Glow-Discharge-Induced Sublimation of Polyimide Precursor Monomers: A Systematic Study

Glow-discharge-induced sublimation (GDS) is used to deposit thin films of polyimide precursor monomers, i.e., 2,4,6trimethyl m-phenylenediamine (TMPD), 4,4ʹ-hexafluoroisopropylidene dianiline (6FDAm), 3,3ʹ-diaminodiphenyl sulfone (DDS), 4,4ʹ-hexafluoroisopropylidene diphthalic anhydride (6FDA), and 3,3ʹ,4,4ʹ-biphenyltetracarboxylic acid dianhydride (BPDA). Monomer films are also deposited by vacuum evaporation (VE) for the sake of comparison. In situ mass spectrometry points out both the sublimation of integer monomer molecules and the presence of molecular fragments in the glow discharge. AFM images of the film surfaces indicate that GDS allows obtention of smoother surfaces with respect to VE for most of the monomers. FT-IR analysis and UV-Vis fluorescence spectroscopy show that the deposition of integer monomer molecules onto the substrate and the partial incorporation of molecular fragments take place. In particular, the fluorescence features of GDS samples are different from those of VE samples and depend on the incorporated molecular fragments whose optical properties are similar to those of amorphous hydrogenated carbon structures.