This master’s project report deals with the process development for patterning thesub-micron features using Deep-UV photolithography. Patterning of the sub-micronstructures in the resists UV26 and ZEP520A-7 has been demonstrated successfully. Using theKarl Süss-MJB4 DUV mask aligner, trenches of width down to 535 nm have been obtained.Good results have been obtained in these experiments considering the development time andthe exposure time, which are found to be shorter compared to previously published results.This provides a faster process and higher throughput. Experimental steps along with thefurther improvement areas are discussed.Equipment used include a Karl Süss-MJB4 DUV mask aligner, an optical microscope anda Scanning Electron Microscope (SEM).

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X-ray imaging exams are widely used procedures in medical diagnosis. Whenever an x-ray imaging procedure is performed, it is accompanied by scattered radiation. Scatter is a significant contributor to the degradation of image quality in breast CT. This work uses our understanding of the physics of Compton scattering to overcome the reduction in image quality that typically results from scattered radiation. By measuring the energy of the scattered photons at various locations about the object, an electron density (ρe) image of the object can be obtained. This work investigates a system modeled using a 2D cross-sectional view of a breast CT geometry. The ρe images can be obtained using filtered backprojection over isogonic curves. If the detector has ideal energy and spatial resolution, a single projection will enable a high quality image to be reconstructed. However, these ideal characteristics cannot be achieved in practice and as the detector size and energy resolution diverge from the ideal, the image quality degrades. To compensate for the realistic detector specifications a multi-projection Compton scatter tomography (MPCST) approach was introduced. In this approach an x-ray source and an array of energy sensitive photon counting detectors located just outside the edge of the incident fan-beam, rotate around the object while acquiring scattering data. The ρe image quality is affected by the size of the detector, the energy resolution of the detector and the number of projections. These parameters, their tradeoffs and the methods for the image quality improvement were investigated. The work has shown that increasing the energy and spatial resolution of the detector improves the spatial resolution of the reconstructed ρe image. These changes in the size and energy resolution result in an increase in the noise. Thus optimizing the image quality becomes a tradeoff between blurring and noise. We established that a suitable balance is achieved with a 500 eV energy resolution and 2×2 mm2 detector. We have also established that using a multi-projection approach can offset the increase in the noise.

In recent years, the electronic behavior of DNA molecules has received much interest ranging from interpreting experimental results to electronic based applications, including DNA sequencing and DNA-based nanotransistors. Here we study the electronic properties of poly(G)- poly(C) double stranded DNA molecules by means of the tight binding approximation to understand how the molecules act under different physical conditions. For instance, the effects of DNA tilting, stretching and compressing on the electronic properties are elucidated. Very interesting features such as a tunable energy band gap and a metal-semiconductor transition are disclosed for DNA under different conditions. / Second order tight binding model -- Tilted DNA molecule -- Strain-dependent DNA electronics.

Since the discovery of conductance quantization within a nanostnucture, investigations have sought out causes to conductance fluctuations beyond the established plateaus. The focus of this work is to show the fundamental effects upon conductance due to longitudinal potentials and double quantum boxes when confined by hardwall boundaries. A theoretical model based upon a tight-binding recursive tureen's function methodology was modified to incorporate potential barrier variations. A qualitative evaluation, as well as, explanation of the model's results and limitations is discussed. / Department of Physics and Astronomy

Charge-induced adsorption is a subject of significance to environmental and biological systems. Ice surface is believed to get charged with potassium deposition. Compared to uncharged ice film, the work function of charged ice film is significantly reduced due to the formation of metastable delocalized excess surface electrons donated by potassium atoms on ice. This charging effect is found to be dependent on temperature. It is also reported that adsorption of carbon tetrachloride would occur drastically on charged ice surface while almost no adsorption was observed on uncharged ice surface at low temperature. In addition, the results strongly agree with the cosmic-ray-driven electron-induced reaction (CRE) model for ozone depletion.

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This thesis describes the experimental study of electron scattering processes from laser-excited barium and ytterbium atoms. These include the electron-impact ionization-excitation from Ba (...6s6p) 1P1 and Ba (...6s5d) 1,3D1,2 to Ba+ (...6p) 2P3/2, the elastic electron scattering from Ba (...6s6p) 1P1 and Ba (...6s5d) 1,3D1,2, and the electron-impact excitation from Yb (...6s6p) 3P1 to Yb (...6s7s) 3S1, Yb (...6s6p) 1P1, and Yb (...6s5d) 3D1,2,3. The experiments utilized electron impact energies in the range of 5 eV to 50 eV. Differential and integral scattering cross sections were determined, and are presented both on absolute and relative scales. By controlling the laser polarization, alignment and orientation parameters characterizing the scattering processes were determined. Additionally, the barium ionization-excitation study observed polarization dependencies of ion line emission fluorescence for radiative decay from Ba+ (...6p) 2P3/2 to Ba+ (...6s) 2S1/2, providing information about the final ionic state composition. Along with experimental measurements of electron-atom collisions, this thesis describes the design and development of a computer-controlled data acquisition system and a laser frequency stabilization system.

HREM imaging was performed using the Jeol 4000ex microscope on specimens prepared from an as-grown ingot of semi-insulating Gallium Arsenide. Various low angle grain boundaries were imaged in the [110] orientation, misorientations varying between 4°-13°. Detailed study of a grain boundary of 11.5° misorientation about the [110] rotation axis has been carried out. Burgers vector analysis showed the presence of perfect 60° and [001] dislocations. Modelling of the [001] dislocation has been carried out using the Tersoff potential, Bond Order Potential and a tight binding Hamiltonian for GaAs, using Chadi (1984) parameters. The dislocation core was associated with an 8-membered and two 5-membered rings. Assum- ing there is a minimum of wrong bonds, we predict that the core has two wrong bonds, one being Ga-Ga, and the other As-As, both in equivalent positions where the two 5-membered rings were appended to the 8-membered ring. The Ga-Ga bond is considerably shorter and hence stronger than the As-As bond. Band structure calculations performed using a Vogl (1983) sp³s* Hamiltonian revealed deep states in the gap, which are associated with atoms in the core only. Using Stadelmann's (1987) EMS program, successful image matching of calculated images of the [001] dislocation has been achieved with the experimental image, using the atomic structure generated by tight binding relaxation. Ga and As being only two atomic numbers apart have similar scattering factors and cannot be easily distinguished in the experimental image. The equivalence of the position of the two wrong bonds greatly eases image matching as it is no longer necessary to know which is the Ga-Ga , and which is the As-As bond. This is the first suggested model of the [001] dislocation in GaAs, to the best of my knowledge. It is found to be similar to the atomic structure of the 90° partial dislocation in silicon (Bigger et al., 1992). No account of segregation of impurities to the grain boundary, or the [001] dislocation core is taken here, though it is very likely that an impurity atom would sit itself in this large space. The relaxed atomic structure for the 60° dislocation showed a doubling of periodicity along the dislocation line, similar to that found in the 30° partial in Si. The core consists of a 7-membered and a 5-membered ring with a minimum of two wrong bonds. In addition to this, quantitative comparisons of the [001] HREM image and simulated structures have been made and an iterative structure refinement carried out in order to achieve the best image matching. The resultant 'experimental-best-fit' structure was not found to be physically or chemically plausible.

Transmission Electron Microscope (TEM) studies have been carried out of emitter regions in polysilicon contacted emitter bipolar transistors. The preparation of suitable TEM thin foils is described. In addition a technique is developed for the observation and quant jtative interpretation of the break-up of the interfacial oxide layers observed in these samples. The effect of annealing the samples prior to emitter dopant implantation (pre-annealing) is investigated for phosphorus and arsenic doped samples, implanted into a polysilicon layer 0.4μm thick, with a dose of 1x10¹⁶cm². Two wafer pre-cleans have been used prior to polysilicon deposition to produce a thin oxide (0-8Å) and a thicker oxide (14Å). In the presence of the thinner oxide, the phosphorus doped samples enhance epitaxial regrowth of the polysilicon layer compared with the arsenic doped or undoped samples. In the presence of the thicker oxide, no difference is observed between the samples. A mechanism is proposed to explain this. The mechanisms controlling the gain of a phosphorus doped device are investigated and a model proposed to explain the observed electrical characteristics. It is concluded that there are two mechanisms responsible for the observed supression of hole current. Firstly tunnelling through the interfacial oxide and secondly some blocking effect of the interface. Carrier transport in the polysilicon is not believed to contribute to this supression. A dopant sensitive etch has been applied to TEM thin foils containing fully processed emitters in state-of-the-art devices. The shape of the emitter dopant distribution is revealed in such devices for the first time, and a 2-D profile is obtained from the emitter. It is shown that reduction in the emitter depth to 8OOÅ or less does not alter the emitter dopant geometry. The technique is demonstrated to be capable of resolving spatial separations of dopant iso-concentration contours of 100Å or less.