Ion/surface interactions: A study of hydrocarbon chain length effects for self-assembled monolayer surfaces

Low and high energy ion/surface scattering techniques are used to investigate chain length effects for self-assembled monolayer (SAM) surfaces consisting of n-alkanethiol molecules on gold substrates. The focus of this work was to probe the structure, packing, and stability of the SAM surfaces using ion/surface interactions. Mechanisms are investigated for low and high energy ion/surface collisions, providing a more complete understanding of mass spectrometry techniques such as tandem mass spectrometry and secondary ion mass spectrometry.; The low energy reactive collisions of two independent probe ions illustrate an odd-even hydrocarbon chain length effect for a wide range of hydrocarbon SAM surfaces. SAM surfaces prepared from alkanethiols ranging from CH ₃(CH₂)₁₀SH to CH₃(CH₂) ₁₇SH chemisorbed to polycrystalline gold are shown to exhibit an odd-even effect where the orientation of the terminal methyl group determines the reaction behavior of the thin film. Imaging TOF-SIMS and XPS show the surfaces to be homogeneously covered and provide evidence for the presence of a thiolate (Au-SR) on the SAM surface.; Chain length effects in hydrocarbon SAM surfaces were investigated using a high resolution TOF-SIMS instrument. Variations in coverage, extent of oxidation, and high mass cluster formation as a function of hydrocarbon chain length of the alkanethiol SAM surfaces were investigated. The formation of high mass gold-sulfur and gold-adsorbate cluster ions was also investigated. Mechanisms for the formation of the large cluster ions are proposed, which build upon a precursor cluster mechanism. The formation of high mass cluster ions is a function of the chain length of the alkanethiol chemisorbed to the gold surface. Their formation depends on the attenuation of the ions by steric effects and van der Waals interactions.; The technique of soft-landing was used to deposit polyatomic ions into the matrix of SAM surfaces. SAM surfaces were successfully modified and subsequent chemical sputtering after ion implantation ejects the ions from the modified surface where they were analyzed and detected. Xenon chemical sputtering is more effective in releasing the trapped ions from the SAM surfaces when compared to argon chemical sputtering.; Laser desorption mass spectrometry was used in a collaborative effort with Professor Dismukes to study the evolution of molecular oxygen from a manganese-oxo cubane core. Laser desorption ionization TOF mass spectrometry indicates the loss of a bound ligand and two oxygen atoms upon photolysis. Nd:YAG laser irradiation of a complex coupled with quadrupole mass spectrometry proved that the two oxygen atoms release from the manganese-oxo cubane core as molecular oxygen.