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Colloidal self assembly is an efficient method for making 3-D ordered nanostructures suitable for materials such as photonic crystals and macroscopic solids for catalysis and sensor applications. Colloidal crystals grown by convective methods exhibit defects on two different scales. Macro defects such as cracks and void bands originate from the dynamics of meniscus motion during colloidal crystal growth while micro defects like vacancies, dislocation and stacking faults are indigenous to the colloidal crystalline structure. This paper analyses the crystallography and energetics of the microscopic defects from the point of view of classical thermodynamics and discusses the strategy for the control of the macroscopic defects through optimization of the liquid-vapor interface. / Singapore-MIT Alliance (SMA)

In this research we consider two different approaches for microfabricating physical templates to be used in template directed colloidal self-assembly experiments. Fabrication of templates, usable with confocal microscopy, forms an essential part of observation and analysis of template directed colloidal self-assembly studies. We use existing laboratory based microfabrication methods for patterning thin glass coverslips and polymeric films. These templates when used for directing colloidal self-assembly along with confocal microscopy analysis provide us with relevant information on the effect of confined geometries of the template on particle packing and order. The first method of template fabrication involves ultraviolet photolithography, thin film deposition, and glass micro machining. Various stages of the process were optimized while selecting reactive ion etch (RIE) and nickel etch mask with a suitable etch recipe for microfabrication of patterns on thin multi-component glass coverslips. Pattern dimensions were shown to be nearly commensurate with patterns on the microfiche, which was used as a field mask. In another approach, mechanical machining for fabricating polymeric templates was attempted on poly(methyl methacrylate) films spin coated on thin glass cover slips. The mechanical machining was implemented using computer numerical control (CNC) machines with the pattern dimensions in the range of 50 Mu m-150 Mu m. The glass and polymeric templates were used in template directed colloidal self-assembly experiments us ing polystyrene or silica particles. Confocal microscopy was used to obtain images of particle packing in template geometries. Imaging of the particles confined in the template geometries show increased particle concentration along pattern walls and corners. Inherent pattern irregularities and roughness possibly resulted in limited order in particle. Using a simple fortran program, image stack generated from confocal microscopy is used for obtaining images of particle packing in four different view planes which includes top, side, cross sectional and diagonal view of the image stack. The results from this research show the application of simple microfabrication processes for creating physical templates for template directed colloidal self-assembly. Confocal microscopy imaging combined with fortran image processing program can provide images of particle packing in different view planes. These images of the particles confined in various pattern geometries illustrate greater possibility of packing order in straight and regular pattern geometries or profiles.

Supramolecular interactions are of great importance in the fabrication of new functional materials. In particular, colloidal assembly via supramolecular pathway has contributed to numerous innovations in material chemistry, on account of its specific, directional and dynamic non-covalent interactions. By taking advantage of the non-covalent supramolecular interactions, tailored complementary colloidal building blocks which are normally incompatible with each other could be integrated interdependently, forming novel hybrid materials with emerging properties. This thesis mainly focuses on the design, preparation and characterization of novel colloidal assemblies based on cucurbit[n]urils host-guest interactions, including hybrid ‘raspberry-like’ colloids, catalytic polymeric nanocomposites, advanced structured colloids, and supramolecular polymer colloidal hydrogel.

Photonic metasurfaces obtain their unique optical properties from the periodic arrangement of sub-wavelength building blocks and can manipulate light in ways that differ significantly from bulk materials. Until recently, metasurfaces have been fabricated using top-down methods on a limited surface area. With the development of directed self-assembly methods and utilization of nanoscale colloids, metasurfaces can be fabricated on a larger scale and with reasonable efforts. In particular, soft nanoimprint lithography, based on the controlled drying of the colloidal solution within a structured template, allows for the precise placement of versatile colloidal building blocks on a substrate of choice. In this dissertation, the material and optical properties of self-assembled plasmonic and photoluminescent nanoparticles are systematically studied in terms of their short- and long-range interactions. It is shown that 1D plasmonic lattices exploit the intrinsic anisotropy and substrate-dependent collective resonant coupling. Likewise, semiconductor nanoparticles organized into linear gratings, result in light-emitting metasurfaces, featuring geometry-dependent amplification of the photoluminescence that can be further promoted to a non-linear amplification regime. Moreover, on flexible substrates, these self-assembled light-emitting metasurfaces can be stacked and twisted, inducing remarkably strong chiral effects and subsequently used for directional light sources, nanolasers, sensing, and labeling applications. Supported by theoretical modeling, this work provides a novel approach to realize anisotropic and non-linear optical properties on centimeter-scaled surface area using soft-lithography and directed self-assembly methods. It bridges the gap between nanoscale colloids and optoelectronics while advancing the integration of metasurfaces into functional devices. / Photonische Metaoberflächen erhalten ihre einzigartigen optischen Eigenschaften durch die periodische Anordnung von Bauelementen im Sub-Wellenlängenbereich und können Licht auf eine Weise manipulieren, die sich deutlich von Ausgangsmaterialien unterscheidet. Bis vor kurzem wurden Metaoberflächen mit Top-Down-Methoden auf einer begrenzten Oberfläche hergestellt. Mit der Entwicklung von Methoden der gerichteten Selbstorganisation und der Nutzung von Kolloiden im Nanomaßstab können Metaoberflächen in größerem Maßstab und mit angemessenem Aufwand hergestellt werden. Insbesondere die Soft-Nanoimprint-Lithographie, die auf der kontrollierten Trocknung der kolloidalen Lösung innerhalb einer strukturierten Template basiert, ermöglicht die präzise Platzierung vielseitiger kolloidaler Bauelemente auf einem Substrat der Wahl. In dieser Dissertation werden die materiellen und optischen Eigenschaften selbstorganisierter plasmonischer und photolumineszenter Nanopartikel im Hinblick auf ihre Kurz- und Langstreckenwechselwirkungen systematisch untersucht. Es wird gezeigt, dass plasmonische 1D-Gitter die intrinsische Anisotropie und die substratabhängige kollektive Resonanzkopplung ausnutzen. Ebenso führen Halbleiter-Nanopartikel, die in linearen Gittern organisiert sind, zu lichtemittierenden Metaoberflächen, welche eine geometrieabhängige Verstärkung der Photolumineszenz aufweisen, die bis zu einem nichtlinearen Verstärkungsregime weitergeführt werden kann. Außerdem können diese selbstorganisierten, lichtemittierenden Metaoberflächen auf flexiblen Substraten gestapelt und verdreht werden, was zu bemerkenswert starken chiralen Effekten führt und anschließend für gerichtete Lichtquellen, Nanolaser, Sensor- und Beschriftungsanwendungen genutzt werden kann. Unterstützt durch theoretische Modellierung bietet diese Arbeit einen neuartigen Ansatz zur Realisierung anisotroper und nichtlinearer optischer Eigenschaften auf zentimetergroßen Oberflächen unter Verwendung von Softlithographie und Methoden der gerichteten Selbstmontage. Sie überbrückt die Lücke zwischen Kolloiden im Nanomaßstab und der Optoelektronik und treibt gleichzeitig die Integration von Metaoberflächen in funktionale Geräte voran.

This thesis aims to shed light on the mechanisms governing the self-assembly of polymer-functionalized gold nanoparticles (AuNPs) in colloidal solutions, with the ultimate goal of enhancing control over the directed assembly of these hybrid nanomaterials (HNMs) for potential sensor applications. State-of-the-art analytical methods were employed to investigate the nano/microscopic forces involved in the self-assembly process. The first step involved the development of a method using energy-filtered transmission electron microscopy (EFTEM) to quantify the polymer grafting density (PGD) for polystyrene (PS)-grafted isotropic and anisotropic AuNPs (nanospheres (NSs) and nanorods (NRs)). This method addressed the lack of techniques capable of quantifying polymer loads for individual nanoparticles. The analysis results, in agreement with values from thermogravimetric (TGA) measurements, revealed no preferential polymer load at the surfaces with higher curvature (tips of AuNRs) for functionalized NRs with a measured PGD of  0.05 chain nm–2. This observation led to discovery of a novel aspect of the self-assembly of anisotropic PS-grafted AuNPs: By reducing the solvent quality for PS brushes through the addition of 20% v/v water to the dimethylformamide (DMF) solution, preferential tip-to-tip assembly of AuNRs occurred, even for species coated with a homogeneous PS layer. The origin and influence of surface charges and electrostatic forces on the preferential tip-to-tip assembly of AuNRs was then examined with Zeta-potential and kelvin probe atomic force microscopy (KPAFM) and through control experiments involving the addition of NaCl electrolyte to the colloidal solution. Changes in assembly rates and modes were monitored by observing shifts in longitudinal/transversal localized surface plasmon resonance (LSPR) peaks in the vis/NIR spectroscopy. The self-assembly kinetics of similar PS-grafted AuNR systems were further studied using a combination of time-resolved vis/NIR spectroscopy, finite-difference time-domain (FDTD) simulations, and additional data from transmission electron microscopy (TEM) analysis. The results indicated faster assembly rates and lower energy barriers for nanorods grafted with thicker PS shells compared to those coated with thinner shells, emphasizing the role of electrostatic repulsive forces in preventing assembly when the polymer spacing between nanorods is smaller. Coarse-grained molecular dynamic (MD) simulations supported the explanation emphasizing on the impact of electrostatic forces on the preferential tip-to-tip self-assembly of PS@AuNRs, as well as the effect of PS layer thickness on the energy barrier for such assemblies. The knowledge gained was applied to design co-assembled structures using blocks of nanorods coated with two distinct molecular weights (12 and 50 kDa), revealing a narcissistic self-assembly signature arising from different assembly rates of each block. Another model system involving gold nanospheres (AuNSs) grafted with thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) brushes was employed in a separate research project to study the assembly/disassembly mechanism of brush-coated nanoparticles. The assembly/disassembly was triggered by changing the solvent conditions for the polymer brushes, through heating/cooling the colloidal solution above/below the lower critical solution temperature (LCST) of the 30 kDa PNIPAM brush (32 °C). Clusters with different sizes and geometries were successfully formed in aqueous solution by varying the ionic strength of solution through changing the concentrations of NaCl electrolyte. No cluster were formed at 40 °C in systems with little to no electrolyte, underlining the role of repulsive electrostatic forces in solution-based self-assembly of colloidal NPs. Moreover, transition from single NPs to 1D/2D assemblies and then growing globular structures with increasing electrolyte concentrations was observed by increasing the electrolyte concentration at temperatures above the LCST. This transition was tracked using polarized angle-dependent dynamic light scattering (DLS) and TEM analysis. Additionally, real-time micrographs and videos of self-assembly in the presence of electrolyte and upon an increase in solution temperature to 40 °C were recorded via in-situ liquid-phase TEM. To the best of author’s knowledge, the employed approaches have not been previously reported to gain deep insights into the assembly of thermo-responsive HNMs in solution and points out to potentials for future analytical studies. Based on the obtained results, scattering measurements in glass fiber nanochannels are planned to provide further insights into the assembly/disassembly process for single clusters. / Das Ziel dieser Arbeit ist es, die Mechanismen der Selbstassemblierung von polymerfunktionalisierten Goldnanopartikeln (AuNPs) in kolloidalen Lösungen zu untersuchen. Dies soll dazu beitragen, die Kontrolle über die gezielte Anordnung dieser hybriden Nanomaterialien (HNMs) für potenzielle Sensoranwendungen zu verbessern. Hierzu kamen moderne Analysemethoden zum Einsatz, um die bei diesem Selbstassemblierungsprozess wirkenden nano-/mikroskopischen Kräfte zu erforschen. Im ersten Schritt wurde eine Methode entwickelt, die auf energiegefilterter Transmissionselektronenmikroskopie (EFTEM) basiert. Diese Methode ermöglichte die Quantifizierung der Polymerpfropfdichte (PGD) für isotrope und anisotrope AuNPs (Nanokugeln (NS) und Nanostäbchen (NR)), die mit Polystyrol (PS) gepfropft wurden. Mit dieser Methode konnte die Polymerbeladung erstmals auf der Ebene einzelner Nanopartikel quantifiziert werden. Die Analyseergebnisse, die mit den Werten thermogravimetrischer Messungen (TGA) übereinstimmen, zeigten, dass bei funktionalisierten Nanopartikeln mit einer PGD von 0,05 Ketten/nm¬2 keine bevorzugte Polymerbeladung an den Oberflächen mit höherer Krümmung (Spitzen der AuNRs) vorhanden ist. Diese Beobachtung führte zur Entdeckung eines neuen Aspekts der Selbstassemblierung von anisotropen PS-gepfropften AuNPs: Durch die Verringerung der Lösungsmittelqualität für PS-Bürsten durch Zugabe von 20 % v/v Wasser zur Dimethylformamid (DMF)-Lösung kam es zu einer bevorzugten Spitze-zu-Spitze-Anordnung von AuNRs, sogar für Nanostäbe, die von einer homogenen PS-Schicht umgeben waren. Der Ursprung und der Einfluss von Oberflächenladungen und elektrostatischen Kräften auf die bevorzugte Spitze-zu-Spitze-Anordnung von AuNRs wurden dann mit Zeta-Potential und Kelvin-Sonden-Atomkraftmikroskopie (KPAFM) sowie durch Kontrollexperimente unter Zugabe von NaCl-Elektrolyt zur kolloidalen Lösung untersucht. Änderungen der Assemblierungsgeschwindigkeit und -Modi wurden durch Beobachtung von Verschiebungen der longitudinalen/transversalen Moden der lokalisierten Oberflächenplasmonenresonanz (LSPR) in der vis/NIR-Spektroskopie verfolgt. Die Selbstassemblierungskinetik ähnlicher PS-gepfropfter AuNR-Systeme wurde mit einer Kombination aus zeitaufgelöster vis/NIR-Spektroskopie, Finite-Differenzen-Zeitbereichssimulationen (FDTD) und zusätzlichen Daten aus der TEM-Analyse weiter untersucht. Die Ergebnisse deuten auf schnellere Assemblierungsgeschwindigkeiten und niedrigere Energiebarrieren für solche Nanostäbchen hin, die mit dickeren PS-Hüllen gepfropft sind, im Vergleich zu solchen, die mit dünneren Hüllen beschichtet sind. Dies unterstreicht die Rolle der elektrostatischen Abstoßungskräfte bei der Verhinderung der Selbstanordnung, wenn der Polymerabstand zwischen den Nanostäbchen kleiner ist. Vergröberte molekulardynamische (MD)-Simulationen unterstützten die Erklärung, wobei der Einfluss elektrostatischer Kräfte auf die bevorzugte Spitze-zu-Spitze-Anordnung von PS@AuNRs sowie die Auswirkung der PS-Schichtdicke auf die Energiebarriere für solche Assemblierungen hervorgehoben wurde. Die gewonnenen Erkenntnisse wurden für das Design von ko-assemblierten Strukturen unter Verwendung von Nanostäbchenblöcken verwendet, die mit zwei unterschiedlichen Molekulargewichten (12 und 50 kDa) beschichtet sind. Dabei wurde eine narzisstische Selbstassemblierungssignatur aufgedeckt, die sich aus unterschiedlichen Assemblierungsraten der einzelnen Blöcke ergibt. Ein weiteres Modellsystem mit Goldnanokugeln (AuNS), die mit thermoresponsiven Poly(N-Isopropylacrylamid)-Bürsten (PNIPAM) gepfropft wurden, wurde in einem anderen Forschungsprojekt verwendet, um den Mechanismus der Assemblierung/ des Zerfalls von bürstenbeschichteten Nanopartikeln zu untersuchen. Die Assemblatbildung/-Zerfall wurde durch Änderung der Lösungsmittelbedingungen für die Polymerbürsten ausgelöst, indem die kolloidale Lösung über/unter die untere kritische Lösungstemperatur (LCST) der 30 kDa PNIPAM-Bürste (32 °C) erhitzt/abgekühlt wurde. Cluster mit unterschiedlichen Größen und Geometrien wurden erfolgreich in wässriger Lösung gebildet, indem die Ionenstärke der Lösung durch Änderung der Konzentrationen des NaCl-Elektrolyten variiert wurde. Bei 40 °C wurden in Systemen mit wenig oder gar keinem Elektrolyten keine Cluster gebildet, was die Rolle der abstoßenden elektrostatischen Kräfte bei der lösungsbasierten Selbstassemblierung kolloidaler NPs unterstreicht. Der Übergang von einzelnen NPs zu 1D/2D anisotropen Assemblaten und dann zu wachsenden kugelförmigen Strukturen wurde beobachtet, indem die Elektrolytkonzentration bei Temperaturen oberhalb der LCST geändert wurde. Dieser Übergang wurde mittels polarisierter, winkelabhängiger dynamischer Lichtstreuung (DLS) und TEM-Analyse verfolgt. Echtzeit-Elektronenmikroskopie der Selbstassemblierung in Anwesenheit des Elektrolyten und bei einer Erhöhung der Lösungstemperatur auf 40 °C wurden mittels In-situ-TEM in einer Flüssigkeitszelle realisiert. Nach bestem Wissen des Autors wurde bisher noch nicht über die angewandten Ansätze berichtet, um tiefe Einblicke in den Aufbau thermoresponsiver HNMs in Lösung zu gewinnen, und sie weisen auf Potenziale für zukünftige analytische Studien hin. Geplante Messungen der Bildung/Deformation einzelner Cluster in optischen Fasern sind geplant, um weitere Einblicke in den Assemblierungsprozess zu erhalten.

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.

Cellulose is the most abundant biopolymer on Earth as it is found in every plant cell wall; therefore, it represents one of the most promising natural resources for the fabrication of sustainable materials. In plants, cellulose is mainly used for structural integrity, however, some species organise cellulose in helicoidal nano-architectures generating strong iridescent colours. Recent research has shown that cellulose nanocrystals, CNCs, isolated from natural fibres, can spontaneously self-assemble into architectures that resemble the one producing colouration in plants. Therefore, CNCs are an ideal candidate for the development of new photonic materials that can find use to substitute conventional pigments, which are often harmful to humans and to the environment. However, various obstacles still prevent a widespread use of cellulose-based photonic structures. For instance, while the CNC films can display a wide range of colours, a precise control of the optical appearance is still difficult to achieve. The intrinsic low thermal stability and brittleness of cellulose-based films strongly limit their use as photonic pigments at the industrial scale. Moreover, it is challenging to integrate them into composites to obtain further functionality while preserving their optical response. In this thesis, I present a series of research contributions that make progress towards addressing these challenges. First, I use an external magnetic field to tune the CNC films scattering response. Then, I demonstrate how it is possible to tailor the optical appearance and the mechanical properties of the films as well as to enhance their functionality, by combining CNCs with other polymers. Finally, I study the thermal properties of CNC films to improve the retention of the helicoidal arrangement at high temperatures and to explore the potential use of this material in industrial fabrication processes, such as hot-melt extrusion.