Low-energy electron induced processes in molecular thin films condensed on silicon and titanium dioxide surfaces

The focus of the presented experimental research is to examine the fundamental physics and chemistry of electron-stimulated reactions upon adsorbate covered single crystal surfaces. Specifically, condensed SiCl4 on the Si(111) surface and condensed H2O on the TiO2 (110) surface have been studied. By varying adsorbate film thicknesses, the coupling strength of the electron target molecule to the substrate and surrounding media dictates the progression of the electron induced reactions.; To investigate the electron interactions with SiCl4 on the Si(111) surface, a multilayer to monolayer approach was taken. Experiments measuring the electron stimulated desorption (ESD) of fragment cations are discussed in Chapter 3. ESD of neutrals was performed on a multilayer (100 ML) coverage of SiCl4 and is discussed in Chapter 4. These experiments remove the influence of the silicon substrate on the electron induced dissociative processes that are monitored via time of flight mass spectrometry (ToF-MS). The results in Chapter 3 and Chapter 4 have been published in Surface Science 593 (2005) 173 and in the Journal of Chemical Physics 124 (2006) 164702, respectively. Results from electron induced reactions within thin films of SiCl4 are presented in Chapter 5. In the low coverage region, the cation and neutral desorption channels are monitored simultaneously, and the adsorbate coupling strength to the silicon substrate is substantially greater. This affects the desorption yields and the autodetachment probability of the transient negative ion (SiCl4-).; Chapters 6--8 discuss work that focuses on the electron-stimulated reactions within the H2O/TiO2 system. A discussion of the interactions of H2O with the TiO2(110) surface is presented in Chapter 6. The transition metal oxide surface is comprised of acidic and basic water adsorption sites along with intrinsic surface defects where surface oxygen atoms are missing. These surface defect sites significantly influence the interactions of water with the TiO2 surface and consequently, govern much of the surface chemistry. Studies on electron induced oxidation of the TiO2(110) surface and sputtering of H2O from the TiO 2(110) surface are discussed in Chapter 7 and Chapter 8, respectively. The water interactions with the TiO2 surface are revealed through the strong electron induced reaction dependencies on the amount of water present on the surface. Summarizing remarks and conclusions are presented in Chapter 9. Chapters 5, 7, and 8 represent papers which will be submitted for publication in the open scientific literature.