Sputter deposition was performed in a Leybold Univex sputter system with a base pressure of 1 × 10 -7 mbar. PTFE and Sigracet substrates were sputtered in direct current (DC) magnetron mode from a 4inch in diameter Ag target at a process pressure of 2 µbar, in Ar atmosphere. The sputter power was set to 120 W, yielding a deposition rate of 2.3 nm/s. The sputter deposition rates were determined by a surface profilometer (KLA-Tencor, Alpha-Step IQ), measuring the step height.