The formation of Ge nanowires in V-grooves has been studied experimentally as well as theoretically. As substrate oxide covered Si V-grooves were used formed by anisotropic etching of (001)Si wafers and subsequent oxidation of their surface. Implantation of 1E17 Ge+ cm^-2 at 70 keV was carried out into the oxide layer covering the V-grooves. Ion irradiation induces shape changes of the V-grooves, which are captured in a novel continuum model of surface evolution. It describes theoretically the effects of sputtering, redeposition of sputtered atoms, and swelling. Thereby, the time evolution of the target surface is determined by a nonlinear integro-differential equation, which was solved numerically for the V-groove geometry. A very good agreement is achieved for the predicted surface shape and the shape observed in XTEM images. Surprisingly, the model predicts material (Si, O, Ge) transport into the V-groove bottom which also suggests an Ge accumulation there proven by STEM-EDX investigations. In this Ge rich bottom region, subsequent annealing in N2 atmosphere results in the formation of a nanowire by coalescence of Ge precipitates shown by XTEM images. The process of phase separation during the nanowire growth was studied by means of kinetic 3D lattice Monte-Carlo simulations. These simulations also indicate the disintegration of continuous wires into droplets mediated by thermal fluctuations. Energy considerations have identified a fragmentation threshold and a lower boundary for the droplet radii which were confirmed by the Monte Carlo simulation. The here given results indicate the possibility of achieving nanowires being several nanometers wide by further growth optimizations as well as chains of equally spaced clusters with nearly uniform diameter.

The formation of Ge nanowires in V-grooves has been studied experimentally as well as theoretically. As substrate oxide covered Si V-grooves were used formed by anisotropic etching of (001)Si wafers and subsequent oxidation of their surface. Implantation of 1E17 Ge+ cm^-2 at 70 keV was carried out into the oxide layer covering the V-grooves. Ion irradiation induces shape changes of the V-grooves, which are captured in a novel continuum model of surface evolution. It describes theoretically the effects of sputtering, redeposition of sputtered atoms, and swelling. Thereby, the time evolution of the target surface is determined by a nonlinear integro-differential equation, which was solved numerically for the V-groove geometry. A very good agreement is achieved for the predicted surface shape and the shape observed in XTEM images. Surprisingly, the model predicts material (Si, O, Ge) transport into the V-groove bottom which also suggests an Ge accumulation there proven by STEM-EDX investigations. In this Ge rich bottom region, subsequent annealing in N2 atmosphere results in the formation of a nanowire by coalescence of Ge precipitates shown by XTEM images. The process of phase separation during the nanowire growth was studied by means of kinetic 3D lattice Monte-Carlo simulations. These simulations also indicate the disintegration of continuous wires into droplets mediated by thermal fluctuations. Energy considerations have identified a fragmentation threshold and a lower boundary for the droplet radii which were confirmed by the Monte Carlo simulation. The here given results indicate the possibility of achieving nanowires being several nanometers wide by further growth optimizations as well as chains of equally spaced clusters with nearly uniform diameter.

The fundamental understanding of the dynamic characteristics of metal dissolution and redeposition behavior at the electrode-electrolyte interface is essential, which provides the basis for the development of advanced energy and conversion devices (such as electrochromic devices, electrocatalysts, and batteries) with superior electrochemical performances. We firstly demonstrate the feasibility of resynthesizing the electrode surface chemistry and tuning the electrochemical reactions at the solid-liquid interface by selectively changing the electrolyte composition and electrochemical cycling conditions. Amorphous TiO2 surface layers can be formed on WO3 electrodes by adding exotic Ti cations to the electrolyte, and slow electrochemical cycling. The dissolution and redeposition of electrodes and surface coatings are intertwined, helping to establish a dissolution-redeposition equilibrium at the interface, which can inhibit metal dissolution, stabilize electrode morphology, and promote electrochemical performance. Since the diffusion layer generated by the dissolution of transition metals is ubiquitous at the electrochemical solid-liquid interface, by combining in situ three-electrode electrochemical reaction cell with advanced spatially resolved synchrotron X-ray fluorescence microscopy and micro-X-ray absorption spectroscopy, we then successfully demonstrate the formation and chemical identification of the diffusion layer. By studying the evolution of diffusion layers(tens of micrometers thick) when using WO3 electrodes in acidic electrolytes, we find that with increasing distance of the dissolved species from the electrode surface, the oxidation state remains largely unchanged, but the local electronic environment of the dissolved W species becomes more distorted. We subsequently report a systematic experimental approach by collecting a series of twodimensional fluorescence images at the electrodes to study electrode dissolution and redeposition under different electrochemical conditions. The results show that (1) metal dissolution and redeposition behaviors greatly evolve under different electrode polarization and electrolyte compositions; (2) metal dissolution and redeposition behaviors are independent of bulk electrolyte pH but depend on interfacial pH; and (3) the accumulation of interfacial dissolved species promotes the formation of polytungstate interfacial networks, which ultimately manifest as temporal heterogeneity of redeposition. Lastly, we provide an in-depth study of the underlying mechanism of electrochemicalcycling induced crystallization at the electrode-electrolyte interface through a combination of advanced synchrotron radiation characterization techniques and an in situ electrochemical reaction setup. We have discovered that (1) foreign cations from the electrolyte engender both tensile and compressive strains inside the crystal; (2) repeated electrode dissolution and redeposition promote crystal growth through a non-classical crystallization pathway of particle attachment, but the initial growth of crystals is inhibited by internal strains; and (3) as the strain accumulates, the crystal rotates or moves, which is the fundamental reason for the dynamic structure evolution of the crystal during electrochemical cycling. To our knowledge, this is the first study of electrochemical-cycling-induced crystallization and its strain evolution. These new findings reveal a previously unknown relationship between crystal growth and its internal strain at the electrode-electrolyte interface. / Doctor of Philosophy / Energy drives the entire economy and human civilization. Energy is needed in every aspect of everyday life, and energy is an essential raw material for making and delivering all the products and services that modern society needs, even though it is invisible to us. Since 2000, the global energy demand has increased tenfold and economic growth has spawned a large number of new energy industries, but billions of people are still in urgent need of clean water, sanitation, nutrition, and medical care. Energy is a key factor in meeting these basic requirements for all of humanity. The increasing global energy demand and the increasing impact of climate change have put enormous pressure on the energy market. Therefore, it is necessary to accelerate the relevant actions of energy transition in the world. Among them, the research and innovation of electrochemical energy storage and conversion technology is a major direction. The electrochemical energy storage and conversion technology heavily relies on the various electrochemical reactions in practical devices such as rechargeable batteries, water electrocatalysts, and energy-saving electrochromic smart windows. Within numerous electrochemical reactions under the application, the solid (electrode)-liquid (electrolyte) interface dominates the most important electrochemical reactions. How to understand thephysicochemical reactions at the interface under electrochemical conditions is of great significance. As a major component of research innovations, this research contributes to the design of rational electrode materials, electrolyte compositions, and more efficient and durable electrochemical performance. From a fundamental perspective, my research enriches the understanding of solid-liquid interface reactions under electrochemical conditions, pointing out that electrode dissolution and redeposition and dynamic structural evolution of solid-liquid interfaces are important for further optimizing electrode material design and improving electrochemical performance.

La réalisation de dispositifs à des dimensions sous-micrométriques et nanométriques demande une maîtrise parfaite des procédés de fabrication, notamment ceux de gravure. La réalisation des ces dispositifs est complexe et les exigences en termes de qualité et de géométrie des profils de gravure imposent de choisir les conditions opératoires les mieux adaptées. Les simulations de l'évolution spatio-temporelle des profils de gravure que nous proposons dans cette thèse s'inscrivent parfaitement dans ce contexte. Le simulateur que nous avons réalisé offre la possibilité de mieux comprendre les processus qui entrent en jeu lors de la gravure par plasma de profils dans divers matériaux. Il permet de tester l'influence des paramètres du plasma sur la forme du profil et donc de déterminer les conditions opératoires optimales. La mise au point de ce simulateur s'appuie sur les concepts fondamentaux qui gouvernent la gravure par plasma. À partir de l'état des lieux des différentes approches numériques pouvant être utilisées, nous avons élaboré un algorithme stable et adaptable permettant de mettre en évidence l'importance de certains paramètres clés pour la réalisation de profils de gravure par un plasma à haute densité et à basse pression. Les capacités de cet algorithme ont été testées en étudiant d'une part la pulvérisation de Si dans un plasma d'argon et d'autre part, la gravure chimique assistée par les ions de SiO2/Si dans un plasma de chlore. Grâce aux comparaisons entre profils simulés et expérimentaux, nous avons montré l'importance du choix de certains paramètres, comme la nature du gaz utilisé et la pression du plasma, la forme initiale du masque, la sélectivité masque/matériau, le rapport de flux neutre/ion, etc. Nous avons aussi lié ces paramètres à la formation de défauts dans les profils, par exemple celle de facettes sur le masque, de parois concaves, et de micro-tranchées. Enfin, nous avons montré que le phénomène de redépôt des atomes pulvérisés entre en compétition avec la charge électrique de surface pour expliquer la formation de profils en V dans le Pt pulvérisé par un plasma d'argon. / Sub-micrometer and nanometer-size device manufacturing requires perfect control of fabrication processing, in particular plasma etching. The fabrication of such devices is complex and the requirements in terms of quality and geometry of the etching profiles impose to use the best adapted operating conditions. Simulation of space and time-etching profile evolution that is proposed in this thesis addresses these issues. The simulator yields a better understanding of the fundamental mechanisms that occur during plasma etching of features in various materials. It enables to test the influence of plasma parameters on the profile shape and thus to determine the optimal operating conditions. The development of the simulator is based on the fundamental concepts in plasma etching. From thorough review of the various numerical approaches available to simulate etching profile evolution, we have developed a stable and flexible algorithm that enables to emphasize the importance of some key-parameters for the realization of etching profiles by high-density and low-pressure plasma. The capabilities of this algorithm were tested on the study of Si sputtering in an argon plasma and of ion-assisted chemical etching of SiO2/Si in a chlorine plasma. From comparisons between simulated and experimental profiles, we have shown the importance of some parameters, like the nature of the gas, the plasma pressure, the initial shape of the mask, the mask/material selectivity, the neutral/ion flux ratio, etc. We also linked these parameters to the formation of defects in the profile, for exemple mask facetting, sidewall bowing and microtrenching. Finally, we have shown that redeposition of sputtered atoms compete with electric surface charging to explain V-shape profiles observed on Pt sputtered in argon plasmas.

La réalisation de dispositifs à des dimensions sous-micrométriques et nanométriques demande une maîtrise parfaite des procédés de fabrication, notamment ceux de gravure. La réalisation des ces dispositifs est complexe et les exigences en termes de qualité et de géométrie des profils de gravure imposent de choisir les conditions opératoires les mieux adaptées. Les simulations de l'évolution spatio-temporelle des profils de gravure que nous proposons dans cette thèse s'inscrivent parfaitement dans ce contexte. Le simulateur que nous avons réalisé offre la possibilité de mieux comprendre les processus qui entrent en jeu lors de la gravure par plasma de profils dans divers matériaux. Il permet de tester l'influence des paramètres du plasma sur la forme du profil et donc de déterminer les conditions opératoires optimales. La mise au point de ce simulateur s'appuie sur les concepts fondamentaux qui gouvernent la gravure par plasma. À partir de l'état des lieux des différentes approches numériques pouvant être utilisées, nous avons élaboré un algorithme stable et adaptable permettant de mettre en évidence l'importance de certains paramètres clés pour la réalisation de profils de gravure par un plasma à haute densité et à basse pression. Les capacités de cet algorithme ont été testées en étudiant d'une part la pulvérisation de Si dans un plasma d'argon et d'autre part, la gravure chimique assistée par les ions de SiO2/Si dans un plasma de chlore. Grâce aux comparaisons entre profils simulés et expérimentaux, nous avons montré l'importance du choix de certains paramètres, comme la nature du gaz utilisé et la pression du plasma, la forme initiale du masque, la sélectivité masque/matériau, le rapport de flux neutre/ion, etc. Nous avons aussi lié ces paramètres à la formation de défauts dans les profils, par exemple celle de facettes sur le masque, de parois concaves, et de micro-tranchées. Enfin, nous avons montré que le phénomène de redépôt des atomes pulvérisés entre en compétition avec la charge électrique de surface pour expliquer la formation de profils en V dans le Pt pulvérisé par un plasma d'argon. / Sub-micrometer and nanometer-size device manufacturing requires perfect control of fabrication processing, in particular plasma etching. The fabrication of such devices is complex and the requirements in terms of quality and geometry of the etching profiles impose to use the best adapted operating conditions. Simulation of space and time-etching profile evolution that is proposed in this thesis addresses these issues. The simulator yields a better understanding of the fundamental mechanisms that occur during plasma etching of features in various materials. It enables to test the influence of plasma parameters on the profile shape and thus to determine the optimal operating conditions. The development of the simulator is based on the fundamental concepts in plasma etching. From thorough review of the various numerical approaches available to simulate etching profile evolution, we have developed a stable and flexible algorithm that enables to emphasize the importance of some key-parameters for the realization of etching profiles by high-density and low-pressure plasma. The capabilities of this algorithm were tested on the study of Si sputtering in an argon plasma and of ion-assisted chemical etching of SiO2/Si in a chlorine plasma. From comparisons between simulated and experimental profiles, we have shown the importance of some parameters, like the nature of the gas, the plasma pressure, the initial shape of the mask, the mask/material selectivity, the neutral/ion flux ratio, etc. We also linked these parameters to the formation of defects in the profile, for exemple mask facetting, sidewall bowing and microtrenching. Finally, we have shown that redeposition of sputtered atoms compete with electric surface charging to explain V-shape profiles observed on Pt sputtered in argon plasmas.

Abstract The aim of the deinking process is to produce deinked pulp from recovered papers (RCPs) with sufficient brightness and cleanliness to fulfil the quality requirements set by the paper grade to be produced. Due to the excessive production costs and material losses of modern deinking processes, there is a need to simplify deinking lines. A prerequisite for this action is that ink content bound to fibres, dirt content and ink fragmentation are minimised in the pulping stage. Thus, it is important to recognise the factors affecting ink behaviour in pulping, to search for new ways to improve ink detachment from RCPs in pulping and to search pulping methods that could efficiently process RCPs printed with various inks. The aim of this thesis was to obtain new information on how the environmental conditions that prevail during the storage and transportation of RCPs affect ink behaviour in subsequent pulping and to find out whether there is further potential to decrease ink content bound to fibres, not only by treating recovered papers chemically before the actual pulping process, but also by removing the detached ink particles during the pulping process. The results show that if some RCPs are very moist and exposed to high temperatures for a reasonable time before the pulping process, the problems in releasing ink from the fibres in pulping become more pronounced and the pulp is dirtier compared to pulp from RCPs that are thermally aged but dry. Properly wetting some RCPs with conventional alkaline deinking chemicals in suitable conditions ahead of the pulping process reduces the ink content that remains bound to the fibres after the pulping process. The efficiency of the pre-wetting treatment in aiding ink detachment from fibres in subsequent pulping is highly dependent on the alkalinity, temperature and duration of the treatment. Semi-continuous ink removal during the pulping process offers the possibility to continue defibering, ink detachment from fibres and dirt fragmentation in pulping without fear of ink redeposition into or onto the fibres, thus resulting in fully disintegrated pulp with lower ink content bound to fibres than in conventional pulping. This enables efficiently simultaneous processing of, for example, papers printed with water-based inks and toners. / Tiivistelmä Siistausprosessin tavoitteena on tuottaa keräyspapereista valmistettua vaaleaa ja puhdasta massaa, jota voidaan käyttää uusien paperituotteiden valmistamiseen. Siistausprosesseja pyritään yksinkertaistamaan nykyisten monimutkaisten prosessien korkeiden tuotantokustannusten ja materiaalitappioiden vuoksi. Eräs edellytys siistausprosessien yksinkertaistamiselle on, että kuiduissa kiinni olevan musteen pitoisuus, massan likapitoisuus ja musteen liiallinen pilkkoutuminen minimoidaan siistausprosessin ensimmäisessä vaiheessa, pulpperoinnissa. Täten on tärkeää tunnistaa musteen käyttäytymiseen pulpperoinnissa vaikuttavat tekijät, etsiä uusia mahdollisuuksia parantaa musteen irrotusta keräyspapereista sekä kehittää pulpperointimenetelmiä, joilla voitaisiin prosessoida tehokkaasti eri painomenetelmillä painettuja papereita. Tämän työn tavoitteena oli saada uutta tietoa siitä miten ympäristöolosuhteet, joille keräyspaperit voivat altistua varastoinnin ja kuljetuksen aikana, vaikuttavat musteen käyttäytymiseen pulpperoinnissa. Lisäksi tavoitteena oli selvittää voitaisiinko kuituihin kiinni jääneen musteen pitoisuutta vähentää esiliottamalla keräyspapereita sopivissa kemiallisissa olosuhteissa ennen pulpperointia ja poistamalla irronneet mustepartikkelit massan seasta pulpperoinnin aikana. Tulokset osoittavat, että jos tietyt keräyspaperit ovat erittäin kosteita ja altistuvat korkealle lämpötilalle riittävän pitkän ajan ennen pulpperointia, tulee musteen irrottaminen kuiduista pulpperoinnissa vaikeammaksi ja tuotettu massa likaisemmaksi, kuin sellaisista keräyspapereista, jotka ovat altistuneet kuivina korkealle lämpötilalle. Kuituihin kiinnittyneen musteen pitoisuutta voidaan vähentää esiliottamalla tiettyjä keräyspapereita alkalisilla siistauskemikaaleilla sopivissa olosuhteissa ennen pulpperointia. Esiliotuksen kyky parantaa musteen irrotusta kuiduista pulpperoinnissa riippuu voimakkaasti esiliotusvaiheen alkalisuudesta, lämpötilasta ja kestosta. Kun irronneet mikroskooppiset mustepartikkelit poistetaan massasta useassa vaiheessa pulpperoinnin aikana, voidaan paperin kuidutusta, musteen irrottamista kuiduista ja likapilkkujen hajottamista jatkaa ilman että haitallista musteen takaisin kiinnittymistä kuituihin tapahtuu. Tämä mahdollistaa esimerkiksi vesipohjaisten musteiden ja lasertulosteiden samanaikaisen prosessoinnin.

Med den ökande trenden av process slutning inom massabruken, så har det indikerats att återvinningen av tvättvätska från de olika tvättsteg troligen resulterar i negativa effekter. Närvaron av olika komponenter kan påverka upplösningen av lignin genom att främja dess återdeponering på massan, och därmed påverka senare steg inom bruket. Denna studie fokuserade på effekten av tvättvätskes sammansättningen, pH och magnesiumjoners innehållet på ligninåterfästningen till fibrerna under brunmassatvätt. Projektets syfte var att finna nya relevanta insikter för dagens verksamheter. För den experimentella proceduren blandades massa- och vätskaprover erhållna från ett barrveds-sulfatmassabruk, relevanta lösningsmodifikationer genomfördes, och dessa placerades i ett vattenbad vid 90 °C. Därefter tvättades och separerades den resulterande blandningen. Kappatal och ISO-ljusstyrka användes för massakaraktärisering, samt UV-VISspektroskopi för tvättvätskor. En ytterligare procedur med alkalisk urlakning utfördes på massan för att identifiera den relativt svaga liginbindningen. Resultaten indikerade att högre ligninhalt och konduktivitet, lägre pH och högre MgSO4 koncentration i tvättvätskor ökar lignininnehållet i massan. Under proceduren identifierades en möjlig konkurrens mellan borttagningen av lignin från fibrerna och återfällningen. Genom att uföra studier på olika bruksvätskor, så påverkades flera variabler systemet samtidigt, vilket förhindrade identifikationen av den dominerande variabeln som potentiellt kunde justeras för att minska återdeponeringen. Det observerades dock att en tillsatts av NaOH i tvättvätskor kunde reducera lignininnehållet i massan, medans däremot en ökning av MgSO4 kunde ha negativa effekter. / With the growing tendency of process closure within pulp mills, recycling liquors into different washing stages was observed to result in likely negative effects. The presence of different components may affect lignin dissolution, by promoting its redeposition onto pulp therefore affecting later stages in the mill. The present study focused on the effect of washing liquor composition, pH, and magnesium ions content on lignin reattachment to fibres during brown stock washing. This project’s motivation was to provide new insights relevant for today’s operations. For the experimental procedure, pulp and liquor samples obtained from a softwood kraft pulp mill were mixed, relevant solution modifications were performed, and these were set inside a water bath at 90 °C. Then, the resulting mixture was washed and separated. Kappa number and ISO brightness were employed for pulp characterization, and UV-VIS spectroscopy for washing liquors. An additional procedure of alkaline leaching was performed on pulp to identify relatively weak lignin attachment. Obtained results indicated that higher lignin content and conductivity, lower pH and higher MgSO4 concentration in washing liquors increase the lignin content in pulp. A competition between lignin removal from fibres and reattachment was identified to be possibly occurring during the procedure. By performing studies on different mill liquors, multiple variables affected the system simultaneously, which hinders the identification of the dominant variable to be potentially adjusted for reducing the redeposition. However, it was seen that adding NaOH in washing liquors could reduce lignin content in the pulp, whereas an increase in MgSO4 could present negative effects.