2009 Volume 50 Issue 3 Pages 523-527
Ti clusters have been prepared by a plasma-gas-condensation cluster deposition system (PGCCD) with controlling an Ar gas flow rate, RAr and a He gas flow rate, RHe, and observed by transmission electron microscopy (TEM) at their as-prepared and annealed states. In Ti clusters whose sizes are about 18 nm, an hcp phase is predominant in the as-prepared state, while TiOX crystallites are formed on the hcp phase cores after annealed at 623 K, revealing a core-shell morphology. In small Ti clusters whose sizes are about 10 nm, an fcc phase coexists with the TiOX phase in the as-prepared state, while the TiOX phase is predominant after annealed at 623 K, revealing no core-shell morphology. The electrical resistivity, ρ, of these cluster assemblies increases with decreasing temperature. After annealed at 623 K, the absolute ρ value of hcp Ti cluster assemblies increases remarkably while that of fcc cluster assemblies does not change so much. These results demonstrate the difference in the oxidation behaviors and morphologies between large and small Ti clusters.