In the year 2000 John Pendry described a new kind of lens that could focus both the propagating and evanescent components of light. This ‘super’ lens, which took the form of a thin slab of silver with a negative effective index of refraction under certain conditions, had the ability to reproduce images much smaller than the wavelength of light, seemingly in violation of the diffraction limit that governed the performance of conventional optics. Despite significant controversy regarding the purported operation of such superlenses, the first experimental samples were fabricated in 2005, with features as small as 63 nm successfully imaged with 365 nm light. These results put to rest disbelief in the feasibility of superlenses and ushered in an era of intense interest in near-field phenomena and negative index materials (NIMs). Despite sustained effort, progress on the practical implementation of superlenses was slow, with a further five years passing before improved experimental results were published. In the meantime, a proliferation of analytical and modelling studies appeared on the behaviour and properties of superlenses, as well as numerous suggestions for improved physical designs, very few of which had accompanying experimental evidence. The primary aim of this thesis arose from these many proposals, namely, to reconcile predictions made about the behaviour of superlenses with observed experimental results. The measurement of the theoretical and practical behaviour of superlenses is addressed in this thesis by the development of a set of characterisation metrics that can be used to describe the imaging performance of a number of near-field imaging systems. These metrics are initially calculated via transfer matrix modelling (TMM), which is a one-dimensional analytical technique traditionally used to find the transmission and reflection coefficients of planar structures. Two families of metrics are derived; one that describes imaging systems in terms of their abilities in generic situations and the other that gives the suitability of an imaging system for application to a given class of object. Transfer functions, bandwidth and peak wavenumber measurements form this first group of characterisation functions, while contrast, pseudo-contrast and correlation coefficients are used to assess the quality of imaging systems when exposed to well-defined input profiles. Both sets of metrics show that the performance of superlenses is highly application-specific, with the fidelity or otherwise of a generated image dependent more on the construction of the superlens than on the maximum spatial frequencies present in the object. The results from the characterisation metrics are also used to guide the design of hypothetical superlens structures; these suggest that sub-diffraction limited resolution may still be available with almost a full wavelength separation between object and image. The quantitative accuracy of the TMM method is assessed by comparison to full-field vector simulations performed via finite element modelling (FEM), these reveal systematic inadequacies in the application of the TMM technique to superlensing applications. These inadequacies stem from near-field mask-lens interactions that are present in superlens experiments but are not accounted for in TMM calculations. A new technique, based on a modified transfer matrix model (M-TMM), is proposed that accounts for the effects between masks and superlenses by approximating masks as solid slabs of known thickness. Results generated via M-TMM are shown to be in better agreement with FEM models than similar TMM data, even when the duty cycle of the actual mask becomes significant and the approximation in M-TMM is at its most coarse. Finally, experiments are designed and executed that directly measure the transfer functions of superlenses and other near-field imaging techniques. The problem of intimate contact between optics components, which normally hinders any such attempts to perform lithography in the near-field, is mitigated by including a flexible layer of poly (dimethylsiloxane) (PDMS) between various components in the mask:lens:resist stack. Furthermore, high spatial frequency data corresponding to low nanometre-scale features are retrieved from masks with periodic, micron-scale patterns, greatly easing the requirements on mask construction for these experiments. The end results show good agreement with FEM and M-TMM data and satisfy the aim of this thesis, which was to bridge the divide between the performance expected and experienced from silver superlenses.

The aim of this project was to improve the imaging performance of planar superlenses for evanescent near-field lithography. An experimental investigation of the performance of superlenses with reduced surface roughness was proposed. Such an investigation poses significant requirements in regards to process control in thin film deposition of silver onto dielectric substrates. Thin film deposition of silver films, onto silicon dioxide substrates, achieved films with root mean square surface roughness as low as 0.8 nm. While these experiments provided good understanding of the deposition process, significant variability of the surface roughness parameter remained an issue. The diffculty of achieving consistent control of surface roughness led to a finite element method simulation study where this parameter could be readily controlled. An improved understanding of how surface roughness affects superlens imaging performance was obtained from the results of this investigation. Furthermore, it was shown that in order to conduct an experimental investigation to verify the simulation results, it would be necessary to improve the imaging capability of super-resolution lithography protocols to achieve 3σ line edge roughness (LER) of <20 nm. Resist-scheme optimisation was identied as an important factor in this regard. Thus, a novel calixarene-based photoresist was formulated and characterised. The resist demonstrated superior imaging capabilities through interference lithography and evanescent near-field optical lithography, capable of resolving 250-nm period half-pitch line gratings with 3σ LER below 10 nm. The development of this novel photoresist will enable future lithographical investigations to be conducted with improved resolution and imaging fidelity.

Abstract Negative index structures could be implemented through surface Plasmon polariton waves generated by nanostructures. We are interested in PMMA grating structure on curved metal surface. In order to fabricate this kind of samples, a series process parameters have been tested and also the lift-off process has been developed. Our results show superlens effect under optical microscope(OM). The sub-wavelength grating image is reconstructed in the non-grating region where the PMMA dielectric layer is not uniform. Surface Plasmon(SPP) waves generated in the grating region propagate to the non-grating region and are scattered out through the non-uniform PMMA layer. The grating information is not resolvable under OM but clear in the reconstructed region. It shows that SPP waves can show super resolution and a simple batch process should be developed in the future.

Semiconductors represent the enabling technology that underpins the many advances that define modern society. One semiconductor that shows considerable promise in the fabrication of new devices is zinc oxide (ZnO). A fundamental understanding of the properties of a material is required in order to exploit its properties. The behaviour of dopants and defects relevant to optoelectronic device fabrication is of particular interest. However, acceptor doping of ZnO is currently controversial, as successful and reproducible acceptor doping has not yet been achieved. Acceptor doping of ZnO using silver (Ag) is explored in this thesis to contribute towards the understanding of defect introduction in ZnO. In addition, there is also increasing interest in exploring materials with unconventional properties, commonly referred to as metamaterials, particularly for optical applications. The previously unexplored unique combination of Ag and ZnO may enable the fabrication of those devices. Several key factors that affect heteroepitaxy film quality, and ultimately its properties, are buffer layers and substrate temperature. A lattice match between sapphire and ZnO was provided by using buffer layers of 1 nm magnesium oxide (MgO) and 7.9 nm low temperature ZnO. The highest quality film was grown at the highest temperature (800°C), with rms roughness of 2.9 nm, carrier concentration of 3.6x10¹⁶ cm⁻³, and mobility of 105 cm²/Vs. In contrast, dopant (Ag) incorporation occurs more readily below 600°C, with dopant incorporation of up to 1020 cm⁻³ measured. Ag manifests as a deep acceptor (up to 94% substitutionally on Zn lattice sites), as evident from decreasing carrier concentration with increasing Ag flux, and DLTS measurements indicating an acceptor trap at 319 meV. This suggests that Ag is suitable for introducing compensation in ZnO, but Ag acceptors are not sufficiently shallow to result in p-type material. However, the unique combination of ZnO and Ag also enables the fabrication of a novel device, namely a superlens. Initial experimental results show the possibility of imaging a 100 nm line as 132 nm, compared with the diffraction-limited resolution of 332 nm for the same line feature.

This work presents the first demonstration of a semiconductor based plasmonic near-field superlens, utilizing highly doped GaAs to generate infrared optical images with a spatial resolution beyond the difraction limit. Being easily transferable to other semiconductor materials, the concept described in this thesis can be exploited to realize spectrally adjustable superlenses in a wide spectral range. The idea of superlensing has been introduced theoretically in 2000, followed by numerous publications including experimental studies. The effect initiated great interest in optics, since in contrast to difraction limited conventional optical microscopy it enables subwavelength resolved imaging by reconstructing the evanescent waves emerging from an object. With techniques like scanning near-field optical microscopy (SNOM) and stimulated emission depletion (STED) being already successfully established to overcome the conventional restrictions, the concept of superlensing provides a novel, different route towards high resolution. Superlensing is a resonant phenomenon, relying either on the excitation of surface plasmons in metallic systems or on phonon resonances in dielectric structures. In this respect a superlens based on doped semiconductor benefits from the potential to be controlled in its operational wavelength by shifting the plasma frequency through adjustment of the free carrier concentration. For a proof of principle demonstration, we investigate a superlens consisting of a highly n-doped GaAs layer (n = 4 x 10^18 cm-3) sandwiched between two intrinsic layers. Recording near-field images of subwavelength sized gold stripes through the trilayer structure by means of SNOM in combination with a free-electron laser, we observe both enhanced signal and improved spatial resolution at radiation wavelengths close to l = 22 µm, which is in excellent agreement with simulations based on the Drude-Lorentz model of free electrons. Here, comparative investigations of a purely intrinsic reference sample confirm that the effect is mediated by the charge carriers within the doped layer. Furthermore, slightly differently doped samples provide indications for the expected spectral shift of the resonance. According to our calculations, the wavelength range to be exploited by n-GaAs based superlenses reaches far into the terahertz region, whereas other semiconductor materials are required to explore the near infrared.

The challenge for lithography today is to continue the reduction of feature size whilst facing severe theoretical and practical limitations. In 2006 Rajesh Menon and Hank Smith proposed a new lithography system named absorbance modulation optical lithography (AMOL) [Menon 2006]. AMOL proposed replacing the normal metal mask of a lithography system with an absorbance modulation layer (AML), made from a photochromic material. This allows, through the competition between two incident wavelengths, the creation of an adaptive absorbance mask. The AML allows intimate contact to an underlying resist and hence the optical near-field may be used to create sub-diffraction limited exposures. The aim of this thesis is to model AMOL and demonstrate the abilities and the limits of the system, particularly focusing on sub-diffraction limited imaging. This thesis describes the construction of a vector electromagnetic simulation to explore the idea and performance of AMOL, and an exploration of the ability of AMOL to propagate sub-diffraction limited images into a photoresist. A finite element method (FEM) model was constructed to simulate the formation of apertures in the AML and light transmission through the system. Three major areas of interest were explored in this thesis; the effect of polarisation on imaging, using a plasmonic reflector layers (PRLs) to improve the depth of focus (DOF), and introducing a superlens to AMOL. Investigations of polarisation demonstrated strong preference for a transverse magnetic (TM) polarised exposing wavelength for near-field exposures. Associated with polarisation, and supporting work with absorbance gratings, the importance of the material parameters of the AML in allowing sub-diffraction limited exposures was discussed. It was also noted that, in common with all near-field systems, the depth of focus (DOF) was poor, worse than comparable metal systems. This thesis also demonstrates that the introduction of a PRL can improve the DOF and process latitude for resist thicknesses up to 60 nm and, although performance was reduced when using a silver PRL, the substantial improvements to the DOF and process latitude make a PRL valuable for an AMOL system. This thesis also models the superlens to an AMOL system, which theoretically allows propagation of the image in the near-field. It is demonstrated that the superlens can project an AMOL image into an underlying resist, but that this image is degraded, especially for thick and non-ideal superlenses. The superlens does have a second useful effect, as it can act as a dichroic filter; decreasing the intensity ratio in the resist by a factor of ten, overcoming issues of resist sensitivity. The superlens can allow image projection and filtering with AMOL, however improvements to the available superlens materials or changes to the AML will be needed to avoid image deterioration. This thesis has developed the first full-vector model of an absorbance modulation optical lithography (AMOL) system. This model has been used to increase the understanding of the complex effects that go into the creation of sub-diffraction limited features with AMOL. In particular the model has been used to investigate polarisation, PRLs and superlenses in AMOL. This thesis demonstrates the ability of AMOL to create narrow apertures and sub-diffraction limited exposures in a photoresist, and describes the limitations of AMOL, including material parameters and DOF. AMOL is a new and interesting lithography technique; this thesis simulates the abilities and challenges of sub-diffraction lithography using an AMOL system.

Les métamatériaux sont des milieux prometteurs pour l'imagerie acoustique. Grâce à ces milieux, il est possible de concevoir des lentilles à faces parallèles pouvant dépasser la limite conventionnelle de résolution d'une lentille et par conséquent améliorer les systèmes d'imagerie. Malgré l'intérêt grandissant des chercheurs pour les métamatériaux, le comportement des ondes acoustiques dans ces milieux n'est pas totalement connu. Nous proposons de développer la problématique de la propagation des ondes acoustiques dans un milieu de type métamatériau en détail dans ce manuscrit. Cette étude a permis d'extraire un critère discriminant un métamatériau d'un matériau classique et d'apporter un regard nouveau sur l'amplification des ondes évanescentes dans les métamatériaux.Nous explorons une piste peu empruntée en vue du dimensionnement de métamatériaux : les milieux aléatoires. Nous nous focalisons sur les milieux à deux dimensions dont les phases sont fluides. Dans cette optique, une phase de validation de techniques d'homogénéisation dynamique existantes est réalisée \textit{via} la comparaison des réponses acoustiques d'un écran de diffuseurs répartis aléatoirement obtenues par des simulations numériques FDTD avec celles prédites par des modèles analytiques. L'étude de ces modèles, utiles au dimensionnement de structures aléatoires présentant des réponses acoustiques ciblées, nous a amené à examiner avec attention leur comportement quasi-statique. Une technique d'homogénéisation permettant de prendre en compte explicitement les interactions entre diffuseurs est proposée dans ce contexte. Développée dans le cadre de la diffusion simple et multiple, elle relie les propriétés mécaniques effectives aux moyennes des champs acoustiques dans un volume représentatif.Finalement, l'analyse du comportement d'un milieu aléatoire \og réaliste \fg~possédant théoriquement des bandes fréquentielles à réfraction négative, grâce à des diffuseurs résonants à basses fréquences, a été menée. Différents régimes de fonctionnement atypiques sont identifiés à l'aide de simulations numériques. La confrontation des réponses de ce milieu avec celles d'un cristal phononique est ensuite présentée et révèle une étonnante similitude entre les deux arrangements. / Metamaterials are promising media for acoustic imaging. For example, such media give the possibility to build flat lenses exhibiting sub-diffraction-limit resolution, thereby improving imaging setup. Despite the growing interest of the researcher for metamaterials, acoustic wave propagation is still not widely known. This work addresses the topic of wave propagation in metamaterials. In this work, we have defined a criterion which differentiate metamaterial from classical material and provide a new insight in the amplification of evanescent waves.We explore how to design metamaterials with random media. We focus on two dimensional media with fluid components. A validation process of existing dynamic homogenization techniques is done via the comparison between the responses of a screen of scatterers obtained by numerical simulations from FDTD with those predict by the analytical models. The study of those models, useful for designing random media with atypical responses, lead us to consider their quasi-static limit. In this context, we propose a homogenization technique which includes explicitly the interactions between scatterers. It is developed for multiple and simple scattering and link the effective properties to the averages of the acoustic fields in a representative volume.Finally, the analysis of the acoustic responses of a realistic random medium having theoretical negative refraction frequency bandwidth, thanks to low frequency resonant scatterers is done. Different atypical responses are identified from the numerical simulations. The comparison between the responses of this medium and those of phononic crystals is presented and shows a surprising similarity of the two arrangements.

This work presents the first demonstration of a semiconductor based plasmonic near-field superlens, utilizing highly doped GaAs to generate infrared optical images with a spatial resolution beyond the difraction limit. Being easily transferable to other semiconductor materials, the concept described in this thesis can be exploited to realize spectrally adjustable superlenses in a wide spectral range. The idea of superlensing has been introduced theoretically in 2000, followed by numerous publications including experimental studies. The effect initiated great interest in optics, since in contrast to difraction limited conventional optical microscopy it enables subwavelength resolved imaging by reconstructing the evanescent waves emerging from an object. With techniques like scanning near-field optical microscopy (SNOM) and stimulated emission depletion (STED) being already successfully established to overcome the conventional restrictions, the concept of superlensing provides a novel, different route towards high resolution. Superlensing is a resonant phenomenon, relying either on the excitation of surface plasmons in metallic systems or on phonon resonances in dielectric structures. In this respect a superlens based on doped semiconductor benefits from the potential to be controlled in its operational wavelength by shifting the plasma frequency through adjustment of the free carrier concentration. For a proof of principle demonstration, we investigate a superlens consisting of a highly n-doped GaAs layer (n = 4 x 10^18 cm-3) sandwiched between two intrinsic layers. Recording near-field images of subwavelength sized gold stripes through the trilayer structure by means of SNOM in combination with a free-electron laser, we observe both enhanced signal and improved spatial resolution at radiation wavelengths close to l = 22 µm, which is in excellent agreement with simulations based on the Drude-Lorentz model of free electrons. Here, comparative investigations of a purely intrinsic reference sample confirm that the effect is mediated by the charge carriers within the doped layer. Furthermore, slightly differently doped samples provide indications for the expected spectral shift of the resonance. According to our calculations, the wavelength range to be exploited by n-GaAs based superlenses reaches far into the terahertz region, whereas other semiconductor materials are required to explore the near infrared.

Composite metamaterials are periodic metal-dielectric structures operating at wavelengths larger than the structure period. If properly designed these structures behave as homogeneous media described by effective permittivity and permeability parameters. These effective parameters can be designed to take values in domains that are not available in naturally occurring media; notably it is possible to design composite metamaterials with simultaneously negative permittivity and permeability, or, in other words, with a negative refractive index. However, in many experimental or numerical studies it is far from obvious that the use of a homogeneous model is justified for a given structure at a given wavelength. This issue is often glossed over in the literature. <br />In this work I take a detailed look at the fundamental assumptions on which effective medium models rely and put forward a method for determining frequency domains where a given structure may or may not be accurately described by homogeneous effective medium parameters. This work opens the door to a more detailed understanding of the transition between homogeneous and inhomogeneous behavior in composite metamaterials, in particular by introducing the novel notions of custom made effective medium model, and of meta-photonic crystal.

In 2000, a controversial paper by John Pendry surmised that a slab of negative index material could act as a perfect lens, projecting images with resolution detail beyond the limits of conventional lensing systems. A thin silver slab was his realistic suggestion for a practical near-field superlens - a 'poor-mans perfect lens'. The superlens relied on plasmonic resonances rather than negative refraction to provide imaging. This silver superlens concept was experimentally verified by the author using a novel near-field lithographic technique called Planar Lensing Lithography (PLL), an extension of a previously developed Evanescent Near-Field Optical Lithography (ENFOL) technique. This thesis covers the computational and experimental efforts to test the performance of a silver superlens using PLL, and to compare it with the results produced by ENFOL. The PLL process was developed by creating metal patterned conformable photomasks on glass coverslips and adapting them for use with an available optical exposure system. After sub-diffraction-limited ENFOL results were achieved with this system additional spacer and silver layers were deposited onto the masks to produce a near-field test platform for the silver superlens. Imaging through a silver superlens was achieved in a near-field lithography environment for sub-micron, sub-wavelength, and sub-diffraction-limited features. The performance of PLL masks with 120-, 85-, 60-, and 50-nm thick silver layers was investigated. Features on periods down to 145-nm have been imaged through a 50-nm thick silver layer into a thin photoresist using a broadband mercury arc lamp. The quality of the imaging has been improved by using 365 nm narrowband exposures, however, resolution enhancement was not achieved. Multiple layer silver superlensing has also been experimentally investigated for the first time; it was proposed that a multi-layered superlens could achieve better resolution than a single layer lens for the same total silver thickness. Using a PLL mask with two 30-nm thick silver layers gave 170-nm pitch sub-diffraction-limited resolution, while for a single layer mask with the same total thickness (60 nm) resolution was limited to a 350-nm pitch. The proposed resolution enhancement was verified, however pattern fidelity was reduced, the result of additional surface roughness. Simulation and analytical techniques have been used to investigate and understand vi ABSTRACT the enhancements and limitations of the PLL technique. A Finite-Difference Time- Domain (FDTD) tool was written to produce full-vector numerical simulations and this provided both broad- and narrowband results, allowing image quality as a function of grating period to be investigated. An analytical T-matrix method was also derived to facilitate computationally efficient performance analysis for grating transmission through PLL stacks. Both methods showed that there is a performance advantage for PLL over conventional near-field optical lithography, however, the performance of the system varies greatly with grating period. The advantages of PLL are most prominent for multi-layer lenses. The work of this thesis indicates that the utilisation of plasmonic resonances in PLL and related techniques can enhance the performance of near-field lithography.