Preparation of Metal Films Containing Nano-Size Channels

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Metallic films prepared by consolidation of ultra-fine particles may contain nano-size pores and channels along the grain boundaries, and they are expected for the application to metallic nano-filters or catalytic materials. In order to prepare the metallic films containing nano-size channels, low-density nanocrysatlline (n-) Au films were prepared by applying the gas-deposition method. The density of n-Au films prepared was about 93 〜 98 % of the bulk Au density and the mean grain size about 10 〜 20 nm. Some of the n-Au films showed gas-permeability of about 10^<-11> mol m/(Pa m^2 s) for helium gas at room temperature, that is larger by mare than two order than those of the plastic films such as the natural rubber. Pore-like dimples with the diameter of 〜 20 nm were found in the STM surface images of n-Au films with the high gas-permeability. The gas-permeability of the n-Au films was decreased in proportional to the square root of the molecular weight of gas. These observations suggest that the gas-permeability of the present n-Au films is due to the channels with the diameter of 〜 20 nm and the area fraction of 〜 1%, where the gas atoms are assumed to permeate the n-Au films as a molecular flow. Further, the n-Au films with the relative density of 〜 95 % showed a high thermal stability, i.e. the mean grain size remained to be about 40 nm after the annealing at 1200 K for 1.8 ks. It suggests that the nano-channels or pores in the specimens play an important role on the high-thermal stability of the present n-Au films