Morphology Control and Functionalization of Nanoporous Metals

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Nanoporous (np-) Au membranes with nm sized open channels were prepared by both the gas-deposition (GD) method and selective etching (SE) of Ag from a Au-Ag alloy. The gas permeability measurement and surface observations by using STM and SEM indicated that, the diameter and area density of the channel in GD np-Au were a few nm and about a few% and those of SE np-Au about 10〜60 nm and about 20%, respectively. The diameter and area density of the channels could be reduced by uniaxial compression of SE np-Au. The resistivity R of the SE np-Au membrane with the BET surface area of 6.4 m^2/g was as high as about 25 times higher than that of the bulk Au and that with 32 m^2/g about 400 times higher. Further, the resistivity showed an abrupt decrease by about 0.1% when the atmosphere around the membrane was started to expose to the air from vacuum. In contrast, the atmospheric change from vacuum to the air caused an abrupt increase of the resistivity by 0.1%. This resistivity change was much reduced when the SE np-Au was exposed to the dried air. These observations suggest that desorption and absorption of water molecules was detected as the increase and decrease in the resistivity, respectively.