Electronic transport in metal-molecular nanoelectronic networks: A density functional theory study

Electronic transport properties of nanoscale networks composed of interconnected molecules/gold nanoclusters are examined via first-principles plane wave scattering density functional theory-based simulations. Au-molecular (benzene/alkanedithiol) junctions and networks, connected in linear chains and Y-, H- and ring-shaped networks were studied. Molecular orbital calculations show HOMO (highest-occupied-molecular-orbital)-LUMO (lowest-unoccupied-molecular-orbital) gaps of chains decreased with length, indicating decreased barrier to electron transport. Orbitals near the gap of benzenedithiol networks show good delocalization whereas those of alkanedithiol molecules were more localized the metallic clusters. The transmission spectra of benzenedithiol-based networks showed increase in number/width of peaks near the Fermi energy as structures were extended due to increased orbital overlapping (spatially/energetically) with each other leading to formation of transmission pathways and electronic energy band-like properties. In contrast, lower transmission was observed for networks having localized orbitals (alkanedithiol molecular networks) with less overlap near the Fermi energy. Transmission spectra were also in good agreement with associated peaks in electronic density of states. In the case of multi-terminal networks, the location of delocalized orbitals can also shift from one branch to another, indicating potential ON/OFF switching behavior is possible. Switching elements and molecular-scale circuits (e.g., logic gates or inverters) based on Y- and H-shaped networks are proposed in analogy to electron waveguide devices and our simulations indicated that low-energy switching operation on the order of 10-50 meV may be possible. These nanoscale molecular electronic networks linked via metallic clusters provide an avenue for engineering electronics at the molecular level by using superstructures of different organic molecules and topologies.