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Abstract

Pyromellitic dianhydride (PMDA) is a precursor molecule for polyimide (PI), a polymer used as coating and dielectric material in microelectronics. Spectroscopic studies have been performed to understand the interface chemistry between PI or the precursor molecules and various metal substrates. New interest in growth of ordered polyimide films from the vapor phase requires detailed understanding of the adsorption and condensation behavior of the molecules involved. In this work, we studied the adsorption and condensation of PMDA on a platinum(lll) surface by means of infrared spectroscopy, thermal programmed desorption, and X-ray photoelectron spectroscopy. PMDA adsorbs in two different phases, depending on the substrate temperature and structure. A crystalline phase is obtained by annealing the as-deposited low-temperature condensate at 275 K or by adsorption above that temperature. However, crystalline growth occurs more than 50 K below the annealing temperature if a crystalline template is offered. For multilayers of crystalline PMDA, vibrational modes with common symmetry are identified. Their relative infrared absorption intensity is used to estimate the degree of order and orientation of the adsorbate with respect to the substrate. For depositions on Pt(lll) at 300 K, multilayer condensation is prohibited below a critical molecular flux rate. PMDA does not bond via a carboxylate group to the Pt(lll) surface, as was reported for other metals and silicon, but it adsorbs flat on this substrate.