Formation of nitrogen-substituted carbon cluster anions by gas-feed Cs-sputtering from different forms of carbon

Abstract:

We have investigated the mechanism of formation of C_n ^- and C_nN^- cluster anions during Cs⁺-ion sputtering from surfaces of different crystallographic forms of carbon (polycrystalline graphite, amorphous C and C₆₀), in the presence of high purity N₂ or NO₂ gas. The normalised yields of sputter-ejected C_nN^- (n? 10) cluster anions display an oscillatory dependence on n: the odd n clusters being more abundant than the even n ones. Significantly, C_nN^- clusters produced from the three different forms of C, show similar oscillatory variations with n. Moreover, the C_nN^- yields follow a single power law decline as a function of cluster size for all three surfaces sputtered, and over a wide range of operating conditions. This strongly indicates that the intrinsic structure of the ion-induced surface does not play a significant role in the formation of sputtered cluster anions. The observed abundance patterns of C_n ^- and C_nN^- clusters also suggest that mono-nitrogen substitution of the carbon clusters does not allow the chain to ring transformation to occur up to n = 10.