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Title: Quantitative Prediction of Elastic and Anelastic Phenomena on the Nanometer Scale
Authors: Ustunel, Hande
Keywords: anharmonic
quality factor
Green's function
phonon-phonon interaction
electron mean-free path
Issue Date: 10-Oct-2005
Abstract: In the past two decades, nanometer scale devices have become increasingly important in various scientific and technological applications such as sensors, actuators and storage devices. This thesis presents a theoretical exploration of some of the vibrational properties of such devices, with an emphasis on quality factor, the fraction of energy lost per period of oscillation in a vibrating system. The thesis introduces a new method for obtaining the ground state structure of defects by looking at their mechanical response. This method involves calculation of the activation volume tensor of the defect using reliable ab initio techniques. As an application, results are presented for the activation volume tensor of a divacancy in silicon, a defect commonly introduced in the fabrication stages of silicon actuators. Comparison of the activation volume tensor to experimental values leads to an unambigious identification of the ground state of this defect, which has proved elusive in the literature to date. Finally, the calculation of the mechanical energy loss caused by divacancies in a silicon oscillator is given. The thesis then turns to the calculation of the electronic mean-free path in carbon nanotubes under high-bias. Electron-phonon interactions have been found to have a considerable effect in the determination of the electron mean-free path. We determine the mean-free path of the nanotubes in the presence of various phonon modes that cause scattering of electrons. The thesis concludes with a consideration of the vibrations of suspended nanotubes, exploring first the dependence of the vibration frequencies on such factors as downward force and built-in slack in the nanotube and then turning to a fundamental loss mechanism intrinsic to any system, namely loss due to phonon-phonon interactions.
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