Cleanliness of a clean-unit system platform consisting of multiply connectable clean boxes with feedback loop is studied and the time dependence of particle count is clarified experimentally and theoretically in order to achieve highly clean environment. Based on this analysis, we have demonstrated airborne particle counts as low as 5 particles/ ft 3 for the diameter of 0.1 m, 0.6 particles for 0.2 m, and 0.01 particles for 0.5 m by a reduction of particle density coming out from the in-wall in the system. The clean-unit system with feedback loop can serve as a platform for cross-disciplinary experiments and production for fields such as nanotechnologies and biotechnologies.

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The surface morphology of gold thin films deposited on poly(ethylene naphtalate) (PEN) organic films has been investigated for quantum cross devices. The surface roughness of gold thin films on the PEN films is 1.5–1.9 nm and the appearance of mound structures is observed. The mound grain sizes are 28.0±4.6 nm for 5-nm-thick gold films and 45.8±5.8 nm for 10-nm-thick gold films. From the result of the scaling investigation of the surface roughness, the surface roughness of 5-nm-thick gold films is 0.22 nm, corresponding to one atomic size, in the scanning scale of 5 nm. These experimental results indicate that gold thin films on PEN films are suitable for use in quantum cross devices, and may open up a novel research field on the electric characteristics of quantum cross devices using a few atoms or molecules leading to high-density memories.

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