Photodissociation of Metal−Silicon Clusters:  Encapsulated versus Surface-Bound Metal

Abstract

Metal-silicon cluster cations of the form MSi(n)+ (M = Cu, Ag, Cr) are produced in a molecular beam with pulsed laser vaporization. These species are mass-selected in a reflectron time-of-flight spectrometer and studied with laser photodissociation at 532 and 355 nm. For the noble metals copper and silver, photodissociation of the n = 7 and 10 clusters proceeds primarily by the loss of metal atoms, indicating that the metal is not located within the interior of silicon cages, and that metal-silicon bonding is weaker than silicon-silicon bonding. Chromium-silicon clusters for n = 7 also lose primarily the metal atom, but at n = 15 and 16 these dissociate via the loss of silicon, producing smaller metal-silicon species. This behavior is consistent with stronger metal-silicon bonding and encapsulated metal structures, as suggested previously by theory. MSi6(+) cations are produced efficiently in all of these photodissociation processes, indicating that these species have enhanced stability compared to other small clusters. Improved values are obtained for the ionization potentials of Si7 and Si10.

The Geometric Structure of Silver‐Doped Silicon Clusters

“…As the ionization energy of Sin [42,43] clusters decreases with cluster size, D1 becomes smaller than D2 for larger sizes and the clusters prefer to dissociate by loss of a neutral dopant atom. Photodissociation data of Si7Ag + and Si10Ag + obtained by Jaeger et al [30] indicate that the preferred dissociation channel of these sizes is via the loss of a neutral Ag atom, in disagreement with the results in Figure 5. The calculated energy difference between D1 and D2 is, however, small for these sizes.…”

“…[26] Experimentally, Jaeger et al found that photodissociation of SinAg + (n = 7 and 10) clusters proceeds primarily by the loss of metal atoms, indicating that silver−silicon bonds in the cluster are weaker than the silicon−silicon bonds. [30] Chuang et al predicted by first−principles calculations that SinAg clusters (n = 1−13) are all exohedral with the Ag atom capping the pure Sin clusters. [31] Another computational study of geometries and electronic properties of SinAg (n = 1−15) clusters has been carried out by D. H. Ziella et al [32] In contrast to the work of Chuang et al, they found endohedral geometries for SinAg with n > 10.…”

Theoretical study of isoelectronicSinMclusters (M=Sc−,TiTorres1, Fernández2, Balbás3 2007Phys. Rev. B1095631View full textAdd to dashboardCite

“…These predictions were later confirmed indirectly by experiments. Thus, experiments on photodissociation of MSi n clusters 26 indicate that, for M = Cr, encapsulation of Cr occurs at n = 15-16. A mass spectrometric stability study of binary MS n clusters, 27 with S = Si, Ge, Sn, Pb, and M = Cr, Mn, Cu, Zn, reveals interesting trends.…”

Structural Identification of Caged Vanadium Doped Silicon Clusters

“…However, if there are insufficient Si atoms to fully enclose the dopant atom, basketlike structures are formed [11]. Although mass spectrometry and photodissociation experiments [8,[16][17][18][19] show an enhanced stability of specific transition-metal doped silicon clusters, no single experiment has yet provided detailed information on their structure. Up to now, mainly indirect evidence is found for the formation of symmetric species by photoelectron and x-ray spectroscopy studies [20][21][22] and chemical probe methods [20,23].…”