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Interaction of Energetic Hydrogen and Deuterium and Lithium Film and NI(110)

Speaker: Yuxin Yang
Series: Final Public Oral Examinations
Location: Lapidus Lounge (E-Quad A210)
Date/Time: Tuesday, September 18, 2018, 2:00 p.m. - 3:30 p.m.

This dissertation presents fundamental surface science studies examining the interaction of energetic hydrogen and deuterium (H/D) species with surfaces related to two applications: plasma-surface interactions in nuclear fusion experiments and plasma-catalytic dry reforming.

Interaction of energetic H/D species with lithium (Li) as a plasma facing component was investigated. The ability of Li and lithium oxide (Li-O) films to retain hydrogen (H) ions was examined at different temperatures. For both films, the total retention dropped with surface temperature, from 95% at 90 K to 35% at 520 K. The sputtering yields of deuterium (D) ions (400-1600 eV D2+) on Li, Li-O and composite Li-C-O films were measured to be around 0.1-0.3, in good agreement with previous simulations and bulk erosion measurements. D retention in pure Li, Li-O and Li-C-O films was also studied as a function of time after these films were exposed to D2+ ion irradiation. The amount of D retained in both Li and Li-O films at 300 K decreased at the same rate by 45% after 16 hours, while the amount of D retained in Li-C-O film was found to be independent of time up to 3 days.

The unique chemistry of energetic H/D species in plasma-catalysis was investigated. The uptake and subsequent thermal desorption of D on a Ni(110) surface were measured using incident gaseous D2 molecules, D atoms, and D2+ ions. Molecular D2 exposures on Ni(110) at 90 K form adsorbed D adatoms at the surface, but do not populate subsurface D binding states under ultrahigh vacuum (UHV) conditions. In contrast, such subsurface states on Ni(110) are readily populated at 90 K by incident D atoms and D2+ ions. Surface-bound D adatoms did not react with coadsorbed CO to form formaldehyde (CD2O) and methanol (CD3OD) in TPD measurements. In contrast, subsurface D formed by incident D atoms can hydrogenate post-adsorbed CO in subsequent TPD measurements to form CD2O and CD3OD. Incident D atoms and D2+ ions were less reactive than subsurface D for the hydrogenation of CO on the Ni(110) surface.