Theoretical investigation of small lathanum carbide clusters

LaC2+, LaC22+, LaC3 and LaC3- clusters have been studied using B3LYP density functional method. Four isomers with C-2v, C-s, C-infinity v and D-infinity h symmetry were presented for LaC2+ and LaC22+. Meanwhile, two spin states, namely, singlet and triplet for LaC2+, doublet and quartet for LaC22+ were considered The results indicated that ring isomers with C-2v and C-s symmetry are the most stable for La-C2(+) at both spin states and for LaC22+ at quartet state. Whereas for LaC22+ at doublet state, linear isomer with C-infinity v symmetry is energetically favored, For LaC3 and LaC3- clusters,, three isomers have been presented for each cluster, that is, two ring isomers with C-2v symmetry ( in one of them, La forms two single bonds with two carbons, and in another, La forms a double bond with carbon), and one linear isomer with C-infinity v symmetry. The results revealed that the ring isomer in which La forms two single bonds with carbons is the lowest in energy.

Ab initio study of C-9 and LaC9+ clusters

The energies and geometries of C-9 and LaC9+ clusters were calculated at HF, MP2 and DFT levels. For C-9, all theoretical levels show that the linear chain is the most stable structure. For LaC9+, two isomers were considered. In the first case La has two single bonds (A), while it forms a double bond in the second (B). Our results showed that in HF calculation, B is marginally more stable than A, while for MP2 and DFT, A is favored. Our results also revealed that there is not enough space for C-9 ring to accommodate lanthanum. Our conclusion agrees well with experiment.

Controlled growth of uniform silver clusters on HOPG

We have investigated growth of silver clusters on three different, i.e. normally cleaved, thermally oxidized and Ar+ ion sputtered highly oriented pyrolytic graphite (HOPG), surfaces. Scanning tunneling microscopy (STM) observations reveal that uniformly sized and spaced Ag clusters only form on the sputtered surface. Ar+ sputtering introduces relatively uniform surface defects compared to other methods. These defects are found to serve as preferential sites for Ag cluster nucleation, which leads to the formation of uniform clusters. (c) 2005 Elsevier B.V. All rights reserved.