Peculiar sponge-like structure of yttrium-iron-garnet nanocrystals on quartz substrate surface

Nanoscale amorphous yttrium-iron-garnet (YIG) particles were prepared by th e alkoxide method. They were dispersed in a kerosene solvent, coated on a q uartz plate substrate, and calcined at a temperature of 1273 K for 2 h. Sur face morphology and cross-sectional microstructure of the thin coated films were examined by atomic force microscopy and transmission electron microsc opy, respectively. During the calcination, amorphous YIG particles were tra nsformed to YIG nanocrystals of approximate to 25 nm in mean diameter, and no extended grain growth or fusion of the multigrains was observed. Each pa rticle was individually crystallized, but interconnected to each other, for ming a sponge-like structure of 600 nm in thickness. Electron diffraction a nd energy dispersion x-ray analysis verified that the sponge-like layer con sisted of YIG nanocrystalline particles. A rather dense intermediate layer of approximate to 100 nm in thickness was formed as a result of interfacial reactions between YIG and SiO2 decomposing to alpha-Fe2O3 and Y2Si2O7. The change in the Si concentration across the interlayer depth was modeled by thermal diffusion. This peculiar sponge-like structure of YIG nanoparticles supports our previous interpretation of the shift of the light absorption spectral peak, i.e., due to this peculiar structure, electrons are localize d in each YIG particle, which act as a quantum dot, attributing to the quan tum size effect observed in the spectral shift. (C) 1999 American Institute of Physics. [S0021-8979(99)09922-3].