Artificial Assembly of Precise Functional Nanostructures
Open Access
- Author:
- Giordano, Andrea Nicole
- Graduate Program:
- Chemistry
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- June 23, 2010
- Committee Members:
- Paul S Weiss, Thesis Advisor/Co-Advisor
Paul S Weiss, Thesis Advisor/Co-Advisor - Keywords:
- scanning tunneling microscopy
self-assembled monolayers - Abstract:
- We used a cyrogenic, ultrastable scanning tunneling microscope (STM) to investigate fundamental questions in the field of surface science. We examined the molecular orientations of bicomponent alkanethiolate self-assembled monolayers (SAMs) through simultaneous constant-current topographic and local barrier-height imaging, which allowed us to develop a STM-based technique to probe both interfaces concurrently. This enabled us to resolve the controversy in topographic image contrast assignment and to make molecular orientation measurements. The measured molecular orientations were found to be in agreement with previous infrared spectroscopy and grazing incidence X-ray diffraction experiments. For longer-chain high-coverage SAMs, such as octanethiolate/decanethiolate SAMs, the domains presenting a (√3 × √3)R30° superstructure in the exposed methyl interface also have a buried thiolate head-group (√3 × √3)R30° structure. For domains containing a c(4 × 2) overlayer in the exposed interface, a more complex buried structure was observed. We investigated the interactions of thiophene with a deuterated Pd{110} surface. Thiophene-induced microfaceting of a D/Pd{110}-(1 × 2) surface in the direction by subsurface deuterium was observed. The propagating facets were found to be out of plane with respect to the underlying Pd{110} substrate by 3.2 ± 0.8°. The microfacets were formed as a consequence of bulk deuterium diffusing up to the subsurface sites, which caused the surface configuration to change from a (1 × 2) to a (1 × 1) structure. We observed that at 4 K, the formation of the microfacets requires the adsorption of thiophene, which lowers the barrier for the population of subsurface sites by bulk deuterium atoms. Conductance spectroscopy revealed the onset voltage to bulk deuterium diffusion to be 0.38 ± 0.02 eV.