Electronic Thesis and Dissertation Repository


Doctor of Philosophy




Dr. Lyudmila Goncharova


Medium energy ion scattering (MEIS) is used to determine the elemental depth profile in the first few hundred angstroms of a sample. The interpretation of MEIS spectra requires an accurate knowledge of the rate at which the ions lose their energy - the stopping cross section, ε. The rate of energy loss has been fairly well investigated, both experimentally and theoretically, in elemental and compound targets at high energies (E>400 keV/amu). However, in the medium ion energy range where stopping cross section typically has a maximum, experimental data are scarce while most of the existing theories fail to give accurate predictions.

In this work, we report accurate measurements of stopping cross sections for ~55−170 keV protons in thin film of Si, Ti and SrTiO3 using MEIS. We developed a new methodology of calculating stopping cross sections from the MEIS spectra. Measured εSi and εTi agree with the values reported in the NIST database within experimental uncertainties. On the other hand, data are systematically lower over the entire energy range probed. Among several factors that could contribute to the observed discrepancy, the following were eliminated: i) the proposed method for calculating stopping cross sections from MEIS spectra is not accurate ii) εTi literature values used to calculate are underestimated.

In the second part of this thesis, we report an observation of self-assembled lateral Si wires (ridges) grown by a vapour-liquid-solid mechanism in a molecular beam epitaxy system. We show that at a sufficiently low flux of Si atoms and high substrate temperature, gold droplets are propelled forward horizontally along two orthogonal <011> directions by the growing silicon wires. The reticular growth closely resembles a self-avoiding random walk in two dimensions, as we confirmed by using a Monte Carlo simulation. We present the experimental results and thermodynamic arguments showing the unique role carbon plays in initiating lateral growth of Si wires on a Si (100) substrate and discuss the means of kinetic control of the growth process.