Die vorliegende Arbeit befasst sich mit der Synthese und Charakterisierung von unterschiedlichen nanostrukturierten Hybridmaterialien ausgehend von nur einem Monomer. Dabei wird ein neuartiges Monomer vorgestellt, welches in einem Prozessschritt ein Hybridmaterial bestehend aus drei Polymeren bilden kann. Dies erweitert das Konzept der Zwillingspolymerisation, bei der zwei Polymere aus einem Monomer erhalten werden. Aus diesem Grund wurde der Überbegriff „Mehrlingspolymerisation“ für die Synthese von zwei oder mehr Polymeren aus nur einem Monomer eingeführt. Ein weiterer Schwerpunkt lag auf der gezielten Beschichtung verschiedener Partikeloberflächen mit nanostrukturierten Hybridmaterialien mittels Zwillingspolymerisation. Dabei wird der Einfluss der Oberfläche auf die Polymerisation verschiedener Zwillingsmonomere untersucht. Durch Nachbehandlung sind daraus poröse Kompositmaterialien zugänglich. Je nach Beständigkeit der Substrate sind diese in den Nachbehandlungsschritten stabil oder werden entfernt und dienen nur als Template zur Strukturierung der porösen Materialien. Es wurden unterschiedliche poröse Kohlenstoffe und Kohlenstoffkompositmaterialien hergestellt und charakterisiert. Ausgewählte Materialien wurden mit Schwefel verschmolzen und in Lithium-Schwefel-Zellen untersucht (Kooperation Dr. S. Choudhury, Leibniz-Institut für neue Materialien Saarbrücken). Die Charakterisierung der Proben erfolgte unter anderem mithilfe der Festkörper-NMR-Spektroskopie, Elektronenmikroskopie, dynamischen Differenzkalorimetrie, Röntgenpulver-diffraktometrie, Infrarotspektroskopie, Raman-Spektroskopie, Thermogravimetrie und Stickstoffsorption.

Selbstorganisierte InAs Nanostrukturen in InP, wie Quantendrähte, Quantenpunkte, und Quantengräben als Referenz, werden bezüglich ihres Wachstums, ihrer Struktur, optischen Eigenschaften und Transporteigenschaften untersucht. Das Stranski-Krastanov Wachstum der Nanostrukturen auf exakt orientiertem und vizinalem InP(001) wird mittels Gasquellen-Molekularstrahlepitaxie untersucht. Ich zeige, dass die Missorientierung des vizinalen InP, weitestgehend unabhängig von den Wachstumsparametern, den Nanostrukturtyp definiert. Optische Polarisation der Interbandübergänge (im 1.55 Mikrometer Bereich) aufgrund des Nanostrukturtyps wird mittels Photolumineszenz- und Transmissionsspektroskopie wird nachgewiesen. Die experimentell unaufwändige 4-Kontakt van der Pauw Hall Messung wird erweitert, um anisotrope Transporteigenschaften zu bestimmen. Der Ladungstägertransport in einer Schicht dicht gepackter, lateral gekoppelter InAs Nanostrukturen ist stark anisotrop mit der Hochbeweglichkeitsrichtung [-110], was parallel zur Richtung der Quantendrähte ist. Die maximalen Anisotropien übersteigen 30 für Elektronen und 100 für Löcher. Die extreme Anisotropie im Falle der Löcher basiert auf diffusem Transport in der [-110], und Hoppingtransport in der [110] direction. Die Elektronenbeweglichkeit bei niedrigen Temperaturen wird duch Grenzflächenrauhigkeitsstreuung in der [110] direction, und Streuung an entfernten Störstellen in der [-110] dominiert. Im Kontext gekoppelter Nanostrukturen, zeige ich, dass die Transportanisotropie auf anisotroper Tunnelkopplung zwischen benachbarten Nanostrukturen beruht, und weniger durch die Form der Nanostruktur bestimmt wird. Transport im Quanten-Hall Regime, und die Schwache Lokalisierung werden untersucht. Ein neuartiges Baulelement basierend auf Gate-konrollierter Transportanisotropie wird vorgeschlagen. Es wird gezeigt, dass modulationsdotierte InAs Quantendrähte für eine Implementierung des Bauelements geeignet sind. / Self-assembled InAs nanostructures in InP, comprising quantum wires, quantum dots, and quantum wells as reference, are studied in terms of their formation, structural properties, optical properties, and anisotropic transport properties. The Stranski-Krastanov growth of InAs nanostructures is studied by gas-source molecular beam epitaxy on both nominally oriented and vicinal InP(001). I demonstrate that the off-cut direction of vicinal substrates - largely independent of growth conditions - determines the nanostructure type. Optical polarization of the interband transitions (in the 1.55 micron wavelength range) arising from the nanostructure type is demonstrated by photoluminescence and transmission spectroscopy. The experimentally convenient four-contact van der Pauw Hall measurement is extended to yield the anisotropic transport properties. The in-plane transport in large ensembles of closely spaced, laterally coupled InAs nanostructures is highly anisotropic with the high-mobility direction [-110], which is parallel to the direction of the quantum wires. The maximum anisotropies exceed 30 for electrons, and 100 for holes. The extreme anisotropy for holes is due to diffusive transport in the [-110], and hopping transport in the [110] direction. The principal electron mobilities at low temperature are dominated by interface roughness scattering in the [110] direction, and by remote impurity scattering in the [-110] direction. In the context of coupled nanostructure, I demonstrate that the transport anisotropy results from directionally anisotropic tunnel coupling between adjacent nanostructures rather than from the nanostructure shape anisotropy. The Quantum-Hall regime, and the weak-localization contribution to conductivity is studied. A novel 5-terminal electronic switching device based on gate-controlled transport anisotropy is proposed. Modulation-doped InAs/InP quantum wires are demonstrated to be a candidate for implementation of the device.

In dieser Arbeit untersuchen wir die ultraschnelle Dynamik von Ladungsträgern und kohärenten Intersubbandpolarisationen in quasi-zweidimensionalen Halbleiternanostrukturen und Halbleiterbauelementen. Insbesondere werden n-Typ modulationsdotierte multiple Quantentöpfe und Quantenkaskadenlaserstrukturen basierend auf dem Materialsystem GaAs/AlGaAs mit der Methode der ultraschnellen Spektroskopie im mittleren Infrarot (3-20 mu) studiert. Ein neuartiger experimenteller Aufbau ist entwickelt worden, der zum ersten Mal das phasen- und amplitudenkontrollierte Formen von ultraschnellen Feldtransienten im mittelinfraroten Spektralbereich erlaubt. Wir untersuchen die Möglichkeit der kohärenten Kontrolle von Intersubbandübergängen. Amplituden- und phasenkonntrollierte Feldtransienten im mittleren Infrarot, die mit unserer neuen Laserquelle erzeugt werden, induzieren resonante Intersubbandanregungen in n-Typ modulationsdotierten GaAs/AlGaAs Quantentöpfen. Die transmittierten elektrischen Feldtransienten werden mit Hilfe des ultraschnellen elektro-optischen Abtastverfahrens gemessen. Unter Anwendung zweier phasengekoppelter Mittinfarotpulse variabler relativer Phase zeigen wir erstmalig die kohärente Kontrolle an linearen Intersubbandpolarisationen mit Dephasierungszeiten unterhalb einer Pikosekunde. Eine Sättigung von mehr als 0.2 wird bei einer Mittinfrarotpulsenergie von nur 1 pJ erreicht. Es wird erstmalig ein direktes, zeitaufgelöstes Experiment an elektrisch betriebenen Quantenkaskadenstrukturen vorgestellt. Diese Untersuchung ermöglicht den Einblick in die Dynamik des Elektronentransports, der mit stationären Methoden nicht meßbar ist. Der ultraschnelle Quantentransport der Elektronen vom Injektor durch die Injektionsbarriere in das obere Lasersubband wird in Femtosekunden-Mittinfrarot-Anreg-Abtast-Experimenten untersucht. Auf diese Weise beobachten wir die ultraschnelle Sättigung und die nachfolgende Wiederherstellung des elektrisch induzierten Gains. Wir beobachten ausgeprägte Gainoszillationen bei angelegtem Vorwärtsstrom und an spektralen Positionen am Gainmaximum. Dies ist ein direkter Beweis für eine kohärente Wellenpaketspropagation vom Injektor in das obere Lasersubband mittels resonantem Tunneln trotz der hohen Ladungsträgerdichte in Quantenkaskadenlasern. Nach der Sättigung ist der elektrisch induzierte Gain bei niedrigen Gitter- und Ladungsträgertemperaturen innerhalb einer Pikosekunde vollständig wiederhergestellt. / In this thesis we investigate the ultrafast dynamics of carriers and coherent intersubband polarizations in quasi-two-dimensional semiconductor nanostructures and devices. In particular, we study n-type modulation doped multiple quantum wells and quantum cascade laser structures based on the GaAs/AlGaAs material system using ultrafast spectroscopy in the mid-infrared spectral range (3-20 mu). A novel experimental setup is developed allowing for the first time the controlled phase and amplitude shaping of ultrafast field transients in the mid-infrared wavelength range. We study the feasibility of coherent nonlinear control of intersubband polarizations. Amplitude and phase-controlled mid-infrared field transients from our new laser source induce resonant intersubband excitations in n-type modulation doped GaAs/AlGaAs quantum wells. The transmitted electric field transients are directly measured by ultrafast electro-optic sampling. We demonstrate for the first time coherent control of linear intersubband polarizations with subpicosecond dephasing times by applying two phase-locked pulses with variable relative phase. A saturation of the intersubband excitation by more than 0.2 is achieved with mid-infrared pulses of only 1 pJ pulse energy. We present for the first time a direct time-resolved experimental study on electrically driven quantum cascade laser structures. These studies provide insight into the dynamics of electron transport, which can not be obtained by stationary measurements. The ultrafast quantum transport of electrons from the injector through the injection barrier into the upper laser subband is investigated in femtosecond mid-infrared pump-probe experiments. In this way we directly monitor the ultrafast saturation and subsequent recovery of electrically induced gain. For forward bias and spectral positions around the gain maximum we observe pronounced gain oscillations. This gives direct evidence for a coherent wave packet motion from the injector into the upper laser subband via resonant tunneling even at the high electron density present in a quantum cascade laser structure. After saturation the electrically induced gain is completely recovered within 1 ps at low lattice and carrier temperatures.

Nous étudions dans cet ouvrage les effets conjugués de l'interaction et du désordre sur la localisation de particules fermioniques. Nous montrons que l'établissement au-dessus du niveau de Fermi d'une interaction attractive de Hubbard entre deux particules évoluant sur un réseau désordonné d'Anderson (bi ou tridimensionnel) mène, dans l'état fondamental, à la création d'une paire de particules localisées. Cette phase biparticulaire apparaît dans un régime de désordre où les particules sans interaction ne sont pas encore localisées (phase métallique du modèle d'Anderson). Cette localisation persiste également pour les états excités tant que ceux-ci décrivent un état où les deux particules liées forment une paire. Cette phase de biparticules localisées par interaction attractive (phase BLS) disparaît néanmoins au profit d'une phase de paires de Cooper délocalisées lorsque les fluctuations du désordre sur le réseau sont suffisamment faibles. Un champ magnétique permet également, en altérant la structure des paires, de délocaliser les particules menant ainsi à la disparition de la phase BLS. Ce modèle quantique de deux particules constitue, pour les systèmes désordonnés, une généralisation du problème de Cooper. Nous montrons alors qu'il est nécessaire d'aller au-delà de l'approximation que constitue l'ansatz de Cooper pour décrire correctement la phase BLS. Ce résultat traduit le fait que, pour les systèmes à N-corps, les techniques de champs moyen utilisant l'appariement des particules suggéré par l'ansatz de Cooper ne permettent pas de traiter de manière correcte les influences conjuguées du désordre et de l'attraction dans les supraconducteurs fortement désordonnés. Une extension de notre modèle, au cas de N>2 fermions en interaction, est envisagé, montrant que l'état fondamental à N-corps entreprends une transition d'un état délocalisé (supraconducteur) vers un état localisé (isolant) lorsque le désordre augmente dans le système.

The aim of this thesis work was to gain understanding of the interactions between talc mineral and surfaces, liquids and chemicals relevant for industrial applications, such as pulp and paper. Talc is used in the pulp and paper industry as a filler pigment, in control of pitch (lipophilic extractives) deposits and as a coating pigment. A deeper understanding of talc interactions will be beneficial in optimizing its use. Long-range attractive interactions between talc and hydrophobic model probes, as well as pitch probes, have been measured using the atomic force microscope (AFM) colloidal probe method. Two procedures for preparation of pitch colloidal probes were developed to allow these studies. Model hydrophobic, nanorough surfaces with surface energy characteristics similar to talc have also been prepared and their interactions with hydrophobic model probes compared to interactions between hydrophobic model probes and talc. It is demonstrated that talc mineral interacts with model hydrophobic particles, as well as with pitch, by long-range attractive forces, considerably stronger than the expected van der Waals force. The possible origin of the measured interaction forces is discussed, and the conclusion is that the main cause is an attractive capillary force due to formation of a gas/vapor capillary between the surfaces. Force measurements using model hydrophobic, nanorough surfaces show that a large-scale waviness does not significantly influence the range and magnitude of the capillary attraction, but large local variations in these quantities are found. It is demonstrated that a large variation in adhesion force corresponds to a small variation in local contact angle of the capillaries at the surfaces. The nature of the surface topographical features influences the capillary attraction by affecting the local contact angle and by pinning of the three-phase contact line. The effect is clearly dependent on the size of the surface features and whether they exist in the form of crevices or as extending ridges. Entrapment of air also affects the imbibition of water in pressed talc tablets. The effects of wetting and dispersion agents on the interactions between talc and hydrophobic probes have also been investigated. It is demonstrated that a common dispersing agent used for talc, poly(acrylic acid), does not affect the capillary attraction between talc and non-polar probes. In fact, the results strongly suggest that poly(acrylic acid) does not adsorb on the basal plane of talc. From this finding it is inferred that the stabilizing effect of this additive most likely is due to adsorption to the edges of talc. In contrast, a wetting agent (the non-ionic triblock copolymer Pluronic PE6400) removes the long-range capillary attraction. It is suggested that such an ability to replace air at the talc surface is of great importance for an efficient wetting agent. The Hamaker constant for talc has also been estimated by using optical data obtained from spectroscopic ellipsometry. It is demonstrated that a nanocrystalline talc mineral, cut in different directions displays very small differences in Hamaker constant between the different crystallographic orientations, whereas a microcrystalline sample displays a significantly higher value. The estimated Hamaker constants are discussed for different material combinations of relevance for the pulp- and paper industry, such as cellulose and calcium carbonate. / Målet med detta avhandlingsarbete var att öka förståelsen för interaktioner mellan talkmineral och ytor, vätskor och kemikalier relevanta för industriella applikationer, såsom papper och massa. Talk används i pappers- och massaindustrin som fyllmedel, för kontroll av hartsrika (lipofila extraktivämnen) avsättningar och som bestrykningspigment. En djupare förståelse för talkinteraktioner kommer att vara användbart för att optimera dess användning. Långväga attraktiva interaktioner mellan talk och hydrofoba modellpartiklar, såväl som mellan talk och hartspartiklar, har uppmätts med hjälp av atomkraftsmikroskopi (AFM) genom att fästa kolloidala partiklar på kraftsensorn. Två metoder för att framställa partiklar gjorda av harts har utvecklats för att möjliggöra dessa studier. Hydrofoba, nanostrukturerade modellytor med ytenergier liknande de för talk har också tillverkats och deras växelverkan med hydrofoba modellpartiklar har jämförts med dem mellan talk och hydrofoba modellpartiklar. Studierna visar att talkmineral växelverkar med hydrofoba modellpartiklar, såväl som med harts, genom långväga attraktiva krafter som är betydligt starkare än den förväntade van der Waals kraften. Möjliga orsaker till de uppmätta växelverkanskrafterna diskuteras och slutsatsen blir att huvudorsaken är en attraktiv kapillärkraft som uppkommer genom att en gas-/ångkapillär bildas mellan ytorna. Kraftmätningar gjorda med hydrofoba nanostrukturerade modellytor visar att en storskalig vågighet inte nämnvärt påverkar storleken av kapillärattraktionen, men stora lokala variationer existerar. Det demonstreras att en stor variation i adhesionskraft motsvaras av en liten variation i lokal kontaktvinkel för kapillärerna på ytorna. Ytornas topografi påverkar kapillärattraktionen genom att påverka den lokala kontaktvinkeln samt genom att trefaskontaktlinjen inte kan röra sig fritt över ytan. Effekten är tydligt beroende av huruvida ytojämnheterna existerar i form av nedsänkningar eller upphöjningar. Instängd luft påverkar också pressade talktabletters uppsugningsförmåga av vatten. Vätnings- och dispergeringsmedels inverkan på växelverkan mellan talk och hydrofoba partiklar har undersökts. Resultaten visar att ett vanligt dispergeringsmedel för talk, polyakrylsyra, inte påverkar kapillärattraktionen. I själva verket tyder data på att polyakrylsyra inte adsorberas på talks basalplan. Utifrån dessa resultat dras slutsatsen att polyakrylsyra stabiliserar talkdispersioner genom att adsorbera på talkkanterna. Ett vanligt vätmedel (nonjonisk triblock sampolymer Pluronic PE6400) tar å andra sidan bort långväga kapillärattraktion. Detta antyder att egenskapen att ersätta luft på talkytan är av stor betydelse för effektiva vätmedel. Hamakerkonstanten för talk har uppskattats genom att utnyttja optiska data från ellipsometrimätningar. Det demonstreras att ett nanokristallint talkmineral kapat i olika riktningar uppvisar mycket små skillnader i Hamakerkonstant mellan de olika kristallografiska orienteringarna, medan ett mikrokristallint prov uppvisar ett betydligt högre värde. De beräknade Hamakerkonstanterna diskuteras för olika materialkombinationer relevanta för pappersindustrin, såsom cellulosa och kalciumkarbonat. / QC 20100813

Im Fokus dieser Arbeit stand die Methode Zwillingspolymerisation zur Synthese organisch-anorganischer Hybridmaterialien. Die simultane Zwillingspolymerisation wird als neues Konzept zur gezielten Herstellung homogener, nanostrukturierter Hybridmaterialien unterschiedlicher Zusammensetzung vorgestellt. Hierfür wurden die Zwillingsmonomere 2,2’-Spirobi[4H-1,3,2-benzodioxasilin] und 2,2 Dimethyl-4H-1,3,2-benzodioxasilin in einem Arbeitsschritt gemeinsam polymerisiert. Die erhaltenen Phenolharz-Siliciumdioxid/Dimethylsiloxan-Hybridmaterialien weisen aufgrund einstellbarer Syntheseparameter unterschiedliche Eigenschaftsprofile auf, die systematisch analysiert wurden. Die Charakterisierung der Produkte erfolgte mit Hilfe der Festkörper-NMR-Spektroskopie, Elektronenmikroskopie, DSC, TGA-MS, sowie durch Extraktionsversuche und die Erzeugung und Analyse poröser Materialien. Neben der simultanen Zwillingspolymerisation wird die Synthese, Charakterisierung und thermisch induzierte Polymerisation literaturunbekannter Silicium-Spiroverbindungen mit einfach- oder zweifach substituierter Salicylalkohol-Einheit beschrieben. Hierbei wurden nanostrukturierte Hybridmaterialien mit teils hohem löslichen Anteil erhalten. Die Produktbildung wird in Abhängigkeit von der Entstehung und Weiterreaktion gefundener Chinonmethid-Strukturen diskutiert.

La spectrométrie Raman, mettant en jeu des phonons de longueur d'onde nanométrique, est une technique de choix pour l'étude des nanostructures. Elle met en évidence les effets de localisation ou de mélange des états électroniques. La cohérence spatiale des modes de vibration, à l'origine du phénomène d'interférence Raman, permet quant à elle de sonder de la structuration spatiale de la matière, tant d'un point de vue électronique qu'acoustique, ouvrant ainsi la voie vers des dispositifs de caractérisation intégrés. La spécificité de l'approche développée dans ce manuscrit réside dans la comparaison entre mesures et calculs de la section efficace de diffusion Raman. Elle apporte une compréhension quantitative des fréquences mais aussi des intensités des pics mesurés. Ainsi, cette démarche a permis d'identifier un nouveau mécanisme de couplage phonon-plasmon qui s'est avéré être le mécanisme dominant la diffusion Raman basses fréquences dans les nano-particules métalliques.

In this thesis, superconducting nanostructures for quantum detection of electromagnetic radiation are studied. In this regard, electrodynamics of topological excitations in 1D superconducting nanowires and 2D superconducting nanostrips is investigated. Topological excitations in superconducting nanowires and nanostrips lead to crucial deviation from the bulk properties. In 1D superconductors, topological excitations are phase slippages of the order parameter in which the magnitude of the order parameter locally drops to zero and the phase jumps by integer multiple of 2\pi. We investigate the effect of high-frequency field on 1D superconducting nanowires and derive the complex conductivity. Our study reveals that the rate of the quantum phase slips (QPSs) is exponentially enhanced under high-frequency irradiation. Based on this finding, we propose an energy-resolving terahertz radiation detector using superconducting nanowires. In superconducting nanostrips, topological fluctuations are the magnetic vortices. The motion of magnetic vortices result in dissipative processes that limit the efficiency of devices using superconducting nanostrips. It will be shown that in a multi-layer structure, the potential barrier for vortices to penetrate inside the structure is elevated. This results in significant reduction in dissipative process. In superconducting nanowire single photon detectors (SNSPDs), vortex motion results in dark counts and reduction of the critical current which results in low efficiency in these detectors. Based on this finding, we show that a multi-layer SNSPD is capable of approaching characteristics of an ideal single photon detector in terms of the dark count and quantum efficiency. It is shown that in a multi-layer SNSPD the photon coupling efficiency is dramatically enhanced due to the increase in the optical path of the incident photon.

Das Schalten und das Auslesen der magnetischen Ausrichtung einzelner winziger magnetischer Informationsspeicher müssen zu wirklich nanoskopischer Dimension entwickelt werden, um mit der Miniaturisierung von modernen, nanoelektronischen Bauteilen Schritt zu halten. Daher sind neue Konzepte, den magnetischen Zustand von Nanostrukturen elektronisch gezielt zu beeinflussen, derzeitig im Mittelpunkt wissenschaftlicher Untersuchungen. Diese Arbeit befasst sich mit dem zuverlässigen Einstellen der Magnetisierung eines rein horizontal kontaktierten, nanoskopischen Magneten, in zwei stabile Zustände. Ein spinpolarisierter Strom wird bei Raumtemperatur in eine Leiterbahn unterhalb des magnetischen Nanopillars injiziert. Spindiffusion durch den Kontakt zwischen der Leiterbahn (Cu) und dem Pillar (CoFe) ruft eine Spin-Akkumulation im Nanopillar hervor, der durch den Spin Transfer Torque-Effekt (STT) vermittelt wird. Bei diesem Prozess verursachen die akkumulierten Elektronenspins ein auftretendes Netto-Moment, das senkrecht auf die Magnetisierungsorientierung des Nanopillars wirkt und so das Schalten ermöglicht. In den STT-induzierten Schaltexperimenten wird der magnetische Zustand des Nanopillars durch eine bildgebendes Messverfahren mittels Rasterröntgentransmissionsmikroskopie (STXM) erfasst. So konnte gezeigt werden, dass sich die Magnetisierung des Pillars auch gegen das Oersted-Feld des Schaltstroms reversibel schalten lässt. / “Changing and detecting the orientation of nanomagnetic structures, which can be used for durable information storage, needs to be developed towards true nanoscale dimensions for keeping up the miniaturization speed of modern nano electronic components. Therefore, new concepts for controlling the state of nano magnets are currently in the focus of research in the field of nanoelectronics. Here, we demonstrate reproducible switching of a purely metallic nanopillar placed on a lead that conducts a spin-polarized current at room temperature. Spin diffusion across the metal-metal (Cu to CoFe) interface between the pillar and the lead causes spin accumulation in the pillar, which may then be used to set the magnetic orientation of the pillar by means of Spin Transfer Torque (STT). In our experiments, the detection of the magnetic state of the nanopillar is performed by direct imaging via scanning transmission x-ray microscopy (STXM)” [1]. Therefore it could be demonstrated, to reversibly switch the nanopillar’s magnetic state even against the Oersted field which is induced by the switching current. Furthermore we could show, that magnetization switching is possible by a pure spin current that is diffusively transported beneath the nanopillar.

Among various nanomaterials, metal nanoparticles are the widely studied ones because of their pronounced distinct properties arising in the nanometer size regime, which can be tailored easily by tuning predominantly their size and shape. During the past few decades, scientists are engaged in developing new synthetic methodologies for the synthesis of metal nanoparticles which can be divided into two broad categories: i) top-down approach, utilizing physical methods and ii) bottom-up approach, employing chemical methods. As the chemical methods offer better control over particle size, numerous chemical methods have been developed to obtain metal nanoparticles with narrow size distribution. However, these two approaches have their own merits and demerits; they are not complementary to each other and also not sustainable for real time applications. Recent focus on the synthesis of metal nanoparticles is towards the development of green and sustainable synthetic methodologies. A solid state route is an exciting prospect in this direction because it eliminates usage of organic solvents thus, makes the overall process green and at the same time leads to the realization of large quantity of the materials, which is required for many applications. However, the major obstacle associated with the development of a solid state synthetic route is the lack of fundamental understanding regarding the formation mechanism of the nanoparticles in the solid state. Additionally, due to the heterogeneity present in the solid mixture, it is very difficult to ensure the proximity between the capping agent and nuclei which plays the most decisive role in the growth process. Recently, employment of amine–borane compounds as reducing agents emerged as a better prospect towards the development of sustainable synthetic routes for metal nanoparticles because they offer a variety of advantages over the traditional borohydrides. Being soluble in organic medium, amine– borane allows the reaction to be carried out in a single phase and due to its mild reducing ability a much better control over the nucleation and growth processes is realized. However, the most exciting feature of these compounds is that their reducing ability is not only limited to the solution state, they can also bring out the reduction of metal ions in the solid state. With the availability of a variety of amine–boranes of varying reducing ability, it opens up a possibility to modulate the nanostructure in both solid and solution states by a judicious choice of reducing agent. Although our current understanding regarding the growth behavior of nanoparticles has advanced remarkably, however, most often it is some classical model which is invoked to understand these processes. With the recent developments in in situ transmission electron microscopy techniques, it is now possible to unravel more complex growth trajectories of nanoparticles. These studies not only expand the scope of the present knowledge but also opens up possibilities for many future developments. Objectives • To develop an atom economy solid state synthetic methodology for the synthesis of metal nanoparticles employing amine–boranes as reducing agents. • To gain a mechanistic insight into the formation mechanisms of nanoparticles in the solid state by using amine–boranes with differing reducing ability. • Synthesis of bimetallic nanoparticles as well as supported metal nanoparticles in the solid state using ammonia borane as the reducing agent. • To develop a new in situ seeding growth methodology for the synthesis of core@shell nanoparticles composed of noble metals by employing a very weak reducing agent, trimethylamine borane and their transformation to their thermodynamically stable alloy counterparts. • Synthesis of highly monodisperse ultra-small colloidal calcium nanoparticles with different capping agents such as hexadecylamine, octadecylamine, poly(vinylpyrrolidone) and a combination of hexadecylamine/poly(vinylpyrrolidone) using the solvated metal atom dispersion (SMAD) method. To study the coalescence behavior of a pair of calcium nanoparticles under an electron beam by employing in situ TEM technique. Significant results An atom economy solid state synthetic route has been developed for the synthesis of metal nanoparticles from simple metal salts using amine–boranes as reducing agents. Amine–borane plays a dual role here: acts as a reducing agent thus brings out the reduction of metal ions and decomposes simultaneously to generate B-N based compounds which acts as a capping agent to stabilize the particles in the nanosize regime. This essentially minimizes the number of reagents used and hence simplifying and eliminating the purification procedures and thus, brings out an atom economy to the overall process. Additionally, as the reactions were carried out in the solid state, it eliminates use of organic solvents which have many adverse effects on the environment, thus makes the synthetic route, green. The particle size and the size distribution were tuned by employing amine–boranes with differing reducing abilities. Three different amine–boranes have been employed: ammonia borane (AB), dimethylamine borane (DMAB), and trimethylamine borane (TMAB) whose reducing ability varies as AB > DMAB >> TMAB. It was found that in case of AB, it is the polyborazylene or BNHx polymer whereas, in case of DMAB and TMAB, the complexing amines act as the stabilizing agents. Several controlled studies also showed that the rate of addition of metal salt to AB is the crucial step and has a profound effect on the particle size as well as the size distribution. It was also found that an optimum ratio of amine–borane to metal salt is important to realize the smallest possible size with narrowest size distribution. Whereas, use of AB and TMAB resulted in the smallest sized particles with best size distribution, usage of DMAB provided larger particles that are also polydisperse in nature. Based on several experiments along with available data, the formation mechanism of metal nanoparticles in the solid state has been proposed. Highly monodisperse Cu, Ag, Au, Pd, and Ir nanoparticles were realized using the solid state route described herein. The solid state route was extended to the synthesis of bimetallic nanoparticles as well as supported metal nanoparticles. Employment of metal nitrate as the metal precursor and ammonia borane as the reducing agent resulted in highly exothermic reaction. The heat evolved in this reaction was exploited successfully towards mixing of the constituent elements thus allowing the alloy formation to occur at much lower temperature (60 oC) compared to the traditional solid state metallurgical methods (temperature used in these cases are > 1000 oC). Synthesis of highly monodisperse 2-3 nm Cu/Au and 5-8 nm Cu/Ag nanoparticles were demonstrated herein. Alumina and silica supported Pt and Pd nanoparticles have also been prepared. Use of ammonia borane as the reducing agent in the solid state brought out the reduction of metal ions to metal nanoparticles and the simultaneous generation of BNHx polymer which encapsulates the metal (Pt and Pd) nanoparticles supported on support materials. Treatment of these materials with methanol resulted in the solvolysis of BNHx polymer and its complete removal to finally provide metal nanoparticles on the support materials. An in situ seeding growth methodology for the synthesis of bimetallic nanoparticles with core@shell architecture composed of noble metals has been developed using trimethylamine borane (TMAB) as the reducing agent. The key idea of this synthetic procedure is that, TMAB being a weak reducing agent is able to differentiate the smallest possible window of reduction potential and hence reduces the metal ions sequentially. A dramatic solvent effect was noted in the preparation of Ag nanoparticles: Ag nanoparticles were obtained at room temperature when dry THF was used as the solvent whereas, reflux condition was required to realize the same using wet THF as the solvent. However, no such behavior was noted in the preparation of Au and Pd nanoparticles wherein Au and Pd nanoparticles were obtained at room temperature and reflux conditions, respectively. This difference in reduction behavior was successfully exploited to synthesize Au@Ag, Ag@Au, and Ag@Pd nanoparticles. All these core@shell nanoparticles were further transformed to their alloy counterparts under very mild conditions reported to date. Highly monodisperse, ultrasmall, colloidal Ca nanoparticles with a size regime of 2-4 nm were synthesized using solvated metal atom dispersion (SMAD) method and digestive ripening technique. Hexadecylamine (HDA) was used as the stabilizing agent in this case. Employment of capping agent with a longer chain length, octadecylamine afforded even smaller sized particles. However, when poly(vinylpyrrolidone) (PVP), a branched chain polymer was used as the capping agent, agglomerated particles were realized together with small particles of 3-6 nm. Use of a combination of PVP and HDA resulted in spherical particles of 2-3 nm size with narrow size distribution. Growth of Ca nanoparticles via colaesence mechanism was observed under an electron beam. Employing in situ transmission electron microscopy technique, real time coalescence between a pair of Ca nanoparticles were detected and details of coalescence steps were analyzed.