School of Physics - Theses
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ItemTEM and structural investigations of synthesized and modified carbon materials( 1999-08)Due to the extreme properties of diamond, such as extreme hardness, high thermal conductivity, high electrical breakdown strength, high electron and hole mobilities and large band gap, it is of interest to study this material in detail. Before advantage can be taken of diamond’s properties for high-temperature, high-power electronic applications successful doping/ion implantation of diamond must be achieved. This requires an understanding of the types of defects produced during ion irradiation. In the present work, type IIa diamond has been irradiated with various doses of 320keV Xe ions at room temperature. Analytical techniques used are electron spin resonance spectroscopy, Raman spectroscopy, transmission electron microscopy and electron energy loss spectroscopy. Previous models have suggested that upon ion impact, amorphous and/or graphitized clusters are formed in diamond, which will overlap at a critical dose to form a semi-continuous graphitized layer. (For complete abstract open document)
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ItemThe physics of faster than light objects( 1990)A new formulation of the theory of tachyons is developed using the same two postulates as in Special Relativity. Use is made of a "switching principle" to show how tachyons automatically obey the laws of conservation of energy, momentum and electric charge. Tachyonic transformations of spacetime position, velocity, momentum, energy, force and acceleration are rigorously derived from first principles. Further tachyonic transformations are derived from Maxwell's equations for the electromagnetic field components E, B, D, H, P and M, current and charge densities, scalar and vector potentials and the electromagnetic field tensor. It turns out that there are two main types of transformations which apply when going from a bradyonic inertial reference frame to a tachyonic inertial reference frame and vice versa. The first type involves the same transformations as apply for subluminal frames, but with the inclusion of factors of either +i or -i when crossing the light barrier. Examples of this type of transformation include spacetime position, energy, momentum, acceleration, electromagnetic scalar and vector potentials, electric charge density and current density. The second general type of transformation has exactly the same form for u 2 < c2 and u2 > c2 , examples of which include velocity, force and the electromagnetic field vectors E, B, D, H, P and M. Here u is the boost speed between the two inertial reference frames. Several examples are given to show how tachyons can produce real and measurable effects. It turns out that the electromagnetic field produced by a charged tachyon takes the form of a "Mach cone", inside which the electromagnetic field is real and detectable. The field outside the cone is imaginary and undetectable because the field has not yet arrived from the source. Tachyons also exhibit a Doppler effect, which is a blueshift for approach and a redshift for recession, just as for bradyons. The transverse Doppler effect is a redshift for c2 < u2 < 2c2 but is a blueshift for 2c2 < u2. Tachyons also produce an "optic boom" effect when the observer contacts the edge of the Mach cone, while inside the cone the observer experiences the "two source effect" t whereby the tachyon appears to be in two separate and mutually receding places. This means that electromagnetic fields and potentials are given by a superposition due to an “earlier” and a “later” source. Further examples include calculations of the magnetic dipole moment of a tachyonic current loop and of the speed of light in a tachyonic dielectric. (Part Abstract)
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ItemDirect observation of charged particle tracks in crystals( 1995)From a general point of view in material science, it is interesting to know, how swiftly moving, heavy ions (such as those ejected from spontaneously occuring nuclear fission events inside natural minerals) interact with solid bulk matter. For example, in geological mineral deposits (such as zircon, apatite, and sphene) one often finds that naturally radioactive isotopes (uranium, thorium etc.) are included in varying degrees of abundance. In particular, single 238 U atoms have a small but finite probability to disintegrate through a spontaneous nuclear fission event, thereby ejecting two highly charged and comparably heavy nuclear fragments with about 250Me V kinetic energy. This fact became known only about 30 years ago when straight-line, needle-like contrast features were observed in electron micrographs of mica (S&B 59, P&W 62). These so called "fission tracks" originate through the damage incurred on the host material containing naturally radioactive isotopes by the fast moving, charged and heavy fission-fragments penetrating the matrix in two oppositely directed straight lines. The length of the tracks is related to the penetration range of the ions, which in turn is determined through the initially available kinetic energy, the atomic number, and charge-state of the projectile as well as the mean density of the target material. (Because the energy level difference between the initial and final state of the nuclear decay event is constant on average, a fixed amount of kinetic energy is available for the two fragments. This fact requires the fission tracks to have a more or less constant longitudinal dimension of around 50µm.) Their thickness, however, could not be determined accurately up to very recently because the image quality remained poor due to the technical limitations in electron-optical engineering in the first few generations of electronrnicroscopes which were commercially marketed after their pioneering development by Ruska some sixty years ago (Rus 49). With the improved performance of the recent generation of high-voltage microscopes a renewed attempt was made to determine a) the electron optical conditions of making fission tracks (or at least short sections thereof) visible in their latent form through transmission electron microscopy, employing a variety of contrast mechanisms, b) the geometrical parameters of the track morphology in the particular instance of 208Pb20+ ions penetrating slabs of zircon crystals at an initial kinetic energy of 14MeV/u, c) the structural conditions as well as the nature and mechanism of the damage formation. Lastly, it was also hoped to be able to image the damaged regions showing atomic-size detail in High Resolution Electron Microscopy (HRTEM), thus making the native structure of the damaging effects of nuclear radiation penetrating bulk matter directly visible for the first time.