The purpose of this Dissertation is to investigate the chemistry at interfaces between organic active materials and two electrodes, namely organic metal oxide cathode and metal anode, in organic photovoltaic (OPV) devices. Poor compatibility and energy level mismatch at organic/transparent metal oxide (TCO) interfaces is a long standing challenge which limits interfacial electron transfer efficiency. Phosphonic acid modifiers on TCO surfaces are able to improve interface compatibility and energy alignment. Chapters 3 and 4 in this Dissertation investigate the fundamental formation, quality and orientation of phosphonic acid monolayers on indium-doped zinc oxide (IZO) surfaces, a model TCO. Metal electrode deposition on organic active layer materials is a common last step of OPV device fabrication. Chapters 5-8 in this Dissertation explore possible molecular processes at organic-metal interfaces when metal deposition occurs under ultra-high vacuum conditions. Choosing octylphosphonic acid (OPA), F₁₃-octylphosphonic acid (F₁₃OPA), pentafluorophenyl phosphonic acid (F₅PPA), benzyl phosphonic acid (BnPA), and pentafluorobenzyl phosphonic acid (F₅BnPA) as a representative group of modifiers, Chapter 3 describes polarization modulation-infrared reflectance-absorbance spectroscopy (PM-IRRAS) of binding and molecular orientation on IZO substrates. Considerable variability in molecular orientation and binding type is observed with changes in PA functional group. OPA exhibits partially disordered alkyl chains, but on average, the chain axis is tilted 57° from the surface normal; F13OPA tilts 26° with mostly tridentate binding; the F₅PPA ring orients 72° from the surface normal with a mixture of bidentate and tridentate binding; the BnPA ring orients 59° from normal with a mixture of bidentate and tridentate binding, and the F₅BnPA ring orients 45° from normal with a majority of bidentate with some tridenate binding. These trends are consistent with what has been observed previously for the effects of fluorination on orientation of phosphonic acid modifiers. The results from PM-IRRAS are well correlated with recent results on similar systems from near-edge x-ray absorption fine structure (NEXAFS) and density functional theory (DFT) calculations. Overall, these results indicate that both surface binding geometry and intermolecular interactions play important roles in dictating orientation of PA modifiers on TCO surfaces. This work also establishes PM-IRRAS as a routine method for SAM orientation determination on complex oxide substrates. In addition to orientation studies the effect of PA deposition method on the formation of close-packed, high-quality monolayers is investigated in Chapter 4 for SAMs fabricated by solution deposition, microcontact printing, and spray coating. The solution deposition isotherm for perfluorinated benzylphosphonic acid (F₅BnPA) on IZO is studied using PM-IRRAS at room temperature as a model PA/TCO system. Fast surface adsorption occurs in the first minute; however, well-oriented high-quality SAMs are reached only after ~48 h, presumably through a continual process of molecular adsorption/desorption accompanied by molecular reorientation. Two other rapid, soak-free deposition techniques, microcontact printing and spray coating, are also explored. SAM quality is compared for deposition of phenyl phosphonic acid (PPA), F₁₃-octylphosphonic acid (F₁₃OPA), and perfluorinated benzyl phosphonic acid (F₅BnPA) by solution deposition, microcontact printing and spray coating using PM-IRRAS. In contrast to microcontact printing and spray coating techniques, 48-168 h solution depositions at both room temperature and 70 °C result in contamination- and surface etch-free close-packed monolayers with good reproducibility. SAMs fabricated by microcontact printing and spray coating are much less well ordered.Oligothiophenes are building blocks of the popular organic donor materials polythiophene and P3HT. In Chapters 6 and 7, interfacial reactions of the model thiophene-based oligomers, ɑ-sexithiophene (ɑ-6T) and 2, 2’:5’, 2”-terthiophene (ɑ-3T), with vapor deposited Ag, Al, Mg and Ca are investigated using surface Raman spectroscopy under ultra-high vacuum conditions. Results indicate that Al and Ca cause reduction of ɑ-6T to tetrahydrothiophene and calcium sulfite, respectively, with Al exhibiting less reactivity than Ca. Partial electron donation from the sulfur atom lone pair electrons to vacant Ag and Mg d or p orbitals is observed, inducing formation of polaron states at the interface. Inter-ring C-C bond rotation is also induced by this electron sharing betweenɑ-6T and both Ag and Mg. This unexpected evolution of ɑ-6T interfaces with low work function metals alters the interfacial energetics through the formation of “gap” states which ultimately impact device performance. Vapor deposited Ag forms nanoparticles on the surface and induces considerable surface enhanced Raman scattering (SERS) of the ɑ-3T along with a change in molecular symmetry and formation of Ag-S bonds; no other reaction chemistry is observed. Vapor deposited Al and Ca exhibit chemical reaction withɑ-3T spectrum initiated by metal-to-3T electron sharing. For Al, the resulting product is predominantly amorphous carbon (a-C) through initial radical formation and subsequent decomposition reactions. For Ca, the spectral evidence suggests two pathways: one leading to ɑ-3T polymerization and the other resulting in thiophene ring opening, both initiated by radical formation through Ca-to-ɑ-3T electron transfer. In Chapter 8, metal penetration depth into ɑ-3T and ɑ-6T films is investigated and compared between Ag, Al, Mg and Ca using Raman and X-ray photoelectron spectroscopies. Mg exhibits the greatest penetration with no observable surface metallization on 50 ML (15 nm) OT surfaces. Ag shows moderate penetration and metallization ability with no reaction chemistry when in contact with ɑ-6T. Al and Ca exhibit the least penetration and greatest metallization abilities, possibly due to reaction chemistry occurring between Al (or Ca) and ɑ-6T. Al and Ca both penetrate up to 10-14 nm intoɑ-6T layers. The penetration process for Ca consists of two distinct phases. Ca tends to be more evenly distributed throughout the entire ɑ-6T film and reduce the native ɑ-6T until the composition of the top 5-7 nm of the ɑ-6T film becomes constant; beyond this point, further Ca deposition penetrates and completely reduces ɑ-6T into CaS throughout the entire 10-14 nm thickness. Al atoms are more concentrated within the top 5-7 nm of the film and gradually penetrate deeper into the film. These results reveal significant but varying depths of the impact of deposited metals on OT thin films during physical vapor deposition; these results further reinforce the critical role of interfacial chemistry on organic electronic device performance.

Les mémoires à pont conducteur (CBRAM) sont une option actuellement étudiée pour la prochaine génération de mémoires non volatiles. Le stockage des données est basé sur la commutation de la résistivité entre les états de résistance élevée (HRS) et faible (LRS). Sous polarisation électrique, on suppose qu'un trajet conducteur est créé par la diffusion des ions de l'électrode active dans l'électrolyte solide. Récemment, une attention particulière a été portée sur les dispositifs contenant un élément semi-conducteur tel que le tellure, fonctionnant avec des courants réduits et présentant moins de défaillances de rétention. Dans ces « subquantum CBRAMs », le filament est censé contenir du tellure, ce qui donne une conductance de 1 atome (G₁atom) significativement réduite par rapport aux CBRAMs standard et permettant ainsi un fonctionnement à faible puissance. Dans cette thèse, nous utilisons la spectroscopie de photoélectrons par rayons X (XPS) pour étudier les réactions électrochimiques impliquées dans le mécanisme de commutation des CBRAMs à base de Al₂O ₃ avec des alliages ZrTe et TiTe comme électrode active. Deux méthodes sont utilisées: i) spectroscopie de photoélectrons par rayons X de haute énergie non destructive (HAXPES) pour étudier les interfaces critiques entre l'électrolyte (Al₂O ₃ ) et les électrodes supérieure et inférieure et ii) les faisceaux d'ions à agrégats gazeux (GCIB), une technique de pulvérisation qui conduit à une dégradation plus faible de la structure, avec un profilage en profondeur XPS pour évaluer les distributions des éléments en profondeur. Des mesures ToF-SIMS sont également effectuées pour obtenir des informations complémentaires sur la répartition en profondeur des éléments. Le but de cette thèse est de clarifier le mécanisme de changement de résistance et de comprendre les changements chimiques aux deux interfaces impliquées dans le processus de « forming » sous polarisation positive et négative ainsi que le mécanisme de « reset ». Pour cela, nous avons effectué une comparaison entre le dispositif vierge avec un état formé, i.e. l'échantillon après la première transition entre HRS et LRS et un état reset, i.e. l'échantillon après la première transition entre LRS et HRS.L'analyse du « forming » positif pour les dispositifs ZrTe / Al₂O ₃ a montré une libération de Te liée à l’oxydation de Zr due au piégeage de l'oxygène de l'Al₂O ₃ sous l’effet du champ électrique. D'autre part, pour les dispositifs TiTe / Al₂O ₃, la présence d'une couche importante d'oxyde de titane à l'interface avec l'électrolyte a provoqué une dégradation permanente de la cellule en polarisation positive. Pour le « forming » négatif, nos résultats montrent un mécanisme hybride, à savoir une combinaison de formation de lacunes d'oxygène dans l'oxyde provoquée par la migration de O2- entraîné par le champ électrique vers l'électrode inférieure et la libération de tellure pour former des filaments conducteurs. De plus, les résultats obtenus par profilométrie XPS et ToF-SIMS ont indiqué une possible diffusion de Te dans la couche d'Al₂O ₃. Lors du « reset », il y a une recombinaison partielle des ions oxygène avec les lacunes d'oxygène près de l'interface TiTe / AlAl₂O ₃ avec une perte de Te. Un mécanisme hybride a également été observé sur les dispositifs ZrTe / Al₂O ₃ pendant le « forming » négatif. En tenant compte du rôle important de la migration d'oxygène dans la formation / dissolution des filaments, nous discutons également des résultats obtenus par XPS avec polarisation électrique in- situ (sous ultravide) pour mieux comprendre le rôle de l'oxydation de surface et des interfaces dans la commutation résistive. / Conducting bridging resistive random accessmemories (CBRAMs) are one option currently investigated for the next generation of non volatile memories. Data storage is based on switching the resistivity between high (HRS) and low (LRS) resistance states. Under electrical bias,a conductive path is assumed to be created by ions diffusion from the active electrode into the solid electrolyte. Recently, special attention has been drawn to devices containing an elemental semiconductor such as tellurium, operating with reduced currents and less retention failures. In these subquantum CBRAM cells, the filament is thought to contain tellurium , yielding a 1-atomconductance (G₁atom) significantly reduced compared to standard CBRAMs and thus allowing low power operation. In this thesis, we use X-rayphotoelectron spectroscopy (XPS) to learn about electrochemical reactions involved in the switching mechanism of Al₂O₃ based CBRAMswith ZrTe and TiTe alloys as active electrode. Two methods are used: i) non-destructive Hard X-ray photoelectron spectroscopy (HAXPES) to investigate the critical interfaces between the electrolyte (Al₂O₃) and the top and bottom electrodes and ii) Gas Cluster Ion Beams (GCIB), a sputtering technique that leads to lower structure degradation, combined with XPS depth profiling to evaluate chemical depth distributions. To FSIMS measurements are also performed to get complementary in-depth chemical information.The aim of this thesis is to clarify the driving mechanism and understand the chemical changes at both interfaces involved in the forming process under positive and negative polarization as well as the mechanism of the reset operation. For that,we performed a comparison between as-grown state, i.e. the pristine device with a formed state,i.e. the sample after the first transition between HRS and LRS, and reset state, i.e. the sample after the first transition between LRS and HRS.Conducting bridging resistive random access memories (CBRAMs) are one option currently investigated for the next generation of non-volatile memories. Data storage is based on switching the resistivity between high (HRS) and low (LRS) resistance states. Under electrical bias,a conductive path is assumed to be created byions diffusion from the active electrode into the solid electrolyte. Recently, special attention has been drawn to devices containing an elemental semiconductor such as tellurium, operating with reduced currents and less retention failures. In these subquantum CBRAM cells, the filament is thought to contain tellurium , yielding a 1-atom conductance (G₁atom) significantly reduced compared to standard CBRAMs and thus allowing low power operation. In this thesis, we use X-ray photoelectron spectroscopy (XPS) to learn about electrochemical reactions involved in the switching mechanism of Al₂O₃ based CBRAMs with ZrTe and TiTe alloys as active electrode. Twomethods are used: i) non-destructive Hard X-rayphotoelectron spectroscopy (HAXPES) toinvestigate the critical interfaces between the electrolyte (Al₂O₃) and the top and bottom electrodes and ii) Gas Cluster Ion Beams (GCIB), a sputtering technique that leads to lower structure degradation, combined with XPS depth profiling to evaluate chemical depth distributions. To FSIMS measurements are also performed to get complementary in-depth chemical information.The aim of this thesis is to clarify the driving mechanism and understand the chemical changes at both interfaces involved in the forming process under positive and negative polarization as well as the mechanism of the reset operation. For that,we performed a comparison between as-grown state, i.e. the pristine device with a formed state,i.e. the sample after the first transition between HRS and LRS, and reset state, i.e. the sample after the first transition between LRS and HRS.

Un composite à matrice métallique et à renfort particulaire de carbure de titane (25vol.%) produit par la société Mecachrome par métallurgie des poudres est l’objet de cette étude. Le process industriel suit trois étapes : broyage à haute énergie des poudres d’acier et de carbure de titane (TiC) ; consolidation de la poudre composite par extrusion ou consolidation isostatique à chaud (HIP) ; traitements thermiques d’austénitisation. Les principales évolutions concernent la taille de particule, la taille de cristallite, le paramètre de maille et la composition chimique du renfort TiC. Dans cette étude, nous nous sommes concentrés uniquement sur l’évolution du renfort (les évolutions de la matrice sont développées dans le travail de M. Mourot). Afin de caractériser les particules de TiC à chaque étape du process, nous avons mis en place une procédure de dissolution chimique sélective de la matrice acier. Le TiC ainsi « extrait » de la matrice a ensuite été caractérisé de façon méthodique par microscopie électronique à balayage (MEB), microscopie électronique en transmission (MET), diffraction des rayons X (DRX) et analyse chimique élémentaire. Ces techniques ont permis de révéler des changements importants indiquant des interactions physico-chimiques durant les étapes d’élaboration du composite. Ces évolutions du renfort et l’étude thermodynamique des systèmes C-Fe-Ti et C-Fe-O-Ti ont permis de proposer les mécanismes réactionnels à prendre en compte lors de l’élaboration du composite acier/TiC / Steel metal matrix composites reinforced with titanium carbide particles (25 vol% ) can be industrially produced by a solid-state process including three main steps: mechanical alloying by high energy milling of steel and titanium carbide powders; consolidation of the powder mixture thus obtained by hot forging, hot extrusion or hot pressing at 1050-1250°C; heat treatment of the resulting composite material. During each of the three steps, the TiC reinforcing particles are submitted to severe mechanical shocks or stresses. Moreover, they can chemically react with impurities of the gas phase during milling or with the steel matrix during consolidation or further heat treatment. As a result, changes are likely to occur in the grain size, crystallite size, morphology and composition of the particles. The aim of this thesis was to point out and characterize these changes. For that purpose, a procedure was developed to selectively dissolve the metal matrix and extract the TiC particles from the starting powder mixture, from the consolidated composite material and from further heat-treated composite samples. The extracted TiC particles were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), chemical microanalysis (CMA) and X-ray diffraction (XRD). This revealed important changes indicative of the physical and chemical interaction phenomena that successively proceed during processing of the steel/TiC composite