THE APPLICATION OF TRANSMISSION ELECTRON-MICROSCOPY TO THE STUDY OF HIGH NUCLEARITY CARBONYL CLUSTERS (HNCCS)

The properties of a variety of HNCC's supported on holey carbon films have been investigated by transmission and analytical electron microscopy; a review of how these techniques can be used to study these crystallographically well-characterized clusters is also presented. Images of the metallic skeleton corresponding to a single cluster unit have been observed for [Ni38Pt6(CO)48H]5-, [Ni34C4(CO)38H]5-, [Pt38(CO)44Hx]2-, [Rh17S2(CO)32]3-, [Ni12Sn(CO)22]2-, and [Ni22Ge(CO)22]2-, and analytical data at low electron beam intensities are consistent with their crystallographically established structures. At increasing current densities, agglomeration into larger particles occurs and these larger particles (2-5 nm) gradually lose the chemical identity of the precursor. Ultimately at current densities of the order of 10(7) A/m2 metal segregation and/or metal alloy particles having close-packed crystal structures are formed together with graphitic carbon from decomposition of the CO ligands. Possible mechanisms for this beam damage are discussed. There is evidence of cluster/substrate interaction resulting in increased stability compared to that observed in solution and in the normal crystalline state.