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The Ginzburg's «generalized jellium» model of the proximity effect in superconductor-dielectric systems is tested against a wide phenomenology occurring in formvar-metal multilayers. The experimental evidence gained from enhanced superconductivity, critical magnetic fields, energy gap and pair-breaking parameter values seems to support the hypothesis that a formvar eigenfrequency plays the same role as the Debye frequency in setting up the superconductivity of these systems.

Low-energy structures, observed in tunnelling characteristics of Al/formvar/Sn and Al/formvar/Al junctions are reported and discussed. Their connection to tbe vibrational excitation spectrum of the insulator is indicated. Arguments are given to interpret them as excited by an inelastic tunnel mechanism of quasi-holes. A spectroscopic classification of these structures is attempted according to some results previously published. The relevance of these results, obtained for an energy range in which no data from current molecular spectroscopy are available, is stressed.

That an inelastic electron tunneling experiment can be a powerful tool to investigate molecular vibrational spectra was first shown by JAc~VVlC and LAMBE (1). Since that t ime much progress has been accomplished on this field: a fairly up-to-date review can be found in WOLF (2). Tunnel junctions where the insulating barrier is a thin (50--100)• film of Polyvinyl Formate have been extensively investigated by our group in the last few years (3.5). For the reader's opportunity let us briefly summarize the main results that have been obtained. First ly it was shown in (3) that, when the insulating barrier is a Formvar film, proper vibrational modes can be transferred from the metallic electrodes to the