Influence of the number of anchoring groups on the electronic and mechanical properties of benzene-, anthracene- and pentacene-based molecular devices

One of the central issues of molecular electronics (ME) is the study of the molecule-metal electrode contacts, and their implications for the conductivity, charge-transport mechanism, and mechanical stability. In fact, stochastic on/off switching (blinking) reported in STM experiments is a major problem of single-molecule devices, and challenges the stability and reliability of these systems. Surprisingly, the ambiguous STM results all originate from devices that bind to the metallic electrode through a one-atom connection. In the present work, DFT is employed to study and compare the properties of a set of simple acenes that bind to metallic electrodes with an increasing number of connections, in order to determine whether the increasing numbers of anchoring groups have a direct repercussion on the stability of these systems. The conductivities of the three polycyclic aromatic hydrocarbons are calculated, as well as their transmission spectra and current profiles. The thermal and mechanical stability of these systems is studied by pulling and pushing the metal-molecule connection. The results show that molecules with more than one connection per electrode exhibit greater electrical efficiency and current stability. Better connections: Calculations show that increasing the number of anchoring groups in model acenes leads to higher conductivity as well as mechanical and current stability (see picture; C gray, H white, S yellow) in molecule-Au electrode contacts. The results have implications for stochastic on/off switching (blinking), which is a major problem of single-molecule electronic devices.