A bulk BCP solution with a concentration of 2 wt% in toluene was used to prepare solutions with concentrations ranging from 0.6 wt% to 1.4 wt%. BCP thin films with thicknesses between 20 to 33 nm were prepared by spin casting 25 μl of the desired polymer solution as shown in Figure on piranha solution-cleaned Si chips at 8500 rpm for 40 s with a WS WS-400BZ-6NPP/120 LITE spin-coater (Laurell Technologies Corporation). The initial film thickness was measured by ellipsometry and is the average of ellipsometric measurements taken at 5 different points on the chip. The variation of thickness with the concentration of the BCP solution is shown in the Figure .