The surface chemistry of methyl and methylene radicals adsorbed on Cu(111)

The interactions of methyl and methylene radicals on Cu(1 1 1) were investi gated with XPS, AES and HREELS under various exposure conditions. The CH2 a nd CH3 radicals are generated through a hot nozzle source with ketene and a zomethane gases. It is shown that with substrate at 300 K, the impinging CH 3 radicals are trapped mainly as CH3(ads), while a part of the adsorbate de composes to form CH2(ads) and H(ads). H atoms are found to desorb at about 380 K, while the chemisorbed hydrocarbon adspecies desorb at about 420 K. I n drastic contrast, exposing the clean Cu surface to methylene radicals res ults nor only in the trapping of CH2(ads), but also in the formation of com plex aromatic species. The adlayer is sensitive to annealing at elevated te mperatures, Desorption and partial conversion to methylidyne take place at around 420 K. The CH(ads) species can survive up to 700 K and then decompos es to form residual carbon above 800 K, In both radical-Cu(lll) systems, su rface coverage appears to saturate near one monolayer. The relative concent rations of different surface species in the adlayer, however, depend on the amount of radical exposure. The reaction properties of the two systems are compared and discussed. (C) 1999 Elsevier Science B.V. All rights reserved .