Model compounds for monitoring surface reactivity in the gas phase




Thiessen, Tanner

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Atomic Layer Deposition (ALD) is a cyclic process in which volatile precursors are reacted with a surface to generate a single layer of atoms or molecules and this process can be repeated to tune the thickness of these layers. Currently ALD is used in the manufacturing of silicon-based semiconductors, but the process faces reactivity issues that hinder its efficiency. A new set of precursors of the form X3SiCo(CO)4 have been proposed to fix these reactivity issues. In order to study the mechanistics of this process, analysis of the interaction between the X3SiCo(CO)4 compounds and the surface must be observed. Due to heterogeneity of the surface and the small number of atoms involved model systems can be a powerful tool to better understand the chemistry occurring at the surface. The model system chosen for this experiment is a compound called silsesquioxane that mimics the silicon surfaces reactivity, but also is available in the aqueous form. The experiment will be analyzed using electrospray ionization mass spectrometry (ESI-MS) coupled with a sample acquisition technique called pressurized sample infusion (PSI). These techniques were chosen because of their ability to handle highly air- and moisture-sensitive compounds as well as their ability to acquire data in real time. In order for mass spectrometry to be used, the precursors had to be charged and this was done by reacting the precursors with phosphine charged tags which generated charged analogues of the ALD precursors. These techniques were also used in a collaboration project to examine the reduction of bis(cyclopendadienyl)titanium(IV) dichloride (Cp2TiCl2) with manganese dust in dry THF with the manual addition of deoxygenated water. This reaction undergoes colour change from the initial red titanium species to the green reduced species and finally deep blue once the deoxygenated water is introduced to solution. ESI-MS was used at each of these colour changes to observe the reaction intermediates and help elucidate the reaction mechanism.



ALD, ESI-MS, Inorganic Synthesis, Silica, air-sensitive, moisture-sensitive