Surface characterization of clean polyimide films by high‐resolution electron energy‐loss spectroscopy

The first high‐resolution (≂10 meV, full width at half‐maximum of the elastic peak) electron energy‐loss spectra from surfaces of clean polyimide thin films are presented and discussed. Changes in the polymer surface composition are recorded after heating in vacuo: curing at T≂500 K for 1 h is necessary to desorb water from the surface and recrystallize the polymer material. A dozen vibrational bands are then clearly resolved, most of them being assigned, with the help of infrared data, to phenyl, carbonyl, CN, and COC species. Low‐energy bands at 410 and 175 cm−1 are tentatively assigned to collective modes of the almost crystalline material. Electron induced vibrational spectra collected in different geometries or with different electron impact energies show mainly modification of the phenyl vibrational bands; information on surface sites and surface structure is deduced. Finally, electronic transitions between 4 and 10 eV and secondary electron emission are also evidenced.