Silicon clusters: chemistry and structure

Nanosurface Chemistry on Size-Selected Silicon Clusters

“…When bulk silicon is heated, atoms evaporate from the surface. Silicon clusters behave very differently; instead of evaporating individual atoms, units of six or ten atoms evaporate (12,13). Thus, for example, Si& dissociates to yield mainly Si& and Si, (13).…”

“…With oxygen the umeactive clusters are those with 13 and 14 atoms. Clusters with 11,13,14,19, and 23 atoms are particularly unreactive toward water. Clusters with 13, 14, and 23 atoms are also particularly unreactive toward ethylene (7,9).…”

“…At temperatures around 400 K an equilibrium, can be established. From measurements of the equilibrium constants as a function of temperature, binding energies of ammonia to the silicon clusters were determined (13). The binding energies are -1 eV.…”

“…At temperatures above 500 K another process, resulting in ammonia more strongly bound to the cluster surface, becomes important. This process presumably results in dissociative chernisorption of ammonia (13). Both molecular adsorption and dissociative chemisorption yield Si,ND: products which cannot be distinguished by simple mass spectrometry alone.…”

“…7. Rate constants for dissociative chemisorption of ammonia on sizeselected silicon cluster ions at 700 K [data from (13)l. The dashed line shows the reactivity of the S i ( l l 1 ) -( 7~ 7) surface toward ammonia at 700 K (34).…”