Figure 2.

Dense line array with a period of (a) 100 nm; (b) 30 nm; (c) 25 nm; and (d) 20 nm. The polystyrene resist was exposed at 5 keV and developed using xylene for 1.5 min at room temperature. The pattern heights measured by AFM are in the range of 25-28 nm that is close to the original film thickness.