This thesis describes the works done during the design and deposition process of the antireflection coating for the materials commonly used as refractive optical elements in thermal imaging systems. These coatings are quite necessary to reduce reflection losses from the surface of the optics and stray light that directly affects the image quality. Germanium, zinc sulfide and zinc selenide were used as substrate material and their optical properties were investigated with infrared ellipsometry and FTIR. Antireflection coatings for each material operating in 8-12 &amp / #956 / m range were designed with Needle Synthesis Technique. In order to shorten the optimization time, commercial software / &ldquo / The Essential Macleod&rdquo / was used. In order to reduce the reflectance losses multilayer structure was used in the coating design, and zinc selenide and lead telluride were used as low and high index materials. In this study the necessary theoretical background and common deposition techniques are reviewed. Samples were produced using the magnetron sputtering. To optimize the v thicknesses of the deposited layers, growth period and rate was controlled. Thicknesses of the samples, following to the deposition were also measured by thickness profilometer. A 3-layer coating, PbTe/ZnSe/PbTe, on ZnS and 2-layer coating PbTe/ZnS on Ge having more than 90% transmittance in 9.7-10.3 &amp / #956 / m wavelength region have been successfully produced. Although, the measured range for 3 and 2- layer coating is narrower than the aimed one, it has been shown that, the method developed in this thesis would yield AR-coatings with broader spectral response if a system having better control on deposition parameters is used. For example, our design and optimization work has suggested that a 7-layer AR coating on germanium, with alternating high and low index layers is expected to give transmittance value greater than 93% in the studied wavelength region.

In order to improve the optical losses of spherical silicon solar cells, new fabrication designs were presented. The new device structures are fabricated based on integration of nanostructures into spherical silicon solar cells. These new device structures include: spherical silicon solar cells integrated with nanostructured antireflection coating layers, spherical silicon solar cells with hemispherical nanopit texturing, and cells integrated with colloidal quantum dots. Silicon spheres were characterized by means of transmission electron microscopy (TEM), single-crystal x-ray diffraction and x-ray powder diffraction to establish the crystallinity nature of the silicon spheres. Furthermore, the material properties of silicon spheres including surface morphology, microwave photoconductivity decay lifetime, and impurity elemental distributions were studied. Silicon nitride antireflection coating layers were developed and deposited onto the spherical silicon solar cells, using a PECVD system. A low temperature hydrogenation plasma technique was developed to improve the passivation quality of the spherical silicon solar cells. The spectral response of silicon spheres with and without a silicon nitride antireflection coating was studied. We have successfully developed and integrated a nanostructured antireflection coating layer into spherical silicon solar cells. The nanostructured porous layer consists of graded-size silicon nanocrystals and quantum-size Si nanoparticles embedded in an oxide matrix. This layer has been characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM), Scanning tunneling TEM, energy filtered TEM, transmission electron diffraction (TED), electron energy loss spectroscopy (EELS), energy dispersive x-ray (EDX), Raman spectroscopy and photoluminescence spectroscopy (PL). We developed a novel technique of electrochemical etching for silicon surface texturing using a liquid-phase deposition of oxide mask. Using a focus ion-beam (FIB) technique, cross-sectional TEM samples were prepared to investigate the nature of texturing and the composition of the deposited mask. The hemispherical nanopit texturing was successfully integrated into spherical silicon solar cells and the etching mechanisms and the chemical reactions were discussed. CdSe colloidal quantum dots with diameter of about 2.8nm were integrated into a graded-density nanoporous layer. This structure was implemented on the emitter of the spherical silicon solar cells and the spectral response with and without incorporation of QDs was studied.

We have studied several metamaterials structures with multiple layers by explaining them theoretically and verifying experimentally. The engineered structures we have designed work either as a perfect absorber or antireflection coating. The multilayer model as we call it Three Layer Model (TLM) has been developed, which gives the total reflection and transmission as a function of reflection and transmission of individual layers. By manipulating the amplitude and phase of the reflection and the transmission of the individual layers, we can get the required functionality of the optoelectronic devices. To get zero reflection in the both perfect absorber and the antireflection coating, the amplitude and phase conditions should be satisfied simultaneously. We have employed the numerical simulation of the structures to verify those conditions for all of the work presented here. As the theoretical retrieval method to extract the effective permittivity and effective permeability of the metamaterial contains air on the both side of the structure, we have dielectric at least on one side practically, that gives a little bit deviated result. We have modified the retrieval method to better fit with the multilayer structure by introducing air on the both side of the resonator using transfer matrix method and use it throughout all the works. We have explained the perfect absorption of the EM wave through Fabry-Perot cavity bounded by the resonator mirror and the metallic film. The metallic film acts as the close boundary whereas the resonator acts as the quasi-open boundary with very high effective permittivity, which leads to the characteristic feature of subwavelength thickness. We have shown numerically that the ultra-thin thickness makes the perfect absorber angular independent. We have also explained the phenomenon of perfect absorption through Impedance Matched Theory and Transmission Line Theory, and showed their matching with TLM. We have also developed the Meta Film Model by considering the resonator as a homogeneous thin film characterized by the effective permittivity and permeability giving rise to the same behavior as the original multilayer structure. We have shown that the resonance of the metamaterial resonator is very far from the resonance of the absorber, it behaves as the medium of high refractive index and very low loss. We have also shown that the density of states of the absorber is increased as compared to the resonator itself. We have investigated that the resonance peaks of the absorber arise from the combination of Fabry- Perot cavity modes and surface plasmon resonance modes. All the modes with increased spacer thickness are assigned with specific names describing the mode profiles. We have shown the application of perfect absorber as a refractive index sensor. It is used as a plasmonic sensor to detect the refractive index change of the chemical and biological samples. To increase the sensitivity, we have etched the dielectric spacer below the resonator, where electric field is localized and enhanced. We have found that the sensitivity (wavelength shift per refractive index change) and the Figure of Merit (FOM*) as an indicator of performance of the device both are enhanced significantly. We have employed metamaterial (MM) anti-reflection (AR) coating to avoid the shortcomings of the conventional thin film coating in three different cases of the structures. At first, we have deployed metamaterial Metal Disk Array (MDA) on the top of conventional coating material (BCB) with homogeneous substrate to enhance the transmission of EM wave. Then conventional AR coating is employed to the dispersive media (metal Hole Array) to enhance the transmission. We have shown that Impedance matched condition has been satisfied not only for homogeneous media, but for dispersive media also. At the end, we have employed the MM AR coating to the MM dispersive media (MHA). The two MM layers may interact with each other and may degrade the SPP wave of the MHA, which is essential to enhance the performance of the devices. To investigate the effect of interaction, we perform the simulation of the MDA, which shows that the resonance of the MDA is far from the antireflection resonance and hence the electric field of the SPP is significantly increased (~30%). With an improved retrieval method, the metasurface is proved to exhibit a high effective permittivity (εeff~30) and extremely low loss (tanδ~0.005). For all of the three AR structures, a classical thin film AR coating mechanism is identified through analytical derivations and numerical simulations. The properly designed εeff and μeff of the meta surface lead to the required phase and amplitude conditions for the AR coating, thereby paving the way for the improved performance of the optoelectronic devices. We have used MHA as a dispersive media to get extraordinary optical transmission (EOT). To understand the behavior of the SPP peaks, we have investigated the shifting and splitting of the spoof SPP resonance by varying the polar angle and azimuthal angle. The amplitude of extraordinary optical transmission also shows angle dependence and exhibits mirror-image or translational symmetries. Our measurements and simulations of the THz spoof SPP waves match very well with the theoretical predictions. The angle dependence results provide the important information for designing THz plasmonic devices in sensor and detector applications.

The Electrostatic Self-Assembly (ESA) technique possesses great advantages over traditional thin film fabrication methods, making it an excellent choice for a number of applications in the fields of linear and nonlinear optics, electronics, sensing and surface coatings. The feasibility of fabricating linear optical interference filters by ESA methods is demonstrated in this thesis work. Basic single-anion/single-cation ESA films are synthesized and their optical parameters -- refractive index and average thickness for individual bilayer -- are investigated to provide a basis for the in-depth design of optical filters. High performance dielectric stack filters and narrowband and wideband antireflection coatings are designed using TFCalc simulation software and are fabricated by ESA. Both bulk film sensitivity and layer sensitivity to manufacturing errors are provided. The significant agreement between simulation and experiment demonstrates the strong capability of ESA to precisely control the refractive index and produce excellent thin film filters. The performance of optical thin film filters is largely enhanced compared to the results of previous methods. The experiment results indicate that the ESA process may be used to fabricate optical filters and other optical structures that require precise index profile control. / Master of Science

A wide variety of nanomaterials ranging from polymer assemblies to organic and inorganic nanostructures (particles, wires, rods etc) have been actively pursued in recent years for various applications. The synthesis route of these nanomaterials had been driven through two fundamental approaches - 'Top down' and 'Bottom up'. The key aspect of their application remained in the ability to make the nanomaterials suitable for targeted location by manipulating their structure and functionalizing with active target groups. Functional nanomaterials like polyelectrolyte based multilayered thin films, nanofibres and graphene based composite materials are highlighted in the current research. Multilayer thin films were fabricated by conventional dip coating and newly developed spray coating techniques. Spray coating technique has an advantage of being applied for large scale production as compared to the dip coating technique. Conformal hydrophobic/hydrophilic and superhydrophobic/hydrophilic thermal switchable surfaces were fabricated with multilayer films of poly(allylaminehydrochloride) (PAH) and silica nanoparticles by the dip coating technique, followed by the functionalization with thermosensitive polymer-poly(N-isopropylacrylamide)(PNIPAAM) and perfluorosilane. The thermally switchable superhydrophobic/ hydrophilic polymer patch was integrated in a microfluidic channel to act as a stop valve. At 70 degree centigrade, the valve was superhydrophobic and stopped the water flow (close status) while at room temperature, the patch became hydrophilic, and allowed the flow (open status). Spray-coated multilayered film of poly(allylaminehydrochloride) (PAH) and silica nanoparticles was fabricated on polycarbonate substrate as an anti-reflection (AR) coating. The adhesion between the substrate and the coating was enhanced by treating the polycarbonate surface with aminopropyltrimethoxylsilane (APTS) and sol-gel. The coating was finally made abrasion-resistant with a further sol-gel treatment on top of AR coating, which formed a hard thin scratch-resistant film on the coating. The resultant AR coating could reduce the reflection from 5 to 0.3% on plastic. Besides multilayered films, the fabrication of polyelectrolyte based electrospun nanofibers was also explored. Ultrathin nanofibers comprising 2-weak polyelectrolytes, poly(acrylic acid) (PAA) and poly(allylaminehydrochloride) (PAH) were fabricated using the electrospinning technique and methylene blue (MB) was used as a model drug to evaluate the potential application of the fibers for drug delivery. The release of MB was controlled in a nonbuffered medium by changing the pH of the solution. Temperature controlled release of MB was obtained by depositing temperature sensitive PAA/poly(N-isopropylacrylamide) (PNIPAAM) multilayers onto the fiber surfaces. The sustained release of MB in a phosphate buffered saline (PBS) solution was achieved by constructing perfluorosilane networks on the fiber surfaces as capping layers. The fiber was also loaded with a real life anti-depressant drug (2,3-tertbutyl-4-methoxyphenol) and fiber surface was made superhydrophobic. The drug loaded superhydrophobic nanofiber mat was immersed under water, phosphate buffer saline and surfactant solutions in three separated experiments. The rate of release of durg was monitored from the fiber surface as a result of wetting with different solutions. Time dependent wetting of the superhydrophobic surface and consequently the release of drug was studied with different concentrations of surfactant solutions. The results provided important information about the underwater superhydrophobicity and retention time of drug in the nanofibers. The nanostructured polymers like nanowires, nanoribbons and nanorods had several other applications too, based on their structure. Different self-assembled structures of semiconducting polymers showed improved properties based on their architectures. Poly(3-hexylthiophene) (P3HT) supramolecular structures were fabricated on P3HT-dispersed reduced graphene oxide (RGO) nanosheets. P3HT was used to disperse RGO in hot anisole/N, N-dimethylformamide solvents, and the polymer formed nanowires on RGO surfaces through a RGO induced crystallization process. The Raman spectroscopy confirmed the interaction between P3HT and RGO, which allowed the manipulation of the composite's electrical properties. Such a bottom-up approach provided interesting information about graphene-based composites and inspired to study the interaction between RGO and the molecular semiconductor-tetrasulphonate salt of copper phthalocyanine (TSCuPc) for nanometer-scale electronics. The reduction of graphene oxide in presence of TSCuPc produced a highly stabilized aqueous composite ink with monodispersed graphene sheets. To demonstrate the potential application of the donor (TSCuPc)'acceptor (graphene) composite, the RGO/TSCuPc suspension was successfully incorporated in a thin film device and the optoelectronic property was measured. The conductivity (dark current) of the composite film decreased compared to that of pure graphene due to the donor molecule incorporation, but the photoconductivity and photoresponsivity increased to an appreciable extent. The property of the composite film overall improved with thermal annealing and optimum loading of TSCuPc molecules.

Passivation of silicon surfaces remains a critical factor in achieving high conversion efficiency in solar cells, particularly in future generations of rear contact cells -the best performing cell geometry to date. In this thesis, passivation is characterised as either intrinsic or extrinsic, depending on the origin of the chemical and field effect passivation components in dielectric layers. Extrinsic passivation, obtained after film deposition or growth, has been shown to improve significantly the passivation quality of dielectric films. Record passivation has been achieved leading to surface recombination velocities below 1.5 cm/s for 1 Ωcm n-type silicon covered with thermal oxide, and 0.15 cm/s in the same material covered with a thermal SiO2/PECVD SiNx double layer. Extrinsic field effect passivation, achieved by means of corona charge and/or ionic species, has been shown to decrease by 3 to 10 times the amount of carrier recombination at a silicon surface. A new parametrisation of interface charge, and electron and hole recombination velocities in a Shockley-Read-Hall extended formalism has been used to model accurately silicon surface recombination without the need to incorporate a term relating to space-charge or surface damage recombination. Such a term is unrealistic in the case of an oxide/silicon interface. A new method to produce extrinsic field effect passivation has been developed in which charge is introduced into dielectric films at high temperature and then permanently quenched in place by cooling to room temperature. This approach was investigated using charge due to one or more of the following species: ions produced by corona discharge, Na⁺, K⁺, Cs⁺, Mg²⁺ and Ca²⁺. It was implemented on both single SiO₂ and double SiO₂/SiN_x dielectric layers which were then measured for periods of up to two years. The decay of the passivation was very slow and time constants of the order of 10,000 days were inferred for two systems: 1) corona-charge-embedded into oxide grown on textured FZ-Si, and 2) potassium ions driven into an oxide on planar FZ-Si. The extrinsic field effect passivation methods developed in this work allow more flexibility in the combined optimisation of the optical properties and the chemical passivation properties of dielectric films on semiconductors. Increases in cell Voc, Jsc and η parameters have been observed in simulations and obtained experimentally when extrinsic field effect passivation is applied to the front surface of silicon solar cells. The extrinsic passivation reported here thus represents a major advancement in controlled and stable passivation of silicon surfaces, and shows great potential as a scalable and cost effective passivation technology for solar cells.

The work deals with a comparison of existing and perspective types of passivation and anti-reflective coating for silicon solar cells. The theoretical part describes the appropriate methodology for the characterization of these layers and focuses on the passivation layers based on Al2O3. The practical part describes design and verification operations of the equipment for measuring of the amount of fixed charge in the passivation layers using corona discharge. It also describes the implementation of equipment and the results of indicative tests for positive and negative polarity of high voltage. The final part discusses the possibility of equipment improving.

This thesis deals with the analysis of nano-structured layers deposited by high-frequency magnetron sputtering on the monocrystalline silicon surface. The content of the work focuses on the magnetron sputtering application as an alternative method for passivation and antireflection layers deposition of silicon solar cells. The procedure of pre-deposite silicon surface cleaning by plasma etching in the Ar/H2 gas mixture atmosphere is suggested. In the next step the silicon nitride and aluminum nitride layers with hydrogen content in Ar/N2/H2 gas mixture by magnetron sputtering are deposited. One part of the thesis describes an experimental pseudo-carbide films deposition from a silicon target in the atmosphere of acetylene (C2H2). An emphasis is placed on the research of sputtered layers properties and on the conditions on the silicon-layer interface with the help of the standard as well as special measurement methods. Sputtered layers structure is analyzed by modern X-ray spectroscopy (XPS) and by Fourier infrared spectroscopy (FTIR). Optical ellipsometry and spectrophotometry is used for the diagnostic of the layers optical properties depending upon the wavelength of incident light. A special method of determining the surface lay-out of the charge´s carrier life in the volume and on the surface of silicon is employed to investigate the passivating effects of the sputtered layers.