Characterization of Magnetic Ni Clusters on Graphene Scaffold after High Vacuum Annealing

TL;DR

This study investigates the stability and chemical changes of magnetic nickel nanoclusters on graphene after high vacuum annealing, revealing their reduction and enhanced stability against oxidation.

Contribution

It demonstrates that nickel nanoclusters on graphene can be reduced and stabilized through high vacuum annealing at relatively low temperatures.

Findings

Nickel nanoparticles oxidize quickly in ambient conditions to form nickel oxide.

High vacuum annealing at 300°C reduces nickel oxide to metallic nickel.

Annealed clusters remain stable with no further oxidation after three weeks in air.

Abstract

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.