Ni-NiO core-shell nanoclusters with cubic shape by nanocluster beam deposition

Ni nanoclusters with cubic shape and uniform size below 10 nm were fabricated by nanocluster beam deposition. Ni-NiO core-shell structure was achieved when the Ni clusters flew through a chamber with constant oxygen feeding (1-3 SCCM, SCCM denotes cubic centimeter per minute at STP). The fraction of oxidized Ni was estimated by means of linear combination fitting to the x-ray absorption near-edge structure data. The hysteresis loop of the oxidized sample (1 SCCM O2) showed a shift of ∼181 Oe with 100 Oe field cooling from 400 K and a coercivity of 48 Oe at room temperature, while the nonoxidized Ni nanoclusters with size of 4-5 nm showed superparamagnetic behavior.