INTERACTIONS OF ENERGETIC HYDROGEN AND DEUTERIUM WITH LITHIUM FILMS AND NICKEL (110)

Abstract

Interactions of incident energetic hydrogen (H) and deuterium (D) species (ions and atoms) with surfaces plays a crucial role in a wide range of fields, including plasma-surface interactions in nuclear fusion experiments, plasma-enhanced catalysis, plasma processing of semiconductors, dangling bond passivation, and interstellar molecular hydrogen production. This dissertation presents fundamental surface science studies examining the interactions of energetic H/D species with surfaces related to two applications: plasma-surface interactions of lithium films utilized in nuclear fusion experiments and plasma-enhanced catalysis of dry reforming.

Interactions of energetic H/D species with lithium (Li) films, of interest as coatings for plasma-facing components in nuclear fusion experiments, was investigated. The ability of Li and lithium oxide (Li-O) films to retain H (from irradiation using 500 eV H2+) was examined over a temperature range of 90-520 K. For both types of films, the total H retention dropped with increasing surface temperature, from 95% at 90 K to 35% at 520 K. The sputtering yields of D ions (from irradiation using 400-1600 eV D2+) on Li, Li-O and composite Li-C-O films were measured to be ~ 0.1-0.3, in good agreement with previous simulations and bulk erosion measurements. The time dependence of D retention in pure Li, Li-O and Li-C-O films was also studied after these films were irradiated by 450 eV D2+ ions. The amount of D retained in both Li and Li-O films at 300 K decreased at the same rate, i.e. by 45% after 16 hours, while the amount of D retained in the Li-C-O film was found to be independent of time for up to three days.

The unique chemistry at metal surfaces of energetic H/D species that are present in plasma-enhanced catalysis was investigated. The D uptake and subsequent thermal desorption of D2 from a Ni(110) single crystal surface were measured using incident gaseous D2 molecules, D atoms, and D2+ ions. Molecular D2 exposures on Ni(110) at 90 K formed D adatoms at the surface, and did not populate subsurface D binding states under ultrahigh vacuum (UHV) conditions. In contrast, such subsurface states of Ni(110) are readily populated at 90 K by incident D atoms and D2+ ions. The reactivity of these various sorbed D states was also studied for the hydrogenation of subsequently adsorbed carbon monoxide (CO) on Ni(110) over the temperature range of 100 – 600 K under UHV conditions using preadsorbed surface D and subsurface D. Related experiments were conducted using D atoms and D2+ ions incident on preadsorbed CO. Surface-bound D adatoms did not react with coadsorbed CO in temperature programmed desorption (TPD) measurements. In contrast, subsurface D formed by incident D atoms or D2+ ions can hydrogenate post-adsorbed CO in subsequent TPD measurements to form formaldehyde (CD2O) and methanol (CD3OD). D atoms and D2+ ions incident on preadsorbed CO were less reactive than subsurface D for the hydrogenation of CO on the Ni(110) surface.