Transmission Electron Microscopy of Granular Nickel/SiO2 Cermet Films

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Abstract
Granular nickel films have been prepared by co-sputtering nickel and silica onto glass substrates at room temperature. Seven films of (Ni)1−x(SiO2)x, where x is the volume fraction of silica, were examined by transmission electron microscopy. For all samples, the microstructure consisted of nickel grains embedded in a matrix of silica. The grain size is observed to decrease linearly with x; the distribution of grain sizes varies from 170 to 310 Å for x≃0.1 and from 40 to 55 Å for x≃0.75. The thickness of the intergranular silica is about 22 Å and is independent of composition. The nickel lattice is observed to expand with increasing x; the fractional expansion is inversely proportional to grain size and attains values as large as 10% for large x. These results will prove useful in the interpretation of the magnetic, electrical, and optical properties of granular metal films. In particular, these results have been applied to the interpretation of the depression in magnetic Curie temperature observed in the (Ni)1−x(SiO2)x system.