Perfluorooctane Sulfonyl Fluoride as an Initiator in Hot-Filament Chemical Vapor Deposition of Fluorocarbon Thin Films

Abstract

We have demonstrated the successful use of an initiator species in hot-filament chemical vapor deposition (HFCVD) of poly(tetrafluoroethylene) thin films from the precursor hexafluoropropylene oxide (HFPO). The introduction of perfluorooctane sulfonyl fluoride (PFOSF) in small concentrations allows the enhancement of deposition rates and increased control over film composition. Endcapping by CF3 groups is possible, which may provide benefits such as enhanced thermal stability and higher hydrophobicity for HFCVD films. Conversion of the PFOSF is high, and HFPO utilization efficiency can be increased significantly. The generation of an initiator radical via the pyrolysis of PFOSF may contribute to enhanced nucleation rates during film growth. Initiation and/or nucleation is rate-limiting at low filament temperatures, and mass transport limitations dominate at higher filament temperatures.

25th Anniversary Article: CVD Polymers: A New Paradigm for Surface Modifi cation and Device Fabrication

“…In analogy to solution‐phase synthesis, the iCVD initiator decomposes to form radical species (Figure 1b) that then activate the chain growth polymerization of the monomers. Initiators successful used for iCVD include perfluorooctane sulfonyl fluoride (PFOS),50 perfluoro‐1‐butanesulfonyl fluoride (PBSF),51 triethylamine (TEA),52 tert‐butyl peroxide (TBPO),53 tert‐amyl peroxide (TAPO),54 and tert‐butyl peroxybenzoate (TBPOP) 55. These initiators contain a labile bond, such as the O‐O bond in peroxides, which can be readily cleaved.…”

“…On the contrary, a structure exclusively made of CF 2 repeating units was successfully obtained by HWCVD176 and iCVD50 at much higher growth rates. HWCVD can be considered as the ancestor of iCVD: it takes place in a similar reactor configuration and the chemical species are thermally broken by a filament.…”

“…PTFE has been also obtained through iCVD, using the initiator perfluorooctane sulfonyl fluoride (PFOS) 50. Thermal decomposition of the PFOS over the heated nichrome filament, produced·(CF 2 ) 7 CF 3 initiating radicals.…”

“…Several generations of graduate students and postdoctoral researchers contributed to the development of these technologies for CVD polymerization and only a few highlights will be mentioned. A separate intentional initiation species was first introduced by doctoral student Hilton Pryce Lewis in 2001,50 yielding a dramatic increase in deposition rate. As CEO of GVD Corporation (gvdcorp.com), Dr. Pryce Lewis has led the scale up, automation, and commercialization of HWCVD and iCVD polymers.…”

Tunable polytetrafluoroethylene electret films with extraordinary charge stability synthesized by initiated chemical vapor deposition for organic electronics applications

“…This technique is known to preserve the original polymer functionality and to maintain a low substrate temperature, due to its mild deposition conditions 19,20 , allowing thus the deposition on flexible organic susbtrates. The iCVD process is already well established for PTFE thin film deposition 21–23 . The technique does not involve any organic solvents, because the thin film is directly polymerized by a free radical polymerization on a substrate, which is cooled to room temperature.…”