FORMATION OF Ni/SiO_2 AND Ag/SiO_2 NANOSPHERE COMPOSITES

摘要

SiO_2 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 SiO_2 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/SiO_2 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 SiO_2) shows only the presence of paramagnetic Ni~(+3). These results suggest that an interfacial reaction at the surface of the SiO_2 nanospheres leads to the formation of ferromagnetic Ni, which deposits onto the spheres and forms a ferromagnetic Ni/SiO_2 nanosphere composite. In the case of the Ag/SiO_2 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.