Oxygen-promoted CD bond formation on a sputtered Ni(111) surface

Abstract

The interaction of carbidic carbon with pure deuterium and with deuterium/oxygen mixtures ( D 2: O 2 = 1:10 −3) on a sputtered unannealed Ni(111) surface was studied using SSIMS, AES and XPS. Negative SSIMS spectra were recorded in situ at 10 −6 Torr of reactant as a function of time and temperature. The results show that in the absence of oxygen, carbidic carbon is not very reactive towards deuterium under the conditions of the experiment. However, when the surface is exposed to a mixture of D 2 and O 2 a partial deuteration of carbidic carbon occurs as evidenced by the behaviour of the C 2D n − secondary ion signal. The extent of deuteration of carbidic carbon on nickel is greater at 298 K than at higher temperatures. The deuteration reaction in the presence of coadsorbed oxygen is accompanied by the formation of adsorbed hydroxyl groups. The latter species are found to be stable on the carbided surface up to a temperature of approximately 470 K in contrast to 420 K for a clean nickel surface. A mechanism is proposed to account for the enhancement of reactivity brought about by coadsorbed oxygen. It is proposed that adsorbed oxygen destabilizes or activates both of the reactants, D ads and carbidic carbon. Coadsorbed OH groups may also play a role in the enhancement mecanism, however we cannot isolate the role of O ads from that of OH ads.