Grazing Incidence X-ray Scattering Studies of Thin Films of an Aromatic Polyimide

Abstract

We report grazing incidence X-ray scattering measurements of the near surface structure of an aromatic polyimide, poly(pyromellitic dianhydride-oxydianiline) (PMDA-ODA). The structure parallel to the film surface was investigated as a function of thermal treatment and film thickness. By variation of the X-ray incidence angle, the X-ray penetration into the polymer was changed from ∼50 Å (surface sensitive) to the polymer film thickness, and the PMDA-ODA structure was studied as a function of this penetration depth. For thick films (≃2500 Å), we found that near the air surface the PMDA-ODA was more ordered than in the bulk of the specimen, and for thermal treatments above 300 °C, a crystalline-like ordering was observed. In the near surface region the PMDA-ODA molecules locally assumed a more planar zigzag conformation. However, the interchain packing, i.e., the coherence of order normal to the chain axis, was markedly improved. Studies of 100-Å-thick films showed that these had a crystalline-like structure comparable to that seen near the surface of the thick films. Investigations were also performed on films ∼400 Å thick where the structure near the air and substrate interfaces could be assessed. While crystalline-like ordering was found near the air surface, no such ordering was evident near the substrate interface. © 1993, American Chemical Society. All rights reserved.