  Magnetic Ni nanoclusters were synthesized by electron beam deposition
utilizing CVD graphene as a scaffold. The subsequent clusters were subjected to
high vacuum (5-8 x10-7 torr) annealing between 300 and 600 0C. The chemical
stability, optical and morphological changes were characterized by X-ray
photoemission microscopy, Raman spectroscopy, atomic force microscopy and
magnetic measurement. Under ambient exposure, nickel nanoparticles was observed
to be oxidized quickly, forming antiferromagnetic nickel oxide. Here, we report
that the majority of the oxidized nickel is in non-stoichiometric form and can
be reduced under high vacuum at temperature as low as 300 0C. Importantly, the
resulting annealed clusters are relatively stable and no further oxidation was
detectable after three weeks of air exposure at room temperature.
