Viscoelastic Properties of Polymers

The attractiveness of hot embossing lithography (HEL) also known as nanoimprint lithog-raphy (NIL) as nanofabrication technique is mainly founded on its simplicity. This lithog-raphy already apparent in the works of S. Chou, 1, 2, 3 who demonstrated that features of a few ten’s of nanometers can be imprinted with a standard laboratory press. The lithog-raphy of embossing reach back into history and are applied today in the production of numerous products, in particular a broad variety of materials is presently micro-moulded in micro-system technology. 4 Although earlier attempts to modify polymer surfaces on a nanometer scale were reported, 5, 6, 7, 8 the work of S. Chou certainly has stimulated the interest of the nanofabrication community, since expectations were raised, that a low cost nanofabrication technique was at hand. Since then, a number of technical realisations and variations to the process have been developed, which are reviewed in considerable detail. 9 Most of them share a common principle: a pattern is transferred into a fluid layer by embossing the mould into it. Usually a thin polymer layer spun on a silicon substrate is moulded by a sequence of steps, which are schematically depicted in Figure 1.