Tesis sobre el tema "Nanoparticule de MgO"

Les nano-objets (fils, particules, films minces) sont connus pour leurs propriétés mécaniques exceptionnelles au regard de leurs homologues massifs. Diverses techniques expérimentales (microscopie électronique à transmission ou à balayage, diffraction des rayons X) sont utilisées pour étudier les nano-objets, complétées par des approches numériques telle que la dynamique moléculaire. Bien que fournissant des détails à l'échelle atomique, la dynamique moléculaire reste limitée en termes de taille et de vitesse de déformation, ouvrant la porte à d'autres méthodes comme la dynamique des dislocations discrète. La dynamique des dislocations discrète permet de décrire l'évolution d'une population de dislocations à l’échelle du grain mais est généralement utilisée dans des ensembles quasi-infinis en utilisant des cellules de simulation particulièrement grandes ou des conditions limites périodiques. Par conséquent, la dynamique des dislocations discrète seule ne peut fournir une description physique des surfaces d’un échantillon, surfaces à l'origine de nombreux processus à l'échelle nanométrique. Cette étude vise à modéliser mieux et plus fidèlement la mécanique des nano-objets en tenant compte des interactions complexes entre les dislocations et les surfaces. Pour ce faire, un nouvel outil appelé El-Numodis a été développé. El-Numodis repose sur le couplage du code de dynamique des dislocations discrète Numodis avec le code d'éléments finis Elmer en utilisant la méthode de superposition. Nous présentons ici les étapes de développement d'El-Numodis (pilotes de couplage, forces d'image des dislocations, algorithme de nucléation, etc.) ainsi que plusieurs applications incluant des problèmes d'élasticité classiques dans lesquels des surfaces sont impliquées. A titre d'exemple, la modélisation de films minces métalliques fcc montre l'influence majeure des surfaces sur la mécanique des nano-objets. Enfin, El-Numodis est utilisé pour modéliser la mécanique de nanoparticules céramiques où la nucléation de dislocation informée de manière atomistique, combinée à la théorie de l'état de transition, permet d'étudier le rôle de la taille, température et de la vitesse de déformation sur la déformation de nanocubes de MgO
Nano-objects (wires, particles, thin films) are known for their outstanding mechanical properties when compared to their bulk counterparts. Various experimental techniques (transmission and scanning electron microscopy, X-ray diffraction) are used to investigate nano-objects, all complemented by computational approaches such as molecular dynamics. While modelling atomic-scale processes in the details, molecular dynamics is limited in terms of sample size and strain rates opening doors to other methods such as the discrete dislocation dynamics. Discrete dislocation dynamics is able to describe the evolution of a dislocation population at the mesoscale but is mostly used to describe quasi-infinite ensembles using either particularly large simulation cells or relying on periodic boundary conditions. Consequently, standalone discrete dislocation dynamics cannot provide a complete description of sample surfaces that are known to be at the roots of several nanoscale processes. This study aims at better and faithfully model the mechanics of nano-objects accounting for the complex interactions between dislocations and surfaces. For this purpose, a new tool called El-Numodis was developed. El-Numodis relies on the coupling of the discrete dislocation dynamics code Numodis with the finite elements code Elmer using the superposition method in which the stress field generated by a dislocation population is corrected at the virtual surfaces of a finite-size sample using a finite-element elastic solver. In this work, we present the main development stages of El-Numodis (coupling drivers, dislocation image forces, nucleation algorithm, etc.) as well as several applications including analytically soluble elasticity problems in which surfaces are involved. As an example, the modelling of face-centered cubic metal thin films practically demonstrates the influence of surfaces on nano-objects mechanics. Finally, El-Numodis is used to model the mechanics of ceramics nanoparticles for which atomistically-informed dislocation nucleation as combined to the transition state theory allow to investigate the role of size, temperature and strain rate on the mechanical properties of MgO nanoparticles

Attualmente, l'accoppiamento fra nanoparticelle metalliche (NP) e materiali foto-attivi rappresenta una via promettente per migliorare le efficienze di dispositivi in applicazioni di fotocatalisi ed energia solare. Nella maggior parte dei casi, il miglioramento dell'efficienza dei dispositivi solari mediante funzionalizzazione con NP core-shell è stato ottenuto attraverso metodi chimici sia per la sintesi che per la deposizione delle NP. Questi metodi sono limitati nella combinazione di materiali di core e shell, così come alcuni inconvenienti legati all'uso di solventi. D'altra parte, le sorgenti di aggregazione di NP basate su magnetron-sputtering, rappresentano un approccio versatile per depositare NP su superfici, con controllo preciso sulle quantità e sulle dimensioni medie, consentendo di ottenere strutture core-shell e/o NP metalliche incorporate in una matrice ultrasottile. Durante il mio progetto di dottorato, esploro le potenzialità nell'applicazione di questa tecnica alle celle solari di perovskite (PSC), con l'obiettivo di studiare le proprietà dei substrati funzionalizzati e di migliorarne l’assorbimento della luce e l'efficienza (PCE). In particolare, le NP core-shell Ag@MgO e Au@MgO vengono depositate sullo strato mesoporoso di TiO2, in PSC a triplo catione. Sono stati considerati ricoprimenti diversi di NP che variano tra l'1 e il 25% e le proprietà strutturali e morfologiche dei substrati funzionalizzati sono state caratterizzate combinando informazioni ottenute da HRTEM, EDX, SEM, AFM e XPS. La struttura delle NP di Ag@MgO è studiata mediante HRTEM ed EDXS, mostrando che il core di Ag presenta una struttura icosaedrica multi-dominio e dimostrando che la crescita di MgO è localizzata attorno ai nuclei di Ag, confermando l’ottenimento di una struttura core-shell. Le proprietà morfologiche delle NP, ad es. le dimensioni laterali e l'altezza, sono determinate rispettivamente tramite SEM e AFM. L'altezza media delle NP H è stimata intorno a 4 nm per le NP di Ag@MgO, e intorno a 6 nm per quelle di Au@MgO, mentre per entrambi i sistemi la dimensione laterale media D è di circa 8 nm. Quest'ultima aumenta in funzione del ricoprimento, cosicché le NP sono caratterizzate da un rapporto D/H variabile tra 1 e 2. Sia per le NP di Ag che per quelle di Au, gli esperimenti di stabilità termica fino a 150°C sono stati monitorati mediante XPS e dimostrano il ruolo benefico svolto da MgO nel preservare la stabilità termica delle NP ed evitarne l'ossidazione. Le trasmissività UV-Vis (T) e le riflettività (R) dei substrati e di quelli arricchiti con NP sono misurate con uno spettrofotometro, determinandone la Optical Loss differenziale (ΔL) per diversi ricoprimenti di NP. Gli spettri ottici dei campioni contenenti Ag@MgO rivelano un picco a 430 nm. Le simulazioni di polarizzabilità delle NP basate su Maxwell-Garnett confermano che il picco è correlato all'assorbimento del LSPR di Ag, mentre la sua posizione dipende dal rapporto D/H. Gli spettri ottici di campioni contenenti Au@MgO rivelano un picco più largo, a 520 nm, mostrando - in accordo con la letteratura e con i risultati delle simulazioni - che la banda di LSPR è più grande che nel caso di NP di Ag. Come ultima fase, viene esaminato l’effetto delle NP di Ag@MgO e Au@MgO nelle PSC. Vengono testati dispositivi con diverso ricoprimento superficiale tra 0 e 25% e per diversi spessori nominali della shell tra 2,5 e 0,6 nm. Per le PSC arricchite con NP di Ag@MgO, il ricoprimento ottimale è di 1,5%, che porta ad un aumento dell’efficienza dei dispositivi del 5%, fino al 17,8%, correlato con l’aumento di JSC e di VOC. D'altro canto, le misure preliminari relative all'incorporazione di NP Au@MgO nelle PSC non hanno determinato un aumento dell'efficienza e meritano ulteriori indagini.
Nowadays, coupling of Metal nanoparticles (NPs) with photo-active materials represents a promising route to enhance device performances in photocatalysis and solar energy applications. In most cases, efficiency improvement in photovoltaic devices by core-shell NP functionalization was obtained via chemical wet methods for both core and shell synthesis and deposition. These methods – though readily suitable for scalability – presents some limitations in combining NP and shell materials, as well as some drawbacks related to the use of solvents. On the other hand, nanocluster aggregation sources based on magnetron-sputtering represent a versatile route to deposit NPs on any selected surface, with precise control of both their quantity and average dimension. Moreover, co-deposition techniques allow to obtain core-shell structures and/or metal NPs embedded in ultra-thin host matrix. During my PhD project, I explore the potentialities of applying this methodology to Perovskite Solar Cells (PSCs), aiming to investigate the properties of these functionalized substrates and, ultimately, to improve their light harvesting and power conversion efficiency (PCE). In particular, Ag@MgO and Au@MgO core-shell NPs are deposited on the mesoporous TiO2 surface Electron-Transport Layer of triple-cation PSCs. Different NP coverage varying between 1-25% has been considered, and the structural and morphological properties of the functionalized substrate has been fully characterized by combining complementary information obtained by HRTEM, EDX, SEM, AFM and XPS. The Ag@MgO NP core-shell structure is investigated with HRTEM and EDXS, showing that the Ag core presents a multi-twinned icosahedral structure and proving that the MgO growth is preferentially localized around the metal cores, i.e. that a core-shell structure is obtained. Furthermore, NP morphological properties, i.e. their lateral size and height, are determined via SEM and AFM, respectively. The average NP height H is estimated around 4 nm and 6nm for Ag@MgO NPs and Au@MgO NPs, respectively, while for both systems the average lateral size D is found around 8 nm. The latter slightly increases as a function of coverage, so that the NP spheroidal shape is characterized by an aspect ratio D/H varying between 1 and 2. For both Ag and Au NPs, XPS annealing experiments performed in UHV up to 150°C demonstrate the beneficial role played by the MgO shell in preserving their thermal stability and avoiding oxidation. The UV-Vis Transmittivity (T) and Reflectivity (R) of pristine and NP-enriched substrates are measured with a spectrophotometer, thus determining the Differential Optical Loss (ΔL) spectra for different NP coverages. For Ag@MgO NP-enriched samples, spectra reveal an intense and broad band, peaked at 430 nm. NP polarizability simulations based on Maxwell-Garnett approach confirm that the band maximum is related to Ag LSPR absorption, while its position depends on the NP aspect ratio. Au@MgO NP spectra reveal a broader optical loss band, peaked at 520 nm, showing - in agreement with literature and with the results of simulations - that the plasmonic loss band is larger than the case with Ag NPs. As last step, the incorporation of core–shell Ag@MgO and Au@MgO NPs into PSCs is investigated. Devices with different NP surface coverage between 0 and 25% and for different nominal shell thickness between 2.5 and 0.6 nm are tested. For Ag@MgO NP-enriched PSCs, the optimum coverage is 1.5%, which leads to a relative increase of 5% in terms of device efficiencies up to 17.8%, related to an increase in both JSC and VOC. On the other hand, preliminary measures of the incorporation of Au@MgO core-shell NPs in PSCs did not result in an efficiency increase and deserve further investigation.

La capture et la valorisation du dioxyde de carbone sont devenus des défis majeurs pour les décennies à venir. Les technologies de capture sont déjà suffisamment matures pour être mises en œuvre à l'échelle industrielle, mais les technologies de valorisation font encore défaut. Ce travail de thèse se concentre sur le développement de nouveaux catalyseurs pour la valorisation chimique du CO2. L'introduction bibliographique souligne le potentiel des oxydes alcalino-terreux pour la capture et la valorisation du CO2 en raison de leur capacité à former facilement des carbonates, ainsi que le développement récent de la chimie des Paires de Lewis Frustrées (FLP) pour l'activation de petites molécules comme le CO2. Nous y proposons une stratégie de synthèse de nanoparticules d'oxyde de magnésium fonctionnalisées avec des ligands boranes pour créer une interaction de type FLP à la surface et augmenter l'activité catalytique des nanoparticules dans la cycloaddition du CO2 sur des époxydes. Dans la première partie de ce travail, la synthèse de nanoparticules d'oxyde de magnésium par précipitation-calcination est étudiée. Les paramètres de réaction tels que la température de calcination et les lavages post-synthèse ont un impact sur la morphologie et l'état de surface des nanoparticules. La deuxième partie de ce travail se concentre sur l'adsorption de boranes sur les nanoparticules de MgO avec et sans présence de CO2. La preuve d'une interaction MgO-CO2-BPh3 est apportée par des analyses de spectroscopie infrarouge. Une interaction unique entre MgO et le chloroborane BCl2Ph est mise en évidence par un changement de couleur visuel des nanoparticules ainsi que par spectroscopie infrarouge. La dernière partie de ce travail se concentre sur l'étude catalytique de la réaction de cycloaddition. La comparaison entre les différents catalyseurs MgO confirme l'importance des paramètres de synthèse des nanoparticules sur leur activité. L'adsorption de boranes modifie l'activité et/ou la sélectivité de MgO en fonction du solvant de réaction. L'ajout de BCl2Ph augmente l'activité du catalyseur MgO d'un facteur 10 mais réduit également sa sélectivité vers la formation du carbonate cyclique. L'impact de la température, de la concentration et de la durée de la réaction sur les performances catalytiques de ce couple nanoparticule-ligand est étudié afin de dévoiler l'origine de cette synergie inédite entre MgO et BCl2Ph
Carbon dioxide capture and valorisation have become major challenges for the future decades. Capture technologies are already mature enough to start being implemented at industrial scale but valorisation technologies are still lacking. This thesis work focuses on the development of new catalysts for CO2 chemical valorisation. The bibliographic introduction emphasizes the potential alkaline earth oxides for CO2 capture and valorisation due to their ability to easily form carbonates, as well as the recent development of Frustrated Lewis Pair (FLP) chemistry for the activation of small molecules like CO2. We propose a strategy to synthesize magnesium oxide nanoparticles functionalised with borane ligands to create FLP-like interaction at the surface and increase the catalytic activity of the nanoparticles in the cycloaddition of CO2 on epoxides. In the first part of this work, the synthesis of magnesium oxide nanoparticles by precipitation-calcination is studied. Reaction parameters like calcination temperature and post synthesis washings are shown to impact the nanoparticles morphology and surface state. The second part of this work focuses on borane adsorption on MgO nanoparticles with and without presence of CO2. Proof of a MgO-CO2-BPh3 interaction is found using infrared spectroscopy analyses. A unique interaction between MgO and the chloroborane BCl2Ph is evidenced by a visual colour change of the nanoparticles and by infrared spectroscopy. The last part of this work focuses on the catalytic study of the cycloaddition reaction. Comparison between the different MgO catalysts confirmes the importance of the nanoparticles synthesis parameters on their activity. Adsorption of borane modifies the MgO activity and/or selectivity depending on the reaction solvent. The addition of BCl2Ph increases the activity of the MgO catalyst by a factor 10 but also reduces the selectivity toward cyclic carbonate. Impact of temperature, concentration and reaction duration on the catalytic performances of this nanoparticle¬ ligand pair is studied to unveil the origin of this unreported synergy between MgO and BCl2Ph

La connaissance d’un système gaz/solide requiert l’analyse de l’adsorption, du premier stade jusqu’à saturation. C’est la motivation de l’analyse des surfaces sous vide. L’approche des surfaces divisées est souvent tronquée. Pratiquée à des pressions suffisamment élevées pour être compatible avec un temps de réaction raisonnable, elle ne permet pas l'analyse de la surface nue à la monocouche. L’objectif du présent travail a été d’établir une continuité d’observation par FTIR, de l’UHV à la pression ambiante, de poudres de MgO, ZnO et ZnxMg1-xO exposées à l’eau ou à l’hydrogène. Il a été montré que les fumées de ZnO se comparent à des cristaux présentant les faces (0001), (0001̅), (101̅0), (112̅0), avec un rapport non-polaire/polaire de 75/25. Par FTIR combinée à la photoémission et à la désorption thermique, trois étapes de l’hydroxylation des fumées de MgO ont été identifiées : défauts ponctuels (10-8 mbar), marches (10-6 mbar) puis terrasses (> 10-5 mbar), avec une restructuration qui prouve que l’eau change la structure de surface de MgO. La représentation commune de la surface de MgO par une suite de facettes (100) est mise en cause. Aux faibles teneurs en zinc, l’oxyde mixte ZnxMg1-xO est formé de cristallites cubiques de même structure que MgO. Le zinc en substitution tend à ségréger vers les sites de basse coordinence où il affecte les propriétés d’adsorption d’eau et d’hydrogène. Par ailleurs, le mélange ZnO-MgO obtenu par combustion d’alliage ZnMg offre une possibilité d’application grâce aux propriétés bactéricides de ZnO et de faible toxicité de MgO. L’ensemble des résultats montre la pertinence de l’étude des poudres pratiquée dans les conditions de l’UHV
The analysis of adsorption from the first stage to saturation is necessary to understand gas/solid interactions. This is the motivation for surface analysis under vacuum. The common approach of dispersed materials surfaces is incomplete since working pressures, that are high enough to achieve reasonable reaction times, do not allow studies of powder surfaces from bare to fully covered. The aim of the present work is to examine the successive changes of ZnO, MgO and ZnxMg1-xO nanopowders upon exposure to water or hydrogen from UHV to the ambient by FTIR. It is shown that ZnO smokes behave in a same way as a collection of single crystals which exhibit (0001), (0001̅), (101̅0) and (112̅0) faces with a non-polar/polar ratio of 75/25. Combining FTIR with XPS and TPD techniques, three stages of hydroxylation were identified on MgO smokes: point defects (10-8 mbar), steps (10-6 mbar) then terraces (> 10-5 mbar). Results indicate a reorganisation of surface structure showing that water adsorption on MgO(100) is an irreversible process. The common model of MgO as a series of (100) facets is questioned. At low concentrations of zinc, the mixed oxide ZnxMg1-xO consists of crystals with similar structure as MgO. A segregation of Zn2+ toward low coordinated surface sites is suggested to explain the changes in reactivity of the ZnxMg1-xO with respect to water and hydrogen at low coverages. Furthermore, the mixture ZnO-MgO produced by combustion of ZnMg alloy combines the antibacterial properties of ZnO and the biocompatibility of MgO, interesting for potential applications. The overall results demonstrate the relevance of the study of powders in ultra-high vacuum conditions

The vulcanization of rubber by sulfur is a large-scale industrial process that improves the mechanical properties of unsaturated rubber by the cross-linking of polymer chains. Microcrystalline ZnO particles are currently used as activator to enhance the efficiency of the crosslinking. Due to their not easy dispersion in the rubber matrix and to the relatively small fraction of ZnO which actually reacts with the other curative compounds, a large amount of oxide is required for the process. This leads to a not homogeneous vulcanization with inefficient polymer network structure and a possible release of the metal in the environment with potentially negative effects. Thus, a possible improvement of ZnO efficiency as activator requires an enhancement of its availability, distribution and capability to release Zn2+ ions in the rubber matrix. Aim of this thesis, is the enhancement of the curing efficiency by employing ZnO nanoparticles (NPs) grown on silica filler particles. A simple low-temperature sol-gel procedure was exploited to grow amorphous spherical ZnO NPs directly on silica surface and linked by Si-O-Zn covalent bonds (ZnO/SiO2) which simultaneously behave as curing agent and reinforcing filler. The morphology and crystal structure of ZnO/SiO2 NPs were investigated by XRD and TEM. The nanometric size was assessed by UV reflectance measure, while the Si-O-Zn bond interaction was studied by NMR, ATR-FTIR and XPS and discussed in relation to the NPs dimensions. The ZnO/SiO2 NPs were used to prepare cured polyisoprene nanocomposites loaded with silica. Moreover, the curing efficiency and dynamic mechanical properties of vulcanized ZnO/SiO2 nanocomposites were compared to those obtained by using microcrystalline ZnO as activator in conventional curing processes. In the case of nanocomposite cured with ZnO/SiO2 NPs showed better curing efficiency, higher cross-linking density and improved mechanical properties than the same composites treated by conventional ZnO particles. In order to explain the better efficiency of ZnO/SiO2 NPs in the vulcanization, the pseudo activation energies of the different stages of the process were evaluated by performing DSC measurements on the nanocomposites. The presence of ZnO/SiO2 NPs induces lower activation energies and, therefore, faster kinetics compared to microcrystalline ZnO, particularly in the first steps of the reactions. This is in agreement with the highest ability of zinc in ZnO/SiO2 to react with curatives, thus improving the cross-linking density. The role of ZnO/SiO2 NPs in the crosslinking reaction was further studied by a model compound vulcanization (MCV) approach, using tetramethylethylene as model monomer and analyzing the cured products by LC-MS chromatography and 1H-NMR spectroscopy. The results evidence a higher crosslinking for ZnO/SiO2 due to the larger amount of more stable mono- and di-sulphide crosslinking chains than for conventional ZnO. The comparison between the two catalysts have been also discussed on the basis of FTIR investigation which evidence in ZnO/SiO2 the formation of highly reactive stearate bridged bidentate zinc complex as possible intermediate in accelerating the cross-linking reaction. These results suggest that the proposed material could be considered as promising system for curing industrial application with reduce zinc loading. Finally, similar activator/filler NPs loaded with CaO and MgO were also prepared and tested to replace the Zn in curing process. Nanosized dimension and high dispersion of the oxides improve the efficiency of this activators with respect to system with unsupported crystalline oxides even if their catalityc activity is confirmed to be much lower than ZnO.

La connaissance d’un système gaz/solide requiert l’analyse de l’adsorption, du premier stade jusqu’à saturation. C’est la motivation de l’analyse des surfaces sous vide. L’approche des surfaces divisées est souvent tronquée. Pratiquée à des pressions suffisamment élevées pour être compatible avec un temps de réaction raisonnable, elle ne permet pas l'analyse de la surface nue à la monocouche. L’objectif du présent travail a été d’établir une continuité d’observation par FTIR, de l’UHV à la pression ambiante, de poudres de MgO, ZnO et ZnxMg1-xO exposées à l’eau ou à l’hydrogène. Il a été montré que les fumées de ZnO se comparent à des cristaux présentant les faces (0001), (0001̅), (101̅0), (112̅0), avec un rapport non-polaire/polaire de 75/25. Par FTIR combinée à la photoémission et à la désorption thermique, trois étapes de l’hydroxylation des fumées de MgO ont été identifiées : défauts ponctuels (10-8 mbar), marches (10-6 mbar) puis terrasses (> 10-5 mbar), avec une restructuration qui prouve que l’eau change la structure de surface de MgO. La représentation commune de la surface de MgO par une suite de facettes (100) est mise en cause. Aux faibles teneurs en zinc, l’oxyde mixte ZnxMg1-xO est formé de cristallites cubiques de même structure que MgO. Le zinc en substitution tend à ségréger vers les sites de basse coordinence où il affecte les propriétés d’adsorption d’eau et d’hydrogène. Par ailleurs, le mélange ZnO-MgO obtenu par combustion d’alliage ZnMg offre une possibilité d’application grâce aux propriétés bactéricides de ZnO et de faible toxicité de MgO. L’ensemble des résultats montre la pertinence de l’étude des poudres pratiquée dans les conditions de l’UHV
The analysis of adsorption from the first stage to saturation is necessary to understand gas/solid interactions. This is the motivation for surface analysis under vacuum. The common approach of dispersed materials surfaces is incomplete since working pressures, that are high enough to achieve reasonable reaction times, do not allow studies of powder surfaces from bare to fully covered. The aim of the present work is to examine the successive changes of ZnO, MgO and ZnxMg1-xO nanopowders upon exposure to water or hydrogen from UHV to the ambient by FTIR. It is shown that ZnO smokes behave in a same way as a collection of single crystals which exhibit (0001), (0001̅), (101̅0) and (112̅0) faces with a non-polar/polar ratio of 75/25. Combining FTIR with XPS and TPD techniques, three stages of hydroxylation were identified on MgO smokes: point defects (10-8 mbar), steps (10-6 mbar) then terraces (> 10-5 mbar). Results indicate a reorganisation of surface structure showing that water adsorption on MgO(100) is an irreversible process. The common model of MgO as a series of (100) facets is questioned. At low concentrations of zinc, the mixed oxide ZnxMg1-xO consists of crystals with similar structure as MgO. A segregation of Zn2+ toward low coordinated surface sites is suggested to explain the changes in reactivity of the ZnxMg1-xO with respect to water and hydrogen at low coverages. Furthermore, the mixture ZnO-MgO produced by combustion of ZnMg alloy combines the antibacterial properties of ZnO and the biocompatibility of MgO, interesting for potential applications. The overall results demonstrate the relevance of the study of powders in ultra-high vacuum conditions

L'objectif de ce travail de doctorat est d'etudier les deplacements atomiques induits par l'interaction electronique entre un ion ou un agregat de haute energie et une cible solide. Le materiau irradie est un monocristal d'oxyde de magnesium contenant des nanoprecipites de metal alcalin (li, na ou rb). Les projectiles utilises sont des ions lourds (kr, sn, pb, u) tres energetiques ( gev) delivres par le grand accelerateur national d'ions lourds de caen, ou des agregats de c#6#0 d'energie 20 mev fournis par l'accelerateur tandem de l'institut de physique nucleaire d'orsay. Ces projectiles deposent la majeure partie de leur energie dans le solide par excitations electroniques et ionisations, et leur perte d'energie electronique est comprise entre 10 et 60 kev/nm dans mgo. L'interaction electronique entre les projectiles et le solide conduit a la formation de defauts ponctuels et etendus dans l'oxyde de magnesium, comme l'ont montre les analyses d'absorption optique, de r. B. S. En geometrie de canalisation et de microscopie electronique en transmission. La section efficace de creation de defauts dans mgo varie comme une fonction puissance avec la perte d'energie electronique des ions incidents et ne depend que peu de la temperature d'irradiation entre 17 et 300 k. Les effets d'ionisation induits par les projectiles dans les echantillons mgo-nanoparticules de metal alcalin provoquent la disparition des particules metalliques. La section efficace de destruction des precipites augmente aussi comme une fonction puissance des pertes d'energie electronique des projectiles dans le solide. La taille des precipites et la vitesse des projectiles sont des parametres importants dans ce processus de modification des inclusions de metal alcalin. Par contre, la temperature d'irradiation entre 17 et 300 k semble avoir peu d'influence sur la destruction des particules metalliques

To briefly summarize the work reported in this PhD thesis, we can say that the study of the solvothermal synthesis of MnO NPs led to procedures to obtain anisotropic MnO NPs starting from manganese(II) oleate and stearate. A detailed investigation on the influence of the reaction conditions on the size, shape, crystal structure and magnetic properties of the obtained nanoparticles was carried out, including a detailed comparison between the two precursors (manganese oleate and manganese stearate) and surfactants (oleic acid and stearic acid) and a thorough investigation of the influence of the precursor : surfactant molar ratio. Having used MnO as antiferromagnetic material for the core-shell structure, we were prompted to further consider the use of MnS, an antiferromagnetic sulfide with the Néel temperature  160 K (higher than the MnO TN = 116 K). The higher Néel temperature makes MnS a good candidate for the building of an exchange-bias coupling. MnS, unlike MnO, presents three different polymorphs: cubic α-MnS (rock-salt), cubic β-MnS (zinc-blende), and hexagonal γ-MnS (wurtzite). Thus, synthetic investigation about MnS NPs was mainly focused on the control of the nanoparticle crystal phase that, in our case, could be achieve through the use of different surfactants. Polymorphism control is a crucial point because different polymorphs exhibit different physical properties, among which, the magnetic behavior. Next, we focused on the synthetic strategy to coat anisotropic MnO NPs with a FeOx coating (FeOx stands for Fe3-xO4-x, 0 ≤ x ≤ 1). We conceived to approach this problem by a two step strategy. First, we set out to develop a procedure to grow a FeOx shell (several nanometers thick) onto large (20-30 nm) isotropic MnO cores; once obtained such procedure, we will optimize it to uniformly coat anisotropic NPs. Using isotropic MnO NPs as cores, many synthetic strategies were devised and assessed with respect to the achievement of growing a significantly thick and uniform iron oxide shell simultaneously preventing the formation of undesired homogeneous iron oxide nanoparticles. We finally developed a procedure able to grow a FeOx shell of up to 6 nm on the MnO core. We are at present working on the development of a multi-step procedure to achieve a thicker and more compact FeOx shell. The synthesis of core-shell MnO@FeOx NPs and their characterization by electron microscopy (C-TEM, electron diffraction, HRTEM, Analytical TEM) are described in detail in the Thesis, while the magnetic characterization are in progress in these days. Besides the main aim of my Thesis research, we decided to explore the feasibility to use MnO nanoparticles having different crystallographic faces as a catalysts in the water splitting reaction. We just started a collaboration with Dott. A. Minguzzi, O. Lugaresi and A. Visibile at the University of Milan to carry out an electrochemical study to investigate whether nanoparticle with different shape, the surface of which are different crystal faces, have unequal catalytic activity in the water splitting reaction. Since the work is at an early stage, here we reported only samples treatment and characterization before the electrochemical tests that are currently in progress. Finally, a complete magnetic characterization of thin-film assemblies of Ni@NiO core-shell nanoparticles, was performed and here reported thanks to a research project carried out in collaboration with the group of Professor S. D’Addato, Dr. P. Luches, and Prof. S. Valeri at CNR NANO S3 and University of Modena and Reggio Emilia. Nanoparticles were synthesized by metal vapor deposition in Modena and their magnetic behavior was investigated in our laboratory by SQUID magnetometry. The Ni@NiO core-shell assemblies prepared by a three-layer procedure (NiO layer – Ni NPs – NiO layer) turned out to display a large exchange bias that could be accurately tuned by varying the thickness of the top NiO layer.

In der vorliegenden Arbeit wurde mit Hilfe eines Photon-STM die Korrelation zwischen optischen Eigenschaften und der lokalen Morphologie an zwei unterschiedlichen Systemen untersucht. Hierfür wurden zum einem oxidgetragene Ensemble von Silber-Partikeln präpariert, wobei sowohl die Partikelform (Kuppel- und Scheibenform) als auch die deponierte Partikeldichte variiert werden konnte. Neben der Präparation solcher Partikel auf Al10O13/NiAl, konnten sphärische Silber-Kolloide geordnet, als auch ungeordnet auf HOPG aufgebracht und untersucht werden. Dabei zeigte sich, dass das Verhältnis von Höhen zu Breiten nicht nur einen signifikanten Einfluss auf die Mie-Resonanz des einzelnen Partikels hat, sondern auch die elektromagnetische Kopplung der Partikel in einem Ensemble stark kontrolliert. Die energetische Lage der Mie-Resonanz zeigt im Fall der kuppelförmigen Ag-Partikel eine starke Abhängigkeit vom Intepartikel-Abstand, was sich in einer Verschiebung zu höheren Energien für eine steigende Partikeldichte äußert. Eine solche Abhängigkeit konnte bei den Ensembles der scheibenförmigen Partikel nicht beobachtet werden. Des weiteren zeigte sich, dass, verglichen mit den ungeordneten Ensembles, die selbstorganisierte langreichweitige Ordnung der Silber-Kolloide auf HOPG nur einen schwachen Einfluss auf die energetische Position der Mie Resonanz hat.Das zweite hier untersuchte System sind dünne MgO Filme unterschiedlicher Dicken auf einem Mo(001) Substrat. Diese zeigen ein reichhaltiges Wachstumsverhalten, welches durch eine Differenz in den Gitterkonstanten von 5.3% begründet ist und erst ab etwa 25 ML zu einem flachen und defektarmen Film führt. Die so induzierte Spannung relaxiert bis zu einer Dicke von etwa 7 ML in einer periodischen Überstruktur die aus abwechselnd flachen und verkippten Ebenen an der MgO-Mo Grenzschicht hervorgeht. Für MgO Filme mit einer Dicke von etwa 12 ML werden dann Schraubenversetzungen, ausgedehnte verkippte Ebenen und Stufenkanten mit einer Orientierung entlang der Richtung beobachtet. Die optische Charakterisierung durch Feldemission von Elektronen aus der STM-Spitze in den MgO-Film wird dominiert von zwei Emissionsmaxima bei Energien von 3.1 eV und 4.4 eV. Die kontrollierte Nukleation von Gold Partikeln und die Erzeugung von Farbzentren im MgO Film erlaubten eine Zuordnung dieser Emissionen zu strahlenden Zerfällen von Exitonen an Ecken, Kinken bzw. Stufen des Magnesiumoxids. Solche Emissionsprozesse konnten allerdings nur unter Einstellungen beobachtet werden, bei denen ein gleichzeitiges Rastern der Oberfläche unmöglich ist. Bei moderaten Einstellungen war auch eine ortsaufgelösten Spektroskopie möglich, wobei dann neue Emissionsmechanismen beobachtet wurden. Dabei sind zwei Prozesse wesentlich; zum einen die Ausbildung von sog. Spitzen-induzierten Plasmonen im Bereich zwischen Spitze und dem Mo-Substrat, zum anderen strahlende Elektronenübergänge zwischen sog. Feldemissionsresonanzen, die sich im Spitze/MgO-Film System ausbilden.
In this thesis, the correlation between the optical properties and the local morphology of supported silver nanoparticle ensembles and MgO thin films deposited on Mo(001) systems is explored by means of Photon-STM. In the first section, dome and disk shaped Ag nanoparticle ensembles with increasing density on an alumina film on NiAl(110) were analyzed as well as ordered and disordered ensembles of Ag nanocolloids on HOPG. The aspect ratio of the Ag nanoparticles was found to have a significant influence not only on the Mie plasmon resonance of a single particle, but also on the electromagnetic coupling within the nanoparticle ensembles. The Mie resonance in the ensemble of dome shaped Ag nanoparticles shows a strong dependence on the interparticle distance, where it shifts to higher energies with increasing particle density, due to destructive interference effects. In the disk-like Ag ensembles, however, the plasmon energy is independent of particle-particle separation. The long-range lateral ordering of size-selected Ag nanocolloids is found to induce a high dipole-dipole coupling within the ensemble. This is mainly reflected by the enhancement of the spectral intensity of the in-plane Mie mode, due to constructive coupling. However, ensembles with either well-ordered or disordered arrangements reveal no important difference in their optical properties, reflecting the weak influence of the long-range order in the particle ensemble. Thin MgO films with different thicknesses were grown on a Mo(001) surface. The stress resulting from the 5.3% lattice mismatch between the MgO(001) and the Mo(001) lattice parameters is found to control the surface morphology of the MgO film until thicknesses of around 25ML at which flat and defect-poor films are obtained. The relaxation of the stress induces a periodic network in the first 7ML of the MgO film, consisting of alternated flat and tilted mosaics. The presence of screw dislocations, steps oriented along the MgO directions, and tilted planes is observed when the MgO films are approximately 12ML thick. In addition, an increase of the MgO work function around these new surface features is revealed from STM spectroscopy. The photon emission induced by field-emitted electron injection from the STM tip into the MgO films is dominated by two emission bands located at 3.1eV and 4.4eV. To check the origin of these bands, further experiments, namely, nucleation of Au particles and creation of F-centers on the MgO surface, have been performed. The nucleation of Au particles at the low coordinated sites is found to quench the MgO optical signal, while the creation or annihilation of F-centers does not alter the MgO emission bands. The 3.1eV and the 4.4eV bands are therefore assigned to the radiative decay of MgO excitons at corner and kink sites, and step sites, respectively. Besides, spatially resolved optical measurements in the tunneling mode of the STM revealed different light emission mechanisms. These radiative processes are mainly related to tip-induced plasmons that form between the tip and the Mo support and to electron transitions between field-emission-resonance states in the STM tip-MgO film junction. The signal from exciton decays at corners and kinks of the MgO surface is however only observed at excitation conditions where the spatial resolution is already strongly reduced.

Metal-based nanomaterials have great potential in biomedical applications due to their physiologic functions and physicochemical properties, favoring biological interactions. Magnesium is abundant in the body, mainly stored in bone, and plays a role in bone cell activities, being essential for normal bone metabolism and remodeling. Accordingly, magnesium-based materials are promising for bone-related applications. Mg(OH)2 nanoparticles appear to exert beneficial effects in bone regeneration strategies, but cellular and molecular mechanisms are poorly investigated. Upon contact with the bone, materials should allow the osteoclast-osteoblast cooperation for a normal process of bone formation and remodeling. Thus, co-culture models of osteoclastic and osteoblastic cells, allowing reciprocal communication, better mimic in vivo conditions. This work aimed two objectives. First, to establish a reproducible co-culture model of osteoblastic and osteoclastic cells, easy to implement, to provide integrated information regarding the cell response to the nanoparticles. Second, to evaluate the bone cell response to Mg(OH)2 nanoparticles in monocultured and co-cultured cells contributing to a better understanding of the involved mechanisms. MG-63 osteoblastic cell line and monocyte THP-1 cell line were selected. MG-63 cells were cultured in basal medium and osteogenic conditions. THP-1 monocytes were differentiated into macrophages with phorbol 12-myristate 13-acetate (PMA) and then into osteoclastic cells by supplementation with M-CSF and RANKL. An indirect co-culture system was set up by using Transwell® inserts to separate the cell populations. PMA-treated THP-1 monocytes were cultured on the bottom of 24-well plates, and inserts containing osteogenicinduced MG-63 cells were fitted on the well-plates. In this system, PMA-treated THP-1 cells were cultured in basal medium and with the osteoclastogenic factors. Monocultures and cocultures were maintained for 1 and 6 days, and each cell population was characterized for the respective phenotype features. Mg(OH)2 nanoparticles, synthesized in pure water or using a green synthesis process, were tested for their dose- and time-dependent effects in these culture systems. Monocultures of MG-63 cells presented high proliferation rate, synthesized ALP, expressed marker genes and were osteoblastic-induced in osteogenic conditions. Monocultured PMA-treated THP-1 macrophages differentiated into osteoclastic-like cells showed high TRAP activity, high percentage of TRAP(+) multinucleated cells and expression of marker genes. The indirect co-culture system allows the same pattern of behavior compared to the respective monocultures. However, MG-63 cells co-cultured with osteoclastdifferentiated THP-1 cells presented significantly increased ALP activity. Also, co-culture with MG-63 cells induced TRAP activity in PMA-treated THP-1 cells kept in basal medium. This shows that the cells’ reciprocal interactions have a significant effect in their phenotype behavior. Mg(OH)2 nanoparticles increased ALP of MG-63 cells, but with significantly higher induction in co-cultured cells. Nanoparticles also induced TRAP activity in THP-1 cells but, in co-cultured conditions, this effect was slightly lower than that observed in THP-1 cells supplemented with M-CSF and RANKL. These observations highlight the relevance of the cell culture model in nanoparticles testing. Summarizing, in a culture model that allows reciprocal cell paracrine interactions, Mg(OH)2 nanoparticles elicited higher inductive effect in osteoblastic behavior compared to that induced in osteoclastic behavior, suggesting an overall effect that favors osteoblastic activity.
Os nanomateriais metálicos têm enorme potencial em aplicações biomédicas devido às suas funções fisiológicas e propriedades físico-químicas, que favorecem as interações biológicas. O magnésio é abundante no organismo, está armazenado nos ossos, e desempenha um papel relevante no metabolismo e remodelação óssea. Consequentemente, os materiais à base de magnésio são promissores para aplicação óssea. As nanopartículas de Mg(OH)2 parecem exercer efeitos benéficos a nível ósseo, mas os mecanismos envolvidos têm sido pouco estudados. Após implantação, os materiais devem permitir as interações celulares garantindo a normalidade do metabolismo ósseo. Assim, os modelos de co-cultura de células osteoclásticas e osteoblásticas, que permitem uma comunicação recíproca, mimetizam as condições in vivo. Este trabalho visou dois objetivos. Primeiro, estabelecer um modelo reprodutível de co-cultura de células osteoblásticas e osteoclásticas, fácil de implementar, permitindo informação integrada sobre a resposta celular às nanopartículas. Segundo, avaliar a resposta das células ósseas às nanopartículas de Mg(OH)2 em células em monocultura e co-cultura, contribuindo para uma melhor compreensão dos mecanismos envolvidos. A linha celular MG-63 foi cultivada em meio basal e osteogénico. As células monocíticas THP-1 foram diferenciadas em macrófagos com forbol 12-miristato 13-acetate (PMA) e, depois, em células osteoclásticas por suplementação com M-CSF e RANKL. O sistema de co-cultura indireta foi implementado utilizando insertos Transwell® para separar as populações celulares. As células THP-1 foram semeadas em placas de 24 poços e diferenciadas em macrófagos, adicionando seguidamente os insertos previamente cultivados com células MG-63 induzidas em meio osteogénico. As células THP-1 foram cultivadas em meio basal ou com os fatores osteoclastogénicos. As culturas foram mantidas durante 1 e 6 dias e as populações celulares caracterizadas fenotipicamente. As nanopartículas de Mg(OH)2, sintetizadas em água pura ou por um processo de síntese verde, foram testadas nestes sistemas de cultura. As células MG-63 apresentaram uma elevada taxa de proliferação, síntese da ALP e expressão de genes específicos, parâmetros que foram induzidos em condições osteogénicas. Os macrófagos THP-1 diferenciados em células osteoclásticas mostraram elevada atividade da TRAP, células multinucleadas TRAP(+) e expressão de genes específicos. A co-cultura permitiu o mesmo padrão de comportamento comparando com as respetivas monoculturas. No entanto, as células MG-63 co-cultivadas com células THP-1 diferenciadas em osteoclastos apresentaram um aumento significativo da atividade da ALP. Além disso, a co-cultura com células MG-63 induziu a atividade da TRAP em células THP-1 mantidas em meio basal. Assim, as interações recíprocas tiveram um efeito significativo no comportamento fenotípico. As nanopartículas de Mg(OH)2 induziram a atividade de ALP das células MG-63, mas o efeito foi significativamente maior nas células co-cultivadas. As nanopartículas também induziram a atividade da TRAP em células THP-1 mas, em condições de co-cultura, este efeito foi ligeiramente inferior ao observado em células THP-1 suplementadas com M-CSF e RANKL. Estas observações realçam a relevância do modelo de cultura na avaliação das nanopartículas. Resumindo, num modelo de co-cultura que permite interações parácrinas celulares, as nanopartículas de Mg(OH)2 provocaram um maior efeito indutivo no comportamento osteoblástico em comparação com o induzido no comportamento osteoclástico, sugerindo um efeito global que favorece a atividade osteoblástica.
Dissertação de Mestrado em Biotecnologia para as Ciências da Saúde

A series of CeO2-MgO nanocomposite oxides were prepared by gel combustion method. The nanocomposite oxides were characterized by XRD, UV and SEM techniques. The presence of well dispersed ceria nanoparticles in MgO matrix was ascertained from the XRD and UV study. SEM study indicated the material to be porous and low density in nature. The CeO2-MgO composite oxide was used as an efficient heterogeneous catalyst for the Knoevenagel condensation of aromatic aldehydes and malononitrile.

碩士
國立交通大學
材料科學與工程學系奈米科技碩博士班
107
In this study, we prepared magnesium oxide (MgO) in the MOF (metal-organic framework) material ZIF-8 for carbon dioxide adsorption and transesterification purpose. Due to the microporosity of ZIF-8, nanoconfinement effect has been adopted to control well-dispersed MgO at ZIF-8 (denoted as MgO@ZIF-8) with different metal oxide loadings. MgO was prepared via wet precipitation of Mg(OH)2, which was further calcinated into MgO. From powder X-ray diffraction (PXRD), MgO crystals in ZIF-8 have small and regulated size, regardless of magnesium loadings. After material properties analysis, we apply our MgO@ZIF-8 for CO¬2 adsorption. 50% MgO@ZIF-8 showed an improved CO2 adsorption capacity (1.23mmol) than those of neat MgO and ZIF-8. On the other hand, CO¬2 desorption was tested with CO2-TPD. It was discovered that the lowest CO2 desorption temperature of 40% MgO@ZIF-8, 345°C, which is lowered by 55 degrees compared to the commercial magnesium carbonate. Finally, we tested the activity of MgO@ZIF-8 for transesterification catalytic reactions. It showed higher catalytic activities than their physically-mixed counterparts, indicative of a synergistic effect between MgO and ZIF-8, explained by a proposed mechanism based on acid-base bifunctional sites on the surface.

碩士
國立中央大學
化學學系
105
Trainsition metal oxide as anode materials in lithium ion batteries have attracted tremendous attention in the past few years because of their characterstics.ZnO is regarded as one of the most promising anode material for lithium ion batteries (LIBs), due to its high theoretical capacity (978 mAh/g), natural abundance, and low cost. Although MgO is electrochemically inactive, its adsorption capacity towards liquid electrolyte functioning as a protective coating and enhancement in ionic conductivity encourages the use of a MgO-decorated composite as an anode for LIBs. The ZnO@CMK-8 and MgO@CMK-8 nanocomposites, composed of ultrafine ZnO and MgO nanoparticles encapsulated in three dimensional (3D) ordered mesoporous carbon CMK-8, has been successfully synthesized and served as promising anode materials in lithium-ion batteries (LIBs) with different concertration, separately. The prepared ZnO@CMK-8 and MgO@CMK-8 have been characterized by various techniques, such as XRD, nitrogen adsorption-desorption, high-resolution TEM, and SEM measurements. Our characterization results demonstrates that both ZnO and MgO nanoparticles can be incorporated into the mesopores of CMK-8 with high dispersion and small particle sizes. As anode materials in lithium ion batteries the composites ZnO@CMK-8-0.5M displays higher initial discharge capacity(2214 mAh/g) than bulk ZnO. MgO@CMK-8-10wt% also demonstrates the better results(744 mAh/g) than rude MgO.

碩士
國立交通大學
材料科學與工程學系所
107
Herein, we report the synthesis of novel intrinsic luminescent curcumin modified nanodiamond derivative (ND-Cur) as an effective probe towards cell imaging and sensory applications. The synthesized ND-Cur was characterized by FTIR, Raman, SEM, DLS and TEM studies. From DLS data, the particle size of ND-Cur was estimated to be 170.6 ± 46.8 nm with a zeta potential (ζ) of +45.38. Between 350 to 450 nm excitations, the photoluminescence spectra of ND-Cur were observed at 536 nm with diverse intensities. However, at 430 nm excitation ND-Cur have the intense smooth peak at 536 nm, henceforth further selectivity studies were carried out at the same excitation value. Notably, the low toxicity and biocompatibility of ND-Cur has been demonstrated by MTT assay and time dependent cell imaging interrogations. Next, during the sensor selectivity investigations towards metal ions, ND-Cur witnessed the diverse selectivity to Mg2+ and Mn2+ ions via intense fluorescence peak shift and “Turn-off” responses, respectively. In presence of Mg2+, the ND-Cur peak at 536 was shifted and displayed two diverse peaks at 498 and 476 nm. On the other hand, with Mn2+ ions, ND-Cur revealed the fluorescent quenching response at 536 nm. The linear range for both Mg2+ and Mn2+ detections were established as 1~100 µM exhibiting nanomolar level limits of detection (LODs). The mechanism, ratiometric changes and binding site were established through PL, FTIR, Raman, SEM, TEM, DLS and Zeta potential analyses. Excitingly, effective determination of Mg2+ and Mn2+ ions by ND-Cur has been validated through cell imaging interrogations.

The properties of bulk 3D materials of metals or semiconductors are manifested with various length scales(e.g., Bohr excitonic radius, magnetic correlation length, mean free path etc.) and are important in controlling their properties. When the size of the material is smaller than these characteristics length scales, the confinement effects operate reflecting changes in their physical behavior. Materials with such confinement effects can be designated as low dimensional materials. There are exceedingly large numbers of low dimensional materials and the last half a century has probably seen the maximum evolution of such materials in terms of synthesis, characterization, understanding and modification of their properties and applications. The field of” nanoscience and nanotechnology”, have become a mature field within the last three decades where, for certain application, synthesis of materials of sizes in the nanometer range can be designed and controlled. Interface plays a very important role in controlling properties of heterogeneous material of every dimensionality. For example, the interface forms in 2D thin films or interface of heterogeneous nanoparticles(0D). In recent times, a large number of remarkable phenomena have triggered understanding and controlling properties arises due to nature of certain interface. In the field of nanoparticles, it is well known that the photoluminescence property depends very strongly on the nature of interface in heterostructured nanoparticles. In the recent time a large variety of heterostructured nanoparticles starting from core-shell to quantum dot-quantum well kind has been synthesized to increase the photoluminescence efficiency up to 80%. Along with improvement of certain properties due to heterostructure formation inside the nanoparticles, the techniques to understand the nature of those interfaces have improved side by side. It has been recently shown that variable energy X-ray Photoemission Spectroscopy (XPS) can be employed to understand the nature of interfaces (internal structure) of such heterostructure nanoparticles in great detail with high accuracy. While most of the previous studies of variable energy XPS, uses photonenergies sensitive to smaller sized particle, we have extended the idea of such nondestructive approach of understanding the nature of buried interfaces to bigger sized nanoparticles by using photon energy as high as 8000eV, easily available in various 3rd generation synchrotron centers. The nature of the interface also plays an important role in multilayer thin films. Major components of various electronic devices, like read head memory devices, field effect transistors etc., rely on interface properties of certain multilayer thin film materials. In recent time wide range of unusual phenomenon such as high mobility metallic behavior between two insulating oxide, superconductivity, interface ferroelectricity, unusual magnetism, multiferroicity etc. has been observed at oxide interface making it an interesting field of study. We have shown that variable energy photoemission spectroscopy with high photon energies, can be a useful tool to realize such interfaces and controlling the properties of multilayered devices, as well as to understand the origin of unusual phenomenon exists at several multilayer interfaces. Chapter1 provides a brief description of low dimensional materials, overall perspective of interesting properties in materials with reduced dimensionality. We have emphasized on the importance of determining the internal structure of buried interface of different dimensionalities. We have given a brief overview and importance of different interfaces that we have studied in the subsequent chapters dealing with specific interfaces. Chapter 2 describes experimental and theoretical methods used for the study of interface and self-assembly reported in this thesis. These methods are divided into two categories. The first section deals with different experimental techniques, like, UV-Visible absorption and photoluminescence spectroscopy, X-Photoelectron Spectroscopy(XPS), X-Ray diffraction, Transmission Electron Microscopy(TEM) etc. This section also includes brief overview on synchrotron radiation and methods used for detail analysis of interface structure using variable energy XPS. In the second part of this chapter, we have discussed theoretical methods used in the present study. \ In Chapter 3A we have combined low energy XPS, useful to extract information of the surface of the nanoparticles, with high energy XPS, important to extract bulk information and have characterized the internal structure of nanoparticle system of different heterogeneity. We have chosen two important heterostructure systems namely, inverted core-shell(CdScore-CdSeshell) type nanoparticles and homogeneous alloy(CdSeS)type nanoparticles. Such internal structure study revealed that the actual internal structure of certain nanomaterial can be widely different from the aim of the synthesis and knowledge of internal structure is a prerequisite in understanding their property. We were able to extend the idea of variable energy XPS to higher energy limit. Many speculations have been made about the probable role of interface in controlling properties, like blinking behavior of bigger sized core-shell nanoparticles, but no conclusive support has yet been given about the nature of such interface. After successfully extending the technique to determine the internal structure of heterostructured nanoparticles to very high photon energy region, we took the opportunity to determine the internal structure of nanoparticles of sizes as large as 12nm with high energy photoemission spectroscopy for the first time. In Chapter 3B we emphasize on the importance of interface structure in controlling the behavior of bigger sized nanoparticles systems, the unsettled issues regarding their internal structure, and described the usefulness of high energy XPS in elucidating the internal structure of such big particles with grate accuracy to solve such controversies. The existence of high density storage media relies on the existence of highly sensitive magnetic sensors with large magnetoresistance. Today almost all sensor technologies used in modern hard disk drives rely on tunnel magnetoresistance (TMR) CoFeB-MgO-CoFeB structures. Though device fabrication is refined to meet satisfactory quality assurance demands, fundamental understanding of the refinement in terms of its effect on the nature of the interfaces and the MgO tunnel barrier leading to improved TMR is still missing. Where, the annealing condition required to improve the TMR ratio is itself not confirmatory its effect on the interface structure is highly debatable. In particular, it has been anticipated that under the proposed exotic conditions highly mobile B will move into the MgO barrier and will form boron oxide. In Chapter 4 we are able to shed definite insights to heart of this problem. We have used high energy photoemission to investigate a series of TMR structures and able to provide a systematic understanding of the driving mechanisms of B diffusion in CoFeBTMR structures. We have solved the mix-up of annealing temperature required and have shown that boron diffusion is limited merely to a sub-nanometer thick layer at the interface and does not progress beyond this point under typical conditions required for device fabrication. We have given a brief overview on the evolution of magnetic storage device and have described various concepts relevant for the study of such systems. The interface between two nonmagnetic insulators LaAlO3 and SrTiO3 has shown a variety of interface phenomena in the recent times. In spite of a large number of high profile studies on the interface LaAlO3 and SrTiO3 there is still a raging debate on the nature, origin and the distribution of the two dimensional electron gas that is supposed to be responsible for its exotic physical properties, ranging from unusual transport properties to its diverse ground states, such as metallic, magnetic and superconducting ones, depending on the specific synthesis. The polar discontinuity present across the SrTiO3-LaAlO3 interface is expected to result in half an electron transfer from the top of the LaAlO 3 layer to each TiofSrTiO3 at the interface, but, the extent of localization that can make it behave like delocalized with very high mobility as well as localized with magnetic moments is not yet clear. In Chapter 5 we have given a description of this highly interesting system as well as presented the outcome of our depth resolved XPS investigation on several such samples synthesized under different oxygen pressure. We were able to describe successfully the distribution of charge carriers. While synthesizing and understanding properties of nanoparticles is one issue, using them for device fabrication is another. For example, to make a certain device often requires specific arrangements of nanoparticles in a suitable substrate. Self-assembly formation can be a potential tool in these regards. Just like atom or ions, both nano and colloidal particles also assemble by themselves in ordered or disordered structure under certain conditions, e.g., the drying of a drop of suspension containing the colloid particles over a TEM grid. This phenomenon is known as self-assembly. Though, the process of assembly formation can be a very easy and cost-effective technique to manipulate the properties in the nano region, than the existing ones like lithography but, the lack of systematic study and poor understanding of these phenomena at microscopic level has led to a situation that, there is no precise information available in literature to say about the nature of such assembly. In Chapter 6 we have described experiments that eliminate the dependence of the self-assembly process on many complicating factors like substrate-particle interaction, substrate-solvent interaction etc., making the process of ordering governed by minimum numbers of experimental parameter that can be easily controlled. Under simplified conditions, our experiments unveil an interesting competition between ordering and jamming in drying colloid systems similar to glass transition phenomenon Resulting in the typical phase behavior of the particles. We establish a re-entrant behavior in the order-disorder phase diagram as a function of particle density such that there is an optimal range of particle density to realize the long-range ordering. The results are explained with the help of simulations and phenomenological theory. In summary, we were able to extend the idea of variable energy XPS to higher energy limit advantageous for investigating internal structure of nonmaterial of various dimensionalities and sizes. We were able to comprehend nature of buried interface indicating properties of heterostructures quantum dots and thin films. Our study revealed that depth resolved XPS combined with accessibility of high and variable energies at synchrotron centers can be a very general and effective tool for understanding buried interface. Finally, we have given insight to the mechanism of spontaneous ordering of nanoparticles over a suitable substrate.

The properties of bulk 3D materials of metals or semiconductors are manifested with various length scales(e.g., Bohr excitonic radius, magnetic correlation length, mean free path etc.) and are important in controlling their properties. When the size of the material is smaller than these characteristics length scales, the confinement effects operate reflecting changes in their physical behavior. Materials with such confinement effects can be designated as low dimensional materials. There are exceedingly large numbers of low dimensional materials and the last half a century has probably seen the maximum evolution of such materials in terms of synthesis, characterization, understanding and modification of their properties and applications. The field of” nanoscience and nanotechnology”, have become a mature field within the last three decades where, for certain application, synthesis of materials of sizes in the nanometer range can be designed and controlled. Interface plays a very important role in controlling properties of heterogeneous material of every dimensionality. For example, the interface forms in 2D thin films or interface of heterogeneous nanoparticles(0D). In recent times, a large number of remarkable phenomena have triggered understanding and controlling properties arises due to nature of certain interface. In the field of nanoparticles, it is well known that the photoluminescence property depends very strongly on the nature of interface in heterostructured nanoparticles. In the recent time a large variety of heterostructured nanoparticles starting from core-shell to quantum dot-quantum well kind has been synthesized to increase the photoluminescence efficiency up to 80%. Along with improvement of certain properties due to heterostructure formation inside the nanoparticles, the techniques to understand the nature of those interfaces have improved side by side. It has been recently shown that variable energy X-ray Photoemission Spectroscopy (XPS) can be employed to understand the nature of interfaces (internal structure) of such heterostructure nanoparticles in great detail with high accuracy. While most of the previous studies of variable energy XPS, uses photonenergies sensitive to smaller sized particle, we have extended the idea of such nondestructive approach of understanding the nature of buried interfaces to bigger sized nanoparticles by using photon energy as high as 8000eV, easily available in various 3rd generation synchrotron centers. The nature of the interface also plays an important role in multilayer thin films. Major components of various electronic devices, like read head memory devices, field effect transistors etc., rely on interface properties of certain multilayer thin film materials. In recent time wide range of unusual phenomenon such as high mobility metallic behavior between two insulating oxide, superconductivity, interface ferroelectricity, unusual magnetism, multiferroicity etc. has been observed at oxide interface making it an interesting field of study. We have shown that variable energy photoemission spectroscopy with high photon energies, can be a useful tool to realize such interfaces and controlling the properties of multilayered devices, as well as to understand the origin of unusual phenomenon exists at several multilayer interfaces. Chapter1 provides a brief description of low dimensional materials, overall perspective of interesting properties in materials with reduced dimensionality. We have emphasized on the importance of determining the internal structure of buried interface of different dimensionalities. We have given a brief overview and importance of different interfaces that we have studied in the subsequent chapters dealing with specific interfaces. Chapter 2 describes experimental and theoretical methods used for the study of interface and self-assembly reported in this thesis. These methods are divided into two categories. The first section deals with different experimental techniques, like, UV-Visible absorption and photoluminescence spectroscopy, X-Photoelectron Spectroscopy(XPS), X-Ray diffraction, Transmission Electron Microscopy(TEM) etc. This section also includes brief overview on synchrotron radiation and methods used for detail analysis of interface structure using variable energy XPS. In the second part of this chapter, we have discussed theoretical methods used in the present study. \ In Chapter 3A we have combined low energy XPS, useful to extract information of the surface of the nanoparticles, with high energy XPS, important to extract bulk information and have characterized the internal structure of nanoparticle system of different heterogeneity. We have chosen two important heterostructure systems namely, inverted core-shell(CdScore-CdSeshell) type nanoparticles and homogeneous alloy(CdSeS)type nanoparticles. Such internal structure study revealed that the actual internal structure of certain nanomaterial can be widely different from the aim of the synthesis and knowledge of internal structure is a prerequisite in understanding their property. We were able to extend the idea of variable energy XPS to higher energy limit. Many speculations have been made about the probable role of interface in controlling properties, like blinking behavior of bigger sized core-shell nanoparticles, but no conclusive support has yet been given about the nature of such interface. After successfully extending the technique to determine the internal structure of heterostructured nanoparticles to very high photon energy region, we took the opportunity to determine the internal structure of nanoparticles of sizes as large as 12nm with high energy photoemission spectroscopy for the first time. In Chapter 3B we emphasize on the importance of interface structure in controlling the behavior of bigger sized nanoparticles systems, the unsettled issues regarding their internal structure, and described the usefulness of high energy XPS in elucidating the internal structure of such big particles with grate accuracy to solve such controversies. The existence of high density storage media relies on the existence of highly sensitive magnetic sensors with large magnetoresistance. Today almost all sensor technologies used in modern hard disk drives rely on tunnel magnetoresistance (TMR) CoFeB-MgO-CoFeB structures. Though device fabrication is refined to meet satisfactory quality assurance demands, fundamental understanding of the refinement in terms of its effect on the nature of the interfaces and the MgO tunnel barrier leading to improved TMR is still missing. Where, the annealing condition required to improve the TMR ratio is itself not confirmatory its effect on the interface structure is highly debatable. In particular, it has been anticipated that under the proposed exotic conditions highly mobile B will move into the MgO barrier and will form boron oxide. In Chapter 4 we are able to shed definite insights to heart of this problem. We have used high energy photoemission to investigate a series of TMR structures and able to provide a systematic understanding of the driving mechanisms of B diffusion in CoFeBTMR structures. We have solved the mix-up of annealing temperature required and have shown that boron diffusion is limited merely to a sub-nanometer thick layer at the interface and does not progress beyond this point under typical conditions required for device fabrication. We have given a brief overview on the evolution of magnetic storage device and have described various concepts relevant for the study of such systems. The interface between two nonmagnetic insulators LaAlO3 and SrTiO3 has shown a variety of interface phenomena in the recent times. In spite of a large number of high profile studies on the interface LaAlO3 and SrTiO3 there is still a raging debate on the nature, origin and the distribution of the two dimensional electron gas that is supposed to be responsible for its exotic physical properties, ranging from unusual transport properties to its diverse ground states, such as metallic, magnetic and superconducting ones, depending on the specific synthesis. The polar discontinuity present across the SrTiO3-LaAlO3 interface is expected to result in half an electron transfer from the top of the LaAlO 3 layer to each TiofSrTiO3 at the interface, but, the extent of localization that can make it behave like delocalized with very high mobility as well as localized with magnetic moments is not yet clear. In Chapter 5 we have given a description of this highly interesting system as well as presented the outcome of our depth resolved XPS investigation on several such samples synthesized under different oxygen pressure. We were able to describe successfully the distribution of charge carriers. While synthesizing and understanding properties of nanoparticles is one issue, using them for device fabrication is another. For example, to make a certain device often requires specific arrangements of nanoparticles in a suitable substrate. Self-assembly formation can be a potential tool in these regards. Just like atom or ions, both nano and colloidal particles also assemble by themselves in ordered or disordered structure under certain conditions, e.g., the drying of a drop of suspension containing the colloid particles over a TEM grid. This phenomenon is known as self-assembly. Though, the process of assembly formation can be a very easy and cost-effective technique to manipulate the properties in the nano region, than the existing ones like lithography but, the lack of systematic study and poor understanding of these phenomena at microscopic level has led to a situation that, there is no precise information available in literature to say about the nature of such assembly. In Chapter 6 we have described experiments that eliminate the dependence of the self-assembly process on many complicating factors like substrate-particle interaction, substrate-solvent interaction etc., making the process of ordering governed by minimum numbers of experimental parameter that can be easily controlled. Under simplified conditions, our experiments unveil an interesting competition between ordering and jamming in drying colloid systems similar to glass transition phenomenon Resulting in the typical phase behavior of the particles. We establish a re-entrant behavior in the order-disorder phase diagram as a function of particle density such that there is an optimal range of particle density to realize the long-range ordering. The results are explained with the help of simulations and phenomenological theory. In summary, we were able to extend the idea of variable energy XPS to higher energy limit advantageous for investigating internal structure of nonmaterial of various dimensionalities and sizes. We were able to comprehend nature of buried interface indicating properties of heterostructures quantum dots and thin films. Our study revealed that depth resolved XPS combined with accessibility of high and variable energies at synchrotron centers can be a very general and effective tool for understanding buried interface. Finally, we have given insight to the mechanism of spontaneous ordering of nanoparticles over a suitable substrate.