An equilibrium model for agglomeration in polycrystalline thin films which considers the energy balance between the grain boundary energy and both surface and substrate interface energies is presented. It predicts that small grain size, low grain boundary energy, and high film surface and interface energies should promote resistance to agglomeration, and shows that the substrate-film interface can play a significant role in the process. It also predicts a critical grain size limiting formation of a discontinuous island structure. This easily calculable value is significantly smaller than that found in previous modeling. The critical grain size, the importance of the substrate interface, and some of the assumptions are shown to be consistent with transmission microscope observations of TiSi2 thin films deposited on Si substrates.
The activation volume, Vact, and the physical grain volume, VTEM, have been investigated on identical structures of exchange coupled composite media with three different contents of silicon dioxide (SiO2) utilised for intergranular exchange decoupling. Time dependence measurements known as the waiting time method have been used to determine Vact. Transmission Electron Microscopy analysis has been carried out to investigate the grain size distribution and the composition distribution at the grain boundaries using bright field high resolution-scanning transmission electron microscopy (BF HR-STEM) and high angle annular dark-field (HAADF) modes. We found that Vact and VTEM decrease as the oxide content is increased. The activation volume and the single grain volume are in excellent agreement for the samples with the highest oxide content indicating complete exchange decoupling. The BF HR-STEM and HAADF STEM images indicate excellent SiO2 segregation at the grain boundaries. This result implies that the activation volume in advanced recording media can be estimated via the correlation to the grain size.
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