AU(111) SURFACE RESTRUCTURING FROM SULFUR ADSORBATES

Open Access
Author:
McGuirk, Garry M
Graduate Program:
Physics
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • Renee Denise Diehl, Thesis Advisor
Keywords:
  • LEED Structure Analysis
  • LEED
  • AES
  • Au(111)-S phases
Abstract:
The development of gold-based catalysts, semi-conductor thin films, thiol-based self-assembled monolayers and sensors requires further atomic-level understanding of S adsorption on gold surfaces. To assist in this understanding, an Au(111) single crystal surface was exposed to SO2 gas prior to adsorption of S under ultra high vacuum conditions (UHV). The adsorption of S was accompanied by formations of three phases observed by Low-Energy Electron Diffraction (LEED), namely the (1x1), (5x5) and (√3x√3)R300 Au(111)-S phases. The (1x1) and (5x5) phases were examined by LEED intensity versus energy (I(E)) analysis. The respective analysis showed best-fit models with top layer spacings of 2.33¬±0.19Å and 1.57±0.14Å. This confirms S can lift an Au(111) surface reconstruction ((1x1) Au(111)-S phase) and S atoms occupy 3-fold FCC hollow sites forming “rosette” structures suggested by a previous study ((5x5) Au(111)-S phase) [1]. A well-ordered “complex” phase was obtained by annealing an S coverage >.6ML from ~450K to ~525K. Within this temperature range, Auger Electron Spectroscopy (AES) measurements showed negligible sulfur loss. Further annealing led to S desorption with conflicting LEED observations presumably resulting from electron beam induced effects.