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Title: Ultrafast spectroscopy of hybrid nanosystems Author: RNDr. Pavel Galář Department: Department of Chemical Physics and Optics Supervisor: prof. RNDr. Petr Malý, DrSc. Abstract: This Ph. D. thesis is focused on physical phenomena located at the interface of hybrid nanostructure composed of polycrystalline diamond and polymer polypyrrole. The main method used in our experimental study was ultrafast laser spectroscopy that allowed us to gain new findings about electron recombination processes in polycrystalline diamond layers, polypyrrole and in their hybrid structures. The research was focused on mutual influence of both components, especially through energy and charge transfer. In the first step of our research we carried out optical characterisation of different kinds of polypyrrole and complex study of recombination processes dynamics of photoexcited charge carriers in polycrystalline diamond. The measurements were realized by the methods of time-resolved photoluminescence and transmission spectroscopy in the time scale from picoseconds to milliseconds. On the basis of the obtained results the model explaining the origin of luminescence signal related to the different kinds of electron recombination processes in non- diamond phase and on surface defects of diamond grains in polycrystalline layers was...

Nano-structured materials are widely applied for various applications like photovoltaics, electrochromics and sensors. A challenging task in all these fields is the functionalization of these materials with a molecule of interest for the desired application. This work demonstrate the post grafting of the most important and commonly used nano-structured material, mesoporous TiO2, with different bifunctional molecular linkers. These compounds basically have two functional groups, the phosphonic acid group which coordinates to the TiO2 surface and a positive and negative head group which controls the surface charge and the potential interaction of the surface with species in solution. These two groups are systematically separated by alkyl group of different chain length which controls the hydrophobicity of the surface. It is shown that the new surface modification technique simplifies the molecular requirements for functional surface modifiers considerably. Using a limited set of organic anchors with adjustable head group charge and hydrophobicity, broad range of molecules can be adsorbed onto TiO2. Different applications based on such modified surfaces were explored and demonstrated. The modified surfaces can be used to incorporate different charged guest molecules, electrochromophores and dyes which enable to probe their electrochemistry and photovoltaic properties on the surface. Supra-molecular self assembly inside the modified pores is possible which can be monitored by different methods. The study includes the prepartaion of the modified surfaces and their characterization using different electrochemical methods, FTIR spectroscopy, Quartz Crystal Microbalance, Contact angle and Scanning Electron Microscopy measurements.

In der vorliegenden Arbeit wird das Prinzip der chemischen Oberflächenmodifikation als allgemeine Synthesestrategie beschrieben. Davon ausgehend werden verschiedene Ansätze der chemischen Funktionalisierung dargestellt, mit denen die Eigenschaften der erhaltenen Materialien eingestellt werden können. Im Fokus der Arbeit stehen Eisenoxid-Nanopartikel, die über die „Benzylalkohol-Route“ dargestellt werden. Es wird auf Basis dieser einfachen und vielseitig anwendbaren Funktionalisierung die Herstellung von neuartigen Hybridmaterialien gezeigt. Zur Funktionalisierung zweier magnetischer molekularer Rezeptoren wurde eine Synthesestrategie entwickelt, bei der organische Gruppen kovalent angebunden wurden. Der erste Rezeptor kann zur Erkennung von Biomarkern und den Metaboliten von Pharmazeutika eingesetzt werden. Die Beschichtung der Oberflächen der Eisenoxid-Nanopartikel gelang dabei durch die Verwendung von Organosilan-basierten Kopplungsreagenzien. Der zweite Rezeptor konnte zur Auftrennung eines racemischen Gemisches eines chiralen cavitand eingesetzt werden. Die Darstellung von Graphenoxid-Eisenoxid-Kompositen gelang erfolgreich durch ein ex-situ Verfahren. Es wurde der Einfluss der Oberflächenfunktionalitäten auf die Beladung und Verteilung der Eisenoxid-Nanopartikel untersucht. Dazu wurden via Diazoniumchemie verschiedene Funktionalitäten auf der Graphenoxid-Oberfläche eingeführt. Die Entwicklung einer wasserfreien one-pot Synthese von Gold-Eisenoxid-hetero-Nanostrukturen beschrieben wurde. Insbesondere wurden die Auswirkungen kleiner organischer Moleküle auf die Bildung der Heterostrukturen untersucht. / This thesis describes diverse approaches of chemical functionalization as a general strategy to tailor material properties depending on the target application. Particular attention was dedicated to the surface chemistry of iron oxide nanoparticles. Crystalline 10 nm-sized magnetite nanoparticles synthesized through the “benzyl alcohol route” exhibit superparamagnetic behaviour. For this reason they are regarded as suitable solid supports for the fabrication of recoverable devices, which is a fundamental requirement for several of the reported studies. Here it is demonstrated, via the fabrication of novel hybrid materials, that the ease of functionalization of iron oxide nanoparticles renders this material a versatile platform for the development of diverse surface chemistries. A covalent organic functionalization strategy was developed for the synthesis of two recoverable magnetic molecular receptors. The first targeted the recognition of drugs metabolites and biomarkers. It is based on the use of organosilanes coupling agents. A second approach aimed to the heterogeneous resolution of a racemic mixture of an inherently chiral cavitand. Graphene oxide-iron oxide composites were successfully fabricated through an ex-situ approach based on non-covalent interactions between the component phases. The effects of surface functionalities on the loading and distribution of iron oxide nanoparticles were studied by introducing selected functionalities at the graphene oxide surface through diazonium chemistry. Finally, the development of a non-aqueous one-pot synthesis route to gold-iron oxide hetero-nanostructures was described. Particular emphasis was dedicated to study the influence of small organic molecules in promoting the formation of the heterostructures.

Increased demand of power, limited fuel resources and environmental concerns have recently prompted a huge thrust on research areas of alternative energy and photovoltaics have been hailed as energy source for future. Particularly, third generation solar cell configurations like dye-sensitized solar cells and quantum dot Schottky barrier solar cells have drawn more attention because of their ease of processability, cheap cost with decent performance, low payback time and portability. Quantum dots are very attractive materials as sensitizers because of their size dependent bandgap tunability, increased oscillator strength and hence higher absorption coefficient, possibility of multiple exciton generation and photochemical robustness. Hence syntheses of quantum dot based hybrid nanostructures have received huge attention among researchers for using it quantum dot sensitized solar cell configuration. This dissertation can be divided in two parts. In the first part two different methods have been reported to prepare interconnected mesoporous nanostructures of wide band gap semiconductors like TiO2 and ZnO which is very important in providing high surface area for absorption or attachment of the sensitizers. In the second part, methods have been developed to establish direct contacts between quantum dots and wide bandgap substrates without molecular linkers which are expected to increase the electron injection rate from quantum dots to TiO2/ZnO. The entire thesis based on the results and findings obtained from the present investigation is organised as follows: Chapter-I provides a general introduction on the working principle of different type of solar cells and then gives a detailed description of the structure and electronic process of dye sensitised solar cells. Then, benefits of quantum dots as sensitizer over dye molecules has been discussed followed by the modification needed in case of quantum dot sensitized solar cells. Chapter-II deals with the materials and methods which essentially gives the information about the materials used for the synthesis and the techniques utilized to characterize the materials chosen for the investigation. Chapter-III describes a hybrid sol-gel combustion technique to synthesize large quantities of highly crystalline and phase-pure anatase powder in a single step. Titanium isopropoxide reacts with oleic acid to form a viscous liquid (oxocarboxoalkoxide) which undergoes non-hydrolytic polycondensation to form TiO2 during combustion. Oleylamine takes part in formation of reverse micelle which expands during combustion giving rise to porous interconnected membrane like microstructure of pore size ~5 nm, BET surface area of ~100 m2/g and porosity of ~ 48%. More importantly, this porous powder having a pre-existing network can be used to form thicker film by doctor blade technique from its paste and at the same time is expected to have better transport properties due to its less particulate nature. Chapter-IV presents a general method to prepare mesoporous structure from rod-like morphologies by partial sintering of a green pellet. Material having inherent anisotropy in their crystal structure tends to grow in a particular direction rather undergoing equiaxial growth. For instance, hexagonal ZnO and tetragonal rutile usually grow as rod-shaped particles. A loose compact of these nanorods give nanoporous morphology upon heating. Advantage of this method is the tunability of pore size by tuning the aspect ratio of the nanorods. Preparation of porous TiO2, ZnO and hydroxyapatite has been demonstrated from their corresponding nanorods. Chapter-V deals with a solvothermal based technique that has been developed for in-situ deposition of nanoparticles on any plane or curved surfaces conformally. This has been demonstrated for nanoparticles of FeCo, Au, Co, CdS on substrates like glass, mica, Si, NaCl, Al2O3 M-plane and also conformal coating of Au nanoparticles on polystyrene latex spheres. CdSe on rutile nanorods, ZnO nanorods and CNTs are promising hybrid nanostructures for third generation photovoltaics and their successful preparation has been detailed in the chapter. The mechanism proposed is based on dominant attractive sphere-plate interaction under high temperature and high autogeneous pressure condition which at reduced density and surface tension of the solvent reduces the dispersibility of the nanoparticle and allow effective spreading of the nanoparticles on the substrate. This method is also advantageous for coating of complicated geometry like inner walls of porous structures. Chapter-VI presents a method to coat chalcogenide nanoparticles on mesoporous TiO2 without any molecular linker which can enhance the electron injection rate from the chalcogenide quantum dots to TiO2. CdS, PbS can be easily synthesized through aqueous chemistry. For deposition of these sulfides, the ion layer gas absorption and reaction (IGLAR) method was modified to form uniform dense nanoparticles on anatase and ZnO surfaces. Nitrate salts of corresponding metal ions are dried directly on the semiconductor surface and instead of exposing it to H2S gas, it was treated with a concentrated sulfide solution. This introduces two competitive process i) dissolution of nitrate salt ii) formation of the metal sulfide. This dissolution step was absent when treated with H2S gas (IGLAR) and hence lead to a continuous coating. We have successfully produced CdS-TiO2 and PbS-TiO2 composites using this approach. Photoelectrochemical measurements on CdSTiO2 composites show an overall efficiency of 2.8% which is among the highest values obtained for this system demonstrating the applicability of the method to engineer interfaces to achieve high efficiency solar cells. Chapter-VI explores the combination of strategies of nanocrystal conversion chemistry with previously described sol-gel combustion technique to create dense and uniformly coated QD sensitized TiO2 electrode without compromising heat-treatment routines which is essential for better adhesion and to enhance performance with reduced leakage. Intimate biphasic oxide mixtures of PbO and CdO with TiO2 are first synthesized by nonhydrolytic solgel process with is followed by combustion to produce porous morphology. This powder can be coated as electrode and can sustain high temperature heat treatment routines and finally can be selectively converted to sulfides with Na2S treatment as TiO2 is immune to sulfidation under this condition. Materials at different stages are characterised by XRD, TEM, EDS, UV-Vis and XPS.

The hybrid nanostructures exhibit excellent performances in various fields such as catalysis, sensing, and energy conversion as compared to their individual ones. The thesis deals with the new methods for the synthesis of different type of hybrids with doped/pristine carbon nanostructures in the form of graphene, multiwall carbon nanotubes (MWCNTs) as one component and metals nanostructures (Ag, Pd, Pt and Au), carbide (Fe3C), metal chalcogenides (Ni3S2 and Co9S8) and oxide (CoO) as the other components. Various synthesis techniques such as modified galvanic replacement reaction at room temperature, hydrothermal, microwave and pyrolysis have been explored for the synthesis of different hybrid nanostructures. Furthermore, various hybrid nanostructures have been explored for various catalytic activities such as oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and 4-nitrophenol (4-NP) reduction. It may be noted that the ORR and OER which are undoubtedly vital for their applications in fuel cells, metal-air batteries and water oxidation reaction. Interestingly, the catalytic activities of these hybrid nanostructures are comparable or better as compared to the commercial benchmark precious catalysts.

Le travail présenté dans cette thèse porte sur l’élaboration de couches minces des biomatériaux biomimétiques nanostructurées par des techniques lasers pulsés et leur évaluation de point de vue physico-chimique et biologique (biocompatibilité, prolifération et différentiation cellulaires avec des biomatériaux). Le but vise à développer une nouvelle méthode de recouvrement d’implants osseux par des techniques laser pulsé avancées (PLD – Pulsed Laser Deposition et MAPLE - Matrix Assisted Pulsed Laser Evaporation). Ces techniques sont utilisées pour la synthèse d’un système biphasique composé de nanoparticules d’hydroxyapatite (HA) associées à des protéines d’adhérence type fibronectine (FN) et vitronectine (VN) déposées sur un substrat type titane. Le support métallique permettra de maintenir la rigidité mécanique, l’hydroxyapatite favorisera la bio-intégration dans le tissu osseux et les protéines accélèreront l’adhérence cellulaire. L’objectif principal est d’accélérer l’adhérence des cellules et formation des tissus sur les implants. Les études de prolifération et différentiation cellulaire suggèrent une prédisposition des cellules à la prolifération induite par les revêtements VN et à la différentiation stimulée par les revêtements FN. Les effets significatifs sur l’attachement, l’adhésion et la prolifération observés dans nos études sont très importants pour la première phase de stabilité mécanique d’un implant. Les couches HA/protéines déposées par laser pourraient permettre de réduire cette phase. / The work presented within the thesis concern the fabrication of biomimetic nanostructured biomaterial thin films by pulsed laser techniques and their evaluation from the physico-chemical and biological (cellular biocompatibility, proliferation and differentiation) points of view. The aim is to develop a new method for coating the osseous implants by advanced pulsed laser techniques (PLD – pulsed laser deposition and MAPLE – matrix assisted pulsed laser evaporation). These techniques are used for the fabrication of a biphasic system composed of hydroxyapatite (HA) nanoparticules associated with large adhesion proteins as e.g. fibronectin (FN) and vitronectin (VN) deposited on a titanium substrate. The metallic substrate will allow keeping the mechanical rigidity; the hydroxyapatite will favor the bio-integration in the osseous tissue while the proteins will accelerate the cellular adhesion. The main objective is to speed up the cellular adhesion and the formation of new tissue around the implant. The cellular proliferation and differentiation studies demonstrated a predisposal to cell proliferation induced by the VN coatings and to cell differentiation by FN. The significant effects on the cell adhesion, proliferation and differentiation observed in our studies are of great importance for the mechanical stability phase of the implant. The layers HA/proteins deposited by laser could reduce the time of this phase.

Functional nanomaterials are gaining attention due to their excellent shape and size dependent optical, electrical and catalytic properties. Synthesizing nanoparticles is no longer novel with the availability of a host of synthesis protocols for a variety of shapes and sizes of particles. What is currently needed is an understanding the fundamentals of shape and size controlled synthesis to produce functional nanomaterials that is simple and general. In addition to simple metallic nanostructures, synthesizing bimetallic and hybrid nanostructures are important for applications. Instead of trying to add functionality to the preformed nanomaterials, it is advantageous to look for cost effective and general synthetic protocols that can yield bimetallic, hybrid nanostructures along with the shape and size control. In this dissertation, a novel synthetic protocol for the synthesis of ultrfine single crystalline nanowires, metallic and bimetallic nanostructures and hybrid nanostructures has been investigated. The key point of the synthesis is that all different functional nanostructures are achieved by the use of noble metal intermediates in organic medium without phase transfer reagents. The roles of capping agents, oriented attachment and aggregation phenomenon have been studied in order to understand the formation mechanisms. Along with the synthesis, formation mechanisms, the optical and catalytic properties of the functional, noble metal, bimetallic and hybrid nanostructures have been studied. The entire thesis based on the results and findings obtained from the present investigation is organized as follows: Chapter I provides a general introduction to functional nanomaterials, their properties and some general applications, along with a brief description of conventional methods for size and shape-controlled synthesis. Chapter II deals with the materials and methods which essentially gives the information about the materials used for the synthesis and the techniques utilized to characterize the materials chosen for the investigation. Chapter III presents a novel method of for synthesizing noble metals nanostructures starting from an intermediate solid phase. The method involves the direct synthesis of noble metal intermediates in organic medium without the use of any phase transfer reagent. Controlled reduction of these intermediates leads to the formation of ultrafine nanocrystallite building blocks. Controlled aggregation of the nanocrystallites under different conditions leads to the formation of different nanostructures ranging from single crystalline nanowires to porous metallic clusters. In this chapter, the details of synthesis of the intermediate phase of gold are presented. This intermediate phase is the rocksalt phase of AuCl that has been experimentally realized for the first time. Manipulation of the AuCl nanocubes leads to the formation of a variety of nanostructures of Au starting from hollow cubes to extended porous structures. Mechanistic details of the formation of the intermediate and the nanostructures are presented in this chapter. Chapter IV deals with the symmetry breaking of an FCC metal (gold) by oriented attachment of metal nanoparticles by the preferential removal of capping agent from certain facets and followed by the attachment of gold nanoparticles along those bare facets. This kind of oriented attachment leads to the formation of 1D nanostructures with high aspect ratios. In this chapter, the synthesis, characterisation, formation mechanism and optical properties of high aspect ratio, molecular scale single crystalline gold nanowires has been described. This represent the first ever successful method to produce ultrafine 1D metallic nanostructures approaching molecular dimensions. Chapter V deals with the formation of hybrid nanostructures by attaching the cubic intermediate phase to a substrate like carbon nanotubes followed by the reduction of the attached intermediates on the tubes. The Pt intermediates have been synthesized and attached on the wall of functionalized CNTs and reduced. The PtCNT nanocomposites been characterized by several spectroscopic and microscopic techniques. The electrocatalytic activity of these nanocomposites towards the methanol oxidation has also been investigated. The composites exhibit high catalytic activity and good long term performance. The presence of functional groups on the CNT surface overcomes some of the limitations of current single metal catalysts that suffer from CO poisoning. Chapter VI deals with the formation of palladium nanostructures ranging from nanoparticles to hierarchical aggregates by controlled aggregation of nanoparticles in an organic medium that is tuned by the dielectric constant of the system. A crystalline intermediate of palladium salt has been synthesized and this intermediate of palladium has been used as the precursor solution for the synthesis of palladium nanostructures. The formation mechanism of the nanoporous Pd cluster is investigated using the modified DLVO approach. The catalytic efficiency of the Pd nanostructures has been investigated using the reduction of pnitrophenol and electrocatalytic hydrogen storage as model reactions. Chapter VII discusses the possibility of achieving functional bimetallic alloys by simultaneous reduction of the cubic intermediate of two different metals with experimental evidences. The synergistic effect of the two different metals gives rise to better catalytic activity. This chapter mainly deals with the synthesis of bimetallic porous nanoclusters of goldpalladium and goldplatinum in an organic medium. Detailed microstructural and spectroscopic characterisation of the bimetallic nanoclusters has been carried out and their electrocatalytic performance, morphological stability also investigated.

Investigations on size dependent phase stability and transformations in isolated nanoparticles have gained momentum in recent times. Size dependent phase stability generates size specific particle microstructure which consequently yields size specific functionality. One important prerequisite for conducting studies on nanoparticles is their synthesis. A substantial amount of research effort has therefore been focused on devising methodologies for synthesizing nanoparticles with controlled shapes and sizes. The present thesis deals with both these two aspects: (a) synthesis of nanoparticles and (b) phase transformations in nanoparticles. The system chosen in this study is AuCu intermetallic nanoparticles. The choice of AuCu nanoparticle was due to the fact that the literature contains abundance of structural and thermodynamic data on Au–Cu system which makes it a model system for investigating size dependence of phase transformations. With respect to synthesis, the present thesis provides methodologies for synthesizing alloyed Au–Cu nanoparticles of different sizes, Au–Cu nano-chain network structures and uniform Au–Cu2S hybrid nanoparticles. For every type, results are obtained from a detailed investigation of their formation mechanisms which are also presented in the thesis. With respect to phase transformation, the thesis presents results on the size dependence of fcc to L10 transformation onset in Au–Cu nanoparticles under isothermal annealing conditions. The present thesis is divided into eight chapters. A summary of results and key conclusions of work presented in each chapter are as follows. The ‘introduction’ chapter (chapter I) describes the organization of the thesis. Chapter II (literature study) presents a review of the research work reported in the literature on the various methodologies used for synthesizing Au–Cu based nanoparticles of different shapes and sizes and on ordering transformation in AuCu nanoparticles. The chapter also presents a brief discussion on the reaction variables that control the process of nucleation and growth of the nanoparticles in solution. Chapter III titled ‘experimental details and instrumentation’ describes the synthesis procedures that were used for producing various nanoparticles in the present work. The chapter also briefly describes the various characterization techniques that were used to investigate the nanoparticles. The fourth chapter titled ‘synthesis and mechanistic study of different sizes of AuCu nanoparticles’ provides two different methodologies for synthesis, referred as ‘two-stage process’ and ‘two-step process’ that have been used for producing alloyed AuCu nanoparticles of different sizes (5, 7, 10, 14, 17, 25 nm). The ‘two-stage’ process involved sequential reduction of Au and Cu precursors in a one pot synthesis process. Whereas, the ‘two-step’ process involved a two-pot synthesis in which separately synthesized Au nanoparticles were coated with Cu to generate alloyed AuCu nanoparticles. In the two-stage synthesis process it was observed that by changing the total surfactant-to-metal precursor molar ratio, sizes of the alloyed AuCu nanoparticles can be varied. ‘Total surfactants’ here include equal molar amounts of oleic acid and oleylamine surfactants. Interestingly, it was observed that there exists a limitation with respect to the minimum nanoparticle size that can be achieved by using the two-stage process. The minimum AuCu nanoparticle size achieved using the two-stage synthesis process was 14 nm. Mechanism of formation of AuCu nanoparticles in the two-stage synthesis process was investigated to find out the reason for this size limitation and also to determine how the synthesis process can be engineered to synthesize alloyed AuCu nanoparticles with smaller (<14nm) sizes. Studies to evaluate mechanism of synthesis were conducted by investigating phase and size of nanoparticles present in the reaction mixture extracted at various stages of the synthesis process. Their studies revealed that (a) the nanoparticle formation mechanism in the two-stage synthesis process involves initial formation of Au nanoparticles followed by a heterogeneous nucleation and diffusion of Cu atoms into these Au rich seeds to form Au–Cu intermetallic nanoparticles and (b) by increasing the relative molar amount of the oleylamine surfactant, size of the initial Au seed nanoparticles can be further reduced from the minimum size that can be achieved in the case when equal molar amounts of oleylamine and oleic acid surfactants are used. The information obtained from the mechanistic study was then utilized to design the two-step synthesis process. In the two-step process, Au nanoparticles were synthesized in a reaction mixture containing only the oleylamine surfactant. Use of only oleylamine resulted in production of pure Au nanoparticles with sizes that were well below 10 nm. These Au nanoparticles were washed and dispersed in a solution containing Cu precursor. Introduction of a reducing agent into this reaction mixture led to the heterogeneous nucleation of Cu onto the Au seed particles and their subsequent diffusion into them to form alloyed AuCu nanoparticles with sizes of ~5, 7 and 10 nm. The study present in this chapter essentially signified that the surfactants used in the reaction mixture not only prevent nanoparticles from agglomerating in the final dispersion but also control their nucleation and growth and therefore can be used as a tool to tune nanoparticle sizes. The fifth chapter titled ‘size dependent onset of FCC-to-L10 transformations in AuCu alloy nanoparticles’ illustrates the effect of AuCu nanoparticle size on the onset of ordering under isothermal annealing conditions. Nanoparticles in this study were annealed in-situ in a transmission electron microscope. Samples were prepared by drop drying a highly dilute dispersion of as-synthesized nanoparticles onto an electron transparent TEM grid. Nanoparticles sitting on the TEM grid were well separated from each other to minimize particle sintering during the annealing operation. It was however observed that during the isothermal annealing, particle coarsening due to atomic diffusion was appreciable for 5 nm particles but negligible for 7 and 10 nm particles. Therefore for this study only 7 nm and 10 nm sized particles were considered. Onset of ordering was determined from the time when first sign of the diffraction spot, corresponding to the ordered phase, appears in the selected area electron diffraction pattern from a region containing large number of AuCu nanoparticles. Through a series of isothermal experiments it was observed that the time for onset of ordering increased with decrease in size of the nanoparticles. It is speculated that the delay in onset of ordering may be due to the fact that with a decrease in nanoparticle size the probability of a nanoparticle containing a fluctuation that shall generate a thermodynamically stable nuclei of the ordered phase decreases. A sharp interface between the ordered and the disordered phase inside the particle was also observed which suggested that the ordering transformation in as-synthesized fcc AuCu nanoparticles is a first order transformation. The sixth chapter titled ‘synthesis and characterization of Au1-xCux–Cu2S hybrid nanostructures: morphology control by reaction engineering’ provides a modified polyol method based synthesis strategy for producing uniform Au–Cu2S hybrid nanoparticles. Detailed compositional and structural characterization revealed that the hybrid nanoparticles are composed of cube shaped Au-rich, Au–Cu solid solution phase and hemispherical shaped Cu2S phase. Interestingly, the hemispherical Cu2S phase was attached to only one facet of the cube shaped phase. A study on the formation mechanism of hybrid nanoparticles was also conducted by characterizing specimens extracted from the reaction mixture at different stages of the synthesis process. The study revealed that the mechanism of formation of hybrid nanoparticles involved initial formation of isolated cube shaped pure Au nanoparticles and Cu–thiolate complex with a sheet morphology. With increase in time at 180°C, the Cu–thiolate complex decomposed and one part of the Cu atoms that were produced from the decomposition were utilized in forming the spherical Cu2S and other part diffused into the Au nanoparticles to form Au–Cu solid solution phase. The chapter also presents a study on the effect of dodecanethiol (DDT) on achieving the hemisphere-on-cube hybrid morphology. In this study it is illustrated that an optimum concentration of dodecanethiol is required both for achieving size and morphological uniformity of the participating phases and for their attachment to form a hybrid nanoparticle. The seventh chapter titled ‘synthesis of Au–Cu nano-chains network and effect of temperature on morphological evolution’ provides methodology for synthesizing fcc Au– Cu nano-chain network structures using polyvinylprrolidone (PVP) surfactant. It was observed that with increase in the molar amount of PVP in the reaction mixture, morphology of the as-synthesized product gradually changed from isolated nanoparticles to branched nano-chain like. The nano-chains contained twins which indicated an absence of continuous growth and possibility of growth by oriented attachment of initially formed Au–Cu nanoparticles. Both in-situ and ex-situ annealing of the nano-chains led to their decomposition into isolated nanoparticles of varying sizes. Annealing also caused fcc-to¬L10 phase transformation. Investigation of the wave length of perturbation leading to breaking of a nano-chain into particles indicated that the surface energy anisotropy affects the splitting of nano-chain network structure into nano-sized particles. The thesis ends with a last chapter where we have presented possible future extension of current work.