The development of nanostructured materials for environmental applications has received considerable attention in recent years. The properties of nanoparticles or nanostructured materials, such as large surface areas or high aspect ratios, translate into large improvements in the performance of existing devices and in the discovery of novel applications. On the other hand, photocatalysis is an attractive technology for the elimination of organic pollutants in water due to its simplicity, ease of implementation and reasonable cost compared to other advanced oxidation processes. A key disadvantage of many photocatalysts is their use in powder form which makes their recovery from treated water costly. In addition, incomplete removal can lead to accumulation over time with adverse effects to the environment. As a result significant effort has been placed in immobilizing photocatalytic materials on different substrates. The immobilization of photocatalyst results in a decrease in photocatalytic performance mainly due to reduction of surface area; therefore, research is now focusing on developing nanostructured materials which combine the attributes of nanotechnology and photocatalysis. In the present thesis, a systematic study of the relationship between properties of supported ZnO nanostructures and their photocatalytic activity was performed. Analysis was carried out by producing ZnO nanostructured films via anodization. The effects of voltage, temperature, reaction time and type of electrolyte on the morphology of ZnO nanostructures was studied. Results show that the type of electrolyte and its concentration determine the morphology and size of the nanostructures. Voltage, time and temperature affect the distribution and density of the nanostructures along the surface and affect the crystal size of the ZnO. The band gaps of the films were in the range of 3.27 and 3.50 eV. Although ZnO is a hydrophilic material, some of the films displayed hydrophobic and super-hydrophobic behaviour. The results obtained in this study and some data already published in the literature were correlated to the synthesis parameters, and were used to devise design guidelines to obtain ZnO films with specific nanostructures and macroscopic properties by controlling the anodization parameters. The photocatalytic activity of the ZnO nanostructured films (ZnO-NFs) were studied using three different photocatalytic reactors, (i) a thermo-stated batch reactor, (ii) a recirculating flat plate reactor, and (iii) a recirculating tubular annular reactor. Phenol and methyl orange (MO) were used as a model compounds. It was found that crystal size does not affect the photocatalytic performance of the films while morphology has an important impact on the degradation of phenol. The stability of the ZnO nanostructures was tested under different levels of oxygen, degradation of phenol occurred even at anoxic conditions following the Mars-van Krevelen mechanism. The formation of new nanostructures produced during the photocatalytic reaction was studied and a mechanism of formation was proposed. The study of the photocatalytic performance in the flat plate reactor showed that there was a mass transfer limitation in the process. ZnO nanostructures showed higher photocatalytic activity and morphology stability in the tubular annular reactor. Degradation of MO and phenol was produced in darkness by the nanostructures supported in Zn foil. It was also demonstrated that oxygen plasma post-treatment enhances the photocatalytic activity of the ZnO-NF by 36% while making the photocatalyst more stable for the photocatalytic degradation of phenol compared to those treated with heat. An electrical current was applied to the photocatalyst in the tubular annular reactor, which improved the degradation of phenol and participated in the formation of nanostructures in the Zn wire surface.

Lighting is a big business, lighting consumes considerable amount of the electricity. These facts motivate for the search of new illumination technologies that are efficient. Semiconductor light emitting diodes (LEDs) have huge potential to replace the traditional primary incandescent lighting sources. They are two basic types of semiconductor LEDs being explored: inorganic and organic semiconductor light emitting diodes. While electroluminescence from p-n junctions was discovered more than a century ago, it is only from the 1960s that their development has accelerated as indicated by an exponential increase of their efficiency and light output, with a doubling occurring about every 36 months, in a similar way to Moore's law in electronics. These advances are generally attributed to the parallel development of semiconductor technologies, optics and material science. Organic light emitting diodes (OLEDs) have rapidly matured during the last 30 years driven by the possibility to create large area light-emitting diodes and displays. Another driving force to specifically use semiconducting polymers is the possibility to build the OLED on conventional flexible substrates via low-cost manufacturing techniques such as printing techniques, which open the way for large area productions. This thesis deals with the demonstration and investigation of heterojunction LEDs based on p-organic semiconductor and n-ZnO nanostructures. The ZnOorganic heterojunctions are fabricated using low cost and simple solution process without the need for sophisticated vacuum equipments. Both ZnO-nanostructures and the organic materials were grown on variety of substrates (i.e. silicon, glass and plastic substrates) using low temperature methods. The growth mechanism of the ZnO nanostructures has been systematically investigated with major focus in ZnO nanorods/nanowires. Different organic semiconductor materials and device configurations are explored starting with single polymer emissive layer ending up with separate emissive and blocking layers, or even blends. Interestingly, the photoluminescence and electroluminescence spectra of the hybrid LEDs provided a broad emission band covering entirely the visible spectrum [∼400-∼800nm]. The hybrid light emitting diode has a white emission attributed to ZnO intrinsic defects and impurities in combination with the electroluminescence from the conjugated polymers. The ZnO nanostructures in contact with a high workfunction electrode constitute an air stable electron injecting contact for the organic semiconductor. Hence, we have shown that a white light emission can be achieved in a ZnO-organic hybrid light emitting diode using cheap and low temperature growth techniques for both organic and inorganic materials. / The series number "1504" is incorrect and is changed in the electronic version to the correct number "1405".

The thesis consists of four parts of which part 1 presents a brief overview of nanomaterials. Parts 2, 3 and 4 contain results of investigations of graphene, nanofilms of noble metal nanoparticles and ZnO nanostructures respectively. Investigations of graphene are described in Part 2 which consists of six chapters. In Chapter 2.1, changes in the electronic structure and properties of graphene induced by molecular charge-transfer have been discussed. Chapter 2.2 deals with the results of a study of the interaction of metal and metal oxide nanoparticles with graphene. Electrical and dielectric properties of graphene-polymer composites are presented in Chapter 2.3. Chapter 2.4 presents photo-thermal effects observed in laser-induced chemical transformations in graphene and other nanocarbons system. Chapter 2.5 describes the mechanical properties of polymer matrix composites reinforced by fewlayer graphene investigated by nano-indentation. The extraordinary synergy found in the mechanical properties of polymer matrix composites reinforced with two nanocarbons of different dimensionalities constitute the subject matter of Chapter 2.6. Investigations of noble metal nanoparticles have been described in Part 3. In Chapter 3.1, ferromagnetism exhibited by nanoparticles of noble metals is discussed in detail while Chapter 3.2 deals with surface-enhanced Raman scattering (SERS) of molecules adsorbed on nanocrystalline Au and Ag films formed at the organic–aqueous interface. Factors affecting laser-excited photoluminescence from ZnO nanostructures are examined in great detail in Part 4.

The present work covers investigation of the growth mechanism and growth kinetics of the ZnO nanowires and nanoneedles fabricated by using high-pressure pulsed laser deposition. The growth model based on the combination of four different flows of the interfacial particles is introduced. A variation of the free energy is given as a major reason of the change of the growth mechanism which appears by using different doped seed layers, growth temperature and the doping of the deposited material. A fabrication of the ultrathin nanowires with a diameter of d < 10 nm at CMOS compatible growth temperature of T = 400°C is demonstrated. The diameter of these nanowires is comparable with the Bohr radius. The growth of the Al and Ga doped and undoped ZnO nanoneedles with a sharp tip was shown. The doping of the nanowires and nanoneedles can be promising for their applications. By using a patterned sapphire substrate, an unidirectional growth of the nanowires and nanoneedles was achieved. These nanostructures are tilted by 58°ZnO with respect to the surface normal.:Bibliographic Record Contents 1 Introduction I Basics and Methods 2 Basic properties and growth concept 2.1 ZnO nanowires and nanoneedles 2.1.1 Applications 2.2 Nanowire and nanoneedle fabrication 2.2.1 Growth mechanisms which require a catalyst 2.2.2 Catalyst-free epitaxial growth mechanism 2.3 Free energy and the growth mechanism 2.4 NW growth techniques 2.5 Aligned tilted growth 3 Growth and characterization 3.1 Preparation of the seed layers by CVD 3.2 Preparation of the seed layers by low pressure PLD 3.3 HP PLD for the NW and NN growth 3.4 Characterization techniques 3.4.1 X-ray Diffraction 3.4.2 Atomic Force Microscopy 3.4.3 Scanning electron microscopy 3.4.4 Energy Dispersive X-ray Spectroscopy 3.4.5 Spectroscopic Ellipsometry 3.4.6 Cathodoluminescence 3.4.7 Angle-varied X-ray photoelectron spectroscopy 3.4.8 Etching of the seed layers 4 Seed layer characterization 4.1 Doping concentration 4.2 Surface morphology 4.3 Crystalline quality 4.4 Surface polarity 4.5 Summary of the Chapter II NW growth: results 5 NW growth characteristics 5.1 Material free energy and the deposited material parameters 5.2 Growth kinetics 5.3 Summary of the Chapter 6 NW growth on doped seed layers 6.1 Al doped seed layers 6.2 NW growth on Ga doped seed layers 6.3 Optical characteristics of the ZnO NWs 6.4 Summary of the Chapter 7 Growth of ZnO(Al) and ZnO(Ga) NWs 7.1 Al-doped ZnO NWs grown on ZnO(Al) seed layers 7.2 Ga-doped ZnO NWs grown on ZnO(Ga) seed layers 7.3 Summary of the Chapter 8 Growth of tilted ZnO NWs and NNs 8.1 Patterning of the substrates . 8.2 Growth of tilted NNs 8.3 Growth of tilted NWs 8.4 Optical properties of the tilted nanostructures 8.5 Summary of the Chapter 9 Summary and outloock 9.1 Summary 9.2 Outlook Acknowledgements Curriculum Vitae List of own Articles List of own Conference Talks and Posters References

Nanotechnology is a technology of the design and the applications of nanoscale materials with their fundamentally new properties and functions. Nanosensor devices based on nanomaterials provide very fast response, low-cost, long-life time, easy to use for unskilled users, and provide high-efficiency. 1-D ZnO nanostructures materials have great potential applications in various sensing applications. ZnO is a wide band gap (3.37 eV at room temperature) semiconductor materials having large exciton binding energy (60 meV) and excellent chemical stability, electrical, optical, piezoelectric and pyroelectric properties. By doping the transition metals (TM) into ZnO matrix, the properties of ZnO nanostructures can be tuned and its room  temperature ferromagnetic behavior can be enhanced, which provide the TM-doped ZnO nanostructures as promising candidate for optoelectronic, spintronics and high performance sensors based devices. The synthesis of ZnO and TM-doped ZnO nanostructures via the low temperature hydrothermal method is considered a promising technique due to low cost, environmental friendly, simple solution process, diverse 1-D ZnO nanostructures can be achieved, and large scale production on any type of substrate, and their properties can be controlled by the growth parameters. However, to synthesize 1-D ZnO and TM-doped ZnO nanostructures with controlled shape, structure and uniform size distribution on large area substrates with desirable properties, low cost and simple processes are of high interest and it is a big challenge at present. The main purpose of this dissertation aims to develop new techniques to synthesize 1-D ZnO and (Fe, Mn)-doped ZnO nanostructures via the hydrothermal method, to characterize and to enhance their functional properties for developing sensing devices such as biosensors for clinical diagnoses and environmental monitoring applications, piezoresistive sensors and UV photodetector. The first part of the dissertation deals with the hydrothermal synthesis of ZnO nanostructures with controlled shape, structure and uniform size distribution under different conditions and their structural characterization. The possible parameters affecting the growth which can alter the morphology, uniformity and properties of the ZnO nanostructures were investigated. Well-aligned ZnO nanorods have been fabricated for high sensitive piezoresistive sensor. The development of creatinine biosensor for clinical diagnoses purpose and the development of glucose biosensor for indirect determination of mercury ions for an inexpensive and unskilled users for environmental monitoring applications with highly sensitive, selective, stable, reproducible, interference resistant, and fast response time have been fabricated based on ZnO nanorods. The second part of the dissertation presents a new hydrothermal synthesis of (Fe, Mn)-doped-ZnO nanostructures under different preparation conditions, their properties characterization and the fabrication of piezoresistive sensors and UV photodetectors based devices were demonstrated. The solution preparation condition and growth parameters that influences on the morphology, structures and properties of the nanostructures were investigated. The fabrication of Mn-doped-ZnO NRs/PEDOT:PSS Schottky diodes used as high performance piezoresistive sensor and UV photodetector have been studied and Fe-doped ZnO NRs/FTO Schottky diode has also been fabricated for high performance of UV photodetector. Finally, a brief outlook into future challenges and relating new opportunities are presented in the last part of the dissertation.

Hybridsolarzellen werden sowohl aus ZnO-Schichten als auch ZnO-Nanostrukturen und Poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b'']dithiophen)-alt-4,7(2,1,3-benzothiadiazol)] (PCPDTBT) hergestellt. Das Wachstum der ZnO-Schichten und Nanostrukturen wird mittels gepulster Laserdeposition (PLD) auf Saphirsubstraten durchgeführt. Die Schichten weisen eine c-Achsenorientierung auf. Die Polarität einer ZnO-Schicht bestimmt die Morphologie der nachfolgend gewachsenen ZnO-Nanostrukturen. Dabei kann die Morphologie kontrolliert zwischen Nanostäbchen auf einer O-terminierten ZnO-Schicht und Nanowänden auf einer Zn-terminierten ZnO-Schicht eingestellt werden. Untersuchungen mittels konvergenter Elektronenbeugung zeigen, dass die Nanostrukturen immer Zn-terminiert sind. Die Grenzfläche zwischen ZnO und PCPDTBT wird mit Photoelektronenspektroskopie untersucht und ergibt eine Vakuumniveauangleichung zwischen beiden Materialien. Prinzipiell ist der Übergang für photovoltaische Aktivität geeignet, jedoch sind die erzielten Wirkungsgrade sehr niedrig. Die Ursache ist eine niedrige Exzitonendissoziationseffizienz, die durch die Benutzung von sol-gel ZnO, kleinen organischen Molekülen und einer niedrigeren Leitfähigkeit vom PLD-ZnO verbessert werden kann. Dennoch beträgt der maximale Wirkungsgrad der Hybridsolarzellen nur 0,21 %. / Hybrid solar cells are built from ZnO layers and ZnO nanostructures and Poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b'']dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT). The growth of the ZnO layers and nanostructures is performed with pulsed laser deposition (PLD) on sapphire substrates. The samples exhibit a c-axis orientation. The polarity of a ZnO layer determines the morphology of subsequently grown ZnO nanostructures. One can control the morphology between ZnO nanorods on an O-terminated layer and nanowalls on a Zn-terminated layer. Studies with convergent electron beam diffraction reveals that the ZnO nanostructures are always Zn-terminated. The interface between ZnO and PCPDTBT is studied with photoelectron spectroscopy and shows a vacuum level alignment between both materials. In principle, the interface is suitable for photovoltaic activity, however, the achieved power conversion efficiencies are very low. This is due to a low exciton dissociation efficiency, which can be improved by the use of sol-gel ZnO, small organic molecules, and a lower conductivity of the PLD ZnO. Nevertheless, the maximum power conversion efficiency amounts to 0.21 %, only.

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.

Zinc oxide (ZnO) is perhaps one of the most widely studied material in the last two decades. It has received so much of attention because of its incredible potential for wide ranging applications. ZnO is a wide band gap semiconductor (Eg = 3.37 eV at 300 K) with a rather large excitonic binding energy (~60 meV). This combination of properties makes it an ideal choice for several optoelectronic devices that can easily work at room temperature. ZnO is a truly multifunctional material possessing several desirable electrical, optical, optoelectronic, and piezoelectric properties. In addition, it is highly amenable to production of various kinds of nanostructures such as nanorods, nanotubes, nanoribbons, nanoneedles, etc., which makes it even more desirable for nanoscale devices. Examples of ZnO based nanodevices could include photodiodes, photodetectors, nano-lasers, field-emission devices and memristors. In order to make such devices, one could need device quality nanostructures that must be reproducible and cost effective. Naturally, one has to look for a synthesis process that has great controls and is relatively inexpensive. The study provided here shows that among the various methods available for ZnO synthesis, the microwave-assisted chemical synthesis offers outstanding advantages in terms of rapid growth of nanostructures, economical use of energy and excellent controls of process parameters. In order to produce device quality ZnO nanostructures using microwave-assisted synthesis, one has to study the effect of various process parameters and optimise them for the desired growth. Therefore, in the current study, first, a systematic study was undertaken to synthesize ZnO nanostructures both in a aqueous and non-aqueous medium and their characterization was carried out in order to understand the effect of microwave power, time of irradiation, pressure, solvent and salt concentration, etc. The goal was to develop synthesis protocols for various kinds of nanostructures that could guarantee reproducibility, good yield, and device quality structures. This study has led to successful growth of ZnO nanostructures on various substrates, vertically aligned ZnO nanorods and templated arrays of desired structures, all with outstanding properties of the structures as confirmed by XRD, MicroRaman, photoluminescence, cathodoluminescence, FESEM, TEM, PFM studies and pole figure analysis. Piezoelectric force microscopy (PFM) and physical property measurement system (PPMS, Quantum Design), have been used to study the multifunctional properties of ZnO nanostructures. The PFM is a powerful technique to measure the local piezoelectric coefficient of nanostructures and nanoscale thin films. PFM works on the converse piezoelectric effect in which electric potential is applied and mechanical strain is measured using a cantilever deflection. The PFM (Brucker’s AFM dimension Scan Assist) was used to characterize individual ZnO nanorods. Extensive studies were carried out with PFM measurements and it was observed that the nanorods consistently showed high piezoelectric coupling coefficients (d33~50-154 pm/V). It was also found that the variation in d33 depended on morphology and size of nanostructure. The multifunctional properties were observed in small ZnO nanocrystals (NCs). Such high values of piezoelectric coupling coefficients open the door for novel ZnO based nanoscale sensors and actuators. The synthesized ZnO nanostructures were further optimized and characterized keeping in view three device applications namely Field emission, Memristors and Gas Sensors. The fabrication and characterization of these three devices with ZnO nanostructure was carried out using electron beam lithography and direct laser writing micromachining. Device fabrication using lithography involved several steps such as substrate cleaning, photoresist spin coating, pre-baking, post-baking, pattern writing, developing, sputtering/deposition of material for lift-off, ZnO growth, and overlay lithography. For field emission devices, high quality, well aligned, c-axis oriented ZnO nano-needles were grown on sputter coated Ti/Pt (20nm/100nm) on SiO2/Si substrate by rapid microwave-assisted method in aqueous medium. The diameter of the tip was found to be 1~2 nm and the length of the rod was approximately 3~5μm. For a particular batch the tip size, morphology, and lengths were found to be the same and highly repeatable. Pole figure analysis revealed that nanorods were highly oriented towards <002> direction. Field-emission measurements using the ZnO nanoneedles arrays as cathode showed very low turn-on electric field of 0.9 V/μm and a very high field enhancement factor ~ 20200. Such a high emission current density, low turn-on electric field, and high field enhancement factor are attributed to the high aspect ratio, narrow tip size, high quality and single crystallinity of the nanoneedles. The high emission current density, high stability, low threshold electric field (0.95 V/μm) and low turn-on field make the ZnO nanoneedle arrays one of the ideal candidates for field-emission displays and field emission sensors. In the suitability of ZnO nanostructures for memristor application it was found that the single crystalline ZnO nanorods were not suitable as they did not show memristive behaviour but the ZnO nanorods with native defects exhibited considerable memristive behaviour. Therefore the microwave-assisted grown ZnO nanorods with defects were used to fabricate memristive devices. Single and multiple ZnO nanorods based memristors were fabricated using electron beam lithography. These devices were characterized electrically by measuring the hysteresis in the I/V characteristics. A high degree of repeatability has been established in terms of growth, device fabrication, and measurements. The switching in single nanorod based devices was found to have “ON-to- OFF” resistance ratio of approximately 104 and current switching ratio (ION/IOFF) of 106. Gas sensing based on electrical resistance change depends on absorption and desorption rate of gases on the analyte which is governed by surface properties, morphologies and activation energy. Therefore, various morphologies of nanostructure were grown for gas sensing application. Through experimentation, the emphasis shifted to c-axis oriented ZnO nanostructures on SiO2 substrate for gas sensing. The c-axis orientation of ZnO nanostructures was preferred mainly due to its huge surface area. The measurements showed that the c-axis oriented ZnO nanorods were excellent hydrogen sensors, able to detect H2 as low concentration as 2 ppm, even when the sensing temperature is as low as 200 ˚C. However, oxygen sensing was achieved at a higher temperature (300 ˚C). Thus, the study undertaken in this thesis presents a microwave based rapid and economical method for synthesizing high quality, device grade ZnO nanostructures, their extensive characterization that shows the multifunctional properties of these structures, and there examples of varied device applications of the synthesized nanostructures as field emitters, memristors, and gas sensors.

In recent years, there has been growing interests on II-VI semiconductor nanostructures, which are suitable for applications in electronics and optoelectronic devices such as solar cells, UV lasers, sensors, light emitting diodes and field emission displays. II-VI semiconductor nanostructures with different morphologies such as wires, belts, rods, tubes, needles, springs, tetrapods, plates, hierarchical structures and so on, have been widely grown by vapor transport methods. However the process conditions used for the growth of nanostructures still remains incompatible for device fabrication. The realization of practical nanoscale devices using nanostructured film depends mainly on the availability of low cost and lower processing temperatures to manufacture high purity nanostructures on a variety of substrates including glass and polymer. In this thesis work, studies have been made on the growth and characterization of II-VI semiconductor nanostructures prepared at room temperature, under high vacuum, without employing catalysts or templates. (i) ZnO nanostructured films with different morphology such as flowers, needles and shrubs were deposited at room temperature on glass and polymer substrates by plasma assisted reactive process. (ii) Zn/ZnO core/shell nanowires were grown on Si substrates under optimized oxygen partial pressure. Annealing of this core shell nanowire in high vacuum resulted in the formation of ZnO nanocanals. (iii) ZnS and ZnSe nano and microstructures were grown on Si substrates under high vacuum by thermal evaporation. The morphology, structural, optical properties and composition of these nano and microstructures were investigated by XRD, SEM, TEM, Raman, PL and XPS. The growth mechanism behind the formation of the different nanostructures has been explained on the basis of vapour-solid (VS) mechanism.