Composite nanostructured organic/inorganic thin films have been synthesized following two different electrochemical procedures. The first one comprises the potentiostatic synthesis of conducting polymers such as polythiophene and polypyrrole as well as optically transparent poly-orto-phenilendiamine or polyaniline, followed by a pulsed potentiostatic embedding of metallic nano-cluster (NC), such as copper, palladium and platinum dots. Controlling the pulse cathodic potential allows to choose the metals oxidation state. This step alone, or combined to a simple chemical reaction, allows to transform metals in semiconducting quantum dots such as Cu2O, CuO and CuI. The second procedure starts with the metallic NCs synthesis using a sacrificial anode as described in the seminal work recently published by M.T. Reets et al. [1]. The dissolution reaction occurs in a solution of alchyl-substituted ammonium salts and results in a colloidal dispersion of nanosized-metallic particles. In the figure a transmission electron micrograph (TEM) of palladium quantum dots (d = 5-7 nm) obtained in our laboratory is shown. A following electrochemical step allows to embed these positively charged colloid particles in an electroactive polymer thin film.
The composite thin films, deposited on suitable substrates, are characterized exploiting the advantages of the combined use of complementary electrochemical, spectroscopical and morphological analysis. In particular the cyclic voltammetric thin film responses are studied along with surface analysis carried out using X-Ray Photoelectron Spectroscopy; information on the bulk composition is obtained from infrared and micro-Raman spectra. Morphological investigation is carried out by TEM.
Preliminary results on the use of such films as active layers in different
kind of devices will be reported. In particular composite films embedding
metals look promising as thin-film-transistors active layers, since metal
inclusions in a polymer matrix have been already proven to enhance organic
thin films field induced mobility. Light emitting diodes using films of
semiconducting dots enclosed in a transparent polymer matrix will be tested
as well.
References
1. M. T. Reetz, W. Helbig, S.A. Quaiser, U. Stimming, N. Bruer, R. Vogel;
Science 267, 367, 1995