Growth Rate and Cross-Linking Kinetics of Poly(divinyl benzene) Thin Films Formed via Initiated Chemical Vapor Deposition

Initiated chemical vapor deposition (iCVD) allows for the formation of highly cross-linked, polymer thin films on a variety of substrates. Here, we study the impact of substrate stage temperature and filament temperature on the deposition and cross-linking characteristics of iCVD from divinyl benzene. Maintaining a constant monomer surface concentration reveals that deposition rates upward of 15 nm/min can be achieved at substrate stage temperatures of 50 degrees C. The degree of cross-linking is limited by the rate of initiation of the pendant vinyl bonds. At a filament temperature of 200 degrees C, the pendant vinyl bond conversion is highly sensitive to the surface concentration of initiator radicals. A significant decrease of the pendant vinyl bond conversion is observed with increasing stage temperatures. At higher filament temperatures, the pendant vinyl bond conversion appears to plateau at approximately 50%. However, faster deposition rates yield lower conversion. This trade-off is mitigated by increasing the filament temperature to increase initiator radical production. A higher flux of initiator radicals toward the surface at a constant deposition rate increases the rate of initiation of pendant vinyl bonds and therefore their overall conversion. At a deposition rate of similar to 7 nm/min, an increase in the filament temperature from 200 to 240 degrees C results in an 18% increase in the pendant vinyl bond conversion.