Optically Transparent, Ultrathin Pt Films as Versatile Metal Substrates for Molecular Optoelectronics

Authors


  • We thank the MIUR (FIRB research projects, Rome, Italy), ESF-SONS project BIONICS EU, Marie Curie EST project SUPER (MEST-CT-2004-008128), and the National Science Foundation (CAREER Award CHE-0237578) for financial support. S.S. is grateful to the Royal Society of Chemistry for a travel grant. We are also indebted to Dr. G. de Portu of the ISTEC-CNR (Faenza) for the X-ray measurements and the IMM-IMETEM-CNR (Catania) for the TEM and CP-AFM measurements.

Abstract

This contribution reports a simple, straightforward method (cool sputtering) of fabricating robust, homogeneous, conductive, and optically transparent ultrathin Pt films. Their morphological, structural, mechanical, electrical, and optical properties are reported. The morphology and structure of these Pt films are investigated by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and X-ray diffraction. The ultrathin Pt films, approximately 20 nm thick, are characterized by a homogenous, polycrystalline structure, with a tendency to adopt a (111) texture upon the thermal treatment. Moreover, thermal treatment (annealing or flaming) of the as-prepared films also substantially improves their chemical and mechanical robustness. F films behave as bulk Pt in terms of electrical resistivity and suitability as working electrodes in cyclic voltammetry experiments. Overall, the unique combination of these excellent features: homogeneity, robustness, and conductivity, in addition to the high optical transparency in the 300–800 nm range of the electromagnetic spectrum, make ultrathin Pt films appropriate for a variety of applications in the field of molecular optoelectronics. The formation of functional molecular self-assembled monolayers (SAMs) on these transparent, conductive films allows their optical monitoring using transmission optical spectroscopy, as well as the probing of their electrical properties. The potential of such Pt films as suitable metal substrates in opto- and nanoelectronics is proven by representative applications, including switching of prototypical photochromic and electrochromic species in SAMs and molecule–metal junctions.

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