Optically Transparent Ultrathin Platinum Films as Versatile Substrates for Monitoring Switching of Self-assembled Monolayers by Uv-vis Spectroscopy in the Transmission Mode

The current applications of electronic devices are converging towards a global interconnection along with portability and compactness. This scenario implies the development of electronic components more and more small, fast, energy efficient and smart as well. The microelectronics industry faces these needs by both scaling and adding novel functions in integrated circuits. By going on such a trend into the future, both new materials and new downscaled architectures at nano level are required. In this context, the development of optically transparent metal substrates suitable to self-assemble functional molecules, such as molecular switches, is of paramount importance. In particular, the self-assembling of optical molecular switches on these substrates would allow the simple monitoring of the optical properties changes by UV-Vis transmission spectroscopy in addition to the detection of the electrical properties changes (Fig.1). We have recently demonstrated the suitability of optically transparent unltrathin platinum films to detect the redox switching of self-assembled monolayers (SAMs) of multifunctional ruthenium complexes by monitoring changes of the absorption spectra in the Vis region with a conventional spectrophotometer [1,2]. These platinum substrates are particularly appropriated for an easy monolayer characterization by transmission UV-Vis spectroscopy. In fact, differently from gold (the most employed material to SAMs purposes) ultrathin films, these platinum substrates are only slightly affected by the metal surface plasmon absorption in the UV-Vis region displaying a good optical transparency between 300-800 nm. Furthermore, platinum is an important material in microelectronic and nanoelectronic devices. Indeed, platinum is preferred over the more exhaustively studied gold because this latter is essentially incompatible with Si CMOS technology due to its high diffusivity and the deep electronic traps it forms in Si. This contribution reports on the preparation of ultrathin platinum films (20-30nm) on transparent quartz substrates and on the optimization of their physical, mechanical and electrical properties. Morphology and thickness of these thin layers have been investigated by Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) measurements. The unannealed films reveal good characteristics of optical transparency, homogeneity and electrical resistance. Annealing processes on these substrates lead to further improvement of both morphological and electrical features without affecting optical transmission properties. Application of these ultrathin platinum films for monitoring chemically and photochemically controlled switching of self assembled monolayers by UV-Vis spectroscopy in the transmission mode is shown.