Palladium-based three-terminal devices for single molecule electronics

L. ARZUBIAGA; F. GOLMAR; R. LLOPIS; F. CASANOVA; L. HUESO

Barcelona

Conferencia; 5th International Conference on Molecular Materials; 2012

One of the goals in the constant downscaling of electronic devices would be exploiting single molecule transistors (SMT). However, building devices that can both enable electrical contact and modulate electron transport through an isolated molecule is a very challenging task. Electromigration is a suitable technique for the fabrication of electrode pairs with a separation of the order of molecular dimensions (1-2nm). It consists on passing a current through a metal wire of nanometric cross-section until the failure of the material. The obtained electrode pairs have a planar architecture, suitable for the addition of a gate electrode. This third electrode is essential for exploring and modulating electron transport through the different energy levels of the molecule [1]. The geometry and sizes of the obtained nanogap electrode pairs can be different, due to the stochastic nature of the electromigration process. This variety in device geometry can complicate the study of SMTs. To begin with, the devices obtained by electromigration can have different electron transport characteristics that are inherent to the nature of the inter-electrode gap [2]. In addition to this, pollutants or solvent traces remaining from the fabrication can give transport characteristics similar to those of a single molecule. On the other hand, several groups have shown an interest in studying nanojunctions of different metals, which can show additional features in charge transport [3]. The possible appearance of all these effects requires a careful study of the as-produced devices (before the addition of the molecule). This way, all the features in electron transport of the SMT that have other source than the studied molecule can be ruled out. In this work we report the fabrication by electromigration of palladium-based three-terminal devices with nanogap electrode pairs. The role of palladium in these devices was compared to other inert noble metals, such as gold. The effect of the electrostatic gate was studied in nominally non-contacted electrodes. Finally, preliminary electrical measurements of fullerene SMTs were performed. [1] H. Song, Y. Kim, Y. H. Jang, H. Jeong, M. A. Reed and T. Lee, Nature 2009, 462, 1039. [2] E. A. Osorio, T. Bjørnholm, J. M. Lehn, M. Ruben and H. S. van der Zant ,J. Phys.: Condens. Matter 2008, 20, 374121. [3] G. D. Scott, J.J. Palacios and D. Natelson, ACS Nano 2010, 4, 2831.