Molecular orbital analysis of the XPS spectrum of a fluorine containing polyimide: PMDA–BDAF

Abstract

The results of XPS measurements and molecular orbital calculations performed on the fluorine containing polyimide, PMDA–BDAF, are presented. The calculated carbon 1s (C1s) core energy level positions are compared with the level positions inferred from the XPS measurements. Within Koopman's approximation, the observed shape of the main XPS peak is consistent with the calculated distribution of C1s levels under this peak. Comparison of the magnitude of the carbonyl XPS peak intensity with the main peak intensity indicates a carbonyl C1s signal deficiency compared with that expected for “ideal bulk stoichiometry” i.e., for a polymer with no crosslinks or chain terminations. Comparison of data obtained from a grazing emission (surface sensitive) geometry with that obtained from a normal emission geometry, which probes more deeply into the bulk, indicates a signal enhancement of the C1s levels associated with carbon atoms of the CF3 groups as one nears the polymer surface. Such enhancement might be due to either actual differences in chemical composition, or to preferential structural ordering near the polymer surface. Copyright © 1988 John Wiley & Sons, Inc.