@article{Semiconductors:2108,
      recid = {2108},
      author = {Edel, Ross Anthony},
      title = {Oxidation of Semiconductors and Semimetals by Supersonic  Beams of O2 with Scanning Tunneling Microscopy  Visualization},
      publisher = {The University of Chicago},
      school = {Ph.D.},
      address = {2019-12},
      pages = {212},
      abstract = {The research presented in this dissertation examines the  oxidation of semiconductor and semimetal surfaces using a  novel, one-of-a-kind instrument that combines a supersonic  molecular beam with an in-line scanning tunneling  microscope (STM) in ultra-high vacuum.  This new approach  to surface reaction dynamics provides spatio-temporal  information on surface oxidation over nanoscopic and  mesoscopic length scales.  We have uncovered the kinetic  and morphological effects of oxidation conditions on three  technologically relevant surfaces: Si(111)-7×7, highly  oriented pyrolytic graphite (HOPG), and GaAs(110). A  complete understanding of the oxidation mechanism of these  surfaces is critical due to their technological  applications and roles as model systems.  Samples were  exposed to O2 with kinetic energies from 0.4-1.2 eV and  impingement angles 0-45° from normal, with STM  characterization between exposures.  In some cases, we were  able to monitor the evolution of specific features by  revisiting the same nanoscopic locations. Our study of  Si(111)-7×7 revealed two oxidation channels, leading to the  formation of dark and bright reacted sites.  The dark sites  dominated the surface and exhibited almost no site  selectivity while the bright sites preferred the corner  sites of the 7×7 unit cell.  Our observations suggest that  two adsorption pathways, trapping-mediated and direct  chemisorption, occur simultaneously.  On HOPG, we found  that different oxygen energies, incident angles, and  surface temperatures produce morphologically distinct  etching features:  Anisotropic channels, circular pits, and  hexagonal pits.  Reaction probability increased with beam  energy and demonstrated non-Arrhenius behavior with respect  to surface temperature, peaking at around 1375 K.  Finally,  oxidation of GaAs(110) was found to proceed by two  morphologically distinct, competing mechanisms: a  homogeneous process leading to layer-by-layer oxide growth,  and a heterogeneous process with oxide islands nucleating  from surface defects.  The rates of both mechanisms change  with O2 kinetic energy, with homogeneous oxidation  dominating at lower energies (<0.7 eV) and heterogeneous  oxidation with higher energies (>1.0 eV).  In all three  cases multiple oxidation mechanisms existed simultaneously  on the surface, which could only be distinguished with  exacting control over reaction conditions and high spatial  resolution.  The results obtained in this work provide  vital information about the morphological evolution and  kinetics of semiconductor and semimetals, offering a  comprehensive overview of the spatio-temporal correlations  that govern oxidation dynamics on surfaces.},
      url = {http://knowledge.uchicago.edu/record/2108},
      doi = {https://doi.org/10.6082/uchicago.2108},
}