No abstract

Here we report on the vapor deposition polymerization of polybenzoxazole precursors. 3,3‘-Dihydroxybenzidine and pyromellitic dianhydride were codeposited onto flat substrates to form poly(amic acid) films. As-deposited films contained poly(amic acid) species as well as unreacted dianhydride and diamine reactants. Quality films were obtained when reactant fluxes were well balanced. Coatings were cured under inert gas conditions and resulted in the conversion to polyimides (150−250 °C) and, at higher temperatures (500−550 °C), to semiaromatic polybenzoxazoles. Physical and chemical changes occurring during the curing process were studied with FT-IR, TGA, and nanoindentation experiments. The fully cured material is brittle and hard, and for thin films (<1 μm), films do not delaminate from glass substrates. Nanoindentation studies of both solution-prepared and vapor-deposited PBO precursors revealed that the elastic modulus improved upon conversion to the imide and benzoxazole forms, and polyimide showed the highest hardness value compared with poly(amic acid) and PBO.

This study examines the use of a nonreactive solvent vapor, tert-butanol, during initiated chemical vapor deposition (iCVD) to promote polymer film dewetting. iCVD is a solventless technique to grow polymer thin films directly from gas phase feeds. Using a custom-built axisymmetric hot-zone reactor, smooth poly(methyl methacrylate) films are grown from methyl methacrylate (MMA) and tert-butyl peroxide (TBPO). When solvent vapor is used, nonequilibrium dewetted structures comprising of randomly distributed polymer droplets are observed. The length scale of observed topographies, determined using power spectral density (PSD) analysis, ranges from 5 to 100 microm and is influenced by deposition conditions, especially the carrier gas and solvent vapor flow rates. The use of a carrier gas leads to faster deposition rates and suppresses thin film dewetting. The use of solvent vapor promotes dewetting and leads to larger length scales of the dewetted features. Control over lateral length scale is demonstrated by preparation of hierarchal "bump on bump" topographies. Vapor-induced dewetting is demonstrated on silicon wafer substrate with a native oxide layer and also on hydrophobically modified substrate prepared using silane coupling. Autophobic dewetting of PMMA from SiOx/Si during iCVD is attributed to a thin film instability driven by both long-range van der Waals forces and short-range polar interactions.

A vapor deposition polymerization technique is applied to grow composite films containing polyimide and copper phthalocyanine (CuPc). Specifically, 4,4(-oxydianiline and 3,3(,4,4(-biphenyl tetracarboxylic dianhydride are co-evaporated in the presence of CuPc. Spectroscopy experiments confirm the formation of polyimide segments and suggest that embedded CuPc molecules have less mobility than pure CuPc films. Electron microscopy and X-ray diffraction (XRD) studies show that the majority of CuPc initially assumes an amorphous phase. Upon curing, partial crystallization of CuPc occurs, forming small crystals (a phase) that are suspended in a polyimide matrix. These crystals exhibit enhanced thermal stability compared to pure vapor-deposited CuPc.