Electron spectroscopic study of nitrogen species adsorbed on copper

Abstract

The interaction of a number of nitrogen containing molecules (NO, NH₃ and N₂H₄) with copper has been investigated by electron spectroscopy. Nitric oxide is shown to be molecularly adsorbed in a linearly bonded configuration at 85 K; this adlayer is unstable above 120 K, resulting in an exclusively oxygen adlayer at 295 K, the nitrogen being desorbed. At 85 K N(1s) peaks observed at 401 and 406 eV are associated with NO^δ–(ads) and NO^δ+(ads) species, the former dissociating and the latter desorbing on thermal activation of the adlayer.

Interaction of nitric oxide with Cu at 295 K results in dissociative chemisorption with both oxygen and nitrogen retained at the surface. The surface concentration suggests that each nitrogen and oxygen adatom is bridge-bonded to two surface copper atoms. Estimates of absolute surface coverages are made by comparing the intensities of the N(1s) and O(1s) peaks with the Cu(2p) substrate intensity, while valence level spectroscopy (He I and II radiation) supplements core-level spectroscopy for discriminating between molecular and dissociated surface species.

Ammonia dissociates at 295 K on copper while with oxidized copper the surface oxide is replaced by an imide-type surface. With hydrazine, adsorption is molecular over the temperature range 85 to 295 K, in contrast to our observations with iron.