We describe the technique used to manufacture a submicron aperture in a nickel microfoil used to look for the Josephson effect in superfluids. The size requirements for a superfluid weak link are briefly discussed. The micromachining is performed by means of a focused Ga ion beam. The ion probe is produced by a liquid-metal-ion source that is known to act as a near pointlike source. The source, optical lens, and deflection assembly are lumped as an attachment to a commercial scanning electron microscope. The obtained machining capabilities and scanning ion images are compatible with a probe size of 150–200 nm, a size that corresponds to our theoretical estimates.
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Sudraud et al. (1987) studied this question.
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