ABSTRACT The confinement of excited charges in carbon nanotubes has significant effect on their optical and electronic properties. The absorption of light generates strongly correlated electron-hole pairs (excitons) in carbon nanotubes. We present a study of the decay of these photogenerated excitons in solutions of semiconducting SWNTs using the degenerate pump probe technique. Under specific experimental conditions, the exciton-exciton reactions on carbon nanotubes were found to correspond to an ideal ID coalescence-diffusion system with distinct regions of reaction-limited and diffusion-limited behaviours. We provided the first experimental evidence for such a system of 'universal behaviour' at longer times which exhibits a power law decay whose exponent and amplitude are independent of the initial population - one of the key characteristics of this reaction-diffusion system. We also show for the first time that exciton-exciton interactions are long-range, and further that the transition between reaction-limited and diffusion-limited regimes is much more abrupt than is predicted by existing theories. A modified theory incorporating a finite reaction length provided an excellent fit to the experimental data for a reaction length of -7 nm. We determined the reaction rate constant of k; = (3.76 ± 0.04) nmfps and the diffusion coefficient of D = (8.1 ± 0.4) nm2/ps from fitting of the asymptotic regimes with rate equations. We also provided the first experimental evidence of sub-diffusive transport of excitons in quasi ID SWNTs through studies of exciton annihilation dynamics in HiPco and CoMoCat SWNTs, where we observed that excitons in HiPco SWNTS exhibit normal diffusive transport where decay follows a Clal power law with decay exponent (a :::::: 0.5), whereas excitons in CoMoCat SWNTs decay more slowly with decay exponent (a :::::: 0.3) as result of sub-diffusive transport. We correlate this slow decay to a higher defect concentration in CoMoCat SWNTs as compared to HiPco measured using Raman spectroscopy and X-ray photoelectron spectroscopy. The experimental results were also compared to results from a Monte Carlo simulation of ID diffusion in a fluctuating potential landscape which shows good agreement with experiment and underlines the necessity to consider spatial aspects (separation of defects and interaction range) in theoretical approaches to the dynamics. The study of excitonic decay in single walled carbon nanotubes is very important in terms of understanding of fundamental photophysics of ID system and their possible application in electronics and photonic devices especially in light emitting devices and non-linear optics. 2

The transmission and effective magnetic properties of a metamaterial consisting of silver nanowires that we call a "silver nanoforest" was investigated using finite element numerical simulations in the optical regime. The variation of these properties with the arrangement and size of the nanowires was also investigated along with resilience to fabrication disorder. The silver nanoforest metamaterial exhibited low loss diamagnetism associated with Fabry Perot interference. In addition to diamagnetism both negative pelmeability and negative refractive index were obtained, but not simultaneously at same' wavelength and geometry. Both negative permeability and negative index experienced significant loss and therefore low transmission due to the plasmonic Origins of these effects. Magnetic responses of the silver nanoforest metamaterial were dampened but not inhibited by disorder, with diamagnetic response being the most resilient magnetic response to disorder.

This thesis is centred on the synthesis and nitrogen functionalisation of two carbon nanostructures, the Carbon Nanotubes (CNTs) and the Diamond Nanoflake Spherules (DNFS). Vertically aligned Multiwalled CNTs (MWCNTs) and DNFS have been successfully synthesised in a Microwave Plasma Enhanced Chemical Vapour Deposition (MPECVD) system. Different plasma sources including Electron Cyclotron Resonance (ECR), Capacitively Coupled Radio Frequency (CCRF) system and a low energy ion source VG AG21 (5 kV) were employed to induce electronic and structural modification to these nanostructures through functionalisation and implantation.

The continuing development of advanced magnetic nanomaterials for electronic devices and medical applications necessitates an understanding of the origins of magnetism at the atomistic level. In this thesis current state of the art modelling methods are developed and applied to a variety of physical problems in order to better understand the origins and limitations of magnetic materials at the nanoscale.

Plasmonic nanostructures are an important class of nanophotonic components capable of localising light near a metal interface on subwavelength scales. Surface plasmon polaritons (SPPs) are confmed to the metal interface and can only be studied in the past in the far-field by indirect investigation of the light resulting from their scattering. They can be studied directly using optical near-field microscopy which is capable of detecting the optical field in proximity to the surface, with sub-wavelength spatial resolution. We have developed a new tool for the investigation of surface plasmonic polaritons in a broad spectral range, the hyperspectral scanning near- field optical microscope, capable of simultaneously recording multiple near-field images in the 500-800nm spectral wavelength range. Using this microscope, the Bloch mode formation in plasmonic crystals, periodically structured metal films, have been studied along with the SPP excitation by the crystals. The role of the film thickness and crystal lattice has been studied in both the far-field and near-field. Novel plasmonic crystals with exotic lattices have been designed which provides additional advantages over the standard square lattice crystals in terms of band structure engineering and designing flat SPP bands, advantageous for applications in light extraction and unidirectional transmission. SNOM has then been used to demonstrate the new plasmonic platform based on VCSEL light source, showing direct SPP excitation on the laser surface and their efficient guiding. Multimode and single mode waveguides, Y -splitters and Mach-Zehnder interferometer configurations wen: realised. Plasmonic waveguide-ring resonators were studied incorporating non linear optical materials and optical switching has been demonstrated. The developed hyperspectral SNOM is a powerful technique for understanding the optical properties of plasmonic nanostructures and evaluating their nanophotonic capabilities. The studied plasmonic components, such as plasmonic crystals, integrated plasmonic waveguides and ring- resonator exhibit unique optical properties that pave the way for applications in photonic device optimisation and developing new concepts of signal guiding and manipulation.

An investigation into domain states' that form spontaneously innanoscale single-crystal structures of BaTi03 and PbZr(042)Ti(o58P3 on cooling through the Curie temperature has been conducted. Through the use of Piezoresponse Force Microscopy (PFM) and Transmission Electron Microscopy (TEM) a hierarchy of structure existing over distinct length scales has been observed revealing large-scale 'superdomains' which are composed of finer-scale 90° stripe 'subdomains'. "The nature of the formation of these superdomains is investigated by considering a higher-level polar ordering to perform roles usually associated with subdomains. In BaTi03 " these superdomains can be considered to possess a resultant polarisation orientated along (110)pseudocubic directions; using PFM to map the resultant polarisations demonstrated that 60°, 90° and 180° superdomain structures can form. Characteristics of thesuperdomains appear to have more in common with an orthorhombic symmetry than with the fine-scale parent tetragonal state. This is rationalised from the orientation of the resultant polarisation and the observed superdomain variants which are generally only seen for orthorhombic systems. Detailed arialysis of the superdomain boundaries reveals that they typically occupy crystallographically defined directions. Complex topologies of domain walls are also seen at superdomain boundaries occasionally including interlinking chains of flux-closure and quadrupole states. For the 180° superdomains composed of a-a subdomains observed in BaTi03 single- crystal free-standing dots, produced by Focused Ion Beam (FIB) milling, their formation is thought to be a response to depolarising fields that should be present in the plane of the structure. This is determined from superdomain scaling adherence to a Landau-Kittel-type relation. A free energy analysis is used to estimate the 180° domain wall energy density to be 20 ± 2 mlm" and to explain the features of the Landau-Kittel-type scaling. Nanoscale structures of wires and dots were produced by means of FIB milling of single-crystal lamellar sheets of PbZr(042)Ti(o58P3' Subsequent investigation through use of TEM revealed complex domain structures that displayed superdomain features. For PbZr(042)Ti(o.58P3 single-crystal nanodots, in the majority of cases, 90° stripe domains were found to form into four distinct 'bundles' or quadrants. Detailed analysis of the dipole orientations in the system was undertaken and led to the conclusion that resultant polarisations, associated with the four quadrant domain bundles, form into a closed loop. This 'polarisation closure' pattern appears to be a highly stable, equilibrium state.

Silver nanowires with diameters of a few tens of nanometers have gained a lot interest recently. An array of such nanowires within a dielectric host matrix are considered as an indefinite anisotropic metamaterial. These metamaterials exhibit negative refraction due to hyperbolic dispersion characteristics for extraordinary waves. The overall purpose of this research is to study the optical characteristics of such an indefinite system. First, an analytical formula was developed which describes the image formation due to a plane parallel slab of such a metamaterial for light emanating from a point source. The results of this analytic flat lens equation were compared with two- dimensional (2D) full wave simulations. One of the objectives of this work was to fabricate such delicate nanostructures. This was achieved by nano-porous alumina templates obtained following the novel two step anodization procedure. Afterwards an electrochemical plating technique was applied to deposit silver into the nano-channels forming a silver nanowire array. The inter-wire distance was only 60 nm so the metamaterial is considered as an effective medium for visible and infrared (IR) light. The optical characteristics of such a system were studied using angular resolved transmission measurements. In particular, a thorough analysis of the transmitted light was applied to determine the principal effective dielectric constants in the visible and IR range. In addition the equifrequency surfaces of the ordinary and extraordinary waves were mapped experimentally in a wave vector diagram for the first time. A comparison of the experimental results with Maxwell-Garnett effective medium theory showed a very good agreement and confirmed the original prediction that the silver nanowire arrays can be described as uniaxial indefinite metamaterials within visible and IR region.

A linear aerosol time-of-flight mass spectrometer has been built to analyse carbon nanotubes. An aerodynamic lens system allows an aerosol-particle beam of controlled dimension and divergence to be formed.

Thiol-passivated gold nanoparticies deposited onto a silicon substrate from an organic solvent form a remarkable variety of self-organised nanostructured and microstructured patterns. The work in this thesis focuses on three key aspects of these systems: (i) their environmental stability, (ii) the formation of nanoparticie rings via condensation of water droplets, and (iii) the morphology of nanoparticie mono layers formed at the water-air interface and transferred to silicon substrates using the Langmuir-Blodgett technique. The nanoparticie structures were studied by combined atomic force microscopy (A FM) and contrast-enhanced optical microscopy. Striking changes in the morphology of self-organised nanoparticie patterns are observed during exposure to high humidity or high temperature environment. Annealing the sample at 1200 C leads to a high degree of nanoparticie sintering promoted by break-up of the initial assembly. Conversely, exposing the sample to a high relative humidity (80%) environment induces layer-by-layer assembly of 3D aggregates with no evidence of sintering. We focus also on the formation of rings of thiol-passivated Au nanoparticies, addressing the controversy in the literature regarding the formation of these structures. We provide compelling evidence that nanoparticie rings formed via the adsorption of droplets of condensed water. This so-called "breath figure" effect plays the dominant role in the dynamics of ring formation via iii evaporative dewetting. Different sizes and size distributions of nanoparticle rings have been created under controlled relative humidity environments ranging from ~50% to 80%. Fmthermore, the dynamic behaviour of water droplets on surface has been examined using a contrast-enhanced optical mIcroscope. Analysis of the observed droplet dynamics shows significant differences between the behaviour of droplets formed on top of a silicon substrate and the nanoparticle films. Finally, the formation of gold nanoparticle assemblies at the water-air interface using the Langmuir-Blodgett deposition technique has also been studied. The LB films were transferred to a solid substrate (silicon) and the nanoparticle assemblies fOlmed close to the contact line imaged by AFM and contrastenhanced optical microscopy. The experimental control parameters resulted in the emergence of variety of nanoparticie morphologies. We propose formation mechanisms for a number of these morphologies.

Manipulation of matter with atomic- or molecular-scale precision plays a central role in the field of nanotechnology. Given the continuous trend to miniaturization undergone by electronic devices in the last few decades, it provides the key to the bottom-up approach, a new concept of building devices for the technological applications of the future. Among the family of the scanning-probe techniques, scanning tunnelling microscope (STM) and atomic force microscope (AFM) have been widely used to image and manipulate individual atoms and molecules. For the research purposes of this thesis, STM is applied solely for imaging. Instead, the AFM technique, operated using the qPlus sensor, is mainly exploited in the framework of manipulation. The object of investigation is the Si(lOO)-2xl reconstructed surface. Although many of the properties of this type of silicon surface are well known, there exist both fundamental questions and potential applications that justify the interest around this material and the need for further research. Silicon surface is also considered an ideal substrate for molecular deposition and positioning, therefore it is used as the substrate on which to perform manipulation of C60 molecules. By using the qPlus AFM technique at cryogenic temperatures, protocols for reproducible controlled manipulation of individual silicon atoms and C60 molecules are described. Experimental results, carried out at zero applied bias, show the possibility to reversibly switch the orientation of silicon dimers through a purely mechanical mechanism based on the formation of a single covalent bond. Data also demonstrate the dependence of a flip event on both the local and non-local surface structure and that only correlated flipping takes place, since three consecutive dimers with the same buckled orientation are never observed after a single manipulation event. Regarding the imaging of C60 molecules, the variety of STM patterns highlights the fundamental role of a controlled functionalized tip in order to correctly interpret the molecular orientation, whereas constant-height AFM mode provides more detailed intramolecular features in comparison with the constant frequency-shift mode. AFM manipulation of C60 by means of a novel software tool appears viable, although a refinement of the technique would be beneficial in terms of reliable quantitative measurements. Furthermore, a novel technique for simultaneous STM (operated in the dynamic mode) and NC-AFM analysis is introduced, which appears valuable at separating geometric and electronic effects in scanning probe images.