Identification of physical and chemical interaction mechanisms for the metals gold, silver, copper, palladium, chromium, and potassium with polyimide surfaces

In this article we briefly review the literature for the evaporated metals gold, silver, copper, palladium, chromium, and potassium on polyimide surfaces and compare these previous results to newer experiments using Fourier transform infrared reflection absorption spectroscopy (FT-IRAS) and near edge X-ray absorption fine structure spectroscopy (NEXAFS). The polyimide films were prepared by vapor phase deposition. Metal coverages range from submonolayer to several monolayers, but special emphasis in this work is put on the interaction of metals with a polyimide surface at very low metal coverages. Before our new results are presented, we discuss the various chemical and nonchemical effects, which can contribute to the change in IR absorption of polymers. For all of the metals except potassium only attenuation of polymer IR bands is observed. For the metal deposits of Au, Cu, Ag, and Pd the attenuation of the IR bands can be explained by a purely physical interaction mechanism, i.e., dynamical dipole screening and changes in the intermolecular dipole-dipole coupling between the polymer macromolecules. Deposition of potassium leads to very different and characteristic changes of the polymer IR bands and of the NEXAFS spectra which can conclusively be explained with an electron transfer from the potassium onto the polyimide. In the case of chromium the IR and NEXAFS data indicate that the chemical and physical interaction of chromium with polyimide is very complex already at the initial stage of the metal/polymer interface formation and cannot be explained conclusively with any of the interaction models suggested in the literature.