the study, the experimental data are summarized. After the determination of interface velocity, experimental data, analytical, and numerical solutions are discussed in the results section. 86

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2009, Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2009, Modern yasamın gereklerine göre şekillenen günümüz kentinde giderek önemini ve önceliğini yitirmeye başlayan “kentsel dış mekanlar”ı ve “yaya”yı yeniden kent yaşamına kazandırmaya yönelik bir çözüm olarak geliştirilen ve pek çok kentte yaygın olarak kullanılan “yayalaştırma uygulamaları”, çoğu zaman öngörüldüğü gibi sonuçlanmayabilmektedir. Gerek tasarım ve uygulama aşamasında bazı temel unsurların hesaba katılmaması, gerekse kullanıma ve kullanıcıya yönelik düzenlemelerin eksikliği ya da yetersizliği, yayalaştırılmış alanların insanların ilgisini çekmekte yetersiz kalmasına sebep olarak, bu mekanların kullanımını ve başarısını olumsuz yönde etkilemektedir. Yayalaştırma uygulamalarındaki bu problemlerden hareketle, bu çalısmada, “yayalara ayrılmış kent mekanlarında mimari unsurların rolü” ne dikkat çekmek istenmiştir. Bu amaçla öncelikle yaya mekanlarını çevreleyen binaların kentsel mekanla etkileşim yüzeyini oluşturan “arayüz” kavramı ele alınmıştır. Arayüzün bina ile kentsel yaya mekanı ilişkisinde etkili olan unsurları, biçim ve kullanım özellikleri olmak üzere iki ana başlıkta toplanmış, bu unsurların kentsel yaya mekanlarının kullanımına ve kalitesine etkisi araştırılmıştır. Araştırmadan edinilen bilgiler ışığında, İstanbul’daki iki yayalaştırma uygulaması üzerinde analiz ve değerlendirmeler yapılmış ve birtakım sonuçlara varılmıştır. Elde edilen bu sonuçların bir anlamda bir rehber oluşturarak, kentsel yaya mekanlarına yönelik yapılmış olan uygulamaların iyileştirilmesinde ya da ileride yapılacak olan çalışmaların başarısında etkili olabileceği düşünülmüştür., As a solution to regain the “urban outdoor spaces” and the “pedestrian” that are gradually losing their precedence and significance in today’s city which is shaped according to the consequences of modern life, “pedestrianization studies” may not result as they are often projected. Whether because of some main factors that are not considered at the design stage or the application stage, or the lack or inafficiency of arrangements for the uses and users, the pedestrian districts sometimes fail to attract people’s attention which affects their use and success negatively. Moving from these problems in pedestrianization applications, this study aims to point to “the role of architectural features in urban spaces allocated to pedestrians”. Setting out with this goal, as the main research subject of the study, the concept of “interface” forming the interaction surface of building with pedestrian space is examined. Afterwards, the effect of form and use features in this interface on the use and quality of the urban pedestrian spaces is tried to be determined. According to the information gathered in the literature review, two different pedestrian districts in Đstanbul is evaluated. Considering the results of these evaluations, it is intended that these results form a guide to the studies regarding urban pedestrian spaces that are already made or will be made in the future., Yüksek Lisans, M.Sc.

Indentation tests are frequently employed at present for the identification of material parameters at different scales. An innovative inverse analysis technique, recently proposed by the Authors, combines the traditional indentation test with the mapping of the residual deformations (imprint), thus providing experimental data apt to be used to identify material parameters in film-substrate systems. In this paper, such methodology is enhanced to permit the identification of the fracture properties of the interface between a coating and its substrate once the bulk material parameters are known. In order to make the inverse problem well posed, a further set of experimental data, namely the horizontal displacement field measured on the film external surface, is considered as available experimental information. The sought material parameters are recovered through recursive calculations of the mechanical response of the film-substrate system, performed by a finite strain numerical simulation. The coating and a significant portion of the underlying bulk material are incorporated in the finite element models built up to this purpose, while delamination is accounted for through cohesive elements. The inverse analysis procedure rests on a batch, deterministic approach and conventional optimization algorithms are employed for the minimization of a suitably defined discrepancy norm. Extensive numerical computations have been performed in order to test the performance of the proposed methodology in terms of result accuracy and computational effort.

We have prepared perpendicular hard/soft bilayers made of a 10 nm L1_0-FePt layer, which has been epitaxially grown on MgO(100) and a Fe layer with thicknesses of 2 and 3.5 nm. The control of the interface morphology allows to modify the magnetic regime at fixed Fe thickness (from rigid magnet to exchange-spring magnet), due to the nanoscale structure effect on the hard/soft coupling and to tailor the hysteresis loop characteristics. Despite the small thickness of the soft layer, the coercivity is strongly reduced compared to the hard layer value, indicating that high anisotropy perpendicular systems with moderate coercivity can be easily obtained.

Composites based on glass fiber reinforced low styrene emission polyester resins have been widely used over the last 10 years, in order to meet increasingly strict safety regulations, particularly in the pleasure boat industry. Previous studies of their mechanical properties suggested that although these resins are generally more brittle than traditional orthophthalic polyester resins this did not adversely affect the properties commonly used for quality control (short beam shear and tensile failure strength of mat reinforced composites). In the present paper results from a more detailed study of damage behaviour are presented. Tests include fracture toughness (K Ic ) tests on resins, fibre/matrix interface energy, detection of composite damage initiation in tension by acoustic emission, composite delamnation (G Ic and G IIc ), and low energy impact. Overall the results indicate that the low failure strain of low styrene emission resins results in significantly lower composite damage resistance.

As saponinas são tensoativos naturais, caracterizadas principalmente por sua atividade espumógena. Ilex paraguariensis A. St. Hil, conhecida como "erva-mate", é uma espécie vegetal rica em saponinas e de importância econômica e cultural para este Estado. Estudos anteriores demonstraram que os frutos imaturos de I. paraguariensis, uma parte do vegetal sem valor comercial, apresenta teores mais elevados de saponinas que as folhas da erva-mate. O objetivo deste trabalho foi avaliar a potencialidade das saponinas dos frutos imaturos de I. paraguariensis como adjuvante espumógeno, sob o ponto de vista físico-químico e tecnológico, bem como a avaliação do potencial de irritação dérmica. Para isso, foram empregados um extrato bruto liofilizado (EXL) obtido por turbólise na proporção de 1:10 droga-solvente em etanol:água (40:60 v/v) como líquido extrator e dois produtos purificados ricos em saponinas, denominados Fr.7090 e P6, obtidos por um processo de fracionamento em fase sólida e eluição com metanol-água (método I) e por um processo de complexação com polímero polivinílico por contato direto (método II), respectivamente. Para a caracterização do perfil das saponinas e monitoramento de processos, foi desenvolvida uma metodologia analítica por CLAE em fase reversa C18, em sistema gradiente acetonitrila: ácido fosfórico 0,5 % com detecção em 205 nm. A atividade de superfície das saponinas foi avaliada através do abaixamento da tensão superficial, CMC, excesso de superfície e área superficial. Os perfis de espumabilidade e estabilidade da espuma das saponinas do EXL e da Fr. 7090 foram avaliados através de medidas da espumabilidade, drenagem, tempo de permanência da espuma e resistência. Como tensoativos de comparação foram utilizados o laurilsulfato de sódio (LSS) e polissorbato 80 (Poli. 80), empregados nas mesmas condições e concentrações que as soluções de saponinas. A influência de eletrólitos sobre os perfis espumógenos foi avaliado utilizando NaCl, KBr, KNO3, MgCl2 e Na2HPO4, mantendo a força iônica constante em 0,024 M. Para a análise das propriedades espumógenas das saponinas, a espuma foi gerada em coluna de vidro por insuflação de ar durante 20 segundos, mantendo um fluxo de 2 L min-1. O perfil de drenagem das espumas das saponinas na concentração de 10 CMC foi avaliado e expresso como percentual de volume de líquido retido na espuma (VLE %), no tempo zero e ao longo de 60 minutos. A estabilidade da espuma das saponinas de Fr.7090 e P6 foi avaliada considerando a altura da coluna de espuma em função do tempo e pelo registro e análise fotográficos da espuma até 480 minutos. Para avaliar a influência do tamanho micelar sobre as propriedades espumógenas dos tensoativos, o diâmetro efetivo das micelas foi determinado por medidas de espalhamento de luz dinâmica. Dados adicionais sobre a sua estabilidade foram obtidos mediante a análise fotográfica bidimensional, em câmara geradora de espuma projetada para esta finalidade. A resistência da espuma foi caracterizada mediante a velocidade de queda de uma esfera através da coluna de espuma, sob condições experimentais padronizadas. A Fr. 7090 apresentou um elevado grau de espumabilidade semelhante ao LSS e superior ao Poli. 80. Quanto ao perfil de drenagem, as saponinas apresentaram um valor de VLE % em 60 minutos (T1h) de 12,0 % e 15,2 %, para o EXL e Fr. 7090, respectivamente, em relação a 7,15 % para ambos tensoativos sintéticos. As saponinas apresentaram um perfil de estabilidade diferenciado, com maior estabilização estrutural com o tempo. As espumas das saponinas apresentaram uma resistência superior aos tensoativos sintéticos, porém, somente a 25 CMC. A adição de eletrólitos às soluções de saponinas influenciou negativamente os perfis espumógeno e de estabilidade da espuma das saponinas. As análises por espalhamento da luz sugerem micelas de dimensões maiores em relação aos tensoativos não-iônicos ou a possível formação de estruturas supramicelares, mesmo baixas concentrações. Pela análise bidimensional, a espuma do EXL apresentou menor alteração da forma e número das bolhas de ar com o tempo, comparado à espuma de LSS. O potencial de irritação dérmica das saponinas foi avaliado pelo teste de irritação primária dérmica de Draize in vivo, em coelhos machos albinos. A avaliação biológica classificou as saponinas como produtos não-irritantes. Pelos resultados, concluiu-se que as saponinas dos frutos imaturos de Ilex paraguariensis apresentam um potencial emprego tecnológico, tanto pelas suas propriedades espumógenas, como pela ausência de irritação cutânea. Saponins are natural surfactants, characterized mainly for its foaming properties. Ilex paraguariensis A. St. Hil, known as "erva-mate", is a rich vegetal specie in saponins and of economic and cultural importance for this State. Previous studies had demonstrated that the immature fruits of I. paraguariensis, one has left of the vegetable without commercial value, presents higher concentrations of saponins that the leaves of "erva-mate". The objective of this work was to evaluate the saponins potentiality of the immature fruits of I. paraguariensis as adjuvant foaming, under the technological and physical-chemical point of view, as well as the evaluation of the cutaneous irritation potential. For this, it had been used a rude extract (EXL) obtained by tubo-extraction using ethanol 40% (v/v) as extractor liquid and two rich purified products in saponins obtained by a process in solid phase and elution with methanolwater (method I) and a complexation process with polyvinyl polymer (method II), respectively. For the characterization of saponins profile was developed an analytical methodology using HPLC in C18 reversed phase, with a system gradient composed by acetonitrile:phosphoric acid 0,5 % with detection in 205 nm. The surface activity of saponins was evaluated through the lower of the superficial tension, CMC, surface density and superficial area. Foambility and stability profiles of the saponins foam of the EXL and Fr. 7090 had been evaluated through foamability mensuraments, draining, permanence time of the foam and resistance of the films. As surfactants of comparison it had been used sodium dodecylsulphate (LSS) and polyssorbate 80 (Poli. 80). These had been analyzed in the same conditions and concentrations of saponins solutions. The electrolytes influence on the foaming profiles was evaluated using NaCl, KBr, KNO3, MgCl2 and Na2HPO4, keeping the constant ionic strenght in 0,024 M. For the analysis of the foams properties of the saponins, the foam was generated in glass column by air insufflation during 20 seconds, with a constant flow of 2 L min-1. The draining profile of the saponins foams in the concentration of 10 CMC was evaluated and expressed as percentile of volume of restrained liquid in the foam (VLE %), in time zero and throughout 60 minutes. The stability of the saponins foam of Fr.7090 and P6 was evaluated considering the height of the foam column in function of the time and for the photographic register and analysis of the foam till 480 minutes. To evaluate the influence of the micellar size on the foaming properties of the surfactants, the effective diameter of micelles was determined by dynamic light scattering mensuraments. Additional data on its stability had been obtained by means of the bidimensional photographic analysis, in generating foam chamber projected for this purpose. The resistance of the foam was characterized by means of the speed of a sphere fall through the foam column, under standardized experimental conditions. Fr. 7090 presented one high degree of similar foambility to the LSS and superior to Poli. 80. As much as to the draining profile, the saponins had presented a value of VLE % in 60 minutes (T1h) of 12,0 % and 15,2 %, for the EXL and Fr. 7090, respectively, in relation to 7,15 % for both synthetic surfactants The saponins showed a differentiated profile of stability, with bigger structural stabilization with the time. The saponins foams had presented a superior resistance to the synthetic surfactants, however, only 25 CMC. The addition of electrolytes had a negative influence on saponins foams profile and stability. The analyses for dynamic light scattering suggest bigger dimensions micelles in relation to the nonionic surfactants or the possible formation of highest micelles, even at low concentrations. To the bidimensional analysis, the EXL foam presented minor alteration of the form and number of the air bubbles with the time, compared with the LSS foam. The potential of the cutaneous irritation of the saponins was evaluated by the test of dermic primary irritation of the Draize test in albinic male rabbits. The biological evaluation classified the saponins as not-irritating products. For the results, it was concluded that the saponins of I. paraguariensis immature fruits presented a technologycal potential use, as for its foaming properties as for the absence of cutaneous irritation.

International audience; We consider strongly degenerate convection-diffusion equations which mix possible parabolic and hyperbolic behaviour. We prove some qualitative properties of the solutions, in the one-dimensional case. In particular we study the evolution in time of the number of connected components of parabolic and hyperbolic regions and the continuity of the interfaces between the two phases.

Atomistic simulations and experimental investigations are combined to study heterojunction interfaces of hybrid polymer solar cells, with the aim to better understand and precisely predict their photovoltaic properties. The focus is on a hybrid ternary model system based on a poly(3-hexylthiophene) (P3HT)/zinc phthalocyanine (ZnPc)/ZnO interface, in which a ZnPc interlayer is applied to improve the performance of the hybrid interface. Theoretical predictions of the ternary system are validated against the properties of a concrete P3HT/ZnPc/ZnO planar heterojunction device. The theoretical predictions closely agree with the photovoltaic properties obtained in P3HT/ZnPc/ZnO solar cells, indicating the strength of the method for modeling hybrid heterojunction interfaces. The theoretical and experimental results reveal that: i) ZnPc molecules in direct contact with a ZnO surface insert new energy levels due to a strong ZnPc/ZnO coupling, ii) electron injection from these new energy levels of ZnPc into ZnO is highly efficient, iii) the ZnPc/ZnO coupling strongly influences the energy levels of the ZnO and P3HT leading to a reduction of the open circuit voltage, and iv) charge carrier recombination at the P3HT/ZnO interface is reduced by the ZnPc interlayer. The intercalation of ZnPc leads to an increase in photocurrent as well as to an overall increase in power conversion.

ÖZET Yüksek Lisans Tezi FARKLI «ATKILANMIŞ YARIİLETKEN MALZEMELERİN ARAYÜZEY POTANSİYEL PROFİLLERİNİN BELİRLENMESİ Emine OZTURK Cumhuriyet Üniversitesi Fen Bilimleri Enstitüsü Fizik Anabilim Deli Danışman: Yrd.. Doç. Dr. Yüksel Ergün Bu çalışmada ilk olarak düşük boyutlu sistemlerin temel özellikleri belirtildikten sonra, bulk Si ve GaAs yarıiletkenlerin özellikleri ve bu konuda yapılan çatışmalar özetlenmiştir. Son olarak, self-consistent (kendi-içinde tutarlı) hesap kuralları verilmiş ve iki GaAs tabakası arasında Si tabakası oluşturularak büyütülen £-katkılanmış GaAs yapısında arayüzey potansiyel profili, self-consistent' olarak hesaplanmıştır. ANAHTAR KELİMELER İki-boyutlu elektron gazı, S/-S katkılama GaAs katmanı, arayüzey potansiyel profili, kuantum kuyusu, altband, band eğilmesi, band enerjisi. ABSTRACT M. Sc. Thesis THE DETERMINATION OF INTERFACE POTENTIAL PROFILES OF DIFFERENTLY DOPED SEMICONDUCTOR MATERIALS Emine ÖZTÜRK Cumhuriyet. University Graduate School of Natural and Applied Science; Department of Physics Supervisor : Dr. Yüksel ERGUN In this study, firstly, the main features of low dimensional systems were reported. Then, general informations about the modulation-doped and £-doped structures were given and the studies about this subject were summarized. Finaffy, seff-consistent calculation rules were expfanied for this aim, interface potential profile in 6-daped GeAs structure grown by forming SHeyer between the two GaAs layers is calculated self-consistently. KEY WORDS : Two-dimensional electron gas (2DEG). Si - S dope, Ga4s layer, interface potential profile, quantum well, subband, band bending, band- energy. 56

ÖZET Geleceğin yarıiletkeni olarak adlandırılan galyum arsenür(GaAs)'ün üzerine, silisyum üzerinde büyütülen silisyum dioksit (Si02) kalitesinde bir yalıtkan tabakanın oluşturulamaması, bu konudaki araştırmaların devam etmesine neden olmaktadır. GaAs üzerinde kaliteli bir yalıtkan tabakanın büyütülmesi, entegre devrelerin tabanını oluşturan MOS ( Metal-Oksit- Yaniletken) yapıların elektronik sanayindeki çok yüksek taşıyıcı hız ile optoelektronik uygulamalarla büyük bir atılım yapabileceği göz önünde tutularak başlatılan bu çalışmada, p-GaAs üzerine anodikleme yöntemiyle altı ayrı elektrolit kullanılarak büyütülen yalıtkan tabakaların (oksit,sülfür ve florür) GaAs-MOS yapısındaki yalıtkan - yarıiletken arayüzeyin elektriksel özelliklerine etkisi incelenmiş olup: 1. p-GaAs'ün üzerine ilk defa anodikleme prosesinde susuz amonyum sülfür ve florür elektrolitleri kullanılarak kaim sülfür ve florür tabakası büyütüldüğü; 2. Büyütülen yalıtkan tabakalarından en düşük dielektrik sabitine 293K'de florür tabakasının, 77K'de ise sülfür tabakasının sahip olduğu; 3. Çalışılan tüm p-GaAs MOS yapılardan düşük akım yoğunluğu (0.1 A/cm ) ile amonyum sülfürlü susuz elekti devre elemanı imalinde kullanılabileceği; '9 mA/cm ) ile amonyum sülfürlü susuz elektrolit kullanılarak oluşturulan yapının 4. Yukarda sözü edilen yapının 77K'deki yüksek frekans C-V eğrisinde histerezis olayının olmayışı ve diğer numunelerin 293K'deki histerezis büyüklüklerine göre de, daha düşük histerezise sahip olması, bu yapının uzun senelerdir sürdürülen ve başarısız kalan GaAs MOS teknolojisinin istediği arayüzey durum yoğunluğunu (NSSFB * 10 cm` ) sağladığı, belirlenmiştir. INVESTIGATION OF INTERFACE PROPERTIES in p-GALLIUM ARSENIDE (GaAs) / ANODIC INSULATOR FELMS SUMMARY There has not been any success in research, which began in 1966, for the development of GaAs-MOS technology which the electronics industry expects to achieve. As GaAs starts to decompose at 450° C, it is necessary that dielectric film growth be conducted at lower temperatures. Although anodic oxidation process has been considered, no real success has been obtained. Because interface states density, Nss which is the reason for the electrical unstability of GaAs-MOS structure, could not be lowered. Even though in last 10 years, another non-native insulator layer formation on GaAs instead of oxide film has been tested (GaAs-MIS structures), no such improvement has been found. The insulator layer (Si02, silicone dioxide) of technological value in Si- MOS structures is of good quality. It is essential that the insulator layer to be chemically and electronically stable. On the other hand the interface state density and charges inside the insulator should be low. This study is aimed at lowering the interface state density which is the most significant parameter in MOS technology. For this purpose the growth of sulfide and fluoride layers on p-GaAs crystals have been achieved. The determination of electrical properties ' of MOS structures (p-Ga As/Anodic Sulfide(AS)/Aluminium(Al)orp-GaAs/AnodicFluoride(AF)/Aluminium(Al)), which was manufactured by growing Al metal on insulator layer and the obtained structural properties of p-GaAs/Anodic Oxide(AO)/Aluminium(Al) were compared with the ones existed in literature. In obtaining each of the three different p-GaAs MOS structures it goes through significant stages. The first one is an ohmic contact and research on this topic still continues. Also in this study there has been some problems in making of p-GaAs/ohmic contact. Long periods of time and various VIexperiences were needed to overcome these problems. The following most important points have been considered in overcoming the problems encountered in making Zn-Au ohmic contact of good quality: 1. p-GaAs crystal surface, on which ohmic contact will be grown, should not be oxidized. 2. When vacuum evaporation method is used for ohmic contact formation, consideration should be that Zn metal is easily oxidized and could not have good adhesion properties for the semiconductor surface, and also melting points of zinc and gold are quite different. 3. Flash annealing should be made to provid the conversion from Schottky contact to ohmic contact. In this process diffusion rate of zinc into the semiconductor is high. Also arsenic can easily evaporate from the GaAs. The remaining gallium forms an alloy with gold. 4. In liquid phase alloying process, the interface between the ohmic contact and GaAs is not clear. Also the obtained ohmic contact resistance could not be reproducible, but it can only be achieved in the order of magnitude. In the light of the above mentioned cases surface polishing, surface etching, metal growing, flash annealing and current-voltage measurement techniques are applied for the manufacture of p-GaAs/ohmic contact. The ohmic contact resistance reached is found to be almost equal to the specific resistance of the semiconductor. The determined specific resistance (2- 2.2x10' Qcm ) is almost equal to the one given in literature. The second step in obtaining the p-GaAs MOS structures is an insulator growth. The encountered difficulties at this stage are given as follows: 1. The crystal surface to be anodized should not be oxidized before the anodization. 2. The obtained insulator layer should indicate homogeneous distribution and be reproducible. 3. After the anodic process the electrical properties of insulator layer should not vary with time. vn4. Minimum current density, in anodization process, could vary according to electrolytes used. 5. The linear regions with different slopes for each anodization V-t curve indicates the change in chemical composition of the layer. 6. The anodization process is a function of the current density, electrolyte type, pH and mixing conditions. 7. The insulator layer obtained by anodization is porous and may contain some electrolyte. Annealing is required to remove this electrolyte. The annealing process also contributes to electrical stability in MOS structures. 8. In order to improve the coating quality by anodization the surface removal should be repeated several times. 9. The difference between the Ga and As ions affects the anodization movement between these ions. This effect should be minimized to obtain a good insulating layer. The anodization process, in the light of the above conditions, have been carried out with oxide, sulfide and fluoride coatings. In anodization process six different electrolyte have been used. The properties of possible compounds have been investigated. The investigation reveals that the anodic oxidation of GaAs leads to Ga203and As203; anodic sulfurization with leads to arsenic sulfide (As2S3) and gallium sulfide (Ga2S3); and anodic fluoridization is presumed to result in gallium fluoride (GaF3) insulating layers. As arsenic oxide is soluble in water, some deficiency of As203 on the oxide layer surface is expected. This supposition has been proven by advanced analytical techniques. The As203 produced during anodic oxidation is expected to undergo a reduction in solubility in electrolytes. This is only possible if electrolytes are saturated with As203 prior to the process. In several studies the tartaric acid + propylene glycol (AGW) system saturated with As203 the produced oxide layer maintained at every level, including the interfaces, a ratio of As203:Ga203=l:l. However, the electrical properties of such GaAs MOS structures have not been found in any literature. Also, there is no information on the saturation of AGW electrolyte, citric acid+ propylene glycol with respect to the effect on oxidation and GaAs MOS structures preparation. Therefore, in this study, AGW (tartaric acid + propylene glycol and citric acid + propylene glycol) systems which give the best results in anodic oxidation together with the saturated solutions of these vintwo electrolytes with arsenic oxide have been used. The effect of saturating with As203 in expanded oxides on the quality of GaAs MOS structures has been investigated. The anodization process at 0.1; 0.3; 0.5 and 0.7 mA/cm current densities using the electrolytes of nonaqueous ammonium sulfide in anodic sulfurization and nonaqueous ammonium fluoride in fluoridization has been carried out. Gallium sulfide grown in anodic sulfidization can be decomposed due to the presence of air and the moisture in air. The stable crystal structure(y) of this compound at normal temperature is zincblend. Thus in sulfidization it is possible to pass through a good quality of GaAs MOS structure by minimizing the dangling bonds at the interface of insulator and GaAs surfaces. During this transitions, the insulating layer should be. protected from atmospheric conditions. At some current densities of anodic fluoridization, as in anodic oxidation, a change in the slope of cell voltage vs. time (V-t) plots has been identified. This may be attributed to the change in chemical composition in the coating layer. This behavior has not been observed in the anodic sulfidization which indicates this homogeneous structure. As in all anodization processes, the grown layer in the anodic oxidation has been identified to have an amorphous structure by X-Rays diffractometer. Removal of the electrolyte present in the amorphous structure by annealing has not been tested. Although there are a number of experimental procedures on this subject, thermal treatment has been purposely avoided because one of the objective of this study was to obtain a high quality insulator layer without heat treatment. The third important phase in the manufacturing of p-GaAs MOS structures is the metal electrode preparation. As metal, relatively pure aluminum has been used in this study. The comparison of electrical properties of p-GaAs MOS structures has been evaluated with the help of- quasi-static I-V and high frequency C-V characteristic measurements. The results are summarized below: 1. The p-GaAs/AO/Al structures produced by anodic oxidation were found to have the same properties as in similar studies reported in literature. 2. The two electrolytes saturated with arsenic oxide used in anodic oxidation has not affected the oxide quality produced in tartaric acid solutions. But some decrease in the dielectric constant of the oxide produced in citric acid solutions were established. This was ascribed to the inability of IXarsen oxide to pass into the electrolyte. This provided an insulating layer with less porosity. 3. The quasi-static I-V characteristic measurements for p-GaAs MOS (p-GaAs/AO/Al, p-GaAs/AS/Al and p-GaAs/AF/Al) structures manufactured by coating anodic oxide, sulfide and fluoride, an expected behavior for each structure, have been observed. The characteristic behavior was observed with anodic sulfidized p-GaAs/AS/Al structure sample at 0.1 mA/cm current density. Compared to the other samples, it was found to be close to the ideal low frequency MOS structure's curve. 4. The anodization quality made in this study, as in all MOS structures,is determined by the interface state density (Nss). Nss should be low for the good quality manufacturing of MOS structure. For obtaining low Nss Values interface state charge density (Qss), insulator's capacity in the accumulation region (C ) and the deviation (A V) between the high frequency C-V and ideal MOS C-V curves should be lowered. In comparing the prepared MOS qualities, the flat band state values of Ngs, Qsg and AV ( NSSFB' QSSFB' AVFB ) have been USed> 5. The CQX and AV values calculated from p-GaAs MOS structures quasi-static I-V characteristic measurements have been compared. In the flat band states the smallest AVpg has been identified in the anodic sulfidized p- GaAs MOS ( p-GaAs/AS/Al ) structure produced at 0.1 mA/cm current density. The CQX values with insulating capacities in the accumulation region vary in the range of 10 and 10` F/cm for all three different growing MOS structures. An increase in the current density of anodization process results in a decrease in Cox values. The smallest value in Cox at 0.1 mA/cm current density has been observed in anodic oxide p-GaAs/AO/Al structure at 293K. In contrast to this, the smallest value of AVpg has been measured in anodic sulfidization. The lowest NSSFB value has been identified in anodic sulfidization. 6. The reason for left deviation (AV) of high frequency C-V curve with respect to the ideal MOS curve at all p-GaAs MOS structures is the positive charges within the insulating layer. The Ga, As ionic bonds produced in the semiconductor surface during anodization are not adequately filled by oxygen, sulfide or fluoride anions. These empty dangling bonds are open to charge transfer. This leads to instability in the electrical properties of p-GaAs MOS structures. In anodic sulfidization the formation of Ga2S3 in GaAs crystal structure reduces the number of unfilled bonds. Therefore, the sulfidization process has produced less value of Ngs.7. In high frequency C-V characteristic measurement curves of the three types p-GaAs MOS structures, hysteresis (AVHIS) with electronic character have been observed. The reason for hysteresis has been attributed to the electrolyte which remain in the pores of the insulating layer. This electrolyte is removed by annealing. But reproducibility in this process is low. For this reason, rather than annealing, an anodic growth without hysteresis is preferred. So far the high frequency C-V curves in anodically oxidized GaAs MOS structures, the hysteresis phenomenon has not been observed. But in this study the high frequency C-V curve for p-GaAs/AS/Al structures obtained under 0.1 mA/cm current density, no hysteresis hâs been observed. This can be explained on the basis of the more volatile nature of the electrolyte used in anodic sulfidization, the formation of Ga2S3 during anodization within the zincblend conforming structure, and the low temperature. Evaluation of the results show that the interface state density (NSSFB) at flat band for p-GaAs/AS/Al structure produced by nonaqueous ammonium sulfide electrolyte at 0.1 mA/cm current density and ambient temperature is found to be 6.5x10 cm`. This shows that this structure can be used for production of circuit elements. The absence of hysteresis in the high frequency C-V curve at 77K is an important development. In addition, in this structure, all other samples at 293K with respect to the magnitude of hysteresis in high frequency C-V curves, have shown lower hysteresis. This structure has achieved the interface state density (Nss=10 cm eV ) which has been sought for many years. The future studies will concentrate on the composition of the in-depth profile of the anodic sulfide layer. Also the behavior of the layer under atmospheric conditions as a function time needs to be investigated. In addition, the reduction of hysteresis with electronic character observed in high frequency C-V curves at room temperatures requires low temperature annealing studies. XI 137

ÖZET DAMLACIK YOĞUNLAŞMASINDA YÜZEY MALZEMESİNİN ÖZELLİKLERİNİN BİRİNCİL VE İKİNCİL ETKİLERİNİN ANALİTİK VE NÜMERİK OLARAK İNCELENMESİ Mahmut AYDIN Yüksek Lisans Tezi, Makina Müh. Bölümü Tez Yöneticisi: Doç.Dr. Cemil YAMALI Eylül 1991, 95 sayfa Bu çalışmada yoğuşma yüzeyinin termal özelliklerinin damlacık yoğuşması, ısı iletimi üzerindeki etkisi, malzeme içinde oluşan sıcaklık dağılımı analitik ve nümerik olarak çözülerek incelenmiştir. Tek ve izole bir damlacık halinde malzemedeki sıcaklık dağılımı Hankel Transformasyonu yardımıyla çözülmüştür. Damlacık yerine direnç modeli kullanılarak oluşturulan model aynı zamanda buhar damla ara yüzey ısı trans fer katsayısını da ele almıştır. Damlaların birbiri üzerinde oluşturdukları etkilersüperpozisyon tekniği kullanılarak hesaplanmıştır. Toplam ısı transferi, yüzeydeki be lirli damlalar için hesaplanıp tüm yüzey üzerinden belirli bir dağılıma göre entegre edilmiştir. Hesaplamalar sonunda, birincil malzeme yüzey etkisinin (% 30 civarında) ikincil malzeme yüzey etkisine gore çok daha fazla olduğu bulunmuştur. Anahtar Kelimeler: Damlacık yoğuşması, Ara yüzey ısı transferi katsayısı, Malzeme yüzey etkisi, Damlacık büyüklük dağılımı, Birincil malzeme yüzey etkisi, İkincil malzeme yüzey etkisi. BİLİM DALI KODU : 625.05.04 vı ABSTRACT AN ANALYTICAL AND NUMERICAL STUDY OF THE PRIMARY AND SECONDARY SUBSTRATE EFFECTS IN DROPWISE CONDENSATION AYDIN, Mahmut M.S. Thesis, Department of Mechanical Engineering Supervisor: Assoc.Prof.Dr. Cemil YAMALI September 1991, 95 pages In this work, the effect of the substrate material on dropwise condensation heat transfer is studied by solving the temperature distribution in the substrate material analytically. A solution to the temperature distribution under a single and isolated droplet is found by using Hankel transformation method. A simple resistance model that replaces the droplet on the condensation surface is assumed. Model also considers, an interfacial heat transfer coefficient at the interface of the vapor and condensate. By superimposing the solutions found for single droplets the interaction effects between the neighboring droplets are found. Total dropwise condensation heat 111transfer is calculated by integrating heat transfer rate through individual droplets over the entire droplet population. Computations showed that the primary substrate ef fect reduces the dropwise condensation heat transfer rate considerably (around 30 %). However, secondary substrate effect does not reduce the dropwise condensation heat transfer rate significantly. Key words: Dropwise condensation, Interfacial heat transfer coefficient, Substrate effect, Dropsize distribution, Primary substrate effect, Secondary sub strate effect. SCIENCE CODE: 625.05.04 IV 110

Le comportement des composants électroniques peut être significativement affecté par les propriétés des surfaces et interfaces dont ils sont constitués et qui tendent à réduire leurs performances en dessous des limites attendues dans le cas idéal. Dans le but de prévenir les effets indésirables induits par les surfaces sur les performances des dispositifs, une discipline scientifique s'est développée autour du terme « passivation » et s'est attachée à mettre en œuvre des traitements de surface associés à des dépôts de diélectriques avec les objectifs suivants : — conférer aux surfaces et interfaces les propriétés électriques requises pour un fonctionnement optimal du dispositif ; — stabiliser les propriétés des surfaces et interfaces en vue de supprimer toute perturbation ou évolution dans le temps des caractéristiques fonctionnelles du dispositif résultant de contraintes extérieures physicochimiques (contamination, oxidation...), thermiques et électriques. Les principales limitations introduites par les surfaces et interfaces dans le fonctionnement des composants électroniques sont présentées, en tenant compte des principales applications visées. L'exposé sera plus particulièrement centré sur le cas des surfaces et interfaces de GaAs et d'InP dont les caractéristiques électroniques spécifiques (blocage du niveau de Fermi et recombinaisons en surface, stabilité) seront examinées en rappelant les différentes hypothèses retenues à ce jour quant à la nature des défauts qui contrôlent ces caractéristiques. Les procédés de passivation développés pour neutraliser ces défauts, en prévenir la création ou en contrôler la répartition seront présentés.

Les proprietes d'un materiau composite dependent a la fois de celles du renfort, de la matrice et de l'interface. Afin de contribuer a la caracterisation des composites ceramiques SiC-SiC, nous avons etudie la microtexture de fibres de carbure de silicium (Nicalon) par des techniques de microscopie electronique par transmission. Nous avons montre que toutes les fibres presentent une phase de carbure de silicium microcristallisee. La taille des domaines diffractants varie de 0,6 a 5 nm selon la fibre. Certaines fibres presentent des segregations de carbone soit amorphe, soit turbostratique.