A self-terminated electrochemical method was used to fabricate microscopic-scale contacts between two Au electrodes in a microfluidic channel. The conductance of contacts varies in a stepwise fashion showing quantization near the integer multiples of the conductance quantum ( ). The mechanism works by a pressure-driven flow parallel to a pair of Au electrodes with a gap on the order of micron in an electrolyte of HCl. When applying a bias voltage between two electrodes, metal atoms are etched off the anode and dissolved into the electrolyte as metal ions, which are then deposited onto the cathode. Consequently, the gap decreases to the atomic scale and then completely closes as the two electrodes form a contact. The electrochemical fabrication approach introduces large variance in the formation and location of individual junctions. Understanding and controlling this process will enable the precise positioning of reproducible geometries into nano-electronic devices.

When materials approach the size of few nanometers, they show properties which are significantly different from their bulk counterpart. Such unique/improved properties make them potential candidate for several emerging applications. At the reduced dimension, controlling the shape of nanocrystals provides an effective way to tune several material properties. In this regard, wet chemical synthesis has been established as the ultimate route to synthesize nanocrystals at ultra-small dimensions with excellent control over the morphology. However, the use of surfactant poses a barrier into efficient realization of its application as it requires a clean interface for better performance. Exercise of available cleaning protocols to clean the surface often leads to coarsening of the nanoparticles due to their inherent high surface curvature. For anisotropic nanomaterials, rounding of the shape is an additional problem. Anchoring nanomaterials onto substrates provides an easy way to impart stability. In this thesis, ultrathin Au nanowires, that are inherently unstable, have been shown to grow over a wide variety of substrates by in-situ functionalization. Use of nanomaterials as device component holds promise into miniaturization of electronics. But device fabrication in such cases require manipulation of nanomaterials with enhanced control. Dielectrophoresis offers an easy way to assemble nanomaterials in between contact pads and hence evolved as a promising tool to fabricate device with a good level of precision. Herein, directed assembly of ultrathin Au nanowires by dielectrophoresis, has been shown as an efficient strategy to fabricate devices based on the wires. Combining more than one nanocrystal, to form a heterostructure, often has the advantage of synergism and/or multifunctionality. Therefore, synthesis of heterostructure is highly useful in enhancing and/or adding functionalities to nanomaterials. There are several routes available in literature for synthesis of heterostructures. Newer strategies are being evolved to further improve performance in an application specific way. In that regard, a good understanding of mechanism of formation is crucial to form the desired product with the required functionality. For example, Au due to high electron affinity has been known to undergo reduction rather than cation exchange with chalcogenides. In this thesis, it has been shown that the final product depends on the delicate balance of reaction conditions and the system under study using CdS-Au as the model system. In yet another case, PdO nanotubes have been shown to form, on reaction of PdCl2 with ZnO at higher starting ratio of the precursors. In-situ generation of HCl provides an effective handle for tuning of the product from the commonly expected hybrid to hollow. Graphene has evolved as a wonder material due to its wide range of practical applications. Its superior conductivity with high flexibility has made it an important material in the field of nanoelectronics. In this thesis, an interesting case of packed crumpled graphene has been shown to sense a wide variety of strain/pressure which has applications in day to day life. The study reported in the thesis is organized as follows: Chapter 1 presents a general introduction to nanomaterials followed by the review of the available strategies to synthesize various 1D nanomaterials. Subsequently, a section on the classification of hybrid followed by the different synthetic protocols adopted in literature to synthesize them, have been provided. A review on the available methodologies for directed assembly of nanomaterials has been presented. Chapter 2 provides a summary of the materials synthesized and the techniques used for characterization of the materials. A brief description of all the synthetic strategy adopted has been provided. The basic principle of all the characterization techniques used, has been explained. A section explaining the principle of dielectrophoresis has also been presented. Chapter 3 presents a general method to grow ultrathin Au nanowires over a variety of substrates with different nature, topography and rigidity/flexibility. Ultrathin nanowires of Au (~2 nm in diameter) are potentially useful for various catalytic, plasmonic and device applications. Extreme fragility on polar solvent cleaning was a limitation in realizing the applications. Direct growth onto substrate was an alternative but poor interfacial energy of Au with most commercial substrates lead to poor coverage. In this chapter, in-situ functionalization of the substrates have been shown to improve Au nucleation dramatically which lead to growth of dense, networked nanowires over large area. Catalysis and lithography-free device fabrication has been demonstrated. Using the same concept of functionalization, SiO2 coating of the nanowires have been shown. A comparative study of thermal stability of these ultrafine Au nanowires in the uncoated and coated form, has been presented. Chapter 4 demonstrates an ultrafast device fabrication strategy with Au nanowires using dielectrophoresis. While dense growth of Au nanowires is beneficial for some applications, it is not so for some others. For example, miniaturization of electronics require large number of devices in a small area. Therefore, there is a need for methods to manipulate nanowires so as to place them in the desired location for successful fabrication of device with them. In this chapter, dielectrophoresis has been used for assembling nanowires in between and at the sides of the contact pads. Alignment under different conditions lead to an understanding of the forces. Fabrication of a large number of devices in a single experiment has been demonstrated. Chapter 5 presents a simple route to synthesize CdS-Au2Sx hybrid as a result of cation-exchange predominantly. Au due to high electron affinity has been shown in literature to undergo reduction rather than cation exchange with CdS. In this chapter, it has been shown that cation exchange may be a dominant product. The competition between cation exchange and reduction in the case of CdS-Au system has been studied using EDS, XRD, XPS and TEM. Thermodynamic calculation along with kinetic analysis show that the process may depend on a delicate balance of reaction conditions and the system under study. The methodology adopted, is general and may be applied to other systems. Chapter 6 presents an one pot, ultrafast microwave route to synthesize PdO hollow/hybrid nanomaterials. The common strategy to synthesize hollow nanomaterials had been by nucleation of the shell material on the core and subsequent dissolution of the core. In this chapter, a one step method to synthesize hollow PdO nanotubes, using ZnO nanorods as sacrificial template, has been shown. By tuning the ratio of the PdCl2 (PdO precursor) to ZnO, ZnO-PdO hybrid could be obtained using the same method. The PdO nanotubes synthesized could be converted to Pd nanotubes by NaBH4 treatment. Study of thermal stability of the PdO nanotubes has been carried out. Chapter 7 demonstrates a simple strategy to sense a variety of strain/pressure with taped crumpled graphene. Detection of ultralow strain (10-3) with high gauge factor is challenging and poorly addressed in literature. Taped crumpled graphene has been shown to detect such low strain with high gauge factor (> 4000). An ultra-fast switching time of 20.4 ms has been documented in detection of dynamic strain of frequency 49 Hz. An excellent cyclic stability for >7000 cycles has been demonstrated. The same device could be used to detect gentle pressure pulses with consistency. Slight modification of the device configuration enabled detection of high pressure. Simplicity of the device fabrication allowed fabrication of the device onto stick labels which could be pasted on any surface, for instance, floor. Hard pressing, stamping with feet and hammering shocks do not alter the base resistance of the device, indicating that it is extremely robust. Sealed arrangement of the graphene allowed operation of the device under water in detection of water pressure. Presence of trapped air underneath the tape enabled detection of air pressure both below and above atmospheric pressure.

Στην παρούσα διδακτορική διατριβή μελετάται η ανάπτυξη λεπτών υμενίων πορωδών ανοδικών οξειδίων του αλουμινίου (αναφέρονται και ως πορώδης ανοδική αλουμίνα) σε υπόστρωμα πυριτίου. Επιπλέον, εξετάζεται η ανάπτυξη εφαρμογών που αφορούν τη χρήση της πορώδους αλουμίνας ως μάσκα και ως μήτρα για την δημιουργία νανονημάτων ή κβαντικών τελειών (νανονησίδων) στο Si. Το πρώτο κεφάλαιο πραγματεύεται τη θεωρία και τους μηχανισμούς που διέπουν την ανάπτυξη πορωδών υμενίων, που προέρχονται από ανοδική οξείδωση (ανοδίωση) τόσο φύλλων αλουμινίου, όσο και υμενίων αλουμινίου σε υπόστρωμα πυριτίου. Επιπροσθέτως, παρατίθεται ο ρόλος που διαδραματίζουν οι ηλεκτροχημικές συνθήκες ανοδίωσης, όπως το pH, η θερμοκρασία και η εφαρμοζόμενη τάση, στα τελικά δομικά χαρακτηριστικά των πορωδών υμενίων. Στο δεύτερο κεφάλαιο παρουσιάζονται τα τεχνολογικά βήματα διεργασιών που αφορούν την προετοιμασία των δειγμάτων τα οποία πρόκειται να ανοδιωθούν, και δίνονται λεπτομέρειες για την πειραματική διάταξη η οποία χρησιμοποιείται κατά την ανοδίωση. Στο τρίτο κεφάλαιο μελετώνται εκτενώς, τρεις παράγοντες που έχουν σημαντική επίδραση στα τελικά δομικά χαρακτηριστικά των πορωδών υμενίων. Κατά τους δύο πρώτους, εξετάζεται η επίδραση του πάχους του προς ανοδίωση υμενίου αλουμινίου πάνω στο Si, καθώς και ο περιορισμός του σε επιφάνειες μερικών τετραγωνικών μικρομέτρων πάνω στο Si, στο μέγεθος και την πυκνότητα των πόρων. Ο τρίτος παράγοντας αφορά το ρόλο της ανοδίωσης του υμενίου του αλουμινίου σε δύο και τρία στάδια σε συνδυασμό με τη χημική εγχάραξή του μετά από κάθε στάδιο ανοδίωσης, στην ανάπτυξη εξαγωνικής συμμετρίας στην κατανομή των πόρων. Το τέταρτο κεφάλαιο, πραγματεύεται την ανάπτυξη εφαρμογών που συνδέονται με τη χρήση της πορώδους αλουμίνας ως μάσκα και ως μήτρα για τη δημιουργία νανοδομών επάνω στο πυρίτιο. Ως εκ τούτου παρουσιάζεται η δημιουργία νανονησίδων Cr, Ti, νανοστηλών Si, και νανονημάτων Au, πάνω στο Si, εφαρμογές στις οποίες τα πορώδη ανοδικά υμένια χρησιμοποιήθηκαν ως ενδιάμεσο στάδιο. Στο πέμπτο κεφάλαιο παρατίθεται η ανάπτυξη διαμέσου της πορώδους αλουμίνας, εξαγωνικά διατεταγμένων νανονησίδων SiO2 στο Si. Επίσης, παρουσιάζεται ο ηλεκτρικός χαρακτηρισμός διατάξεων οι οποίες αποτελούνται από την εν λόγω δομή. Σε ένα επιπλέον βήμα, οι νανονησίδες SiO2 χρησιμοποιούνται για την ανάπτυξη νανοκρυσταλλιτών Si στο εσωτερικό τους μέσω της τεχνικής της ιοντικής σύνθεσης. Τα σημαντικότερα αποτελέσματα και συμπεράσματα που προέκυψαν από την εκπόνηση της παρούσας διδακτορικής διατριβής συνοψίζονται στα εξής: • Βελτίωση της εξαγωνικής συμμετρίας στην κατανομή των πόρων, μέσω ανοδίωσης σε δύο ή τρία στάδια σε συνδυασμό με χημική εγχάραξη του προς ανοδίωση αλουμινίου έπειτα από κάθε στάδιο ανοδίωσης. • Αύξηση της πυκνότητας των πόρων των ανοδικών υμενίων κατά μία τάξη μεγέθους, με περιορισμό του προς ανοδίωση αλουμινίου σε προεπιλεγμένες περιοχές στο Si, επιφάνειας μερικών τετραγωνικών μικρομέτρων. • Ανάπτυξη διατεταγμένων νανοδομών Ti και Cr σε υπόστρωμα Si χρησιμοποιώντας λεπτά υμένια πορώδους αλουμίνας πάνω σε Si. Ιδιαίτερα οι δομές Cr, μπορούν να χρησιμοποιηθούν ως μεταλλική νανοδομημένη μάσκα για την εγχάραξη με ενεργά ιόντα του υποστρώματος Si και τη δημιουργία νανοστηλών Si πάνω σε αυτό. Η δημιουργία νανοστηλών Si, βρίσκει πληθώρα εφαρμογών στη Νανοηλεκτρονική, σε αισθητήρες, Nανοφωτονική, μνήμες κ.τ.λ. • Οι πυκνότητες διεπιφανειακών καταστάσεων που προέκυψαν από τον ηλεκτρικό χαρακτηρισμό της διεπιφάνειας υμενίων πορώδους αλουμίνας με το πυρίτιο, και της διεπιφάνειας πορώδους αλουμίνας – νανονησίδων SiO2 με το πυρίτιο. Οι τιμές που υπολογίστηκαν είναι ενθαρρυντικές, αν ληφθεί υπόψη ο ηλεκτροχημικός τρόπος παρασκευής των εν λόγω σύνθετων υμενίων πάνω στο πυρίτιο. • Ανάπτυξη μεμονωμένων νανοκρυσταλλιτών Si ενσωματωμένων σε νανονησίδες SiO2. Για το σκοπό αυτό συνδυάστηκαν δύο διαφορετικές τεχνολογίες, εκείνη της ιοντικής σύνθεσης και εκείνη της ανάπτυξης νανονησίδων SiO2 διαμέσου λεπτών υμενίων πορώδους αλουμίνας απευθείας σε υπόστρωμα Si. Τέτοιες δομές νανοκρυσταλλιτών έχουν εφαρμογές σε διατάξεις μη πτητικών μνημών, όπου η κατανεμημένη αποθήκευση φορτίου στους νανοκρυσταλλίτες ευνοεί τη χρήση λεπτότερων οξειδίων πύλης και τη δυνατότητα σμίκρυνσης του πάχους των οξειδίων αυτών χωρίς να μειώνεται ο χρόνος αποθήκευσης φορτίου. / In the present thesis, the growth of porous anodic alumina films on Si substrate was studied extensively. Potential applications of porous anodic alumina films formed directly on Si, regarding the use of porous membranes as mask or template for various nanostructures growth directly on Si, are discussed. Chapter one deals with the theory and mechanisms governing porous anodic alumina film growth, either on porous anodic films formed by anodization of aluminum foils, or on porous anodic films developed on Si substrates. Additionally, the effect of different factors (pH, temperature, applied voltage) on the final structural characteristics is presented. In chapter two, the preliminary processing steps regarding sample preparation before the anodization procedure are quoted. Moreover, details about the experimental set-up and the electrochemical conditions used during the sample anodization in the current work are given. In chapter three, the influence of three different factors, in the final structural characteristics, is investigated. Primarily, the impact of the initial aluminum thickness deposited on Si substrate, and secondly the confinement of the aluminum film in areas of a few μm2, in the pore size and pore density are studied. Finally, the influence of the third factor is associated with a three-step instead of a two-step anodization, in combination with an in-between step of aluminum chemical etching, on the ordering and the uniformity of the pores. The deposition of Ti and Cr nanodots arrays on Si, using the porous alumina membrane as a masking layer, is investigated in chapter four. Furthermore, the Ti nanodots are used for the electrodeposition of Au nanodots and nanowires inside the porous alumina films. Additionally, the Cr dots are used as metallic nanostructured mask for the Si etching by reactive ion etching process, that leads to the formation of Si nanopillars on Si substrate. In chapter five the growth of hexagonally ordered SiO2 dots on Si through porous anodic alumina membranes, in various acidic electrolytes, is studied. Moreover, the electrical characterization of the interface of porous alumina film/Si and porous alumina film with SiO2 dots in pore bottoms/ Si is presented. Finally, in the present thesis the technology of fabrication of Si nanocrystals embedded in SiO2 dots arrays through porous alumina membranes on Si substrate is developed for the first time. This was achieved by the combination of ion beam synthesis with the already existing technology of porous anodic alumina growth on Si substrates. The nanocrystals are electrically isolated from the substrate. This technique is promising as an application in non-volatile memory devices. The main achievements accomplished through this study are summarized as follows: • The optimization of pores ordering by developing the porous alumina membrane in two or three processing steps in combination with the chemical etching of Al film, lying above the porous membrane, following each anodization cycle. • The increase of porous density by the confinement of porous alumina film in areas of a few μm2 on Si. • The development of Ti, Cr and nanodots arrays, directly on Si, through porous alumina membranes. The use of Cr nanodots as nanostructured masking layer for the formation of Si nanopillars, formed by etching of Si substrate with RIE, on Si. • The density of interface stages results from the electrical characterization of porous alumina with or without SiO2 dots at each pore bottom, with the Si substrate. The results are encouraging, keeping in mind that the pore membranes and SiO2 dots were electrochemically grown directly on Si substrate. • The development of distinct Si nanocrystalls, embedded in SiO2 dots, combining for the first time two different technologies, that is the fabrication of porous anodic alumina films directly on Si substrate, as well as the ion beam synthesis technique. The proposed technique is promising for the fabrication of non-volatile memory devices.

Controlling the morphology of nanocrystals provides provides a possible pathway to tune properties and hence has been explored in depth. However, to obtain a wider spectrum of properties or for multi-functionality. Other strategies need to be devised. Combining different functional nanostructures to obtain a functional hybrid is one such strategy that holds promise for a wide range of applications. While this is simple in principle, there are no simple and general protocols for synthesis of such functional heterostructure. The challenge lies in producing a hybrid with good control over the structure and chemistry of the interfaces in the system. The use of molecular linkers or physical forces to form the hybrid has several drawbacks in terms of interface quality and stability. In this dissertation, a rational basis is developed for the evolution of symmetry forbidden FCC nanocrystals via wet chemical route which relies on appropriate choice of reagents and the reaction conditions for nucleation and growth. The concept is extended to devise general synthetic strategies for functional nanoheterostrcutres in solution via economic, facile and environment friendly routes. Electron microscopy and X-ray photoelectron spectroscopy has been used as the major tools for structural characterization of the materials and to investigates the reaction/formation mechanism. The properties of the synthesized materials are investigated primarily targeting the nanoelectronic and catalytic applications. The entire study reported in the thesis is organized as follow: chapter I leads to a general introduction of nanocrystals and role in different fields of application. It describes the motivation behind controlling the shape of nanocrystals and combining two or more nanostructures to obtain a functional heterostructure. The existing methodologies to achieve shape control and nanoscale hybrid/heterostructure with active interfaces are elaborated while indicating the role of morphology, interfaces and composition for enhanced activity/performance. The information on the chemical used for synthesis, routers adopted for synthesizing and the basic techniques utilized to characterize the materials in study are detailed in the respective chapters. Chapter 2 provides a study by which one can easily select an appropriate reductant for a metal couple to achieve the desired morphology. Moreover, the role of kinetics and the factors driving the kinetics in obtaining the symmetry breaking shapes like 2-D and I-D for Ag and Au nanocrystals is discussed in detail and validated by experiments. Chapter 3 describes the methodology to attach ultrafine Au nanowires to different nanosubstrates ranging from oxides to carbon (CNT/graphene) where the key step is heteronucleation of the Au (I) precursor on the substrate. Chapter 4 deals with the growth of ultrafine Au nanowires on various substrates and between pre-defined contacts to fabricate nanodevices. The mechanistic investigation directs to the controlled heterogeneous nucleation of the building units (Au nanoparticles) on substrate as the key step followed by its subsequent growth into wires in presence of Au nanoparticles in the medium. Kinetic control of the nucleation and growth step enabled precise control over the population and length of the wires. This is of immense importance for application like catalysis, sensors and nanoelectronics. Moreover, the method enabled the first time electrical transport studies on these wires which revealed an insulating behavior in such metallic wires on progressive lowering of temperature down to few kelvins. The concept of heterogeneous nucleation is extended to design nanoscale heterogeneous in the following three chapters where primarily a precursor coating is formed on a nanosubstrate, viz. ZnO nanorods and graphene, and converted to the phase of interest in a controlled manner to obtain the desired morphology. In each of the chapters the mechanisms of formation of the heterostructure are discussed in detail. Chapter 5 deals with formation of semiconductor based heterostructure like ZnO/CdS in solution by aqueous route. The material has been demonstrated as a potential visible light catalyst for dye degradation with enhanced activity. The interfacial chemistry could be tuned appropriately to achieve high activity in the catalyst by simple wet chemical route. In chapter 6, an ultrafast, facile, green route to obtain oxide supported metal catalyst has been demonstrated. ZnO/Au heterostructures were designed with well defined morphology and studied for low temperature CO oxidation reaction. Detail investigation reveals the surface doping of ZnO with Au the nucleation process leading to active ionic sites for CO oxidation. Chapter 7 demonstrate a rapid and economically viable route to graphene based pt catalysts where a synergistic co-reduction mechanism operates between the metal precursor and the graphic oxide to from the heterostructure. The obtained G-Pt heterostructure exhibits high catalytic activity for methanol oxidation reaction and hydrogen convention at ambient conditions. Finally a conclusion is drawn, highlighting the possibilities and prospects that the study leads to.

This thesis deals with the research work carried out for the development of novel applications by integrating biomolecules with various nanostructures. The thesis is organized as follows: Chapter 1 reviews the properties of nanomaterials which are important to consider while developing them for various biological and other applications. It discusses the factors which affect the cytotoxicity of nanocrystals towards living cells, photocatalytic mechanisms of nanocrystals that work behind the inactivation of bacterial cells and gas sensing properties of nanocrystals. It also mentions about the integration of biomolecules with nanomaterials which is useful for the development of biosensors, materials that are presently used for fabricating biosensors and the challenges associated with designing successful biosensors. Chapter 2 presents the antibacterial and anticancer properties of ZnO/Ag nanohybids. In this study a simple route to synthesize ZnO/Ag nanohybrids by microwave synthesis has been established where ZnO/Ag nanohybrids have shown synergistic cytotoxicity towards mammalian cells. The observed synergism in the cytotoxicity of ZnO/Ag nanohybrids could lead to the development of low dose therapeutics for cancer treatment. Chapter 3 presents photocatalytic inactivation of bacterial cells by pentavalent bismuthates class of materials. AgBiO3 which was obtained from KBiO3 by ion-exchange method was investigated for its photocatalytic inactivation properties towards E.coli and S.aureus cells under dark and UV illumination conditions. Chapter 4 presents the integration of DNA molecules with ZnO nanorods for the observation of Mott-Gurney characteristics. In this study, ZnO nanorods were synthesized hydrothermally and were characterized by TEM and XRD analysis. DNA molecules were immobilized over ZnO nanorods which were confirmed by UV-Vis spectroscopy and confocal florescence microscopy. Solution processed devices were fabricated by using these DNA immobilized nanostructures and I-V characteristics of these devices were taken in dark and under illumination conditions at different wavelengths of light at fixed intensity. Interestingly, Mott-Gurney law was observed in the I-V characteristics of the devices fabricated using DNA immobilized ZnO nanorods. Chapter 5 presents the chemical synthesis of molecular scale ultrathin Au nanowires. These nanostructures were then used for fabricating electronic biosensors. In this study, the devices were fabricated over Au nanowires by e-beam lithography and a methodology to functionalize Au nanowires and then characterize them by florescence microscopy as well as AFM has been established. The fabricated biosensors were employed for the label free, electrical detection of DNA hybridization process. Chapter 6 presents a simple, cost effective and solution processed route to fabricate devices using ultrathin Au nanowires. The devices were then used for sensing ethanol, H2 and NH3. An important property of these devices is that they can sense these gases at room temperature which reduce their operation cost and makes them desirable to use under explosive conditions.

Catalysis using nanostructures has been a topic of substantial interest for fundamental studies and for practical applications in energy and environmental sectors. The growing demand for production of energy and in the cleaning of polluting hazardous vehicles/industrial wastes has led to several studies in catalysis. Despite the substantial growth of heterogeneous catalytic technologies in last decade, they are still far from reaching their full potential in terms of efficiency, selectivity as well as durability. It is often difficult to simultaneously tackle all the mentioned issues with single component catalysts. Most of these challenges are being overcome with heterostructures/supported hybrid catalysts by modifying their interfaces. The properties of heterostructures hybrids arises not only from the individual contributions of the individual components but also from strong synergetic effect arising from the interface. Engineering the interfaces provides pathways to promote the catalytic performance and hence has been explored. In this regard, we have focused on the progress in investigating the active interfaces that affect the performance of metal oxide-metal, semiconductor-metal and coupled semiconductor nanocatalyst hybrids. We explored a wide spectrum of their applications in photo catalytic, electrocatalytic as well as gas-phase reactions and highlighted the importance of the interface for overall performance. The entire study reported in the thesis is organized as follows: Chapter 1 is a general introduction of hybrid nanocatalyst and their role in wide spectra of catalytic reactions in photo/electro catalysis as well as gas-phase reactions. This chapter describes the motivation behind modulating the interface between two or more nanostructures to obtain multifunctional nanocatalysts. Nan catalysts to achieve high throughput with active interfaces are elaborated while indicating the role of morphology, internal induced state, charge transfer, geometric, support, as well as electronic effect for enhanced performance. Motivation behind specific nanocatalyst hybrid, synthesis routes as well as characterization techniques are detailed in the respective chapters. Specific details for different hybrids are described in the following chapters. Chapter 2 describes the synthesis of high dense ultrathin Au wires on ZnO nanorods for electrocatalytic oxidation of ethanol, where the prerequisite step is the formation of amine-modified support. Oleylamine modification not only serves to anchor Au nanowires on ZnO but also passivates surface defects of ZnO, which in turn enhances the photocurrent. In addition to the stability, the support induces electronic effect on Au nanowires, which facilitates redox process at low potential. Most importantly, the support promotes the activity of Au nanowires upon photoirradiation, and thus leading to synergy between electro and photooxidation current. This is of immense importance for photofuel cell technologies. Moreover, the method enabled the first time electrocatalysis on these nanowires that revealed ultrathin nanowires are potentially interesting systems for catalysis applications provided they are stabilized by a suitable support. Chapter 3 deals with the growth of ultrathin Au nanowires on metal oxide (TiO2) coupled with graphene hybrid support in order to overcome the low conductivity of metal oxide. Oleylamine, used for growth of Au nanowires simultaneously functionalizes the support and leads to room temperature GO reduction. With respect to catalytic activity, we also synthesized the binary counterparts (rGO/Au, TiO2/Au ultrathin nanowires) to delineate the contribution of each of the components to the overall electrocatalytic oxidation of ethanol. Comparative analysis of photo and electrocatalytic activity between the different binary and ternary hybrids provides interesting information. Both, electronic effect of TiO2 and electrical conductivity of rGO add their specific beneficial to the nanowires, leading to superior ternary system. Chapter 4 rGO supported ultrathin Au nanowires exhibits high electrocatalytic performance for oxidation of borohydride with a lower onset potential compared to rGO/Au nanoparticles. Electrochemical impedance spectroscopy measurements display abnormal inductive behavior of the synthesized hybrids, indicative of Au surface reactivation. DFT calculations indicate that the origin of the high activity stems from the shift in the position of the Au d-band center. Chapter 5 Different aspect ratio ZnO nanostructures are obtained by varying the solvothermal reaction time. We observed a direct correlation between observed photocatalytic activity, measured photocurrent and length of the ZnO nanorods. Furthermore, photoresponse of the high aspect ratio ZnO nanorods are improved by attaching Au nanoparticles, intimate contact of two components leads to band bending. Thus, the synthesized ZnO/Au heterostructure favors for prominent separation of photogenerated charge carriers. Chapter 6 TiO2 and PbO/TiO2 hybrids are synthesized via non–hydrolytic sol–gel combustion method. Hybrid exhibits higher photocatalytic activity for the degradation of dye than TiO2. The estimated photogenerated species reveals that the origin of enhanced activity stems from the direct oxidization of dye via photogenerated hole rather than radicals. The semiconductors are matched based on their band edge positions, for the formation of energetic radicals to degrade the pollutants. Based on this study, we infer that semiconductors should not neglected (for example Si) based on calculated mismatch of their valence band edges position for photooxidation reaction via radicals. Chapter 7 describes the Pd dopant associated band engineering, a strategy for tuning the optoelectronic properties of ZnO towards enhanced photocatalytic activity. Incorporated Pd heterocation induces internal energy states within the ZnO band gap. The created energy level leads to trends mismatch between photocatalytic activity and measured photocurrent. Formed energy level arrests the photogenerated electrons, which make them not contribute for the photocurrent generation. Hence, the isolated photogenerated hole efficiently oxidizes the pollutants through hydroxyl radicals, and thus leads to enhanced photocatalytic activity. Chapter 8 employed Pd-substituted zinc stannate for CO oxidation as heterogeneous catalyst for the first time. Compared with SnO2 support, zinc stannate based materials exhibits abnormal sudden light-off profiles at selective temperatures. On the basis of DRIFT studies under relevant conditions, we find that the initially formed product gets adsorbed over the catalyst surface. It leads to the accumulation of carbonates as a consequence, both lattice oxygen mobility and further CO interactions are disabled. As soon as Sn redox nature dominates over the accumulated carbonates, this leads to sudden release of lattice oxygen, and thus leads to a sudden full conversion. Therefore, choosing the suitable support material greatly influences the nature of the light-off CO oxidation profile. Chapter 9 Although, reducible oxide supported gold nanostructures exhibits the highest CO oxidation activity; they still suffer from problems such as limited selectivity towards CO in the presence of H2. Both ex-situ and in-situ experiments demonstrate that, Au nanoparticles supported on Zn2SnO4 matrix selectively oxidizes CO. DRIFT experiments revealed that the involvement of OH groups leads to the formation of hydroxycarbonyl under PROX conditions. Chapter 10 This chapter discusses the conclusions for the previous chapters and highlights the possibilities for future scope for the developed nanocatalysts hybrids for energy and environmental applications.