Si wafers were pre-treated with UV-ozone for 5 min. Films were spin coated at 1000-5000 rpm and annealed at 250 ˚C for 10-15 min, depending on target thickness. For sequential applications of polymer film, the native polymer film was removed with 3 rounds of sonication in NMP for 5 min and the remaining polymer monolayer was annealed at 250 ˚C for 5 min. The subsequent polymer film was then spin coated and annealed at the desired thickness.