Platinum Metals Rev., 1996, 40, (1), 25
Platinum Nanochannel Replica Membranes
Nanoscale materials are widely used in electronic and optical devices, and for filtration and biological applications; so there is clearly a need for suitable production and patterning techniques, and some have been discussed here before, Platinum Metals Rev., 1993, 37, (2), 101.
Researchers at the Naval Research Laboratory, Washington D.C., U.S.A., now report the preparation of thin platinum membranes using nanochannel glass replica membrane technology (D. H. Pearson and R. J. Tonucci, Science, 1995, 270, (5233),68–70).
The thin membranes produced, which can be fabricated from platinum, gold, tungsten and molybdenum, contain uniform, nanometre-scale, patterned voids. The metal membranes are formed on nanochannel glass (NCG) wafer substrates. The NCG material is fabricated by a draw process similar to the preparation of optical fibres and the fibres are packed together in a hexagonal close-packed arrangement. The fibres are then repacked and redrawn to achieve the desired packing density and element size, made into wafers, polished and etched. Other packing schemes enable more complex void patterns to be achieved.
The usual deposition techniques are employed to deposit an easily dissolved buffer layer of aluminium onto the NCG, followed by a 75 nm thick layer of platinum by magnetron sputtering. The buffer layer is dissolved in sodium hydroxide and the platinum replica membrane floated off. Thin platinum membranes having a uniform, hexagonal pattern of voids as small as 40 nm in diameter, and possibly less, have been formed. The membranes, displaying good mechanical properties, can be used as masks in pattern deposition onto substrates. This method is said to be an improvement on the usual lithographic techniques and involves fewer steps.