Silicon wafers at sub-jim separation for confined ⁴He experiments

We have successfully achieved a uniform sub-pm gap between two flat silicon surfaces. This is done using two 2 diameter, 0.010 thick silicon wafers, one of which has a small central hole used later for experiments with liquid *He. The other wafer has a Si0₂ pattern made lithographically. The two wafers are bonded together using direct wafer bonding and the uniformity of spacing is found to be better than 1% from IR interference experiments.