Formation of Ni/SiO₂ and Ag/SiO₂ Nanosphere Composites

Abstract

SiO₂ nanospheres have been produced via a high temperature evaporation process and they have been Ni or Ag plated using electroless plating solutions. These samples were examined by Atomic Force Microscopy (AFM) and Magnetic Resonance (MR). The initial SiO₂ nanospheres were about 30 nm in diameter, and the Ni plating layer resulted in a 25nm thick metallic Ni coverage, while the Ag coverage was estimated to be in the 150 nm range. In the case of the Ni/SiO₂ nanosphere composites, the MR signals show the presence of Ni⁺² and Ni⁺³ paramagnetic centers, seen below 40K, and ferromagnetic metallic Ni, which is seen above 40K. The dried Ni plating solution (with no SiO₂) shows only the presence of paramagnetic Ni⁺³. These results suggest that an interfacial reaction at the surface of the SiO₂ nanospheres leads to the formation of ferromagnetic Ni, which deposits onto the spheres and forms a ferromagnetic Ni/SiO₂ nanosphere composite. In the case of the Ag/SiO₂ nanosphere composites, no MR signal is seen from the non-magnetic Ag, but strong paramagnetic behavior has been noted for Co⁺², which originates from the plating solution.