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M.Tech. (Biomedical Technology) / Please read abstract in the full-text document

QC 351 A7 no. 75 / In the first part of this report the class of two-surface optical systems designated as modules, which have zero third-order spherical aberration relative to a pair of conjugate planes one of which is at infinity, has been further analyzed using the parameters of the Delano y,ÿ diagram. For a given set of three indices of refraction n1, n2, and n3, functional relationships among the y,j7 diagram parameters that eliminate simultaneously other Seidel aberrations are derived. Expressions for zero coma, astigmatism, and Petzval curvature are also given. Criteria for selecting the non - optical parameter k, which defines the desired properties of modules, are described. A one -to-one correspondence between the canonical optical parameters defined in previous studies of modules and certain quantities derivable from the y,ÿ diagram representation is shown. Critical values of the free parameters of modules for both the real and the imaginary cases are derived and defined relative to the y,,y diagram parameters. In the second part of this report an analysis is made of a class of modules referred to as the imaginary -case family depending on the new parameter 0. The critical values 00, 0_, and 0 *, which correspond to those obtained for real-case modules, are defined, and the conditions for their existence in the domain of are derived. These critical values, whose counterparts in the real case exist for both refracting and reflecting systems, do not exist for refracting imaginary-case modules when the indices of refraction are restricted to commonly available optical glasses. The critical values of 0 exist and have fixed values for all reflecting module systems. A method is proposed for classifying imaginary-case modules, which would permit comparison for coupling purposes.

>Magister Scientiae - MSc / Photovoltaic (PV) devices based on inorganic-organic hybrid active layers have been extensively studied for over a decade now. However, photoactive hybrid layers of material combinations such as rr-P3HT and SiNWs still require further exploration as candidates for solar cell (SC) fabrication, due to favourable optical absorption and charge carrier mobility associated with them respectively. The ultimate goal of the study is to fabricate ITO/PEDOT:PSS/rr-P3HT:SiNWs/Al SCs with different SiNWs content and investigate the different parameters or factors influencing the performance of these cells. The vertically aligned SiNW arrays on a Si wafer were synthesised via metal assisted chemical etching (MACE) and a method of chemically detaching these wires was developed. The average length and the diameter of the SiNWs obtained were 4.5 μm and 0.2 μm, respectively. Different weight ratios of as-synthesised SiNWs were then incorporated within rr-P3HT to form different hybrid solutions, i.e. rr-P3HT: 0.3 wt% SiNWs, rr-P3HT: 0.7 wt% SiNWs and rr-P3HT: 1.3 wt% SiNWs. In addition, a pure rr- P3HT solution was made for reference purposes. SEM characterisation shows that the SiNWs are randomly distributed across the active area, and that the film becomes progressively inhomogeneous upon addition of SiNWs, whereas the TEM characterisation revealed that there is no chemical interaction between the rr-P3HT and SiNWs. The UV-Vis and PL spectra suggest that there are changes in absorption and emission characteristics upon SiNW incorporation into the rr-P3HT matrix, which may have impacted the charge transfer .The electrical properties of the different hybrid films were probed using Hall Effect measurements, which revealed that the conductivity increases with the increase in the concentration of nanowires (NWs). The increase in conductivity upon the addition of SiNWs in the rr-P3HT matrix was related to an increase of the mobility (μ) of charge carriers in the hybrid films.

A dissertation submitted for the fulfilment of the requirements of the degree of Master of Science to the Faculty of Science, Witwatersrand University, Johannesburg. June 2016. / The combination of effective numerical techniques and scientific intuition to find new and novel types of materials is the process used in the discovery of materials for future technologies. Adding to that, being able to calculate the radiative lifetimes of excitons, exciton properties, and the optical properties by using efficient numerical techniques gives an estimation and identification of the best candidate materials for a solar cell. This approach is inexpensive and stable. Present ab initio methods based on Many-body perturbation theory and density functional theory are capable of predicting these properties with a high enough level of accuracy for most cases. The electronic properties calculated using GaAs as a reference system and the 3D hybird perovskite CH3NH3PbI3 are based on density functional theory. The optical properties are investigated by calculating the dielectric function. The theoretical framework of the radiative lifetime of excitons and calculating the exciton properties are based on Wannier model of the exciton and the Bethe-Salpeter equation. / MT2017

Based on rst principles calculations the structural, mechanical stability and electronic properties of molybdenum chalcogenides 2H-MoX2 (X = S, Se, Te) have been studied using density functional theory (DFT). The generalized gradient approximation (GGA) proposed by Perdew, Burke and Ernzerhof (PBE) was employed together with the projector augmented plane wave (PAW) method. The van der Waals interactions in the Grimme (DFT-D2) and Lundqvist and Langreth (vdW-DF) approximations have been added on top of PBE or revised PBE in order to take into account the weak interactions between layers of 2H-MoX2 (X = S, Se, Te). The structural properties include the equilibrium lattice parameters, the cohesive energy and the formation energy. Besides we have studied the mechanical stability of these compounds by examining the elastic constants using the PBE, vdW-DF, and DFT-D2 approximations. Other quantities related to the mechanical properties such as the Young's modulus, the Poisson's ratio and the bulk modulus were also calculated. Electronic properties of bulk 2H-MoX2 (X = S, Se, Te) have been investigated using density functional theory (via band structure and projected density of state), and a partially self-consistent GW (GW0) approximation. We have investigated electronic properties ( band structure) for monolayers 1H-MoX2 (X = S, Se, Te) using a single shot GW (G0W0) approximation. Optical properties for monolayer 1H-MoX2 (X = S, Se, Te) were studied using the Bethe-Salpeter equation (BSE).

Neste trabalho apresentamos um modelo para bandas de energia do HxMoO3 tanto para baixos como para altos valores de x. A densidade ótica do MoO3 hidrogenado é descrita em termos deste modelo, considerando-se as transições intra-bandas e inter-bandas. Verificamos que a densidade ótica calculada está de acordo com os resultados experimentais / In this work we give a model for the energy bands of HxMoO3 for low and high values of x. The optical density of hydrogenated MoO3 is described in terms of this model including both intraband and interband transitions. The calculated optical density is shown to agree with the experimental results