Zircaloy-2 and its sister alloy, Zircaloy-4, have extensive applications in the nuclear industry as core components in heavy water reactors and fuel cladding in both heavy and light water reactors. Intergranular stresses and texture can greatly affect the mechanical performance of these components. A complete understanding of the development of intergranular constraints and texture in Zircaloy-2 will allow an improved understanding of the plastic deformation of zirconium alloys, and the prediction of in-reactor deformation of tubes made by different manufacturing routes. Neutron diffraction was used to track the development of lattice strain and peak intensity in three dimensions for various crystallographic planes in samples cut from a rolled Zircaloy-2 slab. The samples were subject to room temperature compression or tension in-situ in the neutron spectrometer in each of the three principal directions of the slab. Textures in the deformed samples were measured using neutron diffraction. Strong evidence was found for tensile twinning in tensile tests in the plate normal direction and compression tests in the transverse and rolling directions. The lattice strain development inside the newly formed twins was recorded for the first time in a Zr alloy. An elasto-plastic self-consistent model and a visco-plastic self-consistent model were used to interpret the lattice strain and texture data, respectively. Various slip and twinning modes were considered in both models. Prism <a> slip, basal <a> slip, pyramidal <c+a> slip and tensile twinning were concluded to be indispensable, while pyramidal <a> slip was unnecessary in the modeling. The critical resolved shear stresses and hardening parameters were obtained by simultaneously achieving a ‘best-fit’ with the complete experimental data set. The effects of anisotropic latent hardening due to dislocation interactions were found to be critical, and the inclusion of Lankford coefficients as modeling constraints was necessary. This research provided a comprehensive experimental data set obtained by neutron diffraction, forming a sound basis to investigate active plastic deformation mechanisms and to rigorously test plasticity models and twinning models. The research also made a substantial improvement in understanding the plastic deformation of Zircaloy-2 through polycrystalline modeling by introducing extensive data sets to constrain the modeling parameters. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2007-12-21 11:56:23.743 / NSERC, COG, OPG and Nu-Tech Precision Metals

No description available.

Doctor of Philosophy (PhD) / This thesis aims to establish a sound scientific methodology for the effective and efficient polishing of thermally stable PCD composites (consisting of diamond and SiC) for cutting tools applications. The surface roughness of industrial PCD cutting tools, 0.06 μm Ra is currently achieved by mechanical polishing which is time consuming and costly because it takes about three hours to polish a 12.7 mm diameter PCD surface. An alternative technique, dynamic friction polishing (DFP) which utilizes the thermo-chemical reactions between the PCD surfaces and a catalytic metal disk rotating at high peripheral speed has been comprehensively investigated for highly efficient abrasive-free polishing of PCD composites. A special polishing machine was designed and manufactured in-house to carry out the DFP of PCD composites efficiently and in a controllable manner according to the requirements of DFP. The PCD polishing process and material removal mechanism were comprehensively investigated by using a combination of the various characterization techniques: optical microscopy, SEM and EDX, AFM, XRD, Raman spectroscopy, TEM, STEM and EELS, etc. A theoretical model was developed to predict temperature rise at the interface of the polishing disk and PCD asperities. On-line temperature measurements were carried out to determine subsurface temperatures for a range of polishing conditions. A method was also developed to extrapolate these measured temperatures to the PCD surface, which were compared with the theoretical results. The material removal mechanism was further explored by theoretical study of the interface reactions under these polishing conditions, with particular emphasis on temperature, contact with catalytic metals and polishing environment. Based on the experimental results and theoretical analyses, the material removal mechanism of dynamic friction polishing can be described as follows: conversion of diamond into non-diamond carbon takes place due to the frictional heating and the interaction of diamond with catalyst metal disk; then a part of the transformed material is detached from the PCD surface as it is weakly bonded; another part of the non-diamond carbon oxidizes and escapes as CO or CO2 gas and the rest diffuses into the metal disk. Meanwhile, another component of PCD, SiC also chemically reacted and transformed to amorphous silicon oxide/carbide, which is then mechanically or chemically removed. Finally an attempt was made to optimise the polishing process by investigating the effect of polishing parameters on material removal rate, surface characteristics and cracking /fracture of PCD to achieve the surface roughness requirement. It was found that combining dynamic friction polishing and mechanical abrasive polishing, a very high polishing rate and good quality surface could be obtained. The final surface roughness could be reduced to 50 nm Ra for two types of PCD specimens considered from pre-polishing value of 0.7 or 1.5 μm Ra. The polishing time required was 18 minutes, a ten fold reduction compared with the mechanical abrasive polishing currently used in industry.

Στη συγκεκριμένη διπλωματική εργασία μελετάται η δομή και η λειτουργία φωτοβολταϊκών πλαισίων πολυκρυσταλλικού πυριτίου. Για το σκοπό αυτό είναι απαραίτητη τόσο η θεωρητική μελέτη και περιγραφή της λειτουργίας τους, όσο και η πειραματική προσέγγιση του θέματος. Αρχικά, παρουσιάζεται η δομή των ηλιακών κυττάρων, βασικών δομικών μονάδων των φωτοβολταϊκών πλαισίων. Στην αρχή δίνεται μια περιεκτική περιγραφή της λειτουργίας της p-n επαφής ώστε στη συνέχεια να γίνει ευκολότερα κατανοητός ο τρόπος που επιδρά το φωτοβολταϊκό φαινόμενο στη δομή αυτή. Αναλύονται ορισμένα μεγέθη που χρησιμοποιούνται στην επιστήμη των φωτοβολταϊκών καθώς και οι συνθήκες στις οποίες μετρώνται παγκοσμίως τα ηλιακά κύτταρα/πλαίσια προκειμένου να υπάρχει ένα κοινό μέτρο σύγκρισης. Η μελέτη ολοκληρώνεται με την πειραματική διαδικασία. Σε αυτήν αναλύονται διεξοδικά οι παράγοντες που επηρεάζουν τη λειτουργία των φωτοβολταϊκών σε μια πραγματική εγκατάσταση. Οι παράγοντες αυτοί είναι κυρίως περιβαλλοντικοί (ηλιοφάνεια, θερμοκρασία). Υπάρχουν εξίσου σημαντικοί παράγοντες, όμως, που είναι δυνατό να μεταβληθούν από τον άνθρωπο με τρόπο ώστε να επιτευχθεί η βέλτιστη απόδοση. Πιο συγκεκριμένα, η γωνία κλίσης του πλαισίου και η περίπτωση της σκίασής του είναι απαραίτητο να ληφθούν σοβαρά υπόψη. Τα συμπεράσματα που προέκυψαν έχουν άμεση εφαρμογή στον υπολογισμό και τη μελέτη μιας πραγματικής εγκατάστασης μιας και δίνουν συγκεκριμένες αριθμητικές τιμές. Για παράδειγμα η συνολική αποδιδόμενη ετήσια ενέργεια από ένα πλαίσιο 80Wp τοποθετημένο με γωνία κλίσης ίση με τη βέλτιστη (380) στην περιοχή της Πάτρας είναι 172.038kWh. Αξιοσημείωτη είναι και η σύγκριση των πειραματικών τιμών ισχύος και συντελεστή απόδοσης με τις τιμές του κατασκευαστή και αυτές που προέκυψαν μέσω μοντελοποίησης (σε υπολογιστή με τα προγράμματα Matlab και Mathematica). Αυτές είναι: η μετρούμενη ισχύς του πλαισίου 73,15Watt και συντελεστής απόδοσης η=11,5%, ισχύς διδόμενη από τον κατασκευαστή 81,71Watt με συντελεστή απόδοσης η=12,6% και ισχύς η που προκύπτει από τη μοντελοποίηση 89,95Watt με συντελεστή απόδοσης η=14,2%. Η αιτιολόγηση αυτών των διαφορετικών τιμών ισχύος και των αντιστοίχων συντελεστών απόδοσης αποδίδεται στην αδυναμία να πετύχουμε ίδιες συνθήκες διεξαγωγής αυτών των μετρήσεων καθώς και στην σε σειρά και παράλληλη αντίσταση που δεν είναι δυνατόν να εκτιμηθούν ακριβώς για να εισαχθούν στο μοντέλο. / This thesis studies the structure and performance of polycrystalline silicon solar modules. To do this, not only a theoretical study of their operation is necessary, but also an experimental approach of the subject. In a first step, we can see the structure of polycrystalline silicon solar cells, which compose the solar panels. It was thought useful to give a compact description of the –p-n junction function. This way, the photovoltaic phenomenon’s impact on –p-n junction’s function can be easier understood. Along with the theoretical part, there is an analysis of some values that are used to the photovoltaic science along with the conditions that are used in order to have a common meter of comparison. A study, however, would not be completed if the experimental process did not exist. In this process the factors that influence the photovoltaic operation are analyzed at great length in a real installation. These factors are mainly environmental (sunlight, temperature). There are equally important factors, however, which are possible to be altered in such a way to achieve the most optimal performance. Specifically, the tilt angle and the shading case of the solar module are essential to be taken seriously into consideration. The results can be directly used for the calculation of a real installation and are very helpful as they are quite specific. For example, the total output power with a tilt angle of 380 at Patras-Greece is 172.038kWh. It is also remarkable to have a comparison between the experimental data, the data given by the constructor and the data gathered through simulation method. The values for the output power are 73,15Watt (η=11,5%), 81,71Watt (η=12,6%) and 89,95Watt (η=14,2%) respectively. The explanation of different power factor and output power comes from the inability to achieve exactly the same experimental conditions. Moreover, the shunt and series resistances cannot be calculated exactly due to lack of constructor’s data details.

Στην παρούσα διπλωματική εργασία μελετάται η λειτουργία φωτοβολταϊκών πλαισίων πολυκρυσταλλικού πυριτίου και συγκεκριμένα γίνεται εξαγωγή των dc παραμέτρων (ηλεκτρικά χαρακτηριστικά) του συγκεκριμένου τύπου φωτοβολταϊκού πλαισίου υπό φωτισμό σε πραγματικές συνθήκες λειτουργίας. Αρχικά παρατίθεται η θεωρία για τα ηλιακά κύτταρα που είναι η βασική δομική μονάδα του φωτοβολταϊκού πλαισίου. Για να μπορεί να γίνει εύκολα αντιληπτό σε όλους το φωτοβολταϊκό φαινόμενο, δίδεται μια διεξοδική περιγραφή της λειτουργίας της p-n επαφής. Παράλληλα, μελετώνται κάποια προβλήματα που μπορεί να προκύψουν στις φωτοβολταϊκές εγκαταστάσεις και οι πιθανοί τρόποι σύνδεσης μιας οικιακής εγκατάστασης. Στην συνέχεια ακολουθεί το πειραματικό μέρος. Σε αυτό παρουσιάζεται μια σειρά μετρήσεων που διεξήχθησαν κατά την διάρκεια του ακαδημαικού έτους 2008-2009 και η χάραξη γραφικών παραστάσεων μέσω των οποίων καταδεικνύεται πόσο επηρεάζεται η λειτουργία των φωτοβολταϊκών πλαισίων από κάποιους περιβαλλοντικούς παράγοντες σε διαφορετικές εποχές. Τα συμπεράσματα που προέκυψαν από την πειραματική διαδικασία παρέχουν γνώση για την μελέτη μιας πραγματικής εγκατάστασης στην περιοχή της Πάτρας. Το πιο σημαντικό αποτέλεσμα είναι η ετήσια συνολική αποδιδόμενη ενέργεια από το πλαίσιο πολυκρυσταλλικού πυριτίου των 80W σε κλίση 38 μοίρες στην περιοχή της Πάτρας που είναι 98 KWh/έτος. Στη μελέτη αυτή περιλαμβάνεται και μια πρόταση εγκατάστασης φωτοβολταϊκών στην ταράτσα της φοιτητικής εστίας του Πανεπιστημίου Πατρών. Λαμβάνοντας υπόψιν μας τις ενεργειακές ανάγκες της φοιτητικής εστίας, έγινε προσπάθεια να βρεθεί μια λύση τοποθέτησης των φωτοβολταϊκών πλαισίων, έτσι ώστε το σύστημά μας να είναι λειτουργικό καλύπτωντας όσο το δυνατό τις ανάγκες για ηλεκτρική ενέργεια. Θεωρείται όμως αναγκαίο να αναφερθεί οτι οι πειραματικές μετρήσεις στις οποίες στηρίζεται η μελέτη αυτή συνιστούν ένα μέρος μόνο των μετρήσεων οι οποίες απαιτούνται για την πλήρη ανάπτυξη και διερεύνηση του θέματος που πραγματεύεται η παρούσα Διπλωματική εργασία. / The present thesis studies the operation of polycrystalline silicon solar modules and concretely the export of dc parameters (electric characteristics) of the particular type of solar module under real conditions of operation. Initially, the thesis mentions the theory of the solar cells that are the basic structural unit of solar modules. In order the photovoltaic phenomenon, to be easier understood to all people, an extensive description of operation of p-n junctions is given. At the same time, certain problems which come out in photovoltaic installations are studied and the likely ways of connection of domestic installation. Then, the experimental part follows. At this part, a group of measurements are presented which were made at the duration of academic year 2008-2009 and the mapping out of graphic representations, which shows the influence of the operation of solar modules from certain environmental factors per season. The results that came out from the experimental process constitute knowledge for the study of a real installation at the region of Patras-Greece. The most important result is the annual total energy yield from polycrystalline silicon solar module of 80W αt tilt angle 38 degrees at Patras being 98 KWh/year. It is included in this study an indicative photovoltaic installation at the flat-roof of students‟ housing of University of Patras. Knowing the energy needs of students‟ housing, we try to find a solution of placement of solar modules, so our system to be functional as long as possible for the needs for electric energy. It is however necessary to mention that the experimental measurements on which this study is built constitute a part only of the measurements required for the full development and investigation of the issue addressed by this thesis.

abstract: Zinc telluride (ZnTe) is an attractive II-VI compound semiconductor with a direct bandgap of 2.26 eV that is used in many applications in optoelectronic devices. Compared to the two dimensional (2D) thin-film semiconductors, one-dimensional (1D) nanowires can have different electronic properties for potential novel applications. In this work, we present the study of ZnTe nanowires (NWs) that are synthesized through a simple vapor-liquid-solid (VLS) method. By controlling the presence or the absence of Au catalysts and controlling the growth parameters such as growth temperature, various growth morphologies of ZnTe, such as thin films and nanowires can be obtained. The characterization of the ZnTe nanostructures and films was performed using scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), high- resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD), photoluminescence (PL), Raman spectroscopy and light scattering measurement. After confirming the crystal purity of ZnTe, two-terminal diodes and three-terminal transistors were fabricated with both nanowire and planar nano-sheet configurations, in order to correlate the nanostructure geometry to device performance including field effect mobility, Schottky barrier characteristics, and turn-on characteristics. Additionally, optoelectronic properties such as photoconductive gain and responsivity were compared against morphology. Finally, ZnTe was explored in conjunction with ZnO in order to form type-II band alignment in a core-shell nanostructure. Various characterization techniques including scanning electron microscopy, energy-dispersive X-ray spectroscopy , x-ray diffraction, Raman spectroscopy, UV-vis reflectance spectra and photoluminescence were used to investigate the modification of ZnO/ZnTe core/shell structure properties. In PL spectra, the eliminated PL intensity of ZnO wires is primarily attributed to the efficient charge transfer process occurring between ZnO and ZnTe, due to the band alignment in the core/shell structure. Moreover, the result of UV-vis reflectance spectra corresponds to the band gap energy of ZnO and ZnTe, respectively, which confirm that the sample consists of ZnO/ZnTe core/shell structure of good quality. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2017

A estrutura da florencita foi refinada pelo método de mínimos quadrados, utilizando dados experimentais obtidos através do método de Debye-Scherrer. A coleta dos dados das intensidades integradas foi feita através da leitura do difratograma de pó por um microdensitômetro óptico automático, e empregando métodos de análise numérica para fazer a integração da função (2&#952,Y), tabelada a pontos eqüidistantes. Foram observados 14 picos de difração e as reflexões que se superpunham contribuindo para as intensidades dos picos foram identificadas e suas contribuições levadas em conta através de seus fatores de multiplicidade. O refinamento foi feito com o programa POWLS (Powder Least Squares) e inicialmente foram fornecidos os parâmetros posicionais dos átomos da Goyazita, que é isomorfa com a florencita. As intensidades observadas foram corrigidas pelos fatores de Lorentz-polarização e adsorção. O índice de discordância R atingido para os 14 picos de difração observados foi de 0.097. A fórmula molecular da florencita é CeAl3(PO4)2(OH)6. O composto cristaliza no sistema hexagonal com parâmetros de rede ao=6.96&#197; co=16.33&#197; &#945= &#946 = 90&#176; &#947=120&#176; V=685.07&#1973. O grupo espacial é R3m com Z=3 e densidade calculada igual a 3.67g.cm-3. / The crystal structure of the florencita was refined by least squares using experimental data obtained with the Debye-Scherrer method. An automatic optical microdensitometer was used for the data collection from powder difractogram and numerical analysis methods for the integration of the function (2&#952,Y) which is tabulated at equidistant points. 14 diffraction peaks were observed, reflections which superpose contributing to the same peak were identified and their contributions were taken in account using multiplicity factors. The program POWLS (Powder Least Squares) was used for the refinement and initially the positional parameters of the atoms of the Goyazite, which is isomorfous with the florencita were used. Intensities were corrected for the Lorentz, polarization and absorption factors. The final R factor for the 14 peaks was of 0.097. The molecular formula of the florencitais CeAl3(PO4)2(OH)6. It crystallizes in the hexagonal system, space group R3m with cell ao=6.96&#197; co=16.33&#197; &#945= &#946 = 90&#176; &#947=120&#176; V=685.07&#1973.

Méthodologie de mesures de contraintes avec la méthode multireflection pâturage d'incidence(MGIXD) a été étudié et développé. La géométrie du faisceau parallèle a été appliquée pour mensurationsde stress. Le faisceau incident dans diffractomètres classiques a été collimaté par le miroir Göbel et lesessais de configuration en parallèle ont été effectuées pour Al poudre. Les résultats confirmé que le erreurstatistique et l'erreur d'alignement peuvent être réduits lorsque le miroir Göbel est utilisé. Facteursphysiques ont été prises en compte dans la CSX (analyse aux rayons X du stress): Lorentz - polarisationet facteur d'absorption (LPA) et aussi correction de la réfraction (RC). Les résultats montrent quel'influence de LPA est mineur dans CSX, mais la RC peut influencer de manière significative l'analyse.Dans la thèse de la question de RC a été examiné et comparé avec les approches présentées dans lalittérature. Dans la thèse de deux développements théoriques de la méthode MGIXD ont été présentés: laprocédure de détermination de paramètre c/a et l'influence des défauts d'empilement sur les résultats. Il aété montré que les deux développements améliore de manière significative la qualité de l'analyse desdonnées expérimentales. Dans le présent travail le problème de la X -ray facteurs de stress (XSF) utiliséspour l'interprétation des résultats CSX a été étudiée. Différents modèles théoriques de grains élastoplastiqueinteraction ont été envisagées et appliquées dans la CSX. Vérification de la XSF durant l'essaide traction pour l'échantillon élastique anisotrope (en acier inoxydable austénitique) et pour l'échantillonisotrope (Ti - note2). Anisotropie de XSF a également été observée dans: rectifié alliage Ni, acierinoxydable austénitique poli et revêtement CrN. Les résultats montre que Reuss et modèle de la surfacelibre sont en meilleur accord avec les résultats expérimentaux. Enfin, la méthode MGIXD a été vérifiée enutilisant le rayonnement synchrotron et 3 longueurs d'onde différentes. La méthodologie a été développéepour traiter les données non seulement pour les différents angles d'incidence, mais aussi en utilisantdifférentes longueurs d'onde simultanément. Contraintes en fonction de «vraie profondeur» a été calculéeen utilisant la transformée de Laplace inverse. Analyse Wiliamson-Hall a été appliquée pour les données.Méthode MGIXD a été appliqué pour les mesures de diffraction de dispersion d'énergie dans lequel lefaisceau blanc a été utilisé: 0,3 à 0,18 Å. L' analyse des contraintes a été effectuée en utilisant troisméthodes différentes : la méthode de sin2ψ norme, la méthode de terrain universelle et en utilisantmultireflection analyse . Dans la gamme de profondeur de pénétration à 0-15 um de la convergence desrésultats obtenus à partir de différentes méthodes a été acquise . En outre, les données de synchrotronparfaitement en accord avec les résultats obtenus en laboratoire sur diffractomètre (rayonnement Cu Ka) àproximité de la surface . Pour profondeur supérieure à 14 um points expérimentaux présentent desvariations importantes et ne sont pas d'accord avec les résultats de la méthode standard.Mots clés : contraintes résiduelles, diffraction des rayons X, méthode de l’incidence rasante, miroir Göbel / Methodology of stress measurements with multireflection grazing incidence method (MGIXD)was investigated and developed. The parallel beam geometry was applied. The incident beam in classicaldiffractometers was collimated by Göbel mirror and the tests of parallel configuration were performed for Alpowder. Results confirmed that both statistical error and the misalignment error can be reduced when theGöbel mirror is used. Physical factors were taken into account in XSA (X-ray stress analysis): Lorentzpolarizationand absorption factor (LPA) and also refraction correction (RC). Results showed that theinfluence of LPA correction is minor in XSA but the RC can significantly influence analysis. In the thesisthe issue of RC was considered and compared with approaches presented in the literature. In the thesistwo theoretical developments of the MGIXD method were presented: the procedure of c/a parameterdetermination and the influence of stacking faults on the results was taken into account. It was shown thatboth developments significantly improves the quality of experimental data analysis. In the present work theproblem of X-ray stress factors (XSF) used for the interpretation of XSA results was studied. Differenttheoretical grain elasto-plastic interaction models were considered and applied in XSA. Verification of theXSF was during tensile test for austenitic stainless steel and for the isotropic sample. Anisotropy of XSFwas also observed in: ground Ni alloy, polished austenitic stainless steel and CrN coating. The resultsshows that Reuss and free surface grain interaction models are in the best agreement with theexperimental results. Finally the MGIXD method was verified using synchrotron radiation and 3 differentwavelengths. The methodology was developed to treat data not only for different incident angles but alsousing simultaneously different wavelengths. Stresses vs. z – ‘real depth’ was calculated using the inverseLaplace transform applied to polynomial function. Wiliamson-Hall analysis was applied for collected data.Next multireflection method was applied for the energy dispersion diffraction measurements in which whitebeam containing radiation having different wavelengths was used (λ (Ǻ): 0.3–0.18/ E (keV): 40-68). Thestress analysis was performed using three different methods: standard sin2ψ method, Universal plotmethod and by using multireflection analysis. In the range of penetration depth to 0-15 μm theconvergence of the results obtained from different methods was gained. Moreover the synchrotron dataperfectly agree with the results obtained on laboratory diffractometer (Cu Kα radiation) close to the surface.For depth larger than 14 μm the experimental points exhibit significant spread and do not agree with theresults of standard method

M.Sc. / The efficiency of commercial polycrystalline silicon solar cells is currently 12% and 15% in the case of single crystalline cells. It is possible to lose about half of the open circuit voltage due to inferior contacts on the cell. It is thus clear that inferior contacts can seriously impede the relative low efficiency and care should be taken to make good ohmic contacts. Experiments were done to evaluate the influence of several factors on the quality and stability of the contacts. 1 C2•cm p-type polycrystalline silicon and 3 52.cm n-type single crystalline silicon were primarily used for these experiments. Results of molybdenum contacts on n-type silicon are also presented and the problems with silver epoxy contacts are discussed. It was found that aluminium contacts on p-type polycrystaline silicon improve with temperature and time, while those on single crystaline n-type degrade with temperature and time. These changes are already present at room temperature and are attributed to solid state diffusion of the aluminium into the silicon. This results in a p + layer. In the case of contacts on p-type, the behaviour is that of a Schottky diode. After the solid state diffusion, it becomes possible for the charges to quantum mechanically tunnel through the p+ layer. This results in an improvement of the contact. The contacts on n-type however, are ohmic just after evaporation. Similar to the p-material, the p+ layer causes a p+-n-junction with the depletion layer primarily in the n-type material. This causes a degradation in the contact quality. It is possible to achieve good quality contacts on polycrystaline p-type material, by annealing the contacts above 500°C for one minute. These contacts however, are non-ideal. SEM photographs show that the silicon surface is crated by pits due to solid state diffusion. It is only at these pits that conduction through the Schottkybarrier is possible. Since the area of the pits constitutes only a portion of the total area, only a portion of the surface will partake in conduction. Contact resistance is always present. For pm sized contacts on integrated circuits, the spesific resistance is of the order of 10 -6 Q.cm2. Contacts on solar cells, however, are of millimetre dimensions and the spesific resistance can be four orders of magnitude larger. The conduction through the surface can be modelled as conduction through a surface that is constituted of a mixture of minute ohmic and diode surfaces.

M.Sc. / CuInSe2 (CIS) is considered to be one of the most promising candidates for high efficiency thin film solar cells. The reaction of metallic alloys to a reactive selenium atmosphere (H2Se/Ar or elemental Se vapour) is a promising growth technique to produce CIS thin films of high crystalline quality. However, up to now, the control of the final film quality has been critically influenced by the loss of material and subsequent formation of detrimental binary phases during the high temperature selenization stages. In this study, it is shown that this phenomenon is strongly related to the selenization temperature and, in particular, the ramping procedure followed to the final selenization temperature. Metallic alloys which were selenized in H2Se/Ar at 400°C or slowly heated in 20 minutes to temperatures around 400°C were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD) to have nonuniform surface morphologies, highly defected 0.8-2 !lm sized grains and to contain Cuselenide binary phases. Energy dispersive X-ray spectroscopy (EDS) analysis confirmed the generally reported sharp increase in the Cu/In atomic ratio for these classes of samples. In contrast, rapid heating (in 2 minutes) of identical metallic alloys to temperatures above 400°C, resulted in uniform, dense films with low defect density 1 !lm sized grains void of any evidence of secondary phases. X-ray fluorescence (XRF) Kal,2 measurements of metallic alloys at different stages of selenization revealed no evidence of material losses. XRF depth profiles, however, explained this discrepancy by revealing a pronounced segregation of In towards the Mo back contact when the samples were selenized at 400°C, or slowly heated to temperatures around 400°C. This segregation was dramatically reduced in films rapidly heated and selenized at temperatures above 400°C. For the purpose of comparison, metallic alloys were also reacted to elemental Se vapour. The structural features (grain size and preferred orientation) ofthese films differed significantly from those selenized under similar conditions in H2Se/Ar. The results from this study, including photoluminescence (PL) measurements obtained from these films, were used to affect the fabrication of CIS absorbers with excellent material properties and solar cell devices with moderate conversion efficiencies.